Photochemical imprint of molecular recognition sites in two-dimensional monolayers assembled on Au electrodes: Effects of the monolayer structures on the binding affinities and association kinetics to the imprinted interfaces

Photochemical imprint of molecular recognition sites for phenoxynaphthacene quinone (1a) in two-dimensional monolayers assembled on Au surfaces is accomplished. The photochemical imprint of the molecular recognition sites involves several steps: The primary step includes the assembly of the trans-phenoxynaphthacene quinone monolayer (2a), followed by the rigidification of the monolayer with long-chain alkanethiols that generates a densely packed quinone monolayer. The second process involves the photoisomerization of the monolayer to the ana-quinone state (2b), followed by the nucleophilic displacement of the quinone with butylamine. The association of la to the imprinted sites and the dissociation of the host substrate from the sites are followed by electrochemical means as well as by microgravimetric quartz-crystal-microbalance measurements. The binding of la to the imprinted recognition sites reveals selectivity, and structurally related substrates do not associate to the imprinted sites. The kinetics of association of la to the imprinted sites and of the dissociation of la from the sites is affected by the length of the rigidifying alkanethiols. As the alkanethiol is longer, the association of la to the sites and the dissociation of la from the recognition sites is slower. The slower association of la to perforated monolayers with a long-chain alkanethiol (C₁₈H₃₇SH) is attributed to the blocking of the imprinted sites by the flexible alkanethiol chains. The retardation of the dissociation of la from the imprinted sites rigidified by the long-chain alkanethiols is attributed to the capping of the substrate by the long-chain thiols. The selectivity of the imprinted recognition sites is attributed to a structural fit of la to the imprinted hydrophobic contour and the synergetic stabilization of la in the site by complementary H-bonds.