Syntheses and degradations of fluorinated heterocyclics III. Perfluoroalkyl and perfluoroalkylether-1,3,4-oxadiazoles

2,5-Bis(perfluoro-n-heptyl)-, 2-perfluoroalkylether-5-perfluoro-n-heptyl-, and 2,5-bisperfluoroalkylether-1,3,4-oxadiazoles were synthesized and characterized. 2,5-Bis(perfluoro-n-heptyl)-1,3,4-oxadiazole was thermally and hydrolytically stable at 325°C; however, in the presence of air, degradation took place at 235°C. The perfluoroalkylether analogue exhibited thermal and hydrolytic stability at 325°C; it was found to be unaffected by Jet-A fuel and air at 235°C. At 325°C in air some degradation occured as evidenced by volatiles production, oxygen consumption, and 96% starting material recovery.     

Substituent effects on the tautomer ratios between the hydrazone imine and diazenyl enamine forms in side-chained quinoxalines

The 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 9–11 were synthesized by the reaction of the quinoxalines 6–8 with various p-substituted benzenediazonium salts. Compounds 9–11 showed the tautomeric equilibria between the hydrazone imine A and diazenyl enamine B forms in dimethyl sulfoxide media. The substituent effect on the tautomer ratios of A to B was studied by the nmr spectroscopy to clarify that the presence of the ester group R² on the hydrazone carbon and electron-donating p-substituent R¹ on the side chain benzene ring exhibited a tendency to increase the ratios of the tautomer A .     

Stereoselective synthesis of (Z)-fluoroalkenes directed to peptide isosteres: copper mediated reaction of trialkylaluminum with 4,4-difluoro-5-hydroxyallylic alcohol derivatives

Copper mediated alkyl-transfer reaction of trialkylaluminum (R₃Al) with (E)-4,4-difluoro-5-hydroxyallylic alcohol derivative smoothly proceeded to give the corresponding 2-alkylated 4-fluoro-5-hydroxyhomoallylic alcohol derivative with completely Z and 2,5-syn selective manner. Regio- and stereoselective conversion of the C5-hydroxyl group of the fluoroolefin thus obtained to amino group could be achieved through one-pot mesylation and azidation reaction.     

Generation of functionalized asymmetric benzynes with TMP-zincates. Effects of ligands on selectivity and reactivity of zincates

We have developed new methods for preparing functionalized benzynes through deprotonative zincation as a key reaction using R2Zn(TMP)Li, and we also describes dramatic ligand effects on the benzyne formation. Deprotonative zincation of various meta-substituted bromobenzenes with Me2Zn(TMP)Li proved effective for the one-pot generation of various 3-functionalized benzynes, particularly those electrophilic substituents such as ester, amide, and cyano. On the other hand, zincation with tBu2Zn(TMP)Li, followed by electrophilic trapping (with I2) proved a powerful tool for the preparation of 1,2,3-trisubstituted aromatic compounds.8 The resultant 1,2,3-trisubstituted benzenes are available as precursors for generation of 3-substituted benzynes by halogen-zinc exchange reactions with Me3ZnLi. These methods offer far greater generality than previous methods for the synthesis of functionalized asymmetric benzynes, and should be of value in new syntheses of various natural products and functional materials. In addition, these results underline the utility of spectator ligands on the central metal of ate complexes as a tunable functionality in the development of new ate complex-promoted reactions.     

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%.     

Determination of the change of nuclear charge radius of the119Sn Mössbauer transition by internal conversion

Radioactive¹¹⁹Sb was implanted into six host matrices (CaSnO₃, Pt, Y, Au,-Sn, Pb) and internal conversion electrons of the 23.87 keV transition in¹¹⁹Sn were measured with an iron-free magnetic spectrometer as well as Mössbauer spectra. In the analysis of the conversion spectra of outermost electrons, the overlapping K-LM Auger lines were subtracted using the Auger spectrum of tin measured with another source of^117mSn, and the shake-off effect accompanying the conversion process was considered. From the correlation between the Mössbauer isomer shifts and the intensity ratios of O-shell to N₁-shell conversion electrons, the change of the nuclear charge radius of the 23.87 keV transition of¹¹⁹Sn was deduced to be R/R=(0.87 ± 0.25) × 10^–4 for a uniform charge distribution ofR= 1.2 ×A ^1/3 fm or, equivalently, r²>—=(3.6 ± 1.0) ×10^–3 fm².     

On-column derivatization-capillary electrochromatography with o-phthalaldehyde/alkylthiol for assay of biogenic amines

The elution behaviors of the biogenic amines, histamine (HA) and its metabolite methyl histamine (MHA), were evaluated by means of on-column derivatization (OCD)-capillary electrochromatography (CEC) which employed a monolithic octadecylsilica (ODS) capillary column (20 cm of effective length x 50 microm of inner diameter). Five kinds of alkylthiols, e.g., 2- hydroxyethylthiol (or 2-mercaptoethanol (2-ME)), ethanethiol (ET), 1-propanethiol (1-PT), 2-methyl-1-propanethiol (2-MPT) and 1-butanethiol (1-BT) were separately presented at 5 mM each in the OCD-CEC separation run buffer consisting of 60% acetonitrile in 5 mM o-phthalaldehyde (OPA)-10 mM borate buffer (pH 10). When 2-ME was present in the run buffer solution, both derivatives corresponding to HA and MHA migrated separately, but closely together through the capillary column. Replacement of 2-ME with 1-BT in the run buffer solution caused a delay in their elution profiles on the electrochromatogram and the separation between those two peaks became remarkably improved. The elution times of HA and MHA followed the increase in alkyl chain length or hydrophobicity of thiol, 1-BT > 2-MPT > 1-PT > ET > 2-ME. Performance of on-line preconcentrations of HA and MHA was also evaluated by varying the electrokinetic injection voltage from 1 kV to 8 kV. The peak area counts corresponding to HA recorded about 50 times higher when 2 kV was applied for 240 s to a 0.1 mM HA solution than when 8 kV was applied for 5 s. This method was next applied to a sample of human urine spiked with HA and MHA at levels of 0.1 microM each. Although HA and MHA peaks were not identifiable among the peaks corresponding to the materials in the urine matrix when OPA/2-ME was employed in a run buffer for the OCD-CEC, the separation and identification of their peaks became possible by replacing 2-ME with 1-BT in the run buffer solution.     

Design and synthesis of novel type somatostatin analogs with antiproliferative activities on A431 tumor cells

It was reported that the somatostatin analog TT-232, d-Phe-c(Cys-Tyr-d-Trp-Lys-Cys)-Thr-NH₂, exhibited a highly potent antitumor activity in vitro and in vivo. Using pyrazinone analogs and aliphatic amino acids instead of the disulfide bond, we prepared novel type somatostatin analogs including the sequence essential for antitumor activities, Tyr-d-Trp-Lys. These analogs exhibited antiproliferative effect on A431 tumor cells.     

Mechanisms and kinetics of noncatalytic ether reaction in supercritical water. 2. Proton-transferred fragmentation of dimethyl ether to formaldehyde in competition with hydrolysis

Noncatalytic reaction pathways and rates of dimethyl ether (DME) in supercritical water are determined in a tube reactor made of quartz according to liquid- and gas-phase 1H and 13C NMR observations. The reaction is studied at two concentrations (0.1 and 0.5 M) in supercritical water at 400 degrees C and over a water-density range of 0.1-0.6 g/cm3. The supercritical water reaction is compared with the neat one (in the absence of solvent) at 0.1 M and 400 degrees C. DME is found to decompose through (i) the proton-transferred fragmentation to methane and formaldehyde and (ii) the hydrolysis to methanol. Formaldehyde from reaction (i) is consecutively subjected to four types of redox reactions. Two of them proceed even without solvent: (iii) the unimolecular proton-transferred decarbonylation forming hydrogen and carbon monoxide and (iv) the bimolecular self-disproportionation generating methanol and carbon monoxide. When the solvent water is present, two additional paths are open: (v) the bimolecular self-disproportionation of formaldehyde with reactant water, producing methanol and formic acid, and (vi) the bimolecular cross-disproportionation between formaldehyde and formic acid, yielding methanol and carbonic acid. Methanol is produced through the three types of disproportionations (iv)-(vi) as well as the hydrolysis (ii). The presence of solvent water decelerates the proton-transferred fragmentation of DME; the rate constant is reduced by 40% at 0.5 g/cm3. This is caused by the suppression of low-frequency concerted motion corresponding to the reaction coordinate for the simultaneous C-O bond scission and proton transfer from one methyl carbon to the other. In contrast to the proton-transferred fragmentation, the hydrolysis of DME is markedly accelerated by increasing the water density. The latter becomes more important than the former in supercritical water at densities greater than 0.5 g/cm3.