In this work, we characterize a previously synthesized multi-cationic aminopyrene-based labeling tag for oligosaccharide analysis by capillary electrophoresis with laser-induced fluorescence detection (CE/LIF). The fluorescent tag, 4,4',4''-(8-aminopyrene-1,3,6-trisulfonyl)tris(1-methylpiperazine) (APTMP), was characterized by reaction with standard maltooligosaccharides and the labeling parameters such as fluorescent tag concentration, labeling temperature, and time as well as influence of a reducing agent and its solvent were investigated in terms of labeling efficiency. The nanomolar limit of detection of CE/LIF analysis of APTMP labeled maltopentaose was determined. However, significant amount of the oligosaccharides was reduced to alditols, which negatively affects the yield and rate of the labeling reaction. Under optimized conditions, a highly reproducible labeling by multi-cationic APTMP was obtained; however, the most commonly used labeling by multi-anionic 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt (APTS) is superior compared to APTMP labeling. Lower reactivity of APTMP compared to APTS can be explained by the loss of nucleophilicity induced by substitution of the sulfonate groups with more electron-withdrawing aminosulfonyl ones. On contrary, APTMP is still a promising tag for oligosaccharide labeling followed by CE-MS in a positive ion mode, which is considered to be more sensitive than MS detection of APTS in a negative ion mode.
Keywords: Capillary electrophoresis; Fluorescence; Labeling; Oligosaccharides; Reductive amination.
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