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

Photochemical imprint of molecular recognition sites for phenoxynaphthacene quinone (la) in two-dimensional monolayers assembled on Au surfaces is acc omplished. The photochemical imprint of the molecular recognition sites inv olves several steps: The primary step includes the assembly of the trans-ph enoxynaphthacene 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 th e monolayer to the ana-quinone state (2b), followed by the nucleophilic dis placement of the quinone with butylamine. The association of la to the impr inted sites and the dissociation of the host substrate from the sites are f ollowed by electrochemical means as well as by microgravimetric quartz-crys tal-microbalance measurements. The binding of la to the imprinted recogniti on sites reveals selectivity, and structurally related substrates do not as sociate to the imprinted sites. The kinetics of association of 1a to the im printed sites and of the dissociation of la from the sites is affected by t he length of the rigidifying alkanethiols. As the alkanethiol is longer, th e association of la to the sites and the dissociation of la from the recogn ition sites is slower. The slower association of 1a to perforated monolayer s 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-cha in alkanethiols is attributed to the capping of the substrate by the long-c hain thiols. The selectivity of the imprinted recognition sites is attribut ed to a structural fit of la to the imprinted hydrophobic contour and the s ynergetic stabilization of la in the site by complementary H-bonds.