ASSESSING THE ROLE OF INTERFACIAL ELECTROSTATICS IN ORIENTED MINERAL NUCLEATION AT CHARGED ORGANIC MONOLAYERS

Charged organic-aqueous interface electrostatics are assessed in order to clarify potential electrostatic contributions to oriented mineral nucleation at planar organic surfaces. Fatty acid and acidic phospholi pid monolayers contacting aqueous solutions of sparingly soluble salts serve as model systems. Monolayer electrostatic parameters and ion di stributions in the interfacial aqueous solution are calculated using a Gouy-Chapman-Stern electric double-layer model that incorporates the multiple, multivalent cations and anions found in mineralizing solutio ns. The calculations provide insight into the relationship between sur face-directed crystallization and factors such as ion binding, surface charge density, and interfacial in concentrations. Variations in crys tal nucleation, phase, and morphology observed at charged monolayers a rl: interpreted in terms of calculated departures from lattice ion sto ichiometry and pH lowering within the interfacial aqueous solution. La ttice matching is addressed in terms of Stem layer calculations of Ca2 + ion binding at carboxylic acid monolayers. Arguments are presented s uggesting that near negatively charged surfaces, soluble ionic species concentrations are enhanced relative to free anion concentrations, an d a link between interfacial anion speciation and oriented mineral nuc leation is proposed. Implications for biomineralization and template-d irected crystallization at planar surfaces are discussed.