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- Author or Editor: J. Xing x
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Abstract
The displacement adsorption enthalpies (ΔH) of the refolding of lysozyme (Lys) denatured by 1.8 mol L–1 guanidine hydrochloride (GuHCl) on a moderately hydrophobic surface at 298 K, pH 7.0 and various (NH4)2SO4 concentrations were determined by using a Micro DSC-III calorimeter. The study shows that the effect of salt concentrations on the three fractions of the enthalpy is that with increasing (NH4)2SO4 concentrations, the molecular conformation enthalpy of the adsorbed Lys has probably no distinct change at 1.8 mol L–1 GuHCl; the adsorption affinity enthalpy (exothermic) becomes more negative; and the dehydration enthalpy (endothermic) decreases. At lower salt concentrations, the dehydration, especially squeezing water molecules led by molecular conformation, which leads to an entropy-driving process, predominates over the adsorption affinity (also including the orderly orientation of molecular conformation), while at higher salt concentrations, the latter is prior to the former for contribution to ΔH and induces an enthalpy-driving process. Also, the optimal NH4)2SO4 concentration favoring refolding and renaturing of Lys denatured by 1.8 mol L–1 GuHCl was found.
Abstract
Both microcalorimetric determination of displacement adsorption enthalpies ΔH and measurement of adsorbed amounts of guanidine – denatured lysozyme (Lys) refolding on the surface of hydrophobic interaction chromatography (HIC) packings at 308 K were carried out and compared with that at 298 K. Study shows that both temperature and concentration of guanidine hydrochloride (GuHCl) affect the molecular mechanism of hydrophobic interaction of protein with adsorbent based on the analysis of dividing ΔH values into three kinds of enthalpy fractions. The adsorption in higher concentrations of GuHCl (>1.3 mol L–1) at 308 K is an enthalpy-driving process, and the adsorption under other GuHCl concentrations is an entropy-driving process. The fact that the Lys denatured by 1.8 mol L–1 GuHCl forms a relatively stable intermediate state under the studied conditions will not be changed by temperature.
Summary
The method of high-performance liquid chromatography (HPLC) with diode array detector (DAD) was used and validated for the simultaneous determination of nine flavonoids (rutin, myricetin, quercitrin, quercetin, luteolin, genistein, kaempferol, apigenin, and isorhamnetin) in beagle dog plasma. Plasma sample was pre-treated with acetonitrile (containing 0.05% formic acid). Chromatographic separation was performed on a kromasil C18 column (250 × 4.6 mm, 5 µm) maintained at 35 °C. The mobile phase was a mixture of methanol and 0.2% formic acid with a step linear gradient. At 1.0 mL min−1 flow rate, the eluent of other eight flavonoids was detected simultaneously at 360 nm with good separation except genistein (detected at 254 nm). Under optimum conditions, the correlation coefficient between the peak area and the concentrations for each analyte was all above 0.999. The intra-day and inter-day precisions were less than 10% for all analytes. The limit of detection and the limit of quantification for the selected nine flavonoids were 0.006–0.03 and 0.02–0.12 g mL−1, respectively. The extracted recoveries of selected nine flavonoids were 74.02%–99.37%. The assay has been successfully applied to determine concentrations of nine flavonoids in plasma from beagle dog after being intravenously administrated Ginkgo biloba extract.
Summary
Calorimetric determination of the total enthalpy changes (ΔH i) of guanidine-denatured lysozyme (Lys) during the adsorption with simultaneously refolding on the surface of hydrophobic interaction chromatography packings was carried out at 250.001C. The measured ΔH iin the circumstances should include the changes in the three fractions: adsorption, dehydration and molecular conformation. It was found that when the unfolded Lys molecules are adsorbed and refold on the surface, entropy-driving caused by the dehydration of Lys mainly dominates the foregoing process. The refolding enthalpies of Lys, ΔΔH iwere found to be 10~100 folds higher than that measured in usual solutions.</o:p>
Abstract
The low-temperature heat capacities of 1-hexadecanol have been measured with an automatic adiabatic calorimeter over the temperature range from 80 to 370 K. A solid-liquid phase transition was observed at T m=322.225±0.002 K and the molar enthalpy and entropy of fusion were determined to be 57.743±0.008 kJ mol−1 and 179.19±0.04 J K−1 mol−1, respectively. The purity, the real melting point (T 1) and the ideal melting point without any impurity or absolutely purity (T 0) of the sample under investigation were determined to be 99.162 mol%, 322.21 and 322.34 K, respectively, by fractional melting method. According to the polynomial equation of heat capacity and thermodynamic relationship, the thermodynamic functions of the compound relative to the reference temperature 298.15 K were calculated in the temperature ranges of 80 to 370 K with an interval of 5 K. In addition, further researches of thermal properties for this compound were carried out by means of TG/DTG.
Abstract
Cognitive impairment and dementia are significant health burdens worldwide. Aging, hypertension, and diabetes are the primary risk factors for Alzheimer’s disease and Alzheimer’s disease and related dementias (AD/ADRD). There are no effective treatments for AD/ADRD to date. An emerging body of evidence indicates that cerebral vascular dysfunction and hypoperfusion precedes the development of other AD pathological phenotypes and cognitive impairment. However, vascular contribution to dementia is not currently well understood. This commentary highlights the emerging concepts and mechanisms underlying the microvascular contribution to AD/ADRD, including hypotheses targeting the anterograde and retrograde cerebral vascular pathways, as well as the cerebral capillaries and the venous system. We also briefly discuss vascular endothelial dysfunction, oxidative stress, inflammation, and cellular senescence that may contribute to impaired cerebral blood flow autoregulation, neurovascular uncoupling, and dysfunction of cerebral capillaries and the venous system.
Abstract
The (R)-BINOL-menthyl dicarbonates, one of the most important compounds in catalytic asymmetric synthesis, was synthesized by a convenient method. The molar heat capacities C p,m of the compound were measured over the temperature range from 80 to 378 K with a small sample automated adiabatic calorimeter. Thermodynamic functions [H T–H 298.15] and [S T–S 298.15] were derived in the above temperature range with a temperature interval of 5 K. The thermal stability of the substance was investigated by differential scanning calorimeter (DSC) and a thermogravimetric (TG) technique.
Abstract
The molar heat capacity, C p,m, of a complex of holmium chloride coordinated with L-aspartic acid, Ho(Asp)Cl2·6H2O, was measured from 80 to 397 K with an automated adiabatic calorimeter. The thermodynamic functions H T-H 298.15 and S T-S 298.15 were derived from 80 to 395 K with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimeter (DSC) and thermogravimetric (TG) technique, and the mechanism of thermal decomposing of the complex was determined based on the structure and the thermal analysis experiment.
