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Previous studies have used neutron diffraction to elucidate the hydration of the ceramide and the phosphatidylcholine headgroup in solution. These solution studies provide bond-length resolution information on the system, but are limited to liquid samples. The work presented here investigates how the hydration of ceramide and phosphatidylcholine headgroups in a solution compares with that found in a lipid bilayer. This work shows that the hydration patterns seen in the solution samples provide valuable insight into the preferential location of hydrating water molecules in the bilayer. There are certain subtle differences in the distribution, which result from a combination of the lipid conformation and the lipid-lipid interactions within the bilayer environment. The lipid-lipid interactions in the bilayer will be dependent on the composition of the bilayer, whereas the restricted exploration of conformational space is likely to be applicable in all membrane environments. The generalized description of hydration gathered from the neutron diffraction studies thus provides good initial estimation for the hydration pattern, but this can be further refined for specific systems. [ABSTRACT FROM AUTHOR]

The microscopic hydration of theceramide headgroup has been determinedusing a combination of experimentalboth NMR and neutron diffractiontechniques and computational techniquesempirical potentialstructure refinement (EPSR) and molecular dynamics (MD). The additionof water to ceramide in chloroform solutions disrupts the chloroformsolvation of the ceramide headgroup, and the water forms distinctpockets of density. Specifically, water is observed to preferentiallyhydrate the two hydroxyl groups and the carbonyl oxygen over the amideNH motif. Further assessment of the location and orientation of thewater molecules bound to the ceramide headgroup makes it clear thatthe strongly solvated carbonyl moiety of the amide bond creates ananchor from which water molecules can bridge via hydrogen bondinginteractions to the hydroxyl groups. Moreover, a significant differencein the hydration of the two hydroxyl groups indicates that water moleculesare associated with the headgroup in such a way that they bridge betweenthe carbonyl motif and the nearest neighbor hydroxyl group. [ABSTRACT FROM AUTHOR]

The addition of saturated fatty acids(FA) to phosphatidylcholinelipids (PC) that have saturated acyl chains has been shown to promotethe formation of lyotropic liquid-crystalline phases with negativemean curvature. PC/FA mixtures may exhibit inverse bicontinuous cubicphases (Im3m, Pn3m) or inverse topology hexagonal phases (HII), depending on the length of the acyl chains/fatty acid.Here we report a detailed study of the phase behavior of binary mixturesof dioleoylphosphatidylcholine (DOPC)/oleic acid (OA) and dioleoylphosphatidylethanolamine(DOPE)/oleic acid at limiting hydration, constructed using small-angleX-ray diffraction (SAXD) data. The phase diagrams of both systemsshow a succession of phases with increasing negative mean curvaturewith increasing OA content. At high OA concentrations, we have observedthe occurrence of an inverse micellar Fd3mphase in both systems. Hitherto, this phase had not beenreported for phosphatidylethanolamine/fatty acid mixtures, and assuch it highlights an additional route through which fatty acids mayincrease the propensity of bilayer lipid membranes to curve. We alsopropose a method that uses the temperature dependence of the latticeparameters of the HIIphases to estimate the spontaneousradii of curvature (R0) of the binarymixtures and of the component lipids. Using this method, we calculatedthe R0values of the complexes comprisingone phospholipid molecule and two fatty acid molecules, which havebeen postulated to drive the formation of inverse phases in PL/FAmixtures. These are −1.8 nm (±0.4 nm) for DOPC(OA)2and −1.1 nm (±0.1 nm) for DOPE(OA)2. R0values estimated in this way allowthe quantification of the contribution that different lipid speciesmake to membrane curvature elastic properties and hence of their effecton the function of membrane-bound proteins. [ABSTRACT FROM AUTHOR]

An increasing body of evidence relates the wide range of benefits mineral surfaces offer for the development of early living systems, including adsorption of small molecules from the aqueous phase, formation of monomeric subunits and their subsequent polymerization, and supramolecular assembly of biopolymers and other biomolecules. Each of these processes was likely a necessary stage in the emergence of life on Earth. Here, we compile evidence that templating and enhancement of prebiotically-relevant self-assembling systems by mineral surfaces offers a route to increased structural, functional, and/or chemical complexity. This increase in complexity could have been achieved by early living systems before the advent of evolvable systems and would not have required the generally energetically unfavorable formation of covalent bonds such as phosphodiester or peptide bonds. In this review we will focus on various case studies of prebiotically-relevant mineral-templated self-assembling systems, including supramolecular assemblies of peptides and nucleic acids, from nanoscience and surface science. These fields contain valuable information that is not yet fully being utilized by the origins of life and astrobiology research communities. Some of the self-assemblies that we present can promote the formation of new mineral surfaces, similar to biomineralization, which can then catalyze more essential prebiotic reactions; this could have resulted in a symbiotic feedback loop by which geology and primitive pre-living systems were closely linked to one another even before life’s origin. We hope that the ideas presented herein will seed some interesting discussions and new collaborations between nanoscience/surface science researchers and origins of life/astrobiology researchers. [ABSTRACT FROM AUTHOR]