Effect of surface coverage of gold(111) electrode with cysteine on the chiral discrimination of DOPA

Abstract

The enantioselectivity imparted to a gold electrode by modifying its surface with a self-assembled monolayer (SAM) of cysteine (Cys) was investigated for the electrochemical redox reaction of 3,4-dihydroxyphenylalanine (DOPA). A cyclic voltammetric study of the redox reaction revealed that the enantioselectivity was determined by the surface coverage of the gold electrode with Cys molecules. The electrode modified with approximately 1.8 x 10(14) Cys molecules cm(-2) exhibited enantioselectivity in the voltammogram for the oxidation and reduction of DOPA, while the voltammograms obtained by the electrodes with either more or less surface coverages did not exhibit significant enantioselectivity. It is suggested that the accessibility of DOPA to that area of the gold surface which is not blocked by Cys molecules at an optimum surface coverage, is required for the enantioselective redox reaction of DOPA to proceed.

Mesoporous Encapsulated Chiral Nanogold for Use in Enantioselective Reactions

“…Cysteine (Cys) was chosen as the ligand to realize the chiral selectivity toward the DOPA enantiomers since Cys has been found in the active site of the natural enzymes which recognizes l ‐DOPA, and the interaction between l ‐DOPA and d ‐DOPA with Cys has been also applied to the recognition of DOPA enantiomers . Gold nanoparticles (AuNPs) with peroxidase activity are then applied as active sites in the nanocatalyst because Cys can easily self‐assemble on the surface of AuNPs to obtain Cys‐capped AuNPs ,. The expanded mesoporous silica (EMSN) is chosen as the skeleton for AuNPs, which can hinder the aggregation of neighboring particles and allow the diffusion of substrate and product molecules in and out of the nanozyme .…”

Effect of pH on the Enantiospecificity of Homocysteine Monolayer on Au(111) for the Redox Reaction of 3,4‐Dihydroxyphenylalanine

“…Gold electrodes with predominantly (111)-oriented surfaces with terraces measuring larger than 200 nm were prepared by vapor deposition using the same procedure as described in the previous paper [21]. After flame annealing, the gold electrode was immersed in a 0.5 M ethanolic solution of l-homocystine (HOOC(H 2 N)CHCH 2 CH 2 S-SCH 2 CH 2 CH(NH 2 )COOH), or the disulfide compound of l-Hcy for 24 h. The number of Hcy molecules on the gold surface was calculated to be 1.8 Â 10 14 molecules cm À2 from the electrical charge associated with the reductive desorption of Hcy from the gold electrode, which was determined by linear sweep voltammetry (LSV).…”

“…Especially, the current between the probe molecule and the electrode varies exponentially with the distance between them [22]. Actually, the enantiospecificity of Au electrode modified with SAMs of Cys and Hcy with a proper surface coverage was observed for the redox reaction of 3,4-dihydroxyphenylalanine (DOPA)/dopaquinone couple by cyclic voltammetry with a high sensitivity [14,21], and those studies showed the importance of the structure of SAM.…”

Expression of chirality in molecular layers at surfaces: insights from modelling

“…Roberto Lazzaroni enantioselective catalysis (the specific formation of one enantiomer), 3 chiral sensing (the specific detection of one enantiomer), 4 enantiomer resolution (the separation of enantiomers) 5 and non-linear optical materials (as the even-order non-linear optical responses require a noncentrosymmetric medium). 6 Nevertheless, research on chiral surfaces has developed only recently, mostly because of the difficulty in probing chirality at a surface.…”