Initial Fast Processes

The solid state decomposition of Ba(Br03)2 has been described [34] as proceeding through (i) an initial fast process followed by (ii) a short induction period (iii) a slow linear reaction (iv) an acceleratory stage and finally (v) a deceleration to completion. The activation energy during nucleation (159 kJ mol ) was smaller than that for the main reaction (191 kJ mol ). Irradiation increased the values of the rate coefficients. 

An explanation of the discrepancies was offered by the results from some experiments made by Johannsson et al. [30], employing a more long lived probe, Crfbpy) (t 25 /is), in the AOT-alkane-water system. From the observation of two decay processes, well separated in time as shown in Fig. 7, the authors concluded that small clusters of reverse micelles were present in the microemulsions. The initial fast process, the intramicellar quenching, occurs on the submicrosecond time scale and appears only as an initial drop since it is not resolved on the time scale used with Cr(bpy)3. It is this part of the deactivation that is possible to monitor in normal TRLQ measurements with short-lived probes. The initial drop is followed by a second decay with a characteristic time of a few microseconds before the final, very slow deactivation occurs. The results suggest that the fast exchange... 

Both processes used to manufacture microspheres produce relatively porous structures. Consequently, release of drugs is generally biphasic, with an initial fast release phase followed by a slower... 

The fast, initial degradation process slowed down considerably once the molecular weight had decreased to about 1,000 to 6,000 Daltons. At this point, the residues consisted mostly of carbonate containing oligomers. Under simulated physiological conditions in vitro, the complete erosion of these carbonate containing residues required approximately one year. The in vitro erosion of polyiminocarbonates is therefore best described in terms of a fast, initial phase, followed by a slow second phase (10). 

The adsorption/desorption kinetics of Zn on soils with the removal of organic matter and Fe oxides were studied by Kingery et al. (1999) using traditional batch experiments on the same soil used by Hinz and Selim (1999). Adsorption of Zn on the three soils was kinetically characterized by three kinetic rates a very fast initial retention process within 30 min, an intermediate retention process from 30 min to 8 hours, followed by the very slow process (Fig. 5.5). About 50% of Zn was adsorbed on the three soils within the initial first 30 min. Initially, Zn desorption increased with time during the first 20 minutes from both the untreated soils and the soils without organic matter and Fe oxides. However, after 20 minutes of adsorption, net Zn adsorption from the whole soil and the soil with the... 

Stop-flow experiments have been performed in order to study the kinetics of micellization, as illustrated by the work of Tuzar and coworkers on PS-PB diblocks and the parent PS-PB-PS triblocks [63]. In these experiments, the block copolymers are initially dissolved as unimers in a nonselective mixed solvent. The composition of the mixed solvent is then changed in order to trigger micellization, and the scattered light intensity is recorded as a function of time. The experiment is repeated in the reverse order, i.e., starting from the block copolymer micelles that are then disassembled by a change in the mixed solvent composition. The analysis of the experimental results revealed two distinct processes assigned as unimer-micelle equilibration at constant micelle concentration (fast process) and association-dissociation equilibration, accompanied by changes in micellar concentration (slow process). 

Let us next turn to Model II, representing the C —> B —> X internal-conversion process in the benzene cation. Figure 2 demonstrates that this (compared to the electronic two-state model, Model I) more complicated process is difficult to describe with a MFT ansatz. Although the method is seen to catch the initial fast C —> B decay quite accurately and can also qualitatively reproduce the oscillations of the diabatic populations of the C- and B-state, it essentially fails to reproduce the subsequent internal conversion to the electronic X-state. Jn particular, the MFT method predicts a too-slow population transfer from the C- and B-state to the electronic ground state. 

It is well known that the butene oxidation rate is practically the same in the presence as (initially) in the absence of oxygen, which confirms the validity of a redox model. In contrast to the propene oxidation, the activity does not seem to decline very rapidly with increasing reduction as demonstrated, for instance, by Batist et al. [43]. This is evidence that much more than one surface layer of oxygen can be consumed and, moreover, implies that diffusion of oxygen through the lattice is a fast process. The latter is also confirmed, for instance, by the reduction—oxidation experiments of Beres et al. [47]. 

What are the chemical structures of the intermediates in Eq. 23-37, and why are there so many of them The answer to the last question is that the initial photochemical process is very fast. Subsequent conformational rearrangments and movement of protons are slower, occur in distinct steps, and give rise to the observed series of intermediates. To shed light on these processes many experiments have been done with analogs of retinal,502,505 508 often using very rapid spectroscopic techniques.37,508 These studies have shown that the isomerization of the Schiff base from... 

Radicals initially formed in solution by a bond homolysis will be held together briefly in a cage of solvent molecules. Because radical recombinations and disproportionations are so fast, they can compete with diffusion of the radicals through the layer of solvent molecules that surround them, with the consequence that some of the radicals formed never become available to initiate other processes in the bulk of the solution.98 These recombinations are termed geminate recombinations, and the phenomena that arise from this behavior are cage effects. 

Studies of the pyrene label on actin indicate that the ATP-induced dissociation of actin occurs via a three-step process (steps 1, 2, and c, Scheme 1 Millar and Geeves, 1983). Initial fast equilibrium binding of ATP (controlled by and probably diffusion limited) is followed by an isomerization that alters the environment of the pyrene label on actin. This isomerization is fast in myosin II and much slower for some non-muscle myosins (-500 s-1 for Dictyostelium myosin II Kurzawa et al., 1997 >1000 s-1 for rabbit skeletal myosin II, Geeves andjeffries, 1988 100 s-1 for myosin lb at 20°C Coluccio and Geeves, 1999) and is accompanied by a very rapid... 

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