Strong acceleration of chemical reactions occurring through the effects of rotational excitation on collision geometry.

Accelerating chemical reactions by rotational excitation increases both the energy available for barrier crossing and also changes the distribution of collisions with the barrier, as demonstrated herein on the gas-phase reactions O+HCl(DCl)→OH(OD)+Cl. In the picture, the dependence of the barrier energy Eb on the Jacobi angle γ is given, together with the distribution of collisions with the barrier at j=0 (▪) and 16 (▾). Such a mechanism should arise from large-amplitude oscillatory motions of molecules or reacting atomic groups. It should thus occur also in condensed phases and it should lead to nonenergetic (nonthermal) acceleration of chemical reactions by microwaves.

Temperature-nearly-independent binding constant in several biochemical systems. The underlying entropy-driven binding mechanism and its practical significance.

Arguments are presented in this commentary to show that the model of temperature-nearly-independent binding that we proposed to rationalize the binding characteristics of beta-adrenergic antagonists (Miklavc et al., Biochem Pharmacol 40: 663-669, 1990) in fact provides a consistent interpretation of the temperature-nearly-independent binding constant in all other systems that have been reported in the literature: in the binding of coenzyme NADH to horse liver alcohol dehydrogenase and to octopine dehydrogenase and in the binding of an inhibitor to acetylcholinesterase No such consistent interpretation has been given thus far for any of these systems. It is characteristic of them that the binding takes place in a hydrophobic, sterically constrained environment. One can assume, therefore, that the underlying entropy-driven binding mechanism would reflect the existence and the properties of the steric bottleneck surrounding the binding pocket. We also explain why the temperature effects characteristic of hydrophobic interactions are not found experimentally in these systems, whereas in other, sometimes even structurally similar, systems such temperature effects are clearly present. Further work in necessary to establish more firmly the key features of the temperature-nearly-independent binding mechanism that has been disclosed through our analysis. The binding mechanism in question not only appears in important biochemical systems, but also has the interesting property of being relative unaffected by smaller structural changes.

Could binding sites of a receptor be "seen"? A great challenge to picosecond spectroscopy.

It is shown that the combined picosecond infrared and Raman spectroscopy, developed in investigations of vibrational energy transfer in molecular liquids and in matrix isolated molecules could be adapted to study complexes between small molecules and biological receptors. It should be possible to determine the atomic structure of the receptor binding sites by the method proposed and perhaps even information could be obtained about the structural changes which these sites undergo on binding.