Defined with slow initial step

With many redox systems, coupled reactions take place that make it necessary to choose the appropriate system in accordance with the monomer and the polymerization conditions. If the redox reaction is slow, there will be a low yield of radicals and therefore a low polymerization rate. On the other hand, if the redox reaction is fast compared with the initiation step, the majority of initiating radicals will be consumed by radical termination reactions. Therefore, redox systems are modified by further additives. For example, heavy metal ions may be complexed with substances such as citrates, which adjust their reactivity to a reduced level. Hence, redox systems for technical polymerization are complex formulations which enable one to obtain optimum results at well-defined reaction conditions. 

We have determined the native conformation of the polypeptide by the multiple slow cooling method [78]. To this end, we generated 50 trajectories with random initial configurations at a high temperature (Th = 1.5e/ks), and propagated them in time while decreasing the temperature by 0.02e/kg after every 5 x 10s time steps. The conformation with the lowest energy at the lowest temperature (T) = 0.02e/ks) is then used to define the native state. 

The oxidation of aminopolycarboxylic acids by Ce(IV) produces numerous species which can be used to infer mechanistic pathways. A more well-defined aspect of these systems is revealed in the initial steps of this class of reactions. Prior to the oxidation steps, Ce(IV) forms complexes with these compounds as demonstrated in the studies of Trubacheva and Pechurova (1981) and Hanna and Moehlenkamp (1983). The experimental constraints in the former study with ethylenediaminedisuccinic acid as the substrate resulted in a metastable complex formulated as Ce(OH)(EDDS) with log X,lab = 16.46. The subsequent redox reaction is extremely slow and exhibits a complex hydrogen ion concentration dependence. The latter system, wherein the substrate is A -benzyliminodiacetic acid (BIDA), was described in terms of the sequential reaction ... 

This is a case where another electrochemical technique, double potential step chronoamperometry, is more convenient than cyclic voltammetry in the sense that conditions may be defined in which the anodic response is only a function of the rate of the follow-up reaction, with no interference from the electron transfer step. The procedure to be followed is summarized in Figure 2.7. The inversion potential is chosen (Figure 2.7a) well beyond the cyclic voltammetric reduction peak so as to ensure that the condition (Ca) c=0 = 0 is fulfilled whatever the slowness of the electron transfer step. Similarly, the final potential (which is the same as the initial potential) is selected so as to ensure that Cb)x=0 = 0 at the end of the second potential step whatever the rate of electron transfer. The chronoamperometric response is recorded (Figure 2.7b). Figure 2.7c shows the variation of the ratio of the anodic-to-cathodic current for 2tR and tR, recast as Rdps, with the dimensionless parameter, 2, measuring the competition between diffusion and follow-up reaction (see Section 6.2.3) ... 

The control of the polymerization reaction afforded by ATRP is the result of the formation of dormant alkyl (pseudo)halides. This reduces the instantaneous concentration of the active radicals and thereby suppresses bimolecular termination reactions. The reversible deactivation and activation leads to a slow, but steady growth of the polymer chain with a well defined end group (Scheme 27). Control and properties of the synthesized polymers depend on the stationary concentration of active radicals and the relative rates of propagation and deactivation. When one or less than one monomer unit is incorporated into the polymer chain during one activation step, the polymerization is well controlled. The ATRP equilibrium can be approached from both directions in Scheme 27. Beginning with an alkyl halide and the lower valent metal complex, the process is called direct ATRP. If a conventional thermal initiator like AIBN and the higher valent metal complex are the starting materials, the polymerization process is named reverse ATRP [287]. 

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