Assembly of polyaniline nanotubes by interfacial polymerization for corrosion protection.

Polyaniline (PANI) was synthesized by the oxidation of aniline with ammonium peroxydisulfate as an oxidant in an immiscible organic/aqueous biphasic system and with decylphosphonic acid (DPA) or benzylphosphonic acid (BPA) in the aqueous phase. Nanofibers of aniline oligomers were produced using BPA in the aqueous phase while high quality polyaniline nanotubes were produced using DPA in the aqueous phase. PANI nanotubes have a outer diameter 160-240 nm, an inner diameter of 50-100 nm and a length of the order of several µm. The understanding of the formation of PANI nanotubes was examined by isolation of reaction intermediates and their ex situ characterization by atomic force microscopy. The roles of BPA and DPA on the morphology formation of the PANI nanostructures were discussed. A nanofibrillar template produced by aniline oligomers was found to guide the growth of PANI to nanotubular morphology. PANI nanotubes are thus not derived from DPA vesicles. Preliminary corrosion tests exhibit high corrosion protection efficiency of PANI nanotubes because of their high surface area and corrosion inhibitive properties of DPA dopant.

Characterization of discrete classes of binding sites of human serum albumin by application of thermodynamic principles.

The binding interactions of four ligands differing in acid-base properties with human serum albumin (HSA) were examined as a function of temperature. Binding to HSA decreased with increasing temperature for all four ligands. The bound and free ligand concentrations obtained at different temperatures were satisfactorily fitted to a model that incorporates the effect of temperature as an independent covariable and that directly allows the estimation of the enthalpic and entropic components of the ligand-albumin interaction, along with the precision of this estimation. Using this analysis, the binding of acidic ligands could be resolved into two classes of saturable sites, with the determination of the corresponding number of sites, whereas interpretation of binding data at each isolated temperature allowed only the determination of one saturable plus one non-saturable class of site. The thermodynamic constants indicate that binding of ionizable ligands to HSA involves electrostatic plus hydrophobic interactions, whereas only hydrophobic interactions are involved in binding to a second low-affinity class of site when present. Binding of non-ionizable ligands resembles that of the second class of low-affinity sites of ionizable ligands.