Electrochemical behaviour of natural and biosynthetic polynucleotides at the mercury electrode

By a new potentiostatic double step-sweep method conveniently applicable with common commercial polarographic equipment the adsorption and interfacial behaviour of DNA of different origin and of related biosynthetic polynucleotides has been studied in moderately acid solution (pH 5.6) of different ionic strengths over the whole extended potential range of adsorption up to −1.6 V (SCE) at the HMDE. Furthermore the new method has proved to be an efficient tool to follow the kinetics of the reduction of strongly adsorbed substances to as well strongly adsorbed reduction products. Three potential ranges corresponding to different interfacial situations can be distinguished for the investigated polynucleotides. In the first range between −0.4 and − 1.2 V (SCE) the biopolymer is adsorbed. If the biopolymer has initially a double stranded form progressive irreversible deconformation occurs as well in this potential range furnishing further evidence for the previously developed concept of the sequence of interfacial events. In the second range between −1.2 and −1.6 V biopolymers are adsorbed and (in the double stranded case after prior deconformation) the adenine and cytosine moieties undergo a totally irreversible reduction forming according to the nature of the polynucleotide a more or less completely blocking film of strongly adsorbed reduced biopolymer. In the third range beyond −1.6 V no adsorption and thus reduction occurs. The kinetic parameters k ct and α c n a of the rate determining step of the charge transfer reaction in which the adsorbed biopolymer is reduced have been studied as function of the nature and structure of the polynucleotide, of its base composition and of ionic strength In general the measurements improve significantly the understanding of the complicated behaviour of DNA and related biosynthetic polynucleotides at charged interfaces and confirm in various ways our previous resulis and conclusions.