Acyclic tautomers in crystalline carbohydrates: the keto forms of 1-deoxy-1-carboxymethylamino-D-2-pentuloses (pentulose-glycines)

NMR and X-ray diffraction studies on acyclic carbohydrate keto tautomers of N-(1-deoxy-d-erythro-2-pentulos-1-yl)- and N-(1-deoxy-d-threo-2-pentulos-1-yl)glycines (ribulose-glycine, 1 and xylulose-glycine, 2), are reported. In aqueous solutions, both 1 and 2 exist as a tautomeric mixture, with the beta-furanose as a major form, followed by the alpha-furanose and the acyclic keto tautomer. Both 1 and 2 crystallize as zwitterions in the acyclic keto form. Solid-state 13C NMR spectra reveal the existence of two crystallographically independent molecules in 2 but only one in crystalline 1. The structure of 2 was solved by X-ray diffraction; in the crystal, two conformational isomers, 2a and 2b in a 1:1 ratio, were identified. The conformers are packed in stacks of similar molecules, with a system of intermolecular hydrogen bonds involving all hydroxyl, ammonium, and carboxyl groups. The structural data indicate that the sugar portion of acyclic 2 adopts conformations similar to those proposed for the parent d-xylulose.     

Coordination polymer chains of dimeric pyrogallol[4]arene capsules

Copper seamed dimeric metal-organic pyrogallol[4]arene capsules have been synthesized and engineered into coordination polymer chains, either by direct coordination or with additional bridging ligands. The formation of this copper capsule also demonstrates selective formation of either hexameric or dimeric metal-organic capsules.     

Structure of D-Fructosamine Hydrochloride and D-Fructosamine Hydroacetate

D-Fructosamine derivatives are key intermediates of the early Maillard reaction and have been a subject of numerous studies in food and health sciences due to their implication in the nutritional and organoleptic quality of foods, as well as to complications in diabetes and renal disease. We report the crystal structure analyses of 1-deoxy-β -D-fructopyranos-1-ylamine hydrochloride (1) and -hydroacetate (2) salts. The carbohydrate rings adopt the normal ²C₅ pyranose chair conformation in 1 and 2. Bond lengths and valence angles in 1 and 2 compare well with the average values from related pyranose structures. There are two conformationally nonequivalent molecules in the asymmetric unit in 1. All hydroxyl and ring oxygen atoms, ammonium groups, and chloride ions in 1 are involved in an extensive three-dimensional hydrogen bonding network. The hydrogen bonding network in 2 is formed by one type of infinite chain with attached antidromic cycles.     

Solution-Phase and Magnetic Approach towards Understanding Iron Gall Ink-like Nanoassemblies

Metal-containing tubes: The structures of several iron-containing C-methylpyrogallol[4]arene (PgC(1) ) nanoassemblies were studied in both the solid and solution phases. The nanoassemblies have a tubular architecture with the iron as part of the framework (see picture; gray C, red O, turquoise/blue Fe), and magnetic analysis suggests a canted or spiral arrangement of the iron centers.