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Reversible Electrocatalytic NAD+/NADH Interconversion Mediated by a Pyrazine-Amidate Iridium Complex.

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A new iridium catalyst, [Cp*Ir(pyza)Cl], enables efficient and reversible electrocatalytic conversion between NAD+ and NADH. This catalyst operates at a low overpotential, mimicking the natural redox potential for NAD+/NADH interconversion.

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Area of Science:

  • Organometallic Chemistry
  • Electrocatalysis
  • Biomimetic Chemistry

Background:

  • Nicotinamide adenine dinucleotide (NAD+/NADH) is a crucial redox cofactor in biological systems.
  • Efficient electrocatalytic systems for NAD+/NADH interconversion are vital for bio-inspired energy storage and chemical synthesis.
  • Existing electrocatalysts often suffer from high overpotentials, limiting their practical applications.

Purpose of the Study:

  • To design and synthesize a novel iridium complex, [Cp*Ir(pyza)Cl], for efficient electrocatalytic NAD+/NADH interconversion.
  • To investigate the electrochemical properties and catalytic activity of the new complex.
  • To compare its performance with existing catalysts and assess the reversibility of the NAD+/NADH redox couple.

Main Methods:

  • Rational catalyst design based on ligand electronic properties (pyrazine amidate vs. picolinamidate).
  • Electrochemical characterization including cyclic voltammetry to determine reduction potentials and catalytic activity.
  • Nuclear Magnetic Resonance (NMR) spectroscopy, specifically 1H EXSY NMR, to confirm reaction reversibility and equilibrium.

Main Results:

  • The synthesized complex [Cp*Ir(pyza)Cl] exhibits significantly lower overpotential for NAD+ reduction (-0.29 V) compared to a related complex (-0.65 V).
  • The catalyst operates close to the equilibrium potential of the NAD+/NADH redox couple (E°eq = -0.32 V).
  • Reversible electrocatalytic cycling of NAD+ to NADH and NADH to NAD+ was demonstrated, with a catalytic bias towards reduction.
  • 1H EXSY NMR confirmed rapid equilibrium of the catalyst-hydride and NADH species, indicating similar hydridicity.

Conclusions:

  • [Cp*Ir(pyza)Cl] is a highly effective electrocatalyst for reversible NAD+/NADH interconversion.
  • The catalyst's performance is attributed to the electronic properties of the pyrazine amidate ligand, facilitating bielectronic reduction.
  • This work provides a promising platform for developing artificial systems that mimic biological redox processes.