Voltammetric sensing of glycans modified by osmium(VI)ligand complexes. The influence of N-acetyl neuraminic acid

•Electro-inactive oligosaccharides produce redox peaks after Os(VI)-modification.•Sialoglycan isomers differing by a single bond can be distinguished by voltammetry.•Sialic acid content in oligosaccharides influences their voltammetric responses.•Sialo- and asialo- forms of complex glycan and glycoproteins can be discriminated. A quick and simple way of glycan analysis is combining glycans modification by sixvalent osmium complexes with nitrogenous ligands, particularly with N,N,N´,N´-tetramethylethylenediamine (Os(VI)tem) and their voltammetric analysis. Os(VI)tem-modified oligosaccharides are reduced at the mercury electrode yielding peaks I-III, representing reduction steps of Os(VI) oxocomplexes. In this work we clarified the individual reduction steps and showed analytical applications for Os(VI)tem modified glycans, including distinguishing sialoglycan regioisomer type or discriminating glycans according to the sialic acid content. Presence or absence of sialic acid was tested in complex glycans as well as in glycoproteins.