Apparent ITIES

The ET reaction between aqueous oxidants and decamethylferrocene (DMFc), in both DCE and NB, has been studied over a wide range of conditions and shown to be a complex process [86]. The apparent potential-dependence of the ET rate constant was contrary to Butler-Volmer theory, when the interfacial potential drop at the ITIES was adjusted via the CIO4 concentration in the aqueous phase. The highest reaction rate was observed with the smallest concentration of CIO4 in the aqueous phase, which corresponded to the lowest driving force for the oxidation process. In contrast, the ET rate increased with driving force when this was adjusted via the redox potential of the aqueous oxidant. Moreover, a Butler-Volmer trend was found when TBA was used as the potential-determining ion, with an a value of 0.38 [86]. 

It was shown later that a mass transfer rate sufficiently high to measure the rate constant of potassium transfer [reaction (10a)] under steady-state conditions can be obtained using nanometer-sized pipettes (r < 250 nm) [8a]. Assuming uniform accessibility of the ITIES, the standard rate constant (k°) and transfer coefficient (a) were found by fitting the experimental data to Eq. (7) (Fig. 8). (Alternatively, the kinetic parameters of the interfacial reaction can be evaluated by the three-point method, i.e., the half-wave potential, iii/2, and two quartile potentials, and ii3/4 [8a,27].) A number of voltam-mograms obtained at 5-250 nm pipettes yielded similar values of kinetic parameters, = 1.3 0.6 cm/s, and a = 0.4 0.1. Importantly, no apparent correlation was found between the measured rate constant and the pipette size. The mass transfer coefficient for a 10 nm-radius pipette is > 10 cm/s (assuming D = 10 cm /s). Thus the upper limit for the determinable heterogeneous rate constant is at least 50 cm/s. 

In comprehensive studies, the hydrolysis of some 30 naphthyl esters by human, rat, and mouse liver carboxylesterases was investigated [43], A general trend that was apparent was that the rate of hydrolysis of a- and /3-naphthyl carbonates (7.21, R = alkyl or arylalkyl) catalyzed by human microsomes or rat hydrolases showed a tendency to decrease with increasing lipophilic-ity (range ca. 2 to 5). A similar trend was not seen with naphthyl aryl carbonates nor with a-naphthyl carboxylates. These results tell us that, even with purified enzymes and large series of substrates, it is very difficult indeed to discern sound structure-hydrolysis relationships due to the complexity of the structural and enzymatic factors involved. 

Calculation of bioavailability requires a comparison of the AUcs following a non-intravenous and an intravenous dose, after correction for dose size. Without knowing the bioavaUabU-ity, only apparent clearance and volume of distribution can be calculated, and the ability to make predictions from these values is very limited. 

Initiation is apparently slower than propagation. That is, the nucleophilic-ity of vinyl ethers is higher than their basicity. Other monomers such as p-methoxy-a-methylstyrene are apparently more basic and react rapidly with acid. In addition, the equilibrium monomer concentrations of a-meth-yl styrenes are relatively high ([M] 0.2 mol/L at —30° C). Because they can not polymerize at low concentration, they are ideal monomers for model studies [12,13]. The equilibrium constants of dimerization and tri-merization are much larger than that for the formation of high polymer. Therefore, dimers and trimers can be formed below [M] although high polymers cannot. 

It is apparent from QSAR 1.106 and 1.107, that the hydrophobicrequirements of the substrates vary considerably. As expected, renal clearance is enhanced in the case of hydrophilic drugs, whereas nonrenal clearance shows a strong dependency on hydrophobic-ity. Note that QSAR 1.107 is stretching the limits of the bilinear model with only 10 data points The 95% confidence intervals are also large but, nevertheless, the equations serve to emphasize the difference in clearance mechanisms that are clearly linked to hydrophobicity. 

A difference in the rate constants was observed for the reduction of (-)[Co(diAmsarH2)] with (+) and (-)[Co(sep)]. The enantiomer (-)[Co(sep)] " reduces the protonated diAmsar cage complex with a rate constant that is 10% greater than for its enantiomer 218). This is of the order of selectivity observed in the oxidation of [Co(en)3] by [Co(edta) ] in aqueous conditions, and itis apparent that the effect is not dependent on the complexes being oppositely charged (i.e., the ability to form stable ion pairs). 

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