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1.
C. Teutloff W. Hofbauer S. G. Zech M. Stein R. Bittl W. Lubitz 《Applied magnetic resonance》2001,21(3-4):363-379
Electron paramagnetic resonance (EPR) spectroscopy at W-band (94 GHz) is used to resolve theg-tensors of the radical ions of the primary chlorophyll donor P 700 +? and the quinone acceptor A 1 ?? in photosystem I. The obtainedg-tensor principal values are compared with those of the isolated pigment radicals in organic solvents and the shifts are related to an impact of the protein environment. P 700 +? has been investigated in photosystem I single crystals at 94 GHz. W-band EPR applied to the photoinduced radical pair P 700 +? A 1 ?? is used to correctly assign theg-tensor axes of P 700 +? to the molecular structure of the primary donor. Density functional theory calculations on a model of A 1 ?? in its binding pocket derived from the recent crystal structure of photosystem I were utilized to correlate experimental magnetic resonance parameters with structural elements of the protein. 相似文献
2.
Dalibor Merunka 《Solid State Communications》2004,129(6):375-377
The modified strong dipole-proton coupling (MSDPC) model, which predicted several static and dynamic dielectric properties of KH2PO4 or KDP-type ferroelectrics, was used to investigate the properties of these crystals on the local scale. Results calculated by molecular dynamics (MD) simulation show that both order-disorder and displacive characteristics of one PO4 dipole are present in KDP and KD2PO4 (DKDP). These results correlate with experimental data from NMR and neutron scattering studies of local properties. 相似文献
3.
The secondary acceptor A1 of the electron transport chain(s) of photosystem (PS) I is a phylloquinone (vitamin K1, VK1). Pulse electron paramagnetic resonance and electron nuclear double resonance (ENDOR) experiments at X-band frequencies were performed on the photoaccumulated acceptor radical A 1 ·? and the radical pair state P 700 ·+ A 1 ·? in PS I ofThermosynechococcus elongatus. The data obtained were compared with data from the respective radical anion of VK1 in organic solvents. The unusualg tensor magnitude of A 1 ·? is explained by the hydrophobic binding pocket of this radical. The hyperfine couplings and the spin (and charge) density distribution is very different for A 1 .? in PS I and VK 1 ·? in frozen alcoholic solution. This is attributed to a rather strong one-sided hydrogen bond to A 1 ·? . The presence of a hydrogen bond to A 1 ·? has only a minor effect ong. The hyperfine coupling constants of A 1 ·? determined from the radical pair spectra deviate only slightly from those derived from photoaccumulated A 1 ·? in PS I treated with dithionite at high pH. ENDOR resonances of the proton in a H bond were detected and an estimate of the strength and geometry of this bond to A 1 ·? was obtained. The significance of the hydrogen bond and other (hydrophobic) interactions of A1 with the surrounding are briefly discussed. 相似文献
4.
Muon spin relaxation in zero field and longitudinal field was measured in single crystal samples of KH2PO4 (KDP) and KD2PO4 (DKDP) over a temperature range of 5 K to 300 K. At low temperatures, diamagnetic muons and muon substituted radicals with nuclear hyperfine coupling can be observed. For both KDP and DKDP, a minor change was observed in the dynamics of the muon below 140 K. Above 140 K, the mobility of the muon appears to increase and the diffusion rate becomes faster with increasing temperature. Only a small increase in the relaxation rate is observed in KDP due to the presence of theH
+, suggesting that the relaxation effects probably originate from the31P. 相似文献
5.
Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) techniques were used to investigate the electronic structure of the primary (Q A ?? ) and secondary (Q B ?? ) ubiquinone electron acceptors in reaction centers (RCs) of the photosynthetic bacteriumRhodobacter sphaeroides. To reduce the EPR linewidth, the high-spin Fe2+ present in native RCs was replaced by diamagnetic Zn2+. Experiments were performed both on frozen solutions and single crystals at microwave frequencies of 9, 35 and 94 GHz. Differences in the EPR/ENDOR spectra were observed for Q A ?? and Q B ?? , which are attributed to different environments of the quinones in the RC. The differences exhibited themselves in: (i) the g-tensors, (ii) the17O and13C hyperfine coupling (hfc) constants of the quinones labeled at the carbonyl group, (iii) the1H-hfcs of the quinone ring and (iv) the exchangeable protons hydrogen bonded to the carbonyl oxygens. From these results and from H/D exchange experiments, the following conclusions were drawn: both Q A ?? and Q B ?? have at least two hydrogen bonds of different strengths to the carbonyl oxygens. The hydrogen bonds for Q A ?? are stronger and more asymmetric than for Q B ?? . For Q A ?? the stronger bond (to O4) was assigned to His(M219) and the weaker (to O1) to Ala(M260). For Q B ?? the stronger bond (to O4) was assigned to His(L190), with several weaker bonds (to O1) to Ser(L223), Ile(224) and Gly(L225). From the temperature dependence of the hfcs of the exchangeable protons some dynamic properties of the RC were deduced. Hfcs with more distant nitrogens were observed by electron spin echo envelope modulation (ESEEM). For Q A ?? they were assigned to Nδ of His(M219) and to the peptide backbone nitrogen of Ala(M260) and for Q B ?? to Nδ of His(L190). These interactions indicate the extent of the electron wave function, which is important for the understanding of the electron transfer mechanism. Based on the magnetic resonance results, the function of the quinone acceptors in the reaction center is discussed. 相似文献
6.
B. di Claudio A. M. Rodriguez-Vargas G. Violini 《Zeitschrift fur Physik C Particles and Fields》1979,3(1):75-82
We calculate the σ term with the assumption of Weinberg's smoothness hypothesis and theg A axial coupling constant by using the most recent experimental data and we give a realistic estimation of the errors. We find for σ NN KK values ranging from 493 to 687 MeV, depending on the value assumed forg Σ 2 /4π, but the statistical uncertainty on it is of about 717 MeV. 相似文献
7.
H. Liening 《Zeitschrift für Physik A Hadrons and Nuclei》1974,266(4):287-297
Lifetimes and hfs coupling constants of some excited states of the 4d 9 5p configuration of Pd I have been determined in a level crossing experiment by observing the field dependence of the polarization of the fluorescence radiation in a magnetic field. From the halfwidths of the measured zero field level crossing signals one obtains the mean lifetimes of the following fine structure states:τ(3P 1 0 )=(7.46±0.32)nsec;τ(3 P 2 0 )=(6.9±0.76)nsecτ(3P 1 0 )=(4.99±0.35)nsec;τ(3 D 1 0 )=(4.89±0.40)nsecτ((3D 3 0 )=(6.99±0.49)nsec;τ(3 F 4 0 )=(7.09±0.46)nsec.Δm=2 crossing signals were detected in the3 P 1 0 ,3D 3 0 and3F 4 0 -states of the odd isotope105Pd. A detailed analysis of the experimental curves yields the hfs coupling constantsA andB of these states:A(3P 1 0 )=?(133±2) Mc/sec;B(3 P 1 0 )=(140±30) Mc/secA(3D 3 0 )=?(120±10) Mc/sec;B(3 D 3 0 )=?(660±100) Mc/secA(3F 4 0 )=?(87±2) Mc/sec;B(3 F 4 0 )=?(330±30) Mc/sec. A theoretical calculation of the hfs constants is given on the basis of reduced matrix elements. Within the limit of the errors these values agree with the experimental ones. The nuclear electric quadrupole moment deduced from the measuredB values isQ (105Pd)=(0.8±0.3)·10?24 cm2 (without corrections). 相似文献
8.
Two new di-nitrogen centers, which were labeled M2 and M3, were found together with known W7 and N4 centers in an unusual reddish-brown natural diamond. The following magnetic hyperfine interaction parameters (expressed in MHz) were determined for the two nitrogen atoms:A 1 (1) =117.95(5),A 1 (2) =A 1 (3) =84.48(5),A 2 (1) =7.1(1),A 2 (2) =A 2 (3) =6.6(1) for M2 andA 1 (1) =121.55(5),A 1 (2) =A 1 (3) =85.90(5),A 2 (1) =6.0(1),A 2 (2) =5.4(1),A 2 (3) =5.1(1) for M3. Hyperfine interaction tensors for the nitrogen atom N1 with a larger interaction have axial symmetry about the <111> direction, but those for the other nitrogen atom, N2, appear to be small, almost isotropic. Probable models of the M2 and M3 centers are suggested and discussed. 相似文献
9.
10.
T. V. Bocharova D. S. Sysoev A. N. Vlasova I. G. Maslennikova N. O. Tagil’tseva 《Physics of the Solid State》2014,56(2):353-358
The simulation of the fluoroaluminate matrix with small additives of phosphates has made it possible to create low-scattering glasses with a wide transparency window in the infrared region and to study the fundamental problem on the formation of radiation defects typical for the phosphate matrix (PO 3 2? hole, PO 3 2? electron, and PO 4 2? hole defects). By comparing the spectra of induced optical absorption, electron paramagnetic resonance, and Raman scattering, it has become possible to investigate the generation of defects in the course of the successive formation of the phosphate matrix in fluoroaluminate glass. The feasibility of the formation of PO 4 2? hole centers both in single tetrahedra and upon rupture of P-O-P bridge bonds with the simultaneous formation of PO 3 2? electron centers has been shown. As a result of the revision of the nature and mechanisms of formation of radiation color centers in the studied glasses, it appears promising to introduce cerium (Ce3+) and europium (Eu3+) as protectors into these glasses. 相似文献
11.
LEP measurements of theZ 0 parameters have been used to estimate the value of QED coupling constant at theZ 0 mass. The estimated value α eff -1 (M Z )=128.2±0.9 -0.4 +0.0 (M top) is in good agreement with the expectation of 128.0 ?0.4 +0.2 from the Standard Model. 相似文献
12.
T. Brodkorb J. G. Körner E. Mirkes G. A. Schuler 《Zeitschrift fur Physik C Particles and Fields》1989,44(3):415-432
We present exact expressions for theO(α s 2 ) tree graph four-jet cross-sections in neutral current and charged current deep inelasticep scattering initiated by quarks, antiquarks and gluons including lepton polarization effects. Using helicity amplitudes the partonic cross-sections are given in concise form including all colour, flavour and statistical factors. We explicate the electroweak coupling dependence and state how the partonic cross-sections are folded with the respective parton densities to obtain theep jet cross-sections toO(α s 2 ). We present some numerical results for the neutral current one-photon exchange case. We elaborate on the cut dependence of the jet rates and present differential distributions in some basic kinematical variables. 相似文献
13.
I. Blomqvist B. Bülow A. Fredrikson B. Johnsson G. G. Jonsson K. Lindgren M. Nilsson R. Petersson O. Glomset N. Freed W. Rhodes 《Zeitschrift für Physik A Hadrons and Nuclei》1978,284(3):313-317
The lifetime of the 331.3 keV 0 2 + state in100Zr has been measured at the gas-filled recoil separator for fission products JOSEF. By observing the delayed coincidences between theβ-particles populating the level and theE0 conversion electrons from its decay into the ground state, a half-life of 3.37±0.30 ns has been obtained. From the measured lifetime and the relative intensities of the 0 2 + →0 1 + and 0 2 + →2 1 + transitions, values of 0.493±0.015 for theE0 strength parameterρ, and of 16 single particle units forB(E2,2 1 + → 0 2 + ) have been deduced. The enhanced nature of theE0 transitions suggests mixing of the 0 1 + and 0 2 + states which may be estimated by comparing the experimentalB(E2) values for the 2 1 + →0 1 + and 2 1 + →0 2 + transitions with the predictions of the asymmetric VMI model. 相似文献
14.
K. M. Salikhov Y. N. Pushkar J. H. Golbeck D. Stehlik 《Applied magnetic resonance》2003,24(3-4):467-482
Transient electron paramagnetic resonance (TR-EPR) spectra of the electron-hole pair state P 700 + A0Q K ? in photosystem I are numerically calculated. Parameter variation concerns mainly the exchange integralJ of the precursor spin pair state P 700 + A 0 ? QK and its lifetime τ. A prominent emissive feature in the high-field region (P 700 + part) of the EPR spectrum turns out to be diminished with increasing lifetime τ of the precursor pair state in the case of positive exchange couplingJ>0 (ferromagnetic type). Correspondingly, the emissive feature becomes more pronounced with increasing lifetime τ in the case of negative exchange couplingJ<0 (antiferromagnetic type). These results can be used to interpret the changes in the pattern observed in TR-EPR spectra comparing wild-type and specific A0 mutants. The central ligating amino acid residue to the A0 chlorophyll cofactor is mutated from native methionine (M) to leucine (L) in either the PsaA or the PsaB branch. Changes are observed only for the A-side mutant: M688L(PsaA). They are consistent with the following parameters in the precursor pair P 700 + A 0 ? :J≈0.5÷1.0 mT and τ=1.5÷2 ns (as compared to τ~0.05 ns in the wild type). 相似文献
15.
L. Ricken D. Bohle G. Domogala K. Glasner E. Kuhlmann 《Zeitschrift für Physik A Hadrons and Nuclei》1982,306(1):67-71
Electric quadrupole transition strengths for the 2 1 + ,T=1→0 1 + ,T=1γ-decay branches are summarized for 10≦A≦42 nuclei. In10B the corresponding branch has been remeasured by use of the9Be(p, γ)10B resonance reaction atE p =320 keV; an upper limit of 0.6% is found. The variation of theE2 strengths within each individualT=1 isobaric multiplet reveals the particleor hole-character of the levels involved. The isoscalar 2 1 + →0 1 + transition strengths in 10≦A≦48 nuclei vary between 2 and 20 Weißkopf units showing drastic shell effects. Results for the ratio of neutron and proton matrix elements deduced from analogγ-decay studies and from inelastic pion scattering are compared. 相似文献
16.
Electric monopole transitions between the 0 2 + , 0 1 + and 2 2 + , 2 1 + levels in76Se, populated in the decay of76Br, were investigated by means of conversion electrons and gammaray spectroscopy. TheK-electron intensity ratios ofE0 andE2 transitions connecting the 0 2 + level to the 0 1 + and 2 1 + levels and of theE0 andE2 components in the 2 2 + →2 1 + transition were determined. The ratioX(E0/E2) of theE0 toE2 reduced transition probabilities and, from the available lifetimes, theE0 strength parameters ρ(E0) were deduced for the two transitions. The results are compared with the predictions of current models. 相似文献
17.
We study the effect of vector and axial isovector mesons in the soliton of the SU(2) NJL-model for static hedgehog configurations and on the chiral circle. The Lagrangian reproduces Sakurai's Universality and implements vector dominance through current-field identities. The parameters of the Lagrangian are fixed by means of a heat-kernel expansion up to second order taking theA-π mixing into account. For the corresponding set of parameters we find solitons for constituent quark masses betweenM~265–345 MeV which are much lower than those found without vector mesons. For the valueM=315 MeV which corresponds both to the KSFR relation 2g ρ 2 f π 2 =m ρ 2 and the Weinberg sum rule m A 2 =m ρ 2 the soliton has a clearly negative quark eigenvalue. The soliton mass is about 1100 MeV. For this choise of parameters the radius and axial coupling constant turn out to be too small. 相似文献
18.
We have employed time-resolved LIF spectroscopy in order to investigate perturbations in theA 1 ∑ u + state of the three isotopic Li2 molecules. After a systematic check of more than 2000 individual rotation-vibration levels, 46 levels were found whose anomalous lifetimes can be interpreted by perturbations with thea 3 Π u state. As almost all perturbed levels possess shortened lifetimes the predissociating nature of thea 3 Π u state, caused by interaction with thex 3 ∑ u + continuum, is revealed. On the basis of the Kovács-Budo theory of accidental predissociation we have fitted the molecular constants of thea 3 Π u state, thex 3 ∑ u + potential curve and the electronic parts of the perturbation matrix elements do that the observed lifetimes of all levels in the 78 investigatedA 1 ∑ u + ?a3 Π u term-crossing regions can be understood. 相似文献
19.
I. T. Obukhovsky 《Zeitschrift für Physik A Hadrons and Nuclei》1982,308(3):253-266
The spectrum and eigenfunctions of deuteronlike states in the quark bag for the configurationsS 6 andS 4 P 2 have been studied. The complete tables of the fractional parentage coefficients (f.p.c.) for these configurations in thej-j andL-S coupling schemes are presented. The universal method of calculation of the f.p.c. which is based on the complementarity of the unitary and permutation group, is considered. The method enable one to calculate the Clebsh-Gordon coefficients and the invariant symbols of the noted groups. It is shown that the lowest energy state of the configurationS 1 2/4 P 3 2/2 resembles the partial wave3 D 1 and can, therefore, be coupled to it in a deuteron. On the contrary, the lowest states in the configurationsS 1 2/6 andS 1 2/4 P 1 2/2 resemble the3 S 1-wave. 相似文献
20.
K. -H. Speidel V. Mertens W. Trölenberg M. Knopp H. Neuburger K. Bharuth-Ram J. Gerber 《Zeitschrift für Physik A Hadrons and Nuclei》1984,315(3):319-323
The transient field technique has been used to determine theg-factor of the 4 2 + state at 6.010MeV excitation in24Mg. The deduced value ofg=+0.5(4) is consistent with collective model expectations. Further, the equality within experimental accuracies, of the g-factors of the 2 1 + , 2 2 + , 4 1 + and 4 2 + states agrees with theoretical predictions for thisT=0 self-conjugate nucleus, in contrast to the results for20Ne. 相似文献