Chain recombination rate

Preparation of mixed-metal hemoglobin hybrids is achieved by separation of hemoglobin into its constituent a and P chains, followed by demetallation of one of the chains, reconstitution with MP, and chain recombination, yielding the tetrameric [a2(MP), P2(Fe P)] or [a2(Fe P), P2(MP)] species [11]. Thus, MP FeP electron transfer might in principle occur between aj/Pj or ai/P2 subunits. However, the distance between aj and Pj hemes is over 10 A greater than the and P2. This extra distance is expected, and indeed is found, to reduce ET rates by several orders of magnitude. Hence, for all practical purposes we may treat the a2P2 tetramer in terms of two independent [otj, P2] electron transfer complexes. 

Rate equations of considerable complexity can result from chain reactions, such as the reaction of bromine with hydrogen in the gas phase between 200 and 300 °C to form hydrogen bromide. These are reactions in which a chain carrier is created in an initiation step (here, a Br- atom from dissociation of Br2) and goes on to create more carriers (Br + H2 — HBr + H-, followed by H + Br2 -4 HBr + Br-, and so on) until a recombination step ends the chain. The rate equation for HBr formation has been shown to be ... 

This is the result of one complete link of the chain by the formation of one molecule of water two new active centers are obtained. The reaction is practically thermoneutral. In the first stage of the reaction large numbers of centers are accumulated it is through recombination of these that the reaction heat is released. Recombination ceases when an equilibrium concentration of centers is reached. The recombination rate is proportional to the cube of the pressure. 

Recent studies have shed light on the distance dependence of the rates of ET reactions proceeding through polymethylene chains. The rates of photoinduced forward and thermal charge recombination ET in the series of dyads 34(n) (Figure 27) have been measured for various chain lengths, n = 1-5, 7, and 8 [86],... 

Presence of the processes of structurization in undyed film during the first period of irradiation may be observed while investigating viscosity of irradiated PVA-films, that proves some increase in intrinsic viscosity (see Figure 2.41). Such increase in intrinsic viscosity is not observed in dyed films. Probably PVA structurization after ultra-violet irradiation takes place by recombination radicals of polymer adjacent chains. The rate of radicals accumulation in dyed PVA-films is less (Figure 2.41) and at the same time probability of structurization by recombination PVA macroradicals decreases. 

The high recombination rates of benzylperoxy radicals (Table of VII. 1), resulting in the formation of benzyl alcohol and benzaldehyde ( ) [24, 25], and low stability of benzyl hydroperoxide, BH, do not permit significant selectivity in BH formation already at low extents of oxidation. Benzaldehyde, formed at decomposition of BH and in chain termination reaction ( ), is then oxidized at high rates to benzoic acid. 

The initial distribution is therefore not Gaussian if the chain dissociation rate p, or recombination rate a, depends on the end-to-end distance. 

In particular, for a Gaussian chain with a constant recombination rate a, we find [17]... 

We focus on a Gaussian chain with a constant recombination rate [17]. The number of active chains in the stationary state is again given by (9.53), with 9 (0) being replaced by the one corresponding to the elongational flow... 

We focus on Gaussian chains with a constant recombination rate a in this subsection. Consider a shear deformation... 

The number of active chains for the shear fiow is plotted in Figure 9.19(a) as a function of the shear rate on a logarithmic scale. The recombination rate a is chosen to be unity as a typical example and the chain breakage rate fio at the vanishing end-to-end distance is varied from curve to curve. Both the shear rate y and the chain breakage rate Po are measured in the unit of the coefficient Pi, or equivalently, is set to be unity. For all 0 the number of active chains decreases steadily as a function of y. 

---