催化动力学光度法测定茶叶和中药中的单宁

在盐酸介质中,微量单宁对碘酸钾氧化丙基红的褪色反应有显著的催化作用,据此建立了催化动力学光度法测定微量单宁的新方法。方法的线性范围为0.1～3.0μg/mL,检出限为0.04μg/mL。本法简便、快速、灵敏度高和选择性较好,用于茶叶和中药五倍子、诃子中单宁含量的测定,结果满意。

动力学光度法测定芦丁的研究

在盐酸介质中,微量芦丁对碘酸钾氧化丙基红褪色反应有明显的催化作用,据此建立了测定芦丁含量的动力学光度分析新方法.方法的线性范围为0.01～0.8μg/mL,检出限为9.0×10-9g/mL.方法用于学芦丁片剂和槐米中芦丁含量的测定.

Microwave radiation one-pot synthesis of chloropropyl-functionalized mesoporous MCM-41

Chloropropyl-functionalized mesoporous MCM-41（MCM-41-（CH2）3Cl） was synthesized in alkaline medium by the microwave radiation one-pot method, using cetyltrimethy-lammoniumbromide （CTAB） as novel template, tetraethoxysilane （TEOS） as silica source, and chloropropyltriethoxysilane （C1PTES） as the coupling agent. The microstructure of MCM-41-（CH2）3Cl was characterized by the means of X-ray diffraction （XRD）, nitrogen absorption-desorption, Fourier transform infrared spectroscopy （FT-IR）, scanning electron microscopy （SEM）, and transmission electron microscopy （TEM）. The results show that a successful synthesis of MCM-41-（CH2）3Cl with well structure is obtained. The optimal microwave power is 120 W and the best microwave time is 50 rain. The dosage of chloropropyltriethoxysilane on the structure of chloropropyl-functionalzed MCM-41 was also investigated. It is found that the chloropropyltriethoxysilane volume between 0.8 mL and 1.6 mL is favorable for the formation of highly ordered MCM-41-（CH2）3Cl mesostructure.

Natural Rubber-Grafted-Poly （Methyl Methacrylate）： Influence of Coagulating Agents on Properties and Appearances

Graft copolymers of MMA （methyl methacrylate） with NRL （natural rubber latex） referred to as NR-g-PMMA have been prepared using CHP （cumene hydroperoxide）/TEPA （tetraetbylenepentamine） redox initiator. 1H NMR （proton nuclear magnetic resonance） and FTIR （Fourier transform infrared） analysis have confirmed the occurrence of graft copolymerisations of MMA onto NR that containing 30% and 50% of MMA monomer. The influence of coagulating agents such as formic acid, sulfuric acid and boiling water on the coagulation of NR-g-PMMA latices were investigated. These types of coagulating agent formed compact coagulum and the effect of NR-g-PMMA compounds on cure characteristics, physical properties and appearances were reported.

Preparation of pH-responsive membranes with amphiphilic copolymers by surface segregation method

Novel pH-responsive membranes were prepared by blending pH-responsive amphiphilic copolymers with polyethersulfone(PES) via a nonsolvent-induced phase separation(NIPS) technique. The amphiphilic copolymers bearing Pluronic F127 and poly(methacrylic acid)(PMAA) segments, abbreviated as PMAA n–F127–PMAA n,were synthesized by free radical polymerization. The physical and chemical properties of the blend membranes were evaluated by scanning electron microscopy(SEM), Fourier transform infrared(FTIR) spectrum, water contact angle, Zeta potential and X-ray photoelectron spectroscopy(XPS). The enrichment of hydrophilic PMAA segments on the membrane surfaces was attributed to surface segregation during the membrane preparation process. The blend membranes had signi ficant p H-responsive properties due to the conformational changes of surface-segregated PMAA segments under different pH values of feed solutions. Fluxes of the blend membranes were larger at low p H values of feed solutions than that at high pH values. The pH-responsive ability of the membranes was enhanced with the increase of the degree of PMAA near-surface coverage.

催化动力学光度法测定维脑路通片及槐米中维生素P_4

在HAc存在下,少量维生素P4可催化KBrO3氧化丙基红的反应,导致丙基红在521 nm处吸光度显著减小,据此建立了测定维生素P4含量的催化动力学新体系。其线性范围为0.01～0.9 mg/L,检出限为8.9×10-3 mg/L,催化反应总速率常数为9.90×10-4/s。该方法可用于维脑路通片剂和槐米中维生素P4含量的测定。

High-level soluble expression of the hemA gene from Rhodobacter capsulatus and comparative study of its enzymatic properties

The Rhodobacter capsulatus hemA gene, which encodes 5-aminolevulinic acid synthase （ALAS）, was expressed in Escherichia coil Rosetta （DE3） and the enzymatic properties of the purified recombinant ALAS （RC-ALAS） were studied. Compared with ALASs encoded by hemA genes from Agrobacterium radiobacter（AR-ALAS） and Rhodobacter sphaeroides （RS-ALAS）, the specific activity of RC-ALAS reached 198.2 U/mg, which was about 31.2% and 69.5% higher than those of AR-ALAS （151.1 U/mg） and RS-ALAS （116.9 U/mg）, respectively. The optimum pH values and temperatures of the three above mentioned enzymes were all pH 7.5 and 37 ℃, respectively. Moreover, RC-ALAS was more sensitive to pH, while the other two were sensitive to temperature. The effects of metals, ethylene diamine tetraacetic acid （EDTA）, and sodium dodecyl sulfate （SDS） on the three ALASs were also investigated. The results indicate that they had the same effects on the activities of the three ALASs. SDS and metal ions such as Co^2＋, Zn^2＋, and Cu^2＋ strongly inhibited the activities of the ALASs, while Mn^2＋ exerted slight inhibition, and K^＋, Ca^2＋, Ba^2＋, Mg^2＋, or EDTA had no significant effect. The specificity constant of succinyl coenzyme A [（kcatlKm）^S-CoA] of RC-ALAS was 1.4989, which was higher than those of AR-ALAS （0.7456） and RS-ALAS （1.1699）, showing its high catalytic efficiency. The fed-batch fermentation was conducted using the recombinant strain containing the R. capsulatus hemA gene, and the yield of 5-aminolevulinic acid （ALA） achieved was 8.8 g/L （67 mmol/L） under the appropriate conditions.

Cleavage of the Carboxyl-Terminus of LEACS2, a Tomato 1-Aminocyclopropane-l-Carboxylic Acid Synthase Isomer, by a 64-kDa Tomato Metalloprotease Produces a Truncated but Active Enzyme

1-Aminocyclopropane-1-carboxylic acid （ACC） synthase （ACS） is the principal enzyme in phytohormone ethylene biosynthesis. Previous studies have shown that the hypervariable C-terminus of ACS is proteolytically processed in vivo. However, the protease responsible for this has not yet been identified. In the present study, we investigated the processing of the 55-kDa full-length tomato ACS （LeACS2） into 52-, 50- and 49-kDa truncated isoforms in ripening tomato （Lycopersicon esculentum Mill. cv. Cooperation 903） fruit using the sodium dodecyl sulfate-boiling method. Meanwhile, an LeACS2-processing protease was purified via multi-step column chromatography from tomato fruit. Subsequent biochemical analysis of the 64-kDa purified protease revealed that it is a metalloprotease active at multiple cleavage sites within the hypervariable C-terminus of LeACS2. N-terminal sequencing and matrix-assisted laser desorption/ionization time-of-flight analysis indicated that the LeACS2-processing metalloprotease cleaves at the C-terminal sites Lys^438, Glu^447, Lys^448, Asn^456, Ser^460, Ser^462, Lys^463, and Leu^474, but does not cleave the N- terminus of LeACS2. Four C-terminus-deleted （26-50 amino acids） LeACS2 fusion proteins were overproduced and subjected to proteolysis by this metalloprotease to identify the multiple cleavage sites located on the N-terminal side of the phosphorylation site Ser^460. The results indisputably confirmed the presence of cleavage sites within the region between the α-helix domain （H14） and Ser^460 for this metalloprotease. Furthermore, the resulting C-terminally truncated LeACS2 isoforms were active enzymatically. Because this protease could produce LeACS2 isoforms in vitro similar to those detected in vivo, it is proposed that this metalloprotease may be involved in the proteolysis of LeACS2 in vivo.

The 96-week clinical outcomes after cessation of nucleos(t)ide analog treatment in chronic hepatitis B patients

Background:Chronic hepatitis B(CHB)patients have a high virological relapse rate after cessation of nucleos(t)ide analog(NA)treatment,but the clinical outcome remains unclear.This study aimed to investigate the 96-week clinical outcomes and the risk factors for relapse in CHB after cessation of NAs.Methods:This study was a prospective trial;74 eligible patients were enrolled.The patients underwent NA cessation and follow-up according to the 2012 Asian Pacific Association for the Study of the Liver Guideline.Symptoms,biochemical(aspartate aminotransferase[AST],alanine aminotransferase[ALT],total bilirubin,urea nitrogen,creatinine),virological data(hepatitis B surface antigen[HBsAg],hepatitis B e antigen[HBeAg],hepatitis B e antibody[HBeAb],hepatitis B virus[HBV]DNA levels),and color Doppler ultrasound examination results were recorded and analysed.Results:After NA cessation,19 cases were HBsAg-negative without relapse during the 96-week follow-up.Of the 55 cases of HBsAg-positive after cessation,four types of clinical outcomes were observed.Twelve patients had no relapse during the 96-week follow-up(type A,21.8%),7 patients underwent virological relapses but spontaneously had a non-virological relapse(type B,12.7%),10 patients maintained virological relapse(type C,18.2%),and 26 patients turned to clinical relapse,received NA retreatment,and achieved ALT normalization and negative conversion of HBV DNA within 12 months(type D,47.3%).The 2-year overall cumulative rates of virological and clinical relapses were 58.1%and 24.3%,respectively.Independent factors associated with virological relapse were duration of negative HBV DNA,EOT(end of treatment)HBsAg,and original status of HBeAg.The EOT HBsAg was also an independent factor for clinical relapse.Conclusions:There are four types of clinical outcomes in patients with CHB after cessation of NA treatment.Further research is needed to explore the mechanism of different clinical outcomes.The EOT HBsAg level is an independent factor associated with both virological and clinical relapse.