General Principles Answers

The choice of the best method for answering this question is governed by the specific nature of the system under investigation. Few general principles exist beyond the importance of analyzing a representative sample of suitable purity. Our approach is to consider some specific examples. In view of the diversity of physical methods available and the number of copolymer combinations which exist, a few examples barely touch the subject. They will suffice to illustrate the concepts involved, however. 

WASHING FILTER CAKES. To wash soluble material that may be retained by the filter cake after a filtration, a solvent miscible with the filtrate may be used as a wash. Water is the most common wash liquid. The rate of flow of the wash liquid and the volume of liquid needed to reduce the solute content of the cake to a desired degree are important in the design and operation of a filter. Although the following general principles apply to the problem, these questions cannot be completely answered without experiment. ... 

So far in this chapter, the chemical biology reader has been introduced to examples of biocatalysts, kinetics assays, steady state kinetic analysis as a means to probe basic mechanisms and pre-steady-state kinetic analysis as a means to measure rates of on-catalyst events. In order to complete this survey of biocatalysis, we now need to consider those factors that make biocatalysis possible. In other words, how do biocatalysts achieve the catalytic rate enhancements that they do This is a simple question but in reality needs to be answered in many different ways according to the biocatalyst concerned. For certain, there are general principles that underpin the operation of all biocatalysts, but there again other principles are employed more selectively. Several classical theories of catalysis have been developed over time, which include the concepts of intramolecular catalysis, orbital steering , general acid-base catalysis, electrophilic catalysis and nucleophilic catalysis. Such classical theories are useful starting points in our quest to understand how biocatalysts are able to effect biocatalysis with such efficiency. 

What factors determine the activity of electrocatalysts and are likely to introduce specificity into an electrode reaction At the present time, a complete answer to this question is not possible and we have certainly not reached the stage where it is possible to design electrocatalysts from theoretical considerations. On the other hand a number of general principles can be set out. Thus while metals, alloys, semiconductors (particularly oxides) and complexes have been shown to exhibit catalytic properties, invariably catalysts are based on transition metals and it seems that the design of a catalyst requires the placing of transition-metal ions or atoms in a matrix which serves to optimize their electronic configuration and position with respect to each other. 

Besides the answer to fundamental questions and the test of general principles this method can give access to molecular structural details which are not easily accessible otherwise. The applicability of the isotope method to study conformational equilibria rests on the fact that the increase in force constant and frequency for all isotopes of hydrogen at sterically more constrained positions increases the separation between zero point energy levels of isotopic oscillators. 

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