TY - JOUR

T1 - Electron transfer

T2 - Vs. proton-coupled electron transfer as the mechanism of reaction between amino acids and triplet-excited benzophenones revealed by time-resolved CIDNP

AU - Morozova, Olga B.

AU - Panov, Mikhail S.

AU - Fishman, Natalya N.

AU - Yurkovskaya, Alexandra V.

N1 - Publisher Copyright: © 2018 the Owner Societies.

PY - 2018/8/15

Y1 - 2018/8/15

N2 - Hyperfine coupling constants (HFCCs) of the short-lived radicals of 4-carboxy, 4,4′-dicarboxy, and 3,3′,4,4′-tetracarboxy benzophenones (4-CBP, DCBP, and TCBP, respectively) formed in their photoreaction with tyrosine were obtained from analysis of geminate CIDNP spectra. These HFCCs were compared to HFCCs calculated using density functional theory. From this comparison, it was established that the CIDNP pattern of TCBP originates from contributions of three types of TCBP radical structures: the non-protonated anion radical and two anion radical structures with a protonated carboxylic group at position 3 or 4 (or 3′ or 4′). This allowed us to conclude that the mechanism of the quenching reaction is proton coupled electron transfer (PCET): electron transfer is followed by proton transfer to one of four possible positions with similar probabilities. The same CIDNP pattern and therefore the same reaction mechanism was established for histidine. For 4-CBP and DCBP, triplet quenching proceeds also via PCET, again with formation of the anion radical with a protonated carboxylic group.

AB - Hyperfine coupling constants (HFCCs) of the short-lived radicals of 4-carboxy, 4,4′-dicarboxy, and 3,3′,4,4′-tetracarboxy benzophenones (4-CBP, DCBP, and TCBP, respectively) formed in their photoreaction with tyrosine were obtained from analysis of geminate CIDNP spectra. These HFCCs were compared to HFCCs calculated using density functional theory. From this comparison, it was established that the CIDNP pattern of TCBP originates from contributions of three types of TCBP radical structures: the non-protonated anion radical and two anion radical structures with a protonated carboxylic group at position 3 or 4 (or 3′ or 4′). This allowed us to conclude that the mechanism of the quenching reaction is proton coupled electron transfer (PCET): electron transfer is followed by proton transfer to one of four possible positions with similar probabilities. The same CIDNP pattern and therefore the same reaction mechanism was established for histidine. For 4-CBP and DCBP, triplet quenching proceeds also via PCET, again with formation of the anion radical with a protonated carboxylic group.

KW - DYNAMIC NUCLEAR-POLARIZATION

KW - DENSITY-FUNCTIONAL CALCULATIONS

KW - TRYPTOPHAN-TYROSINE PEPTIDE

KW - AQUEOUS-SOLUTION

KW - PHOTO-CIDNP

KW - HISTIDINE

KW - PHOTOOXIDATION

KW - SPECTROSCOPY

KW - REDUCTION

KW - PROTEINS

UR - http://www.scopus.com/inward/record.url?scp=85051942386&partnerID=8YFLogxK

U2 - 10.1039/c8cp03591a

DO - 10.1039/c8cp03591a

M3 - Article

C2 - 30079421

AN - SCOPUS:85051942386

VL - 20

SP - 21127

EP - 21135

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 32

ER -