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Published on: November 26, 2014
Accurate standard hydrogen electrode potential and applications to the redox potentials of vitamin C and NAD/NADH
Toru Matsui1, Yasutaka Kitagawa, Mitsutaka Okumura
1Department of Chemistry, Graduate School of Science, Osaka University , 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
Abstract:
We computationally evaluated the standard hydrogen electrode (SHE) potential in aqueous phase and the Gibbs energy of a proton from the experimental pKa values of alcohol molecules. From the "golden standard" CCSD(T)/aug-cc-pVTZ level calculation, we estimated the SHE potential as 4.48 V, which is very close to the IUPAC-recommended experimental value of 4.44 V. As applications to the Gaussian-3 (G3) methods, which also reproduce the "golden standard" level calculations, we computed various pKa values and redox potentials for a vitamin series. For vitamin C, we support the experimental result of +0.35 V and predict the pKa value of d-ascorbic acid to be 3.7-3.9. Using a model molecule for nicotinamide adenine dinucleotide (NAD), we reproduced the redox potential and determined the order of the proton/electron addition, based on both the proton affinity and redox potential.
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