Direct analysis of polyols using 3-nitrophenylboronic acid in capillary electrophoresis: thermodynamic and electrokinetic principles of molecular recognition |
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Authors: | Fan Fei Philip Britz-McKibbin |
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Institution: | (1) Department of Chemistry and Chemical Biology, McMaster University, Hamilton, ON, L8S 4M1, Canada; |
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Abstract: | The design of boronic acid sensors for photometric detection of carbohydrates has relied on exploiting differences in the
thermodynamic stability of complex formation for molecular recognition. Herein, we introduce a direct method for analysis
of sugar alcohols using 3-nitrophenylboronic acid (NPBA) as an electrokinetic probe in capillary electrophoresis (CE). Dynamic
complexation of neutral polyols by NPBA during electromigration allows for their simultaneous resolution and UV detection
based on formation of an anionic ternary boronate ester complex in phosphate buffer. Unlike conventional boronic acid sensors,
thermodynamic and electrokinetic processes in CE allow for improved selectivity for the resolution of sugar alcohol stereoisomers
having different vicinal polyol chain lengths even in cases when binding affinity is similar due to differences in their complex
mobility. Three complementary approaches were investigated to compare the thermodynamics of polyol chelation with NPBA, namely
direct binding assays by CE, UV absorbance spectroscopy and an indirect pK
a depression method. Overall, CE offers a convenient platform for characterization of reversible arylboronic acid interactions
in free solution while allowing for direct analysis of complex mixtures of neutral/UV-transparent polyols without complicated
sample handling. |
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