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

Abstract

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.

Vicinal Diol‐Tethered Nucleobases as Targets for DNA Redox Labeling with Osmate Complexes

“…Then, the samples of dihydroxy‐modified DNA ( DNA_4C X and DNA_4A X ) were analyzed by means of ex situ square‐wave voltammetry (AdTS SWV) at a basal plane pyrolytic graphite electrode (PGE; Figure ). The osmylated DNA yielded two SWV signals within the potential range between −1.0 and 0.0 V versus Ag/AgCl/3 m KCl reference electrode: one close to −0.8 V and the other around −0.3 V (in agreement with previous observations with natural or butylacrylate‐decorated nucleic acids modified with OsO 4 complexes and biomolecules modified with Os VI on sugar residues).…”

Electrocatalysis in proteins, nucleic acids and carbohydrates

“…Similarly as in NAs, the osmium adducts of proteins98 and peptides97a can be detected electrochemically at mercury97a and carbon electrodes 98. More details about the electrochemistry of NA and protein adducts with Os(VIII)L complexes can be found in a recent review 99…”

Butylacrylate‐nucleobase Conjugates as Targets for Two‐step Redox Labeling of DNA with an Osmium Tetroxide Complex

“…Analogous adducts are formed via condensation reactions of the cis‐1,2 diols with osmate in the presence of the above mentioned ligands . Due to the presence of the osmium atom, the adducts exhibit well‐pronounced electrochemical and electrocatalytic activity . Both reactions have thus been utilized to introduce electroactive labels into biomacromolecules containing natural target moieties, such as pyrimidine nucleobases in nucleic acids (NA) or sugar residues at the 3′‐OH terminus of RNA, in polysaccharides and glycoproteins .…”

“…Among the natural NA components, pyrimidine nucleobases exhibit reactivity towards the osmium tetroxide reagents (Os,L, such as Os,bpy) while purines are practically unreactive. The C5=C6 double bond in the pyrimidine ring is most readily modified with Os,L in thymine, followed by uracil and 5‐methyl cytosine . Cytosine reacts with Os,L rather slowly which was utilized for selective labeling of thymine residues simply via optimization of reaction conditions .…”