Hydrogenation effect of furan ring of methylene tanshinone quinone on its one-electron reduction potential

Electron transfer processes form the main feature of chemical, biochemical and particularly electrochemical reactions. Theoretical calculation is a practical model for prediction of reduction potential of irreversible reactions or those for which the experimental measuring of that index is not easy (1). The one-electron reduction potentials of methylene tanshinone quinone (A) and methylene dihydrotanshin quinone (B) have been calculated in DMSO in the present work. All structures have been optimized at the B3LYP/6-311G++(d,p) level by the Gaussian 09 program package (2). The one-electron reduction potentials of quinones are calculated as follow: 𝐸𝑁𝐻𝐸 ( 𝑄 ⁄𝑄.−)= 𝐸𝑁𝐻𝐸 ( 𝑃 − 𝐵𝑄 ⁄𝑃 − 𝐵𝑄.−) + Δ𝐺𝑆𝑜𝑙 ∗ 𝐹 (1) Where, ENHE (p-BQ/P-BQ.-) is the reduction potential of para-benzoquinone (P-BQ) in DMSO and F is the Faraday constant (3). The estimated values of reduction potential for A and B are equal to, -0.778 V and -0.836 V, respectively. In fact, hydrogenation of d ring lead to the increase in the reduction potential of quinone A.