Component exchange

Skene, W. G. Lehn, J.-M. Dynamers Polyacylhydrazone reversible covalent polymers, component exchange, and constitutional diversity. Proc. Natl. Acad. Sci. U.S.A. 2004,101, 8270-8275. 

The first and the simplest type is component exchange between phases without growth or dissolution of either phase. Examples include oxygen isotope exchange between two minerals, and Fe -Mg exchange between olivine and garnet or between olivine and melt. This is essentially a diffusion problem. 

Component exchange between phases is controlled by mass transfer. Between solid phases, mass transfer is through diffusion where the exchange of components may be used as a geospeedometer (Lasaga, 1983). Convection rather than diffusion may play a dominant role if fluid phases are involved. In reactions between solid and fluid phases, diffusion in the solid phase is usually the slowest step. However, dissolution and reprecipitation may occur and may accomplish the exchange more rapidly than diffusion through the solid phase. 

Simple component exchange between solid phases is accomplished by diffusion. If only two components (such as Fe " and Mg) are exchanging, the diffusion is binary. The boundary condition is often such that the exchange coefficient between the surfaces of two phases is constant at constant temperature and pressure. The concentrations of the components on the adjacent surfaces may be constant assuming interface equilibrium. The solution to the diffusion equation... 

Quantitative geospeedometry based on component exchange between two phases... 

Heterogeneous reactions are the most common type of reactions in petrology and volcanology. Component exchange between the two phases discussed above... 

On the other hand, main-chain dynamic analogs of polysaccharides have been obtained and their reversibility was demonstrated by component exchange reaction, allowing tuning of their size and composition [68]. 

Fig. 17 Triple dynamic processes operating in pyridyl-hydrazones constitution dynamics by component exchange (left) configuration dynamics by photo and thermoinduced Z,E interconversion (center) coordination dynamics by metal cation bonding and release (right). The three processes allow in principle for long term, short term and locked information storage processes...

Giuseppone N, Lehn JM (2006) Electric-field modulation of component exchange in constitutional dynamic liquid crystals. Angew Chem Int Ed Engl 45 46194624... 

Giuseppone N et al (2004) Generation of dynamic constitutional diversity and driven evolution in helical molecular strands under Lewis acid catalyzed component exchange. Angew Chem Int Ed Engl 43 4902-4906... 

Ruff Y et al (2010) Glycodynamers dynamic polymers bearing oligosaccharides residues -generation, structure, physicochemical, component exchange, and lectin binding properties. J Am Chem Soc 132 2573-2584... 

Without a significant loss of accuracy, (AGJ2)q ( 12.2.3.4.1) can be expressed in terms of the reorganization free energies AGj, and AGjj of the component exchanges ... 

The reorganization free energy for the reaction accompanied by a net chemical change (the cross reaction) and the reorganization free energies for the component exchanges, therefore, are related by ... 

The activation parameters for a cross reaction can be related to those for the component exchange reactions by using the free-energy equation. The value of ASjj can be obtained by differentiating Eq. (d) with respect to temperature [AS = — 8(AG)/6T] ... 

DYNAMICS OF DISTRIBUTION The natural aqueous system is a complex multiphase system which contains dissolved chemicals as well as suspended solids. The metals present in such a system are likely to distribute themselves between the various components of the solid phase and the liquid phase. Such a distribution may attain (a) a true equilibrium or (b) follow a steady state condition. If an element in a system has attained a true equilibrium, the ratio of element concentrations in two phases (solid/liquid), in principle, must remain unchanged at any given temperature. The mathematical relation of metal concentrations in these two phases is governed by the Nernst distribution law (41) commonly called the partition coefficient (1 ) and is defined as = s) /a(l) where a(s) is the activity of metal ions associated with the solid phase and a( ) is the activity of metal ions associated with the liquid phase (dissolved). This behavior of element is a direct consequence of the dynamics of ionic distribution in a multiphase system. For dilute solution, which generally obeys Raoult s law (41) activity (a) of a metal ion can be substituted by its concentration, (c) moles L l or moles Kg i. This ratio (Kd) serves as a comparison for relative affinity of metal ions for various components-exchangeable, carbonate, oxide, organic-of the solid phase. Chemical potential which is a function of several variables controls the numerical values of Kd (41). 

With Figure 17.1b in view we can restate the purpose of the book (1) the purpose is to explore ways of predicting the behavior of materials where movement is driven simultaneously by nonhydrostatic stress and by chemical inhomogeneity or (2) the purpose is to explore ways of predicting the behavior of materials where the response of the material as a chemically invariant continuum has extra behavior superimposed on it, in which individual components exchange sites or interdiffuse. 

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