Photo- and chemically-produced phylloquinone biradicals: EPR and ENDOR study |
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| Affiliation: | 1. Department of Biotechnology, Chemistry and Pharmacy, University of Siena, 53100 Siena, Italy;2. Department of Medical Biotechnology, University of Siena, 53100, Italy;3. Magnetic Resonance Center CERM, University of Florence, 50019 Sesto Fiorentino (Fi), Italy;1. Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk, Russia;2. Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk, Russia;3. Department of Natural Sciences, National Research University – Novosibirsk State University, 630090 Novosibirsk, Russia;4. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk, Russia;5. International Tomography Center, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk, Russia;6. Institute for Inorganic Chemistry, University of Bremen, 28334 Bremen, Germany;7. Department of Physics, National Research University – Novosibirsk State University, 630090 Novosibirsk, Russia;1. Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark;2. The College of Food Science, Shenyang Agricultural University, Dongling Street No.120, Shenyang, China;1. Center for Hyperpolarization in Magnetic Resonance, Magnetic Resonance, Department of Health Technology, Technical University of Denmark, Ørsteds Plads, 2800, Kgs. Lyngby, Denmark;2. Center for Hyperpolarization in Magnetic Resonance, Electromagnetic Systems Group, Department of Electrical Engineering, Technical University of Denmark, Ørsteds Plads, 2800, Kgs. Lyngby, Denmark;1. Department of Electrical Engineering, Technical University of Denmark, Kgs. Lyngby, Denmark;2. Albeda Research, Ole Maaloes vej 3, 2200 København N, Denmark;3. GE Healthcare, Denmark |
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| Abstract: | 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. |
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