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Biomedical subjects

H Eyring

Publications and source records attributed to H Eyring.

At least 73 records · Page 4Linked to original sources
PubMed1975

Collisional energy transfer and quenching of electronic excitation.

The purpose of this paper has been to explore in a preliminary way the nature and mechanism of collisional energy transfer and quenching of electronic excitation. For this purpose, the Born approximation has been used, and the triplet-triplet and singlet-singlet transfer, and the triplet-triplet and singlet-singlet quenching have been studied. It has been shown theoretically that (i) the singlet-singlet transfer constants (or cross sections) are always larger than the triplet-triplet transfer constants (or cross sections) for the same system of donor and acceptor; (ii) for the singlet-singlet transfer, the observed cross section varies linearly with respect to the spectral overlap between the donor emission and the acceptor absorption; (iii) the reason that the quenching constants (or cross sections) are always smaller than the energy transfer constants (or cross sections) is due to the fact that for the quenching the vibration of the acceptor hardly participates in accepting the electronic excitation and for the energy transfer only part of the excited electron energy of the donor is converted into the energy of nuclear motion; and (iv) the polar acceptor molecules are better quenchers than nonpolar acceptor molecules.

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PubMed1975

Magnetic Circular Dichroism of Molecules in Dense Media: Relation Between Magnetic Circular Dichroism and Hammett's Constants.

The linear relation between the magnetic circular dichroism (benzene (1)A(1g) --> (1)B(2u) transition) of monosubstituted and 1,4-disubstituted benzenes and the substituent constants sigma and sigma(R) are compared. In all cases, better linear correlations were found between the magnetic circular dichroism and sigma(R). Three series of 1,4-disubstituted benzenes, XC(6)H(4)I, XC(6)H(4)NO(2), and XC(6)H(4)CO(2)H, have been chosen for the magnetic circular dichroism measurements.

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PubMed1975

Properties of molten magnesium oxide.

The Significant Structure Theory of Liquids has been used to calculate the thermodynamic properties, viscosity, self-diffusion coefficient, and specific conductance of molten magnesium oxide, taking account of the decomposition of MgO to Mg and O(2) species in the gas-like part of the partition function.

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PubMed1975

Fall-off from extrapolated values of all chemical reactions at very high temperatures.

At high temperatures the breaking of chemical bonds becomes relatively easy and the slow step in a chemical reaction shifts to the rate at which energy can seep into the bond that is to break. This has been observed by various investigators. A new general theory of reactions is developed here to explain this limiting rate at high temperatures. In the case of cyclopropane and cyclobutane the theory leads to the conclusion that 20 degrees of freedom form a heat reservoir which feeds the energy into the carbon bond that is to break and that this rate becomes controlling above about 1200 degrees K. This would correspond to 20 of the 21 vibrational bonds of cyclopropane feeding energy into the carbon bond that is to break, and there would be no noticeable rise in the number of bonds for cyclobutane. This theory is especially important for shock tubes and detonations, where this falling-off from the extrapolated low temperature rate becomes glaringly obvious.

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PubMed1974

Effect of chemical substitution on absorption spectra and magnetic circular dichroism of molecules in dense media.

The purpose of this paper has been to study the effect of chemical substitution on the magnetic circular dichroism and absorption spectra for the parent molecule which has the C(2v) symmetry. Four electronic transitions, A(1) --> A(1), A(1) --> B(1), A(1) --> B(2), and A(1) --> A(2) have been considered. In each case, the intensity changes in magnetic circular dichroism and absorption spectra due to substitution have been expressed in terms of number of substituents and positions of substitution.

Journal Article↗
PubMed1974

Study of the franck-condon and herzberg-teller approximations.

Using the Born-Oppenheimer parameter lambda = (m/M)(1/4) as a perturbation parameter, we find that for allowed transitions, the zeroth order approximation of the spectral intensity gives rise to the Condon approximation, the first order vibronic coupling and anharmonic effect appear in the first order approximation of the spectral intensity, which gives us the non-Condon scheme, and only the intensity of the transitions of totally-symmetric modes with nonvanishing normal coordinate displacements is affected by the inclusion of the first order vibronic coupling and anharmonic effect. For symmetry-forbidden but vibronic-allowed transitions, the first nonvanishing term of the spectral intensity is second order with respect to lambda and the B-O couplings do not appear in the calculation of the spectral intensity until the fourth order approximation with respect to lambda; in this case, other high order vibronic couplings and anharmonic effect are competing with the B-O couplings.

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PubMed1974

Applications of the survival theory to ecology.

The Eyring-Stover theory of survival developed in earlier papers can be readily applied to a wide diversity of ecological phenomena, with implications for identifying basic responses of organisms to their environment. We report several examples to demonstrate the generality of the theory.

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PubMed1974

A statistical study of optical rotation for synthetic d,l-copolypeptide solutions.

The right-handed helical fraction H(L) in a D,L-copolypeptide chain is evaluated by a simple probability theory for each L-fraction, p. The curves of optical rotation at a single wavelength against p for poly(gamma-benzyl-D,L-glutamate) and D,L-copolyleucine of a series of different D:L ratios in several positive helix-solvents are calculated with a modified semi-empirical Moffitt equation. From the comparison between the rotations calculated by us and observed by Downie et al., it is shown that to reproduce the observed rotations, the minimum number of right-handed helical nuclei or sequences of L-residues appropriate to the Moffitt equation are eight and four for degrees of polymerization 320 and 1860, respectively.

Journal Article↗
PubMed1974

Atmospheric corrosion.

A model of electrolytic corrosion is developed. It is shown that electrically conducting channels threading through the oxide layer and connecting anodic and cathodic areas, obey the equation for a reactant being catalyzed by its product. The resulting autocatalytic equation is compared with available experimental data and found to be widely applicable and capable of unifying many experimental observations.

Journal Article↗
PubMed1974

Investigation of the composition and formation constant of molecular complexes.

It has been the purpose of the present paper to investigate and explore the conditions under which the linear relation between Delta/C(D) (0) and Delta in the Hanna-Ashbaugh-Foster-Fyfe equation for the evaluation of equilibrium constants holds, (C(D) (0) is initial concentration of a donor and Delta is the observed chemical shift relative to the chemical shift of the acceptor) to obtain the equation representing the exact linear relation between Delta/C(D) (0) and Delta, when the linear relation between Delta/C(D) (0) and Delta holds, and to discuss how to use the Job method in nuclear magnetic resonance measurements to determine the stoichiometry of molecular complexes. We have found that the conventional belief that C(D) (0) should always be chosen to be much greater than C(A) (0) (initial concentration of acceptor) is not necessarily always true and the exact linear relation between Delta/C(D) (0) and Delta is represented by the equation Delta/C(D) (0) = K(1)Delta(0)/(1 + K(1)C(A) (0)) - K(1)Delta/(1 + K(1)C(A) (0))(2), where K(1) is the formation constant of the complex. It is shown that in the Job method of nuclear magnetic resonance measurements one has to plot DeltaC(A) (0) against the mole fraction, and the mole fraction at the maximum should give us the composition of the complex. Theoretical results have been verified experimentally on the weak interaction between naphthalene and methyl iodide.

Journal Article↗
PubMed1974

The significant structure theory applied to amorphous and crystalline polyethylene.

The significant structure theory of liquids has been applied to amorphous and crystalline polyethylene. In this theory the amorphous state, like liquids in general, is assumed to have solid-like structure, gaslike structure, and positional degeneracy which arises from the motion of kinetic segments and from the libration of CH(2) units. This concept leads to a partition function giving the Helmholtz free energy in terms of volume, temperature, and composition.Thermodynamic and transport properties are calculated for amorphous polyethylene. The thermodynamic properties are also calculated for the crystalline solid. The calculated results are in reasonable agreement with the experimental values. No such detailed calculations of polymer properties from a partition function, depending on both volume and temperature, have been previously attempted.

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PubMed1974

Study of vibronic and born-oppenheimer couplings.

The purpose of this paper has been to develop a systematic approach for classifying and distinguishing the relative orders of approximation of various types of couplings like the vibronic (Herzberg-Teller) couplings and Born-Oppenheimer couplings, and for studying the importance of the anharmonicity in the quantitative calculation of the spectral intensity and electronic relaxation. It will be shown that the perturbation parameter introduced by Born and Oppenheimer in separating the electronic and nuclear motion involved in the molecular Schrödinger equation, lambda = (m/M)(1/4), can be used for this purpose by expanding wavefunctions and energies in power series of lambda.

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PubMed1973

Molecular orbital calculations of magnetic circular dichroism spectra: a benzene-indole sequence.

The magnetic circular dichroism of benzene and indole derivatives was measured down to 190 nM. The following pairs of molecules have magnetic circular dichroisms of the opposite sign in the B(2u) absorption region: aniline and benzonitrile, indene and indoline, indole and 4-aminoindole, and 4-aminoindole and 5-aminoindole. The sign and magnitude of the magnetic circular dichroisms observed are in good agreement with those calculated by the semiempirical self-consistent field with configuration interaction Pariser-Parr-Pople method with incorporation of variable pi-electronegativity and sigma-polarization. The energy dominator in the magnetic rotational strength expression serves to limit the important contributions to a few terms only.

Aniline Compounds↗
PubMed1973

Application of the singular perturbation method to reaction kinetics.

The purpose of this paper is to show how to apply the singular perturbation method to the rate equations in reaction kinetics that involve different time scales. The Lindemann scheme has been chosen for illustration, and the steady-state and equilibrium approximations used in the Lindemann scheme are discussed.

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