Although there is a huge interest in redox mediators for the selective electrochemical regeneration of 1,4-NADH, only the class of rhodium compounds with bipyridine ligands, initially introduced by the pioneering work of Wienkamp and Steckhan (Wienkamp, R.; Steckhan, E. Angew. Chem. Int. Ed. Engl. 1982, 21, 782-783, 10.1002/anie.198207822), has been developed over the last few decades. Here we report the first two progenitors of a class of redox mediators for indirect NADH regeneration, namely [Cp*Ir(R '-pica)Cl] {pica = R '-picolinamidate = kappa(2)-R '-pyridine-2-carboxamide ion (-1), 1 R ' = H and 2 R ' = Me}, which exhibit high TOF values (0.51 and 1.34 s(-1) for 1 and 2, respectively), a production rate of up to 3 mu mol h(-1) cm(-2), and a faradaic efficiency of up to 99% for both complexes in 0.1 M phosphate buffer (pH 7, 298 K). The reaction exclusively leads to a mixture of 1,4-NADH, the desired product, and 1,6-NADH always in a 91:9 molar ratio, independently of the redox mediator, degree of conversion, and applied potential. H-1 EXSY NMR unequivocally shows that a rapid equilibrium establishes between 1,6-NADH and 1,4-NADH (K-eq = 10.1, Delta G(0) = -1.4 kcal mol(-1), 298 K), in the presence of 1 and 2, suggesting that the latter are capable of rapidly interconverting the two regioisomers of NADH, thus allowing utilization of the totality of regenerated NADH.

Electrochemical NADH Regeneration Mediated by Pyridine Amidate Iridium Complexes Interconverting 1,4- and 1,6-NADH

Trotta, Caterina;Menendez Rodriguez, Gabriel
;
Zuccaccia, Cristiano;Macchioni, Alceo
2024

Abstract

Although there is a huge interest in redox mediators for the selective electrochemical regeneration of 1,4-NADH, only the class of rhodium compounds with bipyridine ligands, initially introduced by the pioneering work of Wienkamp and Steckhan (Wienkamp, R.; Steckhan, E. Angew. Chem. Int. Ed. Engl. 1982, 21, 782-783, 10.1002/anie.198207822), has been developed over the last few decades. Here we report the first two progenitors of a class of redox mediators for indirect NADH regeneration, namely [Cp*Ir(R '-pica)Cl] {pica = R '-picolinamidate = kappa(2)-R '-pyridine-2-carboxamide ion (-1), 1 R ' = H and 2 R ' = Me}, which exhibit high TOF values (0.51 and 1.34 s(-1) for 1 and 2, respectively), a production rate of up to 3 mu mol h(-1) cm(-2), and a faradaic efficiency of up to 99% for both complexes in 0.1 M phosphate buffer (pH 7, 298 K). The reaction exclusively leads to a mixture of 1,4-NADH, the desired product, and 1,6-NADH always in a 91:9 molar ratio, independently of the redox mediator, degree of conversion, and applied potential. H-1 EXSY NMR unequivocally shows that a rapid equilibrium establishes between 1,6-NADH and 1,4-NADH (K-eq = 10.1, Delta G(0) = -1.4 kcal mol(-1), 298 K), in the presence of 1 and 2, suggesting that the latter are capable of rapidly interconverting the two regioisomers of NADH, thus allowing utilization of the totality of regenerated NADH.
2024
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/1586779
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