Kinetic pathway

Song H, ER Carraway (2005) Reduction of chlorinated ethanes by nanosized zero-valent iron kinetics, pathways, and effect of reaction conditions. Environ Sci Technol 39 6237-6245. 

The potential that develops in an electrochemical system such as a fuel cell can also act to significantly influence the energies, kinetics, pathways, and reaction mechanisms. The double-reference potential DFT method [Cao et al., 2005] described earlier was used to follow the influence of an external surface potential on the reaction... 

Hagan, M.F. Dinner, A.R. Chandler, D. Chakraborty, A.K., Atomistic understanding of kinetic pathways for single base-pair binding and unbinding in DNA, Proc. Natl Acad. Sci. USA 2003,100, 13922-13927... 

Looking back at Table 4.4 the anaerobic cyclic steady state is from the first product of C0(C02) reduction, formaldehyde (HCHO), to [CH2OH] . This step requires a kinetic pathway in redox potential from -0.2 to -0.6 V versus the H2/H+ potential at pH 7, where sulfur is the oxidised waste ... 

It has been assumed so far that the nuclei configurations are in equilibrium in the excited state during the time that the different deexcitation kinetic pathways are active. This means that before de-excitation from the excited to the ground state takes place, the atomic nuclei have found new steady-state equilibrium positions corresponding to the new electronic state. The electronic transition from the ground state to the excited state happens so fast that the... 

Simplified Model for Kinetic pathways of Nalidixic acid in Man... 

Portmann and co-workers then studied the kinetic pathways in man for hydroxynalidixic acid, the active primary metabolite.(26) The rate constants for glucuronide formation, oxidation to the dicarboxylic acid and excretion of hydroxynalidixic acid were calculated. Essentially total absorption of hydroxynalidixic acid was found in every case. Good agreement between experimental and theoretical plasma levels, based on the first order rate approximations used for the model, was found. Again, the disappearance rate constant, kdoi was found to be very similar for each subject, although the individual excretion and metabolic rate constants varied widely. The disappearance rate constant, k was defined as the sum of the excretion rate constant, kg j and the metabolic rate constants to the glucuronide and dicarboxylic acid, kM-j and kgj, respectively. 

How much of an anion stabilizing group is required to provide a kinetic pathway for the release of strain of a cyclobutanone The sulfenylated cyclobutanones offer a probe. Whereas, the bis-phenylthiocyclobutanone 111 cleaves under conditions of... 

Oxidation of unfunctionalized alkanes is notoriously difficult to perform selectively, because breaking of a C-H bond is required. Although oxidation is thermodynamically favourable, there are limited kinetic pathways for reaction to occur. For most alkanes, the hydrogens are not labile, and, as the carbon atom cannot expand its valence electron shell beyond eight electrons, there is no mechanism for electrophilic or nucleophilic substitution short of using extreme (superacid or superbase) conditions. Alkane oxidations are therefore normally radical processes, and thus difficult to control in terms of selectivity. Nonetheless, some oxidations of alkanes have been performed under supercritical conditions, although it is probable that these actually proceed via radical mechanisms. 

While requiring the availability of competitive inhibitors for each of the substrates, Fromm s use of competitive inhibitors to distinguish multisubstrate enzyme kinetic pathways represents the most powerful initial rate method. See Alternative Substrate Inhibition... 

A kinetic term introduced by Ray to designate the bottleneck in a steady-state enzyme kinetic pathway as that step in which the enzyme form accumulates in highest concentration at saturating substrate concentration. Highest accumulation of this enzyme reflects the fact that this species faces the highest barrier that precedes an irreversible step in the forward direction. 

Scheme 10.8 represents proton transfer to hydride ligands with the participation of two proton donor molecules, emphasizing the role of homoconjugated [X- H X] species in the kinetics of the process. Note that the second HX molecule initiates the formation of the solvent-separated or contact ion pair, corresponding to pathway (1) or (2). Following the principles of formal kinetics, pathway (1) can be expressed via... 

In this article we examine several important tin oxide deposition chemistries that employ organometallic precursors. Using heats of formation obtained from ab initio calculations, we analyze these systems in detail to identify likely reaction intermediates and potentially important kinetic pathways. We also review recent work in which a combination of experiments and modeling were used to develop elementary reaction mechanisms for the CVD of tin oxide. A major focus of the discussion is recently developed quantum-... 

Figure 2 shows illustrated mechanism for acetone self-condensation over calcined hydrotalcites, where the enolate ion is formed in a first step followed by two possible kinetic pathways 1) In the first case the subtracted proton is attracted by the basic sites and transferred to the oxygen of the enolate ion to form an enol in equilibrium. 2) In the second case the enolate ion reacts with an acetone molecule in the carbonyl group, to produce the aldol (diacetone alcohol). Finally, the p carbon is deprotonated to form a ternary carbon and then loses an OH group to obtain the final products. 

Olson, J.S. Phillips, G.N., Jr. (1996) Kinetic pathways and barriers for ligand binding to myoglobin. J. Biol. Chem. 271,... 

There is an explicit assumption in the funnel mechanism that there is a kinetic flow down through a series of states that are progressively lower in energy. The assumption that kinetic pathways follow thermodynamic energies downhill is normally unwarranted, because there is not a formal link between kinetics and thermodynamics. (The Hammond postulate and linear free energy relationships... 

If the substrate contains two identical substituents at one terminus of the allylic position such as shown in Scheme 8E.26, the it-allyl intermediate can undergo enantioface exchange via the formation of a a-palladium species at that terminus. This process should occur faster than the nucleophilic addition, which is the enantio-determining step (fc, > 2[Nu ] and 2[Nu ]). Thus, enantioselection can be derived from the relative rate of the nucleophilic addition to each diastereomer the relative stabilities of the two diastereomeric complexes need not have a direct effect on the enantioselectivity (Curtin-Hammett conditions). Although the achiral allylic isomer 120 is expected to follow the same kinetic pathway as the racemic substrate 119, the difference between the results from the two systems often gives an indication as to the origin of enantioselection—complexation or ionization versus nucleophilic addition. 

Holgate, R.H. and Tester, J.W., Oxidation of hydrogen and carbon monoxide in sub-and supercritical water reaction kinetics, pathways, and water-density effects. 2. Elementary reaction modeling, ]. Phys. Chem. Technol., 98, 810-822, 1994. 

Buchanan, M. etal. (2000) Kinetic pathways of multiphase surfactant sydfftiyis. Rev. E Stat. Phys., Plasm., Fluids, Relat. Interdisc. Topics, 62 6895-6905. 

Lewis, S. D., Shields, P. P., and Shafer, J. A. (1985). Characterization of the kinetic pathway for liberation of fibrinopeptides during assembly of fibrin. /. Biol. Chem. 260, 10192-10199. 

Polyatomic ions (as opposed to neutral molecules) may also be unstable with respect to decomposition, polymerisation or disproportionation. However, ions cannot be scrutinised in isolation. In a crystalline solid, there are always counter-ions of opposite charge to be considered, and in solution an ion is surrounded by solvent molecules. The intimacy of the chemical environment of any ion must influence its viability. For example, redox reactions involving electron transfer between cation and anion, or between ion and solvent, may find easy kinetic pathways. We look here at some examples of unstable oxoanions. 

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