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- GEJJI, SHRIDHAR P, et al.
(författare)
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GEOMETRY AND VIBRATIONAL FREQUENCIES OF THE LITHIUM TRIFLATE ION-PAIR - AN AB-INITIO STUDY
- 1993
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Ingår i: J PHYS CHEM-US. - : American Chemical Society (ACS). - 0022-3654. ; 97:44, s. 11402-11407
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Tidskriftsartikel (refereegranskat)abstract
- The optimized geometry, harmonic vibrational frequencies, and infrared absorption intensities of the lithium trifluoromethanesulfonate (triflate) ion pair, CF3SO3-Li have been investigated using the ab initio self-consistent Hartree-Fock and correlated second-order Moller-Plesset perturbation theory with the 6-31G* and lower basis sets. In the optimized structure the lithium cation is bound to two of the oxygens of the SO3 group forming a bidentate complex with C(s) symmetry. A local minimum with a monodentate structure was obtained in the HF/3-21G* calculations. The energy difference between the mono- and bidentate structures of the complex is predicted to be nearly 39 kJ mol-1 in this basis. A splitting of 230 and 158 cm-1 is obtained for the antisymmetric SO3 stretching for the bi- and monodentate coordination of the lithium cation with the free anion, respectively. The infrared spectrum of lithium triflate in poly(propylene oxide) shows a splitting of 43 cm-1. The strong interaction of the metal cation with the anion in the 1:1 complex thus overemphasizes the ''splitting behavior'' observed for lithium triflate dissolved in polymers. In the bidentate (MP2/6-31G*) complex the symmetric SO3 stretching shows a downshift of 38 cm-1, in contrast to an upshift of 47 cm-1 for the monodentate complex. The different signs of these frequency shifts have a purely geometric origin. The dependence of this frequency shift on the position of the Li+ ion is discussed.
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| 4. |
- Hillgren, Anna, 1968-
(författare)
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Investigation of the Freeze-Thawing Process for Pharmaceutical Formulations of a Model Protein
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent advances in recombinant DNA technology have resulted in a great number of proteins with a potential to enter pharmaceutical formulations. The most commonly used method for preparing protein pharmaceuticals is by freeze-drying. Freezing is an important step in this process and therefore a deeper investigation of the freeze-thawing process is qualified.The aim of the thesis was to investigate the protection of protein during freeze-thawing. The effects on the recovered activity of the protein by different protective additives and different temperature history were evaluated, together with the protection mechanism on a molecular level.Lactate dehydrogenase (LDH) was used as a model protein. The systems were examined by differential scanning calorimetry (DSC and MTDSC), IR-, NMR- and fluorescence spectroscopy as well as surface tension measurements.The additives Tween 80 and Brij 35 are non-ionic surfactants and both protected LDH during freeze-thawing in concentrations far below cmc. The non-surface active polymer PEG 6000 had a protecting ability in very low concentrations. The protection was strongly affected by the temperature history; an increased freezing rate decreased the recovered activity. The optimum protecting concentration of Tween was also dependent on the cmc. During freezing below -20ºC no liquid water or amorphous ice was detected, all water was crystallized to polycrystalline ice. The relative degree of crystallinity could be determined by MTDSC at melting but not during crystallization, since it is a very fast process.An interaction between protein and additive is not necessarily required for protection at these low concentrations of additives. An interaction was observed between LDH and PEG but very weak or no interaction at all between LDH and the non-ionic surfactants. The protein was in all cases in the native state.The protective mechanisms are quite complex, but the amount of ice surface created during freezing is crucial for the protection. The non-ionic surfactants are able to hinder the protein from destructive interactions with the ice crystals by competing for adsorption at the ice surface. PEG can prevent LDH from denaturation at the ice surface by adsorption of a PEG hydrate that is formed only with certain temperature history.
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| 5. |
- Johansson, A, et al.
(författare)
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Diffusion and ionic conductivity in Li(CF3SO3)PEG(10) and LiN(CF3SO2)(2)PEG(10)
- 1996
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Ingår i: Polymer. - : Elsevier. - 0032-3861. ; 37:8, s. 1387-1393
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Tidskriftsartikel (refereegranskat)abstract
- Self-diffusion of the cation, the anion and the polymer chain in the low-molecular-weight polymer electrolyte systems Li(CF3SO3)PEG(10) and LiN(CF3SO2)(2)PEG(10) has been studied as a function of temperature using nuclear magnetic resonance spectroscopy.
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| 14. |
- Larsson, Karin, et al.
(författare)
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REORIENTATION OF WATER-MOLECULES IN SOLID HYDRATES - CORRELATION WITH SPECTROSCOPIC AND STRUCTURAL DATA
- 1991
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Ingår i: Journal of the Chemical Society, Faraday Transactions. - : Royal Society of Chemistry (RSC). - 0956-5000 .- 1364-5455. ; 87:8, s. 1193-1200
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Tidskriftsartikel (refereegranskat)abstract
- A review is presented of experimentally known activation energies, E(a), for the 180-degrees flip motion of the H2O molecule about its two-fold axis in 30 different solid hydrates. The relationship between E(a) and other parameters characterizing a hydrogen bond is discussed. Diagrams correlating E(a) with the hydrogen-bond length, R(o ... x, stretching frequency, nu-OH, librational twist frequency, nu-tw, and deuterium quadrupole coupling constant, e2qQ/h, are presented. The dependence of these correlations on the coordination of the water molecule is discussed, and it is clear that the number of atoms coordinating the water molecule is one of the main factors determining the flip activation energy E(a). The activation energy and the librational twist frequency display a strong correlation, with an associated correlation coefficient of 0.90.
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| 16. |
- Ludvigsson, M, et al.
(författare)
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Crystallinity in cast Nafion.
- 2000
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Ingår i: J. Electrochem. Soc.. ; 147, s. 1303-
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Tidskriftsartikel (refereegranskat)
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| 18. |
- OJAMAE, LARS, et al.
(författare)
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SIMULATION OF BAND WIDTHS IN LIQUID WATER SPECTRA - THE BREAKDOWN OF THE FROZEN-FIELD APPROXIMATION
- 1992
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 195:1, s. 97-103
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Tidskriftsartikel (refereegranskat)abstract
- Band shapes of liquid water OH vibrational spectra oblained from molecular dynamics (MD) simulation and from a quantum-mechanical method are investigated. The so-called "frozen-field approximation" applied to the calculation of quantum-mechanical high-frequency vibrational spectra is critically examined. It is demonstrated that the band width of the OH stretching spectrum is seriously overestimated through the neglect of the dynamics of the environment in the frozen-field approximation. We show that the proper inclusion of the dynamics in this quantum-mechanical method leads not only to a correct absolute frequency for the model potential used, but also to the correct description of the band width. The basic steps in this method are: (1) an MD simulation yielding an ensemble of liquid water configurations, (2) a quantum-mechanical uncoupled local-mode calculation of the OH frequency for each molecule, using model potentials for the inter- and intra-molecular interactions, (3) inclusion of the influence from the dynamics of the surroundings by filtering out rapid frequency fluctuations. The remaining discrepancy between experimental and computed OH spectra is attributed to shortcomings in the potential model used.
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