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Spin Configurations (spin + configuration)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

Theory of chemical bonds in metalloenzymes XIII: Singlet and triplet diradical mechanisms of hydroxylations with iron-oxo species and P450 are revisited

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009
Kizashi Yamaguchi
Abstract Electronic structures of the Compound I (CpdI) in P450 are investigated on the basis of spin coupling forms of iron-oxo (Fe(IV)O) cores and radical ligand (,L) groups to generalize previous singlet and triplet diradical (TD) mechanisms for oxygenations of alkanes with Fe( IV)O. Orbital interaction schemes for four lower-lying spin configurations of CpdI with HC bond of substrate are examined to elucidate how magnetic coupling modes correlate with radical reaction pathways for hydroxylation reactions on the basis of the broken symmetry (BS) molecular orbital (MO) model. The configuration correlation diagrams for the four configurations model are depicted on the basis of the isoelectronic analogy among O, O2, and Fe( IV)O, in addition to Coulomb exchange energy on the iron site, which determines its local spin configuration. Important role of ligand spin (,L) of CpdI for regulation of hydroxylation mechanisms is clarified with the aid of the spin coupling forms. Transition states for one quartet and three doublet configurations under the BS MO approximation are examined on the basis of potential curve crossings along reaction pathways. The four transition structures and corresponding radical intermediates for methane and trimethyl methane with CpI are located by the BS hybrid Kohn,Sham density functional theory (DFT) (B3LYP) method to confirm the orbital interaction schemes. Spin density populations obtained by the BS B3LYP calculations are found to be consistent with the theoretical predictions based on the four configurations model. The configuration and state correlation diagrams by BS B3LYP before and after spin projection are also consistent with the BS MO interaction schemes, which provide local SD and TD mechanisms of hydroxylation with CpdI. The present BS MO-theoretical framework is useful for systematic understanding of a lot of recent BS hybrid DFT computational results for hydroxylation reactions with CpdI and configuration correlation diagrams reported by several groups. Implications of the present theoretical and computational results are discussed in relation to several experimental characteristics of hydroxylation reactions with iron-oxo species and P450. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

Metastable spin configuration of two-dimensional hole system in the quantum Hall regime

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006
Katsuyoshi Kodera
Abstract We have observed hysteretic behavior of magnetoresistance with slow dynamics in a GaAs/AlGaAs two-dimensional hole system (2DHS) in quantum Hall regime. The relaxation towards the stable state exhibits a distinct change in behaviour between the filling ranges , > 1 and , < 1, suggesting a spin-related mechanism. The relaxation time scale on the order of an hour was observed at the lowest temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetic-field-induced switching of spin injectionin Zn1,xMnxTe/ZnTe double quantum wells

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004
S. Shirotori
Abstract Magnetic-field-induced switching of the spin configuration and the resultant spin injection direction have been studied in a Zn1,xMnxTe/ZnTe double quantum well. The up- and down-spin excitons are injected from the Zn1,xMnxTe layers to the ZnTe well in weak magnetic fields, where both exciton energies in the Zn1,xMnxTe layer are higher than those in the ZnTe. Above the level crossing field, the down-spin exciton energy in the Zn1,xMnxTe layers becomes lower due to the giant Zeeman effect. Therefore, the up- and down-spin excitons are spatially separated in each layer and the down-spin exciton in the ZnTe layer is injected to the Zn1,xMnxTe. It means that the direction of the excitonic spin injection can be switched by the external field. The injection time increases from 12 psec to 300 psec toward the level crossing field of 2.5 T, since the spin-polarized excitons in those layers are associated and can cause reverse spin injection processes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Theory of chemical bonds in metalloenzymes XIII: Singlet and triplet diradical mechanisms of hydroxylations with iron-oxo species and P450 are revisited

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2009
Kizashi Yamaguchi
Abstract Electronic structures of the Compound I (CpdI) in P450 are investigated on the basis of spin coupling forms of iron-oxo (Fe(IV)O) cores and radical ligand (,L) groups to generalize previous singlet and triplet diradical (TD) mechanisms for oxygenations of alkanes with Fe( IV)O. Orbital interaction schemes for four lower-lying spin configurations of CpdI with HC bond of substrate are examined to elucidate how magnetic coupling modes correlate with radical reaction pathways for hydroxylation reactions on the basis of the broken symmetry (BS) molecular orbital (MO) model. The configuration correlation diagrams for the four configurations model are depicted on the basis of the isoelectronic analogy among O, O2, and Fe( IV)O, in addition to Coulomb exchange energy on the iron site, which determines its local spin configuration. Important role of ligand spin (,L) of CpdI for regulation of hydroxylation mechanisms is clarified with the aid of the spin coupling forms. Transition states for one quartet and three doublet configurations under the BS MO approximation are examined on the basis of potential curve crossings along reaction pathways. The four transition structures and corresponding radical intermediates for methane and trimethyl methane with CpI are located by the BS hybrid Kohn,Sham density functional theory (DFT) (B3LYP) method to confirm the orbital interaction schemes. Spin density populations obtained by the BS B3LYP calculations are found to be consistent with the theoretical predictions based on the four configurations model. The configuration and state correlation diagrams by BS B3LYP before and after spin projection are also consistent with the BS MO interaction schemes, which provide local SD and TD mechanisms of hydroxylation with CpdI. The present BS MO-theoretical framework is useful for systematic understanding of a lot of recent BS hybrid DFT computational results for hydroxylation reactions with CpdI and configuration correlation diagrams reported by several groups. Implications of the present theoretical and computational results are discussed in relation to several experimental characteristics of hydroxylation reactions with iron-oxo species and P450. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source]

Antiferromagnetic-to-ferromagnetic transition induced by aluminum in the Ti(Fe1,xAlx)2 intermetallic compounds: a 57Fe Mössbauer spectroscopy study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2007
N. N. Delyagin
Abstract Mössbauer spectroscopy has been used to investigate the hyperfine field distributions and the local spin configurations of Fe atoms in the magnetically ordered Ti(Fe1,xAlx)2 compounds. The evolution of the spin arrangement of the Fe atoms was observed over the concentration range 0 , x , 0.25 at 5 K. The Al impurity suppresses the ferromagnetic exchange in the Fe(6h) layers and simultaneously provides the conditions for a transition of the Fe(2a) atoms, which are nonmagnetic in the TiFe2 compound, to the states with nonzero magnetic moment. The magnetic behavior of the Fe(2a) atoms is the key factor governing the anti- to ferromagnetic transition in the Ti(Fe1,xAlx)2 compounds. The magnetic ordering temperatures of the Ti(Fe1,xAlx)2 compounds were determined. In addition, the parameters of the electric-field gradient in TiFe2 as well as the relationship between the value of the magnetic moment of the Fe atom and the type of atomic configuration were discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Four-sublattice ferrimagnetic systems: I. Quantum fluctuations of spins at zero temperature

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2004
Rong-ke Qiu
Abstract Within the framework of the linear spin wave approximation, the quantum fluctuations of spins at zero temperature in four-sublattice ferrimagnetic systems are studied by employing retard Green's functions. The effects of exchange constants on the quantum fluctuations of spins are discussed for three different spin-configurations. The magnetic properties of these spin configurations are related to their magnetically structural symmetry. When the parameters of the exchange couplings are adjusted, the crossover of the spin configurations results in the strong quantum fluctuations, owing to the behaviors of the non-three-dimensional magnetically system. When two of the four exchange-constants in the present four-sublattice bulk systems are set to be zero, the system behaves as a non-three-dimensionally magnetic system, although the structure of the system is still three-dimensional. All the exchange couplings involve in the quantum competition of the systems, but the effects of antiferromagnetic and ferromagnetic exchange couplings are different evidently. The antiferromagnetic exchange couplings play an important role in a balance of the quantum competition. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Four-sublattice ferrimagnetic systems: II.

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2004
Effects of the spin quantum number
Abstract The effects of the spin quantum number of each sublattice on the quantum fluctuations are discussed for different spin configurations in four-sublattice ferrimagnetic systems. In multi-sublattice ferrimagnets, although the individual sublattice magnetization vectors do not offset each other, but their deviations vectors can cancel out. Namely, the sum of the deviations of magnetization of sites with same initiate spin direction, equals to that of sites with opposite initiate spin direction ,i , = ,j ,, i and j denote respectively the spins along the up and down initiate spin directions). The role of the spin quantum number of each site on magnetic properties of the system is correlative with properties of the exchange couplings surrounding the site. The results show that the proportion of ferromagnetic and antiferromagnetic exchange couplings, the spin quantum number of each sublattice and the magnetically structural symmetry of the system all play important roles on the quantum fluctuations of the systems. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

New spin configurations in nano-sized magnets near reorientation phase transition

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2006
M. Kisielewski
The cover picture of this issue of physica status solidi (c) has been taken from the article [1]. [source]