Cyclohexane conformation

About: Cyclohexane conformation is a research topic. Over the lifetime, 2267 publications have been published within this topic receiving 12325 citations.

The structure of the saccharide-binding site of concanavalin A.

Abstract: A complex of concanavalin A with methyl alpha-D-mannopyranoside has been crystallized in space group P212121 with a = 123.9 A, b = 129.1 A and c = 67.5 A. X-ray diffraction intensities to 2.9 A resolution have been collected on a Xentronics/Nicolet area detector. The structure has been solved by molecular replacement where the starting model was based on refined coordinates of an I222 crystal of saccharide-free concanavalin A. The structure of the saccharide complex was refined by restrained least-squares methods to an R-factor value of 0.19. In this crystal form, the asymmetric unit contains four protein subunits, to each of which a molecule of mannoside is bound in a shallow crevice near the surface of the protein. The methyl alpha-D-mannopyranoside molecule is bound in the C1 chair conformation 8.7 A from the calcium-binding site and 12.8 A from the transition metal-binding site. A network of seven hydrogen bonds connects oxygen atoms O-3, O-4, O-5 and O-6 of the mannoside to residues Asn14, Leu99, Tyr100, Asp208 and Arg228. O-2 and O-1 of the mannoside extend into the solvent. O-2 is hydrogen-bonded through a water molecule to an adjacent asymmetric unit. O-1 is not involved in any hydrogen bond and there is no fixed position for its methyl substituent.

Structural components of alginic acid. II. The crystalline structure of poly-alpha-L-guluronic acid. Results of x-ray diffraction and polarized infrared studies.

Abstract: A structural investigation of the marine algal polysaccharide poly-α-L-guluronic acid is described. The molecular chains consist of 1 4 diaxially linked L-guluronic acid residues in the 1C chair conformation and are stabilized in a twofold helix conformation by an intra-molecular O(2)H … O(6)D hydrogen-bond. The X-ray fiber diffraction photograph has been indexed to an orthorhombic unit cell in which a = 8.6 A, b (fiber axis) = 8.7 A, c = 10.7 A. A structure corresponding to the space group P212121 is proposed, in which all intermolecular hydrogen bonds interact with water molecules and in which all oxygen atoms except for the inaccessible bridge oxygens are involed. The relationship between the shape and structure of the polyguluronic acid molecule and its biological function is discussed.

Dimeric aluminum-phosphorus compounds as masked frustrated Lewis pairs for small molecule activation.

Abstract: Hydroalumination of aryldialkynylphosphines RP(CC–tBu)2 (R = Ph, Mes) with equimolar quantities of diethylaluminum hydride afforded mixed alkenyl–alkynyl cyclic dimers in which the dative aluminum–phosphorus bonds are geminal to the exocyclic alkenyl groups. Addition of triethylaluminum to isolated 1 (R = Ph) or to the in situ generated species (R = Mes) caused diethylaluminum ethynide elimination to yield the arylethylphosphorus dimers 2 and 3. These possess a chair-like Al2C2P2 heterocycle with intermolecular Al–P interactions. The boat conformation (4) was obtained by the reaction of tBu–P(CC–tBu)2 with di(tert-butyl)aluminum hydride. Despite being dimeric, 2 behaves as a frustrated Lewis pair and activates small molecules. The reaction with carbon dioxide gave cis/trans isomeric AlPC2O heterocycles that differ only by the configuration of the exocyclic alkenyl unit. Four isomers resulted from the reaction with phenyl isocyanate. This is caused by cis/trans isomerization of the initial CO adduct and subsequent rearrangement to the AlPC2N heterocycle, being the CN adduct.