交联聚合物线团的形态和尺寸研究

通过建立低压差下核孔膜过滤稀释液的方法 ,研究了低浓度HPAM与AlCit形成的交联聚合物溶液(LPS)中交联聚合物线团 (LPC)的形态和尺寸 .实验结果表明 ,LPC为球形结构 ,由于交联作用 ,其剪切变形程度有限 .低压差下核孔膜过滤法与动态光散射法 (DLS)和扫描电镜法 (SEM)相结合 ,可较为准确地判断LPC的尺寸范围 ,HPAM相对分子质量为 1 1× 10 7～ 1 4× 10 7、浓度为 0 0 2 % ,NaCl浓度 0 2 % ,交联比 2 0∶1的LPS中LPC的直径小于 1 38μm ,相当多的LPC直径在 4 5 0nm以上 ,平均流体力学直径约为 4 92nm .在一定聚合物浓度范围内 ,相同实验条件下 ,随着聚合物相对分子质量的增大 ,LPC尺寸逐渐增大 .LPS制成干片后 ,LPC的尺寸收缩有限 ,利用SEM法直接观测其形态 ,具有一定的准确性 ,可用此法对其进行研究 .     

STUDIES ON THE PROTEIN CONFORMATION OF PHYTOCHROME

Abstract— The extinction coefficients for large rye phytochrome were found to be: Fluorescence and circular dichroism spectra of large- and small-molecular-weight rye phytochrome give no evidence for a protein conformational change on phototransformation of phytochrome. The large molecule has a fluorescence emission peak at 331 nm when excited at 290 nm, and an excitation peak for this emission at 288 nm. The circular dichroism spectra indicate that large rye phytochrome has about 17–20% a-helix content, 30%β-structure and 50% random coil, and that the small rye phytochrome has about 10–13%α-helix content. The ultraviolet difference spectra for large and small rye phytochrome are similar and differ from the difference spectrum of the small oat phytochrome in the relative size of the 296–298 nm peak. The difference spectra may reflect changes in chromophore absorbance and in the environment of amino acid residues near the chromophore, particularly of tyrosine, and perhaps of tryptophan and cysteine.     

THEORETICAL STUDY OF OPTICAL SPECTRA AND CONFORMATION OF THE CHROMOPHORE OF HYPSORHODOPSIN

Optical spectra of hypsorhodopsin were theoretically analyzed by assuming the unprotonated all-trans form of the Schiff base of the chromophore. The large bathochromic shift of the optical absorption of hypsorhodopsin from that of the retinylidene Schiff base in solution could be easily explained by twisting the double bond of the chromophore; it could not be explained by simple counter anion models. Using the same twisted chromophore conformation for hypsorhodopsin as that of bathorhodopsin obtained by the torsion model, we showed that the calculated absorption wavelength was in fairly good agreement with the experimental value. Our calculated oscillator strengths and rotational strengths were quite similar between hypsorhodopsin and bathorhodopsin. Those theoretical results will be useful when one examines the relation of the chromophore's conformation between hypsorhodopsin and bathorhodopsin experimentally.     

聚对苯二甲酸乙二酯非晶区反式构象结构的探讨

<正> 聚对苯二甲酸乙二酯(PET)的重复单元中有乙撑基。它的碳碳键内旋转产生反式构象(T)和左右式构象(G)。用其不同的构象来表征PET的聚集态结构,对研究结构与性能的关系是十分重要的。许多工作都已指出,乙撑基反式构象的谱带热处理时随结晶度的增加而增加。X-射线衍射的结果证实     

4,4’-二苯甲酰基联苯构象的分子力学研究

4,4’—二苯甲酰基联苯有两个三岔点,属于二元三岔共轭体系。从结构式上看,卽可把它作为二苯甲酮骨架的取代产物,又可看作是在联苯骨架上的取代。作为系统研究三岔共轭体系结构效应的部分工作,我们用QCFF/PI+MCA(Quantum Mechanical Extension of the Consistent Force Field to PI Electron System+Molecular Crystal Analysis)程序研究了其晶态和孤立态(气态)构象。研究结果表明,在孤立态中,联苯基的二个苯环的最小二乘     

核磁共振INDOR法研究若干单糖分子的构型和构象

本文用核磁共振谱的INDOR,研究若干单糖在DMSO溶液中的构型和构象。在单糖分子中,除少数质子如差向异构氢(C₁—H)外,大多数质子处于相似的化学环境中,相邻者又彼此偶合,在常规核磁共振谱上产生的信号重迭交错,形成峰包,无法一一辨认以确定归属。从木糖、阿拉伯糖、甘露糖、鼠李糖等单糖在DMSO中的1NDOR谱,可间接测得C₂～C₄上质子的各组谱线,进而获得每一质子的化学位移及偶合常数。用Karplus方程定出相邻碳上质子的两面角及C—H键取向,因而确证这些分子在DMSO中的立体结构。     

聚肽嵌段共聚物中肽链构象对其自组装行为的影响

两亲性聚肽嵌段共聚物具有良好的生物相容性、生物安全性和可生物降解性,其在选择性溶剂中自组装形成的胶束在药物控释载体方面有着良好的应用前景[1~4].Cho等研究了聚(L-谷氨酸-γ-苯甲酯)(PBLG)-聚氧化乙烯(PEO)嵌段共聚物(PBLG-b-PEO)在水中的自组装性能,发现PBLG-b-PEO在水     

二苯基吡唑啉衍生物发光态构象的研究

本工作在合成了几种不同结构吡唑啉衍生物的基础上,测定了它们在相同极性,不同粘度介质中的荧光量子产率并表明:和1-位氮原子相联苯基的旋转松弛对该类化合物的发光具有决定意义,通过对化合物在极性与非极性溶剂内和在冻结与流动条件下(低温与室温下)荧光强度的比较,证明了二苯基吡唑啉化合物的发光态具有扭曲构象。     

胆红素与胆汁酸盐作用时的构象变化

利用PPP-SCF-CI-DV量子化学程序拟合胆红素以及胆汁酸盐-胆红素水溶液的UV和CD谱, 借以研究胆红素及其与胆汁酸盐复合物的构象性质。发现胆红素与胆汁酸盐作用时, 两个双吡咯生色团的扭角由104°变成112°, 仍保持形成分子内氢键的状态, 其UV及CD谱两个吸收峰间隔的增宽, 主要是胆红素的一侧双吡咯生色团与胆汁酸盐呈疏水性结合的原故; 二羟基和三羟基胆汁酸盐所形成的二元复合物园二色谱的差别, 是胆红素的对映选择性结合造成的。     

不同价态金属离子对DNA构象的影响

用紫外分光光度法研究了不同价态金属离子对DNA大分子溶液构象的影响。研究结果显示: 金属离子与DNA的作用使DNA溶液的紫外吸收值下降, 即呈现减色效应, 同时减色效应的强弱与金属离子的价态有关。随着价态升高, 减色效应增强。由此说明, 金属离子与DNA的作用使DNA的构象趋于缩拢; 且随着金属离子价态升高, 缩拢程度增强, 甚至产生缩合。还用现代多聚电解质理论对以上现象进行了讨论, 结果是令人满意的。     

二维蛋白质模型分子在折叠过程中的构象研究

蛋白质在折叠过程中其构象要发生明显变化 .采用精确计数法 ,计算了在蛋白质折叠的不同阶段其尺寸大小及其分布情况 .发现在折叠的初期 ,分子的尺寸比较大 ,其分布也比较宽 .在折叠的后期 ,分子的尺寸比较小 ,其分布比较窄 .不同的氨基酸序列 ,其分子尺寸的分布也不同 .对于可折叠的氨基酸序列 ,在平均尺寸大小附近出现的几率特别大 .同时还计算了比值SN DN.这里SN 为可设计序列数目 (Thenumberofdesigningsequences) ,DN 为可设计构象数目 (Thenumberofdesignableconformations) ,并有关系- 1 6 8 4 +0 32 5 5N≤SN DN ≤- 0 86 6 4 +0 312 5N　 (N ≥ 13)通过这些研究以提高对折叠过程的认识     

分子链构象变化对高分子液晶相行为的影响

聚肽高分子溶解在含有机酸的有机溶剂中可以在室温条件下形成液晶．随着温度的下降,体系中的酸分子会引起聚肽分子链发生由刚性螺旋结构向柔性无规线团结构的构象转变．这种转变将导致一个由液晶态向非液晶态的相变．在Ｆｌｏｒｙ格子理论和Ｚｉｍｍ Ｂｒａｇｇ理论的基础上,作者已提出了有关这一现象的理论解释,并通过引入一个与温度有关的库恩链长径比ｘｋ,使理论进一步完善,更切实际地解释聚肽液晶的相行为．此外,还讨论了不同分子刚柔性,不同高分子 溶剂作用系数χ对液晶相行为的影响,以及研究了聚肽液晶的有序参数．     

STUDIES ON LYSOZYME: EFFECT OF VISIBLE LIGHT ON THE CONFORMATION OF THE ENZYME IN THE PRESENCE OF METHYLENE BLUE

Abstract— Lysozyme undergoes conformational changes when exposed to visible light in the presence of methylene blue. Ultracentrifugation, gel filtration and end group analysis showed that no peptide bond was cleaved. About 30 per cent of the tryptophan residues were, however, modified. The enzymic activity decreased by 50 per cent. The sedimentation coefficient and helical content decreased; the extinction in the u.v. region between 185 to 210 nm increased. The photooxidized enzyme was more susceptible to trypsinolysis than the native enzyme.     

INVESTIGATION ON THE CONFORMATION OF THE MAIN-CHAIN NEMATIC POLYMER BY SMALL ANGLE X-RAY SCATTERING

The experimental investigation on the conformation of a thermotropic main-chain nematic polymer by small-angle X-ray scattering (SAXS) has been carried out. The average radius of gyration of the polymer has been determined in nematic and isotropic state respectively. The experiment shows that the boundary between domains is not sharp but diffuse, and the diffuse-boundary thickness of the polymer as a function of temperature has been given.     

晶区分子链构象及拉伸取向对聚酰胺-6分子运动的影响

用声频共振法在-150°—170℃范围内测定了晶区构象为α、γ、γ+α型以及经不同拉体程度的聚酰胺-6单纤维的动态力学性质的温度谱。除三个已知的内耗峯—— -110℃(β_a),-40℃(β’_a),50℃(α_a)以外,对晶区为γ构象且含有单体及低聚体的聚酰胶-6观察到一个新的内耗峯,130℃(α’_a)。具有α构象的试样,其α_a内耗峯出现的温度较具有γ构象的试样为高。 经碘处理而未脱碘的聚酰胺-6,(β’_a)内耗峯高度显著增加,进一步证实β’_a内耗峯与自由酰胺基的运动有关。β’_a内耗峯的高度亦随拉伸比的增加而增高,说明在拉伸过程中,酰胺基之间的氢键有破坏的可能性。 出现在130℃处的α’_c内耗峯随拉伸比的增加其高度显著地下降,当拉伸到3.8倍时不再出现α’_c内耗峯。结合晶区分子链构象及碘处理对α’_c内耗峯的影响,我们认力α’_c内耗峯应为γ构象部分的松弛运动。     

ENHANCEMENT OF THE SALT EFFECT ON THE CONFORMATION OF M. L. DNA MOLECULES BY METHYLATION

Methylated Micrococcus luteus DNA (M. L. DNA) in which the DNA methylation level was 2.39% was prepared by using Hhal DNA methylase. (The natural M. L. DNA is completely unmethylated.) The [θ]_(275) value of M. L. DNA was decreased and the —[θ]_(220-250) value was increased with increasing concentration of MgC1_2. The UV spectra of M. L. DNA at different concentration of MgCl_2 showed that a hypochromisity happens at 260nm with increasing concentration of MgC1_2. The heat-releasing of M. L. DNA also increased with increasing concentration of MgC1_2. A11 these results showed that the M. L. DNA molecules tend to shrink in space, The difference between methylated DNA and unmethylated DNA was compared. The sensitivity of methylated DNA to MgC1_2 is 40—70 fold higher than that of the unmethylated M. L. DNA.     

STRUCTURE AND CONFORMATION OF PHOTOSYNTHETIC PIGMENTS AND RELATED COMPOUNDS 7. ON THE CONFORMATION OF THE METHYL ESTER OF (20-METHYLPHYTOCHLORINATO)NICKEL(II)-A BAaERIOCHLOROPHYLL c MODEL COMPOUND

Abstract The crystal and molecular structure of the title compound 4 have been determined by single crystal X-ray crystallography. The structure shows the typical S,-ruffled conformation observed for Ni(II) tetrapyrroles. Compared to the structure of the methyl ester of (13²-demethoxycarbonyl-pheophorbidato a)nickel(II), 4 shows a smaller C_a-C_m-C_m angle and a higher degree of conformational distortion at the methyl-substituted C20 position. This local distortion of the macrocycle might account for the bathochromic shifted absorption spectra of the bacteriochlorophylls c compared to the d-series. Crystal data: C₃₅H₃₈N₄NiO₃; tetragonal, P4₃2₁2, a = 15.335(7) Å, c = 25.11(2) Å, V = 5904, Z = 8, λ(Mo Kα) = 0.71069 Å, μ= 0.701 mm⁻¹, P(000) = 2624, 130 K, R = 0.058 for 5700 reflections with F > 4.0σ(F).     

THE CONFORMATION OF THIOPHENOL IN SOLUTION DETERMINED BY LIQUID CRYSTAL NMR SPECTROSCOPY

Abstract

It has been possible to obtain the proton NMR spectrum of thiophenol and 4-chlorothiophenol dissolved in the nematic phase of a liquid crystalline solvent. The computer iterated spectral analysis allowed the authors to determine the direct dipolar couplings that depend solely on the ratio of the interprotonic distances.¹     

氧鎓盐分子在受限制体系中的电荷转移和发光行为

2,4,6-三芳基氧盐是一类类似于三苯甲烷染料的化合物^[1].其结构中存在两种跃迁矩,分别对应于分子的X-轴方向(2,6-位取代基)和Y-轴方向(4-位取代基).因此,2,4,6-三芳基氧盐的吸收光谱中存在着两个较具特征的吸收峰^[2].