Interaction of Phenylalanine with DPPC membranes by FTIR-ATR: influence of Water Populations In Restricted Environments of Lipid Membrane Interphases

Abstract

The negative free energy previously reported is 8 explained by the stabilization of a PC-Phe (phosphocholine9 phenylalanine) complex in the presence of water shown by the 10 decrease in the symmetric stretching frequency of the 11 phosphate group of the lipid (PO2 −). An entropic contribution 12 due to the disruption of the water network around the phenyl 13 and in the membrane defect may be invoked. The dipole 14 potential decrease is explained by the orientation of the 15 carboxylate opposing to the CO of the lipids with oxygen 16 moiety toward the low hydrated hydrocarbon core. The 17 symmetric bending frequency of NH3 + group of Phe, decreases 18 in 5.2 cm−1 in relation to water congruent with zeta potential 19 shift to positive values. The Phe to DPPC dissociation 20 constant is Kd = 2.23 ± 0.09 mM, from which the free energy change is about −4.54 kcal/mol at 25 °C. This may be due to 21 hydrophobic contributions and two hydrogen bonds