Kinetic behavior, effect

Nonetheless, these methods only estimate organ-averaged radiation dose. Any process which results in high concentrations of radioactivity in organs outside the MIRD tables or in very small volumes within an organ can result in significant error. In addition, the kinetic behavior of materials in the body can have a dramatic effect on radiation dose and models of material transport are constandy refined. Thus radiation dosimetry remains an area of significant research activity. 

It is possible to distinguish between direct and indirect nOes from their kinetic behavior. The direct nOes grow immediately upon irradiation of the neighboring nucleus, with a first-order rate constant, and their kinetics depend initially only on the intemuclear distance r" indirect nOes are observable only after a certain time lag. We can thus suppress or enhance the indirect nOe s (e.g., at He) by short or long irradiations, respectively, of Ha- a long irradiation time of Ha allows the buildup of indirect negative nOe at He, while a short irradiation time of Ha allows only the direct positive nOe effects of Ha on He to be recorded. 

Y(03SCF3)3 to afford a monoaminoalkylation product in good yield in aqueous media.40 Zinc tetrafluoroborate is also highly effective for such couplings in aqueous THF.41 Kobayashi also reported a Mannich-type reaction of imines with silyl enolates catalyzed by neutral salts such as sodium triflate in water as a suspension medium. Unusual kinetic behavior indicates that the presence of the Mannich adduct facilitates the rate of its formation.42... 

A kinetic isotope effect 160/180 of 2% in the spontaneous hydrolysis of the 2,4-dinitrophenyl phosphate dianion, whose ester oxygen is labeled, suggests a P/O bond cleavage in the transition state of the reaction, and thus also constitutes compelling evidence for formation of the metaphosphate 66,67). The hydrolysis behavior of some phosphoro-thioates (110) is entirely analogous 68). 

For reactor design purposes, the distinction between a single reaction and multiple reactions is made in terms of the number of extents of reaction necessary to describe the kinetic behavior of the system, the former requiring only one reaction progress variable. Because the presence of multiple reactions makes it impossible to characterize the product distribution in terms of a unique fraction conversion, we will find it most convenient to work in terms of species concentrations. Division of one rate expression by another will permit us to eliminate the time variable, thus obtaining expressions that are convenient for examining the effect of changes in process variables on the product distribution. 

These results are similar to those with propylene insofar as they indicate dissociative adsorption of the olefin. The hydrogen that yields the hydroxyl has not been identified but it seems reasonable to suppose that, once again, the allylic hydrogen is lost. Results with butene, however, do differ from those with propylene in two respects first, the dissociation (as evidenced by the OH band) is rapid but not instantaneous as found for propylene second, dissociatively adsorbed butene is more easily removed by room temperature evacuation than dissociatively adsorbed propylene. These facts suggests that steric effects are present hence, the kinetic behavior of these two species may be quite different. 

Kim et al. [123] conducted the kinetic study of methane catalytic decomposition over ACs. Several domestic (South Korea) ACs made out of coconut shell and coal were tested as catalysts for methane decomposition at the range of temperatures 750-900°C using a fixed-bed reactor. The authors reported that no significant difference in kinetic behavior of different AC samples was observed despite the differences in their surface area and method of activation. The reaction order was 0.5 for all the AC samples tested and their activation energies were also very close (about 200 kj/mol) regardless of the origin. The ashes derived from AC and coal did not show appreciable catalytic effect on methane decomposition. 

Suppose a solid is to be the subject of a kinetic study (such as decomposition). How would prior irradiating the solid with x-rays or / rays likely affect the kinetic behavior of the solid Explain the origin of the effects. 

The simultaneous determination of trimeprazine and methotrimeprazine in mixtures using the classical peroxyoxalate system based on the reaction between TCPO and hydrogen peroxide was used to validate the new methodology. The reaction was implemented by using the CAR technique, which increased nonlinearity in the chemical system studied by virtue of its second-order kinetic nature. In addition, both drugs exhibited a similar kinetic behavior and synergistic effects on each other, as can be inferred from the individual and combined (real and theoretical) CL-versus-time response curves. 

The time-resolved, chemical behavior of FL depends on the solvent. Irradiation of DAF in cyclohexane gives FLH The lifetime of FL in cyclohexane is 1.4 ns, and the ratio of products obtained (26) indicates that both direct insertion and abstraction-recombination mechanisms are operating (Griller et al., 1984b). Replacement of the cyclohexane by its deuteriated counterpart reveals a kinetic isotope effect of ca 2 (Table 5). 

Considerable progress has been made within the last decade in elucidating the effects of the microenvironment (such as electric charge, dielectric constant and lipophilic or hydrophilic nature) and of external and internal diffusion on the kinetics of immobilized enzymes (7). Taking these factors into consideration, quantitative expressions have been derived for the kinetic behavior of relatively simple enzyme systems. In all of these derivations the immobilized enzymes were treated as simple heterogeneous catalysts. 

The source of the enormous rate enhancements in enzymatic catalysis has been discussed from physical organic points of view (Jencks, 1969 Bruice, 1970). The kinetic behavior is attributed to factors such as an orientation effect, a microenvironmental effect and multifunctional catalysis. The active sites of enzymes are generally located in a hydrophobic hole or cleft. Therefore, the microenvironmental effect is mainly concerned with the behavior of enzyme catalytic groups in this hydrophobic microenvironment and the specific... 

The kinetic behavior of 1,3-dienes has also been investigated in as much detail as that of alkenes52. Some data are collected in Table 4. The effect of a vinyl group on the reactivity of carbon-carbon double bonds toward p-methoxydiphenylcarbenium ion has been compared with that of methyl and phenyl substituents (Table 5). Whereas butadiene reacted 21 times faster than propene, the reactivity of isoprene was significantly lower... 

Another notable example of the anomalous behavior of imidazole ligands is the kinetic tram effect observed for the rates of substitution of 02 for CO in the hemes Fe(TPP)02L ([29], M = Fe, X = 02, L = Py, Pip, or l-Melm) according to Eq.(4)and Table 8 30). One of the three nitrogen donors in question, l-Melm, stabilizes the dioxygen adduct in a manner not to be expected from its basicity. The substitution is clearly of the SN1 type, the elimination of the 02 molecule being the rate-determining step. 

Complications that arise with this simple reaction are twofold. First, because of the low mass of the hydrogen atom its movement frequently exhibits non-classical behavior, in particular quantum-mechanical tunneling, which contributes significantly to the observed kinetic isotope effect, and in fact dominates at low temperature (Section 6.3). Secondly, in reaction 10.2 protium rather than deuterium transfer may occur ... 

Abstract Neuroscientists may wish to quantify an enzyme activity for one of many reasons. In order to do so, the researcher must be able to set up an assay appropriately, and this requires some understanding of the kinetic behavior of the enzyme toward the substrate used. Furthermore, such an understanding is vital if the inhibitory effects of a drug are to be assessed appropriately. This chapter outlines key principles that must be adhered to, and describes basic approaches by which rather complex kinetic data might be obtained, in order that enzyme kinetics and inhibitor kinetics might be studied successfully by the nonexpert. 

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