The Principle of Structure-Energy Correlation

The perturbation models do not make explicit reference to electronic or steric pecularities of individual members of the group. These are absorbed, in parametric form, into the potential constants associated with the perturbation. A qualitative understanding of steric and electronic factors may nevertheless be helpful, not only for finding a suitable functional form of the perturbation, but also for assessing the possible meaning of the corresponding numerical constants in physictil and chemical terms. 

A further point that emerges from perturbation models is an interpretation of enzymatic reactions. If one says that binding energy is utilized to lower the energy of the transition state , it is implied that the transition state binds to the enzyme better than the ground state does. In terms of our model, the enzyme may be considered as perturbing the structure of the substrate in the enzyme-substrate groundstate complex in the direction of the transition-state complex. Compared to the uncatalyzed or unperturbed reaction, the effects on reaction rate can be profound (see Chapter 13). 

Both types of correlation analysis, structure-structure and structure-energy correlations, have much in common with FER s or energy-energy correlations [65]. The three types of correlation are analogous in the sense that they all uncover relationships between observables for which there is no a priori reason to be related. They are thus providing genuine, new information, which needs to be interpreted. 

Structure correlations and FER s are well established by now. The same is not true for structure-energy correlations, possibly because in most cases either only kinetic or only structural data are available for a given compound possibly also, because structure-energy correlations require expertise in different experimental techniques. These difficulties should not be serious obstacles, however, to further development of such correlations X-ray facilities are available in many chemical laboratories, and the X-ray crystallographer will usually be more than willing to collaborate with the chemist. 

Many of the ideas on which this work is based could only be sketched in the available space some of the interpretations are preliminary or incomplete, and some problems, for example, the role of solvent, have hardly been mentioned. In view of the title of this book, Structure Correlation , this seems permissible, and, in any case, the loose ends are amenable to exploration combining reliable experimental data with sound theoretical ideas. 

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