Probing n-octyl alpha-d-glycosides using deuterated water in the lyotropic phase by deuterium nmr

• Main Authors: Iskandar, Wan Farah Nasuha Wan, Salim, Malinda, Patrick, Melonney, Timimi, Bakir A., Zahid, N. Idayu, Hashim, Rauzah
• Format: Article
• Published: Amer Chemical Soc 2021
• Subjects: QD Chemistry
• Online Access: http://eprints.um.edu.my/28418/
• Institution: Universiti Malaya

The lyotropic phase behavior of four common and easily accessible glycosides, n-octyl alpha-D-glycosides, namely, alpha-GlcOC(8), alpha-Man-OC8, alpha-Gal-O(C)8, and a-Xyl-OC8, was investigated. The presence of normal hexagonal (HI), bicontinuous cubic (VI), and lamellar (L-alpha) phases in alpha-Glc-OC8 and alpha-Man-OC8 including their phase diagrams in water reported previously was verified by deuterium nuclear magnetic resonance (H-2 NMR), via monitoring the D2O spectra. Additionally, the partial binary phase diagrams and the liquid crystal structures formed by alpha-Gal-OC8 and alpha-XylOC(8) in D2O were constructed and confirmed using small- and wide-angle X-ray scattering and H-2 NMR. The average number of bound water molecules (n(b)) per headgroup in the L-alpha phase was determined by the systematic measurement of the quadrupolar splitting of D2O over a wide range of molar ratio values (glycoside/ D2O), 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 similar to 2.0. Our findings confirmed that the bound water content of all n-octyl alpha-Dglycosides 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.