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 associate 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 to pH and interfacial charge. These results are correlated with Gouy-Chapman double-layer theory.