EPR spectra of V(V) and Zr(IV) complexes with the HO2 radical

Shuvalov, V. F.; Bazhin, N. M.; Berdnikov, V. M.; Merkulov, A. P.; Fedorov, V.K.

doi:10.1007/bf00746747

Cited by 6 publications

(8 citation statements)

References 3 publications

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“…However, in green plant and algal preparations, only low-intensity EPR triplet signals, which most likely originate outside the reaction center, have been reported, and no unambiguous assignment of a triplet state to the primary photoreactions has been made (4)(5)(6)(7)(8)(9). A component of delayed luminescence observed optically by Shuvalov et al (10,11) was attributed to triplet formation dependent upon the redox state of the reaction center of photosystem I.…”

mentioning

confidence: 91%

Triplet states in photosystem I of spinach chloroplasts and subchloroplast particles.

Frank¹,

McLean²,

Sauer³

1979

Proc. Natl. Acad. Sci. U.S.A.

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We report light-induced electron paramagnetic resonance triplet spectra from samples of chloroplasts or digitonin photosystem I particles that depend upon the dark redox state of the bound acceptors of photosystem I. If the reaction centers are prepared in the redox state P-700 A X- FdB-FdA-, then upon illumination at 11K we observe a polarized chlorophyll triplet species which we interpret as arising from radical pair recombination between P-700+ and A-. This chlorophyll triplet is apparently the analog of the PR state of photosynthetic bacteria [Parson, W.W. & Cogdell, R.J. (1975) Biochim. Biophys. Acta 416, 105-149]. If the reaction centers are prepared in the dark redox state P-700 A X FdB-FdA-, then upon illumination at 11K we observe a different triplet species of uncertain origin, possibly pheophytin or carotenoid. This species is closely associated with the photosystem I reaction center and it traps excitation when P-700 is oxidized.

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mentioning

confidence: 91%

Triplet states in photosystem I of spinach chloroplasts and subchloroplast particles.

Frank¹,

McLean²,

Sauer³

1979

Proc. Natl. Acad. Sci. U.S.A.

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“…Any variable fluorescence from Photosystem I alone in spinach chloroplasts or flashed bean leaves would be too small to have been detected by Kitajima andButler (1975) or Strasser andButler (1976). These authors demonstrated that the redox state of P700 had no effect on the fluorescence yield at 693 or 735nm, but the presence of a very small, system I variable fluorescence would not invalidate their conclusions concerning energy transfer between Photosystems I1 and I.…”

Section: Discussionmentioning

confidence: 88%

“…Either hypothesis predicts an increase in the fluorescence yield (variable fluorescence) at 696 nm during the photooxidation of P700. In fact, Karapetyan et al (1973), Shuvalov et al (1976 and Ikegami (1976) have all reported variable fluorescence from Photosystem I preparations. Schreiber (see Brown, 1976) also found an increase in apparent fluorescence from the CPI, but he calculated that it could be artifactually due to the increase in transmission with P700 bleaching.…”

Section: Discussionmentioning

confidence: 99%

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Fluorescence Spectroscopy of a P700‐chlorophyll‐protein Complex*

Brown

1977

Photochem & Photobiology

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Abstract. Chlorophyll‐protein complexes enriched in the Photosystem I reaction center chlorophyll (P700) exhibit a fluorescence emission maximum at 696 nm at ‐ 196°C The height of this 696 nm emission relative to the emission at 683 nm from antenna chlorophyll a increases proportionally with the P700 concentration while the total fluorescence yield of the complex decreases. The 696 nm emission could possibly be from an absorbing form of antenna chlorophyll a that may be somewhat enriched along with P700 in Photosystem I fractions. However, evidence resulting from glycerol treatment which appears to decrease the rate of resonance energy transfer between antenna chlorophyll and P700 favors the hypothesis that the emission comes from a photooxidized P700 dimer (Chl+‐Chl) absorbing near 690 nm. In turn, this fluorescence evidence provides additional support for the model of a P700 dimer involving exciton interaction. Absorption in the wavelength region of 450 nm specifically excites emission at 696 nm from the P700‐chlorophyll complex.

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“…Blankenship et al (1975) used the new technique of chemically induced dynamic electron polarization (CIDEP) to study the metastable states of Chl after light is absorbed but before redox reactions occur. Shuvalov (1976) studied delayed fluorescence from photosystem I preparations and observed triplet state formation. McIntosh and Bol-ton (1976) using the CIDEP technique mentioned above found possible evidence for triplet state formation by the P680 Chl species.…”

Section: Biological Systemsmentioning

confidence: 99%

Spectroscopy of Chlorophyll in Biological and Synthetic Systems*

Brown

1977

Photochem Photobiol

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Abstract-This review discusses recent spectroscopic studies aimed at discovering the structure, orientation, and function of chlorophyll in u i w . In plant membranes there appear to be at least two distinct types of chlorophyll a. The greater part, over 9Y%, is antenna chlorophyll which absorbs and transfers radiant energy to a few specialized chlorophyll molecules in a reaction center where the actual charge separation occurs.A dimer-oligomer model for antenna chlorophyll has been proposed on the basis of comparative studies of the absorption spectra of chlorophyll in various dry solvents and in uiw. Unfortunately a similarity between essentially structureless broad spectra is very weak evidence for their original identity. Also the requirement of an anhydrous environment for most of the chlorophyll in biological material is an unlikely postulate. A cross-linked, linear polymer model of chlorophyll in oiuu has also been proposed. Recent Resonance Raman spectroscopic results appear to rule out, in large part, either polymer model and once again suggest that it is the various attachments of chlorophyll to proteins which determine its function as antenna pigment in uiw. Circular dichroism measurements of chlorophyll in various plant materials have also led to the conclusion that antenna chlorophyll has strong interaction with protein. However, some doubt still exists as to the interpretation of these CD results. New studies of fluorescence, polarized fluorescence and Resonance Raman spectroscopy of various plant species corroborate the original proposition, based upon deconvolution of absorption spectra, that antenna chlorophyll occurs in uiuo in at least five discrete pools, and that each pool is likely to be located in the same environment in different plants.A new model-systems approach to simulating chlorophyll in uiuo has come through the use of lipid bilayers and liposomes. Charge transfer has been observed between chlorophyll in a lipid phase and phycobiliproteins or cytochrome c.The most promising, newly synthesized model for the reaction center, P700, is a covalently bound dimeric derivative of pyrochlorophyllide a. Its properties are similar to P700 in several respects except for reversible photooxidation which has not yet been observed. By detergent treatments chlorophyllprotein complexes having about 20-40 chlorophyll a molecules for every P700 have been isolated from different plants, and their spectroscopic properties are under investigation in several laboratories. The several hypotheses to explain the shape of the oxidized minus reduced absorption difference spectrum of P700 have not yet been reconciled. The nature of the photosystem I1 reaction center chlorophyll, P680, is also a subject of active investigation. Its absorption difference spectrum appears to have two kinetic components.

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EPR spectra of V(V) and Zr(IV) complexes with the HO2 radical

Cited by 6 publications

References 3 publications

Triplet states in photosystem I of spinach chloroplasts and subchloroplast particles.

Triplet states in photosystem I of spinach chloroplasts and subchloroplast particles.

Fluorescence Spectroscopy of a P700‐chlorophyll‐protein Complex*

Spectroscopy of Chlorophyll in Biological and Synthetic Systems*

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