The calculation of absolute reaction rates is formulated in terms of quantities which are available from the potential surfaces which can be constructed at the present time. The probability of the activated state is calculated using ordinary statistical mechanics. This probability multiplied by the rate of decomposition gives the specific rate of reaction. The occurrence of quantized vibrations in the activated complex, in degrees of freedom which are unquantized in the original molecules, leads to relative reaction rates for isotopes quite different from the rates predicted using simple kinetic theory. The necessary conditions for the general statistical treatment to reduce to the usual kinetic treatment are given.
Since to form a hole the size of a molecule in a liquid requires almost the same increase in free energy as to vaporize a molecule, the concentration of vapor above the liquid is a measure of such ``molecular'' holes in the liquid. This provides an explanation of the law of rectilinear diameters of Cailletet and Mathias. The theory of reaction rates yields an equation for absolute viscosity applicable to cases involving activation energies where the usual theory of energy transfer does not apply. This equation reduces to a number of the successful empirical equations under the appropriate limiting conditions. The increase of viscosity with shearing stress is explained. The same theory yields an equation for the diffusion coefficient which when combined with the viscosity and applied to the results of Orr and Butler for the diffusion of heavy into light water gives a satisfactory and suggestive interpretation. The usual theories for diffusion coefficients and absolute electrical conductance should be replaced by those developed here when ion and solvent molecule are of about the same size.
Recent developments in protein structure make one model for globular proteins especially attractive. This model consists of polypeptide chains folded on themselves to give hydrogen-bonded secondary structures which are in turn folded in a rigid tertiary arrangement through the interaction of amino acid side chains. The implications of the model are examined in terms of possible energy states available to proteins and possible denaturation reactions. Denaturation is defined as change in conformation._ The folding process is considered to be spontaneous and directed by the composition and order of peptide amino acid residues. Reversible thermal denaturation processes are presented as changes in tertiary structure, irreversible processes as changes in secondary structure. The activated complex for denaturation and for enzymic function is discussed and the possibility presented that enzymic activity, reversible denaturation and ion-binding are all aspects of the same protein property.
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