Browsing by Author "Lenné, T"

Now showing 1 - 6 of 6
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    Effects of sugars on lipid bilayers during dehydration - SAXS/WAXS measurements and quantitative model
    (American Chemical Society, 2009-02-26) Lenné, T; Garvey, CJ; Koster, KL; Bryant, G
    We present an X-ray scattering study of the effects of dehydration on the bilayer and chain-chain repeat spacings of dipalmitoylphosphatidylcholine bilayers in the presence of sugars. The presence of sugars has no effect on the average spacing between the phospholipid chains in either the fluid or gel phase. Using this finding, we establish that for low sugar concentrations only a small amount of sugar exclusion occurs. Under these conditions, the effects of sugars on the membrane transition temperatures can be explained quantitatively by the reduction in hydration repulsion between bilayers due to the presence of the sugars. Specific bonding of sugars to lipid headgroups is not required to explain this effect. © 2009, American Chemical Society
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    Kinetics of the lamellar gel-fluid transition in phosphatidylcholine membranes in the presence of sugars
    (Elsevier, 2010-02) Lenné, T; Garvey, CJ; Koster, KL; Bryant, G
    Phase diagrams are presented for dipalmitoylphosphatidylcholine (DPPC) in the presence of sugars (sucrose) over a wide range of relative humidities (RHs). The phase information presented here, determined by small angle X-ray scattering (SAXS), is shown to be consistent with previous results achieved by differential scanning calorimetry (DSC). Both techniques show a significant effect of sucrose concentration on the phase behaviour of this phospholipid bilayer. An experimental investigation into the effect of sugars on the kinetic behaviour of the gel to fluid transition is also presented showing that increasing the sugar content appears to slightly increase the rate at which the transition occurs. © 2010, Elsevier Ltd.
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    Location of sugars in multilamellar membranes at low hydration
    (Elsevier, 2006-11-15) Lenné, T; Bryant, G; Garvey, CJ; Kelderling, U; Koster, KL
    Severe dehydration is lethal for most biological species. However, there are a number of organisms which have evolved mechanisms to avoid damage during dehydration. One of these mechanisms is the accumulation of small solutes (e.g. sugars), which have been shown to preserve membranes by inhibiting deleterious phase changes at low hydration. Specifically, sugars reduce the gel to fluid phase transition temperatures of model lipid/water mixtures. However, there is a debate about the precise mechanism, the resolution of which hinges on the location of the sugars. In excess water, it has been observed using contrast variation SANS that the sugar concentration in the excess phase is higher than in the interlamellar region [Deme and Zemb, J. Appl. Crystallog. 33 (2000) 569]. This raises two questions regarding the location of the sugars at low hydrations: first, does the system phase separate to give a sugar/water phase in equilibrium with a lipid/water/sugar lamellar region (with different sugar concentrations); and second, is the sugar in the interlamellar region uniformly distributed, or does it concentrate preferentially either in close proximity to the lipids, or towards the center of the interbilayer region. In this paper we present the preliminary results of measurements using contrast variation SANS to determine the location of sugars in lipid/water mixtures. © 2006, Elsevier Ltd.
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    Measurement of glucose exclusion from the fully hydrated DOPE inverse hexagonal phase
    (Royal Society of Chemistry, 2010-03-21) Kent, B; Garvey, CJ; Lenné, T; Porcar, L; Garamus, VM; Bryant, G
    The degree of exclusion of glucose from the inverse hexagonal HII phase of fully hydrated DOPE is determined using contrast variation small angle neutron scattering and small angle X-ray scattering. The presence of glucose is found to favour the formation of the non-lamellar HII phase over the fluid lamellar phase, over a wide range of temperatures, while having no significant effect on the structure of the HII phase. Glucose is preferentially excluded from the lipid–water interface resulting in a glucose concentration in the HII phase of less than half that in the coexisting aqueous phase. The degree of exclusion is quantified and the results are consistent with a hydration layer of pure water adjacent to the lipid head groups from which glucose is excluded. The osmotic gradient created by the difference in glucose concentration is determined and the influence of glucose on the phase behaviour of non-lamellar phase forming lipid systems is discussed. © 2010, Royal Society of Chemistry
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    Phospholipid membrane protection by sugar molecules during dehydration-insights into molecular mechanisms using scattering techniques
    (MDPI AG, 2013-04-01) Garvey, CJ; Lenné, T; Koster, KL; Kent, B; Bryant, G
    Scattering techniques have played a key role in our understanding of the structure and function of phospholipid membranes. These techniques have been applied widely to study how different molecules (e. g., cholesterol) can affect phospholipid membrane structure. However, there has been much less attention paid to the effects of molecules that remain in the aqueous phase. One important example is the role played by small solutes, particularly sugars, in protecting phospholipid membranes during drying or slow freezing. In this paper, we present new results and a general methodology, which illustrate how contrast variation small angle neutron scattering (SANS) and synchrotron-based X-ray scattering (small angle (SAXS) and wide angle (WAXS)) can be used to quantitatively understand the interactions between solutes and phospholipids. Specifically, we show the assignment of lipid phases with synchrotron SAXS and explain how SANS reveals the exclusion of sugars from the aqueous region in the particular example of hexagonal II phases formed by phospholipids.© 2011, MDPI Publishing. © 2013, MDPI Publishing
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    Sugar distribution between and around membranes during dehydration
    (Elsevier, 2006-12) Bryant, G; Lenné, T; Koster, KL; Garvey, CJ
    It is now well known that small solutes such as sugars can reduce membrane damage during freezing and dehydration. One of the mechanisms for this protection is that small solutes can hinder deleterious phase transitions, thus preserving membrane integrity. The mechanisms for this can be understood in terms of the hydration forces explanation (HFE) [G. Bryant, K.L. Koster, J. Wolfe, Seed Sci. Res. 11 (2001) 17–25]. At low to intermediate hydrations, the presence of small solutes reduces membrane transition temperatures through their (non-specific) volumetric and osmotic properties. If concentrations are sufficiently high that vitrification occurs, then the transition temperatures are depressed even further. In the fully dehydrated state, direct hydrogen bonding between solutes and membranes may become important. Recently [K. Koster, G. Bryant, Eur. Biophys. J. 32 (2003) 96–105], we showed how solutes can be excluded from inter-membrane regions during dehydration if the solutes are too large, explaining why large solutes (eg polymers) cannot inhibit membrane phase transition. This raises two questions: (1) is there partial exclusion of small and intermediate sized solutes? (2) if so, how does this alter the effects of the solutes? and (3) is there a maximum useful concentration of small solutes? Question (3) is answered in an accompanying paper (see Lenné et al., this volume). In this paper we will present the results of Small Angle Neutron Scattering (SANS) and Small angle X-ray scattering (SAXS) experiments designed to answer the first two questions, and discuss the implications for our understanding of the effects of solutes on membranes during dehydration. © 2010, Elsevier Ltd.