Scaling law for the radius of gyration of proteins and its dependence on hydrophobicity

The scaling law between the radius of gyration and the length of a polymer chain has long been an interesting topic since the Flory theory. In this article, we seek to derive a unified formula for the scaling exponent of proteins under different solvent conditions. The formula is obtained by considering the balance between the excluded volume effect and elastic interactions among monomers. Our results show that the scaling exponent is closely related to the fractal dimension of a protein's structure at the equilibrium state. Applying this formula to natural proteins yields a 2/5 law with fractal dimension 2 at the native state, which is in good agreement with other studies based on Protein Data Bank analysis. We also study the dependence of the scaling exponent on the hydrophobicity of a protein chain through a simple two‐letters HP model. The results provides a way to estimate the globular structure of a protein, and could be helpful for the investigation of the mechanisms of protein folding. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 207–214, 2009     

Effect of hapten structures on specific and sensitive enzyme-linked immunosorbent assays for N-methylcarbamate insecticide metolcarb

Five different haptens of the N-methylcarbamate insecticide metolcarb were designed and synthesized. All of the haptens were conjugated with ovalbumin (OVA) for the coating antigen, and one hapten containing all of the structure of metolcarb was conjugated with bovine serum albumin (BSA) for the immunogen. Two polyclonal antisera were raised against the BSA conjugate, and ten antibody/coating conjugate combinations were selected for studies of assay sensitivity and specificity for metolcarb. A class-specific combination was found, with the I₅₀ of the assay ranged from 0.64 to 20.98 μg mL⁻¹ for seven tested N-methylcarbamate insecticides except for pirimicarb. Considering titer, I₅₀ and cross-reactivity of all combinations of antibody/coating conjugate, a competitive indirect enzyme-linked immunosorbent assay (ELISA) in a homologous system, whose limit of detection (LoD) reached 1.4 ng mL⁻¹, was presented. The results of competitive ELISAs indicated that coating hapten structure can significantly affect not only assay sensitivity but also its specificity.     

Enzyme-linked immunosorbent assays for the insecticide fenitrothion. Influence of hapten conformation and sample matrix on assay performance

This study aimed at developing competitive enzyme-linked immunosorbent assays (ELISAs) for the organophosphorus (OP) insecticide fenitrothion using a monoclonal antibody. The hapten used to obtain the antibody had an ideal structural feature that allowed minimal functional group sacrifice. By using the antibody and a coating antigen, a competitive indirect ELISA was developed, which showed an IC₅₀ of 14 ng mL⁻¹ with a detection limit of 3.0 ng mL⁻¹. A competitive direct ELISA using an enzyme tracer was also developed, which showed an IC₅₀ of 17 ng mL⁻¹ with a detection limit of 1.6 ng mL⁻¹. The antibodies in both assays showed negligible cross-reactivity with the metabolites of fenitrothion and other OP pesticides except with the insecticides parathion-methyl and parathion-ethyl. Recoveries of fenitrothion from fortified rice and lettuce samples were determined and the bias in the recovery values was rationalized by using the standard curves obtained in the matrix extract.     

Computational study on the mechanism for the gas‐phase reaction of dimethyl disulfide with OH

The mechanisms for the reaction of CH₃SSCH₃ with OH radical are investigated at the QCISD(T)/6‐311++G(d,p)//B3LYP/6‐311++G(d,p) level of theory. Five channels have been obtained and six transition state structures have been located for the title reaction. The initial association between CH₃SSCH₃ and OH, which forms two low‐energy adducts named as CH₃S(OH)SCH₃ (IM1 and IM2), is confirmed to be a barrierless process, The S? S bond rupture and H? S bond formation of IM1 lead to the products P1(CH₃SH + CH₃SO) with a barrier height of 40.00 kJ mol^?1. The reaction energy of Path 1 is ?74.04 kJ mol^?1. P1 is the most abundant in view of both thermodynamics and dynamics. In addition, IMs can lead to the products P2 (CH₃S + CH₃SOH), P3 (H₂O + CH₂S + CH₃S), P4 (CH₃ + CH₃SSOH), and P5 (CH₄ + CH₃SSO) by addition‐elimination or hydrogen abstraction mechanism. All products are thermodynamically favorable except for P4 (CH₃ + CH₃SSOH). The reaction energies of Path 2, Path 3, Path 4, and Path 5 are ?28.42, ?46.90, 28.03, and ?89.47 kJ mol^?1, respectively. Path 5 is the least favorable channel despite its largest exothermicity (?89.47 kJ mol^?1) because this process must undergo two barriers of TS5 (109.0 kJ mol^?1) and TS6 (25.49 kJ mol^?1). Hopefully, the results presented in this study may provide helpful information on deep insight into the reaction mechanism. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

溶致液晶中金属纳米粒子的掺杂及其作用机制研究

在用琥珀酸二异辛酯磺酸钠(AOT)构建的具有长程有序结构的层状溶致液晶内, 用不同方式导入预制的亲油或亲水贵金属纳米粒子, 可得到纳米粒子分布在不同介观空间内的无机/有机杂合体. 依据小角X射线散射和偏光显微镜结果, 通过分析掺杂纳米粒子与液晶模板的相互作用, 对掺杂前后体系结构的变化及制得杂合体的稳定性进行了表征. 结果表明, 除考虑掺杂粒子与层状模板空间的匹配外, 体系中静电斥力、范德华引力和Helfrich涨落力之间的平衡是维持液晶结构稳定的基本条件.     

Theoretical study on the mechanism of the gas-phase reaction of diborane(3) anion with carbon disulfide

The complex potential energy surface of the gas-phase reaction of HB(H)BH- with CS2 to give three low-lying products [B2H3S]- + CS, [BH2CS]- + HBS, and [BH3CS] + BS-, involving nine [B2H3CS2]- isomers and 12 transition states, has been investigated at the CCSD(T)/6-311++G(d,p)/B3LYP/6-311++G(d,p) level. Our calculations are in harmony with the recent experimental and theoretical results, and reveal some new bonding and kinetic features of this reaction system. Our theoretical results may help the further identification of the products [BH2CS]- + HBS and [BH3CS] + BS- and may provide useful information on the chemical behaviors of other electron-deficient boron hydride anions.     

On the reaction of metallated acetylenes and allenes with carbon disulfide. Influence of the alkali metal counter-ion and the substituents in the acetylene and allene on the course of the reaction

Addition at low temperatures of carbon disulfide to a solution of the lithium compound

(R¹ = CH₃, C₃H₇, Ph, OCH₃, SCH₃) results in the initial formation of an allenic carbodithioate H₂CCC(R¹)CSSLi, while for R¹ = t-C₄H₉ or SiMe₃ acetylenic carbodithioates R¹CCCH₂CSSLi are formed. The initial products undergo very rapid subsequent reactions. For R¹ = CH₃ or C₃H₇ the lithium compound adds (in the allenic form) in a conjugated fashion to the CCCS system of the allenic carbodithioate. The acetylenic dithioates are deprotonated to give the geminal dithiolates R¹CCCHC(SLi)₂. For R¹ = Ph, OCH₃ or SCH₃, subsequent deprotonation at the terminal carbon atom of the initial allenic dithioate gives enyne dithiolates HCCC(R¹)C(SCH₃)₂; this reaction proceeds more satisfactorily with the potassium compounds.     

Effect of the sol–gel route on the textural characteristics of silica imprinted with Rhodamine B

A series of silica xerogels that support Rhodamine B as a template were synthesized using distinct sol–gel routes, namely, acid‐catalyzed routes, a base‐catalyzed route, acid‐catalyzed with base‐catalyzed (two steps) hydrolytic routes, and a FeCl₃‐catalyzed nonhydrolytic route. The extraction methods (thermal, Soxhlet, water washing, and ultrasound) were also evaluated. The resulting xerogels were characterized through porosimetry using nitrogen adsorption/desorption. The samples were further analyzed through small‐angle X‐ray scattering, Fourier transform infrared spectroscopy, and SEM. The preparation route affected the materials’ textural properties. Extraction was optimized using acid and two‐step routes. The acid route from Rhodamine B to Rhodamine 6G generated the highest selectivity factor (2.5). The nonhydrolytic route produced the best imprinting factor. Competitive adsorption was also used, from which the approximate imprinting factor was 2. The cavity shape generated during the production of the imprinted silica dictates the adsorption behavior, not the magnitude of the surface area.     

Intramolecular catalysis and cyclization in the reaction of α,ω-diaminooligomethylenes with bifunctional sulphonyl chloride. Effect of chain length on polycondensation reaction

As an elementary reaction of polycondensation reactions, rates of the reaction of 1,5-naphthalenedisulphonyl dichloride, a bifunctional fluorescent reagent, with excess α,ω-diaminooligomethylenes were measured by fluorometry in dilute solution. The rate constant, corresponding to that for the reaction of the first step of the polycondensation between the disulphonyl dichloride and the diamines, depended remarkably on the chain length of the diamines. By using 5-dimethylamino-1-naphthalenesulphonyl chloride, a monofunctional fluorescent reagent, and α-aminooligomethylenes, rates of model reactions between the monoamines and the monosulphonyl chloride, the diamines and the monosulphonyl chloride, as well as the monoamines and the disulphonyl dichloride were measured by fluorometry. The remarkable chain length dependence is explained by intramolecular catalysis by the primary amino group.     

Effects of ligand density and pore size on the adsorption of bovine IgG with DEAE ion-exchange resins

Immunoglobulin G is an important plasma protein with many applications in therapeutics and diagnostics, which can be purified effectively by ion exchange chromatography. The ligand densities and pore properties of ion-exchange resins have significant effects on the separation behaviors of protein, however, the understandings are quite limited. In this work, with bovine immunoglobulin as the model IgG, the adsorption isotherms and adsorption kinetics were investigated systematically with series of diethylaminoethyl ion-exchange resins with different ligand densities and pore sizes. The Langmuir equation and pore diffusion model were used to fit the experimental data. The influences of ligand density and pore size on the saturated adsorption capacity, the dissociation constant and the effective diffusivity were discussed. The adsorption capacities increased with the increase of ligand density and the decrease of pore size, and an integrative parameter was proposed to describe the combined effects of ligand density and pore size. It was also found that the effective pore diffusion coefficient of the adsorption kinetics was influenced by pore sizes of resins, but was relatively independent on the ligand densities of resins. For a given protein, the ligand density and pore size should be optimized for improving the protein adsorption.     

A monitor for the specific determination of nickel carbonyl based on the chemiluminescence reaction with ozone and carbon monoxide

The chemiluminescence, measured at 500 nm, allows nickel carbonyl to be measured in the range 1 ppb to several ppm in combustion gases. Interferences from iron pentacarbonyl and nitrogen monoxide are eliminated by optical and spatial discrimination and by choice of the pressure in the reaction chamber.     

Effects of solvent and temperature on the reaction of 1,2,3,4-tetrafluoroanthraquinone with 4-tert-butylbenzenethiol

The reaction of 1,2,3,4-tetrafluoroanthraquinone with 4-tert-butylbenzenethiol in the presence of triethylamine on heating in nonpolar solvents resulted mainly in replacement of the α-fluorine atom, whereas in polar solvents the β-fluorine atom was replaced preferentially or exclusively.     

Direct and specific recognition of glycosaminoglycans by antibodies after their separation by agarose gel electrophoresis and blotting on cetylpyridinium chloride-treated nitrocellulose membranes

A method for the immunodetection of several natural complex polysaccharides (glycosaminoglycans) after their separation by conventional agarose gel electrophoresis, blotting and immobilizing on nitrocellulose membranes derivatized with the cationic detergent cetylpyridinium chloride (CPC), and direct and specific immunodetection by antibodies is described. This new approach is based on the principles that were used to develop the Western blot, and is applied to the separation of the glycosaminoglycans purified from normal human urine. After migration in agarose gel electrophoresis, chondroitin sulfate samples of different origin were blotted and transferred onto nitrocellulose membranes treated with CPC. Immunodetection was performed using the anti-chondroitin-6-sulfate antibody that specifically recognizes intact chondroitin-6-sulfate. By calculating the ratio between the antibody staining (epitope) and alcian blue staining (mass), the epitope density expressed as a percentage, i.e., the number of repetitive epitopes per mass, was obtained. These values were in agreement with the quantitation of 6-sulfated groups of chondroitin sulfate performed by the evaluation of unsatured disaccharide-6-sulfate (DeltaDi6S) produced after treatment with chondroitinase ABC and separated by high-performance liquid chromatography (HPLC). Furthermore, immunodetection of heparan sulfate was performed using the anti-heparan sulfate antibody.     

Effects of the chain length of crosslinking agent and dye-doped amount on the electro-optical properties of polymer-dispersed liquid crystal films prepared by nucleophile-initiated thiol-ene click reaction

ABSTRACT

A series of crosslinking agents with different chain lengths were used to explore their effect on electro-optical properties of dye-doped polymer dispersed liquid crystals (PDLCs) film prepared by nucleophile-initiated thiol-ene click reaction. The influences of dye contents and temperatures on electro-optical properties were also investigated. It was found that the increase in chain length of crosslinking agent leads to the increase in driving voltage and the decrease in memory effect. The decrease in reaction temperature causes a decrease in driving voltage and an increase in transmittance. Particularly, the dye content could be optimised to obtain promising materials with minimum driving voltage and high contrast ratio for display applications.     

Effects of alkyl chain length of monomer and dye-doped type on the electro-optical properties of polymer-dispersed liquid crystal films prepared by nucleophile-initiated thiol-ene click reaction

ABSTRACT

Polymer-dispersed liquid crystal (PDLC) films containing a series of monomers with different alkyl chain lengths were prepared by nucleophile-initiated thiol-ene click reaction. The effect of alkyl chain length of monomers, dye and temperature on electro-optical properties of PDLC films was investigated. It was found that the alkyl chain length and polymerisation rate of monomers together determine the size of liquid crystal (LC) droplets, thus affecting the electro-optical properties of PDLC. In addition, the type and content of dyes could be optimised to obtain PDLC materials with better comprehensive properties for display.     

再生障碍性贫血患者中药治疗前后微量元素变化初步观察

对20例再生障碍性贫血患者（以下简称再障）头发中12种微量元素的含量进行测定，与正常人做对照，结果发现，阴虚型患者锂、钙、锶、铬显著减少，阴虚型患者锌、镁、钡、钙、锂明显下降，阴阳俱虚型患者则12种元素均减少，并对本院治疗再障贫血的24味中药的微量元素的含量也进行测定。结合微量元素变化对指导再障的辩证组方和辩证施治提供新的思路，同时系统观察再障贫血10例治疗前后微量元素的变化情况，从微量元素角度探求再障的发症因素，认为与部分微量元素缺乏有关，补充相关的微量元素，再障患者可恢复健康。     

Effects of ion-pairing and hydration on the SNAr reaction of the F- with p-chlorobenzonitrile in aprotic solvents

Theoretical ab initio calculations including liquid phase optimizations were used to investigate the S(N)Ar reaction of the fluoride ion with p-chlorobenzonitrile in dimethyl sulfoxide solution. The effect of the counter ion and hydration of the fluoride ion with one water molecule was analyzed. The calculations indicate that the gas-phase S(N)Ar reaction is more favorable than the corresponding S(N)2 reactions involving fluoride ion and 2-chlorobutane. However, the substantially higher solvent effect on the S(N)Ar reaction makes the nucleophilic substitution on the aromatic ring less favorable than the aliphatic reaction in the liquid phase. For the anhydrous tetrabutylammonium fluoride system, the theoretical free energy barrier of 22.1 kcal mol(-1) is close to the experimental one of 24.4 kcal mol(-1). The smaller tetramethylammonium cation strongly associates with the fluoride ion and increases the barrier by 5 kcal mol(-1). Similarly, just one water molecule hydrating the fluoride ion has the same effect. An analysis of the reaction involving the ion pair and the free anion in different polarity media predicts an unexpected behavior and indicates there is an ideal solvent polarity for each counter ion.     

三种钢基疏水表面微观形貌的分形特征及其对润湿性的影响

采用化学刻蚀与低表面能物质修饰相结合的方法,通过调控刻蚀时间在304不锈钢、X80管线钢和45#钢表面构造不同的微观形貌;借助扫描电子显微镜采集不同材料表面的微观形貌,并采用接触角测量仪测量其润湿性能;应用Matlab软件编程计算分形参数.结果表明,3种材料构造的疏水表面均具有分形特征,且最佳刻蚀时间为30 min,此时多重分形谱子集维数最大值最靠左,对应的奇异性指数最小,表征表面微观形貌的分形维数也达到最大值;分形维数与接触角线性拟合效果优良,接触角随分形维数的增大而增大.     

Impact of reaction products on the Grignard reaction with silanes and ketones

Grignard reactions with alkoxysilanes or carbonyl compounds produce alkoxymagnesium halides as by-products. Kinetic measurements for reactions of silanes and of a ketone were performed with Grignard reagents, enriched in alkoxymagnesium halides and taken in a great excess.The alkoxide-type reaction products complex tightly with Grignard reagents and enhance in this way their nucleophilicity, thus accelerating the reaction. However, alkoxides branched at α-C atom exert an unfavorable steric hindrance to reaction resulting in a decrease in the reaction rate.