Shigefumi Yamamura

Influence of Magnetic Field upon the Conductance of a Unicomponent Crystal of a Tetrathiafulvalene-Based Nitronyl Nitroxide

A spin-polarized donor, BTBN, which is a dibromotetrathiafulvalene derivative containing a nitronyl nitroxide group in a cross-conjugated manner, was prepared. Upon hole injection from an electrode, the neutral microcrystals of BTBN exhibited nonlinear I-V characteristics that were interpreted in terms of the space-charge-limited conduction (SCLC) mechanism. Moreover, the resistance of BTBN decreased upon application of a magnetic field below 30 K and exhibited a giant negative magnetoresistance of (R(H) - R(0))/R(0) = -76% at 2 K under 5 T. These results show that the transport of carriers in the neutral unicomponent radical crystal can be controlled by the external magnetic field. These findings are important as a basis for developing molecule-based spin electronic devices.

Nature of the hydrogen bond in tetragonal KDP (KH2PO4) observed by maximum entropy method

In order to explore the nature of the hydrogen bond, the electron density distribution of KH 2 PO 4 (KDP) at room temperature was obtained by the maximum entropy method (MEM) using synchrotron radiation X-ray powder diffraction data. In the obtained electron density distribution maps, the contour lines linked the two oxygen atoms of neighboring PO 4 groups and a hydrogen-bonding network was clearly seen. However, no local maxima of electron density due to hydrogen atoms were recognized. This figure of hydrogen bonding in KDP is similar to that in ice (I h ), which is the only hydrogen-bonded compound previously analyzed by MEM. In both cases, the hydrogen atoms are believed to be disordered between the two oxygen atoms. The present study shows that the character of the hydrogen bond in crystalline materials can be described clearly by MEM, even in the case where heavier atoms such as K and P exist besides O atoms.

Imaging of the electron density distributions of hydrogen in LiH and LiOH by maximum entropy method

Abstract In order to explore the electron distribution of hydrogen, an electron density study was carried out by maximum entropy method (MEM) using the single crystal X-ray diffraction data of LiH measured by Vidal-Valat et al. [Acta Crystallogr. A48 (1992) 46–60] and those of LiOH measured by Gottlicher and Kieselbach [Acta Crystallogr. A32 (1976) 185–192]. It was found that the electron distribution of hydrogen in LiH is very spherical as a consequence of high symmetrical crystalline field. It was also recognized that there exists very weak covalent bond between lithium and hydrogen along the 〈100〉 direction. These features were consistent with the results of difference Fourier synthesis and multipole analysis by Vidal-Valat et al. Contrary to the LiH case, the position of hydrogen in LiOH was hardly assigned from the electron density map and only the contribution of hydrogen was recognized as a distortion of electron clouds of OH ellipse. The present study demonstrated that the electron distribution of hydrogen can be detected by MEM but it should be kept in mind that the distribution of electron from hydrogen was severely affected by the crystal field, which may result in the fact that the electron from hydrogen is far from a spherical distribution.

Magnetic Manipulation of Nucleic Acid Base Microcrystals for DNA Sensing

This paper develops a magneto-DNA sensing device composed of a crystalline nucleic acid base, which is a component of DNA on the basis of the dynamic rotation due to its diamagnetic anisotropy under a magnetic field of the mT order. As a basic study, recrystallized nucleic acid bases, such as cytosine, adenine, and guanine, were used for the measurement. We focused on the induced dynamic orientation effect on the nucleic acid base crystals by exposure of the magnetic field at 0.5 T. The morphologically long axis of a cytosine crystal oriented parallel to the applied magnetic fields, while those of adenine and guanine oriented perpendicular to the magnetic field. As a next stage, we traced the angular difference of the magnetic rotation of DNA adhered to guanine crystals comparing the rotation angles of the pre-exposure sample and the during exposure sample with and without DNA. It was revealed that the degree of the magnetic rotation of guanine crystals with DNA was seemingly less than that of guanine crystals without DNA. The difference in angle of the magnetic rotation of the guanine crystal may allow to detect the adhesion of DNA. The method obtained by detecting precise magnetic rotation of nucleic acid base crystals can be applied to the manipulation and sensing of macromolecules in dispersion containing nucleic acid bases, such as DNA and RNA.

Neutron powder diffraction analysis of guanosine dihydrate using MEM

In majority of the crystals of pharmaceutical compounds, hydrogen bonds play a crucial role. Determination of a hydrogen position is highly important, in order to investigate hydrogen bonds especially in the case of hydrates. We have been investigating humidityinduced phase transitions of hydrates systematically [1,2]. Unique characteristics of hydration water molecules have prompted us to explore the phenomena more precisely. Neutron diffraction analysis is a powerful tool to determine hydrogen positions. However, large single crystals are required because of weak neutron diffraction intensities. Under such background, we carried out neutron powder diffraction analysis of guanosine dihydrate using the Maximum Entropy Method (MEM). Neutron powder diffraction data of guanosine dihydrate (C10H13N5O5.2H2O; crystal data: monoclinic space group P21 a = 17 518 b = 11 278 c = 6 658 Å β= 98 17° Z = 4) were measured by iMATERIA at MLF in J-PARC (Figure 1(a)). Rietveld analysis was carried out using atomic coordinates of nonhydrogen atoms determined by X-ray analysis and those of hydrogen atoms which were placed on the geometrically calculated positions using the averaged X-H bond lengths determined by neutron analysis referencing the hydrogen positions estimated by X-ray analysis sing Fo and σ by Riet eld analysis the nuclear density distribution was calculated by MEM (Figure 1(b)). Nuclear densities of the hydrogen atoms of one water molecule (W1 in Figure 1) were elongated, which is consistent with the results of molecular dynamic simulation [2]. The effective usage of MEM to elucidate hydrogen atom positions from neutron powder diffraction data will be discussed together with that of difference Fourier calculations.

Application of maximum entropy method to neutron protein crystallography

Hydrogen atoms or hydrogen bonds play important roles in protein functions. Neutron diffraction is very powerful tool to detect hydrogen atoms. However it is often obtained rather poor resolution data compared with X-ray data due to weak neutron source intensity and large incoherent scattering from hydrogen atoms. The maximum entropy method (MEM) is noble method to obtain high resolution electron or nuclear density distribution from even limited number of diffraction data. The MEM has been applied to not only X-ray data of small molecules but also those of proteins. For the application to neutron data, so far, only small molecules are reported. When preliminary application of the MEM to 1.1 Å resolution partially deuterated neutron protein data (Protein Data Bank ID : 4fc1) is carried out, most of hydrogen and deuterium atoms are observed (Fig. 1). Since this resolution is unusually high, it is of interest that ability of the MEM for usual or low resolution data. In this paper, effects of resolution and data quality for the MEM are examined. Large deuterated crystals are necessary for neutron experiment to reduce incoherent scattering from hydrogen atoms and to improve data resolution. However deuterated condition is not usual for biomolecules. If no deuteration is need for low resolution data by using the MEM, it would be able to observe biomolecules as they are.

Humidity-induced phase transition of xylose isomerase

Dehydroacetic acid or [DHA = 3-acetyl-6-methyl-2H-pyran2,4(3H)-dione], Is an industrially product used as a fungicide, a bactericide and also as an important intermediate in organic synthesis. usually obtained through the auto-condensation of ethyl acetoacetate [1]. However, little is known on ils metal complexes. The Cu and Zn complexes have been reported to be, respectively, a fungicide [2]. and a heat stabilizer for vinyl chloride resins[3]. There are some other reports in the patent literature [3] and also the stability constantes of some complexes have been measured [4]. This has motivated our study of the structural characterization of complexes of dehydroacetic acid. We present here the crystal structures determination of the complexes, [Cu(DHA)2.2DMF], [Cu(DHA)2.2DMSO]. [Cu( DHA )2. 2DMF], has the following structural properties : triclinic, P-1, a = 7.689(5), b = 8.541(5), c = 9.386(5) Å, α = 84.870(5)°, β = 86.964(5)°, γ = 78.852(5)°, V = 601.9(6) Å3 and Z = 1; for [Cu(DHA)2. 2DMSO] : Monoclinic P21/n a = 11.580(5) b = 6.320 (5) c = 16.4024 (5) Å; β = 92.269(5); V = 1201.1(11) Å3 and Z = 2. The metal atoms are, located on an inversion centre, are surrounded by two DHA ligands occupying the equatorial plane. The two axial positions are occupied by O atoms of two solvant molecules. The structures is stabilized by intermolecular C-H....O hydrogen bonds. An electrochemical study (cyclic voltammetry) indicates that the reduction of the two complexes, two steps are indicated out : the first as attributed to the reduction of the metal and the seconde to the reduction of the coordinated ligands.

Temperature-dependent disordered structure of (BEDT-TTF)3Cl2·5H2O

The x=2 composition crystallizes in the C2/c space group (N15) with the doubled unit cell along c-axis. The trimers were found to be of only one type Ni-Cu-Ni. Below TN=20 K a magnetic ordering with the propagation vector k=[1/2,1/2,0] has been found. The magnetic diffraction patterns are well described by the antiferromagnetic structure given by the irreducible representation 2 for both Ni (8f) and Cu (4b) sites. The exchange interactions within the trimers are dominated by Heisenberg-type nearest-neighbor interactions JCuCu=-4.92(6) meV, JCu-Ni=-0.85(10) meV and D_Ni=-0.7(1) for x=2.

Analysis of crystal growth of trigonal ribonuclease A from bovine pancreas

Mechanism of crystal growth is an object to understand and control crystal size and quality. Ribonuclease A (RNaseA) is known to crystallize in the trigonal form using 3 M NaCl and 30% (NH4)2SO4 as precipitants. Crystal growth of trigonal RNaseA was investigated. Solubility curves were determined at 10, 20, and 35°C. It was found that solubility decreases at higher temperature. Negative correlation between solubility and temperature is known for hydrophobic proteins. However, RNaseA is not hydrophobic protein, and high concentration of the precipitants attributes temperature dependence of solubility curve. Crystal morphology changed from a hexagonal bipyramidal surrounded by {1 0 0} and {1 0 1} to a truncated cube surrounded by {1 0 1} with increment of concentrations of the precipitants (Fig. 1). The salt effect on crystal morphology and surface microtopograph will be discussed based on the intermolecular interactions. Besides impurity e ffec t wi l l be d i scussed , because RNaseA of commercial source includes slight amount of deamidated protein and dimeric protein.

Nuclear density distribution in KH2PO4 determined by the combined software system remedy

Abstract The nuclear density distributions for both paraelectric and ferroelectric phases of KH 2 PO 4 (KDP) were obtained by the software system named remedy , which is a combined program system of Rietveld refinement, rietan -98, and the maximum entropy method, mend for neutron diffraction. The experimental data were collected by HRPD at JRR-3M. The specimen used was non-deuterated KDP, which caused no real problem in finding out the accurate proton distributions despite the higher background level. The results show high contrast as for proton distributions; symmetric double maxima between two oxygen atoms for a disordered paraelectric phase and a harmonic single maximum for an ordered ferroelectric phase.