Molecular dynamics simulations of the detoxification of paraoxon catalyzed by phosphotriesterase

Combined QM(PM3)/MM molecular dynamics simulations together with QM(DFT)/MM optimizations for key configurations have been performed to elucidate the enzymatic catalysis mechanism on the detoxification of paraoxon by phosphotriesterase (PTE). In the simulations, the PM3 parameters for the phosphorous atom were reoptimized. The equilibrated configuration of the enzyme/substrate complex showed that paraoxon can strongly bind to the more solvent‐exposed metal ion Zn_β, but the free energy profile along the binding path demonstrated that the binding is thermodynamically unfavorable. This explains why the crystal structures of PTE with substrate analogues often exhibit long distances between the phosphoral oxygen and Zn_β. The subsequent S_N2 reaction plays the key role in the whole process, but controversies exist over the identity of the nucleophilic species, which could be either a hydroxide ion terminally coordinated to Zn_α or the μ‐hydroxo bridge between the α‐ and β‐metals. Our simulations supported the latter and showed that the rate‐limiting step is the distortion of the bound paraoxon to approach the bridging hydroxide. After this preparation step, the bridging hydroxide ion attacks the phosphorous center and replaces the diethyl phosphate with a low barrier. Thus, a plausible way to engineer PTE with enhanced catalytic activity is to stabilize the deformed paraoxon. Conformational analyses indicate that Trp131 is the closest residue to the phosphoryl oxygen, and mutations to Arg or Gln or even Lys, which can shorten the hydrogen bond distance with the phosphoryl oxygen, could potentially lead to a mutant with enhanced activity for the detoxification of organophosphates. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Separation of D‐psicose and D‐fructose using simulated moving bed chromatography

Simulated moving bed (SMB) processes have been widely used in the sugar industries with ion‐exchange resin as a stationary phase. D ‐Psicose, a rare monosaccharide known as a valuable pharmaceutical substrate, was synthesized by the enzymatic conversion from D ‐fructose. The SMB process was adopted to separate D ‐psicose from D ‐fructose. Before the SMB experiment, the reaction mixture including D ‐psicose and D ‐fructose was treated by a deashing process to remove contaminants, such as buffers, proteins, and other organic materials. Four columns packed with Dowex 50WX4‐Ca²⁺ (200–400 mesh) ion‐exchange resins were used in the four‐zone SMB. Single‐step frontal analysis was performed to estimate the isotherm parameters of each monosaccharide. The operating conditions of the SMB process were determined based on the Equilibrium Theory. According to the simulation of the SMB process, the purity and yield of extract product (D ‐psicose) achieved were 99.04 and 97.46%, respectively and those of raffinate product (D ‐fructose) were 99.06 and 99.53%, respectively. Under the optimized operating condition, complete separation (extract purity = 99.36%, raffinate purity = 99.67%) was achieved experimentally.     

TOEPLITZ-TYPE OPERATORS ON LEBESGUE SPACES

Let L be the infinitesimal generator of an analytic semigroup on L 2 (Rn)with Gaussian kernel bounds,and L-α/ 2 be the fractional integrals generated by L for 0< α     

On the non-Riemannian quantity H of a Finsler metric

One of fundamental problems in Finsler geometry is to establish some delicate equations between Riemannian invariants and non-Riemannian invariants. Inspired by results due to Akbar-Zadeh etc., this note establishes a new fundamental equation between non-Riemannian quantity H and Riemannian quantities on a Finsler manifold. As its application, we show that all R-quadratic Finsler metrics have vanishing non-Riemannian invariant H generalizing result previously only known in the case of Randers metric.     

EFFECT OF OVERLAP CONCENTRATION AND PERSISTENCE LENGTH ON DNA SEPARATION IN POLYMER SOLUTIONS BY ELECTROPHORESIS

The persistence length and the overlap concentration(c~*) of poly(ethylene oxide)(PEO) and hydroxyethylcellulose(HEC) with similar molecular weight in 1×TBE buffer were studied by laser light scattering and viscometry.Their effect on DNA separation was investigated by capillary electrophoresis.It was determined that the persistence length of HEC was at least 5 times higher than that of PEO.Therefore,the c~* of HEC was smaller than that of PEO by a factor of ca.2.5.It was also found that the c~* values de...     

新型BrΦnsted-Lewis酸性离子液体的合成及其在松香二聚反应中的应用(英文)

合成、表征了新型 Brφnsted-Lewis 酸性离子液体 1-（3-磺酸）-丙基-3-甲基咪唑氯锌酸盐 （[HO3S-（CH2）3-mim]Cl-ZnCl2）, 并将其用于催化松香二聚反应. 结果表明, [HO3S-（CH2）3-mim]Cl-ZnCl2 （ZnCl2摩尔分数x 〉 0.5）为 Brφnsted 和 Lewis 双酸性, 且以 [HO3S-（CH2）3-mim]Cl-ZnCl2 （x = 0.64） 的催化性能较佳. 在松香 5.0 g, 甲苯15 g, 离子液体质量分数 5%, 反应温度 110℃ 和反应时间 4 h 的较佳实验条件下, 所得产物聚合松香的软化点为 118 ℃. 此外, 该催化剂的使用有利于产物的分离且分离的离子液体催化剂具有良好的重复使用性能.     

新型Br(o)nsted-Lewis酸性离子液体的合成及其在松香二聚反应中的应用

合成、表征了新型Bronsted-Lewis酸性离子液体1-(3-磺酸)-丙基-3-甲基咪唑氯锌酸盐([HO3S-(CH2)3-mim]Cl-ZnCl2),并将其用于催化松香二聚反应.结果表明,[HO3S-(CH2)3-mim]Cl-ZnCl2(ZnCl2摩尔分数x＞0.5)为Bronsted和Lewis双酸性,且以[HO3S-(CH2)3-mim]Cl-ZnCl2 (x=0.64)的催化性能较佳.在松香5.0 g,甲苯15 g,离子液体质量分数5%,反应温度110℃和反应时间4 h的较佳实验条件下,所得产物聚合松香的软化点为118 ℃.此外,该催化剂的使用有利于产物的分离且分离的离子液体催化剂具有良好的重复使用性能.     

利用掠入射X射线技术表征高分子薄膜

掠入射X射线技术是一种表征高分子薄膜的结晶性、厚度、界面粗糙度等物理量的新方法,本文简单介绍了这种技术中X射线反射率法和掠入射X射线衍射法的基本原理、测试和分析方法以及这些方法在高分子薄膜研究中的应用。     

Synthesis of novel biodegradable poly(ethylene glycol) analogue:Water-soluble aliphatic polyester with pendant oligo(ethylene glycol) chains

A novel poly(ethylene glycol)(PEG) analogue composed of aliphatic polyester backbone and pendant oligo(ethylene glycol) short chains is reported.The PEG analogue is a copolymer synthesized by ring-opening alternating copolymerization of succinic anhydride with 2-((2-(2-metho xyethoxy)ethoxy)methyl)oxirane.The structure of the copolymer was confirmed by ~1H NMR spectrum.The effects of the monomer feed ratio on the copolymerization were studied and the polymerization mechanism was given.The PEG analogue di...     

竹炭固相萃取/气相色谱-质谱联用对环境水样中16种多环芳烃的测定

以竹炭为固相萃取吸附材料,考察了其对环境水样中16种多环芳烃的吸附富集能力,采用DB-35MS弹性石英毛细管色谱柱对16种多环芳烃进行分离,气相色谱-质谱联用法对多环芳烃进行定性及定量分析.结果表明,1 000 mg竹炭作为固相萃取吸附剂,10 mL二氯甲烷作为洗脱剂,上样速率5 mL/min,水样中甲醇体积分数为15%的条件下,16种多环芳烃有较好的回收率,竹炭固相萃取柱的穿透体积大于500 mL,通过实验比较竹炭的萃取回收率优于商品化的C18固相萃取柱.16种多环芳烃的质量浓度在10 ～500 ng/L范围内与峰面积的线性关系良好(苯并(k)荧蒽,苯并(a)芘,二苯并(a,h)蒽,苯并(g,h,i)苝为25 ～500 ng/L),相关系数为0.983 6 ～0.998 4.方法的检出限为0.6 ～8.0 ng/L,实际水样的加标回收率为67% ～113%,相对标准偏差为2.1% ～11.3%.通过对白沙河河水的分析表明,该方法能够满足实际水样的测定,竹炭可以作为固相萃取材料应用于水中16种多环芳烃的分析测定.