Ab Initio Conformational Analysis of $\alpha$/$\beta$-D-Xylopyranose at Pyrolysis Conditions

TL;DR

This study computationally explores the conformational space and thermochemistry of α and β D-xylopyranose under pyrolysis conditions, identifying key conformers for understanding biomass decomposition mechanisms.

Contribution

It provides a detailed computational analysis of xylopyranose conformers and thermochemistry relevant to pyrolysis, including a method to select representative conformers for kinetic studies.

Findings

44 and 59 conformers identified for α and β anomers

Boltzmann population analysis used to select key conformers

Conformational and thermochemical data across 298-1068 K

Abstract

Xylopyranose is the principal monosaccharide unit of hemicellulose, one of the three major biopolymers of lignocellulosic biomass. Understanding its decomposition mechanism is increasingly relevant for thermochemical biorefinery research such as pyrolysis. Significant efforts have been made to study its chemical and structural properties using both computational and experimental methods. However, due to its high structural flexibility and numerous hydroxyl groups, various metastable conformers arise. In this work, we performed a computational exploration of the conformational space of both anomeric forms, $\alpha$ and $\beta$ , of D-xylopyranose using the semi-empirical GFN2-xTB method in conjunction with metadynamics and density functional theory simulations for structural optimization and vibrational analysis. Xylopyranose conformers free energy and enthalpy variations are analyzed across temperatures typical of fast biomass pyrolysis (298-1068 K), with the Boltzmann population distribution of the most populated conformers determined. This study provides a detailed computational analysis of the conformational space and thermochemistry of xylopyranose. Additionally, 44 and 59 conformers of the $\alpha$ and $\beta$ anomers were found, for both of which a selection of 10 conformers based on Boltzmann population distribution analysis is performed to reduce the conformational space for ab initio studies of the pyrolysis reaction kinetics.