Mj. Lochhead et al., ASSESSING THE ROLE OF INTERFACIAL ELECTROSTATICS IN ORIENTED MINERAL NUCLEATION AT CHARGED ORGANIC MONOLAYERS, JOURNAL OF PHYSICAL CHEMISTRY B, 101(50), 1997, pp. 10821-10827
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.