Summary The thermal behavior of poly(L-lactic acid) (PLLA) was studied with differential scanning calorimetry (DSC) and polarized optical microscopy. For amorphous PLLA samples, double cold crystallisation peaks were observed in the DSC traces during heating process, being strongly dependent on heating rates. The observation was discussed based on the assumption that the quenched PLLA sample presented some remaining metastable or a precrystalline phase. A small exothermal peak was observed before the main melting peak at low heating rates. The probable reason was discussed through melt-recrystallisation mechanism. Influence of thermal history on the cold crystallisation and melting behavior was also performed on heating process for PLLA samples.
The influence of solution composition (pH, salts, and chelant) on the thermostability of horse liver alcohol dehydrogenase
was studied by differential scanning calorimetry (DSC) in the pH range from7.51 to 9.50 and showing the enzyme catalytic activity.
The experiments demonstrated that the effect of increasing pH on the heat denaturation temperature of the enzyme was slight,
but the denaturation enthalpy was considerably increased, indicating the enzyme conformation alteration by changing pH and
the presence of enthalpy-entropy compensation. The effect of ionic strength on thermostability was not noticeable, i.e., the
electrostatic interactions were not a dominant factor for the thermostability. The anions Cl− and SCN− imposed diverse influence upon the enzyme thermostability, and SCN−can reduce the thermostability considerably. The chelant 1,10-phenanthroline, which can reversibly bind together with the
zinc ions functioning the catalytic action in the enzyme molecules, increases the thermostability considerably. The hydration
of the enzyme plays an important role to the thermostability.
Raw chemicals such as metal nitrates and chlorides were found to affect the thermal decomposition behaviour of EDTA-gel precursors
used for the production of ceramic powders. Fine, homogeneous ceramic powders were produced from nitrate solutions while chlorides
gave segregated phases. In studies on the production of lead zirconate titanate (PZT) using chlorides, the segregation and
loss of lead was observed and shown to be caused by the formation and evaporation of PbCl2. Thermal analysis (DTA/TG) quantitatively proved the suggested reaction mechanism for this phase segregation. Crystallization
of the desired perovskite phase of lead zirconate titanate (PZT) and barium titanate (BT) initiated at temperatures as low
as 250°C in the nitrate-EDTA precursors. Water of crystallization and formation of BaCO3 in the barium titanate precursor were suggested to account for differences in the observed decompositional behaviours of
the BT and PZT precursors.
The stems of Uncaria rhynchophylla (Miq.) ex Havil have a long history of use in traditional Chinese medicine to treat diseases and improve health. There is evident evidence that alkaloids constituents are mainly responsible for the beneficial effects of this plant medicine. The amounts of the major bioactive alkaloids in this plant vary widely with species, habitat, and as such, and establishment of a high-performance liquid chromatography (HPLC) fingerprint for quality control of this herbal medicine is of particular importance. The most alkaloids are used for medicine treatment and research. On the basis of the chromatographic data, a consistent HPLC fingerprint pattern containing 15 common peaks was obtained. Among these common peaks, four were identified as rhynchophylline, isorhynchophylline, corynoxeine, and isocorynoxeine. On the basis of this HPLC fingerprint and principal-components analysis, the quality of fifteen samples from different producing areas of China was objectively assessed. To summarize, the data described in this study offer valuable information for quality control and proper use of U. rhynchophylla (Miq.) ex Havil.
Lead zirconate titanate (PZT) ceramic powder has been synthesized from metal nitrate solutions using the EDTA-gel method with
different nitric acid/EDTA ratios. It was found that the thermal decomposition of the precursor was strongly affected by the
nitric acid/EDTA ratio, the amount of sample, the atmosphere, and the heating rate. Crystallization of the perovskite PZT
phase initiated at external temperatures as low as 250°C, as a result of the exothermic decomposition reaction of the nitrate-EDTA
complexes. Possible reaction schemes are suggested and discussed to describe the thermal decomposition of PZT-EDTA precursors
under different experimental conditions.
This study investigated the influences of drying method (oven-, freeze-, and shade-drying) and extraction solvent (ethanol and water) on the bioactivities of Cirsium setidens. Antioxidant activity was evaluated by DPPH radical scavenging ability, anti-diabetic activity was determined by the inhibitory activity of two enzymes: α-glucosidase and α-amylase, while anti-proliferation activity was assessed by MTT assay of three human cancer cell lines (KB, A549, and PC-3). Results indicated that bioactivities were extremely affected by solvent; water extracts contained more phenolics, exhibited strong anti-diabetic effect, but no activity of anti-proliferation, while the ethanolic extracts rich in flavonoids showed profound DPPH radical scavenging and anti-proliferation ability, yet low activity of antidiabetes. Among the drying methods, freeze-drying extracts preserved more flavonoids and exhibited better activity of anti-proliferation, while shade-drying extracts contained higher phenolics and showed stronger activity on antidiabetes, oven-drying gave the lowest content of phenolics. Hence, antioxidant and anti-diabetic effects were positively related to phenolic content, meanwhile an extremely significant correlation coefficient had been found between anti-proliferation activity and flavonoid content, it can be concluded that drying method and extraction solvent affect bioactivities by phenolic and flavonoid contents.