Self-assembly (SA) on gold substrates of α-helical poly(γ-benzyl-L-glutamate) [(PBLG); molecular weight ∼20 000 kd] with a disulfide moiety attached at its N-terminus (PBLGSS) was investigated. The SA films were compared with control experiments using unlabeled physisorbed (PS) PBLG and Langmuir–Blodgett (LB) deposited PBLG monolayers. Characterization of the films included angle-dependent x-ray photoelectron spectroscopy, reflection–absorption Fourier transform infrared spectroscopy, ellipsometry, and contact angle measurements. For PBLGSS, a SA monolayer was formed wherein the α-helical conformation was retained and the polypeptides were preferentially bound to gold through the disulfide moiety. This terminal bond to the substrate results in a nonplanar distribution of helix axes (i.e., on average tilted up from the gold surface). This is different from the unlabeled PBLG controls, PS film and LB monolayers, wherein, respectively, less polymer was adsorbed and the helices lie in the plane of the gold substrate. Furthermore, polypeptide aggregation in the solution (e.g., in dichloromethane or 1,4-dioxane) appears to have an influence on the self-assembling behavior of these macromolecules relative to known nonaggregating solvents (N,N-dimethylformamide).

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Photolysis of the copolymeric films poly(x)[Ru(Me4bpy>~(vpy>2](PF6)2x, (1 -x)[Ru(vbpy>3](PF6)2-2~ formed by reductive electropolymerization on Pt electrodes (surface coverage = 2 x to 6 x moYcm2) results in loss of the fragment -[ -Ru(Me4bpy)~](PF6)2. For x = 0.4-0.6 electrochemical and angle-resolved X P S measurements before and after photolysis show that film thickness is unaffected by photolysis. Diffusion of ferrocene and substituted ferrocenes through the films was studied by rotated disk voltammetry, from which values for PDs.po~ were derived. Ds,pol is the diffusion coefficient of ferrocene through the film, and P is the partition coefficient within the film. Removal of -[-Ru(Me4bpy)~](PF6)2 by photolysis creates molecular sized voids and increases PDs.po~ by factors of 10-20. The photolyzed films act as size-selective membraneswith PDs,po~, decreasing by as much as 16 as the volume of the ferrocene increases from 150 to 500 A3. The diffusional properties of the films can be varied somewhat by adding substituents to the bpy rings of the leaving group or by partly filling the molecular voids by coordination to pyridyl groups released in the photolysis step.