Guerbet glycolipids from mannose: liquid crystals properties

ABSTRACT

Using mannose as the sugar head, five Guerbet glycolipids with chain ranges from C₈ to C₂₄ were synthesised and studied for their liquid crystal behaviour. Differential scanning calorimetry, optical polarising microscopy and small-angle X-ray scattering were employed to determine the thermal, phase and structure properties. Unlike monoalkylated glycolipids, these Guerbet mannosides showed a glass transition below 0°C, except for α-Man-OC₁₄C₁₀. In the dry state, lamellar was observed for α-Man-OC₆C₂ and α-Man-OC₈C₄, while α-Man-OC₁₂C₈ and α-Man-OC₁₄C₁₀ formed non-lamellar phases, including inverse bicontinuous cubic phase of space group Ia3d and inverse hexagonal phase, respectively. The phase for middle-chain mannoside (α-Man-OC₁₀C₆) could not be assigned conclusively at room temperature, but this metastable phase forms lamellar above 37°C. The partial binary phase diagrams in water were also determined. Under excess water conditions at room and physiological temperatures, these materials form normal micellar solution, lamellar, inverse bicontinuous cubic of space group Pn3m and inverse hexagonal phases. The results were compared with those from other monosaccharide glycolipids from the same sugar Guerbet family. Although these compounds are obvious candidate material for lyotropic applications such as drug carrier and protein crystallisation medium, possible thermotropic application is now being explored.

GRAPHICAL ABSTRACT

KEYWORDS:

• Mannoside
• glycolipids
• liquid crystal
• metastable phase
• thermotropic cubic phase
• non-lamellar phase

Acknowledgments

This Festschrift article is dedicated to Professor Claudio Zannoni who was RH’s Ph.D. external examiner in 1984. In 2015 he was appointed as an Academic Icon to our research group, the Fundamental Science of Self-Assembly, University of Malaya. His excellent scientific works, our stimulating discussions during infrequent encounters in meetings and conferences have encouraged and inspired us in many ways. RH is grateful to be invited again to Erice, which she first visited in 1999 during the birthday celebration of her Ph.D. supervisor and mentor, an eminent scientist Professor Geoffrey R. Luckhurst. We are grateful to all collaborators (past and present) who supported our research undertakings. Finally, we thank them and God bless -is the reward of goodness anything but goodness? (The Qur’an, 55.60).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to thank the Institut Pengurusan dan Pemantauan Penyelidikan, Universiti Malaya PPP and BKP: [Grant Numbers PG132-2015A and BK017-2014]; Ministry of Higher Education Malaysia FRGS: [Grant Number FP040-2015A]; Ministry of Higher Education, Malaysia High Impact Research: [Grant Number UM.C/625/1/HIR/MOHE/05] and The ASEAN-European Academic University Network (ASEA-UNINET) [Travel Grant].