顺式效应的起源: 双取代乙烯衍生物的密度泛函理论研究

一般情况下双取代乙烯衍生物的反式构象要比顺式构象稳定. 但是例外也存在, 例如1,2-二氟乙烯和1,2-二氯乙烯. 这种双取代乙烯衍生物顺式构象的超常稳定性被称之为顺式效应. 该效应的起源和本质目前仍没有定论. 本文以12 个体系(XHC=CHY (X, Y=F, Cl, Br, CN, CH₃, C₂H₆, OCH₃))为例, 对顺式效应的有效性、起源和本质进行系统的密度泛函理论研究, 其中9个体系存在顺式效应, 另外3个为正常体系没有该效应. 采用一系列泛函和基组研究其有效性, 并运用四种分析手段, 如自然键轨道(NBO)、能量分量分析(EDA)、密度泛函活性理论(DFRT)和非共价相互作用(NCI)分析, 剖析该效应的起源和本质. 发现在顺式构象的两个取代基之间存在一种微弱的非共价相互吸引作用. 能量分析表明, 静电效应、立体效应等对顺式效应的存在都起着重要作用, 但是它们均不能单独用来解释顺式效应的起源. 也就是说顺式效应没有一个简单的起源, 它是多种作用合力的结果. 本文采用双变量解释得到比较合理的相关回归系数R²=0.86-0.87,较好地解释了顺式效应的本质和起源.     

Non-linear Interaction of Morphological and Convective Instabilities During Solidification of a Dilute Binary Alloy

We consider the stability of a horizontal, planar solid-meltinterface during the solidification of a dilute binary alloy.Linear theory has shown that instability may occur due to eithersolutal convection in the melt or due to morphological effects.We investigate a system in which two modes of different horizontalwavenumber become unstable simultaneously. One mode representsthe morphological instability and the other represents the convectiveinstability. We carry out a weakly non-linear analysis, in orderto determine the non-linear evolution equations for the amplitudesof these two modes. The coefficients of these equations determinethe non-linear interaction which occurs near the onset of instability.We present an example of the application of the theory to thelead-tin alloy system, and show that the interaction is weak.     

聚合物科学基本术语汇编

基本术语的清晰和严格的定义在科学界具有特殊重要性.随后的命名必须参考这些基本术语,因此,基本术语的准确定义和修订要极为谨慎.1974年高分子命名委员会公布了"聚合物相关术语的基本定义(1974)"文件,发表在Pure Appl.Chem.1974,40,479-491.这些定义是本委员会的工作基础,并由此发展了一些进一...     

THE USE OF TELESCOPING SPATIAL SCALES TO CAPTURE INSHORE TO SLOPE DYNAMICS IN MARINE ECOSYSTEM MODELING

Abstract Ecosystem processes function at many scales, and capturing these processes is a challenge for ecosystem models. Nevertheless, it is a necessary step for considering many management issues pertaining to shelf and coastal systems. In this paper, we explore one method of modeling large areas with a focus at a range of scales. We develop an ecosystem model that can be used for strategic management decision support by modeling the waters off southeastern Australia using a polygon telescoping approach, which incorporates fine‐scale detail at the coastal zone, increasing in scale to a very coarse scale in the offshore areas. This telescoping technique is a useful tool for incorporating a wide range of habitats at different scales into a single model.     

Computation of the Free-Surface Shape of an Inviscid Jet Incident on a Porous Wall

We consider the problem of determining the steady free-surfaceshape of an incompressible, inviscid, irrotational jet incidentupon a porous wall. A fixeddomain method based on the Baiocchitransformation is used to determine accurate numerical approximationsto the free surfaces. Results are presented for cases in whichthe jet is incident either perpendicularly or obliquely to thewall. We also consider the effect of gravity on the above cases,and examine the pressure field in the jet.     

In vivo AND PHOTOPHYSICAL STUDIES ON PHOTOOXIDATIVE DAMAGE TO LENS PROTEINS AND THEIR PROTECTION BY RADIOPROTECTORS

Abstract— Photooxidation, whether initiated by an endogenous or exogenous sensitizer, is an important mechanism in light induced damage to the lens. One of the substrates for this damage is lens protein. A porphyrin sensitizer which binds to lens proteins [ mesotetra ( p -sulfonatophenyl) porphyrin (TPPS)] was found to photooxidize Skh-2 pigmented mice lens protein in vivo. Uroporphyrin, a model for a non-binding photosensitizer, did not induce photooxidative damage to the mouse lens.
The radioprotector 3-amino-2-hydroxypropyl phosphorothioate (WR-77913) was investigated as an agent to retard or negate in vivo photooxidative damage to the lens. Intraperitoneal injections of WR-77913 prior to irradiation reduced the TPPS induced photodestruction of lens protein in Skh-2 pigmented mice.
The mechanism of protection was also investigated. Thiols were found to quench both the triplet state of porphyrins and the reactive intermediate singlet oxygen on the order of 10⁵ and 10⁶ M ^-1 s¹ respectively. These are probably not fast enough to explain most of the protection afforded by thiols. An additional mechanism may be the accelerated photobleaching of porphyrins by thiols which protects tissue by reducing the absorptions due to the porphyrins.     

CONCERNING THE PRODUCTION OF FREE RADICALS IN PROTEINS BY ULTRAVIOLET LIGHT

Abstract— Using electron paramagnetic resonance techniques, the response to u.v. light of several solid proteins and model compounds has been studied in vacuum and at low temperature. Emphasis has been placed on determining the response as a function of the wavelength (Λ 250 nm) and intensity of the incident radiation. Correlation of the parameters of radical production with sample luminescence, molecular amino-acid sequence and tertiary structure, light intensity and total irradiation time has allowed some insight into the mechanisms of free radical formation.
It is shown that the details of amino acid composition, sequence and the tertiary structure of a protein are important in determining both the rate of, and the mechanism for, radical production (two basic mechanisms are described), and in determining the conditions under which sulfur-type radicals can be produced. The results are related to enzyme inactivation and to the u.v. stability of proteins generally.