Computational insights into octyl-D-xyloside isomers towards understanding the liquid crystalline structure: physico-chemical features

ABSTRACT

We applied density functional theory to study octyl-D-xyloside isomers in order to explain the features responsible for the liquid crystal mesophases. Compared to a glucoside, the xylose headgroup has a proton instead of the hydroxymethyl group on C5. Thus, a xyloside has a reduced headgroup volume that renders it less hydrophilic. Our results have shown that the xylose headgroup may adopt stable pyranose and furanose conformations, which may lead to different effective headgroup hydrophilicities. These features are probably responsible for forming two non-equivalent inverse micelles, which are self-assembled into a cubic discontinuous phase with a space group of Fd3m commonly found for xylosides. While different factors are responsible for controlling the relative stability of each isomer, the role of intramolecular hydrogen bonding was highlighted for the investigated single molecule. The polarisable continuum model was used to take into account the solvent effect in order to understand the molecular behaviour in very polar systems. Results from calculations carried out in gas phase were used for comparative purposes. The molecular electrostatic potential calculations for these xylolipids demonstrate sugar amphoterism, which is implicated in the heterogeneity nature of lipid self-assembly.

Graphical Abstract

Abbreviations: AIM: atoms in molecules; DFT: density functional theory; NBO: natural bond orbital

KEYWORDS:

• Glycolipids
• octyl-D-xyloside
• hydrogen bonding
• DFT
• AIM
• NBO

Acknowledgements

The authors gratefully thank the High Impact Research Grant UM.C/625/1/HIR/MOHE/05 (Malaysia) and the Scientific Grant-in Aid for Scientific Research (B-24360127) of the Japan Society for the Promotion of Science (JSPS) for financial support as well as the Center for Information Technology (PTM) for computing facilities. IB is grateful to Prof. Dr. Jean-Frédéric F. Weber from Universiti Teknologi MARA (UiTM), Puncak Alam, Malaysia, for fruitful discussions. We also thank Dr. N. Idayu Zahid from University of Malaya for her help in discussing IR spectra.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental material

The supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the High Impact Research [grant UM.C/625/1/HIR/MOHE/05] (Malaysia) and the Scientific Grant-in Aid for Scientific Research [B-24360127] of the Japan Society for the Promotion of Science (JSPS).