Characterization of free radicals from vitamin K1 and menadione by 2 mm-band EPR, ENDOR and ESEEM

Abstract

The anion and cation radicals of vitamin K 1 and its analog menadione were characterized using the magnetic resonance techniques of Electron Nuclear Double Resonance (ENDOR), Electron Spin Echo Envelope Modulation (ESEEM), and Electron Paramagnetic Resonance (EPR) at X-band and 2 mm-band. The g-factor anisotropy of the radicals at 2 mmband allow them to be distinguished from each other in the solid state. The g-factor matrix of the radical anion of vitamin K~ is virtually identicat with that reported for the reduced A~ acceptor in green plant photosystem I thus demonstrating that reduced A~ is the anion radical of vitamin K 1.

ENDOR and ESEEM studies of ion radicals of artificial dimethoxy- or halogen-1,4-benzoquinones with an alkyl side chain of differing length

“…Values of the isotropic hfi constant obtained in ref. 19 and in this work (see below and Table 3) indicate that the hydroxy group is very close to the nodal plane in frozen solution also.…”

“…As in ref. 19 we assign these additional lines to deuterons of the -OD groups of the respective quinones. Quinone oxygens are expected to be bonded to deuterons (hydrogens) when prepared in strongly acidic solvents.…”

Pulse ENDOR studies on the radical pair P 700 +· A 1 ·− and the photoaccumulated quinone acceptor A 1 ·− of photosystem I

“…Our data for VK i-in alkaline 2-propanol are in agreement with data of ref. 47 and previous measurements [44,48] in ethanol but deviate from the data given for VK~-in n-butanol [49]. The reasons for the differing results in reŸ 49 are not clear at present.…”

Radicals and Radical Pairs in Photosynthesis

“…Ultraviolet irradiation experiments that supposedly selectively destroyed the phylloquinone could not stop ET and the formation of AT (274,275). Very decisive evidence for the assignment of vitamin K, (phylloquinone) to the acceptor A, came from the comparison of the g-tensor of A, measured in Q-band (276) with that of the vitamin K, anion in vitro measured by 2 mm-band EPR (277) 88). Another interesting result was indicated in the paper by Heathcote et al (188): In PS I samples, prepared at pH 10, photoaccumulation at 230 K may yield two A, and two A, singly reduced acceptors per oxidized PToo rather than one of each.…”

“…Ultraviolet irradiation experiments that supposedly selectively destroyed the phylloquinone could not stop ET and the formation of AT (274,275). Very decisive evidence for the assignment of vitamin K, (phylloquinone) to the acceptor A, came from the comparison of the g-tensor of A, measured in Q-band (276) with that of the vitamin K, anion in vitro measured by 2 mm-band EPR (277). For further review of this controversy, see Evans and coworkers and Golbeck (5,144,148).…”