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In the following research acetylation as an unexplored factor in the anomeric effect in carbohydrate chemistry has been examined. Crystallographic data for methyl glycosides and their acetates have been compared and discussed. Some of the methyl glycosides form hydrogen bonding with the participation of acetal oxygen atoms. This seems to have the most significant influence on the structural diagnostic parameters for anomeric effect. Abbreviations: Me-α-Glc: methyl α-D-glucopyranoside; Me-β-Glc: methyl β-D-glucopyranoside; Me-α-Gal: methyl α-D-galactopyranoside; Me-β-Gal: methyl β-D-galactopyranoside; Me-α-Man: methyl α-D-mannopyranoside; Me-β-Man: methyl β-D-mannopyranoside; Ac-Me-α-Glc: methyl 2,3,4,6-tetra-O-acetyl-α-D-glucopyranoside; Ac-Me-β-Glc: methyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside; Ac-Me-α-Gal: methyl 2,3,4,6-tetra-O-acetyl-α-D-galactopyranoside; Ac-Me-β-Gal: methyl 2,3,4,6-tetra-O-acetyl-β-D-galactopyranoside; Ac-Me-α-Man: methyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranoside; Ac-Me-β-Man: methyl 2,3,4,6-tetra-O-acetyl-β-D-mannopyranoside; GIPAW (Gauge Including Projector Augmented Waves) calculations: a DFT based method used for calculating nuclear magnetic resonance parameters; CP/MAS NMR: cross-polarisation (CP) magic angle spinning (MAS) NMR spectroscopy; δss: chemical shift in 13C CP/MAS NMR spectrum; δt: theoretical chemical shift: as derived from GIPAW DFT; dis: distorted multiplet in 1H NMR spectrum. [ABSTRACT FROM AUTHOR]

Abstract: Single-crystal and powder X-ray diffraction, 13C CP/MAS NMR, and DFT-GIAO calculations of shielding constants were performed for methyl 3,4,6-tri-O-acetyl-2-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-glucopyranoside (1) and methyl 2,4,6-tri-O-acetyl-3-O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-α-d-glucopyranoside (2). 1 crystallizes with three molecules whereas 2 with two molecules in an independent part of the unit cell. The macroscopic sample of 1 consists of one polymorph, while for 2 two or three polymorphs were detected. The existence of different numbers of the molecules in the asymmetric units as well as different numbers of polymorphs of 1 and 2 was verified by solid-state NMR spectroscopy. [Copyright &y& Elsevier]

Abstract: The X-ray diffraction patterns, 13C CP MAS NMR spectra, and powder X-ray diffraction analyses were obtained for selected p-nitrophenyl glycosides: α- and β-d-galactopyranosides (1 and 2), α- and β-d-glucopyranosides (3 and 4), and α- and β-d-mannopyranosides (5 and 6). In X-ray diffraction analysis of 1 and 2, characteristic shortening and lengthening of selected bonds were observed in the molecules of 1 due to anomeric effect, and in the crystal lattice of 1 and 2, hydrogen bonds of complex network were detected. In the crystal asymmetric unit of 1 there were two independent molecules, whereas in 2 there was one molecule. For 1 and 3–6 the number of resonances in solid-state 13C NMR spectra exceeded the number of the carbon atoms in the molecules, while for 2 there were distinct singlet resonances in its solid-state NMR spectrum. Furthermore, the powder X-ray diffraction (PXRD) performed for 1–3 and 5 revealed that 1, 3, and 5 existed as single polymorphs proving that the doublets observed in appropriate solid-state NMR spectra were connected with two non-equivalent molecules in the crystal asymmetric unit. On the other hand 2 existed as a mixture of two polymorphs, one of them was almost in agreement with the calculated pattern obtained from XRD (the difference in volumes of the unit cells), and the subsequent unknown polymorph existed in small amounts and therefore it was not observed in solid-state NMR measurements. [Copyright &y& Elsevier]

Abstract: The X-ray diffraction analysis, 13C CP MAS NMR spectra and powder X-ray diffraction patterns were obtained for selected methyl glycosides: α- and β-d-lyxopyranosides (1, 2), α- and β-l-arabinopyranosides (3, 4), α- and β-d-xylopyranosides (5, 6) and β-d-ribopyranoside (7) and the results were confirmed by GIAO DFT calculations of shielding constants. In X-ray diffraction analysis of 1 and 2, a characteristic shortening and lengthening of selected bonds was observed in molecules of 1 due to anomeric effect and, in crystal lattice of 1 and 2, hydrogen bonds of different patterns were present. Also, an additional intramolecular hydrogen bond with the participation of ring oxygen atom was observed in 1. The observed differences in chemical shifts between solid state and solution come from conformational effects and formation of various intermolecular hydrogen bonds. The changes in chemical shifts originating from intermolecular hydrogen bonds were smaller in magnitude than conformational effects. Furthermore, the powder X-ray diffraction (PXRD) performed for 4, 5 and 7 revealed that 7 existed as a mixture of two polymorphs, and one of them probably consisted of two non-equivalent molecules. [Copyright &y& Elsevier]

A series of nitrophenyl β-cyclodextrin derivatives: mono[6-deoxy-6-(4-nitrobenzamido)]-per- O-methyl-β-cyclodextrin (R1&bond;Ph&bond;NO2), mono[6-deoxy-6-(3-nitrobenzamido)]-per-O-methyl-β-cyclodextrin (R2&bond;Ph&bond;NO2) and heptakis[6-deoxy-6-(4-nitrobenzamido)-2,3-di-O-methyl]-β-cyclodextrin [R3&bond;(Ph&bond;NO2)7] were synthesized. Purity and composition of the obtained substances were checked. Electroreduction of nitro groups of the new synthesized compounds was investigated on mercury electrode using cyclic voltammetry and chronocoulometry. The parameters of the reduction processes of &bond;NO2 groups of the investigated compounds were found not to be comparable to the reduction of nitrobenzene under the same experimental conditions. Moreover, the electroreduction of nitro groups in these nitrophenyl derivatives was dependent on pH, the type of the studied compound, and slightly on the solvent composition. All the reactants were strongly adsorbed on mercury electrode. In the case of R3&bond;(Ph&bond;NO2)7, its seven nitro groups were reduced practically at the same potential, and no radical anion formation was observed. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]