X-ray and neutron diffraction studies of the crystal and molecular structure of the predominant monocarboxylic acid obtained by mild acid hydrolysis of cyanocobalamin. Part II. X-ray diffraction studies of wet crystals

The crystal and molecular structure of wet crystals of the O-monocarboxylic acid of cyanocobalamin has been determined. The molecule crystallizes in a monoclinic cell ofa = 14.845,b = 17.435,c = 16.243 A, β = 103.54°, space group P2₁,. Intensity data were collected by diffractometry and the structure solved by Patterson and Fourier methods. Refinement, initially by a least-squares process and latterly by Fourier methods, led to anR of 0.140. Disordered sites were found for the terminal atoms of side chaine; the identification of the acid grouping was not made with certainty. Sites for sixteen water molecules were determined.     

Cover Picture: Solid‐State Scrolls from Hierarchical Self‐Assembly of T‐Shaped Rod–Coil Molecules (Angew. Chem. Int. Ed. 9/2009)

Solid scrolls are reversibly formed by self‐assembly of rod‐shaped molecules with laterally attached coil units, in contrast to the layered structures formed from self‐assembly of planar molecules. As described by M. Lee and co‐workers in their Communication on page 1664 ff., the core structure of the scrolls, which are either filled cylinders or hollow tubes, can be controlled by variation of the length of the coil unit. The cover picture shows aligned tubular scrolls displaying well‐defined in‐plane ordering of the rod segments.

     

Regioselective synthesis and metallation of tributylstannylfluoropyrazines. Application to the synthesis of some new fluorinated liquid crystals diazines. Part 34

Starting from fluoropyrazine, a general synthetic route including metallation and palladium-catalyzed cross-coupling reactions is described to access to rod-like alkylaryl or diarylpyrazines. Among them, some have liquid crystalline properties.     

Microhardness studies of chain-extended PE. I. Correlations to microstructure

The hardness–microstructure correlation of various polyethylene (PE) samples crystallized at high pressure from the melt (chain-extended), with different molecular weights, has been investigated and compared to melt crystallized samples at atmospheric pressure (chain-folded). The hardness, H, of melt crystallized PE is confirmed to increase linearly with the logarithm of the annealing time, t_a, at a constant annealing temperature. The H increase with t_a is discussed in terms of the crystallinity and crystalline lamellar thickness variation. Unusually high hardness values are obtained for samples crystallized or annealed at high pressure as a consequence of the resulting high degree of crystallinity and large crystalline lamellar thickness values. However, it is shown that the high surface free energy value of the chain-extended crystals considerably lowers the hardness values from that of an ideal infinitely thick PE crystal. Analysis of the crystal hardness and the melting temperature data of different polymeric materials emphasizes the close existing relationship between both quantities. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3151–3158, 1999     

胆甾液晶／聚合物多组分体系的结构与性质研究

用Ｘ－射线衍射法详细研究了ＣｈＮ／Ｐｏｌｙ（ＭＭＡ－ｃｏ－ＢＭＡ）共混体系在胆甾相，近晶相及结晶态的分子排列，并给出了将液晶的分子排列冻结在体系中的，从而实现信息存储功能的条件。