Microcalorimetric study of the adsorption of PEGylated lysozyme on a strong cation exchange resin

Adsorption of native as well as mono-, di-, and tri-PEGylated lysozyme on Toyopearl Gigacap S-650M in sodium phosphate buffer is studied by isothermal titration calorimetry and by independent adsorption equilibrium measurements at pH 6 and 25°C. The production and separation of PEGylated lysozyme is discussed. Two different PEG sizes are used (5 kDa and 10 kDa) which leads to six different forms of PEGylated lysozyme which were systematically studied. The sodium chloride concentration is varied according to the elution conditions in the production process. The specific enthalpy of adsorption Δh(p)(ads) is determined from the calorimetric and the adsorption equilibrium data. It was found to be exothermal and constant with increasing adsorber loading for native lysozyme. For all PEGylated forms there is an influence of the adsorber loading on Δh(p)(ads) which is found to become more important with increasing PEGylation degree (total molecular weight of conjugated PEG). At low loadings the adsorption of all PEGylated lysozyme forms is exothermal. With increasing loading the adsorption becomes less exothermal and for the species with higher PEGylation degree also endothermal effects are observed at higher loadings. A thermodynamic analysis is carried out by which the enthalpic and entropic contributions to the binding constants are quantified. The findings are discussed on a molecular level. The results provide insight into the adsorption mechanisms of polymer-modified proteins on chromatographic resins.     

Global existence result for thermoviscoelastic problems with hysteresis

We consider viscoelastic solids undergoing thermal expansion and exhibiting hysteresis effects due to plasticity or phase transformations. Within the framework of generalized standard solids, the problem is described in a three-dimensional setting by the momentum equilibrium equation, the flow rule describing the dependence of the stress on the strain history, and the heat transfer equation. Under appropriate regularity assumptions on the data, a local existence result for this thermodynamically consistent system is established, by combining existence results for ordinary differential equations in Banach spaces with a fixed-point argument. Then global estimates are obtained by using both the classical energy estimate and more specific techniques for the heat equation introduced by Boccardo and Gallouët. Finally a global existence result is derived.     

Zur thermischen Zersetzung von TeSeO4 und Te3SeO8 – Koexistenzbeziehungen im ternären System TeO2/SeO2/Bi2SeO5

Thermal Decomposition of TeSeO₄ and Te₃SeO₈ – Phase Relations in the Ternary System TeO₂/SeO₂/Bi₂SeO₅ The saturation decomposition pressure of TeSeO₄ and Te₃SeO₈ were determined in a membran zero manometer. From the equilibrium data are derived the Enthalpies of formation and the Standard Entropies: Data see Inhaltsübersicht. Thus the coexistence ranges in the ternary triangle TeO₂/SeO₂/Bi₂SeO₅ can be determined. Informations about the melting diagram obtained by thermal analysis of the condensed compositions TeO₂/SeO₂.     

碳元素同素异形体的稳定性

碳元素有多种同素异形体,其稳定性可根据能量判据进行判断。一般认为,石墨是标准状况下碳元素最稳定的同素异形体,其标准摩尔生成焓被定为参考值0k J/mol。近来亦有研究说明金刚石在0K下更稳定。一些文献认为富勒烯比石墨更稳定的说法是错误的,应予纠正。     

Classical, non-classical critical divergences and partial molar properties from adsorption measurements in near-critical mixtures

This paper presents results related to the development of methods for measuring and analyzing dilute solute thermodynamic properties in near-critical solvent mixtures. An analysis of limiting conditions at the system's critical point provides results that were used to analyze capacity factor data for a variety of organic solutes in near-critical mixtures of carbon dioxide and ethane. Both classical and non-classical perspectives were employed in the analysis, with particular focus on solvent mixtures with compositions close to that of the critical azeotrope in the carbon dioxide---ethane system. These solvent mixtures have unique critical divergence properties and the theoretical results obtained for this system are qualitatively borne out by the data taken. Partial molar volumes and enthalpies for several dilute solutes at a range of thermodynamic conditions have been presented in mixtures of 0.26, 0.30 and 0.70 mole fraction ethane in carbon dioxide. The isothermal data were taken at three temperatures (308, 328 and 343 K) and pressures ranged from 50 to 107 bar. The isobaric data were taken at 65.3 and 75.5 bar over a temperature range of 295.5–441 K. The solutes used were benzene, toluene, o-xylene, naphthalene and 2,6-dimethylnaphthalene. Because at the present time such data are not available in the published literature these data were often compared with values obtained by model calculations. Agreement between the two approaches has been fairly good and suggests that the approach taken here should contribute towards developing methods for reliable and rapid thermodynamic property estimation in mixtures.     

CO2 adsorption in LiY and NaY at high temperature: molecular simulations compared to experiments

Grand Canonical Monte Carlo simulations combined with adsorption measurements have been carried out to gain further insight into the CO₂ adsorption process at the microscopic scale in both LiY and NaY faujasites at various temperatures. A new Li⁺−CO₂ force field derived by ab initio calculations was validated by a reasonable agreement between the simulated isotherms and those obtained by experiments in a wide range of temperature (from 323 K to 473 K). In addition, the microscopic mechanisms of CO₂ adsorption in both systems, consistent with the trends observed for the simulated differential enthalpies of adsorption as a function of the loading, were proposed. It was observed that two different types of adsorption behaviour exist for NaY and LiY at 323 K and 373 K, mainly caused by the significant more exposed position of the SII Na⁺ from the six-ring plane of the supercage compared to those occupied by the SII Li⁺, whereas at higher temperature, both faujasites exhibit the same flat profile for the differential enthalpy of adsorption as a function of loading.     

Enthalpies of interaction of N-acetyl amides of sarcosine and N-methyl-L-alanine dissolved in N,N-dimethylformamide at 25°C

Enthalpies of dilution of N-acetyl amides of sarcosine and N-methyl-L-alanine dissolved in N,N-dimethylformamide have been measured calorimetrically at 25°C. The enthalpic pairwise interaction coefficients calculated there from are negative, indicating a energetically favorable interaction. The results were used to make a comparison with other peptides with regard to the methylation of amide groups. Substituting a primary amide hydrogen by a methyl group gives a smaller positive change of the pairwise interaction coefficient than substituting a secondary amide hydrogen.     

FOURIER TRANSFORM INFRARED STUDIES OF POLY (ETHYLENE TEREPHTHALATE) FILM IN THE GLASS TRANSITION REGION

Three specimens from a solution-cast poly (ethylene terephthalate) (PET) film, one being liquid-N_2 quenched from 92℃(Q), one being slowly cooled from 92℃(SC) and one being quenched and sub-T_g annealed at 67℃(AN), have been studied by specimen difference spectra Q-SC and AN-Q and temperature difference spectra T-70 and T_2-T_1 for every 2℃steps on heating to 90℃at 2℃/min. SC and AN showed more gauche conformers than Q. That means that the PET chain has more trans conformers at higher temperatures and some of these are frozen during quenching through T_g. A band at 1340 cm~(-1) has been found to be complex containing overlapping bands reflecting trans in crystalline regions and trans in amorphous regions. The temperature difference spectra on heating through T_g showed that the spectral changes in Q are gradual while a rather abrupt change occurs in AN at 80—82℃for the bands at 1340, 1042 and 1020 cm~(-1). No new conformational structure or new vibrational mode is involved. A kind of locking mechanism is suggested which hinders the molecular vibrational changes in AN below T_g until a sudden release occurs at T_g. These locking sites can be nothing else than sites of tighter local packing of chain segments. Consequently it is believed that inter-chain van der Waals attraction energy plays a dominating role in the volume relaxation and sub-T_g annealing of quenched amorphous polymers.     

聚芳醚酮高温长时间下的断裂行为──2．物理老化的影响

研究了聚芳醚酮在２００℃下长时间放置过程中的密度，热焓，屈服及应力松弛行为随时间的变化规律．结果表明，随放置时间的增长，材料的结构形态与物性随时间的变化速率在１０小时后急剧减慢．文中对物性变化的时间依赖性进行了讨论．在应力松弛过程中出现银纹的现象可归结为物理老化过程中分子链间排列逐渐紧密的结果．