Ab initio analysis of the interaction of CO2 with acetylated d-glucopyranose derivatives

Peracetylated d-glucopyranose has a high solubility in CO₂ and can be a promising phase-change physical solvent or absorbent for CO₂, as reported recently. However, peracetylated d-glucopyranose is unstable under acidic atmospheres, especially in sulfur-containing waste gases, and the possibly major decomposition products are 2,3,4,6-tetra-O-acetyl-d-glucopyranose, 1-thiol-d-glucopyranose tetraacetate, and 1-mercaptoethyl-d-glucopyranose tetraacetate. Therefore, it is highly interesting to investigate the interaction between CO₂ and these three compounds using ab initio calculations, including geometry optimizations with HF/3-21G, B3LYP/6-31+G** and single-point energy calibration with MP2/aug-cc-pVDZ. The results indicate that the electrostatic interactions between the substrates and CO₂ are mainly influenced by the interaction distance and the numbers of negative charge donors or the interacting pairs involved in the complex. It is furthermore found that ΔE increases significantly if S and O atoms could interact with CO₂ simultaneously. The binding energy is irrelevant if one considers the chemical environment of the O atom (i.e. O_Ac, O_E or O_S) or the S atom (i.e. SEt or SH), and the electronegativity difference between the S and O atoms. The three substrates studied are still excellent CO₂-philes, although their average ΔE (–20 kJ/mol) is slightly lower than that of peracetylated d-glucose (–22 kJ/mol), which has one more O atom that can interact with CO₂. Therefore, the applications of carbohydrates can be expanded to include adsorbents for CO₂, SO₂ or both, and the functional groups attached to the carbohydrate can vary from those to the acetyl groups.