Structure-activity relationships Electronic control

For halogenated aromatic hydrocarbons like polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and polychlorinated dibenzo-p-dioxins (PCDDs) the binding to the aryl hydrocarbon (Ah) receptor regulates their toxicity [89]. The Ah receptor controls the induction of one of the cytochrome P450 enzymes in the liver. Toxic responses such as thymic atrophy, iveight loss, immu-notoxicity and acute lethality are associated ivith the relative affinity of PCBs, PCDFs and PCDDs for the Ah receptor [89]. The quantitative structure-activity relationship (QSAR) models predicting the affinity of the halogenated aromatic hydrocarbons ivith the Ah receptor describe the electron acceptor capability as well as the hydrophobicity and polarizability of the chemicals [89[. 

The catalytic activity of grafted molecular fragments might be similar or modified when compared to the original complex. The presence of the support, via electronic or steric effects, might affect positively the selectivity. Moreover, it will favor site isolation and hinder dimerization of the complex bound to the surface. These well-defined materials allow the establishment of structure-activity relationships at the molecular level [37, 39]. The limitation of such systems is that the munber of OH groups on the surface controls the number of chemisorbed species, hence the loading of active phase. 

Supported metal oxide catalysts are a new class of catalytic materials that are excellent oxidation catalysts when redox surface sites are present. They are ideal catalysts for investigating catalytic molecular/electronic structure-activity selectivity relationships for oxidation reactions because (i) the number of catalytic active sites can be systematically controlled, which allows the determination of the number of participating catalytic active sites in the reaction, (ii) the TOP values for oxidation studies can be quantitatively determined since the number of exposed catalytic active sites can be easily determined, (iii) the oxide support can be varied to examine the effect of different types of ligand on the reaction kinetics, (iii) the molecular and electronic structures of the surface MOj, species can be spectroscopically determined under all environmental conditions for structure-activity determination and (iv) the redox surface sites can be combined with surface acid sites to examine the effect of surface Bronsted or Lewis acid sites. Such fundamental structure-activity information can provide insights and also guide the molecular engineering of advanced hydrocarbon oxidation metal oxide catalysts such as supported metal oxides, polyoxo metallates, metal oxide supported zeolites and molecular sieves, bulk mixed metal oxides and metal oxide supported clays. 

In this chapter, the application of this technique to the thin film processing of electroactive polymers is discussed. The fabrication of controlled molecular assemblies of electroactive polymers provides a unique opportunity to investigate the structure-property and structure-function relationships of multilayer thin films containing electrically conductive, optically nonlinear and redox active polymers. These assemblies can also be coupled to appropriate solid supports for application in such molecular electronic devices as ultrathin electrodes and transistors, opticd waveguides and switches, and chemical and biochemical microelectronic sensors. 

During the last two decades it has been found that there is a special group of chemical reactions, essentially redox reactions, for which the catalytic influence of solids can be interpreted in terms of the catalyst s electronic structure and the controlled variations of that structure. The study of single-phase catalysts and the relationship between function and electronic structure of solid state catalysts show that redox reactions may be divided into two classes. Donor reactions are reactions in which the rate-determining step involves an electron transition from the reactant molecule to the catalyst acceptor reactions are those where the reactant must accept electrons from the catalyst in order to form the activated state. Broadly speaking, donor reactions mobilize reducing agents like... 

This paper describes the use of polydentate ligands to optimize the performance of palladium catalysts for CO2 reduction and to probe mechanistic aspects of catalytic reactions. Polydentate ligands can be used to precisely control coordination environments, electronic properties, and specific steric interactions that can lead to new insights into the relationship between catalyst structure and activity. 

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