H. Arakawa et al., Calf-thymus DNA interaction with Cr(III)-gallate and Cr(III)-ethyl gallatestudied by FTIR spectroscopy and capillary electrophoresis, B CHEM S J, 74(6), 2001, pp. 1075-1082
Cr(VI) salts are well known to be carcinogen, and are reduced by various ce
llular components to form cross-linked Cr(III) products. Organic compounds,
such as gallic acid (GA) and ethyl gallate (EGA), reduce Cr(VI) to Cr(III)
to form Cr(III)-gallate [Cr(III)-GA] and Cr(III)-ethyl gallate [Cr(III)-EG
A] as final products. These Cr(In)-tannin complexes are DNA binders. The in
teraction of calf-thymus DNA with Cr(III)-CA and Cr(III)-EGA in aqueous sol
utions at physiological pH were studied at Cr(III)/DNA (phosphate) molar ra
tios (r) of 1:160, 1:80, 1:40, 1:20, 1:10, 1:4, and 1:2 using FTIR spectros
copy and capillary electrophoresis. An analysis by FTIR showed that at low
concentrations (r = 1/80 and 1/40), Cr(III)-GA and Cr(III)-EGA mainly bind
to the guanine N-7 atom of the G-C base pairs with minor perturbations of t
he A-T base pairs. At r > 1/20, a partial helix opening occurred with major
perturbations of the G-C and A-T base pairs. At r > 1/10, aggregation of t
he Cr(III)-tannin-DNA complexes occurred. However, no DNA conformational ch
anges were observed, and the DNA maintained the B-family structure. The bin
ding constants of the Cr(III)-GA-DNA and Cr(III)-EGA-DNA were estimated to
be 3.8 X 10(4) M-1 and 6.2 X 104 M-1, respectively, by Scatchard plots foll
owing capillary electrophoresis. These results suggest that the Cr(III)-tan
nin complexes are external DNA binders, and do not form a chelate with the
DNA(#).