ATR-IR spectroscopic study of the structural changes in the hydrophobic region of ICPAN/DPPC bilayers

Structural changes in the hydrophobic region in the self-aggregates of the long hydrocarbon chain ICPAN (((N,N-dimethyl-N-octyl-2-ammonioethyl)-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate bromide)) homologues and their interaction with a DPPC (dipalmitoylophosphatidylcholine) bilayer were the subject of detailed investigation using ATR infrared spectroscopy. On the base of analysis of the bands assigned to CH2 stretching, scissoring, and rocking and CH wagging vibrations it was revealed that the hydrophobic parts ICPANs adopt a gauche-rich disordering structure. Moreover, it was shown that the micellar- or lamellar-like character of these structures depends on the hydrocarbon chain length. Results obtained from the ICPAN/DPPC mixtures indicate an increase in the conformational disorder in hydrophobic part compare to pure DPPC film. This effect depends on the length of the aliphatic chain of ICPAN homologues and on the relative concentrations of DPPC and ICPAN.