利用尺寸排阻色谱法研究蛋白质的变性

通过比较蛋白质变性时的色谱行为和生物物理特性，提出利用尺寸排阻色谱法研究蛋白质变性时的构象变化，根据色谱参数中保留时间，比较蛋白质变性时体积的相对变化，利用色谱峰数，确定形成变体的数目，根据峰形和峰数的变化，描述蛋白质的伸展程度，利用不同波长下峰高的变化，推断蛋白质变性芳香族基酸残基的暴露情况，利用建立的尺寸排阻色谱观察了液体和固液α－淀粉酶在低温下放置时的变性情况，讨论了变性时间和变性温度对蛋白     

Activity and Conformation of Yeast Alcohol Dehydrogenase (YADH) Entrapped in Reverse Micelles

Yeast alcohol dehydrogenase (YADH) solubilized in reverse micelles of aerosol OT (i.e., AOT or sodium bis (2-ethyl hexyl) sulfosuccinate) in isooctane has been shown to be catalytically more active than that in aqueous buffer under optimum conditions of pH, temperature, and water content in reverse micelles. Studies of the secondary structure conformational changes of the enzyme in reverse micelles have been made from circular dichroism spectroscopy. It has been seen that the conformation of YADH in reverse micelles is extremely sensitive to pH, temperature, and water content. A comparison has been made between the catalytic activity of the enzyme and the α-helix content in the conformation and it has been observed that the enzyme is most active at the maximum α-helix content. While the β-sheet content in the conformation of the entrapped enzyme was found to be dependent on the enzyme–micelle interface interaction, the α-helix and random coil conformations are governed by the degree of entrapment and the extent of rigidity provided by the micelle core to the enzyme structure.     

Evaluation of a direct1H NMR method for determining logK and ΔH values for crown ether -alkylammonium cation complexation

A direct¹H NMR method for determining logK and H values for crown ether-ammonium cation complexation using milligrams of sample was tested and evaluated for accuracy and precision by comparing the results with those obtained using a titration calorimetric method. LogK values for the interactions of a non-chiral crown ether, diketopyridino-18-crown-6 (K₂P18C6), with -phenylethylammonium (PhEt⁺) perchlorate in 50%–50% and 90%–10% (v/v) mixtures of deuterated methanol (CD₃OD) and deuterated chloroform (CDCl₃) at four temperatures and, with -(1-naphthyl)ethylammonium (NapEt⁺) perchlorate in 50%CD₃OD-50%CDCl₃ (v/v) at 25°C were determined by a direct¹H NMR method. Values of H for the interactions of K₂P18C6 with PhEt⁺ in the two solvents were calculated from the temperature dependence of logK. LogK values for the interactions of a chiral crown ether, dimethyldiketopyridino-18-crown-6 (M₂K₂P18C6), with (R) and (S) enantiomers of NapEt⁺ in pure CD₃OD at 25.0°C were also determined by the NMR method. The results were compared with those determined by a calorimetric method at 25.0°C in 50%-50% and 90%–10% (v/v) mixtures of plain methanol and chloroform, in 100% plain methanol, and in a 50%-50% mixture of partially deuterated methanol (with deuterium substitution on the methanol OH group, CH₃OD) and deuterated chloroform. The log K values determined by both methods were found to be in good agreement, but the standard deviations associated with the NMR logK values were two to three times greater. The agreement of the H values determined by the two methods was poor, differing by approximately 10 kJ/mol with the NMR method giving more negative values. The standard deviations associated with the NMR H values were approximately ten times greater than those for the calorimetric values. Ion-pairing was observed for the interaction of perchlorate ion with both free and bound PhEt⁺ in 50%methanol-50%chloroform mixture. It is concluded that the NMR procedure is satisfactory for the determination of logK, but not H values.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Analysis of polar compounds on PEG-40M/KF glass capillary columns

The chromatographic properties of potassium fluoride as an additive to the polyethylene glycol stationary phase were investigated. This unique base in organic chemistry was shown to succeed in yielding good results for the analysis of polar compounds, including the primary amines. Glass capillary columns of high selectivity for primary and secondary aliphatic amines were obtained by the “hexane plug” procedure by which a thin layer of KF is deposited on the inner surface of glass capillary columns. Some possible types of donor-acceptor interactions occuring within the system PEG/KF/solute were considered.     

SOLVENT QUALITY AND SOLUTION BEHAVIOR OF NYLON 12

The refractive index increment,dynamic and static laser light scattering,intrinsic viscosity[η]and Huggins constant(K_H)of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 10-60℃.The intrinsic viscosity,R_H,R_g,A_2,and(~2)~(1/2)(calculated from viscosity data)and"a"values of nylon 12 are found to be higher in m-cresol than in sulphuric acid.All these parameters decrease with the increase in water contents in sulphuric acid.The refractive index increment,K_H and activation energy show an opposite trend to that of[η].The intrinsic viscosity,R_H,R_g,A_2, and(~2)~(1/2) have maximum values around 30-40℃in sulphuric acid/water system,whereas in m-cresol they fall at about 20℃.It has been concluded that the variation in size,interaction parameter(second virial coefficient),[η]and K_H of the polymer solutions with the alteration in solvent composition and temperature are the out come of change in thermodynamic quality of solvents,selective adsorption,hydrogen bonding and conformational transitions.It has also been concluded that the increase in temperature first enhances the quality of the solvent,encourages hydrogen bonding and specific adsorption, and then deteriorates,bringing conformational transitions in the polymer molecules.However,the addition of water to sulphuric acid continuously deteriorates the solvent quality.This characteristic of the solvent system brings conformational changes in the polymer especially at low temperatures.     

Phase changes in the syrian phosphorite–ammonium sulphate system

With a complex of physico-chemical methods for analysis it is proved that in the course of mechanochemical treatment of a Syrian phosphorite and ammonium sulphate mixture new phases have been formed. The thermal analysis proves an increase in the reaction properties of the ammonium sulphate and the Syrian phosphorite which is a prerequisite for the increase in the content of P₂O₅^assimilated , in the activated phosphorite mixtures and the possibility to use them in the production of NP complex fertilizers.     

Structure of bis(2-amino-5-methylpyridinium) tetrachlorozincate at 298 and 150 K

Reaction of 2-amino-5-methylpyridine with zinc chloride and HCl in aqueous solution yields bis(2-amino-5-methylpyridinium) tetrachlorozincate. The complex crystallizes in the monoclinic space group P2₁/c, with minimal tetrahedral distortion of the ZnCl₄ ^2– ion at both 298 and 150 K; at 298 K, a = 8.090(2) Å, b = 14.795(6) Å, c = 15.850(4) Å, = 101.93 (2); at 150 K, a = 8.0986(2) Å, b = 14.7190(5) Å, c = 15.7684(7) Å, = 102.862(2). The anisotropic cell contraction results in significant changes in nonbonding Cl Cl contacts.     

证券分析师会降低博彩型股票推荐评级吗？——来自我国A股市场的经验证据

博彩型股票具有“高风险”和“高投机性”的特点。本文以博彩型股票为研究对象,检验证券分析师是否会显著下调博彩型股票的推荐评级。在此基础上,探讨了投资者对博彩型股票推荐评级做出的反应及评级后的超额收益率情况。结果表明:分析师更可能下调博彩型股票的评级,但在投资者情绪高涨时,下调的可能性有所减小;投资者对分析师的博彩型股票评级存在反应过度的情况。本文结论对于认识证券分析师在资本市场中的作用具有重要的参考价值。     

Parameter estimation in systems of differential equations,based on three-way data arrays and random time changes

Consider a system of n₁ × n₂ differential equations depending on a vector θ of unknown parameters. We suggest an iterative estimation procedure for θ, based on a three-way array of observations. The method involves random time changes driven by multidimensional integrated Ornstein-Uhlenbeck processes.     

Photoinduced Structural Changes in Poly(4-Vinyl Pyridine): A Luminescence Study

In the present work we show a way of controlling photoluminescence (PL) properties through photoinduced quasi-crystal formation in a system based on poly(4-vinyl pyridine) (P4VPy). Under UV irradiation at 380 nm, concentrated solutions of P4VPy in pyridine turn into gel. This phase transition results in changes in the optical properties of this polymer. The position of the PL maximum can be changed continuously from 440 to 480 nm during irradiation. After several minutes of UV irradiation a new red-shifted PL at 492 nm appears upon excitation by light of a wavelength corresponding to that of the initial PL maximum, which is also red-shifted during irradiation. Solutions of P4VPy in pyrimidine show similar behavior, but those in pyridazine do not exhibit such behavior. We have found that the reason for the observed changes in the electronic properties is a photoinduced directional ordering of polymer molecules in a special quasi-crystal formation. The process originates from a structural change in the side chain of P4VPy, namely, protonation of the polymeric pyridine after solvation. During irradiation, the polymeric pyridinium ion interacts with neutral polymeric pyridine molecules. Interchain interaction through hydrogen bonds lead to an electronic property change. We observed that the process of photoinduced sol-gel transformation is reversible. Mechanical perturbation or heating can convert the gel back to a fluid solution. The red-shifted PL is not observed, and the initial PL is blue-shifted to 450 nm and stays there.