No abstract

Modification of nucleic acids with osmium tetroxide reagents (Os,L, such as OsO4,2,2′‐bipyridine, Os,bpy) has been applied in redox DNA labeling, in probing DNA structure as well as in studies of DNA interactions with other molecules. In natural DNA, primarily thymine residues form adducts with the Os,bpy in a structure selective manner. In this paper we introduce a new two‐step technique of DNA modification with the electroactive Os,bpy, consisting in enzymatic construction of DNA bearing butyl acrylate (BA) moieties attached to uracil at C5 or to 7‐deaza adenine at C7, followed by chemical modification of a reactive C=C double bond in the acrylate residue. We demonstrate a facile modification of the BA conjugates in both single‐ and double‐stranded (ds) DNA under conditions when modification within the nucleobase rings in ds DNA is hindered. Various DNA−Os,bpy adducts can easily be analyzed electrochemically and distinguished by different redox potentials. The two‐step procedure appears to be applicable in osmium redox labelling of ds DNA.

No abstract

A label‐free approach that takes advantage of intrinsic electrochemical activity of nucleobases has been applied to study the products of terminal deoxynucleotidyl transferase (TdT) tailing reaction. DNA homooligonucleotides A30, C30 and T30 were used as primers for the tailing reaction to which a dNTP – or a mixture of dNTPs – and TdT were added to form the tails. Electrochemical detection enabled study of the tailing reaction products created by various combinations of primers and dNTPs, with pyrolytic graphite electrode (PGE) being suitable for remarkably precise analysis of the length of tailing reaction products. Furthermore, the hanging mercury drop electrode (HMDE) was able to reveal formation of various DNA structures, such as DNA hairpins and G‐quadruplexes, which influence the behavior of DNA molecules at the negatively charged surface of HMDE. Thus, the described approach proves to be an excellent tool for studying the TdT tailing reactions and for exploring how various DNA structures affect both the tailing reactions and electrochemical behavior of DNA oligonucleotides at electrode surfaces.

The cover picture shows an illustration of a two‐step DNA modification with the electroactive OsO4 2,2’‐bipyridine complex (Os,bpy), consisting in enzymatic construction of DNA bearing butyl acrylate (BA) moieties attached to U or to 7‐deaza A, followed by chemical modification of a reactive C=C double bond in the BA residue. We demonstrate modification of the BA conjugates not only in single‐stranded, but also in double‐stranded (ds) DNA in which modification within the nucleobase rings in is hindered. Various DNA‐Os,bpy adducts can be analyzed electrochemically and distinguished by its redox potentials. For the details see the article by P. Havranová‐Vidláková et al. DOI: 10.1002/elan.201700702