| 1. |
- Ahlgren, Kajsa, 1996, et al.
(författare)
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New insights into the protein stabilizing effects of trehalose by comparing with sucrose
- 2023
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 25:32, s. 21215-21226
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Tidskriftsartikel (refereegranskat)abstract
- Disaccharides are well known to be efficient stabilizers of proteins, for example in the case of lyophilization or cryopreservation. However, although all disaccharides seem to exhibit bioprotective and stabilizing properties, it is clear that trehalose is generally superior compared to other disaccharides. The aim of this study was to understand this by comparing how the structural and dynamical properties of aqueous trehalose and sucrose solutions influence the protein myoglobin (Mb). The structural studies were based on neutron and X-ray diffraction in combination with empirical potential structure refinement (EPSR) modeling, whereas the dynamical studies were based on quasielastic neutron scattering (QENS) and molecular dynamics (MD) simulations. The results show that the overall differences in the structure and dynamics of the two systems are small, but nevertheless there are some important differences which may explain the superior stabilizing effects of trehalose. It was found that in both systems the protein is preferentially hydrated by water, but that this effect is more pronounced for trehalose, i.e. trehalose forms less hydrogen bonds to the protein surface than sucrose. Furthermore, the rotational motion around dihedrals between the two glucose rings of trehalose is slower than in the case of the dihedrals between the glucose and fructose rings of sucrose. This leads to a less perturbed protein structure in the case of trehalose. The observations indicate that an aqueous environment closest to the protein molecules is beneficial for an efficient bioprotective solution.
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| 2. |
- Ahmed, Mukhtiar, et al.
(författare)
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Aromatic Heterocyclic Anion Based Ionic Liquids and Electrolytes
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:4, s. 3502-3512
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Tidskriftsartikel (refereegranskat)abstract
- Five new ionic materials comprising fluorine-free aromatic heterocyclic anions based on pyridine and pyrazine combined with a common n-tetrabutylphosphonium cation, (P4444)+, result in two room temperature ionic liquids (RTILs), one semi-solid, and two organic ionic plastic crystals (OIPCs) with melting points >20 °C. The OIPCs showed a plastic crystalline phase, multiple solid–solid transitions, and plastic crystalline and melt phases. For both the neat RTILs and the Li+ conducting electrolytes, the nature and strength of the ion–ion interactions mainly depend on the position of the nitrogen atom with respect to the carboxylate group in the anions. Furthermore, for the RTILs the ionic conductivity is effected by the electronic structure and flexibility of the ions and the anions diffuse faster than the (P4444)+ cation, but are slowed down in the electrolytes due to the strong electrostatic interactions between the carboxylate group of the anions and the Li+, as shown both experimentally and computationally. Overall, this study describes the effect of structural tuning of aromatic anions on the ion–ion interactions and introduces new ionic materials with promising properties to be used as solid and liquid electrolytes in energy storage devices.
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| 3. |
- Alekseev, A. Yu, et al.
(författare)
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Interplay between structural changes, surface states and quantum confinement effects in semiconducting Mg2Si and Ca2Si thin films
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 25:29, s. 19952-19962
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio techniques have been used to investigate structural changes in semiconducting Mg2Si and Ca2Si thin films (from 17 nm down to 0.2 nm corresponding to the 2D structure) along with band-gap variations due to quantum confinement. Cubic Mg2Si(111) thin films being dynamically stable at thicknesses (d) larger than 0.3 nm displayed an indirect band gap, the reduction of which with increasing d could be reasonably well described by the simple effective mass approximation. Only 2D Mg2Si has a unique structure because of the orthorhombic distortion and the direct band gap. Since the surface energy of cubic Ca2Si(111) films was lower with respect to any surface of the orthorhombic phase, which is the ground state for the Ca2Si bulk, the metastable in-bulk cubic phase in the form of thin films turned out to be preferable in total energy than any orthorhombic Ca2Si thin film for d < 3 nm. Sizable structural distortion and the appearance of surface states in the gap region of Ca2Si thin films with d < 3 nm could be the reason for an odd dependence of the band-gap variation on d.
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| 4. |
- 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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| 5. |
- An, Rong, et al.
(författare)
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Controlling the nanoscale friction by layered ionic liquid films
- 2020
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 22:26, s. 14941-14952
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Tidskriftsartikel (refereegranskat)abstract
- The nanofriction coefficient of ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), on the surfaces of mica and graphite was investigated using atomic force microscopy (AFM). A pronounced layered spatial distribution was found in the IL film formed on the solid substrates and can be divided into 3 well distinguishable regions exhibiting different physical properties with increasing distance from the substrate. We found that the friction coefficient (μ) increases monotonically as the layering thickness decreases, no matter what the thickness of the bulk IL is. This suggests that the layering assembled IL at solid surfaces is more important than the bulk phase in determining the magnitude of the nanoscale friction. The increase in the friction coefficient as the layering thickness decreases is most likely attributed to the assembled ordered IL layers closer to the substrate surfaces having a greater activation barrier for unlocking the surfaces to allow shear.
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| 6. |
- Andersen, Josefine, et al.
(författare)
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Insights into localization, energy ordering, and substituent effect in excited states of azobenzenes from coupled cluster calculations of nuclear spin-induced circular dichroism
- 2024
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 26:12, s. 9179-9196
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Tidskriftsartikel (refereegranskat)abstract
- Nuclear spin-induced circular dichroism (NSCD) is a molecular effect of differential absorption of left- and right-circularly polarized light due to nuclear spins in the molecule. In this work, new tools for its calculation are presented. Specifically, analytic expressions for the computation of the 000000001111110000 000001110000001100 000010000000110110 000010001001100010 000100001011000100 000010010011001100 000001100110110000 000000001110001000 011000001100011000 011100011100011000 000010110100110000 000011100011100000 K term of NSCD have been derived and implemented for the second-order coupled cluster singles and doubles (CC2) model. NSCD results obtained thereby for three derivatives of azobenzenes have been compared with results from time-dependent density functional theory (TD-DFT). The complementary information that could be obtained from NSCD measurements compared to NMR for these three species is discussed. Due to its sensitivity to the local electronic structure, nuclear spin-induced circular dichroism can be used to gain insight into properties of excited states. New computational tools for its calculation are presented.
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| 7. |
- Andersson, John, 1993, et al.
(författare)
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Surface plasmon resonance sensing with thin films of palladium and platinum - quantitative and real-time analysis
- 2022
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 24:7, s. 4588-4594
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Tidskriftsartikel (refereegranskat)abstract
- Surface plasmon resonance (SPR) is a highly useful technique in biology and is gradually becoming useful also for materials science. However, measurements to date have been performed almost exclusively on gold, which limits the possibility to probe chemical modifications of other metals. In this work we show that 20 nm Pd and Pt films work "fairly well" for quantitative SPR sensing of organic films despite the high light absorption. In the interval between total reflection and the SPR angle, high intensity changes occur when a film is formed on the surface. Fresnel models accurately describe the full angular spectra and our data analysis provides good resolution of surface coverage in air (a few ng cm(-2)). Overall, the Pd sensors behave quite similarly to 50 nm gold in terms of sensitivity and field extension, although the noise level in real-time measurements is similar to 5 times higher. The Pt sensors exhibit a longer extension of the evanescent field and similar to 10 times higher noise compared to gold. Yet, formation of organic layers a few nm in thickness can still be monitored in real-time. As a model system, we use thiolated poly(ethylene glycol) to make Pd and Pt protein repelling. Our findings show how SPR can be used for studying chemical modifications of two metals that are important in several contexts, for instance within heterogeneous catalysis. We emphasize the advantages of simple sample preparation and accurate quantitative analysis in the planar geometry by Fresnel models.
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| 8. |
- Andersson, Ove, et al.
(författare)
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Amorphous-like thermal conductivity and high mechanical stability of cyclopentane clathrate hydrate
- 2024
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 26:22, s. 16017-16025
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity κ of cyclopentane clathrate hydrate (CP CH) of type II was measured at temperatures down to 100 K and at pressures up to 1.3 GPa. The results show that CP CH displays amorphous-like κ characteristic of many crystalline clathrate hydrates, e.g., tetrahydrofuran (THF) CH. The magnitude of κ is 0.47 W m−1 K−1 near the melting point of 280 K at atmospheric pressure, and it is almost independent of pressure and temperature T: ln κ = −0.621−40.1/T at atmospheric pressure (in SI-units). This is slightly less than κ of type II CHs of water-miscible solvents such as THF. Intriguingly, unlike other water-rich type II clathrate hydrates of water-miscible molecules M (M·17 H2O), CP CH does not amorphize at pressures up to 1.3 GPa at 130 K and also remains stable up to 0.5 GPa at 240 K. This shows that CP CH is mechanically more stable than the previously studied water-rich type II CHs, and suggests that repulsive forces between CP and the H2O cages increase the mechanical stability of crystalline CP CH. Moreover, we show that κ of an ice-CH mixture, which often arises for CHs that form naturally, is described by the average of the parallel and series heat conduction models to within 5% for ice contents up to 22 wt%. The findings provide a better understanding of the thermal and stability properties of clathrate hydrates for their applications such as gas storage compounds.
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| 9. |
- Andersson, Ove, et al.
(författare)
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Evidence suggesting kinetic unfreezing of water mobility in two distinct processes in pressure-amorphized clathrate hydrates
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:34, s. 20064-20072
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Tidskriftsartikel (refereegranskat)abstract
- Type II clathrate hydrates (CHs) with tetrahydrofuran (THF), cyclobutanone (CB) or 1,3-dioxolane (DXL) guest molecules collapse to an amorphous state near 1 GPa on pressurization below 140 K. On subsequent heating in the 0.2-0.7 GPa range, thermal conductivity and heat capacity results of the homogeneous amorphous solid show two glass transitions, first a thermally weak glass transition, GT1, near 130 K; thereafter a thermally strong glass transition, GT2, which implies a transformation to an ultraviscous liquid on heating. Here we compare the GTs of normal and deuterated samples and samples with different guest molecules. The results show that GT1 and GT2 are unaffected by deuteration of the THF guest and exchange of THF with CB or DXL, whereas the glass transition temperatures (Tgs) shift to higher temperatures on deuteration of water; Tg of GT2 increases by 2.5 K. These results imply that both GTs are associated with the water network. This is corroborated by the fact that GT2 is detected only in the state which is the amorphized CH's counterpart of expanded high density amorphous ice. The results suggest a rare transition sequence of an orientational glass transition followed by a glass to liquid transition, i.e., kinetic unfreezing of H2O reorientational and translational mobility in two distinct processes.
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| 10. |
- Andersson, Rassmus, et al.
(författare)
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Quantifying the ion coordination strength in polymer electrolytes
- 2022
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:26, s. 16343-16352
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Tidskriftsartikel (refereegranskat)abstract
- In the progress of implementing solid polymer electrolytes (SPEs) into batteries, fundamental understanding of the processes occurring within and in the vicinity of the SPE are required. An important but so far relatively unexplored parameter influencing the ion transport properties is the ion coordination strength. Our understanding of the coordination chemistry and its role for the ion transport is partly hampered by the scarcity of suitable methods to measure this phenomenon. Herein, two qualitative methods and one quantitative method to assess the ion coordination strength are presented, contrasted and discussed for TFSI-based salts of Li+, Na+ and Mg2+ in polyethylene oxide (PEO), poly(epsilon-caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC). For the qualitative methods, the coordination strength is probed by studying the equilibrium between cation coordination to polymer ligands or solvent molecules, whereas the quantitative method studies the ion dissociation equilibrium of salts in solvent-free polymers. All methods are in agreement that regardless of cation, the strongest coordination strength is observed for PEO, while PTMC exhibits the weakest coordination strength. Considering the cations, the weakest coordination is observed for Mg2+ in all polymers, indicative of the strong ion-ion interactions in Mg(TFSI)(2), whilst the coordination strength for Li+ and Na+ seems to be more influenced by the interplay between the cation charge/radius and the polymer structure. The trends observed are in excellent agreement with previously observed transference numbers, confirming the importance and its connection to the ion transport in SPEs.
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