Electronic <b>g</b>-Tensors of Semiquinones in Photosynthetic Reaction Centers. A Density Functional Study

and, S. K. Dutta; Kaupp, Martin

doi:10.1021/jp036322h

Cited by 26 publications

(69 citation statements)

References 29 publications

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“…Independent sets of DFT calculations on quinone binding sites have been published in the last decade [9,[19][20][21] (see Table 1). Most of the calculations had been performed prior to the experimental results for the ~3C (and ~70) hfc tensors, in particular for the A~ site in PS I.…”

Section: Comparison With Data For Related Quinone Binding Sites and Dmentioning

confidence: 99%

Single-sided hydroge bonding to the quinone cofactor in photosystem I probed by selective13C-labelled naphthoquinones and transient EPR

et al. 2006

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Hydrogen bonding between the protein and one or both of the two 1,4-quinone carbonyl groups of a benzo-of naphtho-quinone constitutes a significant protein-cofactor interaction in photosynthetic reaction centers. The redistribution of charge and spin density due to a particular H-bonding scheme leaves the largest hyperfine couplings (hfc) at the highest density positions, i.e., the nuclei of the carbonyl groups directly involved in H-bonding. The spin density changes at the ring carbon positions ate accessed experimentally via electron paramagnetie resonance-determined hfc tensor elements of selective ~3C isotope labels in one of the two carbonyl groups. Complete hfc tensor data are presented for each of the ~3C positions in the functional charge-separated state in reaction centers of photosystem I (PS I) isolated from cyanobacteria. A highly asymmetric H-bonding scheme for the A t quinone binding site due to a single dominant H-bond to one carbonyl group is confirmed. A comparison to other weU-studied quinone binding sites of other protein-cofactor systems with more complex H-bonding schemes reveals the uniqueness of the PSI site. The single-sided A~ quinone site provides ah ideal test case for the various sets of density functional theory (DFT) calculations that are currently available. While the overall agreement between experimental and calculated data is quite satisfactory, a significant discrepancy is found for the high-spin-density t3C position associated with the H-bonded carbonyl. The dominant hfc component (and spin density) is underestimated in the DFT calculations, not only for the high-asymmetry case in PS I, but also for other quinone binding sites with less asymmetry that result from more complex H-bonding schemes. The consequences and potential relevance of this finding for biological function are discussed.

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Section: Comparison With Data For Related Quinone Binding Sites and Dmentioning

confidence: 99%

Single-sided hydroge bonding to the quinone cofactor in photosystem I probed by selective13C-labelled naphthoquinones and transient EPR

et al. 2006

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“…Such calculations might moreover be helpful to gain further insight into structural details of the Qa binding site or into mechanisms leading to specific magnetic interactions. So lar, there are several theoretical studies on ubiquinone models which also relate to Qa in bRCs of Rhodobacter sphaeroides [45][46][47][48][49][50][51][52][53]. Most of them [45, The influence of several surrounding amino acids, a bivalent Zn 2+ metal center ~ and geometry relaxation of the ubisemiquinone on the magnetic properties of the Q;" binding site are discussed.…”

Section: Lntroductionmentioning

confidence: 99%

Theoretical investigation of Q A −· -ligand interactions in bacterial reaction centers ofRhodobacter sphaeroides

2006

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Density functional theory was used to caleulate magnetic resonance parameters for the primary stable electron acceptor anion radical (Q2") in its binding site in the bacterial reaction center (bRC) of Rhodobacter sphaeroides. The models used for the calculations of the QA" binding pocket included all short-range interactions of the ubiquinone with the protein surroundings in a gradual manner and thus allowed a decomposition and detailed analysis of the different specific interactions. Comparison of the obtained hyperfine and quadrupole couplings with experimental data demonstrates the feasibility and reliability of calculations on such complex biologically relevant systems. With these results, the interpretation of previously published 3-pulse electron spin echo envelope modulation data could be extended and an assignment of the observed double quantum peak to a specific amino acid is proposed. The computations provide evidence for a slightly altered binding site geometry for the QA ground state as investigated by X-ray crystallography with respect to the QA" anion radical state as accessible vŸ EPR spectroscopy. This new geometry leads to improved fits of the W-band correlated-coupled radical pair spectra of Q2"-P~-91 compared to orientation data from the crystal structure. Finally, a correlation of the 14N quadrupole parameters of His219 with the hydrogen bond geometry anda comparison with previous systematic studies on the influence of hydrogen bond geometry on quadrupole coupling parameters (J. Fritscher: Phys. Chem. Chem. Phys. 6, 4950~-956, 2004) is presented.

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“…In combination with quantum chemical modeling based on density functional theory, they are an important structural diagnostic tool that can reveal these details [9–11]. …”

Section: Introductionmentioning

confidence: 99%

Atomic hydrogen as high-precision field standard for high-field EPR

Stoll

Ozarowski

Britt

et al. 2010

Journal of Magnetic Resonance

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We introduce atomic hydrogen trapped in an octaisobutylsilsesquioxane nanocage (H@iBuT 8 ) as a new molecular high-precision magnetic field standard for high-field EPR spectroscopy of organic radicals and other systems with signals around g = 2. Its solid-state EPR spectrum consists of two narrow lines separated by about 51 mT and centered at g ≈ 2. The isotropic g factor is 2.00294(3) and essentially temperature independent. The isotopic 1 H hyperfine coupling constant is 1416.8(2) MHz below 70 K and decreases slightly with increasing temperature to 1413.7(1) MHz at room temperature. The spectrum of the standard does not overlap with those of most organic radicals, and it can be easily prepared and is stable at room temperature.

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Electronic g-Tensors of Semiquinones in Photosynthetic Reaction Centers. A Density Functional Study

Cited by 26 publications

References 29 publications

Single-sided hydroge bonding to the quinone cofactor in photosystem I probed by selective13C-labelled naphthoquinones and transient EPR

Single-sided hydroge bonding to the quinone cofactor in photosystem I probed by selective13C-labelled naphthoquinones and transient EPR

Theoretical investigation of Q A −· -ligand interactions in bacterial reaction centers ofRhodobacter sphaeroides

Atomic hydrogen as high-precision field standard for high-field EPR

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