Electrochemistry for probing DNA interactions

Chemical modification of DNA bases is called mutagenesis. Mutations are caused by substitutions, deletions and insertions in the base sequence of DNA [97]. Exposure to toxic chemicals is the cause of many human cancers these chemical carcinogens act by chemically damaging the DNA. Thus it is important to identify these compounds and ascertain their potency so that human exposure to them can be minimized. 

Electrochemical methods [85] have shown great potential for studying the adsorption and reactions of biological molecules at electrified interfaces. They have been used by a number of researchers studying metal ion-DNA interactions [98]. 

Studies of metallointercalation agents [99-101] in the presence of dsDNA have been done with solutions containing the redox complexes 

Co(phen) +/2+, Fe(phen)r/3+. Co(bpy) +/2+, Fe(bpy r/3+ and Os(bpy)2+/3+ (where phen = 1,10-phenanthroline and bpy = 2,2 -bipyri-dyl). The binding was interpreted in terms of the interplay of electrostatic interactions of the metal coordination complexes with the charged sugar-phosphate backbone and the intercalative, hydrophobic, interactions within the DNA helix, i.e., the stacked base-pairs. Chronopotentiometric detection of the Co(bpy)3+ indicator was used [102] to monitor the hybridization onto a screen-printed carbon electrode of short DNA sequences from E. coli pathogen in environmental water samples. The couple Co(bpy) 5+/2+ was also used to evaluate the adsorption of DNA on gold electrodes [103-104]. 

A doubly metallated 15 base-pair double helix containing ruthenium and rhodium at each end of the strands [106] showed the efficiency of DNA for coupling electron donors and acceptors over a very long range, greater than 40 A. The DNA double helix was found to behave like a piece of molecular wire with fast electron-transfer rates ( 1010 s l) for the photoinduced electron transfer between the metallointercalators [107-109] and semiempirical Hartree-Fock calculations of HAB for DNA mediated electron transfer [110] were described. 

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