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Charge Concentration (charge + concentration)
Selected AbstractsPolyelectrolyte complex hydrogel composed of chitosan and poly(,-glutamic acid) for biological application: Preparation, physical properties, and cytocompatibilityJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Hahk-Soo Kang Abstract Polyelectrolyte complex (PEC) hydrogels composed of chitosan as a cationic polyelectrolyte and poly (,-glutamic acid) (,-PGA) as an anionic polyelectrolyte were prepared from PEC dispersions based on a chitosan solution to which different amounts of ,-PGA solutions were added to charge equivalency. The chemical structures of the PEC hydrogels were investigated by Fourier transform infrared spectroscopy. The physical properties, fixed charge concentration, crystallinity, mechanical properties, micromorphology, and swelling properties of the PEC hydrogels were also investigated. The total fixed charge concentration of the PEC hydrogels varied as a function of pH on the pK intervals between chitosan (pK = 6.5) and ,-PGA (pK = 2.27). The isoelectric points (IEP) were shifted to a lower pH with a higher weight ratio of ,-PGA to chitosan. The elastic modulus was decreased with the weight ratio increasing from 0 : 1 to 1 : 1 (,-PGA/chitosan) by ionic crosslinking between the amino groups of chitosan and the carboxyl groups of ,-PGA. The results of the swelling study showed that the swelling properties of PEC hydrogels were more affected by the change in the elastic restoring force than by the change in the fixed charge concentration depending on the pH. Also, the cytotoxicity of the PEC hydrogels was investigated using normal human dermal fibroblast (NHDF) cell lines, and the results showed the PEC hydrogels were not toxic. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:386,394, 2007 [source] Towards a generalized vision of oxides: disclosing the role of cations and anions in determining unit-cell dimensionsACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010Ángel Vegas Theoretical calculations of the electron-localization function show that, at the volumes of the two CaO phases (rocksalt and CsCl type), the parent Ca structures (fcc: face-centred cubic and sc: simple cubic, respectively) exhibit charge concentration zones which coincide with the positions occupied by the O atoms in their oxides. Similar features, also observed for the pairs Ca/CaF2 and BaSn/BaSnO3, are supported by recent high-pressure experiments as well as electron-localization function (ELF) calculations, carried out on elemental K. At very high pressures, the elemental K adopts the hP4 structure, topologically identical to that of the K atoms in high-pressure K2S and high-temperature ,-K2SO4. Moreover, the ELF for the hP4 structure shows charge concentration (,,2 electrons) at the sites occupied by the S atoms in the high-pressure K2S phase. All these features confirm the oxidation/high-pressure equivalence as well as the prediction of how cation arrays should be metastable phases of the parent metals. For the first time to our knowledge, the structure type, dimension and topology of several oxides and fluorides (CaO, CaF2 and BaSnO3) are explained in univocal physical terms. [source] On the effect of neglecting anharmonic nuclear motion in charge density studiesACTA CRYSTALLOGRAPHICA SECTION A, Issue 3 2010Kathrin Meindl The effect of neglecting anharmonic nuclear motion when it is definitely present is studied. To ensure the presence of anharmonic nuclear motion a model was used that was previously refined against experimental data including anharmonic nuclear motion, and these calculated structure factors were used as observed data for a multipole refinement. It was then studied how the neglect of anharmonic nuclear motion and noise in the data affects the usual crystallographic quality measure R, the density parameters and the residual density distribution. It is demonstrated that the neglect of anharmonic nuclear motion leads to a characteristic imprint onto the residual density distribution in terms of residual density peaks and holes, in terms of the whole residual density distribution and in terms of the number, location and strength of valence shell charge concentrations (VSCCs). These VSCCs differ from that of the input model in a way which heavily influences and misleads the chemical interpretation of the charge density. This imprint vanishes after taking anharmonic nuclear motion into account. Also the input model VSCCs are restored. The importance of modeling anharmonic nuclear motion is furthermore shown by the characteristic imprint on the residual density distribution, even in the case of a numerically almost unaffected R value. [source] Ab initio determination of the valence electron distribution in the average structure of the incommensurately modulated calaverite AuTe2ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2001Razvan Caracas The valence-electron density distribution of the average structure of incommensurately modulated calaverite, AuTe2, has been computed using density-functional theory. High-density regions, centered around the Au and Te atoms, are not spheric, but present charge concentrations along the Au,Te and Te,Te bonds. The electronic band structure and its corresponding density of states reveal the presence of three electronic band groups, constituted mainly by Te 5s, Au 5d and hybrids of Te 6p + Au 6s + Au 5d orbitals. The electrons belonging to the last block are responsible for the chemical bonds. [source] | ||||||||||