engleski

Undulations of phosphatidylcholine lipid bilayers with incorporated palmitic acid are blurred by lateral proton transfer

Proton transfer along biological interfaces is exceptionally difficult to unravel from both experimental and theoretical perspective [1]. In addition to rather scarce computational studies, experimental endeavours are mostly focused on the incorporation of membrane- anchored pH-sensitive dyes that detect the arrival of a migrating proton. Evidently, the establishment of a probe-free method would serve as considerable breakthrough in deepening our knowledge on lateral proton transfer. In this regard, we have examined lipid multibilayers of 1, 2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) in the absence and the presence of small amount of palmitic acid (PA) (2 %) in buffers of pH values 4 ≤ pH ≤ 9 by FT- IR spectroscopy. Depending on the pH value, PA can be protonated (COOH) or deprotonated (COO−) and, consequently, placed at different depth of a lipid bilayer [3]. The presence of such small amount of PA should not significantly modify characteristic undulations of DPPC multibilayers surface [4], but accompanying proton transfer is expected to leave its signature. The latter are indirectly detected by FT-IR spectroscopy coupled with MCR-ALS with EFA analysis (Fig. 1) that is very sensitive and powerful tool in discerning of coupled events [5]. Experimental observations are corroborated by molecular dynamics (MD) simulations and calorimetric measurements.

lipid multibilayers ; palmitic acid ; IR spectroscopy ; DSC ; multivariate curve analysis

nije evidentirano