Endor and triple resonance in solutions of the chlorophyll a and bis(chlorophyll)cyclophane radical cations

Huber, Martina; Lendzian, Friedhelm; Lubitz, Wolfgang; Tränkle, E.; Möbius, K.; Wasielewski, Michael R.

doi:10.1016/0009-2614(86)80648-0

Cited by 34 publications

(21 citation statements)

References 22 publications

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“…This product has been attributed earlier to a chlorin derivative with a structure similar to chlorophyll a [ 19 ] . The special TRIPLE spectrum obtained from this species was indeed very similar to that of the plant chlorophyll a radical cation [22,35], and none of the observed lines were coincident with those of BChl b+ . This product was, however, not observed when light, oxygen and an excess of ZnTPP?ClOi were rigorously excluded.…”

Section: Resultsmentioning

confidence: 84%

The radical cation of bacteriochlorophyll b. A liquid-phase endor and triple resonance study

Lendzian

Lubitz

Steiner³

et al. 1986

Chemical Physics Letters

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The radical cation of bacteriochlorophyll b (BChl b) is investigated by ENDOR and TRIPLE resonance in liquid solution. The experimental hyperfine coupling constants, ten proton and three. nitrogen couplings, are compared with the predictions from advanced molecular-orbital calculations (RHF INDO/SP). The detailed picture obtained of the spin density distribution is a prerequisite for the investigation of the primary electron donor radical cation in BChl b containing photosynthetic bacteria.

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Section: Resultsmentioning

confidence: 84%

The radical cation of bacteriochlorophyll b. A liquid-phase endor and triple resonance study

Lendzian

Lubitz

Steiner³

et al. 1986

Chemical Physics Letters

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“…The other intense peak, with lower hfc values (a iso + 4.7 MHz), may be assigned to methyl 2 on the basis of the hfcs reported for the Chl a cation 53 and anion 54 at this proton position, taking into account that, in the Hückel approximation, the hfc for a nucleus of a triplet state is expected to be the average of those observed in the respective cation (singly occupied HOMO) and anion (singly occupied LUMO) radicals, since in the triplet state the HOMO and LUMO are both singly occupied 49 . It is worth noting that this is the first time that the transition belonging to methyl 2 protons is clearly detected in a 3 Chl a ENDOR spectrum.…”

Section: Resultsmentioning

confidence: 87%

An unusual role for the phytyl chains in the photoprotection of the chlorophylls bound to Water-Soluble Chlorophyll-binding Proteins

Agostini

Palm

Schmitt

et al. 2017

Sci Rep

104

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Water-Soluble Chlorophyll Proteins (WSCPs) from Brassicaceae are non-photosynthetic proteins which tetramerize upon binding four chlorophyll (Chl) molecules. The bound Chls are highly photostable, despite the lack of bound carotenoids known, in Chl-containing photosynthetic proteins, to act as singlet oxygen and Chl triplet (3Chl) quenchers. Although the physiological function of WSCPs is still unclear, it is likely to be related to their biochemical stability and their resistance to photodegradation. To get insight into the origin of this photostability, the properties of the 3Chl generated in WSCPs upon illumination were investigated. We found that, unlike the excited singlet states, which are excitonic states, the triplet state is localized on a single Chl molecule. Moreover, the lifetime of the 3Chl generated in WSCPs is comparable to that observed in other Chl-containing systems and is reduced in presence of oxygen. In contrast to previous observations, we found that WSCP actually photosensitizes singlet oxygen with an efficiency comparable to that of Chl in organic solvent. We demonstrated that the observed resistance to photooxidation depends on the conformation of the phytyl moieties, which in WSCP are interposed between the rings of Chl dimers, hindering the access of singlet oxygen to the oxidizable sites of the pigments.

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“…Such weak couplings have been previously assigned to the methine protons of Chla'+ in vitro (Scheer et al, 1977;O'Malley & Babcock, 1984), although here, because of the possibility of coupling to protons from the surrounding matrix, this assignment must be considered tentative. The largest proton hyperfine couplings observed for Chla'+ in vitro arise from the protons at positions 7 and 8 on ring IV (Scheer et al, 1977;Huber et al, 1986;Kass et al, 1994). Although these protons are B to the ?r system and give rise to sharp resonances in liquid solution, in frozen solution their inequivalence and immobility lead to resonance broadening [for an example of this effect, see Figure 4 in Rautter et al ( 1 992)].…”

Section: Resultsmentioning

confidence: 92%

ENDOR and Special Triple Resonance Studies of Chlorophyll Cation Radicals in Photosystem 2

Rigby

Nugent²,

O’Malley³

1994

Biochemistry

138

120

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Electron nuclear double resonance (ENDOR) and special triple (ST) resonance spectroscopies have been used to study the cation radicals of the primary donor, P680, and two secondary donor chlorophylls (Chl) in photosystem 2 (PS2). Two different preparations were employed, Tris-washed PS2 membranes and PS2 reaction centers (D1-D2-I-Cytb559 complex). One secondary donor Chl a cation radical, Chl1.+, was generated in the Tris-washed preparation, while the P680.+ radical cation and a further Chl a cation radical, Chl2.+, were produced in the reaction center preparation. The ENDOR spectrum of the primary donor radical cation of photosystem 1 (P700.+) is also presented for comparison. Hyperfine coupling constants for methyl groups have been measured for all three PS2 radical species and assigned by comparison with previously published spectra of Chl a radicals in vitro. Electron spin densities were calculated from these hyperfine couplings. Comparison of ENDOR spectral features with those of Chla.+ in vitro indicates similar values for Chl1.+ and Chl2.+ radicals but an apparent reduction in unpaired electron spin density for P680.+. It has been proposed from the more detailed studies of purple bacterial reaction centers that such a reduction in spin density can be interpreted as a delocalization over two Chl a molecules. Our calculations therefore suggest that P680.+ is a weakly coupled chlorophyll pair with 82% of the unpaired electron spin located on one chlorophyll of the pair at 15 K. Environmental or geometrical changes to the chlorin ring structure to give a novel monomeric primary donor are also possible.(ABSTRACT TRUNCATED AT 250 WORDS)

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Endor and triple resonance in solutions of the chlorophyll a and bis(chlorophyll)cyclophane radical cations

Cited by 34 publications

References 22 publications

The radical cation of bacteriochlorophyll b. A liquid-phase endor and triple resonance study

The radical cation of bacteriochlorophyll b. A liquid-phase endor and triple resonance study

An unusual role for the phytyl chains in the photoprotection of the chlorophylls bound to Water-Soluble Chlorophyll-binding Proteins

ENDOR and Special Triple Resonance Studies of Chlorophyll Cation Radicals in Photosystem 2

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