Enantioselectively catalyzed oxidation of 3,4-dihydroxy-l-phenylalanine by N-lauroyl L or D-histidine-Cu(II) complex in CTABr micelles.

In order to investigate the enzyme model reaction the oxidation of 3,4-dihydihydroxy-L-phenylalanine(L-DOPA) was carried out using optically active catalyst, N-lauroyl L or D-histidine-Cu(II) complex(L or D-LauHis-Cu(II)), showing appreciable enantioselectivity in the presence of the mixed micelles with CTABr.     

Evaluation of chiral bidentate ligand–metal complexes in asymmetric 1,3-dipolar cycloaddition reaction of nitrones with 3-alkenoyl-2-oxazolidinones

For evaluation of a chiral C₂-symmetric bis(oxazoline) ligand, its Lewis acid complexes-catalyzed asymmetric 1,3-dipolar cycloaddition reactions of nitrones with electron-deficient dipolarophiles, 3-(2-alkenoyl)-1,3-oxazolidin-2-ones, have been investigated and it was found that the cycloadditions using a Cu(II)-bis(oxazoline) complex under optimized reaction conditions induced extremely high enantioselectivity.     

Size distribution and characteristics of chemical components in ambient particulate matter.

Ambient particulate matter and gas in Kyoto were investigated by gravimetric analysis, X-ray fluorescence spectrometry, and ion chromatography in order to clarify their behavior and origin. The size distribution and characteristics of the chemical components in ambient particulates collected on PTFE membrane filters using an Andersen air sampler were examined from August 2001 to April 2004. A four-stage filter pack method was used to sample the atmosphere for the determination of gas (SO2, HNO3, HCl, NH3) and particulate matter (SO42, NO3, Cl-, Na+, K+, Ca2+, Mg2+, NH4+) concentrations from October 2002 to April 2004. The concentration of SPM mass was in the range of 6.7 - 80.2 microg/m3. The size distributions of SPM mass were bimodal, peaking at around 0.65 - 1.1 and 3.3 - 4.7 microm, and 40 - 85% of SPM mass was fine particles (< 2.1 microm). Na, Mg, Al, Si, Ca, Cl, and Fe were mainly present in coarse particles (2.1 to 11.0 microm), while S was present in fine particles. The concentrations of Al, Si, Ca, Mg, and Fe in fine particles increased from March to April in 2002, and those in coarse particulates increased in November 2002 and from March to April in 2004. This may be the effect of the continental yellow sand "Kosa." The differences in the size distributions of Al, Si, Ca, Mg, and Fe in particles may depend on differences in their place of occurrence and course of transport from China to Japan. The concentration of HCl gas was higher than that of particulate chloride ion in summer. Nitric acid gas existed at higher concentrations in summer, but fine particulate nitrate ion was observed in winter. The gaseous-to-fine aerosol nitrate fraction became higher at warmer temperatures. Coarse sulfate was below 10%, and SO2 gas and fine particulate sulfate were above 90%.     

Dinuclear calcium complex with weakly NH...O hydrogen-bonded sulfonate ligands

The novel intramolecularly NH...O hydrogen-bonded Ca(II)-aryl sulfonate complex, [Ca2(SO3-2-t-BuCONHC6H4)2(H2O)4]n(2-t-BuCONHC6H4SO3)2n (1), sulfonate anion, (HNEt3)(SO3-2-t-BuCONHC6H4) (2a), (PPh4)(SO3-2-t-BuCONHC6H4) (2b), (n-Bu4N)(SO3-2-t-BuCONHC6H4) (2c), and sulfonic acid, 2-t-BuCONHC6H4SO3H (3), were synthesized. The structures of 1, 2a, and 2b depict the presence of the formation of NH...O hydrogen bonds between the amide NH and S-O oxygen for a series of compounds as determined by IR and 1H NMR analyses both in the solid state and in the solution state. Thus, the NH...O hydrogen bonds with neutral amide groups are available for investigation of the electronic state of the O- anion. The combined data from the IR and 1H NMR spectra indicate that the sulfonic acid, sulfonate anion, and Ca(II) complex have a substantially weak intramolecular NH...O hydrogen bond between the SO3 oxygen and amide NH. In the detailed comparison with the intense NH...O hydrogen bonds for the carboxylate, weak NH...O hydrogen bonds for sulfonate is due to the strong conjugation of the SO3- group with the lower nucleophilicity.     

Mössbauer study on the photochemical reactions of pentacarbonyliron with ethene in low temperature nitrogen matrix

The UV-induced photochemical reactions of pentacarbonyliron with ethene in a low temperature nitrogen matrix were studied by means of the Mössbauer technique. Fe/CO/₄/C₂H₄/ was produced by UV-irradiation of penfacarbonyliron in close proximity to ethene molecules in a pure ethene matrix, or a homogeneous cocondensed matrix. The other products were obtained via thermal reactions with ethene of Fe/CO/₄ trapped in stratified matrices.     

Infrared spectra of the water-nitrogen complexes (H2O)2-(N2)n(n = 1-4) in argon matrices

The infrared spectra of the water-nitrogen complexes trapped in argon matrices have been studied with Fourier transform infrared absorption spectroscopy. The absorption lines of the H20-N2 1:1, 1:2, 1:n, and 2:1 complexes have been confirmed on the basis of the concentration effects. In addition, we have observed a few lines and propose the assignments for the 2:2, 2:3, and 2:4 complexes in the nu1 symmetric stretching and nu2 bending regions of the proton-acceptor molecule, and in the bonded OH stretching region of the proton-donor molecule. The redshifts in the bonded OH stretching mode and blueshifts in the OH bending mode suggest that the hydrogen bonds in the (H2O)2-(N2)n complexes with n = 1-4 are strengthened by the cooperative effects compared to the pure H2O dimer. Two absorption bands due to the 3:n complexes are also observed near the bonded OH stretching region of the H2O trimer.     

Mechanisms of water oxidation catalyzed by the cis,cis-[(bpy)2Ru(OH2)]2O4+ ion

The cis,cis-[(bpy)(2)Ru(III)(OH(2))](2)O(4+) micro-oxo dimeric coordination complex is an efficient catalyst for water oxidation by strong oxidants that proceeds via intermediary formation of cis,cis-[(bpy)(2)Ru(V)(O)](2)O(4+) (hereafter, [5,5]). Repetitive mass spectrometric measurement of the isotopic distribution of O(2) formed in reactions catalyzed by (18)O-labeled catalyst established the existence of two reaction pathways characterized by products containing either one atom each from a ruthenyl O and solvent H(2)O or both O atoms from solvent molecules. The apparent activation parameters for micro-oxo ion-catalyzed water oxidation by Ce(4+) and for [5,5] decay were nearly identical, with DeltaH(++) = 7.6 (+/-1.2) kcal/mol, DeltaS() = -43 (+/-4) cal/deg mol (23 degrees C) and DeltaH(++) = 7.9 (+/-1.1) kcal/mol, DeltaS(++) = -44 (+/-4) cal/deg mol, respectively, in 0.5 M CF(3)SO(3)H. An apparent solvent deuterium kinetic isotope effect (KIE) of 1.7 was measured for O(2) evolution at 23 degrees C; the corresponding KIE for [5,5] decay was 1.6. The (32)O(2)/(34)O(2) isotope distribution was also insensitive to solvent deuteration. On the basis of these results and previously established chemical properties of this class of compounds, mechanisms are proposed that feature as critical reaction steps H(2)O addition to the complex to form covalent hydrates. For the first pathway, the elements of H(2)O are added as OH and H to the adjacent terminal ruthenyl O atoms, and for the second pathway, OH is added to a bipyridine ring and H is added to one of the ruthenyl O atoms.     

A practical synthesis of 4′-thioribonucleosides

A practical synthesis of 4′-thioribonucleosides starting from inexpensive l-arabinose is described. 1,4-Anhydro-2,3-O-isopropylidene-4-thioribitol, which was prepared by using a novel reductive ring-contraction reaction, was converted to the 5-O-silylated sulfoxides. The Pummerer-type thioglycosylation of the sulfoxides gave the 4′-thioribonucleosides stereoselectively.     

Spectroscopic identification of the CO-H2O 2-1 cluster trapped in an argon matrix

The infrared spectra of the carbon monoxide-water cluster as well as the CO monomer and dimer in an argon matrix at cryogenic temperatures have been reinvestigated on the basis of the isotope substitution experiment with 12CO and 13CO. Lines due to the CO-H2O 2-1 cluster in the matrix have been unambiguously identified in the CO and OH stretching regions. The isotope effect on the vibrational frequency of the cluster is observed in the CO stretching vibration but neither in the symmetric nor antisymmetric OH stretching vibrations. Each of the two vibrational lines due to the two CO vibrations of the CO-H2O 2-1 cluster is examined by comparing the expected spectral features at a 12CO/13CO ratio on a simulation with those observed experimentally. The migration of the trapped molecules (CO and H2O) in the matrix is discussed, in which the observed spectral change with the deposition temperature from 14 K to 30 K is explained.     

Endo- and aminopeptidase activities of rat cathepsin H.

Employing soluble denatured protein substrates and their derivatives, the proteolytic activity of rat cathepsin H was investigated. The enzyme showed aminopeptidase activity which sequentially released amino acid from the N-terminal of the substrate. The aminopeptidase activity did not act on N alpha-acetylated peptides and showed moderate ionic-strength dependence when methionyl-methylcoumarylamide was employed as a substrate. These results indicate that the activity essentially requires an N-terminal free amino group of the substrate and recognizes it electrostatically to some extent. On the other hand, the enzyme was also indicated to exhibit endopeptidase activity by employing appropriate N alpha-acetylated peptide substrates. In contrast to the aminopeptidase activity, the endopeptidase activity showed rather strict specificity, preferring hydrophobic residues at P2 and P3 sites. Because of the broad specificity and high efficiency of the aminopeptidase activity, it was difficult to directly observe endopeptidase activity in the digestion of large peptide substrates with a free alpha-amino terminal. Thus, this is the first experimental evidence that indicates endopeptidase activity by assigning internal peptide bonds cleaved by this activity. From this data, we proposed a model of the binding site of this enzyme.