D. Gidalevitz et al., DESIGN OF 2-DIMENSIONAL CRYSTALS AS MODELS FOR PROBING THE STRUCTURE OF THE SOLID-LIQUID INTERFACE, Journal of the American Chemical Society, 116(8), 1994, pp. 3271-3278
Crystals of beta-alanine and the alpha-form of glycine, when grown in
the presence of 3% molar CdCl2, display morphologies which are differe
nt from those obtained from pure water solution. This effect was inter
preted in terms of binding of Cd2+ and Cl- ions to the exposed CO2- an
d NH3+ moieties at the various faces, so changing their relative rates
of growth and leading to the development of new faces. The structure
of the crystal face of beta-alanine most affected by the presence of C
dCl2 was mimicked by a monolayer containing an equimolar mixture of tw
o different amphiphiles octadecylamine (C18H37NH2) and stearic acid (C
17H35COOH) Spread on aqueous solution. Binding of the Cd2+ and Cl- ion
s to such a monolayer has been investigated. X-ray specular reflectivi
ty measurements reveal that the mixed monolayer is fully bound by Cd2 and Cl- ions when their concentration reaches 0.1 M. Grazing incidenc
e X-ray diffraction measurements, using synchrotron radiation, of the
mixed monolayer on pure water and on a 0.1 M CdCl2 solution provide st
rong evidence that the monolayer CO2- and NH3+ head groups are arrange
d in ordered array and the Cd2+ and Cl- ions are bound to the monolaye
r head groups at ordered sites.