A kinetic method for <Emphasis Type="Italic">para</Emphasis>-nitrophenol determination based on its inhibitory effect on the catalatic reaction of catalase

The inhibitory effect of para-nitrophenol on the catalytic reaction of catalase was investigated. Michaelis-Menten kinetic parameters were determined from Lineweaver-Burk plots obtained in the absence or in the presence of the inhibitor. The inhibitor pattern, revealed by the Lineweaver-Burk plots, suggested a fully mixed inhibition mechanism. Spectrophotometric monitoring of the indicator reaction: in conjunction with initial rate measurements was employed for the kinetic determination of the inhibitor. Calibration plots of initial rate vs. para-nitrophenol concentration were linear in the concentration range 0.9·10⁻⁵–2.5·10⁻⁵ mol/L and the detection limit was 3·10⁻⁶ mol/L (417 μg/L) para-nitrophenol. Interferences from other phenolic compounds like orto-cresole, meta-and orto-nitrophenol were observed.     

Absolutely continuous spectrum for the Anderson model on a product of a tree with a finite graph

We prove the almost sure existence of absolutely continuous spectrum at low disorder for the Anderson model on the simplest example of a product of a regular tree with a finite graph. This graph contains loops of unbounded size.     

Thermal stability and the behaviour in organic solvents of some poly(ester-siloxane)urethanes

Three new chemically crosslinked polyurethanes were synthesized. Their behaviour in organic solvents and in dynamic heating conditions was studied. Predictions regarding the thermal stability have been made by using the isoconversion kinetic method.     

Interplay between composition,structural dynamics and thermodynamic data in amino acid nitrates

Journal of Thermal Analysis and Calorimetry - A systematic thermodynamic study has been performed for a series of nitrates having cations derived from the α-amino acids glycine (Gly),...     

Base-free Mizoroki-Heck reaction catalyzed by rhodium complexes

A base-free rhodium-catalyzed Mizoroki-Heck (M-H) reaction using potassium aryltrifluoroborates as the arylating agent of alkenes and acetone as a green "oxidant" is described. Thanks to the ready availability of organoboranes, this reaction should constitute an interesting alternative to conventional M-H reactions using aryl halides.     

Absolutely Continuous Spectrum for the Anderson Model on Some Tree-like Graphs

We prove persistence of absolutely continuous spectrum for the Anderson model on a general class of tree-like graphs.     

Determination of ganglioside composition and structure in human brain hemangioma by chip-based nanoelectrospray ionization tandem mass spectrometry

We report here on a preliminary investigation of ganglioside composition and structure in human hemangioma, a benign tumor in the frontal cortex (HFC) in comparison to normal frontal cortex (NFC) tissue using for the first time advanced mass spectrometric methods based on fully automated chip-nanoelectrospray (nanoESI) high-capacity ion trap (HCT) and collision-induced dissociation (CID). The high ionization efficiency, sensitivity and reproducibility provided by the chip-nanoESI approach allowed for a reliable MS-based ganglioside comparative assay. Unlike NFC, ganglioside mixture extracted from HFC was found dominated by species of short glycan chains exhibiting lower overall sialic acid content. In HFC, only GT1 (d18:1/20:0), and GT3 (d18:1/25:1) polysialylated species were detected. Interestingly, none of these trisialylated forms was detected in NFC, suggesting that such components might selectively be associated with HFC. Unlike the case of previously investigated high malignancy gliosarcoma, in HFC one modified O-Ac-GD2 and one modified O-Ac-GM4 gangliosides were observed. This aspect suggests that these O-acetylated structures could be associated with cerebral tumors having reduced malignancy grade. Fragmentation analysis by CID in MS² mode using as precursors the ions corresponding to GT1 (d18:1/20:0) and GD1 (d18:1/20:0) provided data corroborating for the first time the presence of the common GT1a and GT1b isomers and the incidence of unusual GT1c and GT1d glycoforms in brain hemangioma tumor.      

Determination of Pesticides in Carrots by Gas Chromatography–Mass Spectrometry

ABSTRACT

A sensitive and selective method was developed to determine pesticides in carrots by gas chromatography–mass spectrometry following the development of an optimized extraction procedure. The method was validated for 30 organochlorine pesticides for gas chromatography with electron capture detection obtaining limit of detection from 0.18 to 0.92?µg/kg except for cis- and trans-permenthrin. Twenty-six carrot samples were analyzed and six pesticides were detected. The results compared with the accepted maximum residue levels in correlation to crop origin.     

An Investigation of Plasma-Polymer Interactions by Mass Spectrometry

Surface modification of polymers by low-pressure plasmas has gained scientific and industrial importance for controlling adhesion of coatings, wettability, printability, bio-compatibility and other surface-related properties. However, more is to be learned about the complex interactions at the plasma-polymer interface. The present study is designed to investigate these plasma-polymer surface interactions by means of mass spectrometry. Various polymer specimens (polyethylene, polypropylene, polyethylene terephthalate, and polyimide) were placed directly on an electrode which contains the sampling aperture into a quadrupole mass spectrometer. We have identified various molecular fragments from these polymers, which were liberated by chain scissions provoked by various energetic plasma constituents, in particular, bombarding ions and vacuum ultraviolet (VUV) photons.