Understanding Catalyst Diversity

Although the term diversity is widely used in catalysis, it is ill defined. Diversity can be understood as a spread over a given catalyst space, or as a lack of similarity within a set of compounds [57-59]. Saying that Library a is more diverse than library b can mean that library a covers a wider range of the catalyst space. Alternatively, it can mean that the catalysts in library a are more uniformly spread in the same space. One thing is certain library size alone does not guarantee diversity. 

The solution to this problem lies in defining diversity in space B, the descriptor space [61]. Here the catalysts are quantified in terms of molecular and reaction 

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Now that we understand more about the various types of descriptors in space B, let us return to the problem of catalyst optimization. If we can generate a sufficiently large number of sufficiently diverse structures in space A, and link the spaces A and B, we... 

This review is divided into four main parts. The brief introduction is followed by a section in which the fundamentals of evaluation of EPR spectra are explained, because these are needed to understand the results of the examples that follow. Furthermore, the main features of the experimental equipment used for investigations of working solid catalysts are described. The third section comprises a diversity of examples, chosen because they differ from those presented in recent reviews 9,10,16-18) and because they illustrate a wide variety of problems to which the techniques are well suited. 

In this chapter, an attempt is made to summarize the current state of understanding of the basics of the mechanism, to provide an overview over the diverse and sometimes mysterious compositions of applicable catalyst cocktails , and to review important recent developments and applications of this reaction principle. 

One of the more active and growing areas of research into the study of condensed matter is the investigation of the properties of atomic and molecular clusters. A detailed understanding of clusters is vital to the study of such diverse phenomena as condensation, the dispersion of supported catalysts, cloud formation, molecular generation on interstellar grains, - and the thermodynamic properties of powders. In addition, the study of clusters is of fundamental importance to the understanding of the transition from finite to bulk behavior. 

The understanding of the degradation of natural products such as camphor has been greatly enhanced by understanding the catalytic cycle of the cytochrome P-450 enzyme P-450cam in structural detail.3,4 These enzymes catalyze the addition of 02 to nonactivated hydrocarbons at room temperatures and pressures - a reaction that requires high temperature to proceed in the absence of a catalyst. O-Methyltransferases are central to the secondary metabolic pathway of phenylpropanoid biosynthesis. The structural basis of the diverse substrate specificities of such enzymes has been studied by solving the crystal structures of chalcone O-methyltransferase and isoflavone O-methyltransferase complexed with the reaction products.5 Structures of these and other enzymes are obviously important for the development of biomimetic and thus environmentally more friendly approaches to natural product synthesis. 

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