Development of polyaniline microarray electrodes for cadmium analysis

Disposable screen-printed electrodes (SPCE) were modified using a cosmetic product to partially block the electrode surface in order to obtain a microelectrode array. The microarrays formed were electropolymerized with aniline. Scanning electron microscopy was used to evaluate the modified and polymerized electrode surface. Electrochemical characteristics of the constructed sensor for cadmium analysis were evaluated by cyclic and square-wave voltammetry. Optimized stripping procedure in which the preconcentration of cadmium was achieved by depositing at ?1.20 V (vs. Ag/AgCl) resulted in a well defined anodic peak at approximately ?0.7 V at pH 4.6. The achieved limit of detection was 4 × 10^?9 mol dm^?3. Spray modified and polymerized microarray electrodes were successfully applied to quantify cadmium in fish sample digests.     

Low-pressure pyrolysis of tBu2SO: synthesis and IR spectroscopic detection of HSOH

Sulfenic acid (HSOH, 1 ) has been synthesized in the gas‐phase by low‐pressure high‐temperature (1150 °C) pyrolysis of di‐tert‐butyl sulfoxide (tBu₂SO, 2 ) and characterized by means of matrix isolation and gas‐phase IR spectroscopy. High‐level coupled‐cluster (CC) calculations (CCSD(T)/cc‐pVTZ and CCSD(T)/cc‐pVQZ) support the first identification of the gas‐phase IR spectrum of 1 and enable its spectral characterization. Five of the six vibrational fundamentals of matrix‐isolated 1 have been assigned, and its rotational‐resolved gas‐phase IR spectrum provides additional information on the O–H and S–H stretching fundamentals. Investigations of the pyrolysis reaction by mass spectrometry, matrix isolation, and gas‐phase FT‐IR spectroscopy reveal that, up to 500 °C, 2 decomposes selectively into tert‐butylsulfenic acid, (tBuSOH, 3 ), and 2‐methylpropene. The formation of the isomeric sulfoxide (tBu(H)SO, 3 a ) has been excluded. Transient 3 has been characterized by a comprehensive matrix and gas‐phase vibrational IR study guided by the predicted vibrational spectrum calculated at the density functional theory (DFT) level (B3LYP/6‐311+G(2d,p)). At higher temperatures, the intramolecular decomposition of 3 , monitored by matrix IR spectroscopy, yields short‐lived 1 along with 2‐methylpropene, but also H₂O, and most probably sulfur atoms. In addition, HSSOH ( 6 ), H₂, and S₂O are found among the final pyrolysis products observed at 1150 °C in the gas phase owing to competing intra‐ and intermolecular decomposition routes of 3 . The decomposition routes of the starting compound 2 and of the primary intermediate 3 are discussed on the basis of experimental results and a computational study performed at the B3LYP/6‐311G* and second‐order Møller–Plesset (MP2/6‐311G* and RI‐MP2/QZVPP) levels of theory.     

Structure and bonding in monomeric iron(III) complexes with terminal oxo and hydroxo ligands

We report on the structure and bonding in the title iron(III) complexes, containing the tris[(N'-tert-butylureayl)-N-ethyl]amine ligand, with density functional theory techniques. In agreement with the experimental data, a high-spin electronic state is favored for all of the systems we considered. H bonds between the terminal oxo and hydroxo ligands and NH groups present in the organic ligand coordinated to the metal have a remarkable effect on the overall coordination geometry. In fact, the structure of model complexes without H bonds shows shorter Fe-O bond lengths. This is a consequence of the ability of the H bonds to stabilize a remarkable amount of electron density localized on the terminal oxo and hydroxo ligands. Energy analysis indicates that each H bond stabilizes the nonheme complexes by roughly 35 kJ/mol. Molecular orbital analysis indicates a reduction of two Fe-O bonding electrons on going from a complex with a terminal oxo ligand to a complex with a terminal hydroxo ligand. This reduction in the number of bonding electrons is also supported by frequency analysis.     

Direct electrochemistry of an [FeFe]-hydrogenase on a TiO2 electrode

[FeFe]-hydrogenases are efficient natural catalysts that can be exploited for hydrogen production. Immobilization of the recombinant [FeFe]-hydrogenase CaHydA was achieved for the first time on an anatase TiO(2) electrode. The enzyme is able to interact and exchange electrons with the electrode and to catalyze hydrogen production with an efficiency of 70%.     

Mechanism insights into an unexpected isomerisation reaction observed during conversion of N-benzyl piperazinones to corresponding N-benzyl thio-piperazinones

An interesting and surprising rearrangement was observed during the reaction of 4-N-benzyl piperazinone derivatives with Lawesson’s reagent as a thionating agent. Investigation into the possible mechanism responsible for these results is reported herein.     

Enantioselective capillary electrophoresis for identification and characterization of human cytochrome P450 enzymes which metabolize ketamine and norketamine in vitro

Ketamine, a phencyclidine derivative, is used for induction of anesthesia, as an anesthetic drug for short term surgical interventions and in subanesthetic doses for postoperative pain relief. Ketamine undergoes extensive hepatic first-pass metabolism. Enantioselective capillary electrophoresis with multiple isomer sulfated β-cyclodextrin as chiral selector was used to identify cytochrome P450 enzymes involved in hepatic ketamine and norketamine biotransformation in vitro. The N-demethylation of ketamine to norketamine and subsequently the biotransformation of norketamine to other metabolites were studied via analysis of alkaline extracts of in vitro incubations of racemic ketamine and racemic norketamine with nine recombinantly expressed human cytochrome P450 enzymes and human liver microsomes. Norketamine was formed by CYP3A4, CYP2C19, CYP2B6, CYP2A6, CYP2D6 and CYP2C9, whereas CYP2B6 and CYP2A6 were identified to be the only enzymes which enable the hydroxylation of norketamine. The latter two enzymes produced metabolic patterns similar to those found in incubations with human liver microsomes. The kinetic data of ketamine N-demethylation with CYP3A4 and CYP2B6 were best described with the Michaelis–Menten model and the Hill equation, respectively. This is the first study elucidating the individual enzymes responsible for hydroxylation of norketamine. The obtained data suggest that in vitro biotransformation of ketamine and norketamine is stereoselective.     

Extraction methods of red blood cell membrane proteins for Multidimensional Protein Identification Technology (MudPIT) analysis

Since red blood cells (RBCs) lack nuclei and organelles, cell membrane is their main load-bearing component and, according to a dynamic interaction with the cytoskeleton compartment, plays a pivotal role in their functioning. Even if erythrocyte membranes are available in large quantities, the low abundance and the hydrophobic nature of cell membrane proteins complicate their purification and detection by conventional 2D gel-based proteomic approaches. So, in order to increase the efficiency of RBC membrane proteome identification, here we took advantage of a simple and reproducible membrane sub-fractionation method coupled to Multidimensional Protein Identification Technology (MudPIT). In addition, the adoption of a stringent RBC filtration strategy from the whole blood, permitted to remove exhaustively contaminants, such as platelets and white blood cells, and to identify a total of 275 proteins in the three RBC membrane fractions collected and analysed. Finally, by means of software for the elaboration of the great quantity of data obtained and programs for statistical analysis and protein classification, it was possible to determine the validity of the entire system workflow and to assign the proper sub-cellular localization and function for the greatest number of the identified proteins.     

Site-Specific Differences in Proteasome-Dependent Degradation of Monoubiquitinated α-Synuclein

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