Claude Gey

Substituent distribution on O, N-carboxymethylchitosans by 1H and 13C n.m.r.

The use of the n.m.r. method in the investigation of chitosan carboxymethylation was evaluated. It seems to be the most effective technique to determine concurrently the degree and the position of substitution of the carboxymethylated chitosan derivatives. The 13C-n.m.r., by the DEPT method, 1H-1H and 1H-13C-n.m.r. correlations give much valuable information from the chemical shifts of the complex carboxymethylchitosan spectra. The relative reactivity of the functional groups of chitosan towards carboxymethylation was also determined assuming a higher reactivity of the C-6 position.

13C and 1H n.m.r. spectroscopy of chitosan and N-trimethyl chloride derivatives

Abstract This paper concerns the chemical structure characterization of chitosan and N-trimethyl chloride derivatives at various degrees of quaternization. The assignment of the different signals obtained by n.m.r. spectroscopy is proposed. The values of degrees of quaternization determined by 13C and 1H n.m.r. are compared with those obtained by potentiometry. Methylation of the -OH groups is demonstrated.

Stereochemical course of the hydrolysis reaction catalyzed by chitinases Al and D from Bacillus circulans WL‐12

Chitinases A1 and D were purified from the periplasmic proteins produced by Escherichia coli HB101 harbouring recombinant plasmids carrying respectively the chiA and chiD genes of Bacillus circulans WL‐12. HPLC analysis indicated that during the hydrolysis of chitotriose, both chitinases initially produce N‐acetylglucosamine and only one anomer of chitobiose. 1H NMR spectroscopy of the hydrolysis of chitotetraitol showed that this anomer corresponds to β‐chitobiose, demonstrating that chitinases Al and D act by a molecular mechanism that retains the anomeric configuration. This mechanism is similar to that of lysozymes although both chitinases belong to a family of proteins sharing no demonstrable amino acid sequence similarity with lysozymes.

Structure of a polysaccharide from a Rhizobium species containing 2-deoxy-β-d-arabino-hexuronic acid

The structure of the extracellular polysaccharide (EPS) produced by the Rhizobium sp. B strain isolated from atypical nodules on alfalfa has been determined using a combination of chemical and physical techniques (methylation analysis, high pH-anion exchange chromatography (HPAEC), mass spectrometry and 1-D and 2-D NMR spectroscopy). As opposed to the EPS from other strains of Rhizobium, the EPS from the sp. B strain contains D-Glc together with L-Rha and 2-deoxy-D-arabino-hexuronic acid. It is a polymer of a repeating unit having the following structure: --> 4)-beta-D-Glcp-(1 --> 4)-alpha-L-Rhap -(1 --> 3)-beta-D-Glcp-(1 --> 4)-2-deoxy-beta-D-GlcpA-(1 -->. The polysaccharide also contains 0.6 O-acetyl groups per sugar which have not been located.

Exopolysaccharide production by the Rhizobium meliloti M5N1 CS strain. Location and quantitation of the sites of O-acetylation

Abstract The mutant strain M5N1 CS of Rhizobium meliloti is able to produce, in a Rhizobium complete medium supplemented with fructose or sucrose (1% w/v), a partially acetylated homopolymer of glucuronic acid. During batch cultivation, the polysaccharide production is observed while the pH of the medium decreases slightly. The nature of the carbon source and the control of pH have no effect on the degree of acetylation of the polymer produced in the flasks. About 40% of glucuronic residues of the polymer are monoacetylated at C-3 or at C-2, C-3 substitution is about twice that of C-2 and remains constant during the fermentation.

Complexes of borate ions with guar D-galacto-D-mannan polymer and related model compounds

Abstract The prevailing borate mono- and di-complexes of a series of glycosides, particularly those representing model compounds (methyl β- d -mannopyranoside and methyl α, d -galactopyranoside) of guar d -galacto- d -mannan in aqueous alkaline solution, have been identified by 11 B-n.m.r. spectroscopy, and the associated formation constants determined. These data provide some new insights into the rheological properties displayed by the polymer in alkaline medium (gelation and hydration-delay phenomenon).

Production of a glucoglucuronan by a rhizobia strain infecting alfalfa. Structure of the repeating unit

The Rhizobium sp. T1 strain. which induces nodule formation on alfalfa and clover roots, produces, during growth, an extracellular polysaccharide composed of D-glucose and D-glucuronic acid noted glucoglucuronan. During the bacterial growth, the pH of the medium decreases slightly. The control of pH in the growth medium slightly reduces the glucoglucuronan production. Under the conditions tested in the present work, the weight-average molecular weight of the polymers produced with or without pH control are similar: Mw approximately 2 x 10(6); the repeating unit determined by chemical and NMR analyses corresponds to the disaccharide: --> 3)-beta-D-GlcpA-(1-->4)-beta-D-Glcp-(1 -->.

Glucosamine oligomers: 2. N.m.r. studies on a DP3.

This paper concerns the characterization of the chemical structure of a DP3 glucosamine oligomer. The assignments of nearly all protons are reported. Variations of 1H chemical shifts with pD and temperature are correlated to the pKa of amino groups, and not with substantial conformational changes.