Comparison of the reducing power of aldose solutions

Abstract

Concentration and temperature dependences of the redox potentials of neutral and alkaline solutions of glucose, mannose, galactose, galacturonic acid, and xylose were measured. Axial orientation of the secondary hydroxy groups in epimeric hexopyranoses, oxidation of C 6 to carboxy group, and the lack of primary hydroxy group in going to aldopentopyranose favor increasing (in the order of listing) destabilization of their cyclic structure, formation of the oxo form, and thermally activated retro-aldol reaction of the latter in alkaline medium. This leads to enhancement of their reducing power and chemical reactivity toward 5,5′,7,7′-tetrabromoindigo.Diversity of natural low-molecular carbohydrates and polysaccharides is determined by specificities of stereoisomeric structure of monoses both in crystalline and solvated states. Numerous publications contain data on stereochemical behavior of pyranose ring, solvation, and specific thermodynamic and thermochemical properties of hexoses and pentoses with different configurational orientations of hydroxy groups in their cyclic forms [1][2][3][4][5][6]. This is responsible for deviations of physicochemical parameters of solutions of monosaccharides, their reactivity, and biochemical activity, which are related in turn to tautomeric transformation from cyclic structure to oxo form. Reductive properties of carbohydrate solutions have found various practical applications in the field of organic chemistry, including initiation of chemical transformations of heterocyclic compounds of the thiazine and thiazole series [7], stabilization of solutions of sulfite reducing agents [8], binding of dissolved oxygen in copper-ammonia solutions of cellulose while determining degree of its polymerization [7], biochemical methods for analysis of catalytic properties of enzymes that decompose polysaccharide compounds [9], etc. Antioxidant activity of monosaccharides is used in cosmetology and medicine [10,11].However, up to now there are no systematized published data on relations between the reducing power of sugars and steric configuration of cyclic forms of their molecules and the presence of substituents therein. Therefore, the goal of the present work was to reveal how stereoisomeric and chemical structure of polyhydroxy aldehydes affects their reducing power in solution.As subjects for study we selected chemically pure glucose (Glc), mannose (Man), galactose (Gal), xylose (Xyl), and galacturonic acid (GalA); the structures of their predominant anomers are shown below.

Study of the Ability of Reducing Saccharides to Chemically Transform Lignin

“…At the end of the experiment, the solutions were left stand for 5 min before measuring ORP. This allowed not distorting experiment results because reaction of the reducing agent with oxygen in the system was avoided [11]. Anaerobic and basic conditions could be selected from these preliminary trials based on ORP, as commented in the results section.…”

“…These features influence the nature of intermolecular interactions in the pyranosic cycles and the ability of their transition to the free aldehydic form [11]. Table 1 shows the results of ORP measurements for the different analysed reducing agents.…”

“…These reducing sugars can be released during enzymatic degradation of polysaccharides in lignocellulosic raw materials. It was previously shown [11] that generated low molecular weight products in the acyclic form have reducing power. In the present work it was assumed that the reducing saccharides provide the redox-transformations because unsaturated C=C and C=O bonds present in the lignin structure.…”

Лубяные Волокна – Новые Возможности Для «зеленой» Нанотехнологии

“…1). Известно [19,20], что наиболее высокими восстановительными свойствами из экстрагируемых примесей лубяных волокон обладают α-и β-глюкоза, ксилоза, альдопентозы, которые входят в состав гемицеллюлозных соединений лубяных культур.…”

Biomodification of Flax Fibrous Materials for Increase of Sorption to Organic Compounds

“…e products forming during enzyme treatment migrate in the technological solution. e conditions for the use of these internal reserves in the brous system to reach a level of reduction potential su cient for redox transformations of lignin having been determined [24].…”