Identification of isomeric spin adducts of Leu-Tyr and Tyr-Leu free radicals using liquid chromatography-tandem mass spectrometry

Free radical species are generally short-lived due to their high reactivity and thus direct measurement and identification are often impossible. In this study we used a spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), to trap radical intermediates formed during the oxidation of isomeric dipeptides tyrosine-leucine (Tyr-Leu) and leucine-tyrosine (Leu-Tyr), induced by the hydroxyl radical. To investigate the influence of the amino acid position in the peptide chain on the oxidation and free radical generation, the spin adducts were characterized using LC-MS and MS(n) . We detected carbon and oxygen DMPO adducts and adducts bearing two DMPO, which were analyzed by MS(n) . Both alkoxyl and peroxyl radicals were identified. Radical intermediates were localized in Tyr during oxidation of Tyr-Leu, while radicals were identified in Leu and Tyr during oxidation of Leu-Tyr. DMPO adducts of acyl radical species formed from cleavage of the peptide backbone, promoted by the alkoxyl radical in α carbon of the N-terminal amino acid were observed. The results show that the amino acid position has an influence in the oxidation process, at least on small peptides, and that the α carbon of the N-terminal amino acid is more vulnerable to the attack of the electrophilic hydroxyl radical.     

Simultaneous quantification of morphine and cocaine in hair samples from drug addicts by GC-EI/MS

The development of analytical techniques that enable the use of hair as an alternative matrix for the analysis of drugs of abuse is useful for confirming the exposure in a larger time window (weeks to months, depending on the length of the hair shaft). In the present study a methodology aimed at the simultaneous quantification of cocaine and morphine in human hair was developed and validated. After decontamination, hair samples (20?mg) were incubated with a mixture of methanol/hydrochloric acid (2:1) at 65?°C overnight (~16?h) in order to extract the drugs of the matrix. Purification was performed by solid-phase extraction using mixed-mode extraction cartridges. After derivatization with N-methyl-N-(trimethylsilyl) trifluoroacetamide, blank, standards and samples were analyzed by gas chromatography/electron impact-mass spectrometry (GC-EI/MS). The method proved to be selective, as there were no interferences of endogenous compounds with the same retention time as cocaine, morphine and ethylmorphine (internal standard). The regression analysis for both analytes showed linearity in the range 0.25-10.00?ng/mg with correlation coefficients ranging from 0.9989 to 0.9991. The coefficients of variation oscillated between 0.83 and 14.60%. The limits of detection were 0.01 and 0.02?ng/mg, and the limits of quantification were 0.03 and 0.06?ng/mg for cocaine and morphine, respectively. The proposed GC-EI/MS method provided an accurate and simple assay with adequate precision and recovery for the quantification of cocaine and morphine in hair samples. The proof of applicability was performed in hair samples obtained from drug addicts enrolled in a Regional Detoxification Treatment Center. The importance of hair samples is highlighted, since positives results were obtained when urine immunoassay analyses were negative. Copyright ? 2012 John Wiley & Sons, Ltd.     

High-valent oxo-molybdenum and oxo-rhenium complexes as efficient catalysts for X-H (X = Si, B, P and H) bond activation and for organic reductions

High-valent oxo-complexes have recently emerged as powerful catalysts for the activation of X-H (X = Si, B, P and H) bonds and for the reduction of several functional groups. This new reactivity represents a complete reversal from the traditional role of these complexes as oxidation catalysts and opened a new research area for high-valent oxo-complexes. This tutorial review highlights the work developed using high-valent oxo-molybdenum and oxo-rhenium complexes as excellent catalysts for X-H (X = Si, B, P and H) bond activation and for organic reductions.     

Ionic and radical adsorption on the Au(hkl) surfaces: A DFT study

Adsorption of several ionic and non-ionic species (OH^?, O, O^?, O^2?, H, H⁺ and H^?) on the low-index Miller Au(hkl) surfaces has been investigated by means of density functional theory based methods. The stability order for adsorptions on the three surfaces decreases with the increasing of the coordination number of the outermost gold atoms in each surface, i.e., Au(110) > Au(100) > Au(111), which is in agreement with the experimental evidences. The detailed COOPs analysis of the various adsorption sites for all adsorbates in the surface with the most stable adsorption(s), Au(110), evidenced that adsorption in the gold surfaces may be a function of particle size and charge and substantiates the variability in the order of preferences sites for the adsorption of the different species found in these low-index Miller Au(hkl) surfaces. This variability increases with the increasing of the stability of the adsorptions on the gold surfaces, i.e., the Au(110) presents more variability in the order of preferences sites for the adsorption of different species.     

Preparation of Organometallic Ruthenium–Arene–Diaminotriazine Complexes as Binding Agents to DNA

The reactions of two diaminotriazine ligands 2,4‐diamino‐6‐(2‐pyridyl)‐1,3,5‐triazine (2‐pydaT) and 6‐phenyl‐2,4‐diamino‐1,3,5‐triazine (PhdaT) with ruthenium–arene precursors led to a new family of ruthenium(II) compounds that were spectroscopically characterized. Four of the complexes were cationic, with the general formula [(η⁶‐arene)Ru(κ²‐N,N‐2‐pydaT)Cl]X (X=BF₄, TsO; arene=p‐cymene: 1.BF4 , 1.TsO arene=benzene: 2.BF4 , 2.TsO ). The neutral cyclometalated complex [(η⁶‐p‐cymene)Ru(κ²‐C,N‐PhdaT*)Cl] ( 3 ) was also isolated. The structures of complexes 2.BF4 and 3.H2O were determined by X‐ray diffraction. Complex 1.BF4 underwent a partial reversible‐aquation process in water. UV/Vis and NMR spectroscopic measurements showed that the reaction was hindered by the addition of NaCl and was pH‐controlled in acidic solution. At pH 7.0 (sodium cacodylate) Ru–Cl complex 1.BF4 was the only species present in solution, even at low ionic strength. However, in alkaline medium (KOH), complex 1.BF4 underwent basic hydrolysis to afford a Ru–OH complex ( 5 ). Fluorimetric studies revealed that the interaction of complex 1.BF4 with DNA was not straightforward; instead, its main features were closely linked to ionic strength and to the [DNA]/complex ratio. The bifunctional complex 1.BF4 was capable of interacting concurrently through both its p‐cymene and 2‐pydaT groups. Cytotoxicity and genotoxicity studies showed that, contrary to the expected behavior, the complex species was biologically inactive; the formation of a Ru–OH complex could be responsible for such behavior.     

A low‐temperature polymorph of m‐quinquephenyl

A low‐temperature polymorph of 1,1′:3′,1′′:3′′,1′′′:3′′′,1′′′′‐quinquephenyl (m‐quinquephenyl), C₃₀H₂₂, crystallizes in the space group P2₁/c with two molecules in the asymmetric unit. The crystal is a three‐component nonmerohedral twin. A previously reported room‐temperature polymorph [Rabideau, Sygula, Dhar & Fronczek (1993). Chem. Commun. pp. 1795–1797] also crystallizes with two molecules in the asymmetric unit in the space group P. The unit‐cell volume for the low‐temperature polymorph is 4120.5 (4) ų, almost twice that of the room‐temperature polymorph which is 2102.3 (6) ų. The molecules in both structures adopt a U‐shaped conformation with similar geometric parameters. The structural packing is similar in both compounds, with the molecules lying in layers which stack perpendicular to the longest unit‐cell axis. The molecules pack alternately in the layers and in the stacked columns. In both polymorphs, the only interactions between the molecules which can stabilize the packing are very weak C—H...π interactions.     

Multi-residue analytical methods for the determination of pesticides and PPCPs in water by LC-MS/MS: a review

Residues of pesticides, pharmaceutical and personal care products (PPCPs) are contaminants of world-wide concern. Consequently, there is a growing need to develop reliable analytical methods, which enable rapid, sensitive and selective determination of these pollutants in environmental samples, at trace levels. In this paper, a review of the liquid chromatography-tandem mass spectrometry (LC-MS/MS) based methods for the determination of pesticides and PPCPs in the environment is presented. Advanced aspects of current LC-MS/MS methodology, including sample preparation and matrix effects, are discussed.     

Hydrophilic interaction chromatography in drug analysis

Hydrophilic interaction chromatography (HILIC) is an increasingly popular alternative to conventional HPLC for drug analysis. It offers increased selectivity and sensitivity, and improved efficiency when quantifying drugs and related compounds in complex matrices such as biological and environmental samples, pharmaceutical formulations, food, and animal feed. In this review we summarize HILIC methods recently developed for drug analysis (2006–2011). In addition, a list of important applications is provided, including experimental conditions and a brief summary of results. The references provide a comprehensive overview of current HILIC applications in drug analysis.