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Coupling Constants (coupling + constant)
Kinds of Coupling Constants Selected AbstractsTheoretical study of ribonucleotide reductase mechanism-based inhibition by 2,-azido-2,-deoxyribonucleoside 5,-diphosphatesJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 2 2004Susana Pereira Abstract 2,-Azido-2,-deoxyribonucleoside 5,-diphosphates are mechanism-based inhibitors of Ribonucleotide Reductase. Considerable effort has been made to elucidate their mechanism of inhibition, which is still controversial and not fully understood. Previous studies have detected the formation of a radical intermediate when the inhibitors interact with the enzyme, and several authors have proposed possible structures for this radical. We have conducted a theoretical study of the possible reactions involved, which allowed us to identify the structure of the new radical among the several proposals. A new reactional path is also proposed that is the most kinetically favored to yield this radical and ultimately inactivate the enzyme. The energetic involved in this mechanism, both for radical formation and radical decay, as well as the calculated Hyperfine Coupling Constants for the radical intermediate, are in agreement with the correspondent experimental values. This mechanistic alternative is fully coherent with remaining experimental data. © 2003 Wiley Periodicals, Inc. J Comput Chem 25: 227,237, 2004 [source] A Theoretical Study of the NMR Spin,Spin Coupling Constants of the Complexes [(NC)5Pt,Tl(CN)n]n- (n = 0,3) and [(NC)5Pt,Tl,Pt(CN)5]3- : A Lesson on Environmental Effects.CHEMINFORM, Issue 2 2004Jochen Autschbach No abstract is available for this article. [source] Isotropic 13C Hyperfine Coupling Constants Distinguish Neutral from Anionic Ubiquinone-Derived Radicals,CHEMPHYSCHEM, Issue 18 2009Scott E. Boesch A radical notion: Calculated isotropic 13C hyperfine coupling constants are distinctly different for the anionic ubisemiquinone model UQ., (picture, left) rather than the protonated UQH. (picture, right) and can distinguish between the two in electron transfer proteins such as cytochrome bo3, cytochrome bc1, or photosynthetic reaction centers. [source] Sensitivity-enhanced Experiments for the Measurement of J and Dipolar Coupling ConstantsCHINESE JOURNAL OF CHEMISTRY, Issue 7 2002Dong-Hai Lin Abstract A sensitivity-enhanced IPAP NMR experiment was described in this paper, which separates the 1H- 15N doublets into two different spectra to alleviate the problem of resonance overlaps and achieve the accurate measurement of J and residual dipolar coupling constants in proteins. This experiment offered 20%,60% sensitivity enhancement over the original IPAP experiment, and therefore produced more measurable resonances. Pulsed field gradient was used for coherence selection. Water-flip-back approach was used for water suppression. The sensitivity-enhanced IPAP experiment was employed in the measurement of 1JNH and 1DNH constants of the protein UBC9. [source] A Theoretical Study of the Exchange Coupling in Hydroxo- and Alkoxo-Bridged Dinuclear Oxovanadium(IV) CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2004Antonio Rodríguez-Fortea Abstract A density functional study of exchange coupling in hydroxo- and alkoxo-bridged dinuclear oxovanadium(IV) compounds is presented. Coupling constants calculated for full unmodeled structures are in good agreement with experimentally reported values, confirming the ability of the computational strategy used in this work to predict the exchange coupling in dinuclear VIV compounds. The influence of the configuration of the [VO(,-OR)2VO]2+ core in compounds with two edge-sharing octahedrally coordinated oxovanadium(IV) centers, of the nature of the terminal ligands and of structural distortions on the coupling constant have been analyzed through model calculations. The results indicate that the coupling constant is less affected by these factors than for hydroxo- and alkoxo-bridged CuII compounds. The calculations support the orbital models usually employed in qualitative interpretations of magneto-structural correlations, showing good correlations between the calculated coupling constants and the overlap between the two magnetic orbitals or the square of the orbital gap. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Nucleophilic Addition of Water and Alcohols to Dicyanonitrosomethanide: Ligands with Diverse Bonding Modes in Magnetically Coupled d-Block ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2010Anthony S. R. Chesman Abstract Ligands resulting from the transition-metal-promoted nucleophilic addition of water or an alcohol to dicyanonitrosomethanide ions (dcnm) have been utilised in the formation of a large series of polynuclear complexes. Addition of water to dcnm results in formation of carbamoylcyanonitrosomethanide (ccnm); deprotonation of this ligand gives amidocarbonyl(cyano)nitrosomethanide (acnm), which has been incorporated into the trinuclear complex [Cu3(acnm)2(dmae)2(H2O)2] [dmae = 2-(dimethylamino)ethoxide] (1) which shows strong antiferromagnetic coupling with an exchange coupling constant, J = ,500 cm,1. [Cu(acnm)(NH3)2], (2) marks the first instance of acnm facilitating the formation of a coordination polymer, namely a 1D chain with intramolecular hydrogen bonding. Attempts to synthesise 2 through different reaction conditions instead resulted in the mononuclear [Cu(acnm)(NH3)2(py)] (py = pyridine) (3). The addition of ethanol to dcnm results in cyano[imino(ethoxy)methyl]nitrosomethanide (cenm) which features in the mononuclear [Cu(cenm)2(H2O)2] (4) and polymeric {[Cu(cenm)2]2·H2O}, (5). The latter is the first example of the cenm ligand in a coordination polymer and has a highly unusual coordination mode through the nitrile groups and extremely weak antiferromagnetic coupling. {[Mn3(ccnm)2(EtOH)2(OAc)4]·2EtOH}, (6) and (Et4N)2[Cu(ccnm)4] (7) contain previously unobserved coordination modes of the ccnm ligand while the complex [Mn(cmnm)3Mn(bipy)(MeOH)](ClO4) (8) {cmnm = cyano[imino(methoxy)methyl]nitrosomethanide, bipy = 2,2,-bipyridine} displays weak antiferromagnetic coupling between manganese atoms with J = ,1.44 cm,1. A change in the solvent systems used in the synthesis of 7 results in the formation of the mononuclear complexes [Mn(bipy)2(dcnm)2] (9) or [Mn(bipy)2(H2O)(dcnm)](dcnm)·H2O (10) and [Mn(bipy)2(dcnm)(H2O)](dcnm) (11). The addition of ethlyene glycol monomethyl ether to dcnm gives cyano[imino(2-methoxyethoxy)methyl]nitrosomethanide (cgnm) and the formation of [Cu(cgnm)2(H2O)2] (12). [source] Syntheses, Structures and Magnetic Properties of Dinuclear Copper(II),Lanthanide(III) Complexes Bridged by 2-Hydroxymethyl-1-methylimidazoleEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 5 2008Wei-Xiong Zhang Abstract Three discrete dinuclear copper(II),lanthanide(III) complexes, namely, [CuLn(mmi)2(NO3)3(H2O)2] [Ln = La (1), Sm (2)] and [CuGd(mmi)2(NO3)2(H2O)3][NO3] (3) (Hmmi = 2-hydroxymethyl-1-methylimidazole) were synthesized and structurally characterized by X-ray diffraction analysis. In these complexes, dinuclear cores of CuII and LnIII are consolidated by a pair of ,-1,1- O bridges from mmi at a distance of 3.36,3.46 Å. The temperature dependence of the magnetic susceptibility and the field dependence of the magnetization indicate that 1, 2 and 3 exhibit paramagnetic, antiferromagnetic and ferromagnetic behaviours, respectively. The value of the JCu,Gd coupling constant of 3 [8.7(1) cm,1] is fairly large, which is probably related to the small dihedral angles, , (5.0°), between the two planes of O,Cu,O and O,Gd,O in the CuO2Gd core.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Synthesis, Structure and Magnetic Properties of a Tetranuclear Copper(II) Complex on the Basis of a 2-Substituted Glucopyranoside Schiff Base Ligand,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2006Anja Burkhardt Abstract Condensation of a derivatized 2-aminoglucose fragment with salicylaldehyde affords the new sugar-based Schiff base ligand benzyl 4,6- O -benzylidene-2-deoxy-2-salicylideneamino-,- D -glucopyranoside (H2L). The reaction of the dibasic ligand H2L with [Cu(CH3COO)2]·H2O leads to the formation of the tetranuclear copper(II) complex [{Cu(L)}4] (3) by a self-assembly process. The X-ray structural analysis of complex 3 which crystallizes together with two molecules of chloroform and one molecule of ethanol in the space group P212121 revealed for all copper atoms a NO3 coordination environment with a square-planar geometry. The tetranuclear molecule 3 consists of four chiral building blocks {Cu(L)} with the rare 2,3-coordination of the trans -configured donor atoms of the sugar backbone. The observed coordination mode of the building blocks exemplifies how chitosan-derived polysaccharide ligands can act as a chiral support for transition-metal complexes. The C-3 alcoholate oxygen atoms of the carbohydrate unit is bridging adjacent {Cu(L)} moieties resulting in an eight-membered Cu4O4 ring with a boat-like conformation. Temperature-dependent magnetic measurements of 3 indicate moderate antiferromagnetic interactions between the four copper(II) ions with a coupling constant of J = ,130 cm,1.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Binding of Oxovanadium(IV) to Tripeptides Containing Histidine and Cysteine Residues and Its Biological Implication in the Transport of Vanadium and Insulin-Mimetic CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2005Eugenio Garribba Abstract The complexation of VIVO ion with three tripeptides of biological importance containing L -histidine or L -cysteine (HisGlyGly, GlyGlyHis and GlyGlyCys) has been studied. This study was performed in aqueous solution by the combined application of potentiometric and spectroscopic (electronic absorption and EPR) techniques. The results indicate that these oligopeptides, if a ligand-to-metal molar ratio of 10 or 15 is used, can keep VIVO ion in solution until the deprotonation of the amide group with the donor set (NH2, CO, Nimax) for HisGlyGly or (COO,, CO) for GlyGlyHis and GlyGlyCys. In all the systems, at pH values around neutrality, a VOLH,2 species is formed with an (NH2, N,, N,, COO,) donor set for HisGlyGly, (NH2, N,, N,, Nim) for GlyGlyHis and (NH2, N,,N,, S,) for GlyGlyCys. These species, and those with onedeprotonated amide group coordinated to the VIVO ion, can be detected by EPR spectroscopy. The N,(amide) contribution to the hyperfine coupling constant along the z axis, Az, depends on the total charge of the donor atoms in the equatorial plane. The participation of albumin in the transport of vanadium and insulin-mimetic VIVO compounds is reconsidered based on these results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] A Theoretical Study of the Exchange Coupling in Hydroxo- and Alkoxo-Bridged Dinuclear Oxovanadium(IV) CompoundsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2004Antonio Rodríguez-Fortea Abstract A density functional study of exchange coupling in hydroxo- and alkoxo-bridged dinuclear oxovanadium(IV) compounds is presented. Coupling constants calculated for full unmodeled structures are in good agreement with experimentally reported values, confirming the ability of the computational strategy used in this work to predict the exchange coupling in dinuclear VIV compounds. The influence of the configuration of the [VO(,-OR)2VO]2+ core in compounds with two edge-sharing octahedrally coordinated oxovanadium(IV) centers, of the nature of the terminal ligands and of structural distortions on the coupling constant have been analyzed through model calculations. The results indicate that the coupling constant is less affected by these factors than for hydroxo- and alkoxo-bridged CuII compounds. The calculations support the orbital models usually employed in qualitative interpretations of magneto-structural correlations, showing good correlations between the calculated coupling constants and the overlap between the two magnetic orbitals or the square of the orbital gap. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Generalization of Schrödinger invariance.FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 5-7 2009Applications to Bose-Einstein condensation Abstract The symmetries of non-linear Schrödinger equations with power-law non-linearities are investigated. It is shown that Galilei invariance can be extended to Schrödinger invariance if the coupling constant(s) in non-linearity is treated as dimensionful quantity. This is used to find a new non-stationary solutions from given stationary ones. [source] Davydov's solitons in zigzag carbon nanotubesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2010Larissa Brizhik Abstract Nonlinear mechanism of charge transport in low-dimensional nanosystems is considered, based on the account of the electron,phonon interaction that arises from the deformation dependencies of the on-site and the hopping interaction energies at intermediatevalues of the corresponding coupling constants. In particular, carbon-type hexagonal zigzag nanotubes are studied. It is shown that in the adiabatic approximation the electron,phonon coupling results in the self-trapping of carriers and formation of polaron (soliton) states. We show that the ground state of an electron in a nanotube is a low-dimensional polaron whose symmetry depends on the strength of the coupling. Namely, at relatively weak coupling, the polaron possesses quasi-one-dimensional properties and has an azimuthal symmetry. When the coupling constant exceeds some critical value, the azimuthal symmetry breaks down and two-dimensional polaron on the nanotube surface is formed. There are also polarons formed by the electrons in the conducting band (or by holes in the valence band) in semiconducting zigzag carbon nanotubes. Such polarons are described by the system of coupled nonlinear Schroedinger equations which admits single-band polarons, and entangled (hybridized) polarons. These two types of polarons possess different energies and symmetry properties. Single-band solutions are one-dimensional polarons: they are azimuthally symmetric and localized along the nanotube axis. The entangled polarons are also self-trapped along the nanotube axis, but possess an inner structure and are modulated around the nanotube. The entangled polarons break the azimuthal symmetry and their energy is lower than the energy of single-band polarons. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Convergence radii of the polarization expansion of intermolecular potentialsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009William H. Adams Abstract A new method is presented to evaluate convergence radii of the polarization expansion of interaction energies for pairs of atoms or molecules. The method is based on an analysis of the variation of the perturbed state vector as a function of the coupling constant , and does not require a calculation of perturbation corrections to high order. The convergence radii at infinite interatomic/intermolecular distances R, as well as a remarkably accurate representation of the R dependence of the convergence radii are obtained from simple calculations involving only monomer wave functions. For the interaction of the lithium and hydrogen atoms, the obtained convergence radii agree well with those obtained previously from the large-order calculations of Patkowski et al. (Patkowski et al., J Chem Phys, 2002, 117, 5124), but are expected to be considerably more accurate. Rigorous upper bounds and reasonable approximations to the convergence radii at R = , are obtained for the pairs of lithium, beryllium, boron, neon, and sodium atoms, as well as for the dimer consisting of two LiH molecules. For all the systems studied, the convergence radii are significantly smaller than the unity and rapidly decrease with the increase of the nuclear charge. It is hoped that the results of this investigation will help to analyze and eventually to compute the convergence radii of the symmetry-adapted perturbation theories which utilize the same partitioning of the Hamiltonian as the polarization expansion. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Performance of plane-wave-based LDA+U and GGA+U approaches to describe magnetic coupling in molecular systems,JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2009Pablo Rivero Abstract This work explores the performance of periodic plane wave density functional theory calculations with an on-site Coulomb correction to the standard LDA and GGA exchange-correlation potential,commonly used to describe strongly correlated solids,in describing the magnetic coupling constant of a series of molecular compounds representative of dinuclear Cu complexes and of organic diradicals. The resulting LDA+U or GGA+U formalisms, lead to results comparable to experiment and to those obtained by means of standard hybrid functionals provided that the value of the U parameter is adequately chosen. Hence, these methods offer an alternative efficient computational scheme to correct LDA and GGA approaches to adequately describe the electronic structure and magnetic coupling in large molecular magnetic systems, although at the expenses of introducing an empirical (U) parameter. For all investigated copper dinuclear systems, the LDA+U and GGA+U approaches lead to an improvement in the description of magnetic properties over the original LDA and GGA schemes with an accuracy similar to that arising from the hybrid B3LYP functional, by increasing the on-site Coulomb repulsion with a moderate U value. Nevertheless, the introduction of an arbitrary U value in the 0,10 eV range most often provides the correct ground-state spin distribution and the correct sign of the magnetic coupling constant. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] 1H and 13C NMR conformational study of 2-(benzotriazol-1-yl)-substituted tetrahydrofuransJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2003Alan R. Katritzky Abstract Assignments of the proton and carbon NMR signals for 2-(benzotriazol-1-yl)tetrahydrofurans 1,6 are based on 1H,1H COSY, NOESY, 1H,13C heteronuclear HETCOR, 1H,13C heteronuclear long-range HETCOR-LR and nuclear Overhauser enhancement experiments, and supported by selective spin decoupling experiments. The electronic and steric effects of the 2-benzotriazolyl substituent on the 1H and 13C NMR chemical shifts are evaluated and discussed. Conformational isomers cis and trans are distinguished by the magnitude of the J(H,2,H,3) coupling constant, by one-bond 1J(C,2, H,2) coupling constants and by 13C chemical shifts of the C-2 anomeric carbon. The benzotriazol-1-yl group prefers the pseudo-axial orientation in each of 1,6. The stereochemistry and conformation of 6 are rigorously demonstrated by an x-ray structure. Copyright © 2003 John Wiley & Sons, Ltd. [source] AIM and NBO analysisMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2010In the series of diaminoenones, large high-frequency shifts of the 1H NMR of the NH group in the cis -position relative to the carbonyl group suggests strong NH···O intramolecular hydrogen bonding comprising a six-membered chelate ring. The NH···O hydrogen bond causes an increase of the 1J(N,H) coupling constant by 2,4 Hz and high-frequency shift of the 15N signal by 9,10 ppm despite of the lengthening of the relevant NH bond. These experimental trends are substantiated by gauge-independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3-bis(isopropylamino)-1-(aryl)prop-2-en-1-one (12) for conformations with the Z - and E -orientations of the carbonyl group relative to the NH group. The effects of the NH···O hydrogen-bond on the NMR parameters are analyzed with the atoms-in-molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the NH···O hydrogen bond as compared with that of 1,1-di(pyrrol-2-yl)-2-formylethene (13) where NH···O hydrogen bridge establishes a seven-membered chelate ring, and the corresponding 1J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) ,,*NH hyperconjugative interaction is weakened on going from the six-membered chelate ring to the seven-membered one due to a more bent hydrogen bond in the former case. A dominating effect of the NH bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the 1J(N,H) value as a consequence of the NH···O hydrogen bonding in the studied diaminoenones. Copyright © 2010 John Wiley & Sons, Ltd. [source] Structural determination of ,-lactams by 1H and 13C NMRMAGNETIC RESONANCE IN CHEMISTRY, Issue 12 2009Rubén Montalvo-González Abstract The thermodynamic products (,-lactams) of the degradation of ten different spirocyclic oxaziridines were analyzed by 1H and 13C NMR spectroscopy. The preferred conformations were determined by examining the homonuclear spin,spin coupling constant and the chemical shift effects of the N -substituent and the alkyl group of the aliphatic ring on 1H and 13C NMR spectra. Copyright © 2009 John Wiley & Sons, Ltd. [source] Resolving an apparent discrepancy between theory and experiment: spin,spin coupling constants for FCCFMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2008Janet E. Del Bene Abstract Ab initio equation of motion coupled cluster singles and doubles (EOM,CCSD) and second-order polarization propagator approximation (SOPPA) calculations have been performed to evaluate spin,spin coupling constants for FCCF (difluoroethyne). The computed EOM-CCSD value of 3J(FF) obtained at the experimental geometry of this molecule supports the previously reported experimental value of 2.1 Hz, thereby resolving an apparent discrepancy between theory and experiment. This coupling constant exhibits a strong dependence on the CC and CF distances, and its small positive value results from a sensitive balance of paramagnetic spin-orbit (PSO) and spin-dipole (SD) terms. The three other unique FCCF coupling constants 1J(CC), 1J(CF), and 2J(CF) have also been reported and compared with experimental data. While 1J(CF) is in agreement with experiment, the computed value of 2J(CF) is larger than our estimate of the experimental coupling constant. Copyright © 2008 John Wiley & Sons, Ltd. [source] Improved multiplicity-editing of HMBC NMR spectraMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2006Andrew J. Benie Abstract A new improved multiplicity-edited HMBC experiment is introduced that leads to better J cross-talk suppression in the even (i.e. C + CH2 groups) and odd (i.e. CH + CH3 groups) subspectra. By combining data recorded with three different pulse sequences J cross-talk becomes a second-order effect in ,1J, i.e. the deviation of an actual 1J coupling constant from the value 1J0 used in setting delays , = (1J0),1/2, which is adequate for most applications. As for the original multiplicity-edited HMBC experiment, the improved experiment can be performed with a single excitation delay or implemented in a broadband version similar to broadband HMBC. Copyright © 2006 John Wiley & Sons, Ltd. [source] The dressed nonrelativistic electron in a magnetic fieldMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2006Laurent Amour Abstract We consider a nonrelativistic electron interacting with a classical magnetic field pointing along the x3 -axis and with a quantized electromagnetic field. When the interaction between the electron and photons is turned off, the electronic system is assumed to have a ground state of finite multiplicity. Because of the translation invariance along the x3 -axis, we consider the reduced Hamiltonian associated with the total momentum along the x3 -axis and, after introducing an ultraviolet cutoff and an infrared regularization, we prove that the reduced Hamiltonian has a ground state if the coupling constant and the total momentum along the x3 -axis are sufficiently small. We determine the absolutely continuous spectrum of the reduced Hamiltonian and, when the ground state is simple, we prove that the renormalized mass of the dressed electron is greater than or equal to its bare one. We then deduce that the anomalous magnetic moment of the dressed electron is nonnegative. Copyright © 2006 John Wiley & Sons, Ltd. [source] Forward scattering peak in the electron,phonon interaction and impurity scattering of cuprate superconductorsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2005M. L. Kuli Abstract The important role of the electron,phonon interaction (EPI) in explaining the normal state properties and pairing mechanism in high- Tc superconductors (HTSC) is discussed. A number of experiments are analyzed such as: dynamical conductivity, Raman scattering, neutron scattering, ARPES, tunnelling measurements, and etc. They give convincing evidence that the EPI dominantly contributes to pairing in HTSC oxides. Strong electronic correlations cause the forward scattering peak (FSP) in the EPI and in the non-magnetic impurity potential. The theory based on the FSP (whatever is its origin) explains several puzzling experimental results in ARPES and transport: (1) much smaller transport coupling constant than the pairing one (,tr , ,ph); (2) the ARPES non-shift puzzle , where the nodal kink at 70 meV is unshifted in the superconducting state while the anti-nodal one at 40 meV is shifted; (3) d-wave superconductivity due to the EPI; (4) robustness of d-wave pairing in the presence of nonmagnetic impurities; (5) collapse of the elastic scattering rate near the anti-nodal point in the superconducting state; (6) anomalous temperature dependence of the Hall angle in optimally doped HTSC. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Weak localization and the Mooij rule in disordered metalsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003Mi-Ae Park Abstract Weak localization leads to the same correction to both the conductivity and the McMillan's electron,phonon coupling constant , (and ,tr, transport electron,phonon coupling constant). Consequently the temperature dependence of the thermal electrical resistivity is decreasing as the conductivity is decreasing due to weak localization, which results in the decrease of the temperature coefficient of resistivity (TCR) with increasing the residual resistivity. When , and ,tr are approaching zero, only the residual resistivity part remains and it gives rise to the negative TCR. Accordingly, the Mooij rule is a manifestation of weak localization correction to the conductivity and the electron,phonon interaction. This understanding provides a new means of probing the phonon-mechanism in exotic superconductors and an opportunity of fabricating new novel devices. [source] Spin-Hall effect and spin coherent waves in semiconductors with Rashba spin-orbit interactionPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2008P. Kleinert Abstract Based on rigorous quantum-kinetic equations for the spin-density matrix, spin-charge coupled drift-diffusion equations are derived for a strongly confined twodimensional hole gas. An electric field leads to a coupling between the spin and charge degrees of freedom. For weak spin-orbit interaction, this coupling gives rise to the intrinsic spin-Hall effect that occurs in the diffusive regime. There exists a threshold value of the spin-orbit coupling constant that separates spin diffusion from ballistic spin transport. In the latter regime, undamped spin-coherent oscillations are observed. Their relationship to the zitterbewegung is discussed. The analytic results are compared with an exact microscopic approach valid in the ballistic regime. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Generalized theoretical approach to quasi-one-dimensional molecular magnetsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2006R. Pe Abstract Two quasi-one-dimensional compounds [LnIII(terpy)(DMF)4][WV(CN)8] · 6H2O, where Ln stands for Gd or Sm, were synthesized and the measurements of their magnetic features were carried out. Magnetization was measured at 2K in the field range 0,5 T. To extract physical information from the experimental data a generalization of the theoretical approach given by Verdaguer et al. (Phys. Rev. B 29 , 5144 (1984)) [1] is put forward. That theoretical model is found to fit the data well. It allows for the determination not only of the coupling constant but also of the zero-field splitting parameter. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The role of side chain conformational flexibility in surface recognition by Tenebrio molitor antifreeze proteinPROTEIN SCIENCE, Issue 7 2003Margaret E. Daley AFP, antifreeze protein; DQF-COSY, double quantum filtered correlated spectroscopy; NMR, nuclear magnetic resonance; NOE, nuclear Overhauser enhancement; NOESY, nuclear Overhauser effect spectroscopy; 3J,,, 3-bond scalar coupling constant between spins H, and H, Abstract Two-dimensional nuclear magnetic resonance spectroscopy was used to investigate the flexibility of the threonine side chains in the ,-helical Tenebrio molitor antifreeze protein (TmAFP) at low temperatures. From measurement of the 3J,,1H- 1H scalar coupling constants, the ,1 angles and preferred rotamer populations can be calculated. It was determined that the threonines on the ice-binding face of the protein adopt a preferred rotameric conformation at near freezing temperatures, whereas the threonines not on the ice-binding face sample many rotameric states. This suggests that TmAFP maintains a preformed ice-binding conformation in solution, wherein the rigid array of threonines that form the AFP-ice interface matches the ice crystal lattice. A key factor in binding to the ice surface and inhibition of ice crystal growth appears to be the close surface-to-surface complementarity between the AFP and crystalline ice, and the lack of an entropic penalty associated with freezing out motions in a flexible ligand. [source] Structural Investigation of a High-Affinity MnII Binding Site in the Hammerhead Ribozyme by EPR Spectroscopy and DFT Calculations.CHEMBIOCHEM, Issue 10 2003Effects of Neomycin B on Metal-Ion Binding Abstract Electron paramagnetic resonance spectroscopy and density functional theory methods were used to study the structure of a single, high-affinity MnIIbinding site in the hammerhead ribozyme. This binding site exhibits a dissociation constant Kdof 4.4 ,M in buffer solutions containing 1,M NaCl, as shown by titrations monitored by continuous wave (cw) EPR. A combination of electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) experiments revealed that the paramagnetic manganese(II) ion in this binding site is coupled to a single nitrogen atom with a quadrupole coupling constant,of 0.7 MHz, an asymmetry parameter,of 0.4, and an isotropic hyperfine coupling constant of Aiso(14N)=2.3 MHz. All three EPR parameters are sensitive to the arrangement of the MnIIligand sphere and can therefore be used to determine the structure of the binding site. A possible location for this binding site may be at the G10.1, A9 site found to be occupied by MnIIin crystals (MacKay et al., Nature 1994, 372, 68 and Scott et al., Science 1996, 274, 2065). To determine whether the structure of the binding site is the same in frozen solution, we performed DFT calculations for the EPR parameters, based on the structure of the MnIIsite in the crystal. Computations with the BHPW91 density function in combination with a 9s7p4d basis set for the manganese(II) center and the Iglo-II basis set for all other atoms yielded values of,(14N)=+0.80 MHz, ,=0.324, and Aiso(14N)=+2.7 MHz, in excellent agreement with the experimentally obtained EPR parameters, which suggests that the binding site found in the crystal and in frozen solution are the same. In addition, we demonstrated by EPR that MnIIis released from this site upon binding of the aminoglycoside antibiotic neomycin B (Kd=1.2 ,M) to the hammerhead ribozyme. Neomycin B has previously been shown to inhibit the catalytic activity of this ribozyme (Uhlenbeck et al., Biochemistry 1995, 34, 11,186). [source] Temperature Dependence of Interactions Between Stable Piperidine-1-yloxyl Derivatives and a Semicrystalline Ionic Liquid,CHEMPHYSCHEM, Issue 10 2010Veronika Strehmel Dr. Abstract The stable 2,2,6,6-tetramethylpiperidine-1-yloxyl and its derivatives with hydrogen-bond-forming (-OH, -OSO3H), anionic (-OSO3, bearing K+ or [K(18-crown-6)]+ as counter ion), or cationic (-N+(CH3)3 bearing I,, BF4,, PF6, or N,(SO2CF3)2 as counter ion) substituents are investigated in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide over a wide temperature range. The temperature dependence of the viscosity of the ionic liquid is well described by the Vogel,Fulcher,Tammann equation. Interestingly, the temperature dependence of the rotational correlation time of the spin probes substituted with either a hydrogen-bond-forming group or an ionic substituent can be described using the Stokes,Einstein equation. In contrast, the temperature dependence of the rotational correlation time of the spin probe without an additional substituent at the 4-position to the nitroxyl group does not follow this trend. The activation energy for the mobility of the unsubstituted spin probe, determined from an Arrhenius plot of the spin-probe mobility in the ionic liquid above the melting temperature, is comparable with the activation energy for the viscous flow of the ionic liquid, but is higher for spin probes bearing an additional substituent at the 4-position. Quantum chemical calculations of the spin probes using the 6-31G+d method give information about the rotational volume of the spin probes and the spin density at the nitrogen atom of the radical structure as a function of the substituent at the spin probes in the presence and absence of a counter ion. The results of these calculations help in understanding the effect of the additional substituent on the experimentally determined isotropic hyperfine coupling constant. [source] The Anomalous Deuterium Isotope Effect in the NMR Spectrum of Methane: An Analysis in Localized Molecular OrbitalsCHEMPHYSCHEM, Issue 9 2008Stephan P. A. Sauer Prof. Dr. Anomaly explained: The secondary isotope effect on the carbon,hydrogen indirect nuclear spin,spin coupling constant in methane, which is larger than the primary isotope effect, is explained in terms of contributions to the coupling constant from localized molecular orbitals. [source] A Pragmatic Recipe for the Treatment of Hindered Rotations in the Vibrational Averaging of Molecular PropertiesCHEMPHYSCHEM, Issue 1 2008Brendan C. Mort Dr. Abstract A computational protocol for the treatment of hindered rotations in the vibrational averaging of molecular properties is described. As examples, the specific rotations of (R) -methyloxirane, (1S) -methylnorbornanone, and (S) -epichlorohydrin and the spin-spin coupling constant for are investigated. For each of the four molecules, the relaxed and unrelaxed potential energy surfaces along the rotational coordinate of interest are used to solve the nuclear Schrödinger equation using a pseudospectral method. Analysis of the results demonstrate that the vibrational averaging for low-frequency modes that represent hindered rotations can lead to unphysical behavior at high temperatures while simply neglecting the rotational contributions is also not desirable. The method described in this work connects the (an)harmonic oscillator behavior at low temperatures with the free rotor-like behavior at high temperatures. [source] Cyano-bridged Ln3+ -Cr3+ Binuclear Complexes [Ln(L)x(H2O)yCr(CN)6]·mL·nH2O (Ln=La,Nd, x=5, y=2, m=1 or 2, n=2 or 2.5; Ln=Sm,Dy, Er, x=4, y=3, m=0, n=1.5 or 2.0; L=2-pyrrolidinone): Structure, Magnetism and Spin Density MapCHINESE JOURNAL OF CHEMISTRY, Issue 3 2007Xian-Ru Sun Abstract In order to shed light upon the nature and mechanism of 4f-3d magnetic exchange interactions, a series of binuclear complexes of lanthanide(3+) and chromium(3+) with the general formula [Ln(L)5(H2O)2Cr(CN)6]·mL·nH2O (Ln=La (1), Ce (2), Pr (3), Nd (4); x=5, y=2, m=1 or 2, n=2 or 2.5; L=2-pyrrolidinone) and [Ln(L)4(H2O)3Cr(CN)6] ·nH2O (Ln=Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Er (10); x=4, y=3, m=0, n=1.5 or 2.0; L2-pyrrolidinone) were prepared and the X-ray crystal structures of complexes 2, 6 and 7 were determined. All the compounds consist of a Ln-CN-Cr unit, in which Ln3+ in a square antiprism environment is bridged to an octahedral coordinated Cr3+ ion through a cyano group. The magnetic properties of the complexes 3 and 6,10 show an overall antiferromagnetic behavior. The fitting to the experimental magnetic susceptibilities of 7 give g=1.98, J=0.40 cm,1, zJ,=,0.21 cm,1 on the basis of a binuclear spin system (SGd=7/2, SCr=3/2), revealing an intra-molecular Gd3+ -Cr3+ ferromagnetic interaction and an inter-molecular antiferromagnetic interaction. For 7 the calculation of quantum chemical density functional theory (DFT), combined with the broken symmetry approach, showed that the calculated spin coupling constant was 20.3 cm,1, supporting the observation of weak ferromagnetic intra-molecular interaction in 7. The spin density distributions of 7 in both the high spin ground state and the broken symmetry state were obtained, and the spin coupling mechanism between Gd3+ and Cr3+ was discussed. 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