Interdimer Interaction Research Articles

On Thermo- and Photo-Induced Symmetry-Broken Transformation in Spin–Crossover Complex: Cooperative Activation

We study energetics of a cooperative low-spin (L) to high-spin (H) transformation in a crystal with two sublattices, where thermo- and photo-induced symmetry-broken phases have been recently observed. The model takes into account an intra-dimer antiferromatic coupling and inter-dimer couplings. Cooperative activation processes for switching between LH and HL states and that from LL to HH states of a dimer are analyzed. It is shown that locally (within a dimer) preferred symmetry-broken, LH and HL, states compete with inter-dimer couplings, which stimulates dynamical disorder via a decrease in the energy barrier for a flip between asymmetric configurations. On the other hand, a locally non-preferred symmetric state (HH) is supported by inter-dimer interaction via a cooperative activation mechanism. We conclude that symmetry-broken states can form an intermediate thermo-induced phase or can be observed as a photo-induced one at low temperatures as a result of local equilibrium. The global equilibrium follow...

Magnetic anisotropy of the SrCu2(BO3)2 system as revealed by X-band ESR

X-band electron paramagnetic resonance measurements on a single crystal of the highly frustrated SrCu2(BO3)2 system are shown to provide an essential inspection of the magnetic anisotropy present in this compound. The very broad absorption lines seem to be consistent with the largest anisotropy term, namely, the antisymmetric Dzyaloshinsky-Moriya (DM) interaction allowed by symmetry. However, the previously well-accepted model of only interdimer interaction is generalized with additional intradimer DM terms. Moreover, spin-phonon coupling is recognized as the cause of the line width broadening with increasing temperature.

Attractant binding alters arrangement of chemoreceptor dimers within its cluster at a cell pole.

Many sensory systems involve multiple steps of signal amplification to produce a significant response. One such mechanism may be the clustering of transmembrane receptors. In bacterial chemotaxis, where a stoichiometric His-Asp phosphorelay from the kinase CheA to the response regulator CheY plays a central role, the chemoreceptors (methyl-accepting chemotaxis proteins) cluster together with CheA and the adaptor CheW, at a pole of a rod-shaped cell. This clustering led to a proposal that signal amplification occurs through an interaction between chemoreceptor homodimers. Here, by using in vivo disulfide crosslinking assays, we examined an interdimer interaction of the aspartate chemoreceptor (Tar). Two cysteine residues were introduced into Tar: one at the subunit interface and the other at the external surface of the dimer. Crosslinked dimers and higher oligomers (especially a deduced hexamer) were detected and their abundance depended on CheA and CheW. The ligand aspartate significantly reduced the amounts of higher oligomers but did not affect the polar localization of Tar-GFP. Thus, the binding of aspartate alters the rate of collisions between Tar dimers in assembled signaling complexes, most likely due to a change in the relative positions or trajectories of the dimers. These collisions could occur within a trimer-ofdimers predicted by crystallography, or between such trimers. These results are consistent with the proposal that the interaction of chemoreceptor dimers is involved in signal transduction.

大腸菌アスパラギン酸レセプターTarの極クラスターにおけるダイマー間相互作用とシグナル増幅

大腸菌アスパラギン酸レセプターTarの極クラスターにおけるダイマー間相互作用とシグナル増幅

Coordination Polymers of Ruthenium(II) Acetate with Pyrazine, 4,4′-Bipyridine, and 1,4-Diazabicyclo[2.2.2]octane

A seires of polymer complexes of ruthenium(II) acetate dimers bridged by pyrazine (pyz), 4,4′-bipyridine (4,4′-bpy), and l,4-diazabicyclo[2.2.2]octane (dabco) were prepared and characterized by elemental analysis, infrared and diffuse reflectance spectroscopy, variable temperature magnetic susceptibility, and electrical conductivity. The significant interdimer interaction through the bridging ligands was not observed for the polymers.

1C0930 大腸菌走化性レセプターのダイマー間相互作用に対するメチル化と誘引物質の影響(14.化学受容,一般演題,日本生物物理学会第40回年会)

1C0930 大腸菌走化性レセプターのダイマー間相互作用に対するメチル化と誘引物質の影響(14.化学受容,一般演題,日本生物物理学会第40回年会)

The C=C Stretching Vibrations of κ-(BEDT–TTF)2Cu[N(CN)2]Br and Its Isotope Analogues

The C=C stretching modes in resonance Raman spectra and infrared reflectivity were measured at temperatures between 15 K and 300 K using various polarizations in k-(BEDT-TTF)_2Cu[N(CN)_2]Br, its fully and partially deuterated analogues, and ^{13}C-substituted analogue. The infrared- and Raman-active bands were re-assigned based on the factor group analysis. We found a Raman-active EMV-coupled \nu_3 mode near 1420 cm_{-1}, which shows a large downshift and broadening through the inter-dimer EMV interaction. The mixing of the bridge and ring C=C stretching vibrations depends upon the symmetry of the crystal mode. In contrast to deuterated crystals, the non-deuterated crystals show a splitting in the \nu_2, \nu_3, and \nu_{27} bands.

Crystal structure, physical properties and electronic structure of a new organic conductor β″­(BEDT­TTF)2SF5CHFCF2SO3

A new organic conductor, β″-(BEDT-TTF)2SF5CHFCF2SO3 [BEDT-TTF, hereafter abbreviated ET, refers to bis(ethylenedithio)tetrathiafulvalene], was prepared by electrocrystallization. The crystal structure of this salt was determined by single crystal X-ray diffraction at 298 and 150 K, its physical properties were examined by electrical resistivity, Raman spectroscopy and EPR measurements, and its electronic structure was calculated and compared with that of the analogous salt β″-(ET)2SF5CH2CF2SO3. Whereas β″-(ET)2SF5CHFCF2SO3 has disordered anions and undergoes a metal-to-insulator transition at ∼190 K, β″-(ET)2SF5CH2CF2SO3 has ordered anions and is semiconducting down to ∼100 K, metallic below ∼100 K, and superconducting below 5 K. At room temperature both β″-(ET)2SF5CHFCF2SO3 and β″-(ET)2SF5CH2CF2SO3 have similar electronic band structures and physical properties. When the temperature is lowered, each donor molecule stack becomes dimerized in both salts. However, the interdimer interaction within each donor stack nearly vanishes in β″-(ET)2SF5CHFCF2SO3, but remains substantial in β″-(ET)2SF5CH2CF2SO3.

2P170大腸菌化学感覚レセプターにおけるダイマー間相互作用とシグナル伝達の関連

2P170大腸菌化学感覚レセプターにおけるダイマー間相互作用とシグナル伝達の関連

Quaternary Organization of the Staphylothermus marinus Phosphoenolpyruvate Synthase: Angular Reconstitution from Cryoelectron Micrographs with Molecular Modeling

Digital electron images of frozen-hydrated preparations of the 2.25-MDa Staphylothermus marinus phosphoenolpyruvate synthase (EC 2.7.9.2) have been analyzed by single-particle classification and averaging and iterative quaternion-based angular reconstitution. Contrast transfer function correction of micrographs obtained at different defocus values was used to improve the informational quality of the projection averages. Three-dimensional reconstructions were obtained to roughly 3-nm spatial resolution, in which the 24 identical subunits were arranged to form an octahedral complex, although the amino-terminal nucleotide-binding domain was not resolved. An atomic model of the subunit was generated by homology modeling using as the reference the known X-ray crystallographic structure of the related enzyme pyruvate orthophosphate dikinase (EC 2.7.9.1) from Clostridium symbiosum (Protein Data Bank entry 1DIK). The S. marinus protein could be arranged into an assembly of 12 homodimers to match the three-dimensional reconstruction in terms of shape and size of the homodimers, as well as overall shape and size of the complex. The quaternary model indicated that active sites of three monomers were localized around cavities (or putative channels) centered at the threefold axes of rotational symmetry and that carboxyl-terminal alpha-helical segments of four monomers were localized at the fourfold axes of rotational symmetry where they could facilitate interdimer interaction. The quaternary arrangement also indicated numerous potential hydrophobic and electrostatic interactions at the interdimer interfaces that could contribute further to structural stability.

Unusual crystal structures and properties of nitronylnitroxide radicals. Possible RVB states in molecule-based magnets

We studied two kinds of novel low-dimensional magnetic systems found in the crystals of nitronylnitroxide molecular compounds: Kagome lattice and spin ladder. (i) In the crystals of m -MPYNN · X ( m -MPYNN is m - N -methylpyridinium nitronylnitroxide and X= I, BF 4 , ClO 4 , etc.), m -MPYNN ( S =1/2) exists as a ferromagnetic dimer and the dimers form a triangular lattice with a weak interdimer antiferromagnetic coupling that brings about spin frustration. The magnetic system can be regarded as a spin-1 Kagome antiferromagnet at low temperatures. The low-temperature magnetic measurements revealed a spin-gap ground state, which was possibly identical with the RVB state. The temperature dependence of the heat capacity did not show long-range magnetic ordering down to 0.1 K, but short-range ordering caused by the interdimer interaction. The μ + SR exhibited the temperature-independent depolarization behaviour down to 30 mK, supporting no long-range ordering and a non-magnetic ground state. By replacing the N -methyl group in m -MPYNN with longer alkyl chains, slightly distorted Kagome lattices were obtained, in which the spin gap state collapsed. (ii) The crystal of p -EPYNN · [Ni(dmit) 2 ] ( p -EPYNN is p - N -ethylpyridinium nitronylnitroxide and [Ni(dmit) 2 ] is nickel bis(4,5-dithiolato-1,3-dithiole-2-thione)) includes a ladder structure of [Ni(dmit) 2 ] ( S = 1/2) sandwiched by ferromagnetic chains of p -EPYNN ( S =1/2). The magnetic measurements clearly demonstrated a spin gap of ca . 1000 K for the molecular spin ladder. Impurity effects on the ladder were studied by making a solid solution system, p -EPYNN · [Ni(dmit) 2 ] 1- x · [Au(dmit) 2 ] x with 0 less than or equal to x less than or equal to 0.5. The doping of the non-magnetic [Au(dmit) 2 ] increased Curie defects in the ladder, and resulted in antiferromagnetic behaviour of p -EPYNN at low temperatures.

Ge-induced surface reconstructions on the 4° vicinal Si(100) surface

We report results of a combined study of low-energy-electron diffraction (LEED) and Monte Carlo simulations for the Ge-adsorbed single-domain stepped Si(100) surface. The (4×1) structure, least favored energetically among the (2×1) family of the dimer-induced structures, is found to appear on the Ge-adsorbed Si(001) surface in a limited range of temperatures slightly below room temperature. With mild annealing at ∼370 K, the surface undergoes irreversible transitions initially to a (3×1) and then ultimately to a (2×1) structure after prolonged annealing. We propose that the (4×1) structure consists of an antiferromagnetic arrangement of A-type Ge ad-dimers, which decompose and recombine into C-type ad-dimers for the high-temperature structures upon annealing. In addition, results of Monte Carlo simulations suggest that the (4×1) surface is the most stable structure when the signs of the Ge inter-dimer interaction parameters are exactly opposite to those of the c(4×2)+p(2×1) surface.

Optical Properties of β‘ ‘-(ET)2SF5RSO3 (R = CH2CF2, CHFCF2): Changing Physical Properties by Chemical Tuning of the Counterion

We report the polarized infrared reflectance of β‘ ‘-(ET)2SF5CHFCF2SO3 as a function of temperature. This salt is a derivative of the first fully organic superconductor, β‘ ‘-(ET)2SF5CH2CF2SO3, where the nature of the alkyl group has been modified to contain a chiral center. This small chemical modification has a dramatic effect on the spectral and charge transport properties. The β‘ ‘-(ET)2SF5CHFCF2SO3 complex displays highly anisotropic behavior compared with the superconducting material; the essential difference is observed in the ⊥b direction where the interdimer interaction is weak, in agreement with recent theoretical calculations. The temperature dependence of key anion vibrational modes is discussed in terms of intermolecular hydrogen bonding within the anion pocket. That small chemical modifications of the anion template result in such striking changes in the physical properties suggests that the β‘ ‘-(ET)2SF5RSO3 system is quite close to a Mott phase boundary.

Structural Genealogy of BEDT-TTF-Based Organic Conductors II. Inclined Molecules: θ, α, and κ Phases

Abstract Overlap integrals between HOMO’s of two non-parallel BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) molecules have been calculated. As the dihedral angle between the molecular planes decreases from 180° (parallel) to 90° (perpendicular), the overlap integral increases and attains a maximum around 90°. This accounts for the “universal phase diagram” of the θ-phase; θ-salts vary from an insulator to a metal with decreasing the dihedral angle. The ratio of the lattice constants in the conducting plane, c/a, changes in proportion to the dihedral angle. Thus c/a can be used instead of the dihedral angle. A similar universal phase diagram is applicable to analogous phases like α and α″, and also to the corresponding phases of other donors. The properties of κ-phase salts are similarly scaled by c/a. As c/a increases, the intradimer overlap integral decreases owing to the increase of the intradimer spacing, and correlated insulator, superconductor, and simple-metal phases appear in succession. When c/a increases further, another insulating phase emerges due to the decrease of the interdimer overlaps. Chemical pressure in both θ- and κ-phases reduces c/a, and stabilizes the insulating state. Hydrostatic physical pressure gives the same influence in the θ-phase, but enhances the interdimer interaction in the κ-phase to result in the opposite effect. A diagram is proposed to illustrate which structures of β, β″, θ, and κ are favored by BEDT-TTF and other donors.

Synthesis, spectroscopic studies and magnetic properties of binuclear complexes of the first transition series cations bridged by 2,2′-bipyrimidine

Binuclear complexes [M2Cl4(μ-bpym)], where M = VO2+, FeII, CoII or CuII and bpym = 2,2′-bipyrimidine, and [M2(hfacac)4(μ-bpym)] complexes, where hfacac = hexafluoroacetylacetonate and M = FeII, NiII or CoII have been synthesized and characterized by chemical analysis, conductance measurements, i.r., electronic and e.p.r spectroscopies and by magnetic susceptibility measurements (in the 4.2–291 K range). CoII and FeII are in a high spin state. [(VO)2Cl4(μ-bpym)] is paramagnetic, without significant interactions. [Fe2Cl4(μ-bpym)] shows a singular behaviour explained by an antiferromagnetic intradimer exchange and a ferromagnetic interdimer interaction. All other complexes are antiferromagnetic, with an intramolecular exchange parameter, J, varying from −3.3 cm−1 for CoII/math> to −109 cm−1 for CuII.

Magnetic Properties of Oxygen Physisorbed in Cu-Trans-1,4-Cyclohexanedicarboxylic Acid

Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid having one-dimensional micropores are studied. O2 is well known as a magnetic molecule with S=1. In the case of the low adsorption, temperature dependence of the susceptibility shows the Schottky-type broad peak and the high-field magnetization process has a step at around 34T with saturation moment of 2 μ B/O2. These results are interpreted by the dimer model of S=½ with an antiferromagnetic exchange interaction. Broadening of the step of magnetization with increasing the adsorption may be due to the inter-dimer interaction or the distribution of the intra-dimer exchange interaction. Linear magnetization process which is characteristic of one-dimensional Heisenberg antiferromagnet has not been observed even in the full pore region.

Ferromagnetic Dimer of π-Conjugated Organic Free Radicals 9,9-Bis(p-tolyl)-9,10-dihydroacridin-10-yloxyl

Abstract The magnetic property of the title radical crystals was analyzed by the Bleaney-Bowers equation with J/kB = +8.85 K, which is consistent with the dimetic molecular arrangement with “pseudo-ortho” stacking determined by crystallographic analysis. The inter-dimer interaction was antiferromagnetic.

Neutron Scattering Study on the Structural Phase Transition in KDCO3

Neutron coherent scattering study at the structural phase transition point of KDCO 3 crystal has been carried out. Strong quasielastic diffuse scattering is observed. From the detailed analysis of the intensity distribution in a wide range of the reciprocal space, we conclude as follows: (i) Even at T > T c , the individual dimer is already deformed by the self-trapping of deuterons, thus locally breaking the symmetry of the averaged lattice within the time interval determined by the energy resolution limit of the spectrometer (τ<0.8×10 -11 sec). (ii) The inter-dimer interaction takes place via the strain field induced by the deformed dimers in the self-trapped state. (iii) The structural phase transition is triggered mainly by the strain-mediated indirect interaction between the dimers.

Through-Bond Exchange Coupling and Triplet Excitons in a Dinuclear Copper(II) Macrocyclic Complex

The reaction of the bicyclic cryptand 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosan-5,6,14,15,22,23-hexone (1) with copper(II) leads to the dinuclear complex {1,10-bis(2-aminoethyl)-1,4,7,10,13,16-hexaazacyclooctadecane-5,6,14,15-tetronato(4-)}dicopper(II) (2). 2 crystallizes in the triclinic system (space group P&onemacr;, No. 2), with cell parameters a = 6.751(1) Å, b = 10.153(1) Å, c = 10.748(2) Å, alpha = 71.83(1) degrees, beta = 89.79(1) degrees, gamma = 73.56(1) degrees, and Z = 1. The structure is made up of centrosymmetric neutral dinuclear copper(II) units stacking along the a axis. Each copper(II) ion assumed a distorted-octahedral environment. The basal positions are occupied by four nitrogen atoms, two from deprotonated amide groups and two from the tertiary and primary amines; the apical positions are occupied by one amido nitrogen atom from the same dimer and one amido oxygen atom from a neighboring unit within the stack. The analysis of variable-temperature magnetic susceptibility data reveals the occurrence of a significant intramolecular antiferromagnetic interaction (J = -47 cm(-)(1)) in 2. The analysis of the exchange pathways by extended Hückel calculations shows a strong contribution of the N-C-C-N sigma bonds to the coupling between the two copper(II) ions. The triplet exciton type EPR spectrum of 2 allowed the evaluation of the interdimer interaction (J' approximately 10(-)(3) cm(-1)), a possible description of 2 as a magnetic alternating chain being ruled out.

Structure and magnetism of an exchange coupled system: An NMR approach

A binuclear copper(II) complex [Cu2L(OH)](C1O4)2·2H2O has been synthesized and characterized by X-ray crystallography and1H-NMR studies. The crystal structure shows that the bridging angles between Cu(l)-O(l)-Cu(2) and Cu(l)-O(2)-Cu(2) are 98.9(2)° and 102.2(2)° respectively. The Cu(l)-Cu(2) distance is 3.0097(12)A. This indicates that the interaction between the two copper atoms is antiferromagnetic in nature. The geometry around Cu(l) is distorted square-pyramid with one water molecule occupying the axial fifth position, whereas, the geometry around Cu(2) is distorted square-planar with weak interactions of one of the perchlorate anion. There are eight molecules present in the unit cell. There is an interdimer interaction between the dimers. The temperature-dependent1H-NMR chemical shift studies have been performed on six different protons of this complex which reveals that the exchange coupling constant (− 2J) is same for all protons (208 ± 1 cm−1). However, the hyperfine coupling constant (A′) was found to be different in magnitude as well as in sign. We also report solvent dependent NMR properties.