Superconducting transition temperature and the thickness of CoO2 planes of NaxCoO2·yH2O

The superconductivity of Na_xCoO₂·yH₂O appears in two regions of ν_Q divided by a narrow nonsuperconducting phase in the T_c–ν_Q phase diagram, where T_c and ν_Q are the superconducting transition temperature and ⁵⁹Co-nuclear quadrupole frequency, respectively. It suggests that the existence/nonexistence of the superconductivity depends on the local structure around Co sites or on the thickness of the CoO₂ planes, through the change of the crystal field. We have carried out specific heat measurements on several samples with different ν_Q values distributing over both the superconducting ν_Q regions, and found that the electronic specific heat coefficient γ does not change significantly with ν_Q. It suggests that a topological change of the Fermi surface which has been proposed as a possible origin of the existence of the two superconducting regions, does not take place with the change of the local structure around Co sites or thickness of the CoO₂ planes. We have also carried out neutron inelastic measurements on aligned crystals of Na_xCoO₂·yD₂O, and found that ferromagnetic fluctuations with two-dimensional character observed in the high temperature region lose their intensities with decreasing T and becomes inappreciable below 25 K. It indicates that the hole-pockets near the K points in the reciprocal space do not exist in these crystals. Combining these results, we can exclude, in the entire region of ν_Q, the existence of the hole-pockets, on which arguments of the possible triplet superconductivity are based. The present results are consistent with the singlet pairing which we showed in previous papers.     

Studies on Phosphorus-Containing Polymers. V. Ring-Opening Polymerization of Tetrahydrofuran Catalyzed by Linear Phosphonitrilic Chloride

It was found that linear phosphonitrilic chloride could be used as a catalyst for ring-opening polymerization of tetrahydrofuran. Bulk polymerizations were carried out in a nitrogen atmosphere. After termination of polymerization, the reaction mixture was poured into water, thereby decomposing the catalyst. The product was dissolved in benzene and then subjected to lyophilization. The polymerization of tetrahydrofuran in the presence of linear phosphonitrilic chloride was found to be an equilibrium and a “living” polymerization. The polymerization product includes little phosphorus, and its infrared absorption spectrum agrees well with that of the polymer obtained with PF₅ catalyst. The results of the polymerization using epichlorohydrin as a promoter show that the number of active sites in the molecule of linear phosphonitrilic chloride is considerably smaller. Consequently it is conceivable that the catalytic activity of the linear phosphonitrilic chloride is attributed to its terminal ～～P⁺Cl₃PCl_?6 structure. Furthermore we presume that the polymerization of tetra-hydrofuran in the presence of this catalyst proceeds through a cationic ring-opening mechanism.     

An intermittent frequency offset lock of a transverse Zeeman laser to an iodine stabilized He-Ne laser

A single-mode frequency stabilized laser with modulation-free and moderate power is desired as a light source for an ultra-high resolution interferometer system and/or a rapid laser calibration system. For this purpose, we developed a new stabilized laser system that utilizes intermittent control of a 2 mW transverse Zeeman stabilized He-Ne laser (Zeeman laser) with an iodine stabilized He-Ne laser (I2 stabilized laser). Because of the intermittent control, working time of the I2 stabilized laser is reduced. The Zeeman laser has two operational modes: independent and slave mode. In the independent mode, the Zeeman laser is stabilized through control of Zeeman beat frequency. Temperature dependent drift of the oscillation frequency during the independent mode is periodically corrected by the slave operation utilizing frequency offset locking to the I2 stabilized laser. Frequency instability of the Zeeman laser in independent and slave modes is 7.7X10-11 and 2.0X10-11, respectively, at the sampling time of 100 s.     

Accurate Stabilization of a 3 mW Single-Mode Output He-Ne Laser by Intermittent Frequency Offset Locking to an Iodine Stabilized He-Ne Laser

A high-power, unmodulated frequency standard laser light with low running cost is a powerful tool for industrial measurement involving laser calibration and interferometry in length and shape. To obtain such a laser light, we developed an intermittent frequency offset locked laser (IFOL laser). This laser system, composed of an iodine stabilized He-Ne laser (I₂SL) and a high-powered symmetric three-mode He-Ne laser (HP-3ML, optical output=5 mW), provides two stabilization operational modes: (1) independent mode (I-mode) and (2) slave mode (S-mode). Utilizing the frequency pulling effect, HP-3ML is stabilized at the condition of symmetric three-mode oscillation, and a 3 mW single-mode light with frequency instability of 10^-12 is obtained (I-mode). When the optical frequency deviates from the allowed limit during I-mode, HP-3ML is temporarily offset-locked to I₂SL (S-mode) with frequency resettability of 10^-10 and frequency instability of 10^-12. After completion of the drift reset in S-mode, HP-3ML is stabilized in I-mode again, and then I₂SL is turned off. In a typical case of allowed drift in ±1 MHz, repetitive operation of I-mode for 10 days and S-mode for 5 min was satisfactory. Such an intermittent operation reduces the working time of I₂SL dramatically, resulting in low running cost that enables long-term use in industrial measurement.     

Studies on topical antiinflammatory agents. III. Synthesis of 17 alpha-acyloxy-9 alpha-fluoro-11 beta-hydroxy-16 beta-methyl-1,4-pregnadiene-3,20-dione 21-thio derivatives and related compounds

A series of 21-thio derivatives of 9 alpha-fluoro-11 beta,17 alpha-dihydroxy-16 beta-methyl-1,4-pregnadiene-3, 20-dione 17-esters and related compounds were synthesized and evaluated as topical antiinflammatory agents. These compounds were prepared by the reaction of 9 alpha-fluoro-11 beta,17 alpha,21-trihydroxy-16 beta-methyl-1,4-pregnadiene-3, 20-dione (betamethasone, I) 17-ester derivatives and various mercapto compounds. A structure-activity relationship study revealed that the structural combination of a thio group at the 21-position and an ester group at the 17-position contributed to vasoconstrictive activity. Among these compounds, the 21-methylthio 17-propanoate compound (6) was found to have the most potent activity, being more potent than betamethasone 17-valerate (BV).     

Quenching of a photosensitized dye through single-electron transfer from trivalent phosphorus compounds

Various types of trivalent phosphorus compounds 1 undergo single-electron transfer (SET) to the photoexcited state of rhodamine 6G (Rho+*) in aqueous acetonitrile to quench the fluorescence from Rho+*. The rate constants kp for the overall SET process were determined by the Stern-Volmer method. The rate is nearly constant at a diffusion-controlled limit in the region of E1/2(1) < 1.3 V (vs Ag/Ag+), whereas log kp depends linearly on E1/2(1) in the region of E1/2(1) > 1.3 V, the slope of the correlation line being -alphaF/RT with alpha = 0.2. The potential at which the change in dependence of log kp on E1/2(1) occurs (1.3 V) is in accordance with the value of E1/2(Rho+*) (1.22 V) that has been obtained experimentally. Thus, the SET step is exothermic when E1/2(1) < 1.3 V and endothermic when E1/2(1) > 1.3 V. The alpha-value (0.2) obtained in the endothermic region shows that the SET step from 1 to Rho+* is irreversible in this region. Trivalent phosphorus radical cation 1*+ generated in the SET step undergoes an ionic reaction with water in the solvent rapidly enough to make the SET step irreversible. In contrast, the SET from amines 2 and alkoxybenzenes 3 to Rho+* is reversible when the SET step is endothermic, meaning that the radical cations 2*+ and 3*+ generated in the SET step undergo rapid "back SET" in the ground state to regenerate 2 and 3.     

Stereochemical control in yeast reduction

A substrate which is subjected to yeast reduction has been modified by iodination or phenylsulfonylation. Both substituents improves chemical and optical yields and control the stereochemical course of the reduction.