Residual stress and deformation during rapid cooling process in an epoxy plate

Residual stress in the epoxy plate during a rapid cooling process was measured by the layer removal method and calculated by the linear thermoviscoelastic theory considering specific volume relaxation. The relaxations of the tensile modulus and specific volume were measured by an Instron thermomechanical analyzer. When the starting temperature of the cooling process was near the glass transition temperature of the cured epoxy, the residual stress in the epoxy plate was smaller than when the starting temperature was higher than the glass transition temperature. However, the transient stress in the cured epoxy plate was higher when the starting temperature was near the glass transition temperature than when the starting temperature was higher than the glass transition temperature. The quenched epoxy plate was compressed in the direction parallel to the surface and expanded in the thickness direction.     

Determining molecular structures and conformations directly from electron diffraction using a genetic algorithm.

A global optimization strategy, based upon application of a genetic algorithm (GA), is demonstrated as an approach for determining the structures of molecules possessing significant conformational flexibility directly from gas-phase electron diffraction data. In contrast to the common approach to molecular structure determination, based on trial-and-error assessment of structures available from quantum chemical calculations, the GA approach described here does not require expensive quantum mechanical calculations or manual searching of the potential energy surface of the sample molecule, relying instead upon simple comparison between the experimental and calculated diffraction pattern derived from a proposed trial molecular structure. Structures as complex as all-trans retinal and p-coumaric acid, both important chromophores in photosensing processes, may be determined by this approach. In the examples presented here, we find that the GA approach can determine the correct conformation of a flexible molecule described by 11 independent torsion angles. We also demonstrate applications to samples comprising a mixture of two distinct molecular conformations. With these results we conclude that applications of this approach are very promising in elucidating the structures of large molecules directly from electron diffraction data.     

Retention modeling and simultaneous optimization of pH value and gradient steepness in RP‐HPLC using feed‐forward neural networks

A novel approach is proposed for the simultaneous optimization of mobile phase pH and gradient steepness in RP‐HPLC using artificial neural networks. By presetting the initial and final concentration of the organic solvent, a limited number of experiments with different gradient time and pH value of mobile phase are arranged in the two‐dimensional space of mobile phase parameters. The retention behavior of each solute is modeled using an individual artificial neural network. An “early stopping” strategy is adopted to ensure the predicting capability of neural networks. The trained neural networks can be used to predict the retention time of solutes under arbitrary mobile phase conditions in the optimization region. Finally, the optimal separation conditions can be found according to a global resolution function. The effectiveness of this method is validated by optimization of separation conditions for amino acids derivatised by a new fluorescent reagent.     

微机在“醋酸,磷酸电位滴定”实验中的应用

微机在“醋酸、磷酸电位滴定”实验中的应用王苏文（南京师范大学化学系南京２１００２４）袁立新（南京师范大学物理系南京２１００２４）关键词计算机，Ａ／Ｄ模数转换器，电位滴定许多化学实验使用传统的方法对实验数据进行人工读数、记录、处理等。在这一过程中就必定...     

Protein fold recognition

Summary An important, yet seemingly unattainable, goal in structural molecular biology is to be able to predict the native three-dimensional structure of a protein entirely from its amino acid sequence. Prediction methods based on rigorous energy calculations have not yet been successful, and best results have been obtained from homology modelling and statistical secondary structure prediction. Homology modelling is limited to cases where significant sequence similarity is shared between a protein of known structure and the unknown. Secondary structure prediction methods are not only unreliable, but also do not offer any obvious route to the full tertiary structure. Recently, methods have been developed whereby entire protein folds are recognized from sequence, even where little or no sequence similarity is shared between the proteins under consideration. In this paper we review the current methods, including our own, and in particular offer a historical background to their development. In addition, we also discuss the future of these methods and outline the developments under investigation in our laboratory.     

Structural determinants of steroids for cytochrome P450 3A4-mediated metabolism

Cytochrome P450 3A4 (CYP3A4), a major member of cytochrome P450 isoenzymes, metabolizes the majority of steroids in 6β-position. For the purpose of determining requisite structural features of a series of structurally related steroids for CYP3A4-mediated metabolism, three-dimensional pharmacophore modeling as well as electrotopological state map were conducted for 15 steroids. Though prior studies speculated that the chemical reactivity of the allylic 6β-position might have a greater influence on CYP3A4 selective 6-hydroxylation than steric constraints in the enzyme, our results reveal that for CYP3A4 steroidal substrates, it is not the chemical reactivity of atoms at 6β-site, but the pharmacophoric features, i.e. the two hydrophobic rings together with two H-bond donors, that act as the key factors responsible for determining the CYP3A4 selective 6-hydroxylation of steroids.     

Nanocomposite materials from latex and cellulose whiskers

Composite materials were processed by casting a mixture of aqueous suspensions of latex and microfibrils. These microfibrils, or whiskers, are extracted from a sea animal and are monocrystals of cellulose, with an aspect ratio around 100 and an average diameter of 20 nm. It has been found that the mechanical properties (shear modulus) are increased by more than two orders of magnitude in the rubbery state of the polymeric matrix, when the whisker content was 6% (w/w). This very large effect is discussed on the basis of different types of mechanical models and it is concluded that these whiskers form a rigid network, probably linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.     

任意多阶梯度场强毛细管凝胶电泳中谱带的迁移和展宽

在自行制备的毛细管凝胶电泳柱上，通过实验考察毛细管凝胶电泳（ＣＧＥ）中场强（Ｅ）和组分迁移率（μ）的关系，发现在一般ＣＧＥ使用的场强范围内，μ随Ｅ增大而成近似线性的增加。并讨论了产生这种现象的原因。以此为基础提供了任意多阶梯度场强毛细管凝胶电泳中组分的迁移时间和距离的计算公式，用于编制计算机程序。     

An investigation into the construction of molecular models by the template joining method

Summary The results of a wide-ranging investigation into some of the different methods available for performing the joining of templates to build molecular models show that the choice of algorithm can significantly affect the quality of the results obtained, and different algorithms are most suited to particular categories of join.