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Experimental Indication (experimental + indication)
Selected AbstractsOn the binding mode of urease active site inhibitors: A density functional studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2008M. Leopoldini Abstract The way with which boric acid, a rapid reversible competitive inhibitor, binds the urease active site was explored at density functional B3LYP level of theory. The catalytic core of the enzyme was simulated by two models of different size. In both cases, amino acid residues belonging to the inner and to the outer coordination spheres of nickel ions were replaced by smaller molecular species. Contrary to the experimental indication that attributes the inhibitory ability of this acid to the lack of a nucleophilic attack by the enzyme to the boron atom, we instead found that another possibility exists based on the presence of a strong covalent , bond between boron and urease that we think can be hardly broken to allow any course of the reaction. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Upper electron-excited states in bioluminescence: experimental indicationLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 3 2001N. S. Kudryasheva Abstract The involvement of upper electron-excited states in bacterial bioluminescence process was studied with excitation energy-accepting molecules. The fluorescent aromatic compounds, anthracene and 1.4-bis(5-phenyloxazol-2-yl)benzene, were chosen. Energies of their lowest excited singlet states are higher than the energy of the analogous state of the bioluminescence emitter; their absorption spectra and bioluminescence do not overlap. Hence, the excitation of these molecules by singlet,singlet energy transfer or by light absorption is excluded. Sensitized fluorescence of these compounds in the bioluminescence systems has been recorded, indicating the activity of upper electron-excited states in the bioluminescent process. Copyright © 2001 John Wiley & Sons, Ltd. [source] Determination of the Catalytic Pathway of a Manganese Arginase Enzyme Through Density Functional InvestigationCHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2009Monica Leopoldini Dr. Abstract The catalytic mechanism of dimanganese-containing arginase enzyme has been investigated by DFT calculations. Two exchange-correlation functionals, B3,LYP and MPWB1,K, have been used to construct the potential energy profiles for the hydrolysis of an arginine substrate performed by an arginase active site model system. Two reaction mechanisms have been investigated, one involving a water molecule (mechanism,1) and the other involving a hydroxide ion (mechanism,2) as nucleophilic agent. Results obtained in the gas phase and in the protein environment have indicated that mechanism,1 involving a water molecule entails structural features as well as an activation energy for the rate-determining step that are inconsistent with experimental data available for the arginase enzyme. On the other hand, when a hydroxide ion is present at the Mn2 site, a lower activation energy and a structural arrangement closer to the experimental indication are obtained. [source] Application of High Current and Current Zero Simulations of High-Voltage Circuit BreakersCONTRIBUTIONS TO PLASMA PHYSICS, Issue 10 2006C. M. Franck Abstract This paper reports on the use of computational fluid dynamic (CFD) simulations to predict the interruption behaviour of high-voltage circuit breakers (HV-CB) using the self-blast principle. Two different levels of accuracy of the arc model are proven to be sufficiently accurate for simulating the high-current phase and the period around current zero (CZ). For the high-current phase, a simplified equivalent model of the arc is implemented to predict the pressure build-up, and even more important to accurately trace the hot gas from the arcing zone into the exhausts and the heating volume. A detailed analysis of the gas mixing in the heating volume for different arcing times and current amplitudes showed the optimum geometrical design of the heating volume. For the CZ phase, a more detailed arc model is needed including the effects of ohmic heating, radiative energy transfer, and turbulent cooling fully resolved in space and time. The validation with experiments was done and shows good agreement which justifies the use of the implemented model. With it, scaling laws varying only one parameter at a time (pressure and applied current slope) were derived and confirm previously found empirical laws. This is of particular interest, as it is very difficult to derive such scaling laws from experiments where the scatter is always very large and where it is impossible to vary only one parameter at a time. The influence of the most important geometrical parameters of the nozzle on the interruption performance is shown. In addition to previous experimental indications of this, the simulation reveals that turbulent cooling on the arc edge is the main reason for the difference in interruption performance. Moreover, the exact spatio-temporal build-up of arc resistance and with it the detailed understanding of the arc interruption process is possible and shown here for the first time. These simulations enable us to predict HV-CB performance and to minimise the number of development tests and are routinely used in new development projects. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||