Temperature and pressure effects on the re-orientational dynamics of amino acids

Abstract

Lyotropic liquid crystals of one-, two-or three-dimensional periodicity spontaneously assemble when biological amphiphiles are mixed with a solvent under various conditions of temperature, pressure and hydration. Mesophases formed by lipids include the fluid lamellar, inverse hexagonal and inverse bicontinuous cubic phases. Biologically, the fluid lamellar phase is ubiquitous, being the structure upon which cell membranes are based. The inverse bicontinuous cubic phases which consist of bilayers draped over the primitive (P), double diamond (D) and gyroid (G) periodic minimal surfaces are now also known to occur in-vivo. Although, a significant amount of work has been done to characterize the equilibrium behaviour of all these phases, kinetic and mechanistic studies of lyotropic phase transitions have been largely confined to transformations between lamellar structures and between lamellar to inverse hexagonal phases. This is surprising as the inverse bicontinuous cubic phases perform important biological functions and the mechanism of their formation from the lamellar phase has much in common with the mechanism of membrane fusion and fission during membrane trafficking. In order to further our understanding of their role in biological systems and to continue to exploit their biotechnological potential, a fundamental understanding of the kinetics and mechanisms involved in lamellar to inverse bicontinuous cubic transitions is a key area of study. To address this knowledge vacuum we have used the pressure jump technique to investigate phase transitions involving bicontinuous cubic phases and this has allowed us to gain valuable new insights into the mechanism of lamellar to inverse bicontinuous cubic phase transitions.