The Effect of Steric Constraints on the Adsorption of Phenyltin onto the Dipalmitoylphosphatidylcholine Bilayer

In this paper, we present studies concerning phenyltin adsorption onto the dipalmitoylphosphatidylcholine bilayer. Phenyltin compounds are known to be biologically active, and their molecular geometry makes it possible to study the effect of steric constraints on their ability to penetrate the model lipid membrane. Using a fluorescence probe as a reporter of the amount of adsorbed compound, we evaluated their affinity to the membrane as a function of the membrane state. The amount of the adsorbed compound was found to depend on the adsorbing molecule's geometry and lipid bilayer organization. The fluorescence measurements were supported by the density functional theory (DFT) method of quantum mechanical computations. The penetrant location was correlated with the possible relative positions of its polar and hydrophobic moieties to determine if it could adopt structural requirements of the local membrane environment. Molecules were deformed by a model force, mimicking interactions within the membrane interfacial region. Computations show that the diphenyltin molecule can be deformed to such an extent that it can adopt an amphiphilic conformation. Triphenyltin is different, as its bending requires more energy. Born repulsion energies from hydrophobic fluid into water for phenyltins were also computed in an isodensity-polarized continua model of DFT computation. Our results indicate that the phenyltin compounds incorporate into the interface of the lipid membrane, although diphenyltin integrates more deeply than triphenyltin, which locates on the double layer's surface, and this is due to the fact that the main role is played by steric and not electrostatic interactions.