Characterization of the glycosyltransferase activity of desVII: analysis of and implications for the biosynthesis of macrolide antibiotics

In vitro catalytic activity of DesVII, the glycosyltransferase involved in the biosynthesis of methymycin, neomethymycin, narbomycin, and pikromycin in Streptomyces venezuelae, is described. This is the first report of demonstrated in vitro activity of a glycosyltransferase involved in the biosynthesis of macrolide antibiotics. DesVII is unique among glycosyltransferases in that it requires an additional protein component, DesVIII, as well as basic pH for its full activity.     

C[bond]H- - -O hydrogen bonds in beta-sheetlike networks: combined X-ray crystallography and high-pressure infrared study

Close interactions of the C(alpha)[bond]H- - -O type have been analyzed via X-ray crystallography and high-pressure infrared spectroscopy. The results demonstrate that the C(alpha)[bond]H- - -O interactions can offer an additional stability to the beta-sheet formation. X-ray structural data suggest that while 1-acetamido-3-(2-pyrimidinyl)-imidazolium bromide exhibits a bilayer stacking, the PF(6)(-) salt reveals a beta-sheetlike pattern. The appearance of the free-NH infrared absorption indicates that the conventional N[bond]H- - -O or N[bond]H- - -N hydrogen bonds do not fully dominate the packing for the PF(6)(-) salt. The high-pressure infrared study suggests that the C(alpha)[bond]H- - -O hydrogen bonds are the important determinants for the stability of the PF(6)(-) salt. This study also verifies that the imidazolium C[bond]H stretching frequency shifts to a longer wavelength upon the formation of the C[bond]H- - -O hydrogen bonds.     

Synthesis and Spectra of Bichromophore Compounds Containing Oxazole or Oxadiazole Ring

Fifteen of the bichromophore compounds containing oxazole or oxidation ring have been synthesized. Their structures have been identified by IR, 1H NMR spectra and elemental analysis. The UV spectra, fluorescence spectra and the laser conversion efficiencies have been determined . The results of determination show that the absorption and emission spectra Pf the bichromophore compounds are different from those of the corresponding single chromophore compounds.     

Mossbauer Study of the Effect of Intraligand Substituents on the Spin Crossover in Solid (Dithiocyanato)BIS(N-Substituted-Phenyl-2-Pyridinaldimine) Iron (II)

The spin transition of high-spin (^sT₂?)low-spin (¹A₁) of (dithiocyanato) (N-phenyl-2-pyridinaldimine) iron (II) complexes can be altered by substituents on the phenyl ring. Mössbauer spectra at 78K for the 4-substituted derivatives (with the exception of the 4-OH-substituted derivative) indicate that the fraction of low-spin states increases with decreasing substituent electron-withdrawing ability, as measured by the Hammet σ constant (4-OCH₃<4-CH₃CONH 4-C₆H₅<4-CH₃<4-H<4-Cl<4-NO₂). In addition, the effect of methyl-substitution at the ortho-, meta- or paraposition of the phenyl ring on the spin transition was examined. Mössbauer spectra of these methyl-substituted complexes reveal quite different spin equilibria.     

微分示波电位滴定法 Ⅱ.铂电极上Cu~(2 )的DDTC~-滴定

卜海之等报导,当铂、碳或银电极上沉积有一层Ag-TPB(TPB代表四苯硼钠离子)时,该电极对Ag~ 及TPB~-均有响应,这样的电极可用于Ag~ 及TPB~-的示波电位滴定,其滴定曲线一般为台阶形.若在线路中加一电容就可将电位曲线微分为峰形,并可以荧光点的最大位移指示滴定终点.本文报导用二乙基二硫代氨基甲酸(DDTC~-)滴定Cu~(2 ),目的在于将微分示波电位滴定法应用于一大类为数众多的沉淀反应.     

Recombinant polyclonal antibody libraries

We describe a technology for generating recombinant polyclonal antibody libraries (PCALs) that enables the creation and perpetuation of standardized mixtures of polyclonal whole antibodies specific for a multiantigen (or polyantigen). Therefore, this technology combines the advantages of targeting multiple antigenic determinants -- high avidity, low likelihood of antigen 'escape variants', and efficient mediation of effector functions, with the advantages of using monoclonal antibodies -- unlimited supply of standardized reagents and the availability of the genetic material for desired manipulations. The technology for generating recombinant polyclonal antibody libraries begins with the creation of phage display Fab (antibody) libraries. This is followed by selection of sublibraries with desired antigen specificities, and mass transfer of the variable region gene pairs of the selected sublibraries to a mammalian expression vector for generation of libraries of polyclonal whole antibodies. We review here our experiments for selection of phage display antibody libraries against microbes and tumor cells, as well as the recent literature on the selection of phage display antibody libraries to multiantigen targets.     

活性钴引起α—溴代酮的反应

近年来,活性钛,活性镍等金属试剂正被用于有机合成并引起人们的关注。最近,对活性钴引起有机反应的研究也日益增多。例如在活性钴试剂作用下,卤代芳烃脱卤偶联得到联苯化合物,α,α—二氯二苯基甲烷脱卤得到四苯乙烯,富马酸与二溴甲烷可以发生不对称环丙烷化反应等。本文报道活性钴试剂引起α—溴代酮的反应。     

Electrokinetic flow through an elliptical microchannel: effects of aspect ratio and electrical boundary conditions

The electrokinetic flow of an electrolyte solution through an elliptical microchannel is studied theoretically. The system under consideration simulates the flow of a fluid, for example, in vein. We show that, for a constant cross-sectional area, both the electroosmotic volumetric flow rate and the streaming potential increase monotonically with an increase in the aspect ratio, and both the total electric current and the electroviscous effect may exhibit a local minimum as the aspect ratio varies. Also, for a constant average potential on the channel wall, the difference between the results based on three kinds of boundary conditions, which include constant surface charge, constant surface potential, and charge-regulated surface, is inappreciable if the hydraulic diameter is larger than 1 mum.     

5-苯基-2-(5′-苯基噁唑基-2′)-1,3,4-噁二唑及其5-对位取代苯基衍生物的研究

合成了12个未知的5-苯基-2-(5′-苯基噁唑基-2′)-1,3,4-噁二唑及其5-对位取代苯基衍生物,讨论了化合物的结构与紫外光谱、荧光光谱和激光转换效率间的关系,以及两个化合物在11种溶剂中电子光谱的溶剂效应。     

The Photochemistry of Diazomethane-Hydrogen Sulfide Mixtures. The Decomposition Rate of Chemically Activated Methanethiol

The photochemistry of diazomethane in presence of hydrogen sulfide gas has been studied at 4358 and 3660-Å. Singlet methylene radicals react with hydrogen sulfide to from methanethiol which decomposes at lower pressures. The measured decomposition rate constants are 5.5×10¹⁰ and 9.6×10¹⁰ s^?1 in 4358 and 3660-Å systems, respectively. Singlet methylene inserts into a S-H bond as 200 times fast as into a C-H bond.