Metallic conductivity and ferromagnetic interaction of iron(III) d spins in the needle crystals of (ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide)(2).FeBr(4) salt

The 2:1 charge-transfer (CT) salts (1(2).FeBr(4) and 1(2).GaBr(4)) of ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with FeBr(4)(-) and GaBr(4)(-) counteranions were obtained as needle crystals, whose structures are almost the same as each other. The 1 molecules form a one dimensionally stacked column with alternation of their molecular axis direction, while the counteranions are aligned in parallel with the 1-stacked columns with the direction of their distorted-tetrahedral geometry maintained. The room-temperature electrical conductivities measured on the single crystals of 1(2).FeBr(4) and 1(2).GaBr(4) were 4.6 and 2.1 S cm(-1), respectively. From the temperature dependences of their electrical conductivities in both cases the electrical conducting properties were metallic between ca. 170 and 300 K, but below ca. 170 K converted to be semiconducting and continued till 5 K, although the activation energies are very small (4-10 meV). For 1(2).FeBr(4) very weak and antiferromagnetic interaction occurred between the d spins of FeBr(4)(-) ions in the temperature range of ca. 1-300 K. However, below ca. 15 K the ferromagnetic interaction was reversely preferential possibly by participation of the pi spin of 1.     

5-[4-(1-Hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin as a probe of the transition-state conformation in hydrolase-catalyzed enantioselective transesterifications

5-[4-(1-Hydroxyethyl)phenyl]-10,15,20-triphenylporphyrin (1a) and zinc porphyrin 1b were designed and synthesized to experimentally examine the validity of the transition-state model previously proposed for the lipase-catalyzed kinetic resolution of secondary alcohols. The lipases from Pseudomonas cepacia (lipase PS), Candida antarctica (CHIRAZYME L-2), Rhizomucor miehei (CHIRAZYME L-9), and Pseudomonas aeruginosa (lipase LIP) exhibited excellent enantioselectivity (E >100 at 30 degrees C). Subtilisin Carlsberg from Bacillus licheniformis (ChiroCLEC-BL) also showed high enantioselectivity for 1a (E = 140 at 30 degrees C), and the thermodynamic parameters were determined: DeltaDeltaH = -6.8 +/- 0.8 kcal mol(-1), DeltaDeltaS = -13 +/- 3 cal mol(-1) K(-1). Lipases and subtilisin showed R- and S-preference for 1, respectively. The mechanisms underlying the experimental observations are explained in terms of the transition-state models. The large secondary alcohol 1 is a powerful tool for investigating the conformation of the transition state of the enzyme-catalyzed reactions. The fact that 1 was resolved with high enantioselectivity strongly suggests that the gauche conformation, but not the anti conformation, is taken in the transition state, in agreement with the transition-state models involving the stereoelectronic effect.     

Stereocontrolled synthesis of 8,11-dideoxytetrodotoxin,unnatural analogue of puffer fish toxin

[structure: see text] 8,11-Dideoxytetrodotoxin, an unnatural tetrodotoxin analogue, was synthesized in a highly stereoselective manner from a common intermediate in our synthetic studies on tetrodotoxin. The synthesis features neighboring group participation of trichloroacetamide for stereoselective hydroxylation, protection of ortho ester, and guanidine installation with Boc-protected isothiourea.     

Nucleophilic addition reaction of 2-trimethylsilyloxyfuran to N-gulosyl-C-alkoxymethylnitrones: synthetic approach to polyoxin C

[reaction: see text] The stereoselectivity of nucleophilic addition of 2-trimethylsilyloxyfuran to N-gulosyl-C-alkoxymethylnitrones was investigated. It was found that the selectivity was highly dependent on the bulkiness of the C-substituent of the nitrone. The major adducts were elaborated into the key intermediate of polyoxin C.     

Solitons and Fractal Kerr Response

Optical solitary waves that propagate in a Kerr medium exhibiting a power-law nonlocal response are studied analytically. The first-principles stability analysis based on quantum field theory shows that within the whole range of the exponent (the fractal dimension) the solitary wave can be stabilized.     

Heat capacity of a five-coordinated iron(III) complex with spin S = 32, bromobis(N,N-diethyldithiocarbamato)iron(III), between 0.4 and 300 K

Heat capacity measurements have been made for six kinds of specimens prepared by different methods. Among them, Sample A exhibited a A-type ferromagnetic pahse transition at 1.347 K and a Schottky-type anomaly due to the zero-field splitting around 9K. The total entropy and enthalpy were (11.05 ± 0.04) J K^?1mol^?1 and (97.0 ± 0.4) J mol^?1, respectively. Sample B exhibited a Sehottky-type anomaly around 0.4 K due to the ferro-magnetic dimeric coupling with $\text{J}{}_{\mathrm{D}}\text{k}\text{= + 0.30}\text{K}$ as well as the Schottky-type anomaly at 9K. The total magnetic entropy and enthalpy were (11.45 ± 0.03) JK^?1 mol^?1 and (93.8 ± 0.8) J mol^?1, respectively. The remaining samples are simple mixtures of the λ-type modification and the dimeric modification. Irrespective of the magnetic behavior at low temperatures, all the samples showed a non-magnetic first-order phase transition around 270 K. The heat capacity and entropy of this phase transition have been accounted for in terms of the Frenkel theory of heterophase fluctuation. Construction of an adiabatic-type calorimeter workable between 1.5 and 393 K has been also presented.     

Generalized actions in Zp lattice gauge theory

In Z_p lattice gauge theory we generalize the Wilson action to include all group representations. We review the implications of duality for these models. With Monte Carlo methods, we find a rich phase structure for the cases p = 4 and 5.     

Selective pH gradient formation across a capsule membrane corked with charged synthetic bilayers

Ultrathin, large nylon capsules whose porous membranes were corked with charged, synthetic bilayer-forming amphiphiles (cationic, anionic, zwitterionic bilayers) were prepared. The chemically stable, bilayer-corked capsules can selectively retain 0.1 M aqueous acidic (HCl, HNO₃, H₂SO₄, HClO₄ and p-toluenesulfonic acid) and alkaline solutions (NaOH, Ba(OH)₂, NH₄ OH, and N(Et)₄OH) in the inner aqueous phase depending on the surface charge of corking bilayers: the capsule corked with positively and negatively charged bilayers could selectively store alkalies and acids, respectively, and could keep a selective pH-gradient across the membrane. The zwitterionic bilayer-corking could retain neither acids nor alkalies in the inner aqueous phase. The permeation of these acids and alkalies to the outer phase (pH gradient decreasing across the capsule membrane) could be reversibly controlled by the phase transition of corking bilayers from gel to liquid crystalline state. The selective storage and permeation of acids and alkalies could be explained by the process of permeation of H⁺ or OH^- counter ions across the charged bilayer-corking.     

Clathrate-formation mediated adsorption of methane on Cu-complex crystals

We measured adsorption and desorption isotherms of methane on [Cu(4, 4'-bipyridine)2(BF4)2] (LPC) at 258, 273, and 303 K. Adsorption proceeds almost vertically at a definite pressure, which is named gate pressure. The lower the measurement temperature, the smaller the gate pressure. The temperature dependence of the gate pressure is expressed by the Clapeyron-Clausius equation, giving a thermodynamic evidence on the clathrate formation between the Cu complex and methane.     

Design Consideration for a Two-Distributed-Junction Tuning Circuit

We describe a novel method of designing a tuning circuit with two half-wave distributed junctions separated by a half-wavelength microstripline, which analytically determines the circuit parameters such as the minimum current density of the junctions and the characteristic impedances of the distributed junctions and the microstripline. The tuning circuit was approximated by simple transmission theory and then simplified with ideal circuit components for analysis. We applied Chebyshevs band-pass filter theory, in part, to optimize the circuit design. The analytical results revealed that a high characteristic-impedance ratio between the distributed junctions and the microstripline is necessary to obtain broadband matching using low-current-density junctions. The experimental results for all-NbN SIS mixers we designed with this method demonstrated double-sideband (DSB) receiver-noise temperatures of 6–10 quanta from 710 to 810 GHz for a mixer with a current density of only 4 kA/cm² (estimated C_JR_N product of 37 at 750 GHz). The RF bandwidth was broader than that of a conventional full-wave distributed SIS mixer with the same current density.