| 1. |
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| 2. |
- Padmanabhan, Sandosh, et al.
(författare)
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Genome-Wide Association Study of Blood Pressure Extremes Identifies Variant near UMOD Associated with Hypertension
- 2010
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Ingår i: PLoS Genetics. - : Public Library of Science (PLoS). - 1553-7404. ; 6:10
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Tidskriftsartikel (refereegranskat)abstract
- Hypertension is a heritable and major contributor to the global burden of disease. The sum of rare and common genetic variants robustly identified so far explain only 1%-2% of the population variation in BP and hypertension. This suggests the existence of more undiscovered common variants. We conducted a genome-wide association study in 1,621 hypertensive cases and 1,699 controls and follow-up validation analyses in 19,845 cases and 16,541 controls using an extreme case-control design. We identified a locus on chromosome 16 in the 59 region of Uromodulin (UMOD; rs13333226, combined P value of 3.6x10(-11)). The minor G allele is associated with a lower risk of hypertension (OR [95% CI]: 0.87 [0.84-0.91]), reduced urinary uromodulin excretion, better renal function; and each copy of the G allele is associated with a 7.7% reduction in risk of CVD events after adjusting for age, sex, BMI, and smoking status (H.R. = 0.923, 95% CI 0.860-0.991; p = 0.027). In a subset of 13,446 individuals with estimated glomerular filtration rate (eGFR) measurements, we show that rs13333226 is independently associated with hypertension (unadjusted for eGFR: 0.89 [0.83-0.96], p = 0.004; after eGFR adjustment: 0.89 [0.83-0.96], p = 0.003). In clinical functional studies, we also consistently show the minor G allele is associated with lower urinary uromodulin excretion. The exclusive expression of uromodulin in the thick portion of the ascending limb of Henle suggests a putative role of this variant in hypertension through an effect on sodium homeostasis. The newly discovered UMOD locus for hypertension has the potential to give new insights into the role of uromodulin in BP regulation and to identify novel drugable targets for reducing cardiovascular risk.
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| 3. |
- Schmidt, Amand F., et al.
(författare)
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PCSK9 genetic variants and risk of type 2 diabetes : a mendelian randomisation study
- 2017
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Ingår i: The Lancet Diabetes and Endocrinology. - : ELSEVIER SCIENCE INC. - 2213-8587 .- 2213-8595. ; 5:2, s. 97-105
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Tidskriftsartikel (refereegranskat)abstract
- Background Statin treatment and variants in the gene encoding HMG-CoA reductase are associated with reductions in both the concentration of LDL cholesterol and the risk of coronary heart disease, but also with modest hyperglycaemia, increased bodyweight, and modestly increased risk of type 2 diabetes, which in no way off sets their substantial benefi ts. We sought to investigate the associations of LDL cholesterol-lowering PCSK9 variants with type 2 diabetes and related biomarkers to gauge the likely eff ects of PCSK9 inhibitors on diabetes risk. Methods In this mendelian randomisation study, we used data from cohort studies, randomised controlled trials, case control studies, and genetic consortia to estimate associations of PCSK9 genetic variants with LDL cholesterol, fasting blood glucose, HbA 1c, fasting insulin, bodyweight, waist-to-hip ratio, BMI, and risk of type 2 diabetes, using a standardised analysis plan, meta-analyses, and weighted gene-centric scores. Findings Data were available for more than 550 000 individuals and 51 623 cases of type 2 diabetes. Combined analyses of four independent PCSK9 variants (rs11583680, rs11591147, rs2479409, and rs11206510) scaled to 1 mmol/L lower LDL cholesterol showed associations with increased fasting glucose (0.09 mmol/L, 95% CI 0.02 to 0.15), bodyweight (1.03 kg, 0.24 to 1.82), waist-to-hip ratio (0.006, 0.003 to 0.010), and an odds ratio for type diabetes of 1.29 (1.11 to 1.50). Based on the collected data, we did not identify associations with HbA 1c (0.03%, -0.01 to 0.08), fasting insulin (0.00%, -0.06 to 0.07), and BMI (0.11 kg/m(2), -0.09 to 0.30). Interpretation PCSK9 variants associated with lower LDL cholesterol were also associated with circulating higher fasting glucose concentration, bodyweight, and waist-to-hip ratio, and an increased risk of type 2 diabetes. In trials of PCSK9 inhibitor drugs, investigators should carefully assess these safety outcomes and quantify the risks and benefi ts of PCSK9 inhibitor treatment, as was previously done for statins.
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| 4. |
- Schmidt, Amand F., et al.
(författare)
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Phenome-wide association analysis of LDL-cholesterol lowering genetic variants in PCSK9
- 2019
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Ingår i: BMC Cardiovascular Disorders. - : BMC. - 1471-2261 .- 1471-2261. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: We characterised the phenotypic consequence of genetic variation at the PCSK9 locus and compared findings with recent trials of pharmacological inhibitors of PCSK9. Methods: Published and individual participant level data (300,000+ participants) were combined to construct a weighted PCSK9 gene-centric score (GS). Seventeen randomized placebo controlled PCSK9 inhibitor trials were included, providing data on 79,578 participants. Results were scaled to a one mmol/L lower LDL-C concentration. Results: The PCSK9 GS (comprising 4 SNPs) associations with plasma lipid and apolipoprotein levels were consistent in direction with treatment effects. The GS odds ratio (OR) for myocardial infarction (MI) was 0.53 (95% CI 0.42; 0.68), compared to a PCSK9 inhibitor effect of 0.90 (95% CI 0.86; 0.93). For ischemic stroke ORs were 0.84 (95% CI 0.57; 1.22) for the GS, compared to 0.85 (95% CI 0.78; 0.93) in the drug trials. ORs with type 2 diabetes mellitus (T2DM) were 1.29 (95% CI 1.11; 1.50) for the GS, as compared to 1.00 (95% CI 0.96; 1.04) for incident T2DM in PCSK9 inhibitor trials. No genetic associations were observed for cancer, heart failure, atrial fibrillation, chronic obstructive pulmonary disease, or Alzheimer's disease - outcomes for which large-scale trial data were unavailable. Conclusions: Genetic variation at the PCSK9 locus recapitulates the effects of therapeutic inhibition of PCSK9 on major blood lipid fractions and MI. While indicating an increased risk of T2DM, no other possible safety concerns were shown; although precision was moderate.
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| 5. |
- Ashuiev, Anton, et al.
(författare)
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Geometry and electronic structure of Yb(iii)[CH(SiMe3)2]3 from EPR and solid-state NMR augmented by computations
- 2024
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 26:11, s. 8734-8747
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Tidskriftsartikel (refereegranskat)abstract
- Characterization of paramagnetic compounds, in particular regarding the detailed conformation and electronic structure, remains a challenge, and – still today it often relies solely on the use of X-ray crystallography, thus limiting the access to electronic structure information. This is particularly true for lanthanide elements that are often associated with peculiar structural and electronic features in relation to their partially filled f-shell. Here, we develop a methodology based on the combined use of state-of-the-art magnetic resonance spectroscopies (EPR and solid-state NMR) and computational approaches as well as magnetic susceptibility measurements to determine the electronic structure and geometry of a paramagnetic Yb(III) alkyl complex, Yb(III)[CH(SiMe3)2]3, a prototypical example, which contains notable structural features according to X-ray crystallography. Each of these techniques revealed specific information about the geometry and electronic structure of the complex. Taken together, both EPR and NMR, augmented by quantum chemical calculations, provide a detailed and complementary understanding of such paramagnetic compounds. In particular, the EPR and NMR signatures point to the presence of three-centre–two-electron Yb-γ-Me-β-Si secondary metal–ligand interactions in this otherwise tri-coordinate metal complex, similarly to its diamagnetic Lu analogues. The electronic structure of Yb(III) can be described as a single 4f13 configuration, while an unusually large crystal-field splitting results in a thermally isolated ground Kramers doublet. Furthermore, the computational data indicate that the Yb–carbon bond contains some π-character, reminiscent of the so-called α-H agostic interaction.
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| 6. |
- Blahut, Jan, et al.
(författare)
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Proton-detected fast-magic-angle spinning NMR of paramagnetic inorganic solids
- 2021
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 11:47, s. 29870-29876
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Tidskriftsartikel (refereegranskat)abstract
- Fast (60 kHz) magic angle spinning solid-state NMR allows very sensitive proton detection in highly paramagnetic organometallic powders. We showcase this technique with the complete assignment of H-1 and C-13 resonances in a high-spin Fe(ii) polymerisation catalyst with less than 2 mg of sample at natural abundance.
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| 7. |
- Carvalho, José P., et al.
(författare)
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Separation of quadrupolar and paramagnetic shift interactions with TOP-STMAS/MQMAS in solid-state lighting phosphors
- 2020
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 58:11, s. 1055-1070
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Tidskriftsartikel (refereegranskat)abstract
- A new approach for processing satellite-transition magic-angle spinning(STMAS) and multiple-quantum magic-angle spinning (MQMAS) data, basedon the two-dimensional one-pulse (TOP) method, which separates thesecond-rank quadrupolar anisotropy and paramagnetic shift interactions viaa double shearing transformation, is described. This method is particularlyrelevant in paramagnetic systems, where substantial inhomogeneous broadeningmay broaden the lineshapes. Furthermore, it possesses an advantage overthe conventional processing of MQMAS and STMAS spectra because it overcomesthe limitation on the spectral width in the indirect dimension imposedby rotor synchronization of the sampling interval. This method was appliedexperimentally to the 27Al solid-state nuclear magnetic resonance of a seriesof yttrium aluminum garnets (YAGs) doped with different lanthanide ions,from which the quadrupolar parameters of paramagnetically shifted and bulkunshifted sites were extracted. These parameters were then compared withdensity functional theory calculations, which permitted a better understandingof the local structure of Ln substituent ions in the YAG lattice.
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| 8. |
- Lu, Xinnan, et al.
(författare)
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Ni2P Nanoparticles Embedded in Mesoporous SiO2 for Catalytic Hydrogenation of SO2 to Elemental S
- 2021
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:6, s. 5665-5676
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Tidskriftsartikel (refereegranskat)abstract
- Highly active nickel phosphide (Ni2P) nanoclusters confined in a mesoporous SiO2 catalyst were synthesized by a two-step process targeting tight control over the Ni2P size and phase. The Ni precursor was incorporated into the MCM-41 matrix by one-pot synthesis, followed by the phosphorization step, which was accomplished in oleylamine with trioctylphosphine at 300 °C so to achieve the phase transformation from Ni to Ni2P. For benchmarking, Ni confined by the mesoporous SiO2 (absence of phosphorization) and 11 nm Ni2P nanoparticles (absence of SiO2) was also prepared. From the microstructural analysis, it was found that the growth of Ni2P nanoclusters was restricted by the mesoporous channels, thus forming ultrafine and highly dispersed Ni2P nanoclusters (<2 nm). The above approach led to promising catalytic performance following the order u-Ni2P@m-SiO2 > n-Ni2P > u-Ni@m-SiO2 > c-Ni2P in the selective hydrogenation of SO2 to S. In particular, u-Ni2P@m-SiO2 exhibited SO2 conversions of 94% at 220 °C and ∼99% at 240 °C, which are higher than the 11 nm stand-alone Ni2P particles (43% at 220 °C and 94% at 320 °C), highlighting the importance of the role played by SiO2 in stabilizing ultrafine nanoparticles of Ni2P. The reaction activation energy Ea over u-Ni2P@m-SiO2 is ∼33 kJ/mol, which is lower than those over n-Ni2P (∼36 kJ/mol) and c-Ni2P (∼66 kJ/mol), suggesting that the reaction becomes energetically favored over the ultrafine Ni2P nanoclusters.
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| 9. |
- Lu, Xinnan, et al.
(författare)
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Nickel Phosphide Nanoparticles for Selective Hydrogenation of SO2 to H2S
- 2021
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:7, s. 6568-6582
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Tidskriftsartikel (refereegranskat)abstract
- Highly mesoporous SiO2-encapsulated NixPy crystals, where (x, y) = (5, 4), (2, 1), and (12, 5), were successfully synthesized by adopting a thermolytic method using oleylamine (OAm), trioctylphosphine (TOP), and trioctylphosphine oxide (TOPO). The Ni5P4@SiO2 system shows the highest reported activity for the selective hydrogenation of SO2 toward H2S at 320 degrees C (96% conversion of SO2 and 99% selectivity to H2S), which was superior to the activity of the commercial CoMoS@Al2O3 catalyst (64% conversion of SO2 and 71% selectivity to H2S at 320 degrees C). The morphology of the Ni5P4 crystal was finely tuned via adjustment of the synthesis parameters receiving a wide spectrum of morphologies (hollow, macroporous-network, and SiO2-confined ultrafine clusters). Intrinsic characteristics of the materials were studied by Xray diffraction, high-resolution transmission electron microscopy/scanning transmission electron microscopy-high-angle annular dark-field imaging, energydispersive X-ray spectroscopy, the Brunauer-Emmett-Teller method, H-2 temperature-programmed reduction, X-ray photoelectron spectroscopy, and experimental and calculated P-31 magic-angle spinning solid-state nuclear magnetic resonance toward establishing the structure-performance correlation for the reaction of interest. Characterization of the catalysts after the SO2 hydrogenation reaction proved the preservation of the morphology, crystallinity, and Ni/P ratio for all the catalysts.
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| 10. |
- Sanders, Kevin J., et al.
(författare)
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Broadband MAS NMR spectroscopy in the low-power limit
- 2018
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 697, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the performance of broadband adiabatic inversion pulses in the high-power (short high-powered adiabatic pulse, SHAP) and low-power (single-sideband-selective adiabatic pulse, S(3)AP) RF regimes on a spin system subjected to large anisotropic interactions. We show by combined experimental results and spin dynamics simulations that when the magic-angle spinning rate exceeds 100 kHz S(3)APs begin outperforming SHAPs. This is especially true for low-gamma nuclei, such as Li-6 in paramagnetic Li-ion battery materials. Finally, we show how S3APs can be improved by combining multiple waveforms sweeping over multiple sidebands simultaneously, in order to produce inverted sideband profiles free from intensity biasing.
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| 11. |
- Schlagnitweit, Judith, et al.
(författare)
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Observing an Antisense Drug Complex in Intact Human Cells by in-Cell NMR Spectroscopy
- 2019
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Ingår i: ChemBioChem. - : Wiley. - 1439-4227 .- 1439-7633. ; 20, s. 2474-2478
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Tidskriftsartikel (refereegranskat)abstract
- Gaining insight into the uptake, trafficking and target engagement of drugs in cells can enhance understanding of a drug's function and efficiency. However, there are currently no reliable methods for studying untagged biomolecules in macromolecular complexes in intact human cells. Here we have studied an antisense oligonucleotide (ASO) drug in HEK 293T and HeLa cells by NMR spectroscopy. Using a combination of transfection, cryoprotection and dynamic nuclear polarization (DNP), we were able to detect the drug directly in intact frozen cells. Activity of the drug was confirmed by quantitative reverse transcription polymerase chain reaction (qRT-PCR). By applying DNP NMR to frozen cells, we overcame limitations both of solution-state in-cell NMR spectroscopy (e.g., size, stability and sensitivity) and of visualization techniques, in which (e.g., fluorescent) tagging of the ASO decreases its activity. The capability to detect an untagged, active drug, interacting in its natural environment, represents a first step towards studying molecular mechanisms in intact cells.
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| 12. |
- Aleksis, Rihards, et al.
(författare)
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Artefact-free broadband 2D NMR for separation of quadrupolar and paramagnetic shift interactions
- 2019
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Ingår i: Solid State Nuclear Magnetic Resonance. - : Elsevier BV. - 0926-2040 .- 1527-3326. ; 101, s. 51-62
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Tidskriftsartikel (refereegranskat)abstract
- Two new two-dimensional, broadband, solid-state NMR experiments for separating and correlating the quadrupolar and shift interactions of spin I = 1 nuclei in paramagnetic systems are proposed. The new pulse sequences incorporate the short, high-power adiabatic pulses (SHAPs) into the shifting d-echo experiment of Walder et al. [J. Chem. Phys., 142, 014201 (2015)], in two different ways, giving double and quadruple adiabatic shifting d-echo sequences. These new experiments have the advantage over previous methods of both suppressing spectral artefacts due to pulse imperfections, and exhibiting a broader excitation bandwidth. Both experiments are analysed with theoretical calculations and simulations, and are applied experimentally to the H-2 NMR of deuterated CuCl2 center dot 2H(2)O, and two deuterated samples of the ion conductor oxyhydride BaTiO3-xHy prepared using two different methods. For the CuCl2 center dot 2H(2)O sample, both new methods obtain very high-quality spectra from which the parameters describing the shift and quadrupolar interaction tensors, and their relative orientation, were extracted. The two BaTiO3-xHy samples exhibited different local hydride environments with different tensor parameters. The H-2 spectra of these oxyhydrides exhibit inhomogeneous broadening of the H-2 shifts, and so whilst the quadrupolar interaction parameters were easily extracted, the measurement of the shift parameters was more complex. However, effective shift parameters were extracted, which combine the effects of both the paramagnetic shift tensor and the inhomogeneous broadening.
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| 13. |
- Aleksis, Rihards, et al.
(författare)
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Low-power synchronous helical pulse sequences for large anisotropic interactions in MAS NMR : Double-quantum excitation of N-14
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 153:24
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Tidskriftsartikel (refereegranskat)abstract
- We develop a theoretical framework for a class of pulse sequences in the nuclear magnetic resonance (NMR) of rotating solids, which are applicable to nuclear spins with anisotropic interactions substantially larger than the spinning frequency, under conditions where the radiofrequency amplitude is smaller than or comparable to the spinning frequency. The treatment is based on average Hamiltonian theory and allows us to derive pulse sequences with well-defined relationships between the pulse parameters and spinning frequency for exciting specific coherences without the need for any detailed calculations. This framework is applied to the excitation of double-quantum spectra of N-14 and is used both to evaluate the existing low-power pulse schemes and to predict the new ones, which we present here. It is shown that these sequences can be designed to be gamma -encoded and therefore allow the acquisition of sideband-free spectra. It is also shown how these new double-quantum excitation sequences are incorporated into heteronuclear correlation NMR, such as H-1-N-14 dipolar double-quantum heteronuclear multiple-quantum correlation spectroscopy. The new experiments are evaluated both with numerical simulations and experiments on glycine and N-acetylvaline, which represent cases with moderate and large quadrupolar interactions, respectively. The analyzed pulse sequences perform well for the case of a moderate quadrupolar interaction, however poorly with a large quadrupolar interaction, for which future work on pulse sequence development is necessary.
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| 14. |
- Aleksis, Rihards, et al.
(författare)
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Probing the electronic structure and hydride occupancy in barium titanium oxyhydride through DFT-assisted solid-state NMR
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 24:46, s. 28164-28173
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite-type oxhydrides such as BaTiO3−xHy exhibit mixed hydride ion and electron conduction and are an attractive class of materials for developing energy storage devices. However, the underlying mechanism of electric conductivity and its relation to the composition of the material remains unclear. Here we report detailed insights into the hydride local environment, the electronic structure and hydride conduction dynamics of barium titanium oxyhydride. We demonstrate that DFT-assisted solid-state NMR is an excellent tool for differentiating between the different feasible electronic structures in these solids. Our results indicate that upon reduction of BaTiO3 the introduced electrons are delocalized among all Ti atoms forming a bandstate. Furthermore, each vacated anion site is reoccupied by at most a single hydride, or else remains vacant. This single occupied bandstate structure persists at different hydrogen concentrations (y = 0.13–0.31) and a wide range of temperatures (∼100–300 K).
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| 15. |
- Aleksis, Rihards, et al.
(författare)
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Separation of quadrupolar and paramagnetic shift interactions in high-resolution nuclear magnetic resonance of spinning powders
- 2021
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 155:9
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Tidskriftsartikel (refereegranskat)abstract
- Separation and correlation of the shift anisotropy and the first-order quadrupolar interaction of spin I = 1 nuclei under magic-angle spinning (MAS) are achieved by the phase-adjusted spinning sideband (PASS) nuclear magnetic resonance (NMR) experiment. Compared to methods for static samples, this approach has the benefit of higher sensitivity and resolution. Moreover, the PASS experiment has the advantage over previous MAS sequences in the ability to completely separate the shift anisotropy and first-order quadrupolar interactions. However, the main drawback of the pulse sequence is the lower excitation bandwidth. The sequence is comprehensively evaluated using theoretical calculations and numerical simulations and applied experimentally to the H-2 NMR of a range of paramagnetic systems: deuterated nickel(II) acetate tetrahydrate, deuterated copper(II) chloride dihydrate, and two forms of deuterated oxyhydride ion conductor BaTiO3-xHy. Our results show that despite the issue with broadband excitation, the extracted shift and quadrupolar interaction tensors and the Euler angles relating the two tensors match well with the NMR parameters obtained with static NMR methods. Therefore, the new application of the PASS experiment is an excellent addition to the arsenal of NMR experiments for H-2 and potentially N-14 in paramagnetic solids.
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| 16. |
- Brant, William, et al.
(författare)
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Selective Control of Composition in Prussian White for Enhanced Material Properties
- 2019
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Ingår i: Chemistry of Materials. - : AMER CHEMICAL SOC. - 0897-4756 .- 1520-5002. ; 31:18, s. 7203-7211
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Tidskriftsartikel (refereegranskat)abstract
- Sodium-ion batteries based on Prussian blue analogues (PBAs) are ideal for large-scale energy storage applications due to the ability to meet the huge volumes and low costs required. For Na2-xFe[Fe(CN)(6)](1-y)center dot zH(2)O, realizing its commercial potential means fine control of the concentration of sodium, Fe(CN)(6) vacancies, and water content. To date, there is a huge variation in the literature of composition leading to variable electrochemical performance. In this work, we break down the synthesis of PBAs into three steps for controlling the sodium, vacancy, and water content via an inexpensive, scalable synthesis method. We produce rhombohedral Prussian white Na1.88(5)Fe[Fe-(CN)(6)]center dot 0.18(9)H2O with an initial capacity of 158 mAh/g retaining 90% capacity after 50 cycles. Subsequent characterization revealed that the increased polarization on the 3 V plateau is coincident with a phase transition and reduced utilization of the high-spin Fe(III)/Fe(II) redox couple. This reveals a clear target for subsequent improvements of the material to boost long-term cycling stability. These results will be of great interest for the myriad of applications of PBAs, such as catalysis, magnetism, electrochromics, and gas sorption.
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| 17. |
- Carvalho, José P., et al.
(författare)
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Frequency-swept adiabatic pulses for broadband solid-state MAS NMR
- 2021
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 324
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Tidskriftsartikel (refereegranskat)abstract
- We present a complete description of frequency-swept adiabatic pulses applied to isolated spin-1/2 nuclei with a shift anisotropy in solid materials under magic-angle spinning. Our theoretical framework unifies the existing descriptions of adiabatic pulses in the high-power regime, where the radiofrequency (RF) amplitude is greater than twice the spinning frequency, and the low-power regime, where the RF power is less than the spinning frequency, and so links the short high-powered adiabatic pulse (SHAP) and single-sideband-selective adiabatic pulses (S3AP) schemes used in paramagnetic solid-state NMR. We also identify a hitherto unidentified third regime intermediate between the low- and high-power regimes, and separated from them by rotary resonance conditions. We show that the prevailing benchmark of inversion performance based on (super) adiabatic factors is only applicable in the high- and intermediate-power regimes, but fails to account both for the poor performance at rotary resonance, and the impressive inversion seen in the low-power regime. For low-power pulses, which are non-adiabatic according to this definition of (super) adiabaticity, the effective Floquet Hamiltonian in the jolting frame reveals “hidden” (super) adiabaticity. The theory is demonstrated using a combination of simulation and experiment, and is used to refine the practical recommendations for the experimentalist who wishes to use these pulses.
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| 18. |
- Carvalho, José P., et al.
(författare)
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Half-integer-spin quadrupolar nuclei in magic-angle spinning paramagnetic NMR : The case of NaMnO2
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- A combination of solid-state NMR methods for the extraction of shift and quadrupolar parameters for half-integer nuclei in the structurally complex NaMnO2 Na-ion cathode material, under magic-angle spinning (MAS) is presented. We show that the integration of the Magic-Angle Turning experiment with Rotor-Assisted Population transfer can be used both to identify shifts and to extract a range of magnitudes for their quadrupolar coupling. We also demonstrate the applicability of the the two-dimensional one pulse (TOP) based double-sheared Satellite Transition Magic-Angle Spinning (TOP-STMAS) showing how it can yield a spectrum with separated shift and second-order quadrupolar anisotropies, which in turn can be used to analyse a quadrupolar lineshape free of bulk magnetic susceptibility induced shift dispersion and determine both isotropic shift and quadrupolar products. Combining all these experiments, the shift and quadrupolar parameters for all observed Na environments were extracted and yielded excellent agreement with the density functional theory (DFT) based models that were reported in previous literature. We expect these methods to open the door for new possibilities for solid-state NMR to probe half-integer quadrupolar nuclei in paramagnetic materials and other systems exhibiting large shift dispersion.
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| 19. |
- Carvalho, José P., et al.
(författare)
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Half-integer-spin quadrupolar nuclei in magic-angle spinning paramagnetic NMR : The case of NaMnO2
- 2022
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 340
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Tidskriftsartikel (refereegranskat)abstract
- A combination of solid-state NMR methods for the extraction of 23Na shift and quadrupolar parameters in the as-synthesized, structurally complex NaMnO2 Na-ion cathode material, under magic-angle spinning (MAS) is presented. We show that the integration of the Magic-Angle Turning experiment with Rotor-Assisted Population transfer (RAPT) can be used both to identify shifts and to extract a range of magnitudes for their quadrupolar couplings. We also demonstrate the applicability of the two-dimensional one pulse (TOP) based double-sheared Satellite Transition Magic-Angle Spinning (TOP-STMAS) showing how it can yield a spectrum with separated shift and second-order quadrupolar anisotropies, which in turn can be used to analyze a quadrupolar lineshape free of anisotropic bulk magnetic susceptibility (ABMS) induced shift dispersion and determine both isotropic shift and quadrupolar products. Combining all these experiments, the shift and quadrupolar parameters for all observed Na environments were extracted and yielded excellent agreement with the density functional theory (DFT) based models that were reported in previous literature. We expect these methods to open the door for new possibilities for solid-state NMR to probe half-integer quadrupolar nuclei in paramagnetic materials and other systems exhibiting large shift dispersion.
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| 20. |
- Carvalho, José P., 1993-
(författare)
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Probing Paramagnetic Systems by Solid-State NMR Spectroscopy
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Paramagnetic systems have a wide range of applications ranging from energy storage or conversion to catalytic processes, metalloproteins and light-emitting materials. Over the recent years nuclear magnetic resonance (NMR) spectroscopy has become an established tool for studying the structural and electronic properties of these systems, largely because it can provide a link between the structure and the bulk properties. This progress was only possible due to improved probe technology and better radiofrequency irradiation schemes, since the hyperfine interaction between nuclei and the unpaired electrons generally hampers both the acquisition and interpretation of the spectra and, therefore, techniques that are standard for diamagnetic systems often perform poorly when applied to paramagnetic systems.The aim of the present thesis is to continue the development of solid-state paramagnetic NMR and address some of the remaining limitations and bottlenecks in the acquisition and spectral interpretation. One specific area for which great improvements have been seen is the development of new broadband excitation and inversion sequences for systems under Magic-Angle Spinning (MAS) which employ adiabatic pulses. In this work, we provide a more rigorous understanding of the adiabatic pulses in solid-state MAS NMR applicable to both the design of new and improved pulse schemes, and their application in studies of an increased variety of systems, whilst avoiding potential implementation pitfalls.We also demonstrate how a thorough understanding of the hyperfine interaction combined with quantum chemistry calculations can link bulk magnetic properties and magnetic resonance signatures both in solid-state NMR and Electron Paramagnetic Resonance (EPR), thus providing an accurate description of the geometry and electronic configuration of an organoytterbium complex with applications in heterogeneous catalysis.Lastly, we explore the development of methods suitable for quadrupolar nuclei (spin I>1/2) in paramagnetic systems which have, so far, lagged behind their spin 1/2 counterparts. We focus more specifically on half-integer quadrupoles for which we propose a new method of processing Multiple-Quantum and Satellite-Transition MAS spectra which permits the separation of shift and quadrupolar interactions into orthogonal dimensions and evaluate the performance and limitations of the state-of-the-art methods for extraction of both quadrupolar and shift anisotropy tensor parameters on structurally complex systems.We anticipate that the work developed throughout this thesis can help extend the fields of application of solid-state paramagnetic NMR.
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| 21. |
- Eklof, Daniel, et al.
(författare)
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Mysterious SiB3: Identifying the Relation between alpha- and beta-SiB3
- 2019
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Ingår i: ACS Omega. - : AMER CHEMICAL SOC. - 2470-1343. ; 4:20, s. 18741-18759
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Tidskriftsartikel (refereegranskat)abstract
- Binary silicon boride SiB3 has been reported to occur in two forms, as disordered and nonstoichiometric alpha-SiB3-x, which relates to the alpha-rhombohedral phase of boron, and as strictly ordered and stoichiometric beta-SiB3. Similar to other boron-rich icosahedral solids, these SiB3 phases represent potentially interesting refractory materials. However, their thermal stability, formation conditions, and thermodynamic relation are poorly understood. Here, we map the formation conditions of alpha-SiB3-x and beta-SiB3 and analyze their relative thermodynamic stabilities. alpha-SiB3-x is metastable (with respect to beta-SiB3 and Si), and its formation is kinetically driven. Pure polycrystalline bulk samples may be obtained within hours when heating stoichiometric mixtures of elemental silicon and boron at temperatures 1200-1300 degrees C. At the same time, alpha-SiB3-x decomposes into SiB6 and Si, and optimum time-temperature synthesis conditions represent a trade-off between rates of formation and decomposition. The formation of stable beta-SiB3 was observed after prolonged treatment (days to weeks) of elemental mixtures with ratios Si/B = 1:11:4 at temperatures 1175-1200 degrees C. The application of high pressures greatly improves the kinetics of SiB3 formation and allows decoupling of SiB3 formation from decomposition. Quantitative formation of beta-SiB3 was seen at 1100 degrees C for samples pressurized to 5.5-8 GPa. beta-SiB3 decomposes peritectoidally at temperatures between 1250 and 1300 degrees C. The highly ordered nature of beta-SiB3 is reflected in its Raman spectrum, which features narrow and distinct lines. In contrast, the Raman spectrum of alpha-SiB3-x is characterized by broad bands, which show a clear relation to the vibrational modes of isostructural, ordered B6P. The detailed composition and structural properties of disordered alpha-SiB3-x were ascertained by a combination of single-crystal X-ray diffraction and Si-29 magic angle spinning NMR experiments. Notably, the compositions of polycrystalline bulk samples (obtained at T amp;lt;= 1200 degrees C) and single crystal samples (obtained from Si-rich molten Si-B mixtures at T amp;gt; 1400 degrees C) are different, SiB2.93(7) and SiB2.64(2), respectively. The incorporation of Si in the polar position of B-12 icosahedra results in highly strained cluster units. This disorder feature was accounted for in the refined crystal structure model by splitting the polar position into three sites. The electron-precise composition of alpha-SiB3-x is SiB2.5 and corresponds to the incorporation of, on average, two Si atoms in each B-12 icosahedron. Accordingly, alpha-SiB3-x constitutes a mixture of B10Si2 and B11Si clusters. The structural and phase stability of alpha-SiB3-x were explored using a first-principles cluster expansion. The most stable composition at 0 K is SiB2.5, which however is unstable with respect to the decomposition beta-SiB3 + Si. Modeling of the configurational and vibrational entropies suggests that alpha-SiB3-x only becomes more stable than beta-SiB3 at temperatures above its decomposition into SiB6 and Si. Hence, we conclude that alpha-SiB3-x is metastable at all temperatures. Density functional theory electronic structure calculations yield band gaps of similar size for electron-precise alpha-SiB2.5 and beta-SiB3, whereas alpha-SiB3 represents a p-type conductor.
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| 22. |
- Eklöf, Daniel, et al.
(författare)
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Mysterious SiB3 : Identifying the Relation between α- and β-SiB3
- 2019
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:20, s. 18741-18759
-
Tidskriftsartikel (refereegranskat)abstract
- Binary silicon boride SiB3 has been reported to occur in two forms, as disordered and nonstoichiometric alpha-SiB3-x, which relates to the alpha-rhombohedral phase of boron, and as strictly ordered and stoichiometric beta-SiB3. Similar to other boron-rich icosahedral solids, these SiB3 phases represent potentially interesting refractory materials. However, their thermal stability, formation conditions, and thermodynamic relation are poorly understood. Here, we map the formation conditions of alpha-SiB3-x and beta-SiB3 and analyze their relative thermodynamic stabilities. alpha-SiB3-x is metastable (with respect to beta-SiB3 and Si), and its formation is kinetically driven. Pure polycrystalline bulk samples may be obtained within hours when heating stoichiometric mixtures of elemental silicon and boron at temperatures 1200-1300 degrees C. At the same time, alpha-SiB3-x decomposes into SiB6 and Si, and optimum time-temperature synthesis conditions represent a trade-off between rates of formation and decomposition. The formation of stable beta-SiB3 was observed after prolonged treatment (days to weeks) of elemental mixtures with ratios Si/B = 1:11:4 at temperatures 1175-1200 degrees C. The application of high pressures greatly improves the kinetics of SiB3 formation and allows decoupling of SiB3 formation from decomposition. Quantitative formation of beta-SiB3 was seen at 1100 degrees C for samples pressurized to 5.5-8 GPa. beta-SiB3 decomposes peritectoidally at temperatures between 1250 and 1300 degrees C. The highly ordered nature of beta-SiB3 is reflected in its Raman spectrum, which features narrow and distinct lines. In contrast, the Raman spectrum of alpha-SiB3-x is characterized by broad bands, which show a clear relation to the vibrational modes of isostructural, ordered B6P. The detailed composition and structural properties of disordered alpha-SiB3-x were ascertained by a combination of single-crystal X-ray diffraction and Si-29 magic angle spinning NMR experiments. Notably, the compositions of polycrystalline bulk samples (obtained at T <= 1200 degrees C) and single crystal samples (obtained from Si-rich molten Si-B mixtures at T > 1400 degrees C) are different, SiB2.93(7) and SiB2.64(2), respectively. The incorporation of Si in the polar position of B-12 icosahedra results in highly strained cluster units. This disorder feature was accounted for in the refined crystal structure model by splitting the polar position into three sites. The electron-precise composition of alpha-SiB3-x is SiB2.5 and corresponds to the incorporation of, on average, two Si atoms in each B-12 icosahedron. Accordingly, alpha-SiB3-x constitutes a mixture of B10Si2 and B11Si clusters. The structural and phase stability of alpha-SiB3-x were explored using a first-principles cluster expansion. The most stable composition at 0 K is SiB2.5, which however is unstable with respect to the decomposition beta-SiB3 + Si. Modeling of the configurational and vibrational entropies suggests that alpha-SiB3-x only becomes more stable than beta-SiB3 at temperatures above its decomposition into SiB6 and Si. Hence, we conclude that alpha-SiB3-x is metastable at all temperatures. Density functional theory electronic structure calculations yield band gaps of similar size for electron-precise alpha-SiB2.5 and beta-SiB3, whereas alpha-SiB3 represents a p-type conductor.
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| 23. |
- Eklöf-Österberg, Carin, 1987, et al.
(författare)
-
Dynamics of Hydride Ions in Metal Hydride-Reduced BaTiO3 Samples Investigated with Quasielastic Neutron Scattering
- 2019
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:4, s. 2019-2030
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite-type oxyhydrides, BaTiO3-xHx, have been recently shown to exhibit hydride-ion (H-) conductivity at elevated temperatures, but the underlying mechanism of hydride-ion conduction and how it depends on temperature and oxygen vacancy concentration remains unclear. Here, we investigate, through the use of quasielastic neutron scattering techniques, the nature of the hydride-ion dynamics in three metal hydride-reduced BaTiO3 samples that are characterized by the simultaneous presence of hydride ions and oxygen vacancies. Measurements of elastic fixed window scans upon heating reveal the presence of quasielastic scattering due to hydride-ion dynamics for temperatures above ca. 200 K. Analyses of quasielastic spectra measured at low (225 and 250 K) and high (400-700 K) temperature show that the dynamics can be adequately described by established models of jump diffusion. At low temperature, <= 250 K, all of the models feature a characteristic jump distance of about 2.8 angstrom, thus of the order of the distance between neighboring oxygen atoms or oxygen vacancies of the perovskite lattice and a mean residence time between successive jumps of the order of 0.1 ns. At higher temperatures, >400 K, the jump distance increases to about 4 angstrom, thus of the order of the distance between next-nearest neighboring oxygen atoms or oxygen vacancies, with a mean residence time of the order of picoseconds. A diffusion constant D was computed from the data measured at low and high temperatures, respectively, and takes on values of about 0.4 X 10(-6) cm(-2) s(-1) at the lowest applied temperature of 225 K and between ca. 20 X 10(-6) and 100 X 10(-6) cm(-2) s(-1) at temperatures between 400 and 700 K. Activation energies E-a were derived from the measurements at high temperatures and take on values of about 0.1 eV and show a slight increase with increasing oxygen vacancy concentration.
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| 24. |
- Eklöf-Österberg, Carin, 1987, et al.
(författare)
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The role of oxygen vacancies on the vibrational motions of hydride ions in the oxyhydride of barium titanate
- 2020
-
Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 8:13, s. 6360-6371
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite-type oxyhydrides, BaTiO3-xHx, represent a novel class of hydride ion conducting materials of interest for several electrochemical applications, but fundamental questions surrounding the defect chemistry and hydride ion transport mechanism remain unclear. Here we report results from powder X-ray diffraction, thermal gravimetric analysis, nuclear magnetic resonance spectroscopy, inelastic neutron scattering (INS), and density functional theory (DFT) simulations on three metal hydride reduced BaTiO3 samples characterized by the simultaneous presence of hydride ions and oxygen vacancies. The INS spectra are characterized by two predominating bands at around 114 (omega(perpendicular to)) and 128 (omega(parallel to)) meV, assigned as fundamental Ti-H vibrational modes perpendicular and parallel to the Ti-H-Ti bond direction, respectively, and four additional, weaker, bands at around 99 (omega(1)), 110 (omega(2)), 137 (omega(3)) and 145 (omega(4)) meV that originate from a range of different local structures associated with different configurations of the hydride ions and oxygen vacancies in the materials. Crucially, the combined analyses of INS and DFT data confirm the presence of both nearest and next-nearest neighbouring oxygen vacancies to the hydride ions. This supports previous findings from quasielastic neutron scattering experiments, that the hydride ion transport is governed by jump diffusion dynamics between neighbouring and next-nearest neighbouring hydride ion-oxygen vacancy local structures. Furthermore, the investigation of the momentum transfer dependence of the INS spectrum is used to derive the mean square displacement of the hydride ions, which is shown to be in excellent agreement with the calculations. Analysis of the mean square displacement confirms that the hydrogen vibrational motions are localized in nature and only very weakly affected by the dynamics of the surrounding perovskite structure. This insight motivates efforts to identify alternative host lattices that allow for a less localization of the hydride ions as a route to higher hydride ion conductivities.
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| 25. |
- Etman, Ahmed S., et al.
(författare)
-
Insights into the Exfoliation Process of V2O5 center dot nH(2)O Nanosheet Formation Using Real-Time V-51 NMR
- 2019
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:6, s. 10899-10905
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured hydrated vanadium oxides (V2O5 center dot nH(2)O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5 center dot nH(2)O nano-sheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5 center dot nH(2)O nanosheets from the V2O5 and VO2 precursors in real using solution- and solid-state V-51 NMR. Solution-state V-51 NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28](4-) and the hydrated dioxova-nadate cation [VO2 center dot 4H(2)O](+), and during the exfoliation process, decavanadate was formed, while the amount of [VO2 center dot 4H(2)O](+) remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state V-51 NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5 center dot nH(2)O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state V-51 signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials.
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| 26. |
- Etman, Ahmed S., et al.
(författare)
-
Insights into the Exfoliation Process of V2O5· nH2O Nanosheet Formation Using Real-Time 51V NMR
- 2019
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:6, s. 10899-10905
-
Tidskriftsartikel (refereegranskat)abstract
- Copyright © 2019 American Chemical Society. Nanostructured hydrated vanadium oxides (V2O5·nH2O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5·nH2O nanosheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5·nH2O nanosheets from the V2O5 and VO2 precursors in real time using solution- and solid-state 51V NMR. Solution-state 51V NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28]4- and the hydrated dioxovanadate cation [VO2·4H2O]+, and during the exfoliation process, decavanadate was formed, while the amount of [VO2·4H2O]+ remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state 51V NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5·nH2O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state 51V signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials. ©
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| 27. |
- Georgouvelas, Dimitrios, et al.
(författare)
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Residual Lignin and Zwitterionic Polymer Grafts on Cellulose Nanocrystals for Antifouling and Antibacterial Applications
- 2020
-
Ingår i: ACS APPLIED POLYMER MATERIALS. - : American Chemical Society (ACS). - 2637-6105. ; 2:8, s. 3060-3071
-
Tidskriftsartikel (refereegranskat)abstract
- Hybrid materials from nanocellulose, lignin, and surface- grafted zwitterionic poly(sulfobetaine methacrylate) (PSBMA) chains are prepared to attain antifouling bio-based nanomaterials with enhanced antibacterial performance. The grafting of PSBMA from both cellulose and lignocellulose nanocrystals (CNC and LCNC, respectively) is attempted; however, the materials' analysis with FTIR, XPS, and solid-state C-13 NMR reveals that the grafting on LCNC is negligible. Antifouling and antibacterial performances of CNC and LCNC, as well as PSBMA-grafted CNC, are evaluated by using quartz crystal microbalance with dissipation monitoring, confocal microscopy, and the agar diffusion method using bovine serum albumin and E. coli ACTT 8937 as protein model and bacterial model, respectively. The results demonstrate that the grafting of CNC with PSBMA improves the antifouling and antibacterial activity of the material compared to pristine CNC and LCNC.
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| 28. |
- Le Marchand, Tanguy, et al.
(författare)
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1H-Detected Biomolecular NMR under Fast Magic-Angle Spinning
- 2022
-
Ingår i: Chemical Reviews. - : American Chemical Society (ACS). - 0009-2665 .- 1520-6890. ; 122:10, s. 9943-10018
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Forskningsöversikt (refereegranskat)abstract
- Since the first pioneering studies on small deuterated peptides dating more than 20 years ago, 1H detection has evolved into the most efficient approach for investigation of biomolecular structure, dynamics, and interactions by solid-state NMR. The development of faster and faster magic-angle spinning (MAS) rates (up to 150 kHz today) at ultrahigh magnetic fields has triggered a real revolution in the field. This new spinning regime reduces the 1H–1H dipolar couplings, so that a direct detection of 1H signals, for long impossible without proton dilution, has become possible at high resolution. The switch from the traditional MAS NMR approaches with 13C and 15N detection to 1H boosts the signal by more than an order of magnitude, accelerating the site-specific analysis and opening the way to more complex immobilized biological systems of higher molecular weight and available in limited amounts. This paper reviews the concepts underlying this recent leap forward in sensitivity and resolution, presents a detailed description of the experimental aspects of acquisition of multidimensional correlation spectra with fast MAS, and summarizes the most successful strategies for the assignment of the resonances and for the elucidation of protein structure and conformational dynamics. It finally outlines the many examples where 1H-detected MAS NMR has contributed to the detailed characterization of a variety of crystalline and noncrystalline biomolecular targets involved in biological processes ranging from catalysis through drug binding, viral infectivity, amyloid fibril formation, to transport across lipid membranes.
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| 29. |
- Ma, Zili, et al.
(författare)
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Exploring the Origins of Improved Photocurrent by Acidic Treatment for Quaternary Tantalum-Based Oxynitride Photoanodes on the Example of CaTaO2N
- 2020
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:1, s. 152-160
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Tidskriftsartikel (refereegranskat)abstract
- Quaternary tantalum-based oxynitrides ATa(O,N)(3),with electronic band gaps between 1.8 and 2.4 eV, are promising materials for photochemical water-splitting. The tailoring of their surface properties is a critical aspect to obtain efficient hole extraction. We report on the origin of improved photoelectrochemical (PEC) water oxidation by means of acidic treatment for this class of compounds on the example of cubic CaTaO2N particles. We address the effect of acidic treatment by using complementary physical characterization techniques, such as X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, H-1 and N-1 solid-state nuclear magnetic resonance (NMR) spectroscopy, electron microscopy, and electronic band structure calculations at the density functional theory level. In combination with PEC measurements, solid-state NMR indicates that the restructured surface displays a meaningfully higher concentration of terminating OH groups. Subsequent deposition of a nickel borate (NiBi;) catalyst on the acid-treated surface yields a higher percentual upsurge of photocurrent in comparison to pristine CaTaO2N. Our results highlight the application of solid-state NMR spectroscopy for understanding the semiconductor-catalyst interface in photochemical devices.
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| 30. |
- Mitoudi-Vagourdi, Eleni, et al.
(författare)
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Synthesis and Physical Properties of the Oxofluoride Cu-2(SeO3)F-2
- 2018
-
Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 57:8, s. 4640-4648
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Tidskriftsartikel (refereegranskat)abstract
- Single crystals of the new compound Cu-2(SeO3)F-2 were successfully synthesized via a hydrothermal method, and the crystal structure was determined from single-crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma with the unit cell parameters a = 7.066(4) (A) over circle, b = 9.590(4) (A) over circle, and c = 5.563(3) (A) over circle. Cu-2(SeO3)F-2 is isostructural with the previously described compounds Co2TeO3F2 and CoSeO3F2. The crystal structure comprises a framework of corner- and edge-sharing distorted [CuO3F3] octahedra, within which [SeO3] trigonal pyramids are present in voids and are connected to [CuO3F3] octahedra by corner sharing. The presence of a single local environment in both the F-19 and Se-77 solid-state MAS NMR spectra supports the hypothesis that O and F do not mix at the same crystallographic positions. Also the specific phonon modes observed with Raman scattering support the coordination around the cations. At high temperatures the magnetic susceptibility follows the Curie-Weiss law with Curie temperature of Theta = -173(2) K and an effective magnetic moment of mu(eff) similar to 2.2 mu(B). Antiferromagnetic ordering below similar to 44 K is indicated by a peak in the magnetic susceptibility. A second though smaller peak at similar to 16 K is tentatively ascribed to a magnetic reorientation transition. Both transitions are also confirmed by heat capacity measurements. Raman scattering experiments propose a structural phase instability in the temperature range 6-50 K based on phonon anomalies. Further changes in the Raman shift of modes at similar to 46 K and similar to 16 K arise from transitions of the magnetic lattice in accordance with the susceptibility and heat capacity measurements.
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| 31. |
- Mondal, Arobendo, et al.
(författare)
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Large-Scale Computation of Nuclear Magnetic Resonance Shifts for Paramagnetic Solids Using CP2K
- 2018
-
Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 14:1, s. 377-394
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale computations of nuclear magnetic resonance (NMR) shifts for extended paramagnetic solids (pNMR) are reported using the highly efficient Gaussian-augmented plane-wave implementation of the CP2K code. Combining hyperfine couplings obtained with hybrid functionals with g-tensors and orbital shieldings computed using gradient-corrected functionals, contact, pseudocontact, and orbital-shift contributions to pNMR shifts are accessible. Due to the efficient and highly parallel performance of CP2K, a wide variety of materials with large unit cells can be studied with extended Gaussian basis sets. Validation of various approaches for the different contributions to pNMR shifts is done first for molecules in a large supercell in comparison with typical quantum-chemical codes. This is then extended to a detailed study of g-tensors for extended solid transition-metal fluorides and for a series of complex lithium vanadium phosphates. Finally, lithium pNMR shifts are computed for Li3V2(PO4)(3), for which detailed experimental data are available. This has allowed an in-depth study of different approaches (e.g., full periodic versus incremental cluster computations of g-tensors and different functionals and basis sets for hyperfine computations) as well as a thorough analysis of the different contributions to the pNMR shifts. This study paves the way for a more-widespread computational treatment of NMR shifts for paramagnetic materials.
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| 32. |
- Nedumkandathil, Reji, et al.
(författare)
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Hydride Reduction of BaTiO3 ? Oxyhydride Versus O Vacancy Formation
- 2018
-
Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 3:9, s. 11426-11438
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the hydride reduction of tetragonal BaTiO3 using the metal hydrides CaH2, NaH, MgH2, NaBH4, and NaAlH4. The reactions employed molar BaTiO3/H ratios of up to 1.8 and temperatures near 600 °C. The air-stable reduced products were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy, thermogravimetric analysis (TGA), and 1H magic angle spinning (MAS) NMR spectroscopy. PXRD showed the formation of cubic products - indicative of the formation of BaTiO3-xHx - except for NaH. Lattice parameters were in a range between 4.005 Å (for NaBH4-reduced samples) and 4.033 Å (for MgH2-reduced samples). With increasing H/BaTiO3 ratio, CaH2-, NaAlH4-, and MgH2-reduced samples were afforded as two-phase mixtures. TGA in air flow showed significant weight increases of up to 3.5% for reduced BaTiO3, suggesting that metal hydride reduction yielded oxyhydrides BaTiO3-xHx with x values larger than 0.5. 1H MAS NMR spectroscopy, however, revealed rather low concentrations of H and thus a simultaneous presence of O vacancies in reduced BaTiO3. It has to be concluded that hydride reduction of BaTiO3 yields complex disordered materials BaTiO3-xHy?(x-y) with x up to 0.6 and y in a range 0.04-0.25, rather than homogeneous solid solutions BaTiO3-xHx. Resonances of (hydridic) H substituting O in the cubic perovskite structure appear in the ?2 to ?60 ppm spectral region. The large range of negative chemical shifts and breadth of the signals signifies metallic conductivity and structural disorder in BaTiO3-xHy?(x-y). Sintering of BaTiO3-xHy?(x-y) in a gaseous H2 atmosphere resulted in more ordered materials, as indicated by considerably sharper 1H resonances.
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| 33. |
- Nedumkandathil, Reji, et al.
(författare)
-
Hydride Reduction of BaTiO3 – Oxyhydride vs O-Vacancy Formation
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We investigated the hydride reduction of tetragonal BaTiO3 using the metal hydrides CaH2, NaH, MgH2, NaBH4 and NaAlH4. The reactions employed molar BaTiO3:H ratios of up to 1.8 and temperatures near 600 °C. The air stable reduced products were characterized by powder X-ray diffraction (PXRD), transmission electron microscopy, thermogravimetric analysis (TGA) and solid-state 1H NMR spectroscopy. PXRD showed the formation of cubic products - indicative of the formation of BaTiO3-xHx - except for NaH. Lattice parameters were in a range between 4.005 Å (for NaBH4 reduces samples) and 4.033 Å (for MgH2 reduced samples). With increasing BaTiO3:H ratio, CaH2, NaAlH4 and MgH2 reduced samples were afforded as two-phase mixtures. TGA in air flow showed significant weight increase of up to 3.5 % for reduced BaTiO3, suggesting that metal hydride reduction yielded oxyhydrides BaTiO3-xHx with x values larger 0.5. 1H NMR, however, revealed rather low concentrations of H, and, thus a simultaneous presence of O vacancies in reduced BaTiO3. It has to be concluded that hydride reduction of BaTiO3 yields complex disordered materials BaTiO3-xHy□(x-y) with x up to 0.6, y in a range 0.05 – 0.2 and (x-y) > y, rather than homogeneous solid solutions BaTiO3Hx. Resonances of (hydridic) H substituting O in the cubic perovskite structure appear in the -2 to -60 ppm spectral region. The large range of chemical shifts and breadth of the signals signifies the structural disorder in BaTiO3-xHy□(x-y). Sintering of BaTiO3-xHy□(x-y) in a gaseous H2 atmosphere resulted in more ordered materials as indicated by considerably sharper 1H resonances.
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| 34. |
- Nedumkandathil, Reji, et al.
(författare)
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Investigation of the Order–Disorder Rotator Phase Transition in KSiH3 and RbSiH3
- 2017
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:9, s. 5241-5252
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Tidskriftsartikel (refereegranskat)abstract
- The β–α (order–disorder) transition in the silanides ASiH3 (A = K, Rb) was investigated by multiple techniques, including neutron powder diffraction (NPD, on the corresponding deuterides), Raman spectroscopy, heat capacity (Cp), solid-state 2H NMR spectroscopy, and quasi-elastic neutron scattering (QENS). The crystal structure of α-ASiH3 corresponds to a NaCl-type arrangement of alkali metal ions and randomly oriented, pyramidal, SiH3– moieties. At temperatures below 200 K ASiH3 exist as hydrogen-ordered (β) forms. Upon heating the transition occurs at 279(3) and 300(3) K for RbSiH3 and KSiH3, respectively. The transition is accompanied by a large molar volume increase of about 14%. The Cp(T) behavior is characteristic of a rotator phase transition by increasing anomalously above 120 K and displaying a discontinuous drop at the transition temperature. Pronounced anharmonicity above 200 K, mirroring the breakdown of constraints on SiH3– rotation, is also seen in the evolution of atomic displacement parameters and the broadening and eventual disappearance of libration modes in the Raman spectra. In α-ASiH3, the SiH3– anions undergo rotational diffusion with average relaxation times of 0.2–0.3 ps between successive H jumps. The first-order reconstructive phase transition is characterized by a large hysteresis (20–40 K). 2H NMR revealed that the α-form can coexist, presumably as 2–4 nm (sub-Bragg) sized domains, with the β-phase below the phase transition temperatures established from Cp measurements. The reorientational mobility of H atoms in undercooled α-phase is reduced, with relaxation times on the order of picoseconds. The occurrence of rotator phases α-ASiH3 near room temperature and the presence of dynamical disorder even in the low-temperature β-phases imply that SiH3– ions are only weakly coordinated in an environment of A+ cations. The orientational flexibility of SiH3– can be attributed to the simultaneous presence of a lone pair and (weakly) hydridic hydrogen ligands, leading to an ambidentate coordination behavior toward metal cations.
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| 35. |
- Papawassiliou, Wassilios, et al.
(författare)
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Crystal and electronic facet analysis of ultrafine Ni2P particles by solid-state NMR nanocrystallography
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- Structural and morphological control of crystalline nanoparticles is crucial in the field of heterogeneous catalysis and the development of reaction specific catalysts. To achieve this, colloidal chemistry methods are combined with ab initio calculations in order to define the reaction parameters, which drive chemical reactions to the desired crystal nucleation and growth path. Key in this procedure is the experimental verification of the predicted crystal facets and their corresponding electronic structure, which in case of nanostructured materials becomes extremely difficult. Here, by employing P-31 solid-state nuclear magnetic resonance aided by advanced density functional theory calculations to obtain and assign the Knight shifts, we succeed in determining the crystal and electronic structure of the terminating surfaces of ultrafine Ni2P nanoparticles at atomic scale resolution. Our work highlights the potential of ssNMR nanocrystallography as a unique tool in the emerging field of facet-engineered nanocatalysts. Structural and morphological control of crystalline nanoparticles is crucial in heterogeneous catalysis. Applying DFT-assisted solid-state NMR spectroscopy, we determine the surface crystal and electronic structure of Ni2P nanoparticles, unveiling NMR nanocrystallography as an emerging tool in facet-engineered nanocatalysts.
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| 36. |
- Papawassiliou, Wassilios, et al.
(författare)
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Resolving Dirac electrons with broadband high-resolution NMR
- 2020
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Detecting the metallic Dirac electronic states on the surface of Topological Insulators (TIs) is critical for the study of important surface quantum properties (SQPs), such as Majorana zero modes, where simultaneous probing of the bulk and edge electron states is required. However, there is a particular shortage of experimental methods, showing at atomic resolution how Dirac electrons extend and interact with the bulk interior of nanoscaled TI systems. Herein, by applying advanced broadband solid-state 125Te nuclear magnetic resonance (NMR) methods on Bi2Te3 nanoplatelets, we succeeded in uncovering the hitherto invisible NMR signals with magnetic shielding that is influenced by the Dirac electrons, and we subsequently showed how the Dirac electrons spread inside the nanoplatelets. In this way, the spin and orbital magnetic susceptibilities induced by the bulk and edge electron states were simultaneously measured at atomic scale resolution, providing a pertinent experimental approach in the study of SQPs.
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| 37. |
- Pell, Andrew J.
(författare)
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A method to calculate the NMR spectra of paramagnetic species using thermalized electronic relaxation
- 2021
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 326
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Tidskriftsartikel (refereegranskat)abstract
- For paramagnetic species, it has been long understood that the hyperfine interaction between the unpaired electrons and the nucleus results in a nuclear magnetic resonance (NMR) peak that is shifted by a paramagnetic shift, rather than split by the coupling, due to an averaging of the electronic magnetic moment caused by electronic relaxation that is fast in comparison to the hyperfine coupling constant. However, although this feature of paramagnetic NMR has formed the basis of all theories of the param-agnetic shift, the precise theory and mechanism of the electronic relaxation required to predict this result has never been discussed, nor has the assertion been tested. In this paper, we show that the standard semi-classical Redfield theory of relaxation fails to predict a paramagnetic shift, as does any attempt to correct for the semi-classical theory using modifications such as the inhomogeneous master equation or Levitt & ndash;di Bari thermalization. In fact, only the recently-introduced Lindbladian theory of relaxation in magnetic resonance [J. Magn. Reson., 310, 106645 (2019)] is able to correctly predict the paramagnetic shift tensor and relaxation-induced linewidth in pNMR. Furthermore, this new formalism is able to pre-dict the NMR spectra of paramagnetic species outside the high-temperature and weak-order limits, and is therefore also applicable to dynamic nuclear polarization. The formalism is tested by simulations of five case studies, which include Fermi-contact and spin-dipolar hyperfine couplings, g-anisotropy, zero-field splitting, high and low temperatures, and fast and slow electronic relaxation.
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| 38. |
- Pell, Andrew J., et al.
(författare)
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Paramagnetic NMR in solution and the solid state
- 2019
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Ingår i: Progress in nuclear magnetic resonance spectroscopy. - : Elsevier BV. - 0079-6565 .- 1873-3301. ; 111, s. 1-271
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Forskningsöversikt (refereegranskat)abstract
- The field of paramagnetic NMR has expanded considerably in recent years. This review addresses both the theoretical description of paramagnetic NMR, and the way in which it is currently practised. We provide a review of the theory of the NMR parameters of systems in both solution and the solid state. Here we unify the different languages used by the NMR, EPR, quantum chemistry/DFT, and magnetism communities to provide a comprehensive and coherent theoretical description. We cover the theory of the paramagnetic shift and shift anisotropy in solution both in the traditional formalism in terms of the magnetic susceptibility tensor, and using a more modern formalism employing the relevant EPR parameters, such as are used in first-principles calculations. In addition we examine the theory first in the simple non-relativistic picture, and then in the presence of spin-orbit coupling. These ideas are then extended to a description of the paramagnetic shift in periodic solids, where it is necessary to include the bulk magnetic properties, such as magnetic ordering at low temperatures. The description of the paramagnetic shift is completed by describing the current understanding of such shifts due to lanthanide and actinide ions. We then examine the paramagnetic relaxation enhancement, using a simple model employing a phenomenological picture of the electronic relaxation, and again using a more complex state-of-the-art theory which incorporates electronic relaxation explicitly. An additional important consideration in the solid state is the impact of bulk magnetic susceptibility effects on the form of the spectrum, where we include some ideas from the field of classical electrodynamics. We then continue by describing in detail the solution and solid-state NMR methods that have been deployed in the study of paramagnetic systems in chemistry, biology, and the materials sciences. Finally we describe a number of case studies in paramagnetic NMR that have been specifically chosen to highlight how the theory in part one, and the methods in part two, can be used in practice. The systems chosen include small organometallic complexes in solution, solid battery electrode materials, metalloproteins in both solution and the solid state, systems containing lanthanide ions, and multi-component materials used in pharmaceutical controlled-release formulations that have been doped with paramagnetic species to measure the component domain sizes.
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| 39. |
- Rzepka, Przemyslaw, et al.
(författare)
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Nature of Chemisorbed CO2 in Zeolite A
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:35, s. 21497-21503
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Tidskriftsartikel (refereegranskat)abstract
- Formation of CO32- and HCO3- species without the participation of the framework-bridging oxygen atoms (-O-) upon chemisorption of CO2 in zeolite vertical bar Na-12 vertical bar-A is revealed. The transfer of O and H atoms is very likely to have proceeded via the involvement of residual H2O or -OH groups. A combined study by the solid-state H-1 and C-13 MAS NMR, quantum chemical calculations, and in situ infrared spectroscopy showed that the chemisorption mainly occurred by the formation of HCO3-. However, at a low surface coverage of physisorbed and acidic CO2, a significant fraction of HCO3- was deprotonated and transformed into CO32-. We expect that a similar chemisorption of CO2 would occur for low-silica zeolites and other basic silicates of interest for capture of CO2 from the gas mixtures.
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| 40. |
- Seymour, Ieuan D., et al.
(författare)
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Characterizing Oxygen Local Environments in Paramagnetic Battery Materials via O-17 NMR and DFT Calculations
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 138:30, s. 9405-9408
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Tidskriftsartikel (refereegranskat)abstract
- Experimental techniques that probe the local environment around O in paramagnetic Li-ion cathode materials are essential in order to understand the complex phase transformations and O redox processes that can occur during electrochemical delithiation. While Li NMR is a well-established technique for studying the local environment of Li ions in paramagnetic battery materials, the use of O-17 NMR in the same materials has not yet been reported. In this work, we present a combined O-17 NMR and hybrid density functional theory study of the local O environments in Li2MnO3, a model compound for layered Li-ion batteries. After a simple O-17 enrichment procedure, we observed five resonances with large O-17 shifts ascribed to the Fermi contact interaction with directly bonded Mn4+ ions. The five peaks were separated into two groups with shifts at 1600 to 1950 ppm and 2100 to 2450 ppm, which, -with the aid of first principles calculations, were assigned to the O-17 shifts of environments similar to the 4i and 8j sites in pristine Li2MnO3, respectively. The multiple O environments in each region were ascribed to the presence of stacking faults within the Li2MnO3 structure. From the ratio of the intensities of the different O-17 environments, the percentage of stacking faults was found to be ca. 10%. The methodology for studying (17)Oshifts in paramagnetic solids described in this work will be useful for studying the local environments of O in a range of technologically interesting transition metal oxides.
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| 41. |
- Siebeneichler, Stefanie, et al.
(författare)
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Frustration and 120° Magnetic Ordering in the Layered Triangular Antiferromagnets AFe(PO3F)2 (A = K, (NH4)2Cl, NH4, Rb, and Cs)
- 2022
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 34:17, s. 7982-7994
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Tidskriftsartikel (refereegranskat)abstract
- A new family of oxofluorophoshates, AFe(PO3F)2 (A = K, (NH4)2Cl, NH4, Rb, and Cs), was synthesized via ionothermal methods using PF6 ionic liquids. Single-crystal and powder X-ray diffraction reveal that AFe(PO3F)2 with A = (NH4)2Cl crystallizes in a trigonal structure, while AFe(PO3F)2 with A = NH4, Rb, and Cs crystallizes in a triclinic structure. Dimorphic KFe(PO3F)2 crystallizes in both the trigonal and triclinic forms. The structures of all compounds feature Yavapaiite-like Fe(PO3F)2 slabs, which are characterized by triangular Fe layers, planar in the case of the trigonal structure and undulated in the case of the triclinic one. Magnetization measurements reveal all compounds to order antiferromagnetically at low temperatures. The trigonal phases AFe(PO3F)2 (A = K and (NH4)2Cl) display complex magnetic H–T phase diagrams. The observation of magnetization plateaus at Msat/3 (Msat = saturation magnetization) indicates the existence of the up–up–down (UUD) and V-phases at applied magnetic fields in the magnetically ordered state. Powder neutron diffraction measurements of KFe(PO3F)2 confirm the 120° spin structure at zero fields. Along c, the magnetic moments form a commensurate spiral since the spins in each plane are rotated by 90° with respect to the adjacent one. To our knowledge, this is the first time such a non-centrosymmetric version of the 120° spin structure with a 90° rotation between nearest planes has been reported.
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| 42. |
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| 43. |
- Stamou, Christina, et al.
(författare)
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Indium(III) in the "Periodic Table" of Di(2-pyridyl) Ketone : An Unprecedented Transformation of the Ligand and Solid-State In-115 NMR Spectroscopy as a Valuable Structural Tool
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:7, s. 4829-4840
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Tidskriftsartikel (refereegranskat)abstract
- Reactions of di(2-pyridyl) ketone, (py)(2)CO, with indium(III) halides in CH3NO2 have been studied, and a new transformation of the ligand has been revealed. In the presence of In-III, the C=O bond of (py)(2)CO is subjected to nucleophilic attack by the carbanion -:CH2NO2, yielding the dinuclear complexes [In2X4{(py)(2)C(CH2NO2)(O)}(2)] (X = Cl, 1; X = Br, 2; X = I, 3) in moderate to good yields. The alkoxo oxygens of the two eta(1):eta(2):eta(1)-(py)(2)C(CH2NO2)(O)- ligands doubly bridge the In-III centers and create a {In-2(mu(2)-OR)(2)}(4+) core. Two pyridyl nitrogens of different organic ligands and two terminal halogeno ions complete a distorted-octahedral stereochemistry around each In(III) ion. After maximum excitation at 360 or 380 nm, the solid chloro complex 1 emits blue light at 420 and 440 nm at room temperature, the emission being attributed to charge transfer within the coordinated organic ligand. Solid-state In-115 NMR spectra, in combination with DFT calculations, of 1-3 have been studied in detail at both 9.4 and 14.1 T magnetic fields. The nuclear quadrupolar and chemical shift parameters provide valuable findings concerning the electric field gradients and magnetic shielding at the nuclei of indium, respectively. The experimentally derived C-Q values are 40 +/- 3 MHz for 1, 46 +/- 5 MHz for 2, and 50 +/- 10 and 64 +/- 7 MHz for the two crystallographically independent InIII sites for 3, while the diso values fall in the range 130 +/- 30 to -290 +/- 60 ppm. The calculated C-Q and asymmetry parameter (eta(Q)) values are fully consistent with the experimental values for 1 and 2 and are in fairly good agreement for 3. The results have been analyzed and discussed in terms of the known (1, 3) and proposed (2) structural features of the complexes, demonstrating that In-115 NMR is an effective solid-state technique for the study of indium(III) complexes.
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| 44. |
- Szewczyk, Ireneusz, et al.
(författare)
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Electrochemical Denitrification and Oxidative Dehydrogenation of Ethylbenzene over N-doped Mesoporous Carbon : Atomic Level Understanding of Catalytic Activity by N-15 NMR Spectroscopy
- 2020
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 32:17, s. 7263-7273
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Tidskriftsartikel (refereegranskat)abstract
- Spherical mesoporous carbon (with a particle size in the range of 40−75 μm) was synthesized by nanoreplication of a hard silica template using sucrose as the carbon precursor. The mesoporous carbon with BET surface areas higher than 1200 m2/g was doped with N by a treatment in an aqueous solution of nitric acid and/or in a flow of gaseous ammonia. The highest N content (3.2 wt % of N in bulk) was obtained when both modification methods were combined. Complementary physicochemical characterization techniques, including scanning electron microscopy (SEM), low-temperature N2 adsorption, powder X-ray diffraction (XRD), and Raman spectroscopy revealed the morphology, structure, and textural properties of the synthesized N-loaded carbon materials. For the identification of the detailed chemical structure on the surface of the carbons, 1H, 13C, and 15N solid-state nuclear magnetic resonance (NMR) measurements were performed, and the data were supported by chemical shift calculations with accurate quantum chemistry methods and X-ray photoelectron spectroscopic (XPS) analyses. All NMR experiments were performed at natural isotope abundance. The verified experimental data clearly showed that after the introduction of the N-containing moieties by the combined methods of treatment, a high concentration of pyridinic N at the edge, and pyrrolic N being external to the edge, was achieved for the mesoporous carbon. The distributed N surface species promoted the catalytic activity in the oxidative dehydrogenation of ethylbenzene to styrene but did not significantly influence the efficiency of the carbon materials in the electrochemical reduction of nitrate ions.
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| 45. |
- Wahlström, Niklas, 1990-, et al.
(författare)
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Cellulose from the green macroalgae Ulva lactuca: isolation, characterization, optotracing, and production of cellulose nanofibrils
- 2020
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X.
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Tidskriftsartikel (refereegranskat)abstract
- We report (1) successful extraction and characterization of cellulose from northern hemisphere green macroalgae Ulva lactuca (Ulva fenestrata) collected along the Swedish west coast and cultivated indoors under controlled conditions, followed by (2) its utilization in the production of lignin-free cellulose nanofibrils (CNF). Cellulose was extracted by sequential treatment with ethanol, hydrogen peroxide, sodium hydroxide, and hydrochloric acid, yielding a cellulose-rich insoluble fraction. The extracted cellulose was disintegrated into CNF using a mechanical homogenization process without any further enzymatic pre-treatments. In addition, regenerated cellulose was prepared. XRD characterization of the CNF showed characteristic peaks for the cellulose I allomorph and confirmed that the nanofibrils were semicrystalline with a crystallinity index of 48%. Regenerated cellulose was mostly amorphous with an XRD pattern indicating the presence of the cellulose II allomorph. The cellulose fractions were essentially free from inorganic substances and thermally stable up to around 260 degrees C. Structural mapping with CP-MAS C-13-NMR sustains the cellulose content of CNF and regenerated cellulose, respectively, yet ion chromatography identified the presence of 10-15% xylose in the fractions. Optotracing was used as a novel and non-disruptive tool to selectively assess the polysaccharide composition of the cellulose fractions and produced CNF aiming to shed light on this hitherto non-resolved origin of xylose in Ulva cell wall matter. Fluorescence excitation and emission spectra of a panel of 4 oligothiophenes identified and verified the presence of cellulose and sustain the conclusion that the isolated fractions consist of cellulose intertwined with a small amount of a xylose-containing glucan copolymer. [GRAPHICS] .
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| 46. |
- Winterlich, Meghan, et al.
(författare)
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A biocompatible ZnNa2-based metal-organic framework with high ibuprofen, nitric oxide and metal uptake capacity
- 2020
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Ingår i: Materials Advances. - : Royal Society of Chemistry (RSC). - 2633-5409. ; 1:7, s. 2248-2260
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Tidskriftsartikel (refereegranskat)abstract
- Metal organic frameworks (MOFs) have received significant attention in recent years in the areas of biomedical and environmental applications. Among them, mixed metal MOFs, although promising, are relatively few in number in comparison with their homometallic analogues. The employment of benzophenone-4,4'-dicarboxylic acid (bphdcH(2)) in mixed metal MOF chemistry provided access to a 3D MOF, [Na2Zn(bphdc)(2)(DMF)(2)](n) (NUIG1). NUIG1 displays a new topology and is a rare example of a mixed metal MOF based on 1D rod secondary building units. UV-vis, HPLC, TGA, XRPD, solid state NMR and computational studies indicated that NUIG1 exhibits an exceptionally high Ibuprofen (Ibu) and nitric oxide adsorption capacity. The MCF-7 cell line was used to assess the toxicity of NUIG1 and Ibu@NUIG1, revealing that both species are non-toxic (cell viability > 70%). NUIG1 exhibits good performance in the adsorption of metal ions (Co-II, Ni-II, Cu-II) from aqueous environments, as was demonstrated by UV-vis, EDX, ICP, SEM and direct and alternate current magnetic susceptibility studies. The colour and the magnetic properties of the M@NUIG1 species depend strongly on the kind and the amount of the encapsulated metal ion in the MOF pores.
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| 47. |
- Yang, Jinqin, et al.
(författare)
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Computational insight into the hydrogenation of CO2 and carbamic acids to methanol by a ruthenium(II)-based catalyst : The role of amino (NH) ligand group
- 2021
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Ingår i: Molecular catalysis. - : Elsevier BV. - 2468-8231. ; 506
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Tidskriftsartikel (refereegranskat)abstract
- Methanol is a liquid hydrogen carrier and potential platform molecule, and significant efforts are currently devoted to hydrogenate CO2 to methanol. In this work, hydrogenations of CO2 and captured CO2 (as dimethyl-carbamic acid, DMCA, and methylcarbamic acid, MCA) to methanol over Ru-MACHO (pre)catalysts were studied with a Ru-II-catalyst model by Density Functional Theory (DFT) calculations. For the hydrogenation of CO2, the concerted reaction was the rate-determining step involving a synchronous hydride transfer and proton transfer from the Ru-II-catalyst to coordinatively saturated intermediate methanediol. In the hydrogenation cycles of DMCA and MCA, the first hydride transfer reactions were more difficult than the concerted hydride and proton transfer from the Ru-II-catalyst to the aldehyde group of intermediate formaldehyde. These first hydride transfer reactions were identified as the rate-determining steps. The hydrogenations of DMCA and MCA were found much more favourable in methanol production than the direct CO2 hydrogenation, however, formamides could be main intermediate products due to the easier C-O breakage than C-N breakage in gem diols, and during the further hydrogenation of formamides, formaldehyde could be the main intermediate due to the easier C-N breakage than C-O breakage in alkanolamines. In all three hydrogenation cases, the amino (NH) ligand of the Ru-II-catalyst initially remained chemically innocent, and intermediates were stabilized by N-H center dot O hydrogenbonding interactions (HBIs) facilitating the continuation of catalytic hydrogenation cycles, but the NH ligand took part in multi-bond concerted reactions to produce eventually methanol.
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