Amphipilic and mesogenic carbohydrates XII. New thermotropic mesogens based on perfluoroalkyl-substituted carbohydrates

In continuing studies of amphiphilic and mesogenic carbohydrates, the mesomorphic properties of a new group of perfluoroalkylated amphiphilic mesogens are discussed. Smectic A phases dominate the mesomorphic behaviour of the new materials, but one compound exhibits a columnar mesophase and three others have SmA-SmC* transitions. The synthesis of these materials has already been reported and involved dithionite-mediated O- and S-perfluoroalkylations with 1-iodoperfluoroalkanes.     

Poly­sulfonyl­amines. CLXXI. [Di­(methane­sulfonyl)­amido‐κN]­bis(2‐picoline‐κN)copper(I)

The title compound, [Cu(C₂H₆NO₄S₂)(C₆H₇N)₂], consists of monomeric mol­ecules in which the Cu atom displays planar but irregular coordination by three N‐atom donors; Cu—N = 2.1054 (12) (amide N), 1.9514 (12) and 1.9589 (12) Å, and N—Cu—N = 141.24 (5), 111.54 (5) and 107.20 (5)°. Intramolecular Cu⋯O contacts are observed. The packing involves (interconnected) layer formation via C—H⋯O interactions in two directions, three hydrogen bonds combining to form layers parallel to (101) and five to form layers parallel to (10).     

Microbial and Enzymatic Synthesis of Optically Pure D- and L-3-Trimethylsilyl-alanine by Deracemization of D,L-5-Trimethylsilyl-methyl-hydantion

Summary.  The sterospecificities of hydantoinases and N-carbamoyl amino acid amidohydrolases (N-carbamoylases) from different microbial sources were investigated for the stereoselective syntheses of the unnatural silicon-containing amino acids D- and L-3-trimethylsilyl-alanine (3) from the respective racemic hydantoin D,L-1. In a preparative biotransformation, whole resting cells of Agrobacterium sp. IP I 671, immobilized in a Ca-alginate matrix, were used for the synthesis of amino acid D-3 in 88% yield and 95% enantiomeric excess. Since the purified D-N-carbamoylase from Agrobacterium sp. IP I 671 was shown to be 100%D-selective, the enantiomeric purity of 95% of D-3 arising from the transformation with the immobilized cells must be explained by the participation of a further, L-selective N-carbamoylase or, which is more likely, by racemization of the final hydrolysis product by the action of an amino acid racemase. Isolated hydantoinases from Bacillus thermoglucosidasius, Thermus sp., Arthrobacter aurescens DSM 3745, and Arthrobacter crystallopoietes DSM 20117 turned out to be stereospecific for the conversion of the D-form of hydantoin D,L-1. The enantiomerically pure L-form of 3 was also prepared. It was synthesized from racemic N-carbamoyl amino acid D,L-2 by enantiomer-specific hydrolysis of the L-form in presence of L-N-carbamoylase from Arthrobacter aurescens DSM 3747. Received December 20, 1999. Accepted January 7, 2000     

Suprema of chains of operators

Let E{{\mathcal E}} be a real Banach space of operators ordered by a cone K{{\mathcal K}}. We give a sufficient condition for that each chain which is bounded above has a supremum. This condition is satisfied in several classical cases, as for the Loewner ordering on the space of all symmetric operators on a Hilbert space, for example.