An ultrasensitive and highly selective determination method for quinones by high-performance liquid chromatography with photochemically initiated luminol chemiluminescence

Quinones are a class of compounds of substantial toxicological and pharmacological interest. An ultrasensitive and highly selective chemiluminescence (CL) method was newly developed for the determination of quinones based on the utility of photochemically initiated luminol CL. The method involved ultraviolet (UV) irradiation of quinones to generate reactive oxygen species (ROS) through the unique photosensitization reaction accompanied with the photolytical generation of 3,6-dihydroxyphthalic acid (DHPA) from quinones. The photoproducts were detected by luminol CL reaction. Interestingly, it was noticed that DHPA had enhancement effect for the luminol CL. The generation of the enhancer (DHPA) in association with the oxidant (ROS) in the photochemical reaction greatly increases the sensitivity and selectivity of the proposed luminol CL method. In order to elucidate the type of ROS produced by the photosensitizaion reaction in relation to the proposed CL reaction, we investigated the quenching effect of selective ROS scavengers in the luminol CL. Although several ROS were generated, superoxide anion was the most effective ROS for the generated CL. Moreover, the enhancement mechanism of DHPA for luminol CL was confirmed. The enhancement was found to be through the formation of stabilized semiquinone anion radical that provided long-lived CL. The generation of the semiquinone radical was confirmed by electron spin resonance technique. Furthermore, we developed an HPLC method with on-line photochemical reaction followed by the proposed CL detection for the determination of four quinones. A luminol analogue, L-012, was used for its high sensitivity. The detection limits for quinones obtained with the proposed method (S/N = 3) were in the range 1.5–24 fmol that were 10–1000 times more sensitive compared with the previous methods. Finally, the developed HPLC-CL system was successfully applied for the determination of quinones in airborne particulate samples collected at Nagasaki city.     

Highly sensitive method for determination of N-nitrosamines using high-performance liquid chromatography with online UV irradiation and luminol chemiluminescence detection

A new method for the measurement of N-nitrosamines in part-per-trillion concentrations from water samples without preconcentration steps has been developed. This method is based on online UV irradiation after high-performance liquid chromatographic separation and subsequent luminol chemiluminescence detection without addition of an oxidant. It was confirmed that N-nitrosamines in basic aqueous solution were transformed to peroxynitrite by UV irradiation. The detection limits for this method were 1.5 ng/L, 2.9 ng/L, 3.0 ng/L, and 2.7 ng/L for N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N-nitrosopyrrolidine, respectively, at a signal-to-noise ratio of 3. The calibration graphs were linear in the range of 5–1000 ng/L for these N-nitrosamines. This method was used for the determination of N-nitrosamines in tap water, river water, and industrial plant effluent samples. The recoveries of N-nitrosodimethylamine, N-nitrosomorpholine, N-nitrosomethylethylamine, and N-nitrosopyrrolidine present in tap water sample at a concentration of 10 ng/L (mean ± standard deviation, n = 4) were (94.8 ± 2.7)%, (102.0 ± 6.9)%, (99.3 ± 3.9)%, and (102.8 ± 2.5)%, respectively. These results indicate that our proposed method can be applied satisfactorily to the determination of N-nitrosamines in water samples.     

Development of 14-epi-19-nortachysterol and its unprecedented binding configuration for the human vitamin D receptor

In the study of the synthesis of 14-epi-19-norprevitamin D(3), we found 14-epi-19-nortachysterol derivatives through C6,7-cis/trans isomerization. We also succeeded in their chemical synthesis and revealed their marked stability and potent VDR binding affinity. To the best of our knowledge, this is the first isolation of stable tachysterol analogues. Surprisingly, 14-epi-19-nortachysterol derivatives exhibited an unprecedented binding configurations for the ligand binding pocket in hVDR, C5,6-s-trans and C7,8-s-trans triene configurations, which were opposite the natural C7,8-ene-configuration of 1α,25(OH)(2)D(3).     

Simultaneous determination of five polyether ionophores using liquid chromatography with one-step fluorescent derivatization

We present a selective method for simultaneous determination of five polyether ionophores such as salinomycin (SAL), monensin (MON), narasin (NAR), semduramicin (SEM) and lasalocid (LAS) in aquatic samples using a liquid chromatography with one-step fluorescent derivatization of 2-(4-hydrazinocarbonyl-phenyl) 4,5-diphenylimidazole (HCPI) and 4-(4,5-diphenyl-1H-imidazol-2-yl) benzoyl chloride hydrochloride (DIB-Cl). Fluorescent one-step derivatization for SAL, MON, NAR and SEM using HCPI and for LAS using DIB-Cl was monitored by an LC/fluorescence detector (E(x), 340 nm; E(m), 465 nm). Chromatographic separation was performed on a TSK-GEL ODS-120T (4.6 × 150 mm, 3 μm) column using a mobile phase of 0.1% formic acid in acetonitrile and 0.5 mM ammonium formate in water (70/30, v/v). The limits of detections were 0.01 μg/mL (50 pg) for LAS, 0.05 μg/mL (250 pg) for SAL, NAR and SEM, and 0.1 μg/mL (500 pg) for MON, respectively. The recoveries for water samples were indicated to be the range of 79.6 ± 6.4 - 99.0 ± 4.4% with associated precision values (between-day for 3 days) for repeatability. Based on solid-phase extraction, the limit of quantitation values indicated 0.1 ng/mL for SAL, MON, NAR and SEM, and 0.01 ng/mL for LAS in water samples.     

Determination of glyoxylic acid in urine by liquid chromatography with fluorescence detection, using a novel derivatization procedure based on the Petasis reaction

The Petasis reaction is the multi-component reaction of a carbonyl compound, amine, and arylboronic acid to form an α-amino acid or a β-aminoalcohol. In this work, as the first analytical application of the Petasis reaction, a high-performance liquid chromatographic (HPLC) method with fluorescence detection was developed for determination of glyoxylic acid. The glyoxylic acid was derivatized with 1-pyreneboronic acid, as fluorescent arylboronic acid, in the presence of N-methylbutylamine, as amine, to give a fluorescent α-amino acid. HPLC separation of the fluorescent derivative was performed within 30 min on an octyl column eluted with a gradient prepared from acetonitrile and 50 mmol L(-1) acetate buffer (pH 4.0). The detection limit (S/N=3) for glyoxylic acid was 5.0 nmol L(-1) (20 fmol/injection). The method can be used to determine the concentration of glyoxylic acid in human urine without interference from biological components.     

Nucleation reaction dynamics of Pt nanoparticles observed by the heterodyne transient grating method

The nucleation reaction dynamics of platinum nanoparticles in the photoreduction process of H(2)Pt(IV)Cl(6) solution were investigated by the heterodyne transient grating (HD-TG) method. The formation mechanism of platinum nanoparticles was considered, supported by information obtained from UV/VIS absorption spectroscopy during the reaction and SEM images of the generated nanoparticles. In particular, the roles of poly(N-vinyl-2-pyrrolidone) (PVP) as a protective polymer and ethanol as a solvent were studied. The chemical species involved in the reaction can be identified from the diffusion coefficients obtained from HD-TG measurements; the species observed by UV pulse irradiation were assigned to H(2)Pt(IV)Cl(6) as a reactant species and H(2)Pt(II)Cl(4) and Pt nuclei as product species. It was observed that the amounts of the reactant and product species increased, and many homogeneous nanoparticles were generated, by an increase in PVP concentration. The addition of ethanol to the solvent showed a larger effect on the enhancement of the reduction of H(2)Pt(IV)Cl(6) than that of PVP; however, it did not lead to Pt nuclei formation in the order of seconds. Nevertheless, because nanoparticle formation was confirmed by UV/VIS absorption spectroscopy and SEM images, the formation of nanoparticles following nuclei formation must have proceeded via a slow reaction. Therefore, nucleation and nanoparticle formation are considered to occur on a longer time scale than 10 s in water/ethanol solvent.     

Rhodium-catalyzed convenient synthesis of functionalized tetrahydronaphthalenes

Convenient as well as convergent synthesis of functionalized tetrahydronaphthalenes has been accomplished under mild reaction conditions by the cationic rhodium(I)/H₈-BINAP complex-catalyzed [2+2+2] cycloaddition of 1,7-octadiyne derivatives with functionalized monoynes. The effect of the diyne tether lengths was investigated, which revealed that 1,6-heptadiyne and 1,7-octadiyne exhibit higher reactivity than 1,8-nonadiyne. Mechanistic studies indicated that the present rhodium-catalyzed [2+2+2] cycloaddition proceeds through the rhodacyclopentadiene intermediate generated by oxidative coupling of a diyne with rhodium. On the other hand, in the reactions of diynes and dimethyl acetylenedicarboxylate, the rhodacyclopentadiene intermediate generated by oxidative coupling of a diyne and a monoyne with rhodium would also be involved.     

Micropatterning of copper on a poly(ethylene terephthalate) substrate modified with a self-assembled monolayer

We have developed a technique for the site-selective electroless deposition of Cu on poly(ethylene terephthalate) (PET) substrate modified with an organic self-assembled monolayer (SAM). The PET substrate was first modified with a silica-like layer by being dip-coated in an acetone solution of 3-aminopropyltrimethoxysilane and treated with UV light. The PET substrate was further modified with thiol groups using a 3-mercaptopropyltrimethoxysilane-SAM and then irradiated by UV light through a photomask to prepare thiol-group regions and OH-group regions. Cu was then deposited on only the thiol-group regions of the substrate by electroless deposition in a neutral solution with no catalysts by using dimethylamineborane as a reducing reagent. This site-selective deposition process can control the deposition conditions by an organic thin film fabricated on a surface-modified PET substrate, and thus can be applied to other low heat-resistant substrates.     

Optical Detection of Nonequilibrium Swelling Behavior of a Polymer Gel upon Solvent Substitution

We report a novel transient swelling and shrinking behavior of a thin poly(acrylamide)-based gel film upon solvent substitution between water and ethylene glycol. These size changes could be optically detected through a change in the Bragg diffraction wavelength for the colloidal crystal of charged polystyrene latex particles that was fixed in the gel. The transient size change that was observed in this study could not be explained on the basis of the equilibrium characteristics, but it was attributable to the transient variation of osmotic pressure in the gel.