Electrochemical characteristics of viologen carboxylic acid derivatives assembled onto Au electrode as a synthetic receptor for electron-rich compounds

Electrochemical characterization in monolayer assemblies formed by covalent linkage of synthesized 1,1 '-[1,4-phenylenebis(methylene)]bis(2-carboxyeth yl)-4,4 ' -bipyridium (PBB) to cystamine, chemisorbed onto gold electrodes, were examined. The surface coverage of PBB corresponded to r = 2.4 x 10(-1 0) mol cm(-2). The equilibrium binding constants of charge-transfer complex es formed by the receptor, resulting in a redox-active monolayer surface wi th five aromatic compounds (tiron, hydroquinone sulfonic acid, and three ki nds of ferrocene derivative) and sodium hexachloroiridate (III), were measu red in aqueous media using the differential pulse voltammetric method. The values obtained from tiron were K-o = 330 000 M-1 of PBB4+ -modified electr ode and K-r= 4200 M-1 of PBB2+-modified electrode. Furthermore K-o values o f the three kinds of ferrocene derivative were increased in order of negati ve charge number. The coulomb force between host and guest was influenced b y host-guest interaction. On the other hand, the value obtained from monoca tionic (ferrocenylmethyl) trimethylammonium ion repulsed positively charged PBB-modifed electrode was K-r/K-o = 0.019. The reduction of tetracationic PBB to dicationic one decreased the pi -acceptor character of the receptor PBB-modified electrode. (C) 2001 Elsevier Science Ltd. All rights reserved.