Photoregulation of the binding of synthetic polyelectrolytes to phosphatidylcholine bilayer membranes

The structure and permeability of phosphatidylcholine bilayer membranes prepared in the presence of azobenzene and spirobenzopyran modified poly(methacrylic acid) and poly(2-ethylacrylic acid) were studied as a function of the isomeric state of the bound chromophores. Poly(methacrylic acid) modified with 10.4 mole% azobenzene units (PMAZ) and poly(2-ethylacryIic acid) modified with 4 mole% azobenzene units (PEAZ) were prepared by free radical polymerization of the corresponding acrylic acid with N-4-(phenylazo)phenyl methacrylamide. Poly(methacrylic acid) modified with 1.5 mole% spirobenzopyran units (PMSP) and poly(2-ethyIacryIic acid) modified with 5.2 mole% spirobenzopyran (PESP) units were prepared by first incorporating pendant nitrosalicylaldehyde units into the polymer with subsequent conversion to the spirobenzopyran units. Each of these polymers undergoes a transition from a collapsed coil to an expanded chain and this transition is unaffected by the conformation of the pendant chromophore. The ability of these polymers to associate with phosphatidylcholine bilayer membranes is dependent upon the nature of the chromophore. With PMAZ and PEAZ a greater extent of polymer-lipid association was detected when the azobenzene was in the trans conformation as compared to the cis azobenzene conformation. For PMSP and PESP greater association was detected when the chromophore was in the spiropyran conformation as compared to the merocyanine form. Larger extents of association were observed as broadening of the vesicle phase transition. The change in polymer-lipid association is attributed to the difference in polarity of the two forms of the chromophores. The permeability of the membranes could be sensitized to light only in the presence of PEAZ and PESP. With PEAZ the permeability of the membranes could be reversibly photomodulated