Wan Iskandar WFN, Salim M, Patrick M, Timimi BA, Zahid NI, et al.
The journal of physical chemistry. B •
The lyotropic phase behavior of four common and easily accessible glycosides, -octyl α-d-glycosides, namely, α-Glc-OC, α-Man-OC, α-Gal-OC, and α-Xyl-OC, was investigated. The presence of normal hexagonal (H), bicontinuous cubic (V), and lamellar (L) phases in α-Glc-OC and α-Man-OC including their phase diagrams in water reported previously was verified by deuterium nuclear magnetic resonance (H NMR), via monitoring the DO spectra. Additionally, the partial binary phase diagrams and the liquid crystal structures formed by α-Gal-OC and α-Xyl-OC in DO were constructed and confirmed using small- and wide-angle X-ray scattering and H NMR. The average number of bound water molecules () per headgroup in the L phase was determined by the systematic measurement of the quadrupolar splitting of DO over a wide range of molar ratio values (glycoside/DO), especially at high glucoside composition. The number of bound water molecules bound to the headgroup was found to be around 1.5-2.0 for glucoside, mannoside, and galactoside, all of which possesses four OH groups. In the case of xyloside, which has only three OH groups, the bound water content is ∼2.0. Our findings confirmed that the bound water content of all -octyl α-d-glycosides studied is lower compared to the number of possible hydrogen bonding sites possibly due to the fact that most of the OH groups are involved in intralayer interaction that holds the lipid assembly together.
Zahid NI, Conn CE, Brooks NJ, Ahmad N, Seddon JM, et al.
Langmuir : the ACS journal of surfaces and colloids •
Synthetic branched-chain glycolipids are suitable as model systems in understanding biological cell membranes, particularly because certain natural lipids possess chain branching. Herein, four branched-chain glycopyranosides, namely, 2-hexyl-decyl-α-D-glucopyranoside (α-Glc-OC10C6), 2-hexyl-decyl-β-D-glucopyranoside (β-Glc-OC10C6), 2-hexyl-decyl-α-D-galactopyranoside (α-Gal-OC10C6), and 2-hexyl-decyl-β-D-galactopyranoside (β-Gal-OC10C6), with a total alkyl chain length of 16 carbon atoms have been synthesized, and their phase behavior has been studied. The partial binary phase diagrams of these nonionic surfactants in water were investigated by optical polarizing microscopy (OPM) and small-angle X-ray scattering (SAXS). The introduction of chain branching in the hydrocarbon chain region is shown to result in the formation of inverse structures such as inverse hexagonal and inverse bicontinuous cubic phases. A comparison of the four compounds showed that they exhibited different polymorphism, especially in the thermotropic state, as a result of contributions from anomeric and epimeric effects according to their stereochemistry. The neat α-Glc-OC10C6 compound exhibited a lamellar (Lα) phase whereas dry α-Gal-OC10C6 formed an inverse bicontinuous cubic Ia3d (QII(G)) phase. Both β-anomers of glucoside and galactoside adopted the inverse hexagonal phase (HII) in the dry state. Generally, in the presence of water, all four glycolipids formed inverse bicontinuous cubic Ia3d (QII(G)) and Pn3m (QII(D)) phases over wide temperature and concentration ranges. The formation of inverse nonlamellar phases by these Guerbet branched-chain glycosides confirms their potential as materials for novel biotechnological applications such as drug delivery and crystallization of membrane proteins.