Reactivity of Ester Linkages and Pentaammineruthenium(III) at the Monolayer Assembly/Solution Interface

The rate of base-mediated ester hydrolysis in monolayers of 11-mercaptoundecyl isonicotinate on gold is monitored by infrared spectroscopy and cyclic voltammetry. The hydrolysis product, a surface-confined alcohol, can be converted to a trifluoroacetate, increasing the sensitivity of infrared monitoring. Pentaammineruthenium(II) can be attached to the pendant isonicotinate either prior to or after monolayer assembly, leading to monolayers with a highly-charged monolayer/solution interface and a built-in electrochemical probe. The rate of ester hydrolysis within the monolayer is controlled by steric factors associated with monolayer packing and by the amount of charge at the monolayer/solution interface. The stability of the pendant Ru(III) complex is very sensitive ro pH and interfacial char ge. These results are correlated with Gouy-Chapman double-layer theory.