Precipitation within unilamellar vesicles. Part 1. Studies of silver(I) oxide formation

Abstract

The precipitation of small (ca. 10 nm) Ag₂O crystallites within unilamellar vesicles has been studied by electron microscopy and light scattering. Many single-domain intravesicular crystallites have been observed by high-resolution imaging, indicating that crystallisation often initiates at a single site on the inner membrane surface followed by slow crystal growth. Under certain experimental conditions no nucleation has been observed below an extravesicular pH (pH_out) of ca. 11.0 due to negligible diffusion of OH^– across the membrane. Above a pH_out of 11.0 the rate of precipitation has been found to be dependent on the rate of crystal growth. Semi-quantitative experiments have shown that the kinetics are first order with respect to intravesicular silver(I) concentration and first order with respect to extravesicular OH^– concentration between a pH_out of 11.0 and 12.0. The general possibility of control of precipitation by a vesicle membrane is discussed.