Determination of 15NH3 by gas chromatography-mass spectrometry. Application to the measurement of putrescine oxidation by human plasma

A convenient and sensitive method for the determination of 15NH3 has been developed. Ammonia was purified from sample solutions by a modified microdiffusion method, derivatized with pentafluorobenzoyl chloride to pentafluorobenzamide (PFBA) and determined by gas chromatography-mass spectrometry using a multiple ion detector. PFBA was eluted from the gas chromatographic column within 2 min and resulted in a simple mass fragmentation pattern. The 15N/14N ratio was accurately determined with picomole amounts of PFBA by measuring the molecular ions of PFBA and [15N]PFBA. The method was applied to the assay of putrescine oxidation by human plasma. 15NH3 was produced by incubating 15N-labelled putrescine with plasma. The 15NH3 production was time dependent and strongly inhibited by the addition of aminoguanidine, an inhibitor of diamine oxidase. Exceedingly high 15NH3 production from [15N]putrescine was observed in the plasma from pregnant women. In contrast, only trace amounts of 15NH3 were formed in the plasma from normal men and non-pregnant women. The method seems to be applicable to various biological systems that produce ammonia as a metabolic product.     

Aberration correction and its automatic control in scanning electron microscopes

An automatic aberration correction method has been implemented in scanning electron microscopes (SEM). Necessity of the automatic aberration correction is discussed. The procedure of the automatic aberration correction is explained in detail, where deconvolution techniques are used in order to extract probe information from SEM images. Due to the precise digitization and the usage of proper combinations of correction fields, linearity has been found between the amplitude of each aberration and the corresponding field strength. Experimental results are shown which demonstrate that the aberrations are corrected automatically by a linear feedback control method. After the automatic aberration correction, the image quality has been improved drastically.     

Two-dimensional self-assembled structures of melamine and melem at the aqueous solution-Au(111) interface

Self-assembled structures of melamine and the condensed melamine derivative melem were investigated at aqueous solution-Au(111) interfaces by cyclic voltammetry and in situ scanning tunneling microscopy (STM) observation. The adsorption/desorption behaviors of both molecules on Au(111) surfaces could be controlled by varying the electrochemical potential and solution concentration. In the negative potential region, self-assembled structures of melem and melamine were constructed by double hydrogen bonding systems between nitrogen atoms of triazine rings and amine groups. In addition, melem formed a closely packed structure at potentials of between -0.3 and -0.15 V or in solutions at higher concentrations.     

Reactivity of copper(II)-alkylperoxo complexes

Copper(II) complexes 1a and 1b, supported by tridentate ligand bpa [bis(2-pyridylmethyl)amine] and tetradentate ligand tpa [tris(2-pyridylmethyl)amine], respectively, react with cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH(3)CN to provide the corresponding copper(II) cumylperoxo complexes 2a and 2b, the formation of which has been confirmed by resonance Raman and ESI-MS analyses using (18)O-labeled CmOOH. UV-vis and ESR spectra as well as DFT calculations indicate that 2a has a 5-coordinate square-pyramidal structure involving CmOO(-) at an equatorial position and one solvent molecule at an axial position at low temperature (-90 °C), whereas a 4-coordinate square-planar structure that has lost the axial solvent ligand is predominant at higher temperatures (above 0 °C). Complex 2b, on the other hand, has a typical trigonal bipyramidal structure with the tripodal tetradentate tpa ligand, where the cumylperoxo ligand occupies an axial position. Both cumylperoxo copper(II) complexes 2a and 2b are fairly stable at ambient temperature, but decompose at a higher temperature (60 °C) in CH(3)CN. Detailed product analyses and DFT studies indicate that the self-decomposition involves O-O bond homolytic cleavage of the peroxo moiety; concomitant hydrogen-atom abstraction from the solvent is partially involved. In the presence of 1,4-cyclohexadiene (CHD), the cumylperoxo complexes react smoothly at 30 °C to give benzene as one product. Detailed product analyses and DFT studies indicate that reaction with CHD involves concerted O-O bond homolytic cleavage and hydrogen-atom abstraction from the substrate, with the oxygen atom directly bonded to the copper(II) ion (proximal oxygen) involved in the C-H bond activation step.     

Liquid-liquid biphasic synthesis of layered zinc hydroxides intercalated with long-chain carboxylate ions and their conversion into ZnO nanostructures

A method for synthesizing layered zinc hydroxide compounds in high yields is developed using an immiscible liquid-liquid system in one pot. Long-chain carboxylate ions such as heptanoate, decanoate, and dodecanoate were successfully intercalated between zinc hydroxide layers in one process starting from a xylene-water system. Typically, a xylene phase dissolving the respective carboxylic acids was allowed to stand in contact with an aqueous phase dissolving zinc nitrate hexahydrate and urea. During keeping the resultant biphasic system at 80 °C, urea was thermo-hydrolyzed to supply OH(-) in the aqueous phase while the carboxylic acids were continuously transferred from the xylene phase under the distribution law. The aqueous phase was then supersaturated, and a solid phase of layered basic zinc carboxylate was precipitated as films on glass substrates through heterogeneous nucleation and subsequent two-dimensional crystal growth. Crystal structures and morphology of the films were modulated by the kind of the carboxylic acids employed. The layered basic zinc carboxylate films could be converted to nanostructured, mesoporous ZnO films by heating at 450 °C in air. The relationship between the initial solution compositions and the final solid products was systematically examined to discuss reaction mechanisms in the biphasic systems.     

Synthesis of heterosegment-junctioned hybrid nanotubes of polythiophene and heterometallic nanoparticles by sequential template-based electropolymerization

New heterosegment-junctioned hybrid nanotubes of polythiophene and heterometallic nanoparticles (Pd, Au NPs) have been synthesized by sequential electropolymerization of terthiophene-modified Pd and Au NPs in a nanoporous template.     

Combined effects of high pressure and sodium hydrogen carbonate treatment on pork ham: improvement of texture and palatability

In this study, the combined effects of high pressure and sodium hydrogen carbonate (NaHCO₃) treatment on the physical and chemical properties, and palatability of pork ham, a tough and under-utilized meat, were investigated. Assessment of meat properties with heat treatment, after exposure to NaHCO₃ and high pressure treatment, revealed an increase in water content, and decreased weight reduction and rupture stress. The free amino acid content of meat samples increased with NaHCO₃ and high pressure treatment. The effect of high pressure processing was especially notable at a pressure of 300 MPa. Sensory evaluation showed that meat subjected to high pressure processing after NaHCO₃ treatment was tender and juicy. In addition, the sample produced minimal residue in the mouth and was characterized by a good taste.     

Calcite and fluorite as catalyst for the Knövenagel condensation of malononitrile and methyl cyanoacetate under solvent-free conditions

When milled together with calcite or fluorite, malononitrile and methyl cyanoacetate readily underwent Knövenagel condensation with aromatic aldehydes, giving the corresponding arylidenemalononitriles and (E)-α-cyanocinnamic esters in good to excellent yield.     

Dendrimer N-heterocyclic carbene complexes with rhodium(I) at the core

Novel dendrimer N-heterocyclic carbene complexes with rhodium(I) located at the core were synthesized, and a positive dendrimer effect was found in the hydrosilylation of ketones catalyzed by them.     

Measurement of temporal changes in vocal tract area function from 3D cine-MRI data

A 3D cine-MRI technique was developed based on a synchronized sampling method [Masaki et al., J. Acoust. Soc. Jpn. E 20, 375-379 (1999)] to measure the temporal changes in the vocal tract area function during a short utterance /aiueo/ in Japanese. A time series of head-neck volumes was obtained after 640 repetitions of the utterance produced by a male speaker, from which area functions were extracted frame-by-frame. A region-based analysis showed that the volumes of the front and back cavities tend to change reciprocally and that the areas near the larynx and posterior edge of the hard palate were almost constant throughout the utterance. The lower four formants were calculated from all the area functions and compared with those of natural speech sounds. The mean absolute percent error between calculated and measured formants among all the frames was 4.5%. The comparison of vocal tract shapes for the five vowels with those from the static MRI method suggested a problem of MRI observation of the vocal tract: data from static MRI tend to result in a deviation from natural vocal tract geometry because of the gravity effect.