Evaluation of an ODS column modified with zwitterionic/nonionic mixed surfactants and its application to direct injection determination of inorganic anions.

An octadecylsilica (ODS) column modified with zwitterionic/nonionic mixed surfactants was evaluated for the direct injection determination of inorganic anions in biological fluids by ion chromatography. A zwitterionic surfactant (sulfobetaine-type) and a nonionic surfactant (polyoxyethylene-type) were used for a stationary-phase modification. When aqueous electrolyte solutions with concentrations of sub-mM to several mM were used as a mobile phase, the zwitterionic surfactant coated on the ODS surface exhibited unique separation selectivity for ionic species, while the nonionic surfactant coated on the ODS might have formed a hydrophilic network over the ODS surface and restricted matrix proteins from adsorbing on the stationary phase. Consequently, the mixed surfactant-modified column system allowed an efficient ion chromatographic separation of inorganic anions as well as a size-exclusive removal of column-fouling proteins. This separation system was applied to the direct injection determination of UV-absorbing anions in human saliva. The detection limits for nitrite, nitrate, iodide and thiocyanate were 3.1, 2.7, 4.5 and 25 microM, respectively, with UV detection at 210 nm (injection volume; 20 microl), and their relative standard deviations for 5 replicate measurements of saliva samples spiked with 100 microM each of those anions were 1.4, 0.9, 2.2 and 5.5%, respectively.     

Translational medicine of the glutamate AMPA receptor

Psychiatric and neurological disorders severely hamper patient’s quality of life. Despite their high unmet needs, the development of diagnostics and therapeutics has only made slow progress. This is due to limited evidence on the biological basis of these disorders in humans. Synapses are essential structural units of neurotransmission, and neuropsychiatric disorders are considered as “synapse diseases”. Thus, a translational approach with synaptic physiology is crucial to tackle these disorders. Among a variety of synapses, excitatory glutamatergic synapses play central roles in neuronal functions. The glutamate α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) is a principal component of glutamatergic neurotransmission; therefore, it is considered to be a promising translational target. Here, we review the limitations of current diagnostics and therapeutics of neuropsychiatric disorders and advocate the urgent need for the promotion of translational medicine based on the synaptic physiology of AMPAR. Furthermore, we introduce our recent translational approach to these disorders by targeting at AMPARs.     

Freezing transition of wetting film of tetradecane on tetradecyltrimethylammonium bromide solutions

We have performed ellipsometry and surface tensiometry at tetradecyltrimethylammonium bromide (TTAB) aqueous solution surface coexisting with tetradecane lens as a function of the molality of TTAB and the temperature under atmospheric pressure. From the theoretical analysis of the coefficient of ellipticity, it was clarified that the liquid monolayer comprising the surfactant and alkane is formed at higher surfactant concentrations by the wetting transition of tetradecane lens on the aqueous solution, and the solid monolayer is formed by lowering temperature (freezing transition). The results of the surface tension measurement support the occurrence of wetting transition and the freezing transition. A phase diagram of the wetting film was constructed by ellipsometry and surface tensiometry, of which the mixed solid monolayer had never been reported before. From the thermodynamic analysis of the phase diagram, it is also demonstrated that the TTAB surface density decreases accompanied with the freezing transition, which agrees with surface densities of TTAB calculated from surface tension vs. concentration curves.     

Selective determination of 2,4-xylenol by gas chromatography/supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry

Gas chromatography/supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (GC/SSJ/REMPI/TOF-MS) was employed for isomer-selective determination of 2,4-xylenol in river and seawater samples. The sample containing 2,4-xylenol was measured using argon, rather than helium, as the GC carrier gas to cool the analyte molecule sufficiently. The instrumental detection limit (IDL) achieved at a flow rate of 1 mLmin(-1) was 14 pg. Although this value was comparable to the value (ca. 10 pg) obtained by gas chromatography/electron impact/quadrupole mass spectrometry (GC/EI/QMS). When the flow rate was increased to 8 mLmin(-1), interference from the 2,5-xylenol isomer was completely suppressed. The IDL was degraded to 83 or 160 pg at a flow rate of 5 or 8 mLmin(-1), respectively. The recovery of 2,4-xylenol from the river and the seawater samples was 85 and 93%, respectively. The time for analysis was only 10 min per one sample in GC/SSJ/REMPI/TOF-MS. These results suggest that GC/SSJ/REMPI/TOF-MS is useful for the selective measurement of 2,4-xylenol, which has been designated a Class I chemical substance in the Pollutant Release and Transfer Register (PRTR).     

Ionic polymers and oligomers with expanded π-conjugation system derived from through-space interaction in piperazinium ring

Reactions of N-(2,4-dinitrophenyl)-4-arylpyridinium chlorides (aryl (Ar) = phenyl and 4-pyridyl) with piperazines caused the ring opening of the pyridinium ring and yielded polymers that consisted of 5-piperazinium-3-aryl-penta-2,4-dienylideneammonium chloride units [N(CH(R)CH₂)₂N⁺(Cl⁻)CHCHC(Ar)CHCH, RH, Me, and phenyl]. However, the same reactions occurring in the presence of piperidine yielded oligomers that consisted of 5-piperazinium-3-aryl-penta-2,4-dienylideneammonium chloride units having piperidine and/or piperazine rings at both ends. ¹H NMR spectra suggested that π-electrons of the penta-2,4-dienylideneammonium group of the polymers and the oligomers were delocalized. UV-vis measurements revealed that the π-conjugation system expanded along the polymer and oligomer chains due to the orbital interaction between electrons on the two nitrogen atoms of the piperazinium ring. Conversion of the piperazinium ring from the boat form to the chair form caused decrease in the π-conjugation length. The rate constants of the conversion of the oligomers depended on their chain lengths. The surface of pellets that were molded from the polymers and oligomers exhibited metallic luster. These polymers and oligomers underwent electrochemical oxidation in solution.     

Corrosion and passivation behavior of Mg-Zn-Y-Al alloys prepared by cooling rate-controlled solidification

Highly corrosion-resistant nanocrystalline Mg-Zn-Y-Al multi-phase alloys have been prepared by consolidation of rapidly solidified (RS) ribbons. The relation between corrosion behavior and microstructure evolution of Mg-Zn-Y-Al alloys with a long period stacking ordered phase has been investigated. In order to clarify the influence of rapid solidification on the occurrence of localized corrosion such as filiform corrosion, several Mg_96.75Zn_0.75Y₂Al_0.5 (at.%) alloys with different cooling rates are fabricated by the gravity casting, copper mould injection casting and melt-spinning techniques and their corrosion behavior and microstructures are examined by the salt water immersion test, electrochemical measurements, GDOES, XRD, SEM and TEM. To clarify the effect of aluminium addition on the improvement in corrosion resistance of the alloys, several Mg_97.25−xZn_0.75Y₂Al_x alloys with different aluminium contents are fabricated by consolidating RS ribbons and the formation of corroded films on the Mg-Zn-Y-Al alloys have been investigated. Rapid solidification brings about the grain refinement and an increase in the solid solubility of zinc, yttrium and aluminium into the magnesium matrix, enhancing microstructural and electrochemical homogeneity, which in turn enhanced corrosion resistance. The addition of aluminium to magnesium can modify the structure and chemical composition of surface films and improves the resistance to local breakdown of the films.     

Aragonite twinning in gastropod nacre

Aragonite twinning in gastropod nacre has been investigated using scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD), and transmission electron microscopy (TEM) with the focused ion beam (FIB) sample preparation technique. At the growth front of nacre, Haliotis discus hannai and Omphalius rusticus form a “stack-of-coins” structures, which consist of pseudo-hexagonal and elliptical aragonite tablets, respectively. SEM, EBSD, and TEM analyses revealed that these tablets are monolithic single crystal and almost free of the {1 1 0} twins that are common in aragonite of biotic or abiotic origin. The longest diagonal of the hexagon and the longer axis of the ellipse are parallel to the a-axis of aragonite. The crystal orientation of each tablet in a stack, measured by TEM-Kikuchi pattern analysis, is almost the same but there is occasionally {1 1 0} twin-like relationship between adjacent tablets along the stacking. On the other hand, the fibrous aragonite layer formed prior to the nacreous structure is composed of polycrystalline aragonite with high density of {1 1 0} twins. TEM observation suggests that the interlamellar organic sheet prevents the inheritance of the twins, by selecting only single domain of the twins, through the mineral bridge.     

Host-guest interactions in the supramolecular incorporation of fullerenes into tailored holes on porphyrin-modified gold nanoparticles in molecular photovoltaics

Novel gold nanoparticles modified with a mixed self-assembled monolayer of porphyrin alkanethiol and short-chain alkanethiol were prepared (first step) to examine the size and shape effects of surface holes (host) on porphyrin-modified gold nanoparticles. The porphyrin-modified gold nanoparticles with a size of about 10 nm incorporated C60 molecules (guest) into the large, bucket-shaped holes, leading to the formation of a supramolecular complex of porphyrin-C60 composites (second step). Large composite clusters with a size of 200-400 nm were grown from the supramolecular complex of porphyrin-C60 composites in mixed solvents (third step) and deposited electrophoretically onto nanostructured SnO2 electrodes (fourth step). Differences in the porphyrin:C60 ratio were found to affect the structures and photoelectrochemical properties of the composite clusters in mixed solvents as well as on the SnO2 electrodes. The photoelectrochemical performance of a photoelectrochemical device consisting of SnO2 electrodes modified with the porphyrin-C60 composites was enhanced relative to a reference system with small, wedged-shaped surface holes on the gold nanoparticle. Time-resolved transient absorption spectroscopy with fluorescence lifetime measurements suggest the occurrence of ultrafast electron transfer from the porphyrin excited singlet states to C60 or the formation of a partial charge-transfer state in the composite clusters of supramolecular complexes formed between porphyrin and C60 leading to efficient photocurrent generation in the system. Elucidation of the relationship between host-guest interactions and photoelectrochemical function in the present system will provide valuable information on the design of molecular devices and machines including molecular photovoltaics.     

Reaction of octafluorocyclopentene with various carbon nucleophiles

The treatment of octafluorocyclopentene with organolithium reagents gave the corresponding symmetrical disubstituted perfluorocyclopentenes in good to high yields. The reaction with Grignard reagents led to the monosubstituted perfluorocyclopentenes, which were subjected to the further nucleophilic substitution reaction using another Grignard or aryllithium reagents, unsymmetrical disubstituted perfluorocyclopentenes being obtained in high yields.     

Radical [3 + 2] cycloaddition reaction with various alkenes using iodomethylcyclopropane derivatives as new homoallyl radical precursors

Radical iodine atom transfer [3 + 2] cycloaddition with various alkenes using dimethyl 2-(iodomethyl)cyclopropane-1,1-dicarboxylate and 1,1-bis(phenylsulfonyl)-2-(iodomethyl)cyclopropane as new precursors of a homoallyl radical species smoothly proceeds to give functionalized cyclopentane derivatives in good yields.