Many lipid molecules that constitute biological membranes are unsaturated and are therefore susceptible to oxidation . For polyunsaturated lipids this process can occur spontaneously, whereas for monounsaturated phospholipids, such as POPC and cholesterol, to initiate the reaction a highly oxidizing component (e.g. a singlet oxygen) is required . Since the biological function of membranes is directly associated with their composition, any biophysical alteration generated by lipid oxidation can positively or negatively affect the functioning of the membrane. For example, oxidative stress has been successfully used for the treatment of skin diseases. On the other hand, it is well known that lipid oxidation may be related to serious diseases such as cancer, hypertension, diabetes, Parkinson's, Alzheimer's, Huntington's and Sclerosis .
Here we present a synchrotron SAXS investigation of large unilamellar vesicles (LUVs) composed by different mixtures of POPC and POPC-OOH (the hydroperoxized form of the POPC molecule). SAXS data analysis has been performed within the SDP (Scattering Density Profile) method , by using a new representation of the volume fraction probability of each chemical group of the lipid based on the error function . Results show that the inclusion of the POPC-OOH lipid leads to a decrease in lipid bilayer thickness and suggest that the OOH group is located on the polar head / paraffinic chain interface, in agreement with recent Molecular Dynamics Simulations outcome .
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