Facile Preparation of Oxodiperoxymolybdenum(Pyridine)(Hexamethylphosphoric Triamide) (MoOPH)

The title compound is known and used as an oxidizing agent. The most useful application of it is the oxidation of the carban-ions obtained from esters, lactones, ketones, nitriles, aldehydes, sulphones and amides in order to obtain the hydroxy derivatives. The known method of synthesis of MoOPH involves the oxidation of MOO₃ obtain to MOO₅ with 30% hydrogen peroxide. We tried to MOO₅ according to procedure described by Vedejs and unfortunately about 50% of the unreacted MOO₃ had t o be filtered off from the MOO₅ solution after 3.5 h. stirring at 40°C, so the yield of MOO₅ HMPTH 0 was about 30%. We needed a bigger amount of title reagent and we started from molybdic acid monohydrate instead of MOO₃ and 30% hydrogen peroxide. The reaction appeared slightly exotherrnic and took place in half an hour at 4O°c. All molybdic acid was dissoled and gave a yellow clear solution of Moo₅. Addition of equimolar amount of HMPT gave the required MOO₅HMPTH₂O complex as a fine yellow crystalls in 61.9% yield. The complex after water removed in vacuum dessicator and the addition of pyridine according to the literature afforded Mo0₅PyHMPT, which was used succesfully in our hydroxylation reactions.     

FOULING PREVENTION WITH FLUIDIZED PARTICLES IN EVAPORATION OF TRADITIONAL CHINESE MEDICINE EXTRACT

The present investigation shows that comparing with the evaporation of vapor-liquid two-phase flow boiling system, heat transfer is enhanced by adding proper inert solid particles into the traditional Chinese medicine liquid whichis under evaporation. As a result, fouling prevention effects are evident in such three-phase flow boiling evaporator.     

CI AM1 study of the electronic structure of isomeric formyl benzonaphthyridines

For six isomeric formyl derivatives of 1,5-, 1,6- and 4,6-benzonaphthyridines the electronic structure and UV spectral values have been calculated by CI AM1 method. Correlations of the calculated and observed wave number values of considered compounds show good compatibility.     

Period-doubling bifurcation to alternans in paced cardiac tissue: crossover from smooth to border-collision characteristics

We investigate, both experimentally and theoretically, the period-doubling bifurcation to alternans in heart tissue. Previously, this phenomenon has been modeled with either smooth or border-collision dynamics. Using a modification of existing experimental techniques, we find a hybrid behavior: Very close to the bifurcation point, the dynamics is smooth, whereas further away it is border-collision-like. The essence of this behavior is captured by a model that exhibits what we call an unfolded border-collision bifurcation. This new model elucidates that, in an experiment, where only a limited number of data points can be measured, the smooth behavior of the bifurcation can easily be missed.     

Anomalous behavior of the dielectric constant of hafnium silicates: a first principles study

We present an extensive ab initio study of the structural and dielectric properties of hafnium silicates Hf(x)Si(1-x)O(2) that accounts for the observed anomalous dependence on composition of the static dielectric constant in the entire x range. The results reveal that this complex behavior reflects that of the structural development with x, from silica to hafnia, and clarify how different growth processes can also lead to scattered sets of data. Several simple models proposed thus far to explain part of the experimental data are shown to be inadequate. It is argued that silicate layers with low hafnium content form at the HfO(2)/Si interface and play a crucial role in preserving high electron mobility in the channel.     

Synthesis of mono- and 1,4-dicarbonyl compounds based on the oxygenation of phosphonate carbanions. Synthesis of dihydrojasmone,allethrone and methylenomycin b

Oxidation of the α-alkylthio-substituted phosphonate carbanions was found to give the corresponding carbonyl compounds. A new synthesis of 1,4-dicarbonyl systems involving the oxygenation of phosphonate carbanions as a key step is described. Total synthesis of dihydrojasmone and allethrone and formal synthesis of methylenomycin B is reported.     

Dependence of transition state structure on substrate: the intrinsic C-13 kinetic isotope effect is different for physiological and slow substrates of the ornithine decarboxylase reaction because of different hydrogen bonding structures

Ornithine decarboxylase is the first and the rate-controlling enzyme in polyamine biosynthesis; it decarboxylates l-ornithine to form the diamine putrescine. We present calculations performed using a combined quantum mechanical and molecular mechanical (QM/MM) method with the AM1 semiempirical Hamiltonian for the wild-type ornithine decarboxylase reaction with ornithine (the physiological substrate) and lysine (a "slow" substrate) and for mutant E274A with ornithine substrate. The dynamical method is variational transition state theory with quantized vibrations. We employ a single reaction coordinate equal to the carbon-carbon distance of the dissociating bond, and we find a large difference between the intrinsic kinetic isotope effect for the physiological substrate, which equals 1.04, and that for the slow substrate, which equals 1.06. This shows that, contrary to a commonly accepted assumption, kinetic isotope effects on slow substrates are not always good models of intrinsic kinetic isotope effects on physiological substrates. Furthermore, analysis of free-energy-based samples of transition state structures shows that the differences in kinetic isotope effects may be traced to different numbers of hydrogen bonds at the different transition states of the different reactions.     

Some composting and biodegradation effects of physically or chemically crosslinked poly(lactic acid)

Polylactide (PLA) crosslinked by using both triallyl isocyanurate (TAIC) and electron radiation or using dicumyl peroxide (DCP) was studied with the aim of examining the behaviour of the modified polymer under various environmental conditions. Thus, the polymer samples were subjected to composting in an industrial pile, exposed to proteinase K, or incubated in sea water. The number-average molecular weight (M_n), melt flow index (MFI), crystallinity (χ), tensile strength (σ_M) and mass loss (in the case of samples treated with proteinase K) were determined. It was found that neat PLA irradiated with high-energy electrons underwent degradation that increased during composting. As a result, the value of M_n of this polymer dramatically decreased. It appeared that PLA crosslinked with TAIC and electron radiation contained, in addition to the crosslinked phase, a phase strongly degraded by this radiation, which facilitated hydrolytic degradation during composting. The σ_M value of PLA crosslinked with TAIC and electron radiation rapidly decreased during composting, whereas that of PLA crosslinked chemically and composted for three weeks slightly increased. As the electron radiation dose increased, the mass loss of PLA containing TAIC and treated with proteinase K decreased, which indicated that the physical crosslinking of PLA hindered enzymatic degradation of this polymer. Important changes in both neat and physically crosslinked PLA incubated in sea water for nine weeks were not detected.