Browsing by Author "Hunt, T"

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    Grazing incidence neutron scattering investigations of lateral phase separation in oriented mixed lipid bilayers
    (Saha Institue of Nuclear Physics, 2012-07-25) Kent, B; Bryant, G; Hunt, T; Kruezer, M; Stroble, M; Garvey, CJ
    Since they were first proposed more than a decade ago, lipid rafts have been shown to carry out essential roles within plasma membranes. At a fundamental level, lipid rafts represent a demixing or phase separation of different components within the membrane. Mixtures of saturated and unsaturated lipids are thought to undergo phase separation due to energetic cost of hydrophobic packing, and that the addition of a hybrid lipid containing both saturated and unsaturated tails may stabilise domains in well defined sizes by lowering the interfacial free energy between the unsaturated and saturated phases (Figure 1). By selectively deuterating lipid species, surface heterogeneity of scattering length densities due to the presence of lipids domains can be probed with off-specular grazing incidence neutron scattering. We examined mixed lipid systems of deuterated saturated lipid (DPPC), hydrogenated hybrid lipid (POPC) and a hydrogenated unsaturated lipid (DOPC) using grazing incidence neutron scattering measurements on the BIOREF reflectometer (Helmholtz-Zentrum Berlin fur Materialien und Energie GmbH, Berlin, Germany). Simultaneous in situ infrared spectroscopy was employed to study phase transitions and phase separation of the lipids. Specular and off-specular scattering was recorded using a two-dimensional area detector and time-of—flight data. Repeat spacings of the lipid bilayers from specular scattering showed distinct phase separation behavior of these systems at 30 °C when compared to 55 °C. These changes are correlated to changes in the smectic length scale of the lipid bilayer and the characteristic height-height correlation function determined from the Fourier transform of the decay of the integrated intensity of the Bragg sheets as a function of qll3.
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    Study of the effect of Penetratin on the gyroid to diamond phase transition in Myverol
    (Australian Institute of Physics, 2012-02-01) Goder, JND; Rafi, NAM; Bryant, G; Hunt, T; Kent, B; Garvey, CJ
    Cell-penetrating peptides (CPPs), such as penetratin, have aroused a lot of interest in both the academic and applied research areas for their ability to penetrate cell membranes [1]. Even though there has been much work done, mostly on bilayer membranes, we still do not fully understand the mechanisms involved during this phenomenon. In our investigation, we are going to focus on the phase transition of Myverol/Saline system from Gyroid to Diamond cubic phase in the presence of penetratin, to get an understanding of how CPPs work in a more complex system. We use a Myverol/Saline system that exhibits these types of phase behaviors at specific compositions [2]. We plan to use a variety of Small Angle Scattering techniques in an attempt to elucidate the transitional phase behavior of the Myverol/Saline system with varying concentrations of penetratin. From this we hope to develop a model system for investigating the role of a simple peptide in changing the packing of amphiphilic molecules. In this study, we are making the use of 2 complementary techniques, Small Angle X-ray Scattering (SAXS) and small angle neutron scattering (SANS), to investigate the Myverol/Saline system as functions of both temperatures and peptide composition. We also hope to carry out DSC measurements in parallel with the SAXS. We will report on preliminary SAXS experiments carried out at the Australian Synchrotron.