Search

Abstract: In situ time-resolved energy dispersive X-ray diffraction (EDXD) was applied to investigate the hydration kinetics of oriented dioleoylphosphocoline (DOPC) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) membranes. The long-range order in the investigated lipid multilayers has been found to vary as a function of hydration in a nonmonotic way. In the first stage, water adsorption increased the long-range order along the normal to the lipid bilayer whereas, in the second one, a progressive loss of interbilayer coherence was observed. Possible molecular mechanisms underlying the experimental observations are discussed. [Copyright &y& Elsevier]

In situ energy dispersive x-ray diffraction was used to investigate the effect of hydration on the structure of caveolae membranes. The structure of caveolae membrane was found to be strongly dependent on hydration. At low hydration two lamellar phases with distinct repeat spacings were found to coexist with segregated cholesterol crystallites. Upon hydration, the lamellar phases did swell, while diffraction peak of cholesterol crystals disappeared suggesting that cholesterol molecules redistributed homogeneously within the caveolae membrane. At full hydration, unbinding of caveolae membrane occurred. Upon dehydration the system returned to the bound state, demonstrating that the unbinding transition is fully reversible. [ABSTRACT FROM AUTHOR]

In situ enersgy dispersive x-ray diffraction was used to study theeffect of hydration on the structure of dioleoylphosphatidylcholine (DOPC) bilayers in the biologically relevant liquid-crystalline phase. A broad range of relative humidity (RH) was investigated (0.45≤RH≤1) and two hydration regimes were found. From RH=0.45 up to RH∼0.94, the structure of DOPC bilayers was found to change slightly. At RH∼0.94, a distinctive structural change was observed. From RH∼0.94 up to full hydration, a strong increase in the head group size, coupled with a marked decrease in the hydrophobic core thickness, was observed. Possible molecular mechanisms underlying experimental observations are discussed [ABSTRACT FROM AUTHOR]

In situ time-resolved energy dispersive x-ray diffraction (EDXD) was applied to investigate the effect of hydration on the structure of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)-oriented membranes. The measurements allowed a very high density time sampling of the evolution of the structural properties of the DOTAP bilayer such as the lamellar d-spacing, the membrane thickness, and the size of the interbilayer water region. Time-resolved EDXD has been found to provide important information on the role played by free water molecules on the structure and fluidity of lipid bilayer. [ABSTRACT FROM AUTHOR]

Energy dispersive x-ray diffraction was applied to investigate the hydration kinetics of highly aligned 1,2-dioleoyl-3-trimethylammonium-propane membrane system. First, the adsorption of water into the lipid film results in a continous gain of interbilayer spatial coherence until a maximum is reached. Further, adsorbed water molecules behave as bulk water promoting loss of spatial coherence and leading to a progressive lowering and broadening of diffraction peaks. The possible molecular origin of this phenomenon is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The supramolecular structure of Niosomal vesicles (Niosomes) made of a binary mixture of polysorbate 20 (Tween 20) and Cholesterol in aqueous solution was investigated by means of synchrotron small angle X-ray scattering (SAXS). Solid-supported Niosomal membranes at full hydration exhibit the same structural properties, as determined by in situ energy dispersive X-ray diffraction (EDXD), than their counterpart in solution. Both Niosomes and solid-supported Niosomal membranes are made of highly swollen bilayers rich in Tween 20 coexisting with Cholesterol crystallites. EDXD patterns from oriented samples suggest that at least some Cholesterol crystals are aligned along the normal to the solid support. [Copyright &y& Elsevier]

Abstract: Effect of lipid hydration on the structure of lamellar lipoplexes made of the cationic lipid 3-[N-(N,N-dimethylaminoethane)-carbamoyl]cholesterol (DC-Chol), the neutral ‘helper’ lipid dioleoylphosphatidylethanolamine (DOPE) and calf-thymus DNA was investigated by synchrotron small angle X-ray diffraction (SAXD). Here, we show that lipid hydration is the key factor regulating the equilibrium structure of lipoplexes. Thermotropic behavior was also investigated between 5 and 65°C. Both the membrane thickness and the water layer thickness were found to decrease linearly as a function of temperature while the one dimensional DNA rod lattice between lipid bilayers was found to enlarge. Structural results were interpreted in terms of recently proposed theoretical models. [Copyright &y& Elsevier]

The analysis of the thermal behaviorof octyl- (OAC) and decylammoniumchloride (DAC) has provided relevant new information. OAC shows apolymorphic phase transition that starts at 308 K and is completedat 313 K, between a monoclinic and a tetragonal structure, which belongsto a space group different from what was observed for other alkylammoniumchlorides. At the melting temperature (463 K), the growing of a strongfirst sharp diffraction peak (FSDP) occurring at a d-spacing of ca. 21.0 Å was observed. DAC is characterized bytwo phase transitions at 318 (Td1) and 323 K (Td2). At Td1, the LT polymorph coexists with a new-formedphase. At Td2the LT polymorph is replaced by a furtherpolymorphic modification of DAC that becomes the only one at 328 K.This second phase transition signals the occurrence of a phase, closelyrelated to the LT polymorph of HeAC, that crystallizes in the tetragonalcrystal system a= ca. 5.00 Å and c= ca. 28.5 Å, P4/nmmspacegroup. DAC melting starts at 458 K and is accompanied, as in the caseof OAC, by the growing of a strong FSDP at a d-spacingof ca. 24.8 Å. A parallel DSC study confirmed the above-mentionedtransitions. In addition, the structural properties of OAC/water andDAC/water mixtures were studied using an integrated approach, whichcombines X-ray diffraction and molecular dynamics (MD) techniques.A very good agreement between theoretical and experimental diffractionpatterns has been obtained for both investigated mixtures. A thoroughanalysis of the MD trajectories shows that strong anion–waterinteractions are present in the mixtures, where Cl–forms a rather unstructured first hydration shell of water moleculesbound to the anion in a linear Cl···H–O configuration.Moreover, cations and anions were found to interact with each other,and to form “solvent-shared ion pairs”, in which oneor more water molecules are shared between Cl–andthe alkylammonium cation. [ABSTRACT FROM AUTHOR]