The role of the anion in the reaction of reducing sugars with ammonium salts

Reactions of reducing sugars with ammonia and its compounds are important commercially, particularly in the preparation of flavors and caramel colors. However, such reactions generally produce a complex series of products ranging from simple molecules to complex polymeric materials, particularly since commercial systems generally involve mixtures of sugars as opposed to single sugars. This complexity has made understanding the mechanisms of such reactions difficult. Therefore, investigatory work has generally been focused on model systems. Herein we report one such study with model systems: the effects of the nature of the anion of the reactions of reducing sugars with ammonium salts. D-Glucose was reacted in aqueous solution with each of the following ammonium salts: acetate, bicarbonate, carbonate, chloride, citrate, formate, monohydrogenphosphate (DAP), sulfate, and sulfite. These reactions were carried out in a Parr bomb at 93 degrees C for 2.5 h. The initial pH of the reaction mixtures was adjusted to pH 8.0 at 25 degrees C. The resulting mixtures were analyzed by LC-MS, and the results were analyzed by comparing the product yields and distributions with those obtained with DAP. The major reaction product of interest was 2,6-deoxyfructosazine, as it had been shown to be a marker for the polymeric material formed from such reactions. It was found that ammonium salts of weak acids were much more effective in effecting the desired reactions than were those of strong acids; however, none was as effective as DAP.     

In vitro and in vivo reactions of nucleic acids with reducing sugars

Reducing sugars such as glucose and glucose 6-phosphate have been shown to nonenzymatically react with the amino groups of proteins. The modification of proteins by reducing sugars can alter both physical characteristics and biological functions. Analogous to the reaction observed with proteins, the amino groups of DNA bases are also able to react nonenzymatically with reducing sugars. The modifications of DNA by reducing sugars result in the time- and sugar-concentration-dependent changes in biological properties. In this communication we review data describing in vitro and in vivo models we have used to investigate the biological consequences of the nonenzymatic glycosylation of DNA.     

The reaction of some dicarbonyl sugars with aminoguanidine.

The reactions of aminoguanidine (guanylhydrazine) with 3-deoxy-D-erythro-hexos-2-ulose (1a), 3-deoxy-D-glycero-pentose-2-ulose (1b), D-erythro-hexos-2-ulose (1c), and D-glycero-pentose-2-ulose (1d) were examined at 37 degrees at a solution pH of 7.0 (phosphate buffer). For 1a and 1b, two major products were observed and shown respectively to be the 5- and 6-substituted 3-amino-1,2,4-triazine derivatives. The ratios of the products were independent of the amount of aminoguanidine present or the order of mixing the reagents prior to the experiments. For 1c and 1d, only the 5-substituted triazine derivatives were formed. No evidence for hydrazone or bishydrazone formation was observed.     

Structure characterization of human serum proteins in solution and dry state.

The present report describes application of advanced analytical methods to establish correlation between changes in human serum proteins of patients with coronary atherosclerosis (protein metabolism) before and after moderate beer consumption. Intrinsic fluorescence, circular dichroism (CD), differential scanning calorimetry and hydrophobicity (So) were used to study human serum proteins. Globulin and albumin from human serum (HSG and HSA, respectively) were denatured with 8 m urea as the maximal concentration. The results obtained provided evidence of differences in their secondary and tertiary structures. The thermal denaturation of HSA and HSG expressed in temperature of denaturation (Td, degrees C), enthalpy (DeltaH, kcal/mol) and entropy (DeltaS kcal/mol K) showed qualitative changes in these protein fractions, which were characterized and compared with fluorescence and CD. Number of hydrogen bonds (n) ruptured during this process was calculated from these thermodynamic parameters and then used for determination of the degree of denaturation (%D). Unfolding of HSA and HSG fractions is a result of promoted interactions between exposed functional groups, which involve conformational changes of alpha-helix, beta-sheet and aperiodic structure. Here evidence is provided that the loosening of the human serum protein structure takes place primarily in various concentrations of urea before and after beer consumption (BC). Differences in the fluorescence behavior of the proteins are attributed to disruption of the structure of proteins by denaturants as well as by the change in their compactability as a result of ethanol consumption. In summary, thermal denaturation parameters, fluorescence, So and the content of secondary structure have shown that HSG is more stable fraction than HSA.     

Studies on reactions of oxidizing sulfur-sulfur three-electron-bond complexes and reducing alpha-amino radicals derived from OH reaction with methionine in aqueous solution

The technique of pulse radiolysis with spectrophotometric detection has been used to investigate the possibility of electron transfer reactions between oxidizing sulfur-sulfur three-electron-bond complexes (Met2/S thereforeS+), or reducing alpha-amino radicals (CH3SCH2CH2CH.NH2) derived from reaction of methionine with OH radicals and hydroxycinnamic acid (HCA) derivatives, riboflavin (RF) or flavin adenine dinucleotide (FAD), respectively. The HCA derivatives, such as caffeic acid, ferulic acid, sinapic acid and chlorogenic acid, widely distributed phenolic acids in fruit and vegetables, have been identified as good antioxidants previously can rapidly and efficiently repair oxidizing three-electron-bond complexes via electron transfer. RF and FAD can oxidize reducing alpha-amino radicals derived from methionine. The electron transfer rate constants approximately 10(9) dm3 x mol(-1)x s(-1) were determined by following the build-up kinetics of species produced.