Synthesis and structure-activity relationship of a new series of potent angiotensin II receptor antagonists: pyrazolo[1,5-a]pyrimidine derivatives.

We have already reported 7-oxo-4,7-dihydropyrazolo[1,5-a]pyrimidine-3-carboxylic acid derivatives, which are potent in vitro angiotensin II (AII) antagonists, but have no oral antihypertensive activity. Removal of the carboxylic acid and replacement of the heteroaromatic system afforded potent in vitro antagonists. Removal of the carbonyl oxygen and changing the position of the biphenyltetrazole substituent were critical to the display of oral activity. To improve the in vitro and oral activities, modifications were made of the substituents at the 3- and 5-positions of the pyrazolo[1,5-a]pyrimidine. Structure-activity studies showed the methyl substituent at the 3-position to be essential for potent in vivo activity. We present the design, syntheses, and biological data of a series of pyrazolo[1,5-a]pyrimidine derivatives, which are orally active AII receptor antagonists.     

Electronic tuning of dye lasers by an electrooptic birefringent Fabry-Perot etalon

An electrooptic birefringent Fabry-Perot etalon is described for a wavelength selector of dye lasers. The laser emission was electronically tuned with a linewidth of several angstroms over 135 Å. This was achieved by changing the applied voltages from -1.2 to +1.2 kV to the etalon constructed from a 3.6 mm long, LiTaO₃ crystal.     

A study of the composition of the {111} planes of GaP on an atomic scale

Atom-probe field-ion microscope (FIM) analyses were performed on specimens of the compound semiconductor GaP. A set of experimental conditions was found which allows the study of GaP employing the straight time-of-flight atom probe. The purposes of the investigation were to show the step-like field-evaporation behavior — corresponding to each atomic layer of the {111} planes — and to determine the composition of each plane of atoms. This type of information is based on the periodicity of the GaP crystal (zinc blende structure) and is of potential value for the study of a wide range of physical problems involving compound semiconductors. Our studies showed that the composition of each {111} plane can indeed be determined. The overall stoichiometry of the GaP was found to be related to the background gas hydrogen and the number of ions field evaporated per pulse. The observations are explained in terms of possible fieldevaporation mechanisms involving the main background gas in the FIM — hydrogen.     

Field evaporation end form at 4.2 K

Field evaporation end forms of tungsten and iridium have been observed at several temperatures. At 21 K and above, the surfaces contain atoms in metastable positions which give rise to decorated zone lines, double plane edges and superstructures, but at 4.2 K these are scarcely observed. These results imply that at the higher temperatures an edge atom may migrate to a surface site before it evaporates, while at 4.2 K the edge atom may evaporate without surface migration. A considerable part of the migration energy is probably due to a field induced dipole-dipole repulsion.     

Role of electrolytes on charge recombination in dye-sensitized TiO(2) solar cell (1): the case of solar cells using the I(-)/I(3)(-) redox couple

Performance of dye-sensitized solar cells (DSCs) was investigated depending on the compositions of the electrolyte, i.e., the electrolyte with a different cation such as Li(+), tetra-n-butylammonium (TBA(+)), or 1,2-dimethyl-3-propylimidazolium (DMPIm(+)) in various concentrations, with and without 4-tert-butylpyridine (tBP), and with various concentrations of the I(-)/I(3)(-) redox couple. Current-voltage characteristics, electron lifetime, and electron diffusion coefficient were measured to clarify the effects of the constituents in the electrolyte on the charge recombination kinetics in the DSCs. Shorter lifetimes were found for the DSCs employing adsorptive cations of Li(+) and DMPIm(+) than for a less-adsorptive cation of TBA(+). On the other hand, the lifetimes were not influenced by the concentrations of the cations in the solutions. Under light irradiation, open-circuit voltages of DSCs decreased in the order of TBA(+)> DMPIm(+) > Li(+), and also decreased with the increase of [Li(+)]. The decreases of open-circuit voltage (V(oc)) were attributed to the positive shift of the TiO(2) conduction band potential (CBP) by the surface adsorption of DMPIm(+) and Li(+). These results suggest that the difference of the free energies between that of the electrons in the TiO(2) and of I(3)(-) has little influence on the electron lifetimes in the DSCs. The shorter lifetime with the adsorptive cations was interpreted with the thickness of the electrical double layer formed by the cations, and the concentration of I(3)(-) in the layer, i.e., TBA(+) formed thicker double layer resulting in lower concentration of I(3)(-) on the surface of the TiO(2). The addition of 4-tert-butylpyridine (tBP) in the presence of Li(+) or TBA(+) showed no significant influence on the lifetime. The increase of V(oc) by the addition of tBP into the electrolyte containing Li(+) and the I(-)/I(3)(-) redox couple was mainly attributed to the shift of the CBP back to the negative potential by reducing the amount of adsorbed Li cations.     

Preparation and properties of polymers with biphenyl units in the chain: Syntheses of solvent-soluble substituted polyphenylenes

Benzidinetetrazonium chloride (BTC)–CuCl and BTC–FeCl₂ complexes were thermally converted to benzene-soluble poly-4,4′-biphenylene plus small amounts of insoluble material. The soluble fraction was more stable than the insoluble fraction when heated at 300–500°C, although the solubility decreased. BTC in water was converted to an insoluble material by addition of alkali or cuprous ammonia solution. The C/(H + Cl) ratio indicated the existence of three to five side groups for each twenty phenyl groups of the insoluble fraction, while that of the soluble fraction showed few such groups. The number increased to one or more side groups for each phenyl nucleus as both soluble and insoluble fractions were heated to 500°C. A thin film of soluble fraction deposited on a copper plate showed an electrical conductivity in the range 10^?2–10^?3 ohm^?1 cm^?1 at 25°C and an energy gap (ΔE_g) of 0.2–0.3 eV. However, a compressed specimen of the same soluble fraction showed little conductivity. Solventsoluble samples of substituted poly-4,4,-biphenylene were prepared by the same procedure. These materials cracked on processing, and accurate conductivity measurements could not be made.     

Stepped light-induced transient measurements of photocurrent and voltage in dye-sensitized solar cells: application for highly viscous electrolyte systems

To measure electron diffusion coefficients (D) and electron lifetimes (tau) of dye-sensitized solar cells (DSC), we introduced stepped light-induced transient measurements of photocurrent and voltage (SLIM-PCV), which can simplify the optical setup and reduce measurement time in comparison to conventional time-of-flight and frequency-modulated measurements. The method was applied to investigate the influence of the viscosity of a thermally stable high-boiling-point solvent on the energy conversion efficiency of DSCs. By systematic study of the influence of the viscosity, the species of cations as the counter charge of I(-)/I(3)(-), and the concentrations of electrolytes, we concluded that a lower dye cation reduction rate due to slower iodine diffusion is a limiting factor for a highly viscous electrolyte system. On the other hand, comparable values of D and increased values of tau were observed in a highly viscous electrolyte. By employing 0.5 M TBAI and 0.05 M I(2) in propylene carbonate, the efficiency of the DSC became comparable to that of a DSC using conventional electrolytes consisting of LiI, imidazolium iodide, and 4-tert-butylpyridine in methoxyacetonitrile. The simultaneous evaluation of D and tau through the appropriately simple measurement realizes fast optimization of the efficient and reliable DSC composed of thermally stable but often viscous electrolytes.     

(Pi-allyl)palladium complexes bearing diphosphinidenecyclobutene ligands (DPCB): highly active catalysts for direct conversion of allylic alcohols

The (pi-allyl)palladium complex bearing an sp2-hybridized phosphorus ligand (DPCB-OMe: 1,2-bis(4-methoxyphenyl)-3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutene) efficiently catalyzes direct conversion of allylic alcohols in the absence of activating agents of alcohols such as Lewis acids. N-Allylation of aniline proceeds at room temperature to afford monoallylated anilines in 90-97% yields. C-Allylation of active methylene compounds is also successful at 50 degrees C using a catalytic amount of pyridine as a base, giving monoallylation products in 85-95% yields. The catalytic mechanism involving hydrido- and (pi-allyl)palladium intermediates has been proposed on the basis of stoichiometric examinations using model compounds of presumed intermediates.