Kinetics implications

The fact that the aliosterically preferred conformation may be relatively rare in the library of conformations available to the receptor may have kinetic implications. Specifically, if the binding site for the modulator appears only when the preferred conformation is formed spontaneously, then complete conversion to alios terically modified receptor may require a relatively long period of equilibration. For example, the allosteric p38 MAP kinase inhibitor BIRB 796 binds to a conformation of MAP kinase requiring movement of a Phe residue by 10 angstroms (so-called out conformation). The association rate for this modulator is 8.5 x 105 M-1 s-1, 50 times slower than that required for other inhibitors (4.3 x 107 M 1 s-1). The result is that while other inhibitors reach equilibrium within 30 minutes, BIRB 376 requires 2 full hours of equilibration time [8],... 

Some limitations of optical microscopy were apparent in applying [247—249] the technique to supplement kinetic investigations of the low temperature decomposition of ammonium perchlorate (AP), a particularly extensively studied solid phase rate process [59]. The porous residue is opaque. Scanning electron microscopy showed that decomposition was initiated at active sites scattered across surfaces and reaction resulted in the formation of square holes on m-faces and rhombic holes on c-faces. These sites of nucleation were identified [211] as points of intersection of line dislocations with an external boundary face and the kinetic implications of the observed mode of nucleation and growth have been discussed [211]. 

In this section we will consider the kinetic implications of both general classes of parallel reactions. 

This section discusses the kinetic implications of series reactions. We will be concerned only with those cases where the progress of the various stages of the overall transformation is not influenced by either parallel or reverse reactions. The discussion will again be limited to constant volume systems. 

Depending upon the mechanism that is employed by the organism to accumulate the solute, internalisation fluxes can vary both in direction and order of magnitude. The kinetics of passive transport will be examined in Section 6.1.1. Trace element internalisation via ion channels or carrier-mediated transport, subsequent to the specific binding of a solute to a transport site, will be addressed in Section 6.1.2. Finally, since several substances (e.g. Na+, Ca2+, Zn2+, some sugars and amino acids) can be concentrated in the cell against their electrochemical gradient (active transport systems), the kinetic implications of an active transport mechanism will be examined in Section 6.1.3. Further explanations of the mechanisms themselves can be obtained in Chapters 6 and 7 of this volume [24,245]. 

In both reactions, electron transfer induces the dissolution of the solid phase i.e., reductive and oxidative dissolution, respectively. Although no kinetic implications follow directly from the thermodynamic considerations, there are cases where the redox rate is related to the redox equilibrium (see e.g., Eq. 9.12). 

The occurrence of significant interpenetration of solvent shells has several kinetic implications clearly all r-depen-dent contributions will be affected, especially the exponential-... 

Rapp R.P. and Watson E.B. (1986) Monazite solubility and dissolution kinetics implications for the thorium and light rare Earth chemistry of felsic magmas. Contrib. Mineral. Petrol. 94, 304-316. 

Greenblatt DJ, Divoll M, Abernethy DR, et al. Benzodiazepine kinetics implications for therapeutics and pharmacogeriatrics. Drug Metab Rev 1983 14 251-292. 

The development of the miscibility gap for W < 0 and the antiphases ( Tjeq) for W > 0 have entirely different kinetic implications. For decomposition, mass flux is necessary for the evolution of two phases with differing compositions. Furthermore, interfaces between these two phases necessarily develop. The evolution of ordered phases from disordered phases (i.e., the onset of nonzero structural order parameters) can occur with no mass flux macroscopic diffusion is not necessary. Because the 77+q-phase is thermodynamically equivalent to the 7/iq-phase, the development of 77+q-phase in one material location is simultaneous with the evolution of r lq-phase at another location. The impingement of these two phases creates an antiphase domain boundary. These interfaces are regions of local heterogeneity and increase the free energy above the homogeneous value given by Eq. 17.14. The kinetic implications of macroscopic diffusion and of the development of interfaces are treated in Chapter 18. 

This stoicheiometric definition of mechanism is quite precise, but in formulating the kinetic implications we shall avoid the position that this can be tied down in precise terms. To do this would be to stultify the imagination of the practitioner and make absolute a procedure whose validity can only be established by experiment. Nevertheless we shall show that under the above conditions it is possible to construct an entire kinetic expression for 0t, by the introduction of certain hypotheses. Such an expression is not necessarily unique and only experiment can establish one form of kinetics as a sufficiently accurate description of the course of the reaction. ... 

Bankfalvi, A., Ofner, D., Schmid, K. W., Schmitz, K. J., Breukelmann, D., Krech, R., and Bocker, W. 1999. Standardized in situ AgNOR analysis in breast pathology Diagnostic and cell kinetic implications. Pathol. Res. Pract. 195 219-229. 

Harvey, M.C., Schreiber, M.E., Rimstidt, J.D. and Griffith, M.M. (2006) Scorodite dissolution kinetics implications for arsenic release. Environmental Science and Technology, 40(21), 6709-14. 

MuirN, Nichols JD, Clifford JM, et al. The influence of dosage form on aspirin kinetics implications for acute cardiovascular use, Curr Med Res Opin 1997 13 547-553. 

There are several kinetic implications of the spillover phenomena. As an example, consider a simple reaction A + B - C which occurs with A, B, and C adsorbed and with the surface reaction (A + B, on a single type of active site ) controlling. The reaction rate can be written, following a Langmuir-Hinshelwood model, as... 

Like a DO loop in FORTRAN, the chain must be started and eventually be terminated. It is started by an additional reaction that serves as source of chain carriers. This is called initiation. It is terminated by a reaction that, once in a while, consumes chain carriers without generating others. This is called termination. The steps of the DO loop are called propagation. Typically, chain carriers are species (atoms or free radicals) with unpaired electrons. They resemble catalysts in that they arise again after having been consumed, but differ in having extremely short life spans that prevent their isolation. Moreover, the initiation and termination steps and their kinetic implications set chain reactions apart from catalysis as well as from any other kinds of chemical reactions. 

Pinchbeck, P. H., The kinetic implications of an empirically fitted yield surface for the vapour-phase oxidation of naphthalene to phthalic anhydride, Cheni. Eng. Sci., 6, 105-111 (1957). 

Admittedly this scheme is daunting in its complexity and the kinetic implications are as yet unclear. Early studies on p-GaP, p-GaAs and other Group III-V (13-15) semiconductors reported onset of cathodic photocurrents (attributable to HER) only at potentials far removed (ca. 0.6 V) from V[b (see, e.g., Ref [264]). This was attributed to steps 33b and 33h in the above scheme. More recent work [91] has shown that the HER at illuminated p-InP-electrolyte contacts is accompanied by a photocorrosion reaction, leading to indium formation on the semiconductor surface. Representative PEIS data from this study are shown in complex plane format in Figure 28. Note that unlike in the cases above (e.g.. Figure 27), multiple relaxa-... 

Fischman GS, Petuskey WT (1985) Thermodynamic analysis and kinetic implications of chemical vapour deposition of SiC from Si-C-Cl-H gas systems. J Am Ceram Soc 68 185-190... 

The operative parameters which can be regulated to optimize the stack performance are MEA humidification, reactant pressure, stack temperature, and stoichiometric ratio. While the role of membrane humidification, already partially discussed in Sect. 3.2, is closely considered in Sect. 4.5 and in case studies (Chaps. 6 and 7), the influence of the other parameters is examined here with reference to the stack of Fig. 3.5. These effects have already been described from a thermodynamic point of view (see Sect. 3.1), while kinetic implications are considered in this section for their importance in determining the stack efficiency. 

Since the electrochemical reaction (3.13) is exothermic (Table 3.1), a potential loss should be expected by thermodynamics however, the results reported in Fig. 3.7 evidence that kinetic implications are prevalent in determining the global effect of temperature on stack efficiency, in particular the increase in the exchange current density and the improvement of mass transport properties can be invoked to explain the behavior represented. 

More elaborately, complex formation can be viewed as in Fig. 2 (the detailed kinetic implications of this refinement to the basic Eigen mechanism are covered by Benton and Moore [71]). It is reasonable to relate the rate coefficient for the dissociative slow stage with that for solvent exchange, since breaking of a metal ion—solvent bond is involved in both processes. 

Brownlie and Ingold [23] have also examined the kinetic implications of the production of nitroxidfes or of hydroxylamines in the system, using an aliphatic nitroxide, 2,2,6,6-tetramethyl-4-piperidone nitroxide (A), two stable aromatic nitroxides, 4,4 -dimethoxydiphenyl (B), and 4,4 -dinitro-diphenyl (C), and the hydroxylamines produced therefrom. Using the... 

The enzyme contains FAD as a prosthetic group and the steady-state kinetics implicate a ping-pong mechanism. Since dihydrofolate is a potent competitive inhibitor of NADPH-methylenetetrahydrofolate oxidoreduction, it was thought that... 

In the following section, we will discuss the kinetic implications of the dynamical changes in catalyst morphology during methanol synthesis. First, we will present an analysis of steady state kinetic experiments using a static, microkinetic model where it is assumed that the number of sites are constant. Then, we will introduce the dynamic aspect into the microkinetic modeling and also discuss some recent transient experiments. 

The nature of the anomeric effect operative in the S—C—P system will be considered taking into account (1) thermodynamic, (2) MM- and MO-based, (3) X-ray crystallographic, (4) spectroscopic, and (5) kinetic implications. It must be added that solvent studies were shown to be not useful to reveal... 

Kinetic Implications of Anomeric Effect in S—C—P System These were discussed in Section IV.A.l. 

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