Interaction of the Imidazole Ring with Surface Anchored Polypyrrole Latex Particles

Sterically stabilized polypyrrole latex particles attached to Au substrates were observed to adsorb imidazole and histidine from aqueous solutions by ellipsometry. In initial studies the imidazole ring adsorption was mainly irreversible, but after electrochemical reduction-oxidation cycling of the particles in HCl solution only reversible adsorption of the heterocyclic compounds was observed. Adsorption experiments on control surfaces containing the different components of the latex particles identified iron species incorporated during synthesis as the probable irreversible adsorption sites. The reversible adsorption sites were possibly due to the acidic properties of the polypyrrole core in the particles. Copyright 1998 Academic Press. Copyright 1998Academic Press

A Physicochemical Study of Polypyrrole-Silica Nanocomposites by Inverse Gas Chromatography

Three polypyrrole-silica nanocomposites were characterized by inverse gas chromatography (IGC) at 60 and 80degreesC using both linear and branched alkane probes. The IGC data for these materials were compared with those obtained for the ultrafine silica sol and polypyrrole (PPy) bulk powder reference materials. The London components of the surface energies (gammasd) of the nanocomposites were in the range 115-225 mJ m-2 at 60degreesC. These values are much higher than those obtained for either the polypyrrole powders or the colloidal silica sol, which suggests that the nanocomposites have significant microporosity. The gammasd values for the nanocomposites decrease in the order chloride-doped PPy > sulfate-doped PPy > tosylate-doped PPy, which is the same trend as that found for the heat of adsorption (DeltaHa) of a given n-alkane. DeltaHa values of the linear and branched alkanes are up to three times higher than the heats of vaporization, which confirms that the nanocomposites (and, to a lesser extent, the polypyrrole powders) have high adsorption capacities for these solutes. For a series of alkane isomers (e.g., C7H16 or C8H18), the difference between the DeltaHa values for the nanocomposites and the corresponding polypyrrole powders decreased as the degree of branching for these probes was increased. These observations suggest that the more sterically hindered probes are excluded from the microporous interior of the nanocomposites. Copyright 1997 Academic Press. Copyright 1997Academic Press

Adsorption of DNA onto Polypyrrole-Silica Nanocomposites

DNA adsorption onto polypyrrole (PPy) powder, a colloidal silica sol, and three polypyrrole-silica nanocomposite particles (untreated and amine- or carboxylic acid-functionalized) was investigated at neutral pH using sodium phosphate buffer. The extent of DNA adsorption was found to be 32 and 22 mg/g for the aminated silica sol and aminated PPy-silica particles respectively, and 6.5 mg/g for the carboxylated particles. DNA adsorption onto the unfunctionalized PPy-silica particles occurs to a lesser extent, whereas no adsorption was detected for the colloidal silica sol. Our results suggest that DNA adsorption is mainly governed by electrostatic and hydrophobic interactions. DNA is adsorbed onto polypyrrole chloride bulk powder and also onto the aminated PPy-silica particles, which both have cationic binding sites. The silica sol and the unfunctionalized PPy-silica particles both possess a net negative surface charge at this pH, which probably accounts for the zero or very low adsorbed amounts of DNA on these substrates. DNA adsorption onto the carboxylated PPy-silica particles may be enhanced by hydrogen bonding relative to the unfunctionalized polypyrrole-silica particles.