Diels–Alder derivatization for sensitive detection and characterization of conjugated linoleic acids using LC/ESI-MS/MS

The utility of Diels–Alder derivatization with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) for liquid chromatography/electrospray ionization tandem mass spectrometry of conjugated linoleic acids (CLAs) was examined. PTAD rapidly reacted with the CLAs, and the resulting derivatives were highly responsive in electrospray ionization mass spectrometry operating in the positive-ion mode. The derivatives produced characteristic product ions during tandem mass spectrometry, which enabled the sensitive detection [limit of detection 18 fmol (signal-to-noise ratio of 5)] and the identification of the conjugated diene position. The PTAD derivatization also significantly increased the reversed-phase liquid chromatography separation selectivity for the most biologically active CLA isomers: cis-9,trans-11-CLA and trans-10,cis-12-CLA. The PTAD derivatization was applied to analyses of food and biological samples; the major CLAs in milk and beef fat samples were successfully identified, and trace amounts of CLAs in human saliva were detected with a simple pretreatment and short analysis time.     

The work function reduction of the Pt field emitter

We have carried out the field emission experiments to measure the temperature dependence of the work function of Pt field emitter and found that the work function steeply decreases more than 2 eV by annealing at relatively low temperature above about 500 K in ultra high vacuum. The maximum reduction of the work function was 2.59 eV. The reduced work function was restored the original value of Pt clean surface by applying high voltage of only 20% of Pt evaporation field. The experimental results are tentatively interpreted in terms of the formation of complex cyanides on the emitter shank during the electrochemical etching in KCN solution and the surface diffusion of potassium atoms formed by the thermal decomposition of the complex cyanides to the emitter cap.     

Dress-up chiral columns for the enantioseparation of amino acids based on fluorous separation

In this paper, we report a new type of chiral high-performance liquid chromatography (HPLC) column—a so-called dress-up chiral column—featuring a chiral stationary phase adsorbed reversibly in a commercial fluorous HPLC column through fluorous interactions. We synthesized perfluroalkylated proline derivatives as chiral stationary phase compounds and then adsorbed them reversibly in the fluorous HPLC column through the pumping of their solutions. By using this dress-up chiral column and fluorophobic elution of an aqueous copper(II) sulfate/MeOH mixture, we could enantioseparate seven racemic amino acids within 40 min. When we washed the dress-up chiral column with fluorophilic tetrahydrofuran or MeOH, the adsorbed chiral stationary phase compounds desorbed from the column, completely destroying its enantioseparation ability. The relative standard deviation of the retention times, the number of theoretical plates, and the resolution for each of four preparations of the dress-up columns were all less than or equal to 9.53 % in 20-times repeated analysis, and were all less than or equal to 18.7 % in four different preparations, respectively.     

Simultaneous analysis of cationic, anionic, and neutral compounds using monolithic CEC columns

A new capillary electrochromatography (CEC) column for the simultaneous analysis of cationic, neutral, and anionic compounds using CEC-ESI-MS is described. Three different silica monolith columns were prepared by changing the poly(ethylene glycol) (PEG) contents for comparison of the separation property of these columns. Different separation programs were used for the simultaneous separation of different charged compounds under the same conditions. The column prepared with 80 mg of PEG separated typical compounds within 15 min using 1 M formic acid as the electrolyte. The analytes migrated in the order of cationic, neutral, and anionic compounds, which means that the migration order was mainly determined by the electrophoresis. The hydrodynamic flow by pressure from the inlet side was significant for a stable analysis to be achieved. The effect of the composition of the sheath liquid was also examined. All analytes (14 amino acids, thiourea, urea, citric acid, and ATP) were detectable when 1% acetic acid in 50% (v/v) methanol was used as the sheath liquid.     

Behavior of Zn, Cu, Pb and Cd in biota of Yangtze Estuary

The contents of zinc, copper, lead and cadmium were measured in the dominant species (plants: Scripus triquetor and Phrgrmites australis, macrobenthos: llyoplax deschampsin, Helice tridens tientsinensis, Bullacta exarata and Corbicula fluminea, and migrating waders: Calidris ruficollis and C. alpina) of the ecosystem of Yangtze Estuary, China, from 1995-1998. Results show that:     

Reaction of grayanotoxin-II with thallium (III) nitrate

Reaction of grayanotoxin-II (1) with thallium nitrate gave 3(S), 20-epoxy-6 (S), 14 (R), 16 (R)-trihydroxy-5-oxo-5, 10-seco-ent-kaur-1 (10) -ene (2). The structure of 2 was elucidated by the X-ray diffraction analysis of its reduction product (3).     

Supramolecular Strategies for Controlling Reactivity within Confined Nanospaces

Nanospaces are ubiquitous in the realm of biological systems and are of significant interest among supramolecular chemists. Understanding chemical behavior within nanospaces offers new perspectives on biological phenomena in nature and opens the way to highly unusual and selective forms of catalysis. Supramolecular chemistry exploits weak, yet effective, intermolecular interactions such as hydrogen bonding, metal‐ligand coordination, and the hydrophobic effect to assemble nano‐sized molecular architectures, providing reactions with remarkable rate acceleration, substrate specificity, and product selectivity. In this minireview, the focus is on the strategies that supramolecular chemists use to emulate the efficiency of biological processes, and elucidating how chemical reactivity is efficiently controlled within well‐defined nanospaces. Approaches such as orientation and proximity of substrate, transition‐state stabilization, and active‐site incorporation will be discussed.     

Simultaneous determination of dl-lactic acid and dl-3-hydroxybutyric acid enantiomers in saliva of diabetes mellitus patients by high-throughput LC–ESI-MS/MS

A simultaneous determination method for the enantiomers of chiral carboxylic acids by the combination of ultraperformance liquid chromatography and mass spectrometry (UPLC-MS/MS) has been developed. (S)(+)-1-(2-Pyrrolidinylmethyl)-pyrrolidine (S-PMP) was used as the derivatization reagent for the high-throughput determination of biological chiral carboxylic acids, i.e., lactic acid (LA) and 3-hydroxybutyric acid (HA). The S-PMP efficiently reacted with the carboxylic acids under mild conditions at room temperature in the presence of 2,2'-dipyridyl disulfide and triphenylphosphine. The resulting S-PMP derivatives were highly responsive in the electrospray ionization (ESI)-MS operating in the positive-ion mode and gave characteristic product ions during the MS/MS, which enabled the sensitive detection using selected reaction monitoring. The derivatization was effective for the enantiomeric separation of the chiral carboxylic acids, and the resolution values of DL-LA and DL-HA were 4.91 and 9.37, respectively. Furthermore, a rapid separation of the derivatives of DL-LA and DL-HA within 7?min was performed using the UPLC system. The limits of detection on the column were in the low femtogram range (5-12?fg). The proposed procedure was successfully applied for the determination of the D- and L-isomers of LA and HA in the saliva of diabetes mellitus (DM) patients and healthy volunteers. The D-LA in DM patients was clearly higher than that in normal subjects. The derivatization followed by UPLC-ESI-MS/MS enabled the enantiomeric separation and detection of trace amounts of LA and HA in human saliva with a simple pretreatment and small sample volume.     

Oxidative degradation of 8-nitroquinoline with hydrogen peroxide in acetic acid a possible mechanism through 3,4-epoxide of quinoline ring

The treatment of 8-nitroquinoline with hydrogen peroxide and acetic acid at 60°C afforded 7-nitroindole, 7-nitro-2-oxindole, 2-amino-3-nitrobenzoic acid, 2-amino-3-nitrobenzaldehyde, 3,4-dihydro-3, 4-trans-dihydroxy-8-nitrocarbostyril, 3,4-trans-dihydro-3-hydroxy-4-acetoxy-8-nitrocarbostyril, and 1-(2-amino-3-nitrophenyl)-2-hydroxy-ethanone. The reaction mechanism acceptable in elucidating the formation of these products involves, at the initial step of reaction, an epoxidation of the 3,4-double bond of the 1,2-dihydro adduce of quinoline ring.