Electrochemical behaviour of biological macromolecules

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Biomacromolecules play a key role in basic life processes. The complexity of their structures and properties has up to now been a bar to a theoretical treatment of their adsorption onto electrically charged surfaces. On the other hand, research into the interactions of biomacromolecules with electrodes has brought forward much important information on the properties and conformation of these substances in solution and on electrode surfaces. In the last five years significant progress has been made in the study of the properties and structure of genetic material (DNA) using polarographic (voltammetric) methods in conjunction with mercury electrodes. By means of these methods it is possible to distinguish single-strand DNA from double-strand DNA (on the basis of differences in their adsorbability and reducibility) and to detect minor local changes in the structure of the DNA double helix. Apart from the cathodic signals previously observed, which are caused by reduction of adenine and cytosine residues, the anodic signal (using cyclic voltammetry) caused by guanine residues is useful for this purpose. The application of cyclic voltammetry in conjunction with adsorptive preconcentration of DNA has allowed an increase in the sensitivity by about two orders of magnitude, so that submicrogram amounts of DNA can now be analysed electrochemically. Osmium tetroxide and chloroacetaldehyde have been used as DNA structural probes, capable of introducing a stable electroactive marker into the polynucleotide chain. The presence of this marker in DNA can be detected with high sensitivity using electrochemical methods. Osmium-labelled DNA can be determined by means of stripping voltammetry at nanogram quantities. Thanks to the great increase in sensitivity and the application of electroactive structural probes it is now possible to use electrochemical methods in the analysis of recombinant-DNA molecules of viruses and plasmids, which play an important role in the current development of molecular biology and genetics. Osmium is a suitable electroactive marker not only for nucleic acids but also for proteins and other biomacromolecules.