The study of biological membranes has been for quite some time a challenging endeavour for researchers, who must exploit a variety of methodologies. In recent years, molecular modelling is probably the field of research that has more enthusiastically contributed with information at the atomic level. A detailed description of a lipid bilayer has to take in consideration all important factors that affect the membrane behaviour and stability. pH is recognizably one of these factors even though it is usually ignored due to its high complexity in terms of modelling.The presence of negatively charged groups in the membrane gives rise to a surface electrostatic potential. The negative charges come mainly from anionic lipids which are prone to protonation under certain conditions. It is not so uncommon to find this fact neglected in the literature. Many studies, both experimental and theoretical, tend to �simplify� the problem by using zwitterionic phospholipids in their membrane models. In the available modelling studies on anionic and negatively charged lipids, their charges are fixed and the authors claim that the pKavalues are too low to allow for any protonation. This approach can be compromised, considering that biological membranes can share protons as �acid-anion� dimers and those anionic lipids thus trap and conduct protons along the headgroup domain of bilayers that contain such anionic lipids (1). The �acid-anion� mechanism suggests that some of these anionic lipids can retain protons at higher pH values, hence altering their structural properties.Here, we introduce a new method that allows the inclusion of pH in molecular dynamics simulations of lipid bilayers. The results on the application of the method to a lipid bilayer constituted by oleic acid will be presented.Acknowledgements: We thank FCT for financial support (Project PTDC/QUI-BIQ/113721/2009)1. Haines, Proc. Nat. Acad. Sci. USA, 80, 160 (1983)

pH effects on lipid bilayer structures: A computational study

246th National Meeting (2013)

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