Search results for "Molecular oxygen"
showing 10 items of 22 documents
FIA-fluorimetric determination of adrenaline in pharmaceutical formulations by oxidation with molecular oxygen
1998
The fluorimetric determination of adrenaline is carried out in a continuous-flow assembly and by means of the molecular dissolved oxygen. The sample solution merges with an NaOH stream, then the resulting mixture is heated at 73 °C and led to the flow-cell of the fluorimeter. The flow-assembly is very simple and the procedure is quick (107 samples h−1) reproducible (R.S.D. 0.6%), selective and suitable to be applied to determination of adrenaline in formulations. Calibrations graph are linear over the ranges 0.05–15 and 20–40 mgl−1.
Oxygen depletion in dense molecular clouds: a clue to a low O2 abundance?
2011
Context: Dark cloud chemical models usually predict large amounts of O2, often above observational limits. Aims: We investigate the reason for this discrepancy from a theoretical point of view, inspired by the studies of Jenkins and Whittet on oxygen depletion. Methods: We use the gas-grain code Nautilus with an up-to-date gas-phase network to study the sensitivity of the molecular oxygen abundance to the oxygen elemental abundance. We use the rate coefficient for the reaction O + OH at 10 K recommended by the KIDA (KInetic Database for Astrochemistry) experts. Results: The updates of rate coefficients and branching ratios of the reactions of our gas-phase chemical network, especially N + C…
A Superoxovanadium(V) Complex Linking the Peroxide and Dioxygen Chemistry of Vanadium.
2001
A missing link: A superoxovanadium(V) complex is the first reaction intermediate in the oxidative conversion of a peroxovanadium(V) complex into a vanadyl(IV) complex and molecular oxygen. The superoxo species appears also to play an essential role in the formation of the peroxovanadium(V) complex from the vanadyl(IV) complex and molecular oxygen.
Oxidation of adrenaline and noradrenaline by solved molecular oxygen in a FIA assembly.
2002
A simple and effective procedure is proposed for the study and simultaneous determination of adrenaline and noradrenaline. The fluorimetric determination of both substances is performed in a flow injection assembly and by oxidation of both drugs with the solved molecular oxygen. The influence of different parameters is empirically studied and the interpretation of the reaction mechanism is also added. The determination of adrenaline is monitored at 450 nm and the outputs at 520 nm correspond to the adrenaline and noradrenaline global amount; for both lectures lambda(exc) 329 nm. The influence of temperature is relevant and analytical determination occurred at 55 degrees C by immersing the s…
Reaktionskinetik der polymerisationshemmung durch molekularen sauerstoff. (Versuche mit methylmethacrylat)
1956
Wahrend der Inhibierungsperiode findet eine streng alternierende Copolymerisation zwischen molekularem Sauerstoff und dem monomeren Methacrylat statt. Die Alternierung kommt dadurch zustande, das die Anlagerung von O2 an ein radikalisches Kettenende mit einer um mindestens 5 Grosenordnungen hoheren Geschwindigkeitskonstante erfolgt als die Anlagerung des Monomeren. Die Reaktionsfahigkeit des Sauerstoffs bei dieser Reaktion entspricht somit der eines freien Radikals. Die Lange der hierbei auftretenden Reaktionsketten liegt in der Grosenordnung 102, das ist 2 Grosenordnungen kleiner als die Ketten bei der normalen Polymerisation. Der Abbruch der Copolymerisationsketten erfolgt zwischen zwei R…
Highly dispersed encapsulated AuPd nanoparticles on ordered mesoporous carbons for the direct synthesis of H2O2 from molecular oxygen and hydrogen
2012
AuPd nanoparticles (<3 nm) have been encapsulated on the pores of a nanostructured CMK-3 carbon prepared by a nanocasting procedure. This material has been shown to be an excellent catalyst for the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen.
Reaktionskinetik der Polymerisationshemmung durch molekularen Sauerstoff
1957
Die Polymerisationshemmung geschieht bei Styrol nach demselben Mechanismus wie er kurzlich fur Methylmethacrylat berichtet wurde1. Wahrend der Inhibierungsperiode findet streng alternierende Copolymerisation zwischen molekularem Sauerstoff und dem monomeren Styrol statt. Die fur die Anlagerung von O2 an das Radikal RM · masgebende Konstante kMO2 ist etwa von der Grosenordnung 106–107, d. h. die Reaktionsfahigkeit des Sauerstoffs in dieser Reaktion entspricht der eines Radikals. Bruttogeschwindigkeit und kinetische Kettenlange wahrend der Inhibierungsperiode werden auf Grund des Reaktionsmechanismus berechnet und experimentell bestatigt. The inhibition mechanism in the polymerization of styr…
Laccase: A Review of Its Past and Its Future in Bioremediation
2011
Laccases are multicopper proteins that use molecular oxygen to oxidize a broad spectrum of organic compounds by a radical-catalyzed reaction mechanism. Many articles over the past 15 years have touted the diverse potential applications of laccase in various biotechnological processes. This review covers the natural roles of the enzyme, its structural properties, substrates, reaction mechanism, and inhibitors, as well as its applications regarding the detoxification and bioremediation of polluted wastewaters and soils. Other applications are briefly covered as well. The authors critically assess the advantages, shortcomings, and future needs relating to laccase availability, effectiveness, a…
Influence of stoichiometry on high temperature intrinsic defects in fused silica
1992
Abstract The set of intrinsic defects, their generation, interactions and recombination reactions are discussed, including the participation of atomic and molecular oxygen, which allows one to take into account the stoichiometry of fused silica. The mathematical solution of the set of equations, which characterizes the equilibrium concentrations of intrinsic defects, gives the specific values of intrinsic defect concentrations at different temperatures and stoichiometries. The influence of such intrinsic defects frozen in at room temperature on the spectroscopic characteristics of fused silica is analyzed.
Entrapping of O2 Molecules in Nanostructured Silica Probed by Photoluminescence
2013
We studied the emission of the O2 molecules embedded in fumed silica (amorphous silicon dioxide) nanoparticles differing for diameters and specific surface. By using a 1064 nm laser as a source we recorded both the O2 emission and the Raman signal of silica. Our experimental data show that the O2 emission/Raman signal (at 800cm-1) ratio decreases with increasing the specific surface both for the as received and the loaded samples. By performing a thermal treatment (600 °C for 2h) we modified the structure and the water content of the smallest nanoparticles without observing any significant change in the O2 emission/Raman signal ratio. Our data are explained by a shell model showing that the…