Molecular weight distribution of the methyl methacrylate (MMA) polymer separated from the MMA-grafted silk fiber

The molecular weight distribution of poly-methyl methacrylate (poly-MMA) chains separated from MMA-grafted silk fibers obtained by using potassium persulfate (KPS) and tri-n-butylborane (TBB) as initiator of the graft-copolymerization reaction have been examined by gel permeation chromatography (GPC). GPC elution pattern of poly-MMA chains shows a bimodal molecular weight distribution. The two peaks have been identified as heavy and light component. The average molecular weight of the heavy component ranges from 48.5 to 200 kD for poly-MMA copolymerized by the KPS reaction system and from 336 to 816 kD for the poly-MMA copolymerized by the TBB reaction system. The light component has an average molecular weight lower than 1,000 D and its value is almost similar in all the samples examined. Scanning electron microscopy (SEM) analysis revealed the presence of MMA oligomers formed on the fiber surface during grafting. The molar ratio between poly-MMA chains and silk fibroin attains a constant value that seems to be specific for a certain reaction system. A linear correlation has been observed between the weight gain and the average molecular weight of the poly-MMA chains. These findings suggest the effect of grafting parameters on the molecular weight and molecular weight distribution of the grafted polymer, as well as its influence on the physical properties and textile performances of MMA-grafted silk fibers.     

The crystal structure of thermostable mutants of chimeric 3-isopropylmalate dehydrogenase, 2T2M6T

A chimeric 3-isopropylmalate dehydrogenase (IPMDH), 2T2M6T,was produced by replacing the amino acid sequences of the Thermusthermophilus enzyme with those of the Bacillus subtilis enzymefrom residues 75 to 113. Decreased thermostability of the chiaiericenzyme was recovered by either evolutionary engineering (I93L)or site-directed mutagenesis (S82R). The 3-D structures of themutants have been determined by X-ray diffraction at 2.1 Åresolution. Although S82R was refined routinely, (I93L) requiredthe preliminary rigid-body refinement of each domain. The X-factorswere reduced to 0.18 for both mutants. Removal of the unfavorabletorsion angle at isoleucine 93 may have made I93L more thermostablethan 2T2M6T. In the case of S82R, the replaced arginine residuecontributed to the extra hydrogen bond with water molecules.The large replaced residue decreased the entropy of the solvent,which may have caused the improvement in enzyme thermostability.Denatu ration by heating may be interpreted from these structuralresults.     

Effect of preparation conditions on the characteristics of exfoliated graphite

Exfoliated graphite (EG) was prepared from graphite intercalation compounds (GICs) synthesized electrochemically with different electricity consumption from 10.83 to 40.00 A h/kg. Effects of electricity consumption on the synthesis of GICs and of exfoliation temperature on different parameters of EG, i.e. exfoliation volume, volatile content, specific surface area and pore volume measured by mercury porosimetry, length and width of worm-like particles, and distance between neighboring balloons based on the zigzag model for worm-like particles of EG, were studied. These parameters were found to depend strongly on the electricity consumption and also on exfoliation temperature. Exfoliation volume, volatile content, specific surface area and pore volume on EG prepared at 1000 °C increased with increasing electricity consumption, but the distance between neighboring balloons was found to decrease. These results reveal marked development of pores in EG samples. Raising exfoliation temperature increased exfoliation volume, specific surface area and pore volume up to 800 °C. Above this temperature these parameters tended to be stable.     

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Copper-Containing Molten Salt: II, Divalent Copper Salts, CuCl2 and CuSO4

The ion-exchange mechanism between copper and alkali ions, when 20R₂O · 10Al₂O₃· 70SiO₂ (R = Li, Na, and K) glasses are immersed in divalent copper-containing molten salts in air and nitrogen at 550°C, has been investigated. In molten CuCl₂, the ion-exchange behavior in both air and nitrogen was very close to that in molten CuCl in air reported previously. This is explained by assuming that CuCl₂ decomposes into CuCl and Cl₂ at 550°C and the Cu⁺ ions thus formed mainly diffuse in glasses to replace alkali ions, where Cl₂ acts as an oxidizing agent just like oxygen. In the case of molten CuSO₄─₂SO₄, a small amount of Cu⁺ which is present in the molten state plays a primary role in the Cu ⇌ R⁺ ion exchange process, although the contribution of direct Cu²⁺⇌ 2R⁺ ion exchange cannot be ignored.     

Protective Effects of Voluntary Exercise on Hepatic Fat Accumulation Induced by Dietary Restriction in Zucker Fatty Rats

Weight control based on dietary restriction (DR) alone can cause lipid metabolic failure and progression to fatty liver. This study aimed to investigate the effect of exercise on preventing DR-induced hepatic fat accumulation in Zucker fatty (ZF) rats by focusing on the relationship between adipose tissue lipolysis and hepatic fat uptake. Six-week-old male ZF rats were randomly assigned to obese, DR, or DR with exercise (DR + Ex) groups. The DR and DR + Ex groups were fed a restricted diet, with the latter also undergoing voluntary exercise. After 6 weeks, hepatic fat accumulation was observed in the DR group, whereas intrahepatic fat was markedly reduced in the DR + Ex group. Compared with the obese (Ob) group, the DR group exhibited 2.09-fold expression of hepatic fatty acid translocase (FAT)/CD36 proteins (p < 0.01) and 0.14-fold expression of hepatic fatty acid-binding protein (FABP)1 (p < 0.01). There were no significant differences between the DR + Ex group and the Ob group. FAT/CD36 and hepatic triglyceride (TG) expression levels were strongly positively correlated (r = 0.81, p < 0.001), whereas there was a strong negative correlation between FABP1 and hepatic TG expression levels (r = −0.65, p < 0.001). Our results suggest that hepatic fat accumulation induced by DR in ZF rats might be prevented through exercise-induced modifications in FAT/CD36 and FABP1 expression.     

Preparation of Sn‐Doped Zinc Phosphate Amorphous Thin Film and its Emission Properties

Using liquid‐phase synthesis, SnO – ZnO – P₂O₅ amorphous coating films exhibiting broad emission of Sn²⁺ center were prepared. It is found that the P – O – Zn bonds of the film were generated during the heat‐treatment. The emission property due to Sn²⁺ depended on the heat‐treatment temperature, which correlated with the residual chloride ion content. Although the peak position of the photoluminescence (PL) excitation band was almost constant, that of PL red‐shifted with increasing amount of SnO, which was quite different from the result observed for SnO – ZnO – P₂O₅ bulk glass containing Sn²⁺ center.