新马兜铃内酯的晶体结构

从绵毛马兜铃的根茎中分离出一种新的倍半萜内酯, 它的分子式由高分辨质谱数据确定为C~1~5H~2~0O~2, 它的结构用单晶X射线衍射法测定, 晶体属三斜晶系, 空间群为P1, a=0.6275(3)nm, b=0.8057(4)nm, c=1.3622(6)nm; α=88.78(4)°,β=91.44(4)°, γ=105.20(4)°; Z=2.3107。     

异雷公藤内酯四醇的晶体结构

在Rigakui AFC5R四圆衍射仪上测定了异雷藤内酯四醇的晶体结构.晶体属单斜晶系的空间群P2~1,晶胞参数为:a=1.021(1),b=1,126(1),c=1.8209(9)nm,β=98.84(5)°V~c=2.09(3)nm^3,Z=4.表2     

The crystal structure of polyacrylonitrile

Polyacrylonitrile (PAN) has been prepared by a free-radical mechanism using azobisisobutyronitrile as the initiator. Fibres were produced by extruding a solution of this polymer into dilute sodium thiocyanate. Wide-angle X-ray analysis showed that the resulting fibres exhibited a moderate degree of crystalline order. An orthorhombic unit-cell has been proposed to account for the observed reflections, the cell constants are: $\text{a = 21·48 ± 0·02}\text{A}\text{?}\text{; b = 11·55 ± 0·03}\text{A}\text{?}\text{; c = 7·096 ± 0·003}\text{A}\text{?}$. A helical structure has been proposed for PAN with four monomer units per crystallographic repeat. The probability of a syndiotactic configuration has been suggested to account for the meridional reflections; the calculated density of the proposed cell (1·199 g cm^?3) was found to agree very well with values quoted in the literature.     

The crystal structure of L-arginine

We report the crystal structure of L-arginine, one of the last remaining natural amino acids for which the crystal structure has never been determined; structure determination was carried out directly from powder X-ray diffraction (XRD) data, exploiting the direct-space genetic algorithm technique for structure solution followed by Rietveld refinement.     

The crystal structure of hcc-CuAsSe

The crystal structure of synthetic copper arsenic selenide CuAsSe, has been determined by a three-dimensional single-crystal X-ray examination using film data. The crystals, of orthorhombic space group Pbcn, have Z = 24 in a unit cell of dimensions a = 11.75 ± 0.02, b = 6.79 ± 0.01, and c = 19.21 ± 0.03 Å. The structure was solved by Patterson projection and electron density methods and isotropically refined to R = 0.125 for 300 observed reflections. The structure of CuAsSe is related to the B6 structure of 6H ZnS as CuAsS is to the B3 structure of zincblende. Alternately in Jagodzinski nomenclature CuAsSe has hcc packing rather than ccc packing of CuAsS.     

The crystal structure of nonactin

An X-ray crystal structure investigation of the macrotetrolide antibiotic nonactin is reported. The shape of the molecule is discussed with special reference to the conformational changes involved in passing from free nonactin to the K⁺-complex.     

雷公藤内脂四醇的晶体结构

雷公藤系卫矛科植物( Tripterygium wlfordii Hook. f) , 1972) 年,Kupechan从分得三种环二萜内酯类化合物,显示出较强的抗白血压病活性。为了寻找低毒有效的类似物,本文从雷公藤根皮乙醇提取物的氯仿溶出部分,反复经硅胶柱层析分理,得到一种新的环氧二萜酯;雷共藤内酯四醇(Tripletraolide)。在乙酸乙酯重结晶,得无色长极状晶体,m.p.258~260℃。经高分辩质谱确定其分子为C~0H~26O~8,M~r=394.2。     

The crystal structure of triphenylallyltin

The crystal structure of (C₆H₅)₃SnCH₂CHCH₂ has been determined. The asymmetric unit consists of two molecules of triphenylallyltin having virtually the same conformation. Their geometrical parameters exclude p_π-d_π bonding between the metal and the allyl double bond, and seem to be in a better agreement with a σ-π conjugation effect.