An anomalous course of the reduction of 2‐(3‐oxo‐3,4‐dihydro‐quinoxalin‐2‐yl)benzene diazonium salt. Synthesis of a new quinoxalino[1,2‐c][1,2,3]benzotriazine system

By diazotization of 3‐(2‐aminophenyl)quinoxaline‐2(lH)‐one la and 3‐(2‐aminophenyl)‐6,7‐dimethylquinoxaline‐2(lH)‐one 1b followed by the reaction with sodium sulphite new quinoxalino[1,2‐c]‐[1,2,3]benzotriazins 4a and 4b were prepared, respectively.     

Evidence of covalent interaction of fumaric acid esters with sulfhydryl groups in peptides

Fumaric acid esters, namely dimethylfumarate, have been used for the treatment of psoriasis for many years. Still, their mode of action is not fully clear. Because addition of nucleophiles to the double bonds of fumarates can occur (Michael analogous addition), a study of the interaction of fumarates with cysteine and cysteine-containing peptides possessing nucleophilic sulfhydryl group was carried out. Experiments were performed in aqueous medium at pH 7.4 and at 37 degrees C to simulate physiological conditions. It was proven by mass spectrometric measurements using an ion-trap and time-of-flight instrument that a covalent bond can form between fumarates and the sulfhydryl group of cysteine or cysteinyl residues in peptides. Structures of the interaction products were elucidated by multistage mass spectrometry applying collision-induced dissociation. Higher reactivity of dimethylfumarate in comparison to monomethylfumarate and fumaric acid was observed.     

Utilization of capillary electrophoresis/mass spectrometry (CE/MSn) for the study of anthocyanin dyes

Hyphenation of capillary electrophoresis with electrospray ionization mass spectrometry was utilized for the monitoring of anthocyanins in wine and wine musts. CE/MS was performed in two electrolytes: 1) an acidic one (chloroacetate-ammonium, pH 2) and 2) a basic one with high selectivity towards derivatives containing vicinal hydroxy groups (borate-ammonium, pH 9). The setup of MS was optimized and the fragmentation of common anthocyanins was studied in detail. Attention was also focused on the fragmentation of anthocyanidin skeleton. The anthocyanidins substituted with hydroxy groups fragment via a cascade of neutral losses of water and carbon monoxide. Fragmentation of anthocyanidins containing a methoxy group on their B-ring starts with the cleavage of methane and/or methyl radical. The optimized method was utilized for the monitoring of changes in anthocyanin profile in red wines as well as the process of release of anthocyanins to wine must.     

Capillary electrophoresis-mass spectrometry - a fast and reliable tool for the monitoring of milk adulteration

The development of a rapid, simple and accurate analytical method aimed at the detection and quantification of bovine milk in either ovine or caprine milk samples by means of CE-MS analyses of whey proteins with high-ionic strength and presence of acidic running buffer is described. The high-ionic strength buffer was used in order to minimize the problems with the adsorption of the proteins onto the fused-silica capillary wall. The acidic running electrolyte, pH 1.9, was used to support the production of positive ions in electrospray. Highly linear dependences of the ratio of the sum of non-bovine beta-lactoglobulins (ovine or caprine) to the total beta-lactoglobulins in milk mixture (bovine plus ovine or bovine plus caprine) vs. the volume percentage of added bovine milk in ovine (or caprine) milk were obtained. This technique allowed the fast and reliable evaluation of milk adulteration. The amount of bovine milk added into the "non-bovine" ones can be well within the concentration range of 5-95%.     

Ionization and fragmentation of monochloro-isomers of 3-hydroxy-2-phenyl-4(1H)-quinolinone

Electron ionization (EI), methane chemical ionization (CI), and collision-induced dissociation (CID) mass spectra of complete series of positional monochloro-isomers of 3-hydroxy-2-phenyl-4(1H)-quinolinone are evaluated and discussed. It is shown that in the CI experiments, in addition to the protonated precursor molecules, odd-electron molecular ions are formed and this affects the appearance of the CID spectra. The influence of different direct probes and other experimental parameters such as the pressure of the reagent gas, isolation width, or collision energy was studied. EI, CI and CID spectra of the positional isomers show essentially the same fragmentation pathways but comparisons of the relative signal intensities of various product ions reveal some positional effects. Different isomers are also distinguished. The compounds can be divided into two groups using diagnostic ions (chloro substitution of the quinolinone moiety or the phenyl ring) or identified using a created spectral database. It was demonstrated that the reproducibility of the CID spectra is fully satisfactory for isomer identification, and that the created database can be applied for comparison of spectra measured over an extended time period (1 month) or spectra obtained during the direct analysis of a reaction mixture extract. Explanation of the fragmentation of the isomers is supported by exploratory density functional theory (DFT) calculations, e.g. rationalization of the relatively higher importance of the M(+.)-H(.)-Cl(.)-CO fragmentation pathway during EI than during CID, and vice versa for the pathway M(+.)-Cl(.)-CO. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Synthesis of some polycyclic 1,2,4‐triazines disposing of acidic N‐H group

7‐(6‐Azauracil‐5‐yl)‐isatin 1 was converted through its thiosemicarbazone 2 to 6‐(6‐azauracil‐5‐yl)‐2,3‐dihydro‐5H‐1,2,4‐triazino[5,6‐b]indol‐3‐thione 3 and through the thiosemicarbazone of appropriate isatinic acid to 2‐(2‐thio‐6‐azauracil‐5‐yl)‐6‐(6‐azauracil‐5‐yl)‐aniline 4. The course of the cyclocondensation of this compound was studied and the reaction was found to proceed in both possible ways, resulting in a mixture of compound 3 and regioisomer 6‐(2‐thio‐6‐azauracil‐5‐yl)‐2,3‐dihydro‐5H‐1,2,4‐triazino[5,6‐b]‐indol‐3‐one 5. Substituted aniline 4 was oxidized to 2,6‐bis‐(6‐azauracil‐5‐yl)‐aniline 7 , which served for the preparation of hydrazone 8 , cyclization of which led to 1‐[2,6‐bis‐(6‐azauracil‐5‐yl)‐phenyl]‐6‐azauracil‐5‐carbonitrile 9. This is the first tricyclic 6‐azauracil with vicinal arrangement of 6‐azauracil rings.     

Electrochemical reduction of chloridazon at mercury electrodes, and its analytical application

The electrochemical behavior of the herbicide chloridazon, I (pyrazon), at different pH is described. The electrode reaction (one wave in acidic media and another in alkaline media), investigated using direct current and pulse voltammetry, controlled-potential coulometry, and HPLC-MS, is a combination of the electroreduction (two-electron in the first step) and a kinetic process as a result of which simple compounds (HCl, NH3) are released and, moreover, a five-membered pyrrole cycle is formed in strongly acid media. Products of the kinetic reaction are further reducible. The dissociation constant of I, pKa = 2.96, was found spectrophotometrically. Fast-scan differential pulse voltammetry (FSDPV) was used for determination of I; the detection limit was 2.7 x 10(-8) mol L(-1) (0.006 microg L(-1)) at pH 2.3. Chloridazon was determined in spiked drinking and river water.     

Characterization of natural organic colorants in historical and art objects by high‐performance liquid chromatography

High‐performance liquid chromatography plays an important role in analysis of historical organic colorants. A number of papers have been published in this field over the last 30 years. Classification of the most commonly used natural dyes and an overview of high‐performance liquid chromatography methods with main focus on recent works (2008 to the beginning of 2014) are provided. The review deals with an entire analytical protocol covering sample preparation, chromatographic separation, and suitable detection (UV/visible and fluorescent spectroscopy and mass spectrometric techniques). High‐performance liquid chromatography has been successfully used in the complete characterization of some organic dyestuffs present in historical and art objects. The possibilities and difficulties for identification of natural sources of historical colorants are also discussed.