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用X射线晶体学方法测定了含有保护基的三肽(Z-Pro-Ala-Thr(But)_2)的晶体结构和分子构象.其结晶属正交晶系,空间群为P2_12_12_1,晶胞参数a=29.557A,b=11.583A,c=8.830A,z=4.用PW-1100四圆衍射仪收集衍射强度数据,用直接法解结构,使用MULTAN-80计算机程序系统.用块矩阵最小二乘方法修正结构,最终的R=0.088(不包括氢原子). 分子中丙氨酸的构象趋近屏蔽式,形成肽链的转折.脯氨酸与保护基之间形成的“肽键“是顺式结构.脯氨酸侧链的吡咯烷环五个原子不在一个平面上,C~β和C~γ分别向相反方向偏离平面.相邻的肽基团平面之间的交角都接近90°.分子之间存在氢键,它使分子沿晶体z方向无限伸展形成分子链.晶体沿x和y方向的分子间作用力为范氏力.保护基(Z)在分子堆积中起重要作用。 相似文献
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镧系元素具有形成高配位数的特点,但由简单配位形成的多面体,最高配位数只能达到九,例如,[Ln(H_2O)_9]~(+[2])。有些从化学式来看符合九配位的化合物,如LnCl_3(H_2O)_6实际结构是八配位[LnCl_2(H_2O)_6]~(+[3])或六配位[LnCl_3(H_2O)_3]·3H_2O~[4])。这种情况促使我们对另一系列化合物LnCl_3(urea)_6~[5]产生兴趣。我们根据堆积模型推测LaCl_3(urea)_6的实际结构应当是[LaCl_2(urea)_6]~+Cl~-(见图1、2)。培养了这一化合物的单晶,进行了结构测定。本文报道有关结果。 相似文献
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棕色固氮菌中细菌铁蛋白的初步X射线晶体学研究 总被引:1,自引:0,他引:1
从棕色固氮菌中分离出的细菌铁蛋白-细胞色素b-(557),是一种较特殊的蛋白质,除与其他类型铁蛋白类似,含有一个铁核外,还含有血红素辅基.文中还用亲合层析方法纯化细菌铁蛋白,在含有MgCl_2的溶液中可获得砖红色立方晶体.用微量透析方法,晶体最大的尺寸可达0.4 ×0.4×0.1mm~3.晶体表现为光学的各向同性.进行初步的X射线晶体学研究,拍摄未加层线屏的小角徘循照片,可初步确定其空间群为立方晶系的1432,晶胞参数为230A.文中还讨论了细菌铁蛋白立方晶胞中可能含有8个分子,并推导出其分子量为8.26×10~5,分子的直径为115A,分子具有32对称性。 相似文献
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The rhombohedral crystal structure of [Trp]~(B1)-insulin has been refined, using data to 2 and atomic coordinates of 2-zinc porcine insulin as starting model, and through the use of the restrained least-squares method, to an R value of 0.24. The result of refinement shows that in comparison with the 2-zinc insulin structure, some changes in local conformation occur, and are asymmetric for the two independent molecules related by a local two-fold axis. The obvious conformational changes are found to be in molecule 1, at its B-chain N-terminus and A13-residue region. 相似文献
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The three forms of glyceraldehyde-3-phosphate dehydrogenase from Palinurus versicolor muscle, namelyapo native enzyme, apo calboxymethylated enzyme and the enzyme carrying two fluorescent NAD deriva-tives per tetramer have been crystallized. The space groups and unit cell dimensions of these crystals areisomorphous to each other and to those of three corresponding holo-enzymes saturated with NAD~+ reportedin a previous paper suggesting that binding of coenzyme to the apo enzymes does not lead to significantconformational changes involving domain movement as demonstrated in the case of glyceraldehyde-3-phos-phate dehydrogenase from Bacillus stearothermophilus. 相似文献
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The crystal structure and molecular conformation of the synthetic oligopeptide (Z-Pro-Ala-Thr (But)_2) have been determined by X-ray analysis. The crystal is orthorhombic, spacegroup P2_12_12_1, with four molecules per unit cell of dimensions: a = 29.557, b = 11.583 andc = 8.830A. The diffraction data were collected using a PW-1100 four-circle diffractometer.The strueture was solved by direct methods, using the MULTAN-80 system of computerprograms and refined by the block-diagonal least-squares method. 7he final R value is 0.088(for non-hydrogen atoms). The Ala residue in this peptide is nearly in an eclipsed conformation. The peptide bondbetween Z and Pro is cis. The two atoms, C~β aud C~γ, are displaced on opposite sides of thepyrrolidine ring plane. The dihedral augles between the neighbouring peptide or carboxylgroups are all close to 90°. Hydrogen bonds link the peptides forming a chain in the zdireetion. The stacking of the peptides in the x and y directions is the result of the van derWaals fo 相似文献
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Rh(acac)(CO)_2是烯烃氢甲酰化、氢硅化及一氧化碳加氢反应重要催化剂.晶体具有红绿二色性·在4000至80cm~(-1)范围测定了其红外和拉曼光谱;采用简化的一般价力场(SGVFF),对观测谱带进行了简正坐标分析。1 实验方法Rh(acac)(C0)_2按文献方法合成,并重结晶。红外光谱:用CsI压片在P-E 983G红外光谱仪上测试了4000~180cm~(-1)范围内的光谱,分辨率2cm~(-1).550~80 cm~(-1)波段在Digilab FTS-20E/D-V真空型傅氏光谱仪上得到。 相似文献