Rate constants, for elimination

These results are in accordance with the findings of Boothe and coworkers26, who found that the reactions of four diastereomeric 2-bromo-3-phenylsulfinylbutanes with tributyl-tin radicals generate /3-phenylsulfinyl sec-butyl radicals (8) which eliminate PhSO radicals to form the 2-butenes in a stereoselective manner. The stereoselectivities observed in this free radical elimination must result from the fact that the rate constant for elimination is greater than that for rotation about the C—C bond. Furthermore, a neighboring phenyl group on the radical center seems to stabilize the radical enough so that the internal rotation can compete with the -elimination reaction. It is also noteworthy that the small... 

Key AUC Area under the curve, Cmax maximal serum concentrations, Tmax time to reach peak concentrations, Vd volume distribution, K rate constant for elimination, T2 Elimination half-life, and CIT Total body clearance time. (Wojcicki et al. 1995)... 

Using ku as the rate constant for uptake and ke as the rate constant for elimination leads to the following definition of bioconcentration factor ... 

Br nsted Coefficients and Rate Constants for Elimination from Alkyl bromides0... 

MRTC in a one-compartment body model is the inverse of the rate constant for elimination. In a multiple-compartment model, where the multiple dosing plasma half-life is useful, MTRC is given by the volume of the central compartment where drug concentrations are measured divided by clearance. MRT in Equation 17.32 is the ratio of AUMC/AUC. 

When the rate constant (%) for elimination of HBr from l-bromo-2-phenylethane is compared with the rate constant ( d) for elimination of DBr from 2-bromo-... 

Jos.selson and Sidell (1978) investigated the effect of intravenous thiamine hydrochloride on the elimination of pralidoxiinc chloride 5 mg/kg body weight administered intravenously. The addition of thiamine lengthened the elimination half-life and the oxime concentration increa.sed, whereas the intercompartment clearances and rate constant for elimination of oxime declined. The authors. suggested that either thiamine and PAM compete for a common secretory mechanism or thiamine alters the membrane transport of PAM. PAM is excreted preferentially in acid urine (Berglund etal., 1962) and intravenou.s sodium bicarbonate markedly reduces PAM excretion,... 

Once the values of distribution rate constant and the post-distribution rate constant, as well as the values of the two empirical constants A andU (the two y-axis intercepts) are obtained by the methods described above, or are taken to be the values reported in the literature, the micro rate constants for elimination and inter-compartmental transfer can be generated using Equation 13.6 ... 

Finally, the same result is obtained by applying Eq. A. 15 to this case. In this instance, the coefficients Af are A and B and A equals the rate constant for elimination from the central compartment, namely kiQ. 

Similarly, in the case of a two-compartment drug given by intravenous bolus, total MRT is the sum of MRT in the central compartment (MRTo Eqs A.39, A.41 and A.42) plus MRT in the tissue compartment (MRCpen Eq. A.43). The reciprocal of MRTc is kio, a pure rate constant for elimination of dmg. Even when compartmental analysis cannot be used, MRTpe,i can provide important information about a dmg s distribution into tissue. For example, the ratio MRTpen/ MRT indicates the percentage of time a dmg spends in tissue while MRTc/MRT shows the percentage of time the dmg spends in that part of the body which is in fast equiUhrium with Wood. 

Km the first-order rate constant for metabolism of dmg or [in context] the Michaelis constant in non-linear pharmacokinetics Ko the zero-order elimination rate constant Mother the first-order rate constant for elimination of dmg by a process other than metabolism or renal excretion Kio for a two-compartment dmg, the first-order rate constant for elimination of dmg from the central compartment Ki2 for a two-compartment drug, the first-order rate constant for transfer from the central to the peripheral compartment K21 for a two-compartment drug, the first-order rate constant for transfer from the peripheral to the central compartment MAT mean absorption time mean residence time in the gastrointestinal tract synonymous with MRTgit... 

Elimination becomes more competitive with substitution as the number of alkyl substituents on the substrate increases. Table 10.2 shows rate constants for Sn2 and E2 reactions of a series of alkyl bromides with sodium ethoxide in ethanol at 55°C. The rate constant for elimination increases along the series from ethyl bromide to propyl bromide to isobutyl bromide. The more substituted alkenes formed with propyl bromide and (to a greater extent) with isobutyl bromide are more stable than the alkene formed from ethyl bromide. Because the transition structures have some double bond... 

Nitrile-forming eliminations from 2,4,6-trinitrobenzaldehyde 0-oxime derivatives promoted by amines in MeCN have been studied kinetically. The reactions are second-order and exhibit substantial Hammett p and Brpnsted ft values. The second-order rate constant for elimination from ( )-2,4,6-trinitrobenzaldehyde 0-pivaloyloxime promoted by /-Pr2NH in MeCN falls on a single line in the Hammett plot for different j0-aryl substituents, which have been shown to react by the E2 mechanism. The change of the /3-aryl group from phenyl to thienyl to furyl shifted the reaction mechanism from E2 to ElcE) f ... 

At all three temperatures studied, the reaction rate constants for elimination increase by 30% after fluorination, while those for the direct hydrogenolysis stay almost unchanged. The adsorption constants of MCHA in the HDN of MCHA decrease a little by fluorination. 

A simple relationship based on equation (S) then exists between the rate constant for elimination,. and the biological half life of the compound which is defined as the time interval within which the drug amount falls to half the initial amount ... 

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