Effect of Anomeric and Exocyclic Hydroxymethyl Conformers on Intramolecular Hydrogen Bonds in Maltoside: A DFT Approach

Abstract

Glycolipids with their unique structural diversity are used for various applications including food and medicine. For the optimal use of these lipids, it is vital to understand their behaviour at molecular level to design suitable lipids for use. Disaccharide glycolipids, namely n–dodecyl–α–D–maltoside (C12–α–Mal) and n–dodecyl–β–D–maltoside (C12–β–Mal) are chosen in this study since they can form a closed niosomes which can be used as drug delivery agent. A density functional theory (DFT) calculation on C12–α–Mal and C12–β–Mal was performed to optimize their geometry and calculate their electronic properties using Gaussian 09 software. The B3LYP level of theory with 6–31G and 6–31 + G (d,p) basis sets, and the polarizable continuum model (PCM) were used to determine the effects in explicit water condition. The AIM (Atoms in Molecule) was used to calculate the inter- and intra-molecular hydrogen bonding interactions. It is found that, the anomeric orientation of alkyl chain influences the exocyclic rotamer’s conformation and the bond lengths of hydroxyl groups in maltosides. A specific pair of conformers, gt_tg, shows the lowest energy for both the glycosides in the solvent phase. A visual analysis on the HOMO-LUMO orbital within the sugar rings elucidate the exocyclic group being the primary aspects that influences the glycosides behaviours. Among all the hydroxymethyls’ conformations the gt_tg pair of conformers can be found in both the glycolipids in the intramolecular hydrogen bond analysis using the AIM formalism, and this conformer can be considered as not affected by the anomeric orientation of the alkyl chain.