Photo- and chemically-produced phylloquinone biradicals: EPR and ENDOR study

Tatyana A. Konovalova; Lowell D. Kispert; Kevin Redding

doi:10.1016/j.nainr.2003.08.003

Photo- and chemically-produced phylloquinone biradicals: EPR and ENDOR study

Tatyana A. Konovalova, Lowell D. Kispert, Kevin Redding

Research output: Contribution to journal › Article › peer-review

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 (Δm_s=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 (Δm_s=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 (Δm_s=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.

Original language	English (US)
Pages (from-to)	255-260
Number of pages	6
Journal	Journal of Photochemistry and Photobiology A: Chemistry
Volume	161
Issue number	2-3
DOIs	https://doi.org/10.1016/j.nainr.2003.08.003
State	Published - Jan 30 2004
Externally published	Yes

Keywords

Biradicals
Electron nuclear double resonance
Electron paramagnetic resonance
Electron transfer
Phylloquinone

ASJC Scopus subject areas

Chemistry(all)
Chemical Engineering(all)
Physics and Astronomy(all)

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@article{ced0eec80f114dfd86689b9a5e82ec45,

title = "Photo- and chemically-produced phylloquinone biradicals: EPR and ENDOR study",

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 {\AA}, respectively, were estimated from the D parameter of photo-generated and chemically prepared phylloquinone biradicals.",

keywords = "Biradicals, Electron nuclear double resonance, Electron paramagnetic resonance, Electron transfer, Phylloquinone",

author = "Konovalova, {Tatyana A.} and Kispert, {Lowell D.} and Kevin Redding",

year = "2004",

month = jan,

day = "30",

doi = "10.1016/j.nainr.2003.08.003",

language = "English (US)",

volume = "161",

pages = "255--260",

journal = "Journal of Photochemistry and Photobiology A: Chemistry",

issn = "1010-6030",

publisher = "Elsevier",

number = "2-3",

}

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

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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