Transition-metal saccharide chemistry: synthesis and characterization of d-glucose, d-fructose, d-galactose, d-xylose, d-ribose, and maltose complexes of Co(II)

Mechanism of the transition-metal-catalyzed mutarotation reaction of N-(p-chlorophenyl)-beta-D-glucopyranosylamine in methanol

Rate constants for the mutarotation reaction of N-(p-chlorophenyl)-beta-D-glucopyranosylamine (NGlc) in methanol have been determined in the presence of transition metal chlorides (MCl(2)), at 25 degrees C. The activity of the metal ions catalyzing the alpha-pyranoside<-->beta-pyranoside interconversion has been found to increase in the following series: Mn(2+)<Co(2+)<Ni(2+)<Zn(2+)<Cu(2+). The pHs of the methanolic solutions of the chlorides were measured and acidity constants of the [MCl(CH(3)OH)(5)](+) ions and NGlc were determined in this solvent. Addition of NGlc to the salt solutions resulted in lowering their pH. Raising the methyloxonium ion concentration in the solutions resulted in rapid increase in the rate of mutarotation in the presence of MCl(2). It is suggested that in solutions of NGlc and MCl(2), the CH(3)OH(2)(+) ions are generated by solvolysis of the salts and additionally by dissociation of the hydroxyl group at C-6 of the glucosylamine molecule taking place during complexation of the metal ions. A scheme has been derived for interaction of deprotonated NGlc molecules with the transition metal ions.

Structural characterization of hexoses and pentoses using lead cationization. An electrospray ionization and tandem mass spectrometric study

The analytical potential of the complexation of isomeric underivatized hexoses (D-glucose, D-galactose, D-mannose, D-talose, D-fructose), methylglycosides (1-O-methyl-alpha-D-glucose and 1-O-methyl-beta-D-glucose) and pentoses (D-ribose, D-xylose, D-arabinose and D-lyxose) by Pb(2+) ions, was investigated by electrospray ionization and tandem mass spectrometry (MS/MS). Pb(2+) ions react mainly with monosaccharides by proton abstraction to generate [Pb(monosaccharide)(m) - H](+) ions (m = 1-3). At low cone voltage, a less abundant series of doubly charged ions of general formula [Pb(monosaccharide)(n)](2+) is also observed. The maximum number n of monosaccharides surrounding a single Pb(2+) ion depends on the metal : monosaccharide ratio. Our study shows that MS/MS experiments have to be performed to differentiate Pb(2+)-coordinated monosaccharides. Upon collision, [Pb(monosaccharide) - H](+) species mainly dissociate according to cross-ring cleavages, leading to the elimination of C(n)H(2n)O(n) neutrals. The various fragmentation processes observed allow the C(1), C(2) and C(4) stereocenters of aldohexoses to be characterized, and also a clear distinction aldoses and fructose. Furthermore, careful analysis of tandem mass spectra also leads to successful aldopentose distinction. Lead cationization combined with MS/MS therefore appears particularly useful to identify underivatized monosaccharides.

Sugar interaction with metal ions. FT-IR study on the structure of crystalline galactaric acid and its K+, NH4+, Ca2+, Ba2+, and La3+ complexes

The FT-IR spectra of galactaric acid and its K+, NH4+, Ca2+, Ba2+, and La3+ salts have been recorded and interpreted. Spectroscopic evidence shows that the dimeric carboxylic groups of the free acid are dissociated upon formation of the salt, and the asymmetric and symmetric stretching vibrations of the anionic COO- group in these salts are observed at about 1600 and 1400 cm-1, respectively. The two carboxylic groups of the galactarate coordinate with Ca2+ ions in a monodentate form. One of the carboxylic groups in the Ba2+ salt coordinates in a monodentate state; another group interacts with three cations in a tetradentate form. In the K+, NH4+, and La3+ salts, the COO- groups coordinate in a polydentate manner with the cations. By comparison of the spectra of the salts with that of the free acid, it is concluded that the hydroxyl groups of the galactarate skeleton take part in metal-oxygen interaction, and the hydrogen-bonding network is rearranged upon sugar metalation. The degree of participation of the sugar OH groups in metal-galactarate interaction is varied from the K+ and NH4+ salts to the Ca2+, Ba2+, and La3+ salts.

Transition-metal saccharide chemistry and biology: saccharide complexes of Cu(II) and their effect on in vivo metallothionein synthesis in mice

Monosaccharide (D-Glc, D-Fru, D-Gal, D-Xyl, D-Rib) and disaccharide (Mal) complexes of Cu(II) were synthesized from two different precursors, viz. [NEt4]2 [CuCl2Br2] and CuCl2.2H2O, in nonaqueous media, and isolated in the solid state. The complexes were found to be primarily dimeric and trimeric and water soluble. These were characterized by diffuse reflectance, aqueous solution absorption, CD, FTIR, magnetic susceptibility, EPR, EXAFS, XANES, and elemental analysis. Aqueous solution stability in the pH range 4-8 was studied by cyclic voltammetry and absorption spectroscopy. The effect of subcutaneously injected Cu-Fru, Cu-Xyl, and Cu-Rib complexes on the in vivo metallothionein synthesis in mice was found to be significant in liver, but not in brain, in accordance with the observed copper accumulation in these tissues.