Cyclic voltammetric studies with gold wire electrodes covered with lipoyl gamma-cyclodextrins: positional isomerism effect of the modified cyclodextrins on monolayer quality and electrochemical responses on soluble probes
I. Suzuki et al., Cyclic voltammetric studies with gold wire electrodes covered with lipoyl gamma-cyclodextrins: positional isomerism effect of the modified cyclodextrins on monolayer quality and electrochemical responses on soluble probes, MAT SCI E C, 17(1-2), 2001, pp. 143-148
Four positional isomers of gamma -cyclodextrins (gamma -CyD) having two lip
oyl residues were prepared for investigating the effect of the positional i
somerism of the lipoyl residues on the quality of the resulting monolayers
deposited on gold wire electrodes. Charges associated with reductive desorp
tion of lipoyl residues from the gold surface revealed that the 6(A),6(E)-i
somer (4) formed a nearly defect-free monolayer from its 1 mM solution, whe
reas the 6(A),6(C)-, 6(A) 6(D) -isomers (2 and 3, respectively) covered 86%
and 89%, respectively, of the gold surface, and 6(A),6(B)-isomer (1) cover
ed only 60% of the gold surface. The cyclic voltammetric responses of Fe(CN
)(6)(3-) on the 1-4-modified electrodes was partly blocked by the 1-4 monol
ayers, and the largest inhibition was achieved by 1 monolayer. The cyclic v
oltammetric responses of ferrocenecarboxylic acid (FCA) was slightly affect
ed by the presence of 1-4 monolayers. Ursodeoxycholic acid, which is an exc
ellent guest for gamma -CyD, reduced the anodic current of FCA at the 1-4-m
odified electrodes, and the degree in the reduction caused by the monolayer
s was in the order of 4 > 3 > 2 = 1. This order indicated that the cavity o
f 4 was the most active ones to bind a guest in a solution phase, while the
cavities of 1 and 2 was less active. These results indicate that in monola
yer film, the positional isomerism of disubstituted-CyDs actually influence
d the electrode responses. (C) 2001 Elsevier Science B.V. All rights reserv
ed.