Abstract
The Kd values for the SO -23 -complex with 2, 7, 9-tricarboxy-PQQ were determined from pH 5.5 to 10.5. It was found that SO -23 and not HSO3 - is the nucleophile in this reaction. The midpoint potentials (Eo’) were also measured in this pH range for this quinone. A plot of Eo’ vs. pH produced a pKa = 8.44 for the dihydroquinone. As expected, a plot of Eo’ vs. the Kd for the PQQ-sulfite complex was linear. When NH +4 , was included, the sulfite adduct rapidly formed, however, a slow appearance of an unidentified species was evident. Eo’ for tricarboxy-PQQ + NH +4 were measured. pH titrations were carried out for oxidized tricarboxy-PQQ ± NH +4 and for the dihydroquinone form of this cofactor. The resulting pKa values are compared to corresponding literature values for PQQ analogs.
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© 1989 Kluwer Academic Publishers
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McIntire, W.S. (1989). Reaction of 2, 7, 9-Tricarboxy-PQQ with Nucleophiles. In: Jongejan, J.A., Duine, J.A. (eds) PQQ and Quinoproteins. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-0957-1_34
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DOI: https://doi.org/10.1007/978-94-009-0957-1_34
Publisher Name: Springer, Dordrecht
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