Anomalous behavior of linear resistivity arising in intergrain ordering process of weak-sintered ceramic system YBa2Cu4O8

Faint electric resistivity behavior is searched experimentally near and below intergrain ordering temperature of weakly sintered ceramic YBa₂Cu₄O₈ (Y124). For this purpose, a new method to detect linear and nonlinear resistivity sensitively by combination of pulse delta method and numerical Fourier-transformation has been designed. Making use of the experimental system for several weak sintered Y124 samples, it is revealed that linear resistivity just above the intergrain ordering point first drops toward zero steeply with decreasing temperature, and then turns abruptly upward to forms faint maximum at lower temperature. Such a novel behavior of ‘revival of resistivity’ is confirmed to be reproducible, and considered to be an essential frustration effect for d-wave type grain system with irregular or inhomogeneous ceramic structure.     

Frequency dependence of H2O2 generation from distilled water

The frequency dependence of H2O2 generation from H2O by a sonochemical reaction was detected experimentally. The results are in good agreement with previous experimental results, which indicate that in sonochemical reactions, frequencies higher than 90 kHz are more effective than frequencies of several tens of kilohertz. The phonon concept of acoustic waves makes it clear that energy depends on frequency, i.e. on the condition of equal phonon density; higher frequency means higher energy. The concentration and accumulation of acoustic energy will be performed through a bubble surface. From the analogy of photoelectric effects, the frequency dependence of the sonochemical reaction was discussed using the phonon concept.     

Ground-State Properties ,of C, O, and Ne Isotopes in Hartree——Fock-Bogoliubov Calculation with Gogny Interaction

Ground-state properties of C, O, and Ne isotopes are described in the framework of Hartree-Fock-Bogoliubov theory with density-dependent finite-range Gogny interaction D1S. We include all the contributions to the Hartree-Fock and pairing feld arising from Gogny and Coulomb interaction as well as the center of mass correction in the numerical calcu/ations. These ground-state properties of C, O, and Ne isotopes are compared with available experimental results, Hartree-Fock plus BCS, shell model and relativistic Hartree--Bogoliubov calculations. The agreement between experiments and our theoretical results is pretty well. The predicted drip-line is dependent strongly on the model and effective interaction due to their sensitivity to various theoretical details. The calculations predict no evidence for halo structure predicted for C,O, and Ne isotopes in a previous RHB study.     

How well can we reconstruct the $t\bar{t}$ system near its threshold at future ee linear colliders?

We developed a new method for the full kinematical reconstruction of the system near its threshold at future linear e ⁺ e ^- colliders. In the core of the method lies likelihood fitting which is designed to improve measurement accuracies of the kinematical variables that specify the final states resulting from decays. The improvement is demonstrated by applying this method to a Monte Carlo sample generated with various experimental effects including beamstrahlung, finite acceptance and resolution of the detector system, etc. In most cases the fit takes a broad non-Gaussian distribution of a given kinematical variable to a nearly Gaussian shape, thereby justifying phenomenological analyses based on simple Gaussian smearing of the parton-level momenta. The standard deviations of the resultant distributions of various kinematical variables are given in order to facilitate such phenomenological analyses. A possible application of the kinematical fitting method and its expected impact are also discussed. Received: 4 March 2003 / Published online: 23 May 2003 RID="a" ID="a" e-mail: ikematsu@post.kek.jp RID="b" ID="b" e-mail: fujiik@jlcuxf.kek.jp RID="c" ID="c" e-mail: hioki@ias.tokushima-u.ac.jp RID="d" ID="d" e-mail: sumino@tuhep.phys.tohoku.ac.jp RID="e" ID="e" e-mail: tohrut@hiroshima-u.ac.jp     

Single-crystal-to-single-crystal photocyclization of 4-(2,4,6-triisopropylbenzoyl)benzoic acid in the salt crystal with (S)-phenylethylamine

Ultraviolet irradiation of a salt crystal of 4-(2,4,6-triisopropylbenzoyl)benzoic acid with (S)-phenylethylamine promoted single-crystal-to-single-crystal photocyclization to give an enantiopure (R,R)-cyclopentenol and almost racemic cyclobutenol. The reaction paths were elucidated by X-ray crystallographic analysis of the crystal before and after irradiation.     

Chiral distortion in a Mn(IV)(salen)(N3)2 derived from Jacobsen's catalyst as a possible conformation model for its enantioselective reactions

The Mn (IV)(salen)(N 3) 2 complex ( 3) from Jacobsen's catalyst is synthesized, and the X-ray crystal structures of 3 as well as the starting Mn (III)(salen)(N 3)(CH 3OH) complex ( 2) are determined in order to investigate the conformation of the high-valent Mn (IV)(salen) molecule in comparison with that of Mn (III)(salen). The asymmetric unit of the crystal of 3 contains four complexes, all of which adopt a nonplanar stepped conformation effectively distorted by the chirality of the diimine bridge. The asymmetric unit of 2 also contains four complexes. Two of them show a stepped conformation of a lesser degree, but the other two adopt a bowl-shaped conformation. Comparison of the structural parameters shows that the Mn center in 3 is coordinated from both sides by two external axial N 3 ligands with significantly shorter bond lengths, which could induce greater preference for the stepped conformation in 3. The CH 3CN solution of 3 shows circular dichroism with a significantly strong band at 275 nm as compared to 2, suggesting that 3 may adopt a more chirally distorted conformation also in solution. The circular dichroism spectrum of 3 is slightly altered with isodichroic points from 298 to 253 K and shows no further change at temperatures lower than 253 K, suggesting that the solution of 3 contains an equilibrium between two conformers, where a low-energy conformer with more chiral distortion is predominantly favored even at room temperature. Complexes 2 and 3 are thoroughly characterized using various techniques including cyclic voltammetry, magnetic susceptibility, UV-vis, electron paramagnetic resonance, (1)H NMR, infrared spectroscopy, and electrospray ionization mass spectrometry.     

Simultaneous determination of the binding of amantadine and its analogues to synthetic melanin by liquid chromatography after precolumn derivatization with dansyl chloride

For the determination of amantadine (1-ADA), 2-adamantanamine (2-ADA), memantine (MEM), and rimantadine (RIM) in melanin binding studies, the simultaneous determination of 1-ADA or 2-ADA, MEM, and RIM is investigated by high-performance liquid chromatographic assay with dansyl chloride as a fluorescent derivative reagent. Dansyl derivatives with fluorescent intensity are detected at an excitation wavelength of 370 nm and an emission wavelength of 506 nm. Retention times of 1-ADA, 2-ADA, MEM, and RIM derivatives are 12.2, 12.2, 15.2, and 16.6 min, respectively. The peak of 1-ADA derivative coelutes with the 2-ADA derivative. The limits of detection for 1-ADA, 2-ADA, MEM, and RIM are 0.014, 0.007, 0.012, and 0.020microM, respectively (signal-to-noise ratio of 3:1). In the intra- and interday assay, the range of standard deviation to the average of 1-ADA, 2-ADA, MEM, and RIM is 4.6-12.7%. Their recovery is also good. The ranking order for synthetic melanin binding among these compounds is RIM > MEM > 2-ADA = 1-ADA. The method is simple, sensitive, and reproducible for simultaneously measuring 1-ADA or 2-ADA, MEM, and RIM. Also, it is useful to investigate their binding kinetics to melanin.     

Conformation of solvent N,N-dimethylpropionamide in the coordination sphere of the zinc(II) ion studied by Raman spectroscopy and DFT calculations

Solvation structure of the zinc(II) ion in N,N-dimethylpropionamide (DMPA) was studied by Raman spectroscopy at varying temperature and by quantum mechanical calculations. No significant ion-pair formation was found for the Zn(ClO4)2 solution in the molality range m(Zn) < 1.5 mol kg(-1), and the solvation number of the zinc(II) ion was determined to be 4, indicating that 6-coordination of DMPA is sterically hindered. Interestingly, DMPA molecules are under equilibrium between planar cis and nonplanar staggered conformers, and the latter is more preferred in the coordination sphere, while the reverse is the case in the bulk. The DeltaG degrees , DeltaH degrees , and TDeltaS degrees values of conformational change from planar cis to nonplanar staggered in the coordination sphere were obtained to be -0.9, -8.5, and -7.5 kJ mol(-1), respectively. Density functional theory (DFT) calculations show that the planar cis conformer is more favorable than the nonplanar staggered one in the 1:2 cluster, as is the case for a single DMPA molecule and H(DMPA)+, indicating that there hardly occurs solvent-solvent interaction through the metal ion in the Zn2+-DMPA 1:2 cluster. On the other hand, the SCF energy of [Zn(planar cis-DMPA)4-n(nonplanar staggered DMPA)n]2+ (n = 0-4) decreases with increasing n, implying that the nonplanar staggered conformer is preferred in the solvate ion. It is thus concluded that solvent-solvent interaction through space, or solvation steric effect, plays a crucial role in the conformational equilibrium in the coordination sphere of the four-solvate metal ion.     

Diversity oriented synthesis of conjugate dienes and alkenylcyclopropanes utilizing silyl group-substituted titanium carbene complexes as bimetallic synthetic reagents

Diversity oriented synthesis of conjugate dienes and alkenylcyclopropanes by the sequential reactions using silyl group-substituted titanium carbene complexes was studied. Dienylsilanes were obtained by the olefination of carbonyl compounds with γ-silylvinylcarbene complexes. Cyclopropanation of 1-alkenes with the vinylcarbene complexes produced (E)-(β-silylvinyl)cyclopropanes with high stereoselectivity. The reaction of β-(trialkylsilyl)carbene complexes with zinc alkoxides of homopropargyl alcohols produced 6-silyl-3,5-hexadien-1-ols with high regio- and stereoselectivity. The (E)-alkenylsilanes thus obtained were transformed into a range of unsaturated compounds by the palladium-catalyzed or copper(I)-promoted cross-coupling with organic halides with retention of configuration.     

A role for highly conserved carboxylate, aspartate-140, in oxygen activation and heme degradation by heme oxygenase-1.

Heme oxygenase (HO) catalyzes the oxygen-dependent degradation of heme to biliverdinIXalpha, CO, and free iron ion via three sequential monooxygenase reactions. Although the distinct active-site structure of HO from cytochrome P450 families suggests unique distal protein machinery to activate molecular oxygen, the mechanism and the key amino acid for the oxygen activation have not been clear. To investigate the functionality of highly conserved polar amino acids in the distal helix of HO-1, we have prepared alanine mutants: T135A, R136A, D140A, and S142A, and found drastic changes in the heme degradation reactions of D140A. In this paper, we report the first evidence that D140 is involved in the oxygen activation mechanism in HO-1. The heme complexes of HO mutants examined in this study fold and bind heme normally. The pK(a) values of the iron-bound water and autoxidation rates of the oxy-form are increased with R136A, D140A, and S142A mutations, but are not changed with T135A mutation. As the wild-type, T135A, R136A, and S142A degrade heme to verdohemeIXalpha with H(2)O(2) and to biliverdinIXalpha with the NADPH reductase system. On the other hand, D140A heme complex forms compound II with H(2)O(2), and no heme degradation occurs. For the NADPH reductase system, the oxy-form of D140A heme complex is accumulated in the reaction, and only 50% of heme is degraded. The stopped flow experiments suggest that D140A cannot activate iron-bound dioxygen and hydroperoxide properly. To investigate the carboxylate functionality of D140, we further replaced D140 with glutamic acid (D140E), phenylalanine (D140F), and asparagine (D140N). D140E degrades heme normally, but D140N shows reactivity similar to that of D140A. D140F loses heme degradation activity completely. All of these results indicate that the carboxylate at position 140 is essential to activate the iron-bound dioxygen and hydroperoxide. On the basis of the present findings, we propose an oxygen activation mechanism involving the hydrogen-bonding network through the bridging water and D140 side chain.