Specific rotation of monosaccharides: a global property bringing local information

Theoretical study of the pyrolysis of β-1,4-xylan: a detailed investigation on unimolecular concerted reactions

A theoretical study of the thermal decomposition of β-1,4-xylan, a model polymer of hemicelluloses, is proposed for the first time. A mechanism based on unimolecular concerted reactions is elaborated in a comprehensive way. Elementary reactions, such as dehydrations, retro-aldol, retro Diels-Alder, retro-ene, glycosidic bond fissions, isomerizations, etc., are applied to β-1,4-xylan, as well as to the fragments formed. At each stage of the construction of the mechanism, the fragments previously retained are decomposed and the low energy paths are selected to define new fragments. Energy barriers are computed at the CBS-QB3 level of theory and rate coefficients of important reactions are calculated. It is shown that the main reaction pathways can be modelled by reactions involving two specific fragments, which react in closed sequences, similarly to chain-propagating reactions. The proposed reaction scheme allows to predict important species observed during the pyrolysis of xylan, such as aldehydes or CO. In addition, we show that dehydrations require high activation energy and cannot compete with the other reactions. Therefore, it seems difficult to explain, by means of unimolecular homogeneous gas phase reactions, the significant formation of specific species such as furfural as reported by several authors.

Three-Dimensional Structures of Carbohydrates and Where to Find Them

Analysis and systematization of accumulated data on carbohydrate structural diversity is a subject of great interest for structural glycobiology. Despite being a challenging task, development of computational methods for efficient treatment and management of spatial (3D) structural features of carbohydrates breaks new ground in modern glycoscience. This review is dedicated to approaches of chemo- and glyco-informatics towards 3D structural data generation, deposition and processing in regard to carbohydrates and their derivatives. Databases, molecular modeling and experimental data validation services, and structure visualization facilities developed for last five years are reviewed.

The effect of sodium chloride concentration on the mutarotation and structure of d-xylose in water: Experimental and theoretical investigation

The effect of NaCl concentration on the structure of d-xylose in H₂O was studied. It was found that NaCl could prolong the equilibrium time between the two main configurations, α-xylopyranose and β-xylopyranose. The proportion of α-xylopyranose was slightly increased in NaCl-H₂O solution than that in H₂O, and the alteration of NaCl on α-xylopyranose and β-xylopyranose was different. Theoretical calculations demonstrated that NaCl was more favorable to stabilize the structure of α-xylopyranose. Na⁺ had attraction with O atoms (α: O₆; β: O₆ and O₁), with the outflow of electron from C atom to O atom on the C₁-O₆ bond, which was beneficial to the transformation between chain form and pyran forms. Cl^- had interaction with the hydroxyl groups of xylose. The interaction between xylose and NaCl, was also evidenced by the variation of ³⁵Cl and ²³Na NMR spectra. The findings could provide guidance for understanding the conformational change and design of xylose conversion ways. It also provided valuable information for making efficient use of hemicellulose.