Osmium Tetroxide Complexes as Versatile Tools for Structure Probing and Electrochemical Analysis of Biopolymers

Osmium tetroxide complexes with nitrogenous ligands and analogous complexes of six-valent osmium proved excellent tools for selective labeling of biopolymers (nucleic acids, proteins and polysaccharides). Reactions of these species with target moieties within the biopolymer molecules (pyrimidine nucleobases, tryptophan residues or sugar moieties) are facile at physiological conditions and are in general structure-selective, allowing their application in DNA and protein structure probing. The modification products can be detected by a variety of widely accessible analytical techniques, including biochemical (enzymatic) approaches, immunoassays, chemical DNA sequencing, spectrophotometry and electrochemistry. Particularly the electrochemical techniques are promising for utilization in biosensors and routine bioassays due to the possibility of highly sensitive and selective detection of the labeled biopolymers adducts based on distinct electrochemical properties of the introduced osmium moieties. Utilization of the osmium tags in probing DNA structural transitions, sensing of DNA hybridization, damage and DNA methylation, labeling of peptides and proteins, probing accessibility of tryptophan residues in proteins and their complexes, and labeling of sugar moieties, are reviewed.