Orbital steering, entropy, and rate accelerations

Some important conceptual and quantitative differences are described between the “orbital steering” and entropy descriptions of the rate accelerations in intramolecular and enzymic reactions that may be brought about by geometric constraints other than distortion. The treatments differ by a factor of 103 – 104 in the maximum rate acceleration that may be obtained from these constraints. The estimation of a “proximity factor” without taking adequate account of the translational and overall rotational entropy terms gives a misleading value for this factor. The conclusion is reaffirmed that increasing the probability of reaction by restricting the free translational and rotational movement of reacting groups can play a large role in the catalytic power of enzymes