| 1. |
- Mohr, Claudia, et al.
(författare)
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Molecular identification of organic vapors driving atmospheric nanoparticle growth
- 2019
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Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Particles formed in the atmosphere via nucleation provide about half the number of atmospheric cloud condensation nuclei, but in many locations, this process is limited by the growth of the newly formed particles. That growth is often via condensation of organic vapors. Identification of these vapors and their sources is thus fundamental for simulating changes to aerosol-cloud interactions, which are one of the most uncertain aspects of anthropogenic climate forcing. Here we present direct molecular-level observations of a distribution of organic vapors in a forested environment that can explain simultaneously observed atmospheric nanoparticle growth from 3 to 50nm. Furthermore, the volatility distribution of these vapors is sufficient to explain nanoparticle growth without invoking particle-phase processes. The agreement between observed mass growth, and the growth predicted from the observed mass of condensing vapors in a forested environment thus represents an important step forward in the characterization of atmospheric particle growth.
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| 2. |
- Banerjee, Ambar, 1985-, et al.
(författare)
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Accessing metal-specific orbital interactions in C–H activation with resonant inelastic X-ray scattering
- 2024
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 15:7, s. 2398-2409
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Tidskriftsartikel (refereegranskat)abstract
- Photochemically prepared transition-metal complexes are known to be effective at cleaving the strong C–H bonds of organic molecules in room temperature solutions. There is also ample theoretical evidence that the two-way, metal to ligand (MLCT) and ligand to metal (LMCT), charge-transfer between an incoming alkane C–H group and the transition metal is the decisive interaction in the C–H activation reaction. What is missing, however, are experimental methods to directly probe these interactions in order to reveal what determines reactivity of intermediates and the rate of the reaction. Here, using quantum chemical simulations we predict and propose future time-resolved valence-to-core resonant inelastic X-ray scattering (VtC-RIXS) experiments at the transition metal L-edge as a method to provide a full account of the evolution of metal–alkane interactions during transition-metal mediated C–H activation reactions. For the model system cyclopentadienyl rhodium dicarbonyl (CpRh(CO)2), we demonstrate, by simulating the VtC-RIXS signatures of key intermediates in the C–H activation pathway, how the Rh-centered valence-excited states accessible through VtC-RIXS directly reflect changes in donation and back-donation between the alkane C–H group and the transition metal as the reaction proceeds via those intermediates. We benchmark and validate our quantum chemical simulations against experimental steady-state measurements of CpRh(CO)2 and Rh(acac)(CO)2 (where acac is acetylacetonate). Our study constitutes the first step towards establishing VtC-RIXS as a new experimental observable for probing reactivity of C–H activation reactions. More generally, the study further motivates the use of time-resolved VtC-RIXS to follow the valence electronic structure evolution along photochemical, photoinitiated and photocatalytic reactions with transition metal complexes.
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| 3. |
- Das, Sambit Kumar, 1994-, et al.
(författare)
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Simulating non-adiabatic dynamics of photoexcited phenyl azide : Investigating electronic and structural relaxation en route to the formation of phenyl nitrene
- 2024
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Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 30:7
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Tidskriftsartikel (refereegranskat)abstract
- Excited state molecular dynamics simulations of the photoexcited phenyl azide have been performed. The semi-classical surface hopping approximation has enabled an unconstrained analysis of the electronic and nuclear degrees of freedom which contribute to the molecular dissociation of phenyl azide into phenyl nitrene and molecular nitrogen. The significance of the second singlet excited state in leading the photodissociation has been established through electronic structure calculations, based on multi-configurational schemes, and state population dynamics. The investigations on the structural dynamics have revealed the N−N bond separation to be accompanied by synchronous changes in the azide N−N−N bond angle. The 100 fs simulation results in a nitrene fragment that is electronically excited in the singlet manifold.
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| 4. |
- Karmakar, Anirban, 1983, et al.
(författare)
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A new methanol solvate and Hirshfeld analysis of π-stacking in 2,3,6,7,10,11-hexahydroxytriphenylene solvates
- 2013
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Ingår i: Acta Crystallographica Section C: Crystal Structure Communications. - 0108-2701 .- 1600-5759. ; C69:3, s. 251-254
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Tidskriftsartikel (refereegranskat)abstract
- The structure of 2,3,6,7,10,11-hexahydroxytriphenylene (hhtp)methanol monosolvate, C18H12O6•CH3OH, has triclinicsymmetry (space group P1). The compound has a threedimensionallayered network structure formed by intermolecularhydrogen bonding. Structure analysis with Hirshfeldsurfaces is shown to be a sensitive method for comparing π -stacking effects in the five known solvates of hhtp. The titlestructure shows slightly weaker π -stacking than the dihydrate,but stronger π -stacking than the other three solvates.
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| 5. |
- Lutz, Anna, 1986, et al.
(författare)
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Gas to Particle Partitioning of Organic Acids in the Boreal Atmosphere
- 2019
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Ingår i: Acs Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 3:7, s. 1279-1287
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Tidskriftsartikel (refereegranskat)abstract
- Gas to particle partitioning of carboxylic acids was investigated using a high-resolution chemical ionization time-of-flight mass spectrometer (HR-CI-ToF-MS) with the filter inlet for gases and aerosol (FIGAERO). Specifically, the partitioning coefficients of 640 components with unique molecular composition were calculated from an assumed linear relationship between [particle]/[gas] versus the mass of the organic fraction (M-org) according to Raoult's law, i.e., equilibrium phase partitioning. We demonstrate that, using the full data set, most of the compounds do not follow a linear relationship. This is especially the case for low- and high-molecular-weight species. Using a subset of the data, with concurrent low sulfate ambient observations ([SO42- < 0.4 mu g m(-3)), the relationship improved significantly and K-i could be derived from the slope of a linear regression to the data. The 100 species with the highest R-2 (>= 0.7) of this regression are presented. The restrictions during high sulfate conditions can be explained by changes in either the equilibrium conditions (e.g., the activity coeffient, gamma(i)) or uptake kinetics (mass transfer limitation). This study demonstrates that partitioning of compounds in the complex ambient atmosphere follows ideal Raoult's law for some limited conditions and stresses the need for studies also in more polluted environments.
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| 6. |
- Hagman, Benjamin, et al.
(författare)
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Steps Control the Dissociation of CO2 on Cu(100)
- 2018
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 140:40, s. 12974-12979
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Tidskriftsartikel (refereegranskat)abstract
- CO2 reduction reactions, which provide one route to limit the emission of this greenhouse gas, are commonly performed over Cu-based catalysts. Here, we use ambient pressure X-ray photoelectron spectroscopy together with density functional theory to obtain an atomistic understanding of the dissociative adsorption of CO2 on Cu(100). We find that the process is dominated by the presence of steps, which promote both a lowering of the dissociation barrier and an efficient separation between adsorbed O and CO, reducing the probability for recombination. The identification of steps as sites for efficient CO2 dissociation provides an understanding that can be used in the design of future CO2 reduction catalysts.
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| 7. |
- Renier, Olivier, et al.
(författare)
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Shape Preserving Single Crystal to Amorphous to Single Crystal Polymorphic Transformation Is Possible
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 143:48, s. 20202-20206
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Tidskriftsartikel (refereegranskat)abstract
- Many crystalline materials form polymorphs and undergo solid–solid transitions between different forms as a function of temperature or pressure. However, there is still a poor understanding of the mechanism of transformation. Conclusions about the transformation process are typically drawn by comparing the crystal structures before and after the conversion, but gaining detailed mechanistic knowledge is strongly impeded by the generally fast rate of these transitions. When the crystal morphology does not change, it is assumed that crystallinity is maintained throughout the process. Here we report transformation between polymorphs of ZnCl2(1,3-diethylimidazole-2-thione)2 which are sufficiently slow to allow unambiguous assignment of single crystal to single crystal transformation with shape preservation proceeding through an amorphous intermediate phase. This result fundamentally challenges the commonly accepted views of polymorphic phase transition mechanisms.
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| 8. |
- Rzepka, Przemyslaw, et al.
(författare)
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CO2-Induced Displacement of Na+ and K+ in Zeolite INaKI-A
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:30, s. 17211-17220
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption technologies offer opportunities to remove CO2 from gas mixtures, and zeolite A has good properties that include a high capacity for the adsorption of CO2 . It has been argued that its abilities to separate CO2 from N-2 in flue gas and CO2 from CH4 in raw biogas can be further enhanced by replacing Na+ with K+ in the controlling pore window apertures. In this study, several compositions of I Na12-xKxI-A were prepared and studied with respect to the adsorption of CO2 N-2, and CH4, and the detailed structural changes were induced by the adsorption of CO2. The adsorption of CO2 gradually decreased on an increasing content of K+, whereas the adsorption of N-2 and CH4 was completely nulled already at relatively small contents of K. Of the studied samples, INa9K3I-A exhibited the highest CO2 over N-2/CH4 selectivities, with a(CO2/N-2 ) > 21 000 and a(CO2/CH4) > 8000. For samples with and without adsorbed CO2 analyses of powder X-ray diffraction (PXRD) data revealed that K+ preferred to substitute Na+ at the eight-ring sites. The Na(+ )ions at the six-ring sites were gradually replaced by K+ on an increasing content, and these sites split into two positions on both sides of the six-ring mirror plane. It was observed that both the eight-ring and six-ring sites tailored the maximum adsorption capacity for CO2 and possibly also the diffusion of CO2 into the alpha-cavities of INa12-xKxI-A. The adsorption of CH4 and N-2 on the other hand appeared to be controlled by the K+ ions blocking the eight-ring windows. The in situ PXRD study revealed that the positions of the extra-framework cations were displaced into the a-cavities of INa12(_)x,KxI-A on the adsorption of CO2 . For samples with a low content of K+, the repositioning of the cations was consistent with a mutual attraction with the adsorbed CO(2 )molecules.
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| 9. |
- Seisenbaeva, Gulaim, et al.
(författare)
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Molecular insight into the mode-of-action of phosphonate monolayers as active functions of hybrid metal oxide adsorbents. Case study in sequestration of rare earth elements
- 2015
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 5:31, s. 24575-24585
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Tidskriftsartikel (refereegranskat)abstract
- The insight into the molecular aspects of ligand grafting and potential maximal capacity of hybrid organic-inorganic adsorbents bearing phosphonate ligand monolayers as active functions was obtained by single crystal X-ray studies of ligand-functionalized titanium alkoxide complexes. The attachment of molecules occurs generally in the tripodal vertical fashion with the minimal distance between them being about 8.7 angstrom, resulting in 0.19 nm(2) as the minimal surface area per function. In the present experimental work the theoretical loading capacity could almost be achieved for functionalization of mesoporous nanorods of anatase with imino-bis-methylphosphonic acid (IMPA, NH(CH2PO3H2)(2)) or aminoethylphosphonic acid (AEPA, H2NC2H4PO3H2). The products had the same morphology as the starting material, as was established by SEM and optical microscopy. The size and structure of the individual nanoparticles of the constituting inorganic component of the material were preserved and practically unchanged through the surface modification, as established by powder XRD and EXAFS studies. The surface area of the inorganic-organic hybrids decreased somewhat from the initial similar to 250 m(2) g(-1), on adsorption of AEPA (0.21 mmol g(-1)) to similar to 240 m(2) g(-1), and on adsorption of IMPA (0.17 mmol g(-1)) to similar to 190 m(2) g(-1). The ligands were bound effectively to the surface according to TGA, EDS and FTIR analyses and remained in the mono-deprotonated form. The produced hybrid adsorbents had for the selected pH (3.5) high capacities towards adsorption of Rare Earth Element (REE) cations, but with equilibria achieved relatively slowly. The composition of the surface complexes was determined as M : L = 1 : 1 for IMPA, but varied for the AEPA from 1 : 3 to 1 : 1 dependent on the REE, which can be interpreted in terms of charge compensation as the major driving force behind binding. The cation desorption in strongly acidic media for recuperation of the adsorbed REE and the relative capacity of the re-used adsorbent have been quantified.
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| 10. |
- Svensson Grape, Erik, et al.
(författare)
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A Robust and Biocompatible Bismuth Ellagate MOF Synthesized Under Green Ambient Conditions
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 142:39, s. 16795-16804
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Tidskriftsartikel (refereegranskat)abstract
- The first bioinspired microporous metal-organic framework (MOF) synthesized using ellagic acid, a common natural antioxidant and polyphenol building unit, is presented. Bi2O(H2O)2(C14H2O8)·nH2O (SU-101) was inspired by bismuth phenolate metallodrugs, and could be synthesized entirely from nonhazardous or edible reagents under ambient aqueous conditions, enabling simple scale-up. Reagent-grade and affordable dietary supplement-grade ellagic acid was sourced from tree bark and pomegranate hulls, respectively. Biocompatibility and colloidal stability were confirmed by in vitro assays. The material exhibits remarkable chemical stability for a bioinspired MOF (pH = 2-14, hydrothermal conditions, heated organic solvents, biological media, SO2 and H2S), attributed to the strongly chelating phenolates. A total H2S uptake of 15.95 mmol g-1 was recorded, representing one of the highest H2S capacities for a MOF, where polysulfides are formed inside the pores of the material. Phenolic phytochemicals remain largely unexplored as linkers for MOF synthesis, opening new avenues to design stable, eco-friendly, scalable, and low-cost MOFs for diverse applications, including drug delivery.
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