Effect of Chain Branching on Orientational Ordering in Glycolipid Self-assembly by 2H-NMR using Extrinsic Probes

The structure and dynamics of molecular solids, liquid crystals, and thin films of membrane lipids may be elucidated from the use of deuterium NMR (2H-NMR) spectroscopy. The 2H-NMR spectrum of a deuterated material (either selectively or fully) is rather simpler to interpret compared with the corresponding proton NMR (1H-NMR). Here, we apply this technique to understand the effect of chain branching on orientational order of the glycolipid self-assembly by using deuterated probes. The 2H-NMR resonance of n-octanol-d17 in n-octyl-β-D-glucopyranoside (β-GlcOC8) and the branched-chain glycolipid 2-hexyldecyl-β-D-glucopyranoside (β-GlcOC10C6) were measured at different temperatures. We also measured the 2H-NMR spectrum of 2-ethyl-n-hexanol-α,α-d2, a branched-chain alcohol which is selectively deuterated at α-position in β-GlcOC8. All systems gave quadrupolar splittings in their respective 2H-NMR spectra, which are attributed to the formation of anisotropic phase. The n-octanol-d17 dissolved in β-GlcOC8 give us spectra in the lamellar phase and when used with a branched-chain lipid, i.e. β-GlcOC10C6, gave us new spectra in the inverse hexagonal phase. The magnitude of the quadrupolar splittings of the n-octanol-d17 is indicative of the degree of orientational ordering in the given system. The results show that the quadrupolar splitting is larger in β-GlcOC8 lipid than in β-GlcOC10C6.