Oxidation computer model prediction

Jones JP, Mysinger M, Korzekwa KR. Computational models for cytochrome P450 a predictive electronic model for aromatic oxidation and hydrogen abstraction. Drug Metab Dispos 2002 30 7-12. 

Oxidant air pollution is one of several competing mortality factors which acts in all age classes, and it has already been shown to interact synergistically with another mortality factor—the pine bark beetle—to hasten death. Other interactions must be identified and evaluated. A complex predictive computer model will be required to handle such massive amounts of data and eventually quantify the important impacts of oxidant air pollution on this forest ecosystem. 

For the last 20 to 25 years, computer modelling has been used increasingly to interpret combustion phenomena. When the chemistry is the main interest, for example, in predicting ignition delay times or predicting product profiles, large comprehensive mechanisms can be used which in theory cover every species possible in the total oxidation. In most treatments differential equations are written for the reactants, intermediate species and for the final products. These are solved by standard mathematical treatments and profiles of concentration - time produced for all species. This approach will be discussed in detail in Chapter 4. 

The oxidative deterioration of most commercial polymers when exposed to sunlight has restricted their use in outdoor applications. A novel approach to the problem of predicting 20-year performance for such materials in solar photovoltaic devices has been developed in our laboratories. The process of photooxidation has been described by a qualitative model, in terms of elementary reactions with corresponding rates. A numerical integration procedure on the computer provides the predicted values of all species concentration terms over time, without any further assumptions. In principle, once the model has been verified with experimental data from accelerated and/or outdoor exposures of appropriate materials, we can have some confidence in the necessary numerical extrapolation of the solutions to very extended time periods. Moreover, manipulation of this computer model affords a novel and relatively simple means of testing common theories related to photooxidation and stabilization. The computations are derived from a chosen input block based on the literature where data are available and on experience gained from other studies of polymer photochemical reactions. Despite the problems associated with a somewhat arbitrary choice of rate constants for certain reactions, it is hoped that the study can unravel some of the complexity of the process, resolve some of the contentious issues and point the way for further experimentation. 

Like the N- m e t h y I - 2 - ad a m a n ta n o ne species above, 5-aza-2-adamantanone N-oxide exhibits axial selectivity by a margin of 96 4 on reduction with NaBH4 in isopropanol. Cieplak model predicts axial selectivity for the overall electron-attracting character of the N+-0 bond. The Anh-Felkin model fails as it is opposite of the Cieplak model in concept and allows attack of a nucleophile anti to the more electron-deficient bond on the a carbon. The computed 3D structures of 5-aza-2-adamantanone N-oxide and its protonated derivative are shown in Fig. 12. 

Olson (10) where a series of ion/molecule reactions were combined with acetylene oxidation reactions and a computational model developed. This model gave ion profiles reasonably similar to those actually observed in sooting flames, and also predicted concentrations of ions sufficiently high that they might be considered as soot nucleation sites. Aspects of an ionic mechanism... 

Studies of the reaction mechanisms for a number of simple compounds in supercritical water have been carried out, but even these seem to be complex. For example the oxidation of carbon monoxide can involve 21 elementary reactions [23]. Computer modelling is required and programs designed for combustion processes are sometimes used. The rates of oxidation of carbon monoxide are substantially lower than those predicted by gas-phase models and the proportion of hydrogen produced by the concurrent water-gas shift reaction is unexpectedly high. The differences are explained in terms of lower diffusivities compared with the gas phase, as a result of solvent cages . Because of difficulties with fundamental studies, much work on reactions is empirical and directed towards particular processes. Some of this work relevant to toxics destruction is given in the next section. 

A computational model based on molecular dynamics was developed to predict the miscibility of indomethacin in the carriers polyethylene oxide (PEO), glucose, and sucrose (Gupta et al. 2011). The cohesive energy density and the solubility parameters were determined by simulations using the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field. The simulations predicted miscibility for indomethacin with PEO (A5 < 2), borderline miscibility with sucrose (A5 < 7), and immiscibility with glucose (A5 > 10 Table 2.2). 

ABSTRACT. We describe an apparatus by which the detonation products of an explosive can be identified and whose relative concentrations can be determined quantitatively. These measurements can be made on products that have been formed in less than one microsecond after the passage of the detonation wave. The technique is based on the rapid quenching of chemical reactions by virtue of the free expansion of the products into vacuum. Of course, products that have been formed over a longer period of time and under different pressure/temperature conditions can also be studied. Time resolved molecular-beam mass spectrometry is used, so that whether detonation occurred or not in forming the products can be determined. We describe optical techniques, principally Schlieren photographs, that also confirm detonation. We report measurements made on six standard explosives, PETN, RDX, HMX, HNS, TNT and TATB, and one research explosive, nitric oxide. For none of the standard explosives do we measure product distributions that agree with model predictions based on equilibrium assumptions. A computer model of the free expansion is described briefly and its importance to the interpretation of the data is emphasized. 

Computational Models for Cytochrome P450 A Predictive Electronic Model for Aromatic Oxidation and Hydrogen Abstraction. 

The overall simulation of high-temperature corrosion processes under near-service conditions requires both a thermodynamic model to predict phase stabilities for given conditions and a mathematical description of the process kinetics, i.e. solid state diffusion. Such a simulation has been developed by integrating the thermodynamic program library, ChemApp, into a numerical finite-difference diffusion calculation, InCorr, to treat internal oxidation and nitridation of Ni-base alloys [10]. This simulation was intended to serve as a basis for an advanced computer model for internal oxidation and sulfidation of low-alloy boiler steels. 

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