Copper complex catalyzed asymmetric monosulfonylation of meso-vic-diols

Asymmetric desymmetrization of meso-vic-diols was performed by tosylation in the presence of copper(II) triflate and (R,R)-Ph-BOX as a catalyst. The method was successfully applied to asymmetric desymmetrization of cyclic and acyclic meso-vic-diols in high enantioselectivity with up to >99% ee.     

An ultramicro assay for human plasma prekallikrein activity by phosphorimetry

A highly sensitive method for the phosphorimetric assay of prekallikrein in human blood plasma is described. Prekallikrein is converted to kallikrein (active form) by reaction at 0°C with actin. p-Nitroaniline, formed enzymatically from H-d-prolyl-l-phenylalanyl-l-arginyl-p-nitroanilide, is extracted with ether and determined phosphorimetrically in a mixture of ether and ethanol. The method is precise and highly sensitive, requiring as little as 0.25 μl of human blood plasma. The limit of detection for p-nitroaniline formed enzymatically is 5 pmol.     

Production of theasinensins A and D, epigallocatechin gallate dimers of black tea, by oxidation-reduction dismutation of dehydrotheasinensin A

Theasinensins A and D are B,B′-linked dimers of (−)-epigallocatechin 3-O-gallate connected through R and S biphenyl bonds, respectively, and are major constituents of black tea. Enzymatic oxidation of epigallocatechin 3-O-gallate produced dehydrotheasinensin A, and the structure was shown to be equivalent to an o-quinone of theasinensin A. When the aqueous solution of dehydrotheasinensin A was heated, theasinensin D was produced along with galloyl oolongtheanin. On the other hand, dehydrotheasinensin A was converted to theasinensins A and D along with oxidation products in phosphate buffer at pH 6.8 at room temperature. The results strongly suggested that theasinensins in black tea were produced by oxidation-reduction dismutation of dehydrotheasinensin.     

Effective momentum transfer cross section for excess electrons in liquid argon

The momentum-transfer cross section of excess electrons Q in liquid Ar (estimated on the assumption that the characteristic energy 3eD/2μ is equal to the mean agitation energy ge) is compared with the original momentum-transfer cross section Q₁ used for the calculation of D and μ. Differences between Q and Q₁ are discussed and comparisons made between 3eD/2μ and gE.     

Selective determination of N-terminal tyrosine containing peptides by a novel fluorescence reaction with borate,hydroxylamine and cobalt(II)

A fluorimetric method is proposed for determining N-terminal tyrosine-containing peptides, of which some peptides such as enkephalins and kyotorphin are of physiological importance. An intense fluorescence is produced when the peptide is heated at 100°C for 3 min in a weakly alkaline medium containing borate, hydroxylamine and cobalt(II). The fluorescent species is stabilized with β-mercaptoethanol, with excitation and emission maxima at 335 and 430 nm, respectively. The method is highly selective for N-terminal tyrosine-containing peptides, with a detection limit of 43–69 pmol ml^?1.     

Fluorimetric enzyme immunoassay for serum β2-microglobulin based on the horseradish peroxidase-labeled Fab′ fragment of immunoglobulin

A sensitive sandwich-type enzyme immunoassay for human β₂-microglobulin in serum is described. Rabbit anti-human β₂-microglobulin IgG is coated on a styrene-maleic anhydride copolymer bead, which is incubated with β₂-microglobulin in serum sample at 30°C for 1 h, and again incubated at 30°C for 1 h with a conjugate of anti-β₂-microglobulin Fab′ (a fragment of rabbit anti-human β₂-microglobulin IgC) and horseradish peroxidase to form a sandwich-type immunocomplex. The conjugate is prepared with a heterobifunctional reagent, N-succinimidyl-3-(2-pyridyldithio)propionate. The peroxidase activity of the immunocomplex is measured spectrofluorimetrically by use of 3-(p-hydroxyphenyl)propionic acid. The method permits precise assay of 0.05–10 ng of β₂-microglobulin in serum, with calibration linearity up to 1.0 ng of protein.     

Enantioselective total synthesis of (+)-tricycloclavulone

The first total synthesis of (+)-tricycloclavulone having a unique tricyclo[5,3,0,01,4]decane skeleton and six chiral centers was achieved in a highly stereoselective manner. It includes a catalytic enantioselective [2+2]-cycloaddition reaction using novel chiral copper catalyst, extremely effecting an intramolecular ester transfer reaction, and asymmetric reduction of the carbonyl group on the alpha-chain using Noyori's chiral ruthenium catalyst.     

Intramolecular excimer emission of triply bridged [3.3.N](3,6,9)carbazolophanes

The photophysical properties of a series of triply bridged [3.3.n](3,6,9)carbazolophanes ([3.3.n]Cz, n = 3, 4, 5, 6) were studied as a model compound for a fully overlapped carbazole excimer. In these [3.3.n]Cz molecules, a plane angle of the two carbazole moieties changed systematically from nearly parallel to oblique, with increases in the length of the methylene chain n bridging at the 9-position of each carbazole ring. Absorption bands of [3.3.n]Cz showed the blue-shift and the splitting for (1)L(a) <-- (1)A and (1)L(b) <-- (1)A transition bands of the reference carbazole monomer, respectively. These spectral changes in [3.3.n]Cz were explained by Kasha's molecular exciton theory with the distance r and dihedral angle theta between the carbazole moieties in the ground state. In both liquid and glass matrixes, [3.3.n]Cz showed intramolecular excimer emission. The emission peak wavelength changed from 409 nm (n = 6) to 480 nm (n = 3) depending on r in the ground state. The dependence of the peak wavelength on r clearly showed that relative configurations of carbazole moieties in the ground state were preserved even in the excimer states. The smaller radiative rate of the excimer emission than the reference monomer was explained by the dimer symmetry of [3.3.n]Cz.     

Temperature dependence of radiation effects in polyethylene: Cross‐linking and gas evolution

High‐density polyethylene (HDPE) and low‐density polyethylene (LDPE) were irradiated in vacuo at 30–220 and 30–360°C, respectively, with γ‐rays at doses of 10–400 kGy. Temperature dependence of cross‐linking and gas evolution was investigated. It was found that cross‐linking was the predominant process up to 300°C and the gel point decreased smoothly with temperature. The increase of G(x) with temperature was likely attributed to the temperature effect on addition of radicals to the double bonds present in the polymer. Above 300°C, the gel fraction at a given dose decreased remarkably with temperature and turned to zero at 360°C. The molecular weight variation determined with gel permeation chromatography (GPC) indicated the enhanced degradation at 360°C by radiation. G‐values of H₂ increased with temperature and varied with dose. The compositions of the C₁–C₄ hydrocarbons evolved depended on the structures of side branches. Raising the temperature favored the formation of unsaturated hydrocarbons, and the yield of unsaturated relative to saturated hydrocarbons decreased with dose. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1541–1548, 1999     

Stability of oxygen anions and hydrogen abstraction from methane on reduced SnO2 (110) surface

The stability of oxygen anions and the hydrogen abstraction from methane on a reduced SnO₂ (110) crystal surface have been studied theoretically using a point-charge model. The geometric and electronic structures for the present molecules are calculated by means of a hybrid Hartree–Fock/density functional method at the B3LYP/6-311+G(3df, 3pd) level of theory. The calculations of the energies on the point-charge model are performed using these optimized geometries. It is found that a low concentration of the active oxygen species O⁻ and O₂⁻ is expected on the reduced SnO₂ surface. The activation energies for the abstraction of hydrogen atom from methane on the reduced SnO₂ surface are obtained: 12 kcal/mol for O⁻ species and more than 48 kcal/mol for O₂⁻ species, indicating that O⁻ species on the surface is the main active center for the dissociation of a C(SINGLE BOND)H bond of methane, which is in agreement with the other oxide catalysts. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 669–678, 1998