A fourier transform infrared spectroscopic study of the molecular interaction in synthetic bilayer membrane

Fourier transform infrared spectroscopy is used to study the molecular interaction between gramicidin D and bilayer membranes, dioctadecadimethylammonium bromide (2C₁₈N⁺2C₁Br^-), and 1,2-di-palmytoyl-l-α-phosphatidylcholine (DPPC). Frequencies and bandwidths of the symmetric CH₂ stretching band measured as a function of temperature are used to study variation of packing of alkyl chains. The bilayer membrane prepared from 2C₁₈N⁺2C₁Br^- is found to have a gel to liquid crystal phase transition at 42°C. The presence of gramicidin in the membrane causes an increase in the mobility of the alkyl chain and also a decrease in the abruptness of the transition. The frequencies of amide I and II bands of gramicidin reflecting secondary structures of polypeptides are used to identify its conformation in membranes and to study the interaction between gramicidin and the matrices. Gramicidin is found to have hydrophobic interaction with 2C₁₈N⁺2C₁Br^-, whereas it has both hydrophobic and hydrophilic interactions with DPPC.