Characterization of O2 (1Δg)-derived oxidation products of tryptophan: A combination of tandem mass spectrometry analyses and isotopic labeling studies

The fragmentation mechanisms of singlet oxygen [O(2) ((1)Delta(g))]-derived oxidation products of tryptophan (W) were analyzed using collision-induced dissociation coupled with (18)O-isotopic labeling experiments and accurate mass measurements. The five identified oxidized products, namely two isomeric alcohols (trans and cis WOH), two isomeric hydroperoxides (trans and cis WOOH), and N-formylkynurenine (FMK), were shown to share some common fragment ions and losses of small neutral molecules. Conversely, each oxidation product has its own fragmentation mechanism and intermediates, which were confirmed by (18)O-labeling studies. Isomeric WOH lost mainly H(2)O + CO, while WOOH showed preferential elimination of C(2)H(5)NO(3) by two distinct mechanisms. Differences in the spatial arrangement of the two isomeric WOHs led to differences in the intensities of the fragment ions. The same behavior was also found for trans and cis WOOH. FMK was shown to dissociate by a diverse range of mechanisms, with the loss of ammonia the most favored route. MS/MS analyses, (18)O-labeling, and H(2)(18)O experiments demonstrated the ability of FMK to exchange its oxygen atoms with water. Moreover, this approach also revealed that the carbonyl group has more pronounced oxygen exchange ability compared with the formyl group. The understanding of fragmentation mechanisms involved in O(2) ((1)Delta(g))-mediated oxidation of W provides a useful step toward the structural characterization of oxidized peptides and proteins.     

Synthesis of pentabromopseudilin and other arylpyrrole derivatives via Heck arylations

Pentrabromopseudilin and other 2 and 3-arylpyrrole derivatives were synthesized through the Heck–Matsuda reaction involving endocyclic enecarbamates and N-protected 3-pyrrolines, respectively. The overall processes permitted an easy and efficient access to these structural motifs present in several bioactive compounds. Attempts to synthesize the compound isopentabromopseudilin led to a tribromo aryl maleimide. We hypothesize that this latter compound is the putative product arising from the unusual thermal instability of isopentabromopseudilin.     

Absolute configuration of strictosidinic acid

The absolute configuration of strictosidinic acid, (2S,3R,4S)‐3‐ethenyl‐2‐(β‐d ‐glucopyranosyloxy)‐4‐{[(1S)‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐1‐yl]methyl}‐3,4‐dihydro‐2H‐pyran‐5‐carboxylate, was determined from its sodium chloride trihydrate, poly[[diaqua((2S,3R,4S)‐3‐ethenyl‐2‐(β‐d ‐glucopyranosyloxy)‐4‐{[(1S)‐2,3,4,9‐tetrahydro‐1H‐pyrido[3,4‐b]indol‐2‐ium‐1‐yl]methyl}‐3,4‐dihydro‐2H‐pyran‐5‐carboxylate)sodium] chloride monohydrate], {[Na(C₂₆H₃₂N₂O₉)(H₂O)₂]Cl·H₂O}_n. The strictosidinic acid molecule participates in intermolecular hydrogen bonds of the O—H...O and O—H...Cl types. The solid‐state conformation was observed as a zwitterion, based on a charged pyridine N atom and a carboxylate group, the latter mediating the packing through coordination with the sodium cation.     

Poly[di‐μ‐aqua‐[μ6‐N‐(4‐bromophenylsulfonyl)dithiocarbimato]dipotassium] and poly[di‐μ‐aqua‐[μ4‐N‐(4‐iodophenylsulfonyl)dithiocarbimato]dipotassium]

The rigid organic linkers N‐(4‐bromophenylsulfonyl)dithiocarbimate(2−) and N‐(4‐iodophenylsulfonyl)dithiocarbimate(2−) crystallize with two potassium cations and two water molecules in their asymmetric units, forming the title coordination polymers, [K₂(C₇H₄BrNO₂S₃)(H₂O)₂]_n and [K₂(C₇H₄INO₂S₃)(H₂O)₂]_n. The anions and the water molecules link the potassium cations into broad two‐dimensional networks, which are further linked by K...halide interactions.     

Fast sequential multi-element determination of Ca,Mg, K,Cu, Fe,Mn and Zn for foliar diagnosis using high-resolution continuum source flame atomic absorption spectrometry: Feasibility of secondary lines,side pixel registration and least-squares background correction

The fast sequential multi-element determination of Ca, Mg, K, Cu, Fe, Mn and Zn in plant tissues by high-resolution continuum source flame atomic absorption spectrometry is proposed. For this, the main lines for Cu (324.754 nm), Fe (248.327 nm), Mn (279.482 nm) and Zn (213.857 nm) were selected, and the secondary lines for Ca (239.856 nm), Mg (202.582 nm) and K (404.414 nm) were evaluated. The side pixel registration approach was studied to reduce sensitivity and extend the linear working range for Mg by measuring at wings (202.576 nm; 202.577 nm; 202.578 nm; 202.580 nm; 202.585 nm; 202.586 nm; 202.587 nm; 202.588 nm) of the secondary line. The interference caused by NO bands on Zn at 213.857 nm was removed using the least-squares background correction. Using the main lines for Cu, Fe, Mn and Zn, secondary lines for Ca and K, and line wing at 202.588 nm for Mg, and 5 mL min^− 1 sample flow-rate, calibration curves in the 0.1–0.5 mg L^− 1 Cu, 0.5–4.0 mg L^− 1 Fe, 0.5–4.0 mg L^− 1 Mn, 0.2–1.0 mg L^− 1 Zn, 10.0–100.0 mg L^− 1 Ca, 5.0–40.0 mg L^− 1 Mg and 50.0–250.0 mg L^− 1 K ranges were consistently obtained. Accuracy and precision were evaluated after analysis of five plant standard reference materials. Results were in agreement at a 95% confidence level (paired t-test) with certified values. The proposed method was applied to digests of sugar-cane leaves and results were close to those obtained by line-source flame atomic absorption spectrometry. Recoveries of Ca, Mg, K, Cu, Fe, Mn and Zn in the 89–103%, 84–107%, 87–103%, 85–105%, 92–106%, 91–114%, 96–114% intervals, respectively, were obtained. The limits of detection were 0.6 mg L^− 1 Ca, 0.4 mg L^− 1 Mg, 0.4 mg L^− 1 K, 7.7 µg L^− 1 Cu, 7.7 µg L^− 1 Fe, 1.5 µg L^− 1 Mn and 5.9 µg L^− 1 Zn.     

Optimization of matrix solid-phase dispersion extraction method for the analysis of isoflavones in Trifolium pratense

A method based on matrix solid-phase dispersion (MSPD) has been developed for the determination of 12 isoflavones in Trifolium pratense L. Dried leaf samples were blended with C₁₈, placed in small columns and isoflavones extracted with dichloromethane–methanol. Analyses were performed by high performance liquid chromatography with diode array detection (HPLC-DAD) with 2-methoxyflavone as internal standard. Several dispersants, eluents and clean-up steps were tested during the optimization of the process in order to obtain the best selectivity and yields. Mean recoveries ranged from 70% to 119%, with relative standard deviations <18%. The limits of detection were between 0.006 mg/l for biochanin A and 0.108 mg/l for daidzin. The performance of the optimized method in real samples was compared with a conventional method based in solid–liquid extraction (SLE).     

Fast analysis of multiple pesticide residues in apple juice using dispersive liquid–liquid microextraction and multidimensional gas chromatography–mass spectrometry

A method for the rapid trace analysis of 24 residual pesticides in apple juice by multidimensional gas chromatography–mass spectrometry (MD-GC/MS) using dispersive liquid–liquid microextraction (DLLME) was developed and optimized. Several parameters of the extraction procedure such as type and volume of extraction solvent, type and volume of dispersive solvent and salt addition were evaluated to achieve the highest yield and to attain the lowest detection limits. The DLLME procedure optimized consists in the formation of a cloudy solution promoted by the fast addition to the sample (5 ml) of a mixture of carbon tetrachloride (extraction solvent, 100 μl) and acetone (dispersive solvent, 400 μl). The tiny droplets formed and dispersed among the aqueous sample solution are further joined and sedimented (85 μl) in the bottom of the conical test tube by centrifugation. Once extracted, all the 24 pesticides were directly injected and separated by a dual GC column system, comprising a short wide-bore DB-5 capillary column with low film thickness connected by a Deans switch system to a second chromatographic narrower column, with identical stationary phase. The instrumental setting used, in combination with carefully optimized operational fast GC and MS parameters, markedly decreased the retention times of the targeted analytes. The total chromatographic run was 8 min. Mean recoveries for apple juice spiked at three concentrations ranged from 60% to 105% and the intra-repeatability ranged from 1% to 21%. The limits of detection of the 24 pesticides ranged from 0.06 to 2.20 μg/L. In 2 of a total of 28 analysed samples were found residues of captan, although at levels below the maximum limit legal established.     

Novel conductive characteristics of ITO:Ti films deposited by spin coating from colloidal precursor

Transparent semiconducting ITO:Ti thin films, prepared by a sol–gel process, has been deposited by spin-coating technique onto alkali-free glass substrates. The as-coated films were annealed in ambient air at 550 °C for 1 h and further annealed in a reducing atmosphere. The influences of the Ti content in the sol on the surface morphology, microstructure, optical properties and electrical resistivity have been investigated. These properties were found to depend on the Ti content in the coating sol. Ti addition led to dense smooth layers with larger crystallite size (20–30 nm). Double layers synthesized with Ti:ITO = 0.53 wt% and submitted to reducing treatment in forming gas exhibited the lowest sheet resistance R_□ = 60 Ω_□ with an average transmittance of 87% at 550 nm.