High-Field EPR Study of Carotenoid and Chlorophyll Cation Radicals in Photosystem II

Lakshmi, K. V.; Reifler, Michael J.; Brudvig, Gary W.; Poluektov, Oleg G.; Wagner, and Arlene M.; Thurnauer, Marion C.

doi:10.1021/jp002558z

Cited by 47 publications

(67 citation statements)

References 24 publications

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“…1) in 1:I (v/v) H20/CD3OH (methanol added for glassification). In these experiments, which included the electron spin echo (ESE) field sweep and Mims ENDOR [29] measurements, the D-band spectrometer [30] of Argonne National Laboratory was used. The measurement temperature was about 8 K, as determined from the ENDOR spectra (see below).…”

Section: Methodsmentioning

confidence: 99%

High-field pulsed EPR and ENDOR of Gd3+ complexes in glassy solutions

et al. 2005

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In this work D-band pulscd electron paramagnetic resonance was uscd to record the fieldsweep spectra of several Gd 3~ comp[exes in g[assy water-methanol solutions. These spectra were analyzed by a specially developed stochastic superposition model that predicted the essential features of the distribution of the crystal ficld interaction (CFI) paramcters in glassy systems. Asa result of this analysis, the CFI distribution~ tbr the studied complexes wcre evaluated. The D-band Mims ~H electron-nuclear double resonance spectra were free from CFI-related distortions, which allowed us to accuratety determine the hyperfine interaction (HFI) parameters tbr water ligand protons and to unequivocally establish that the HFI distribution is solely related to the distribution of the Gd-H distances.

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Section: Methodsmentioning

confidence: 99%

High-field pulsed EPR and ENDOR of Gd3+ complexes in glassy solutions

et al. 2005

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“…The C'+-P-P~: -radical pair spectrum is a broad derivative-like signal because of the small g-tensor difference between the 13-carotene radical cation and the porphyrin radical anion [43,44] accompanied by a large inhomogeneous line width of both radicals [42,45].…”

Section: Spectral Analysis Of the Spin-correlated Radical Pairmentioning

confidence: 99%

EPR-detected photoinduced electron transfer in three structurally related molecular triads

et al. 2006

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A comparative electron paramagnetic resonance (EPR) study has been performed on a series of structurally related molecular triads which undergo photoinduced electron transfer and differ one from the other in terms of the acceptor or donor moieties. The molecular triads, C-P-C6o , TTF-P-C6o and C-P-PF, share the same free-base tetraarylporphyrin (P) as the primary electron donor, which after light excitation initiates the electron transfer process, but differ either in terms of the electron acceptor (fullerene derivative, C6o , versus fluorinated free-base porphyrin, PF), or in terms of the final electron donor (carotenoid polyene, C, versus tetrathiafulvalene, TTF). AII these molecular triads can be considered artificial photosynthetic reaction centers in their ability to mimic several key properties of the reaction center primary photochemistry. Photoinduced charge separation and recombination have been followed by time-resolved EPR in a glass of 2-methyltetrahydrofuran and in the nematic phase of the uniaxial liquid crystal E-7. All the triads undergo photoinduced electron transfer, with the generation of charge-separated states in both the low-dielectric environment of the 2-methyltetrahydrofuran glass and in anisotropic E-7 medium. Different photochemical pathways have been recognized depending on the specific donor and acceptor moieties constituting the molecular triads. In the presence of the tetrathiafulvalene electron donor singlet-and triplet-initiated electron transfer routes are concurrently active. Recombination to the low-lying carotenoid triplet state occurs in the carotene-based triads, while singlet recombination is the only active route for the TTF-P-C6o triad, where a low-lying triplet state is lacking. Long-lived charge separation has been observed in the case of TTF-P-C6o: about 8 p.s for the singlet-born radical pair in the glassy isotropic matrix and about 7 ~ts for the triplet-born radical pair in the nematic phase of E-7. For all the molecular triads, a weak exchange interaction (J ~ I G) between the electrons in the final spin-correlated radical pair has been evaluated by simulation of the EPR spectra, providing evidence for superexchange electronic interactions mediated by the tetraarylporphyrin bridge.

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“…[20] ENDOR spectroscopy: The pulsed EPR experiments were performed with frozen (8 K) solutions of 1 mm Gd-L 1 in 1:1 (v/v) H 2 O/CD 3 OH (methanol added for glassification). In these experiments, which included the electron spin echo (ESE) field sweep and Mims ENDOR [21] measurements, the D-band (130 GHz) spectrometer [22] of Argonne National Laboratory was used.…”

Section: Preparation Of Compoundmentioning

confidence: 99%

When are Two Waters Worse Than One? Doubling the Hydration Number of a Gd–DTPA Derivative Decreases Relaxivity

Caravan

Amedio

Dunham

et al. 2005

Chemistry A European J

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The synthesis of a novel ligand, based on N-methyl-diethylenetriaminetetraacetate and containing a diphenylcyclohexyl serum albumin binding group (L1) is described and the coordination chemistry and biophysical properties of its Gd(III) complex Gd-L1 are reported. The Gd(III) complex of the diethylenetriaminepentaacetate analogue of the ligand described here (L2) is the MRI contrast agent MS-325. The effect of converting an acetate to a methyl group on metal-ligand stability, hydration number, water-exchange rate, relaxivity, and binding to the protein human serum albumin (HSA) is explored. The complex Gd-L1 has two coordinated water molecules in solution, that is, [Gd(L1)(H2O)2]2- as shown by D-band proton ENDOR spectroscopy and implied by 1H and 17O NMR relaxation rate measurements. The Gd-H(water) distance of the coordinated waters was found to be identical to that found for Gd-L2, 3.08 A. Loss of the acetate group destabilizes the Gd(III) complex by 1.7 log units (log K(ML) = 20.34) relative to the complex with L2. The affinity of Gd-L1 for HSA is essentially the same as that of Gd-L2. The water-exchange rate of the two coordinated waters on Gd-L1 (k(ex) = 4.4x10(5) s(-1)) is slowed by an order of magnitude relative to Gd-L2. As a result of this slow water-exchange rate, the observed proton relaxivity of Gd-L1 is much lower in a solution of HSA under physiological conditions (r1(obs) = 22.0 mM(-1) s(-1) for 0.1 mM Gd-L1 in 0.67 mM HSA, HEPES buffer, pH 7.4, 35 degrees C at 20 MHz) than that of Gd-L2 (r1(obs) = 41.5 mM(-1) s(-1)) measured under the same conditions. Despite having two exchangeable water molecules, slow water exchange limits the potential efficacy of Gd-L1 as an MRI contrast agent.

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High-Field EPR Study of Carotenoid and Chlorophyll Cation Radicals in Photosystem II

Cited by 47 publications

References 24 publications

High-field pulsed EPR and ENDOR of Gd3+ complexes in glassy solutions

High-field pulsed EPR and ENDOR of Gd3+ complexes in glassy solutions

EPR-detected photoinduced electron transfer in three structurally related molecular triads

When are Two Waters Worse Than One? Doubling the Hydration Number of a Gd–DTPA Derivative Decreases Relaxivity

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