Weakening of a Polyethylene Chain by Methyl Side Groups

The effect of methyl side groups on the strength of a single polyethylene chain is calculated with Density Functional Theory. Using transition state theory, the scission rate is calculated as function of stress for bonds next to a methyl side group. The increase in the scission rate due to the presence of the side group is maximal at zero stress/strain, where it is enhanced by a factor of 5,000. This increase results from a hyperconjugation interaction between the methyl side group and the radical that is formed during the scission process. The calculated scission rate is used as input for a model in which a fiber consists of independent chains. With the help of the model we estimate how much the tensile strength of polyethylene fiber can deteriorate due to the presence of methyl side groups. The strength of the fiber is reduced with 6% for a concentration of one side group in 10 main chain carbon atoms.     

An expeditious synthesis of an analogue of (−)-steviamine by way of the 1,3-dipolar cycloaddition of a nitrile oxide with a 1-C-allyl iminosugar

In our continuing effort to develop inhibitors of the mycobacterial galactan biosynthesis, we planned to synthesize original iminosugar-based analogues of UDP-galactofuranose by way of the 1,3-dipolar cycloaddition reaction between a 1-C-allyl iminosugar and a nitrile oxide, followed by the reductive cleavage of the resulting isooxazoline. In initial studies, it was found that this last step led in one pot to a new polyhydroxylated indolizidine derivative closely related to the recently isolated (−)-steviamine, in good yield, by way of a sequence involving at least five individual reactions. The activity of this new compound as a glycosidase inhibitor was evaluated against a panel of glycosidases and compared to (−)-steviamine.     

变温红外法研究聚对苯二甲酸乙二酯分子链的松弛运动及其构象转变

在30～170 ℃范围内逐渐升温过程中,用红外光谱仪原位检测无定形聚对苯二甲酸乙二酯（PET）薄膜红外光谱图的变化情况。通过特征谱带吸光度与温度的变化特点,研究了PET分子链在热变化过程中的松弛运动及冷结晶过程中分子链的构象变化。实验结果表明在冷结晶过程中,随PET结晶的不断完善,对应左右式(gauche)构象的吸收峰减弱,对应反式(trans)构象的吸收峰增强,并计算出CH2面外摇摆振动结晶前和结晶后反式构象和左右式构象的相对百分含量随温度的变化关系,以及玻璃化转变和冷结晶的温区范围。     

嵌段高分子尾形链构象性质的Monte Carlo研究

基于简立方格点模型对AB两嵌段高分子尾形链的构象性质及其链节的空间分布进行了MonteCarlo模拟.结果表明,链的尺寸、形状和链节的空间分布等统计性质和B链节与平面壁之间的相互吸引能有关.随着B链节与壁之间的吸引能的增加,链的尺寸和形状均呈现出先下降后升高的变化趋势,而且B链节的比例越大,这种变化越明显.     

Conformation and Biological Activity of Cyclic Peptides

Cyclic peptides containing biologically active hormone sequences are suitable models for studying conformation-activity relationships. In such models the usual flexibility of peptide chains is reduced by their cyclic arrangement. However, conformational analysis of such systems by experimental means is possible only if a single conformer predominates at equilibrium, and criteria for this are put forward. NMR spectroscopic methods, including many recent advances, are discussed in relation to their ability to contribute to peptide conformational analysis.     

烷基取代聚硅烷共聚物的侧基对螺旋构象的影响

以手性化合物n-癸基-(S)-(+)-2-甲基丁基二氯硅烷(Si1)和非手性化合物n-癸基-2-乙基丁基二氯硅烷(Si2)为单体合成了聚硅烷共聚物[P(Si1-co-Si2)].通过改变Si1和Si2的投料比,聚合得到一系列P(Si1-co-Si2).通过核磁表征P(Si1-co-Si2)为无规共聚物.利用圆二色谱(CD)和紫外吸收光谱研究系列共聚物的手性传递行为.研究发现,Si2的均聚物在其对应的紫外吸收带324 nm处没有CD信号.当加入Si1共聚后,产生CD信号,随着Si1含量的增加,共聚物的CD信号迅速增强,当Si1摩尔分数为2%时可诱导共聚物形成单手螺旋优势构象.当Si1含量达到70%时,信号强度最大.在P(Si1-co-Si2)中Si1含量增加的过程中,共聚物的紫外吸收带同时发生蓝移.当Si1含量达到50%时,分子量较低的样品具有较强的光学活性,并且随着分子量的增大,紫外吸收红移.研究结果初步表明,聚硅烷共聚物的螺旋结构由手性侧基决定,但非手性侧基的奇偶性却没有体现.     

pH值对丝素蛋白构象转变的影响

模仿家蚕吐丝过程中伴随丝素蛋白自然脱水的纤维化过程,研究了再生丝素蛋白在各种pH值的磷酸盐缓冲溶液体系中自然干燥脱水成膜后的构象转变.利用激光拉曼散射光谱及其二维相关光谱,定性分析了丝素蛋白酰胺区(1600～1700cm^-1)散射峰的相关组成及结构.在此基础上,利用¹³CCP-MAS固体核磁共振谱对丝素蛋白丙氨酸C_β峰(δ14.5～22)进行了解析拟合.从而确定了体系中与Silk及Silk构象相关的组成含量与pH值的关系.结果表明,pH=5.2的酸性溶液有利于蚕丝丝素蛋白从Silk向Silk构象转变,而中性与碱性溶液(pH=6.9和8.0)则对丝素蛋白的构象转变影响甚小.     

Studies on the Side Chain Liquid Crystalline Copolymer Containing Nonlinear Optical Groups *

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良溶剂中接枝型聚两性电解质单链构象的布朗动力学模拟

采用布朗动力学研究了在良溶剂中荷电平衡的接枝聚两性电解质(GPA)的单链构象转变行为,讨论了主链链长、支链数及电荷密度对GPA分子链构象转变的影响.研究发现,随着静电相互作用的增强,GPA分子链构象转变过程由线团、主链与支链间的折叠、链段塌缩和电荷配对形成偶极子与四极子等4个阶段构成.与线型聚两性电解质不同,GPA存在的额外支链间空间排斥与静电排斥作用随着分子结构的变化而改变,并影响构象转变行为.在强静电相互作用下,良溶剂中的GPA链由于溶剂化作用会再伸展,以保证偶极子完全配对成四极子.减小主链长度或电荷密度或增加支链数目都会增大体系的排斥力和主链的刚性,阻滞分子链的塌缩,并使得分子链再伸展的幅度增大.     

Synthesis of N-acetyl Glucosamine Analogs as Inhibitors for Hyaluronan Biosynthesis

Elevated hyaluronan expression is a hallmark of many types of cancer. Therefore, inhibition of hyaluronan biosynthesis can potentially slow the growth of tumor cells. Herein, we explore a chain termination strategy to reduce hyaluronan synthesis by tumor cells. Several analogs of glucosamine were prepared, which contained modifications at the C-3 positions. These analogs can possibly cap the nonreducing end of a growing hyaluronan chain, thus lowering the amount of hyaluronan synthesized. Upon incubation with pancreatic cancer cells, a fluorine-containing glucosamine analog was found to exhibit significant inhibitory activities of hyaluronan synthesis. Furthermore, it drastically reduced the proliferation of cancer cells.

Supplemental materials are available for this article. Go to the publisher's online edition of Journal of Carbohydrate Chemistry to view the supplemental file.     

表面增强拉曼散射光谱研究聚苯胺纳米棒的构象转变

采用电化学沉积法制备了聚苯胺(Polyaniline,PANI)纳米棒、树枝状银和纳米颗粒银基体。并利用表面增强拉曼散射光谱技术(Surface-enhanced Raman Scattering,SERS)研究了PANI纳米棒的分子链在Ag金属表面的构象变化。实验结果表明由于Ag金属表面的等离子共振效应,PANI分子中N原子的孤对电子与Ag的自由电子产生共轭效应,使得PANI分子链上的电荷重新分布,结果 C—H面内弯曲振动频率和C—C键的伸缩频率向低波数方向移动(蓝移);拉曼散射频率增强的基团在金属表面倾向垂直于分子链的主轴,拉曼散射频率减弱的基团在金属表面倾向平行于分子链主轴。     

大环烷构象

综述了40多年来大环烷构象的研究进展，将大环烷分为偶数和奇灵敏环分别对其构象研究进行讨论，得出大环烷构象的一般规律，并介绍了有关大环化合物构象的命名法则。     

RCM as a tool to freeze conformation of monosaccharides: synthesis of a β-mannopyranoside mimic adopting a conformation close to the biologically relevant B2,5 boat

The synthesis of a β-d-mannopyranoside analog, fully identical to the naturally occurring d-mannopyranose in terms of hydroxyl pattern, and displaying a skew-boat conformation close to a B_2,5 boat strongly believed to be adopted by the oxycarbenium transition state during glycosidic bond cleavage of β-mannane by family 26 β-mannanase, is described. The conformationally locked analog has been obtained by tethering the C-2 and C-5 carbon atoms of the sugar ring with a three carbon bridge using RCM methodology. Conformation of the mannose analog has been confirmed by NMR and molecular modelling.     

LB膜技术对葡萄糖氧化酶分子构象的影响

利用π－Ａ曲线、布儒斯特角显微镜（ＢＡＭ）及ＣＤ光谱对葡萄糖氧化酶（ＧＯＤ）的甲醇溶液铺展在ＣｄＣｌ２水溶液和纯水表面上形成的单分子膜进行了研究，以了解ＧＯＤ分子的自组和折叠情况，发现甲醇或者ＣｄＣｌ２都能ＧＯＤ分子更加疏水，易形成单分子膜，铺展在ＣｄＣｌ２溶液上比铺展在纯水上更加能使ＧＯＤ的单分子膜排列紧密，在表面压较高时，能观察到形成了第二层膜，并且使ＧＯＤ分子的构象从β－折叠片向α－螺旋转变     

Influence of N-Methylation and Conformation on Almiramide Anti-Leishmanial Activity

The almiramide N-methylated lipopeptides exhibit promising activity against trypanosomatid parasites. A structure–activity relationship study has been performed to examine the influences of N-methylation and conformation on activity against various strains of leishmaniasis protozoan and on cytotoxicity. The synthesis and biological analysis of twenty-five analogs demonstrated that derivatives with a single methyl group on either the first or fifth residue amide nitrogen exhibited greater activity than the permethylated peptides and relatively high potency against resistant strains. Replacement of amino amide residues in the peptide, by turn inducing α amino γ lactam (Agl) and N-aminoimidazalone (Nai) counterparts, reduced typically anti-parasitic activity; however, peptide amides possessing Agl residues at the second residue retained significant potency in the unmethylated and permethylated series. Systematic study of the effects of methylation and turn geometry on anti-parasitic activity indicated the relevance of an extended conformer about the central residues, and conformational mobility by tertiary amide isomerization and turn geometry at the extremities of the active peptides.     

磁场对大分子构象的影响研究进展

对近年来有关磁场对大分子构象的影响研究进展进行了较全面综述.     

肽链体系中的长程电子转移: 多肽构象和旁链间距对电子转移矩阵元的影响

用AM1半经验方法,优化了吲哚和苯酚中性分子、正离子自由基和负离子自由基的几何构型。用线性反应坐标近似和溶剂效庆的类导体屏蔽模型（COSMO）构造吲哚正离子和苯酚中性分子间电子转移的双势阱,用以估算多肽链中色氨酸和酪氨酸之间的电子转移的反应热和内重组能。优化TrpH-(Pro)n-TyrOH(n=0-3)多肽模型分子的结构和构象,用能级分裂因子的极小值方法计算了这些多肽体系的电子转移矩阵元。     

侧链型偶氮聚电解质自组装和膜结构研究

研究了4种侧链型偶氮聚电解质的自组装过程及其对自组装膜结构的影响.用聚电解质上的偶氮基团作为“探针”,研究了自组装过程中出现的生色团取向、解吸附和非线性增长等现象.这些侧链型偶氮聚电解质均具有较好的自组装性,但其自组装行为有很大差异.在不同的pH条件下,聚电解质的电离程度不同,导致吸附过程和自组装膜结构亦明显不同.自组装膜的增长和结构取决于体系中吸附和解吸的平衡.偶氮生色团端基的亲水或疏水性对自组装膜的增长有明显的影响.偶氮聚电解质自组装过程不同阶段出现的非线性增长现象,分别反映了基底、溶液性质和聚电解质结构等因素的影响.     

一种通过分子间氢键自组装的侧链液晶聚合物

一种通过分子间氢键自组装的侧链液晶聚合物邢佩祥，赵英英，汤心颐，姜炳政（吉林大学化学系，长春，１３００２３）（中国科学院长春应用化学研究所高分子物理开放实验室）关键词氢键，侧链液晶聚合物，近晶相，自组装自Ｒｉｎｇｓｄｏｒｆ［１］等提出在介晶基团与主链...     

从麦克斯韦速度分布函数直接推导高分子链末端距分布函数

利用高分子链末端距分布与小分子运动速度分布之间的相关性 ,从熟知的麦克斯韦速度分布函数直接推导出高分子链末端距的径向分布函数 ,并从量变到质变的观点对高分子和小分子运动的统计规律进行讨论