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The electron paramagnetic resonance (EPR) parameters (g factors [g.sub.[parallel]], [g.sup.[perpendicular]] and hyperfine structure constants [A.sub.[parallel]], [A.sub.[]]) and the local structure of the tetragonal [Cu.sup.2+] center in trigonal ZnSe[F.sub.6] x 6[H.sub.2]O crystal are theoretically investigated from the perturbation formulas of these parameters for a 3[d.sup.9] ion in tetragonally elongated octahedra. In the calculated formulas, the contributions to the EPR parameters from ligand orbital and spin-orbit coupling are included on the basis of the cluster approach in view of moderate covalency of the studied systems, the required crystal-field parameters are estimated from the superposition model, which enables correlation of the crystal-field parameters and hence the EPR parameters with the tetragonal distortion of the studied [[Cu[([H.sub.2]O).sub.6]].sup.2+] cluster. According to the calculations, the ligand octahedra around [Cu.sup.2+] are suggested to suffer relative elongation [tau] ([approximately equals] 0.085 [Angstrom]) along the [001] (or [C.sub.4]) axis for the tetragonal [Cu.sup.2+] centers in ZnSe[F.sub.6] x 6[H.sub.2]O crystal, due to the Jahn-Teller effect. The results are discussed. Key words: electron paramagnetic resonance (EPR), crystal fields, local structure, [Cu.sup.2+], ZnSe[F.sub.6] x 6[H.sub.2]O. Les parametres de resonance paramagnetique electronique (EPR) (les facteur g, [g.sub.[parallel]], [g.sub.[]], et les constantes de structure hyperfine [A.sub.[parallel]], [A.sub.[]]) et la structure locale du centre tetragonal [Cu.sup.2+] dans le cristal trigonal ZnSe[F.sub.6] x 6[H.sub.2] sont ici soumis a une etude theorique a partir des formules de perturbations de ces parametres pour un ion 3[d.sup.9] dans un octaedre allonge tetragonalement. Dans nos calculs, nous incluons les contributions aux parametres provenant des orbitales ligands et du couplage spin-orbite sur la base d'une approche cluster visant des systemes de covalence moderee. Nous estimons les parametres du champ cristallin a partir d'un modele de superposition qui permet les correlations des parametres du champ cristallin et nous etudions ainsi les parametres EPR avec la distorsion tetragonale du cluster etudie [[Cu[([H.sub.2]O).sub.6]].sup.2+]. Nos calculs suggerent que les ligands octaedres autour de [Cu.sup.2+] souffrent de la relative elongation [tau] ([approximately equals] 0.085 [Angstrom]) le long de [001], ou axe [C.sub.4], pour les centres tetragonaux [Cu.sup.2+] dans le cristal ZnSe[F.sub.6]-6[H.sub.2]O, a cause de l'effet Jahn-Teller. Nous analysons les resultats. [Traduit par la Redaction] Mots-cles: parametre de resonance paramagnetique electronique (EPR), champs cristallins, structure locale, [Cu.sup.2+], ZnSe[F.sub.6]-6[H.sub.2]O. PACS Nos.: 76.30.Fc, 71.70.Ch, 75.10.Dg, 71.70.Ej., 1. Introduction ZnM[F.sub.6] x 6[H.sub.2]O (M = Ge, Se, Si, Zr) belongs to the family of isostructural fluosilicate hexahydrates having CsCl-type structure with space group R[bar.3]. In these crystals, [Zn.sup.2+] [...]

Opiate addiction has a high rate of relapse. The accumulating evidence shows that electroacupuncture (EA) may be effective for the treatment of opiate relapse. However, the change of expression of CB1-Rs and CB2-Rs involve in 2Hz EA anti-relapse pathway is still unclear. To explore the changes of expression of CB1-Rs and CB2-Rs, heroin self-administration (SA) model rats were adopted and treated using 2Hz EA. The expressions of CB1-Rs and CB2-Rs were observed using immunohistochemistry method. The results showed that, compared with the control group, active pokes in the heroin-addicted group increased, while the active pokes decreased significantly in 2Hz EA group compared with heroin-addicted group. Correspondingly, the expression of CB1-Rs in prefrontal cortex (PFC), hippocampus (Hip), nucleus accumbens (NAc) and ventral tegmental area (VTA) all increased significantly while the expression of CB2-Rs in those relapse-relevant brain regions decreased obviously in heroin-addicted group when compared with the control group. In addition, the expression of CB1-Rs obviously decreased in the 2Hz EA group while the expression of CB2-Rs in those relapserelevant brain regions increased significantly when compared with the heroin-addicted group. It indicated that 2Hz EA could attenuate the heroin-evoked seeking behaviors effectively. The anti-relapse effects of 2Hz EA might be related to the decrease of CB1-Rs and increase of CB2-Rs expression in relapse-relevant brain regions of heroin SA rats. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR) parameters ( g factors g∥, g⊥ and hyperfine structure constants A∥, A⊥) and the local structure of the tetragonal Cu2+ center in trigonal ZnSeF6·6H2O crystal are theoretically investigated from the perturbation formulas of these parameters for a 3d9 ion in tetragonally elongated octahedra. In the calculated formulas, the contributions to the EPR parameters from ligand orbital and spin-orbit coupling are included on the basis of the cluster approach in view of moderate covalency of the studied systems, the required crystal-field parameters are estimated from the superposition model, which enables correlation of the crystal-field parameters and hence the EPR parameters with the tetragonal distortion of the studied [Cu(H2O)6]2+ cluster. According to the calculations, the ligand octahedra around Cu2+ are suggested to suffer relative elongation τ (≈ 0.085 Å) along the [001] (or C4) axis for the tetragonal Cu2+ centers in ZnSeF6·6H2O crystal, due to the Jahn-Teller effect. The results are discussed. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR) parameters [i.e. g factors g i ( i= x, y, z) and hyperfine structure constants A i] and the local lattice structure for the Cu2+ centre in Tl2Zn(SO4)2·6H2O (TZSH) crystal were theoretically investigated by utilising the perturbation formulae of these parameters for a 3d9 ion under rhombically elongated octahedra. In the calculations, the admixture of d orbitals in the ground state and the ligand orbital and spin-orbit coupling interactions are taken into account based on the cluster approach. The theoretical EPR parameters show good agreement with the observed values, and the Cu2+-H2O bond lengths are obtained as follows: R x≈1.98 Å, R y≈2.09 Å, R z≈2.32 Å. The results are discussed. [ABSTRACT FROM AUTHOR]

The spin-Hamiltonian parameters (the g factors gi and the hyperfine structure constants Ai, i = x, y, z) and local structure of the Cu2+ center in PbTiO3 are theoretically studied by using the perturbation formulae of these parameters for a 3d9 ion in an orthorhombically elongated octahedra. The orthorhombic center is attributed to Cu2+ occupying the host Ti4+ site associated with a nearest-neighbouring oxygen vacancy VO along the c-axis, and the impurity Cu2+ off-center displacement ΔZL (≈0.18 Å) is smaller than that of the host Ti4+ site (ΔZH ≈ 0.3 Å). Meanwhile, the planar Cu2+-O2- bonds are found to experience the relative variation ΔR (≈ 0.098 Å) along the a- and b-axes, respectively, due to the Jahn-Teller effect and the size mismatching substitution of Ti4+ by Cu2+. The theoretical spin-Hamiltonian parameters based on the above defect structure agree well with the observed values. [ABSTRACT FROM AUTHOR]

The electron paramagnetic resonance (EPR) parameters (gfactorsgx,gy,gzand hyperfine structure constantsAx,Ay,Az) for Cu2+in (NH4)2Mg(SO4)2·6H2O (DHMS) crystal are theoretically investigated using the high-order perturbation formulas of these parameters. In the calculations, the ligand orbital and spin–orbit coupling for the impurity Cu2+are taken into account; the required crystal-field parameters are estimated from the superposition model which enables correlation of the crystal-field parameters and hence the EPR parameters with the local structure of the impurity center. The ligand orbital and the spin–orbit coupling contributions are included on the basis of the cluster approach. Based on the calculation, the theoretical EPR parameters show good agreement with the observed values. The results are discussed. [ABSTRACT FROM AUTHOR]

One feature of the amino acid sequence of P2X receptors identified from mammalian species, Xenopus laevis and zebrafish is the conservation of ten cysteines in the extracellular loop. Little information is available about the role of these conserved ectodomain cysteines in the function of P2X receptors. Here, we investigated the possibility that ten conserved cysteine residues in the extracellular loop of the rat P2X4 receptor may regulate zinc potentiation of the receptor using a series of individual cysteine to alanine point mutations and functional characterization of recombinant receptors expressed in Xenopus oocytes. For the C116A, C132A, C159A, C165A, C217A and C227A mutants, 10µM zinc did not significantly affect the current activated by an EC40 concentration of ATP. By contrast, 5µM zinc shifted the ATP concentration-response curve to the right in a parallel manner for both the C261A and C270A mutants and the magnitudes of those shifts were similar to that of the wildtype receptor. Interestingly, for the C126A and C149A mutants, 5µM zinc potentiated ATP-activated current, but increased the maximal response to ATP by 90% and 81% respectively, without significantly changing the EC50 value of ATP. Thus, these results suggest that cysteines and disulfide bonds between cysteines are differentially involved in the potentiation of the rat P2X4 receptor by zinc. [ABSTRACT FROM AUTHOR]