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

Abstract

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

Electrochemistry of redox-active self-assembled monolayers

“…There are two ways SAM attachment can be accomplished: (1) incorporating a coordinating ligand into the monolayer that binds to the metal center or (2) forming a bond between a functional group on the monolayer surface and a functional group on a ligand of the metal center. Both approaches have been used to immobilize metalloproteins and small molecule redox centers on SAMs [17,45,127,128,157,192,236,305,312,314]. …”

“…Several groups have reported using a terminal group of the SAM as a metal binding ligand [221,312,314]. Van Ryswyk et al utilized the lability of H 2 O in [Ru(NH 3 ) 5 (H 2 O)] 2+ [314].…”

“…Van Ryswyk et al utilized the lability of H 2 O in [Ru(NH 3 ) 5 (H 2 O)] 2+ [314]. The aquo ligand was replaced by terminal pyridine functionalities in a monolayer of 11-mercaptoundecyl isonicotinamide [314]. The reaction was carried out by soaking the monolayer-coated electrodes in a solution of [Ru(NH 3 ) 5 (H 2 O)](PF 6 ) 2 in THF under argon.…”

Reactions and Reactivity in Self-Assembled Monolayers

“…Monolayers of pure ester hydrolyze extremely slowly, probably because of the blocked access to the carbonyl functional group (see Scheme 13). [121] Mixed monolayers of the isonicotinate ester and nonanethiol that have ca. 25 % of the surface covered with isonicotinate groups are, however, susceptible to hydroxidemediated hydrolysis.…”

Biosurface Organic Chemistry: Interfacial Chemical Reactions for Applications to Nanobiotechnology and Biomedical Sciences

“…In contrast, at χ = 0.25 the initial rate of the hydrolysis greatly increased to be 0.2 × 10 −3 min −1 . 5 The acceleration of reaction rates in monolayers could be achieved by either enforced juxtaposition of the reactive functional groups or favorable orientation of the reactive groups. Oliver and Kumar investigated the kinetics of the acyl transfer reaction between thioester and amine (i.e., the amide bond formation) in a monolayer at the air-water interface.…”