A modification of the nudged elastic band method for finding minimum energy paths is presented. One of the images is made to climb up along the elastic band to converge rigorously on the highest saddle point. Also, variable spring constants are used to increase the density of images near the top of the energy barrier to get an improved estimate of the reaction coordinate near the saddle point. Applications to CH4 dissociative adsorption on Ir~111! and H2 on Si~100! using plane wave based density functional theory are presented. © 2000 American Institute of Physics. @S0021-9606~00!71246-3#

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A climbing image nudged elastic band method for finding saddle points and minimum energy paths

The phenomenon of growth, decline and death—aging—has been the source of considerable speculation (1, 8, 10). This cycle seems to be a more or less direct function of the metabolic rate and this in turn depends on the species (animal or plant) on which are superimposed the factors of heredity and the effects of the stresses and strains of life—which alter the metabolic activity. The universality of this phenomenon suggests that the reactions which cause it are basically the same in all living things. Viewing this process in the light of present day free radical and radiation chemistry and of radiobiology, it seems possible that one factor in aging may be related to deleterious side attacks of free radicals (which are normally produced in the course of cellular metabolism) on cell constituents.* Irradiation of living things induces mutation, cancer, and aging (9). Inasmuch as these also arise spontaneously in nature, it is natural to inquire if the processes might not be similar. It is believed that one mechanism of irradiation effect is through liberation of OH and HO 2 radicals (12). There is evidence, although indirect, that these two highly active free radicals are produced normally in living systems. In the first place, free radicals are present in living cells; this was recently demonstrated in vivo by a paramagnetic resonance absorption method (3). Further, it was shown that the concentration of free radicals increased with increasing metabolic activity in conformity with the postulates set forth some years ago that free radicals were involved in biologic oxidation-reduction reactions (11, 13). Are some of these free radicals OH and/or HO2, or radicals of a similar high order of reactivity, and where might they arise in the cell? The most likely source of OH and HO2 radicals, at least in the animal cell, would be the interaction of the respiratory enzymes involved

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Aging: A Theory Based on Free Radical and Radiation Chemistry

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Brownian motion in a field of force and the diffusion model of chemical reactions

Stanford Moore, William Stein, and Anfinsen were awarded the Nobel Prize in Chemistry in 1972 for \"their contribution\n to the understanding of the connection between chemical structure and catalytic activity of the active center of the ribonuclease\n molecule.\" In his Nobel Lecture, Anfinsen provided a sketch of the rich history of research that provided the foundation\n for his work on protein folding and the \"Thermodynamic Hypothesis,\" and outlined potential avenues of current and\n future scientific exploration.

https://web.iitd.ac.in/~amittal/1973_Anfinsen_Science.pdf

Principles that Govern the Folding of Protein Chains

We demonstrate in this work that the surface tension, water-organic solvent, transfer-free energies and the thermodynamics of melting of linear alkanes provide fundamental insights into the nonpolar driving forces for protein folding and protein binding reactions. We first develop a model for the curvature dependence of the hydrophobic effect and find that the macroscopic concept of interfacial free energy is applicable at the molecular level. Application of a well-known relationship involving surface tension and adhesion energies reveals that dispersion forces play little or no net role in hydrophobic interactions; rather, the standard model of disruption of water structure (entropically driven at 25 degrees C) is correct. The hydrophobic interaction is found, in agreement with the classical picture, to provide a major driving force for protein folding. Analysis of the melting behavior of hydrocarbons reveals that close packing of the protein interior makes only a small free energy contribution to folding because the enthalpic gain resulting from increased dispersion interactions (relative to the liquid) is countered by the freezing of side chain motion. The identical effect should occur in association reactions, which may provide an enormous simplification in the evaluation of binding energies. Protein binding reactions, even between nearly planar or concave/convex interfaces, are found to have effective hydrophobicities considerably smaller than the prediction based on macroscopic surface tension. This is due to the formation of a concave collar region that usually accompanies complex formation. This effect may preclude the formation of complexes between convex surfaces.

Protein folding and association: insights from the interfacial and thermodynamic properties of hydrocarbons.

Application of Absolute Reaction Rate Theory to the Racemization of Certain Sterically Hindered Compounds1

Semilocalized orbitals are defined and applied to the hydrogen molecule. The basic criteria for the analytic form of this kind of orbital is that it shall assume either molecular or atomic orbital form for certain special values of the variational parameters. A binding energy of 4.20 ev is found in comparison with 3.60 and 3.76 ev obtained from the best molecular and atomic orbital calculations. The physical interpretation of the results is briefly discussed.

Semilocalized Orbitals. I. The Hydrogen Molecule

A simple quantitative method for determining the amount of mechanical strength contributed by the various types of bonds in hair fiber has been developed. The effects of various types of reagents, ...

Mechanical Properties and the Structure of Hair

The approximation is made that the dividing surface between a liquid and its vapor phase is a monomolecular layer, in which a molecule has a free volume larger than for an interior molecule and a potential energy less than for the latter. By introducing the approximation into the significant structure theory of liquids, a partition function fN is derived which involves the terms belonging to the surface as well as to the bulk liquid. The surface tension is calculated by γ = (∂A/∂Ω)N,V,T, where A is the Helmholtz free energy which equals —kTlnfN, Ω is the surface area, N the total number of molecules in the system, V the volume of the liquid, and T the absolute temperature. The surface tensions of nonpolar substances at various temperatures are calculated with good results. Our theory is compared with other theories, and it is found that the present theory most satisfactorily predicts the surface tensions at various temperatures.

Significant Structure Theory of Surface Tension

The activation energies of the reactions H+CH4=CH3+H2 (1) and D+CH4=CH3D+H (2) have been calculated by using the semi‐empirical method in combination with the treatment of directed valence used by Van Vleck and Voge. The activation energies for reactions (1) and (2) were found to be 9.5 kcal. and 37 kcal. This result agrees with the prediction of 40 kcal. of Rice and Teller for reaction (2). In addition it is found that the energy surface corresponding to the reaction H+CH4 contains a basin 8 kcal. deep corresponding to a stable CH3–H–H molecule. The rapid recombination of H atoms in the presence of methane, observed by Farkas and Melville is interpreted in terms of this CH3–H–H intermediate. The experimental data on the reactions of hydrogen and deuterium atoms with hydrocarbons have been reinterpreted in terms of atom‐cracking reactions of the type D+C2H5→C2H5D→CH3D+CH3.

Henry Eyring

Papers

Application of Absolute Reaction Rate Theory to the Racemization of Certain Sterically Hindered Compounds1

Semilocalized Orbitals. I. The Hydrogen Molecule

Mechanical Properties and the Structure of Hair

Significant Structure Theory of Surface Tension

Reactions Involving Hydrogen and the Hydrocarbons