Radial distribution function of liquid argon according to significant structure theory

The significant structure theory of liquids is tested by evaluating the radial distribution function. The calculations are based on face-centered cubic quasi-lattice structure, and the fluctuation in volume is used to describe the thermal displacements of molecules. It is shown that the local structure of liquids has inhomogeneous distributions. The correlation at long ranges becomes negligible because of the fluidized vacancies in our model. The calculations are performed for liquid argon, and the results are in good agreement with experiments.

Calculations of the circular dichroism of adenosine derivatives constrained in the syn form

The rotational strengths of the four longer wavelength transitions, B(2u), B(1u), and the two E(1u), of adenosine derivatives constrained in the syn form have been investigated theoretically and experimentally. The theory combines a complete neglect of differential overlap version S (CNDO/S) description of the base with a generalized bond exciton method by means of a matrix method. Rotational strength wheels for these transitions showing the rotational strength as a function of the glycosidic rotational angles are presented and sector rules discussed. Similar sector rules are predicted for purine nucleoside derivatives containing the 6-amino substituent, regardless of heteroatom content at positions 1 or 3 of the base. The sector rules for the B(2u) rotational strength of purine nucleosides lacking the 6-amino substituent are strongly influenced by aza substitution. The circular dichroism spectra of 3-deazaadenosine, 8-(alpha-hydroxyisopropyl)-adenosine, and other purine nucleosides having a strong preference for the syn conformation are presented and compared with the theoretical results.

A theoretical study of resonance Raman scattering from molecules: High pressure effect

The main purpose of this paper has been to study the high pressure effect on the resonance Raman scattering (RRS) of molecules in a dense medium. In deriving the RRS cross section under high pressure, a different approach from that presented in the previous papers has been used, and the resulting expression for the RRS cross section can be used to treat both pressure and temperature effects.

Mechanisms of triboluminescence

The purpose of this paper has been to develop the theoretical treatment of the triboexcitation mechanisms due to the electric field effect and the pressure effect and to show how to analyze the triboluminescent spectra to determine the external factors that affect or induce the triboluminescence.

Elementary transition state theory of the Soret and Dufour effects

The elementary transition state approach has been used to obtain a simple model theory for the Soret effect (thermal diffusion) and the Dufour effect. The flow of heat in the Dufour effect is identified as the transport of the enthalpy change of activation as molecules diffuse. The theory as now formulated applies only to thermodynamically ideal mixtures of substances with molecules of nearly equal size. The results of the theory conform to the Onsager reciprocal relationship. When the results were fit to data on thermal diffusion for two liquid systems, a close fit was obtained and yielded reasonable values of between 2 and 3 kcal mol(-1) for enthalpy changes of activation and differences between the entropy changes of activation for the two components of between 0 and 1 cal K(-1) mol(-1).

Significant structure theory applied to electrolyte solution

The significant structure theory has been successfully applied to an aqueous NaCl solution. Liquid water is assumed to have a domain structure and the ions are hydrated by water molecules. The partition function is composed of the partition function for the water and that for the salt, and the excess free energy term from the Debye-Hückel theory is also added. The thermodynamic properties, such as molar volume, vapor pressure, entropy of vaporization, and heat capacity, as well as the dielectric constant are calculated over the whole concentration ranges and wide temperature ranges. The agreement between theory and experiment is satisfactory.

Quantum statistical theory of optical phenomena

The purpose of this paper is to develop a density matrix formulation for optical phenomena that can be applied to both steady and transient states and to both resonance and off-resonance regions. To demonstrate the application, this theory has been applied to the steady-state one-photon and two-photon processes. We have found that, in the resonance region, the conventional equation used is incomplete; other terms that are comparable in importance have been ignored.

Solution of the time-dependent schrödinger equation by the laplace transform method

The time-dependent Schrödinger equation for two quite general types of perturbation has been solved by introducing the Laplace transforms to eliminate the time variable. The resulting time-independent differential equation can then be solved by the perturbation method, the variation method, the variation-perturbation method, and other methods.

A general treatment of relaxation phenomena

The singular perturbation method has been applied to solve the quantum mechanical Liouville equation for the relaxation phenomenon of the system in thermal contact with a heat bath. The master equation derived gives the proper expressions for both diagonal and off-diagonal elements of the density matrix and is capable of describing the time-dependent behavior of the system in the time range comparable with the reciprocal of the damping constants and the time range t --> infinity compared with the reciprocal of the damping constants.

Quantum statistical theory of rate processes

A general quantum mechanical approach for treating a great number of rate processes is developed and the temperature dependence of the rate constants is discussed.

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.

Medium-induced radiationless transitions and effect of solvent on radiationless transitions

The purpose of this paper has been to investigate the effect of solvent on radiationless transitions. Two types of the solvent effect have been studied: one is the so-called medium-induced radiationless transition, i.e., the radiationless transition induced by the interaction between the solute and solvent, and the other is the effect of solvent on the radiationless transition through the change in energy gap induced by the solute-solvent interaction.

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.

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.

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.

Stochastic Model of Unimolecular Reactions and the RRKM Theory

A stochastic model of unimolecular reactions has been adopted for investigation of the validity and limitation of the RRKM theory. The error caused by the steady-state approximation for distribution of energized molecules is small, while the assumption of the internal energy equilibration of energized molecules might cause serious errors for reactions of low activation energies.

THE NATURE AND CONTROL OF REACTIONS IN BIOLUMINESCENCE : WITH SPECIAL REFERENCE TO THE MECHANISM OF REVERSIBLE AND IRREVERSIBLE INHIBITIONS BY HYDROGEN AND HYDROXYL IONS, TEMPERATURE, PRESSURE, ALCOHOL, URETHANE, AND SULFANILAMIDE IN BACTERIA

On the basis of available data with regard to the chemical and physical properties of the "substrate" luciferin (LH₂) and enzyme, luciferase (A), and of kinetic data derived both from the reaction in extracts of Cypridina, and from the luminescence of intact bacteria, the fundamental reactions involved in the phenomenon of bioluminescence have been schematized. These reactions provide a satisfactory basis for interpreting the known characteristics of the system, as well as the theoretical chemistry with regard to the control of its over-all velocity in relation to various factors. These factors, here studied experimentally wholly with bacteria, Photobacterium phosphoreum in particular, include pH, temperature, pressure, and the drugs sulfanilamide, urethane, and alcohol, separately and in relation to each other. Under steady state conditions of bacterial luminescence, with excess of oxidizable substrate and with oxygen not limiting, the data indicate that the chief effects of these agents center around the pace setting reactions, which may be designated by the equation: A + LH₂ → ALH₂ following which light emission is assumed proportional to the amount of the excited molecule, AL*. The relation between pH and luminescence intensity varies with (a), the buffer mixture and concentration, (b), the temperature, and (c), the hydrostatic pressure. At an optimum temperature for luminescence of about 22° C. in P. phosphoreum, the effects of increasing or decreasing the hydrogen ion concentration are largely reversible over the range between pH 3.6 and pH 8.8. The relation between luminescence intensity and pH, under the experimental conditions employed, is given by the following equation, in which I₁ represents the maximum intensity, occurring about pH 6.5; I₂ the intensity at any other given pH; K₅ the equilibrium constant between hydrogen ions and the AL_-; and K₆ the corresponding constant with respect to hydroxyl ions: See PDF for Equation The value of K₅, as indicated by the data, amounts to 4.84 x 10⁴, while that of K₆ amounts to 4.8 x 10⁵. Beyond the range between approximately pH 3.8 and 8.8, destructive effects of the hydrogen and hydroxyl ions, respectively, were increasingly apparent. By raising the temperature above the optimum, the destructive effects were apparent at all pH, and the intensity of the luminescence diminished logarithmically with time. With respect to pH, the rate of destruction of the light-emitting system at temperatures above the optimum was slowest between pH 6.5 and 7.0, and increased rapidly with more acid or more alkaline reactions of the medium. The reversible effects of slightly acid pH vary with the temperature in the manner of an inhibitor (Type I) that acts independently of the normal, reversible denaturation equilibrium (K₁) of the enzyme. The per cent inhibition caused by a given acid pH in relation to the luminescence intensity at optimum pH, is much greater at low temperatures, and decreases as the temperature is raised towards the optimum temperature. The observed maximum intensity of luminescence is thus shifted to slightly higher temperatures by increase in (H⁺). The apparent activation energy of luminescence is increased by a decrease in pH. The value of ΔH‡ at pH 5.05 was calculated to be 40,900 calories, in comparison with 20,700 at a pH of 6.92. The difference of 20,200 is taken to represent an estimate of the heat of ionization of ALH in the activation process, and compares roughtly with the 14,000 calories estimated for the same process, by analyzing the data from the point of view of hydrogen ions as an inhibitor. The decreasing temperature coefficient for luminescence in proceeding from low temperatures towards the optimum is accounted for in part by the greater degree of ionization of ALH. At the optimum temperature and acid reactions, pressures up to about 500 atmospheres retard the velocity of the luminescent oxidation. At the same temperature, with decrease in hydrogen ion concentration, the pressure effect is much less, indicating a considerable volume increase in the process of ionization and activation. In the extremely alkaline range, beyond pH 9, luminescence is greatly reduced, as compared with the intensity at neutrality, and under these conditions pressure causes a pronounced increase in intensity, presumably by acting upon the reversible denaturation equilibrium of the protein enzyme, A. Sulfanilamide, in neutral solutions, acts on luminescence in a manner very much resembling that of hydrogen ions at acidities between pH 4.0 and pH 6.5. Like the hydrogen ion equilibrium, the sulfanilamide equilibrium involves a ratio of approximately one inhibitor molecule to one enzyme molecule. The heat of reaction amounts to about 11,600 calories or more in a reversible combination that evidently evolves heat. Like the action of H ions, sulfanilamide causes a slight shifting of maximum luminescence intensity in the direction of higher temperatures, and an increase in the energy of activation. The effect of sulfanilamide on the growth of broth cultures of eight species of luminous bacteria indicates that there is no regular relationship among the different organisms between the concentration of the drug that prevents growth, and that which prevents luminescence in the cells which develop in the presence of sulfanilamide. p-Aminobenzoic acid (PAB) antagonizes the sulfanilamide inhibition of growth in luminous bacteria, and the cultures that develop are luminous. When (PAB) is added to cells from fully developed cultures, it has no effect on luminescence, or causes a slight inhibition, depending on the concentration. With luminescence partly inhibited by sulfanilamide, the addition of PAB has no effect, or has an inhibitory effect which adds to that caused by sulfanilamide. Two different, though possibly related, enzyme systems thus appear to limit growth and luminescence, respectively. The possible mechanism through which both the inhibitions and the antagonism take place is discussed. The irreversible destruction of the luminescent system at temperatures above that of the maximum luminescence, in a medium of favorable pH to which no inhibitors have been added, proceeds logarithmically with time at both normal and increased hydrostatic pressures. Pressure retards the rate of the destruction, and the analysis of the data indicates that a volume increase of roughly 71 cc. per gm. molecule at 32° C. takes place in going from the normal to the activated state in this reaction. At normal pressure, the rate of destruction has a temperature coefficient of approximately 90,000 calories, or about 20,000 calories more than the heat of reaction in the reversible denaturation equilibrium. The data indicate that the equilibrium and the rate process are two distinct reactions. The equation for luminescence intensity, taking into account both the reversible and irreversible phases of the reaction is given below. In the equation b is a proportionality constant; k' the rate constant of the luminescent reaction; A₀ the total luciferase; A_0i the total initial luciferase at time t equals 0; k_n the rate constant for the destruction of the native, active form of the enzyme; k_d the rate constant for the destruction of the reversibly denatured, inactive form; t the time; and the other symbols are as indicated above: See PDF for Equation For reasons cited in the text, k_n evidently equals k_d. Urethane and alcohol, respectively, act in a manner (Type II) that promotes the breaking of the type of bonds broken in both the reversible and irreversible reactions and so promotes the irreversible denaturation. This result is in contrast to the effects of sulfanilamide, which at appropriate concentrations may give rise to the same initial inhibition as that caused by urethane, but remains constant with time. The inhibition caused by urethane and alcohol, respectively, increases as the temperature is raised. As a result, the apparent optimum is shifted to lower temperatures, and the activation energy for the over-all process of luminescence diminishes. An analysis for the approximate heat of reaction in the equilibrium between these drugs and the enzyme, indicates 65,000 calories for urethane, and 37,000 for alcohol. A similar analysis with respect to the effect of hydroxyl ions as the inhibitor gives 60,300 calories. The effects of alcohol and urethane are sensitive to hydrostatic pressure. Moderate inhibitions at optimum temperature and pH, caused by relatively small concentrations of either drug, are completely abolished by pressures of 3,000 to 4,000 pounds per square inch. At optimum temperature and pH, increasing concentrations of alcohol caused the apparent optimum pressure for luminescence to shift markedly in the direction of higher pressures. Analysis of the data with respect to concentration of alcohol at different pressures indicated that the ratio of alcohol to enzyme molecules amounted to approximately 4, at 7,000 pounds, but only about 2.8 at normal pressures. This phenomenon was taken to indicate that more than one equilibrium is established between the alcohol and the protein. A similar interpretation was suggested in connection with the fact that analysis of the relation between concentration of urethane and amount of inhibition at different temperatures also indicated a ratio of urethane to enzyme molecules that increased with temperature in the equilibria involved. Analysis of the data with respect to pressure and the inhibition caused by a given concentration of alcohol at different temperatures indicated that the volume change involved in the combination of alcohol with the enzyme must be very small, while the actual effect of pressure is apparently mediated through the reversible denaturation of the protein enzyme, which is promoted by alcohol, urethane, and drugs of similar type.

The Mechanical Properties of Rat Tail Tendon

The load-strain and stress-relaxation behavior of wet rat tail tendon has been examined with respect to the parameters strain, rate of straining, and temperature. It is found that this mechanical behavior is reproducible after resting the tendon for a few minutes after each extension so long as the strain does not exceed about 4 per cent. If this strain is exceeded, the tendon becomes progressively easier to extend but its length still returns to the original value after each extension. Extensions of over 35 per cent can be reached in this way. Temperature has no effect upon the mechanical behavior over the range 0–37°C. Just above this temperature, important changes take place in the mechanical properties of the tendon which may have biological significance. The application of the techniques used here to studies of connective tissue disorders is suggested. Some of the mechanical properties of tendon have been interpreted with a simple model.

Biochemical and biophysical approaches to improving the anticancer effectiveness of Ara-adenine

Ara-C at very low dosage has been reported to decrease the host toxicity of ara-AMP or ara-A in combination with 2'-deoxycoformycin, a potent adenosine deaminase inhibitor, while increasing the toxicity to intracerebral L1210 leukemia. The possibility of increasing the selectivity of ara-A by prior administration of ara-C is explored. The importance of deoxynucleoside kinases, some of which may be cancer-induced, in obtaining selective anticancer effects is discussed. The possibility of a conformational basis for the differing degrees of selectivity and activity of various novel arabinosyl nucleosides is evaluated. The levels of cyclic nucleotides, which have opposing effects on leukemia, may possibly be manipulated to interfere with the growth of cancer cells. Approaches to minimizing major metabolic distortions, such as the progressive accumulation of dATP associated with the use of potent adenosine deaminase inhibitors and which limit the therapeutic effects of ara-A, are proposed.

Rate constant of vibrational redistribution in molecules using adiabatic approximation model

By means of the proposed adiabatic approximation model for vibrational redistribution [Lin, S. H. (1980) Chem. Phys. Lett. 70, 492-499], the calculations of various rate constants caused by different couplings have been given in detail. By two methods it has been demonstrated that the rate constant caused by the Born-Oppenheimer mechanism, corrected by the non-Condon approximation, has the same order of magnitude as that contributed by the anharmonic mechanism. Furthermore, the important effect of molecular rotation on the rate constant based on the Coriolis coupling has been demonstrated.

Optical activity and electronic absorption spectra of some simple nucleosides related to cytidine and uridine: all-valence-shell molecular orbital calculations

The circular dichroism and electronic absorption of three simple model systems for cytidine and uridine have been measured to 190 nm. The molecular spectral properties (excitation wavelengths, oscillator strengths, rotational strengths, and polarization directions) and electronic transitional patterns were investigated by using wave functions of the entire nucleoside with the goal of establishing the reliability of the theoretical method. The computed electronic absorption quantities were shown to be in satisfactory agreement with experimental data. It was found that the computed optical rotatory strengths of the B2u and E1u electronic transitions and lowest observed n-pi transition are in good agreement with experimental values. Electronic transitions were characterized by their electronic transitional patterns derived from population analysis of the transition density matrix. The theoretical rotational strengths associated with the B2u and E1u transitions stabilize after the use of just a few singly excited configurations in the configuration interaction basis and, hypothetically, are more reliable as indicators of conformation in pyrimidine nucleosides related to cytidine.

Reaction kinetics in living systems

In this report we treat reaction rates, equilibrium theory, and irreversible thermodynamics as different aspects of a single discipline. In biological reactions the rate is ultimately controlled by enzymes and other proteins of complex structure and high molecular weight. The needed formalism can be placed in one-to-one correspondence with appropriate electrical and mechanical networks. An enzyme molecule has zwitter ions anchored in the polypeptide chain, which enable it to distort the substrate by electrostatic polarization. Water weakens the induced or existing polar bonds and so speeds reaction. Several biological processes, such as luminescence, catalysis, nerve excitation, and anesthesia, in which enzymatic reactions play a major part are discussed from this point of view. We also have discussed the energy consumption and coupling effect in living systems. It is likely that a small fraction of bonds can become energy rich through the process of quenching and that unsymmetrical barriers in biological systems act like transistors in making the driving forces more efficient by a valve effect.

Quantum statistical mechanical theory of diffusion and reaction on solid surfaces

We present the derivation of the general kinetic equations of diffusion and diffusion with interaction (or chemical reaction) on solid surfaces (or in dense media) by using the density matrix method. We indicate several problems to which this formalism applies and, in particular, discuss the damping effect on diffusion.