TY - JOUR
T1 - Photo- and chemically-produced phylloquinone biradicals
T2 - EPR and ENDOR study
AU - Konovalova, Tatyana A.
AU - Kispert, Lowell D.
AU - Redding, Kevin
N1 - Funding Information:
This work was supported by the US Department of Energy through an Energy Biosciences grant (DE-FG02-00ER15097) to K.R. and a Chemical Sciences grant (DE-FG02-86ER13465) to L.K.
PY - 2004/1/30
Y1 - 2004/1/30
N2 - Phylloquinone biradical triplet species were generated by 300 nm irradiation of frozen (77 K) solutions or by treatment with AlCl3. The shape of the (Δms=1) electron paramagnetic resonance (EPR) signal of the triplet is axially symmetric (E=0) with D=19±0.5 mT for photo-induced and D=11.2±0.5 mT for chemically induced radicals. A half-field signal (Δms=2) in the region of g≈4 was detected in both cases, confirming its assignment as a triplet. An additional line arising at the center of the (Δms=1) signal with g=2.0048±0.0002 was assigned to the phylloquinone radical anion (PhQ•-). Electron nuclear double resonance (ENDOR) measurements of the triplet revealed the sign of the D parameter. For photo-generated radicals it appeared to be negative, which is the characteristic of radical dimers with well-separated partners (biradicals). Spin-spin distances of 5.3 and 6.3 Å, respectively, were estimated from the D parameter of photo-generated and chemically prepared phylloquinone biradicals.
AB - Phylloquinone biradical triplet species were generated by 300 nm irradiation of frozen (77 K) solutions or by treatment with AlCl3. The shape of the (Δms=1) electron paramagnetic resonance (EPR) signal of the triplet is axially symmetric (E=0) with D=19±0.5 mT for photo-induced and D=11.2±0.5 mT for chemically induced radicals. A half-field signal (Δms=2) in the region of g≈4 was detected in both cases, confirming its assignment as a triplet. An additional line arising at the center of the (Δms=1) signal with g=2.0048±0.0002 was assigned to the phylloquinone radical anion (PhQ•-). Electron nuclear double resonance (ENDOR) measurements of the triplet revealed the sign of the D parameter. For photo-generated radicals it appeared to be negative, which is the characteristic of radical dimers with well-separated partners (biradicals). Spin-spin distances of 5.3 and 6.3 Å, respectively, were estimated from the D parameter of photo-generated and chemically prepared phylloquinone biradicals.
KW - Biradicals
KW - Electron nuclear double resonance
KW - Electron paramagnetic resonance
KW - Electron transfer
KW - Phylloquinone
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U2 - 10.1016/j.nainr.2003.08.003
DO - 10.1016/j.nainr.2003.08.003
M3 - Article
AN - SCOPUS:0347026683
VL - 161
SP - 255
EP - 260
JO - Journal of Photochemistry and Photobiology A: Chemistry
JF - Journal of Photochemistry and Photobiology A: Chemistry
SN - 1010-6030
IS - 2-3
ER -