Thermodynamics study of gramicidin S and dipalmitoylphosphatidylcholine model membrane interactions based on the FTIR spectroscopy

The Fourier Transform Infrared Spectroscopy was utilized in the study to in vestigate the thermodynamics of the main phase transition of dipalmitoylpho sphatidylcholine (DPPC) model membrane in the vicinity of the antibiotic pe ptide gramicidin S (GS). Based on the two-state thermotropic phase behavior of DPPC, linear extrapolation method was employed to monitor the stability of GS-DPPC interacting systems at different peptide concentrations. The ma in phase transition temperature (T-m) and the enthalpy change (DeltaH(m)) w ere observed as GS concentration was raised. In addition, an evident reduct ion in the energy at maximum stability (DeltaG(s)) was obtained with the in corporation of GS. These thermodynamics results together with FTIR data ind icated a destabilization effect imposed on the acyl chains of DPPC by GS pr esence. All these results showed the strong interactions of this peptide wi th DPPC model membrane. The results obtained by employing the thermodynamic s approach using the FTIR spectral data gave a quantitative description and some additional information such as the values of DeltaG(s),DeltaH(m) and better estimates of T-m of DPPC and gramicidin containing DPPC systems. (C) 2001. Elsevier Science B.V. All rights reserved.