Competition of natural polyamines with dimethylsilyl analogues and monovalent cations in presence of a charged dipalmitoylphosphatidylglycerol monolayer

The interaction at the air/water interface of dipalmitoylphosphatidylglycerol (DPPG) with natural and dimethylsilyl polyamines are investigated first in the presence of NaCl in the subphase. Next, experiments are performed to study the competition between natural polyamines and dimethylsilyl analogues. The results obtained by surface pressure and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) with NaCl, are compared with those obtained with distilled water. A decrease of the DPPG mean molecular area is observed due to the local diminution of the Na⁺ concentration close to the polar head group and the simultaneous onset of interactions between the amino group of natural polyamines and the polar head group of DPPG. The same effects occur with azhepsi, followed by an insertion of the hydrophobic dimethylsilyl group. Near the polar head groups DPPG, a substitution of the Na⁺ by the amino groups of polyamines occurs.

For the competition experiments, whereas a partial substitution is possible after putrescine and spermine adsorption, it is almost complete after spermine adsorption. Since the number of amino groups of azhepsi and spermine are the same, hydrophobic interactions due to the presence of dimethylsilyl group occur between azhepsi and the alkyl chains of DPPG. This favoured insertion of azhepsi provides a basis for understanding of the action of dimethylsilyl derivatives in the case of an antitumour strategy.