Showing papers on "Intermolecular force published in 1978"
Book•
01 Apr 1978
TL;DR: In this article, an extension of the donor-acceptor concept, characterized by the comparison between equilibrium structures in different molecular environments, is presented, in which changes in the positions of the nuclei are taken into account and the question of the nature of the molecular forces is no longer important.
Abstract: Recent developments in various areas of chemistry have been decisively influenced by the principles of structure and mechanism and by the ideas of coordination chemistry, in particular by the donor-acceptor approach, A unified view of almost all kinds of molecular forces is provided by quantum mechanics, and for practical purposes have been classified according to model assumptions, namely, dispersion, polarization, electrostatic, and short-range forces. The latter are divided into two- and three-center covalent chemical bonds, metallic bonds, and exchange-repulsion forces. This approach allows statements of principle and systematic analysis. However, quantitative predictions on concrete large systems are virtually impossible, and there are no general rules that account for structural and chemical changes due to intermolecular interactions. Chemists are therefore left with qualitative descriptions in which the changes in electron densities are considered. Such models as the MO theory or the resonance concept unrealistically assume that the nuclei remain in fixed positions. Further difficulties are encountered in the attempted description on the "nature" of the chemical bond, e.g., the forces involved. In order to avoid these difficulties an extension of the donor-acceptor concept, characterized by the comparison between equilibrium structures in different molecular environments, will be presented in this book. In this way, changes in the positions of the nuclei can be taken into account and the question of the nature of the molecular forces is no longer important.
1,640 citations
TL;DR: In this paper, a model that relies on the knowledge of the molecular electrostatic potential, which is derived from a molecular wave function by using the usual methods for calculating the mean expectation value of an operator, is discussed.
Abstract: Publisher Summary This chapter discusses a model that relies on the knowledge of the molecular electrostatic potential, which is derived from a molecular wavefunction by using the usual methods for calculating the mean expectation value of an operator. In its basic premises the model employs quantum mechanics, with only the approximations necessary in molecular quantal calculations. The model is also discussed regarding its relationships with the Hellmann–Feynman theorem. The electrostatic potential V itself is examined in order to show how the electrostatic potential reflects the characteristics of the electronic distribution of a molecule and then the reliability of V is discussed as a reactivity index. The shape of the electrostatic potential and its relationship to the electronic molecular structure is discussed with the aid of various examples. One of them includes the glycine tautomers and the corresponding anion example. The chapter also discusses the electrostatic molecular potential in terms of local group contributions.
1,116 citations
TL;DR: The structure of α-chitin has been determined by X-ray diffraction, based on the intensity data from deproteinized lobster tendon Least-squares refinement shows that adjacent chains have alternating sense (i are antiparallel) In addition, there is a statistical distribution of side-chain orientations, such that all the hydroxyl groups form hydrogen bonds as discussed by the authors.
543 citations
TL;DR: The consistency of these calculations supports the conclusion that the most important molecular energies for the main transition in lecithin bilayers are the hydrocarbon chain interactions and the rotational isomeric energies, and that the main phase transition is analogous to the melting transition in the alkanes from the hexagonal phase to the liquid phase, but with some modifications.
534 citations
Book•
01 Jan 1978
TL;DR: In this article, the authors describe the Human Genome and beyond as a set of concepts and applications of physics and describe the state of a system with respect to energy conversion and conservation.
Abstract: (NOTE: Most chapters begin with Concepts and Applications and end with Summary, References, Suggested Readings and Problems.) Preface. About the Authors. 1. Introduction. The Human Genome and Beyond. Transcription and Translation. Ion Channels. 2. The First Law: Energy Is Conserved. Energy Conversion and Conservation. Describing the State of a System. Phase Changes. Chemical Reactions. Molecular Interpretations of Energy and Enthalpy. Mathematics Needed for Chapter 2. 3. The Second Law: The Entropy of the Universe Increases. Historical Development of the Second Law: The Carnot Cycle. A New State Function, Entropy. The Second Law of Thermodynamics: Entropy Is Not Conserved. Molecular Interpretation of Entropy. Measurement of Entropy. Chemical Reactions. Third Law of Thermodynamics. Gibbs Free Energy. Helmholtz Free Energy. Noncovalent Reactions. Use of Partial Derivatives in Thermodynamics. 4. Free Energy and Chemical Equilibria. Chemical Potential (Partial Molar Gibbs Free Energy). Reactions of Gases: The Ideal Gas Approximation. Nonideal Systems. The Equilibrium Constant and the Standard Gibbs Free Energies of the Reactants and Products. Galvanic Cells. Biochemical Applications of Thermodynamics. Mathematics Needed for Chapter 4. 5. Free Energy and Physical Equilibria. Phase Equilibria. Membranes. Active and Passive Transport. Colligative Properties. Molecular-Weight Determination. Internet. 6. Molecular Motion and Transport Properties. Kinetic Theory. Molecular Collisions. Mean Free Path. Diffusion. Sedimentation. Determination of Molecular Weights from Sedimentation and Diffusion. Viscosity. Electrophoresis. Size and Shape of Macromolecules. 7. Kinetics: Rates of Chemical Reactions. Kinetics. Reaction Mechanisms and Rate Laws. Temperature Dependence. Transition-State Theory. Electron Transfer Reactions: Marcus Theory. Ionic Reactions and Salt Effects. Isotopes and Stereochemical Properties. Very Fast Reactions. Diffusion-Controlled Reactions. Photochemistry and Photobiology. Photosynthesis. Mathematics Needed for Chapter 7. 8. Enzyme Kinetics. Enzyme Kinetics. Michaelis-Menten Kinetics. Competition and Inhibition. Mathematics Needed for Chapter 8. 9. Molecular Structures and Interactions: Theory. The Process of Vision. Origins of Quantum Theory. Quantum Mechanical Calculations. Schrodinger's Equation. Particle in a Box. Tunneling. Simple Harmonic Oscillator. Rigid Rotator. Hydrogen Atom. Electron Distribution. Molecular Structure and Molecular Orbitals. Intermolecular and Intramolecular Forces. Noncovalent Interactions. Molecular Dynamics Simulation. Outlook. Schrodinger's Equation. Some Useful Operators. Mathematics Needed for Chapter 9. 10. Molecular Structures and Interactions: Spectroscopy. Electromagnetic Spectrum. Color and Refractive Index. Absorption and Emission of Radiation. Proteins and Nucleic Acids: Ultraviolet Absorption Spectra. Fluorescence. Optical Rotatory Dispersion and Circular Dichroism. Circular Dichroism of Nucleic Acids and Proteins. Vibrational Spectra, Infrared Absorption, and Raman Scattering. Nuclear Magnetic Resonance. Interactions in Nuclear Magnetic Resonance. 11. Molecular Distributions and Statistical Thermodynamics. Binding of Small Molecules by a Polymer. The Random Walk. Helix-Coil Transitions. Statistical Thermodynamics. Mathematics Needed for Chapter 11. 12. Macromolecular Structure and X-Ray Diffraction. Visible Images. X Rays. Determination of Molecular Structure. Electron Diffraction. Neutron Diffraction. Electron Microscopy. Mathematics Needed for Chapter 12. Appendix. Answers. Index.
295 citations
TL;DR: In this article, a solution theory based on thermodynamic perturbation theory was proposed for the prediction of phase equilibrium surfaces, critical loci, three-phase lines, and azeotropic loci for mixtures containing constituents with strong directional intermolecular forces.
252 citations
TL;DR: In this article, the authors used pseudomonomolecular probes for microfluidity measurements in aqueous micellar solutions with sodium dodecyl sulphate, and showed that diphenylpropane showed a clearly lower micro-fluidity.
169 citations
TL;DR: In this paper, angle-dependent uv photoemission measurement has been used to study variations in the intermolecular polarization effect at the surface of thin condensed anthracene films.
Abstract: A type of angle-dependent uv photoemission measurement has been used to study variations in the intermolecular polarization effect at the surface of thin condensed anthracene films. The top molecular layer exhibits a 1.2-eV relaxation energy in response to the polarization of the hole state created in photoemission event. The second and subsequent layers exhibit a different value of about 1.5 eV. This result corresponds to the observation of a surface electronic molecular-ion state on a molecular solid.
165 citations
TL;DR: It is demonstrated that hydrophobicity is the major source of stabilization free energy in FMN binding to flavodoxin and in NAD binding to the two dehydrogenases: it contributes 25 to 30 kcal/mol to the free energy of dissociation, more than required in order to compensate for the loss of six degrees of translational/rotational freedom by the coenzyme.
Abstract: We calculate the loss of surface area accessible to solvent associated with coenzyme binding in Clostridium flavodoxin, in dogfish lactate dehydrogenase, and in lobster glyceraldehyde-3-phosphate dehydrogenase. The coenzymes are nearly buried in the complexes and lose on the order of 600 A*, while the proteins lose a similar amount of accessible surface area. Some of the loss can be attributed to conforma- tion changes in the protein, at least in the case of lactate de- hydrogenase, where we show that the apoenzyme has a larger Hydrophobic, electrostatic, and van der Waals forces are involved in all the various types of interactions made by the polypeptide chain of a protein: interactions with itself to fold into a globular structure; association with other chains to form multisubunit complexes; and the binding of small ligands. Thus when structural data are available from x-ray crystallography, the geometrical arrangement of polar atoms shows the presence of intra- and intermolecular hydrogen bonds and charge in- teractions and the volume of the Voronoi polyhedron around each atom describes the atomic packing (Richards, 1974; Chothia & Janin, 1975). The role of hydrophobicity can be assessed using the concept of accessible surface area (Lee & Richards, 1971). For a given protein atom this is the area of the surface over which the center of a water molecule can be placed while it is in van der Waals contact with the atom and not penetrating any other protein atom. Each square angstrom of protein accessible surface that is removed from contact with the solvent gives a hydrophobic free energy of 25 cal (Chothia, 1974). How do these different forces create the specific strong bonds that are essential for biological systems? From an analysis of the structure of the interfaces that occur between protein monomers, we concluded that hydrophobicity is the major force stabilizing protein-protein association; van der Waals forces and hydrogen bonds (i.e., complementarity) play
127 citations
TL;DR: In this article, a coherent distinct differential cross section was separated into intramolecular and intermolecular contributions for X-ray-diffraction studies on liquid acetonitrile at 20°C at a wavelength of 0·7 A.
Abstract: X-ray-diffraction studies on liquid acetonitrile at 20°C were carried out at a wavelength of 0·7 A. The data were corrected for polarization, absorption, Compton scattering and multiple scattering. The coherent distinct differential cross section was separated into intramolecular and intermolecular contributions. Whereas from the intramolecular coherent cross section the structure of the molecule in the liquid was determined, the intermolecular coherent cross section, together with intermolecular contributions from neutron-scattering data on CD3C14N and CD3C15N, was employed to determine three expansion coefficients of the molecular pair-correlation function.
TL;DR: Probable differences between corresponding helical forms of chondroitin 6-sulfate and dermatan sulfate are discussed both from the viewpoint of differences in the recorded diffraction patterns and in terms of the minimum stereochemical changes required by the different constitution of these related polymers.
TL;DR: Numerical comparisons with the best available data on the homonuclear inert-gas dimers are presented which demonstrate the accuracy one can obtain with this simple and computationally fast model.
Abstract: The assumptions made in the Gordon-Kim model for the forces between closed-shell systems are stated and their validity and limitations discussed. The model is compared with other interaction potential theories. The various modifications of the original model are classified and a more detailed discussion than hitherto of the reason and method for modifying the model is given. Two classes of modifications give a more reasonable description than the others. Two simplified models within one of these two classes are introduced here. Finally numerical comparisons with the best available data on the homonuclear inert-gas dimers are presented which demonstrate the accuracy one can obtain with this simple and computationally fast model.
TL;DR: In this paper, a theoretical interpretation of the OH stretching region of the vibrational spectrum of ice Ih derived from a study of extended models is presented. But the model is not suitable for the case where the intermolecular coupling is comparable in strength to the inter-atomic coupling.
Abstract: We describe a theoretical interpretation of the OH stretching region of the vibrational spectrum of ice Ih derived from a study of extended models. The principle conclusions are the following: (i) The breadth and distribution of vibrational modes, and of intensity in the Raman and infrared spectra, are dominated by the influence of strong intermolecular coupling. The intermolecular coupling is comparable in strength to the intramolecular coupling. Long range couplings between molecules not directly hydrogen bonded mainly serve to make the features of the spectrum more diffuse than they would otherwise be, but have no great influence on the spectral distribution. (ii) The intramolecular OH stretch‐OH stretch coupling in ice Ih is of opposite sign to that in the gas phase. (iii) The vibrational modes of ice Ih are found to be complex mixtures of molecular motions, so identification of regions of the Raman or infrared spectra with particular isolated molecule modes is not useful. Rather good agreement is obtained between the Raman and infrared spectra predicted and those observed. Some deficiencies of the model, associated with residual discrepancies between theory and experiment, are discussed.
TL;DR: In this paper, the Van der Waals theory of liquids is extended to nematogenic solutions and the molecular hard cores are taken to be spherocylindrical or spherical in shape and their contribution to the free energy of the system is evaluated using scaled-particle theory.
Abstract: In the Van der Waals theory of liquids, very short-ranged intermolecular repulsions are approximated by hard-particle exclusions and somewhat longer-ranged intermolecular attractions are subject to a self-consistent mean-field treatment. This approach, which has recently been applied to pure nematogens, is here extended to nematogenic solutions. The molecular hard cores are taken to be spherocylindrical or spherical in shape and their contribution to the free energy of the system is evaluated using scaled-particle theory. The general theory, applicable to mixtures of any number of rodlike or effectively spherical molecules is derived and its applications to various types of nematogenic systems are discussed. Finally, the way in which the theory could be modified to treat species whose molecular shapes cannot satisfactorily be approximated by spheres or spherocylinders is indicated.
TL;DR: In this article, a semi-empirical approximation for the exchange energy (E x ), coupled with a tractable representation of the Coulomb energy ( E C ), has been found to yield very accurate results for the isotropic part of the interaction energy between two closed shell systems.
TL;DR: The results of a critical review of vibrational data, their assignments, and force field constants of polyethylene and the related homologous series of n−alkanes are presented in this article.
Abstract: The results of a critical review of vibrational data, their assignments, and force field constants of polyethylene and the related homologous series of n‐alkanes are presented. The vibrational frequencies derived from Raman spectroscopy, infrared spectroscopy, and neutron inelastic scattering were collected from the literature. We have reviewed the vibrational band assignments starting from the comprehensive treatment of the n‐alkanes by Schachtschneider and Snyder [1,2]1 and including subsequent reassignments. Theoretical calculations of the vibrational frequencies were reviewed with emphasis on the various models used for molecular structure and force fields. Lattice dynamical calculations of polyethylene were performed using a valence force field for intramolecular interactions and a force field derived from a nonbonded atom‐atom potential function for intermolecular interactions. The molecular and lattice structural parameters were taken from x‐ray and neutron diffraction studies of polyethylene and s...
TL;DR: In this article, the moment of van der Waals forces between two anisotropic uniaxial thick plates separated by a thick gap filled with isotropic material is found.
Abstract: We find the moment of the van der Waals forces between two anisotropic uniaxial thick plates separated by a thick gap filled with isotropic material. Errors which occurred in [2, 3] in a discussion of this effect are pointed out.
TL;DR: Intermolecular pair-potential energy functions for all the unlike interactions of the monatomic gases were given by direct inversion of experimental measurements of low density binary mixture viscosity and diffusion coefficients.
Abstract: Intermolecular pair-potential energy functions are given for all the unlike interactions of the monatomic gases The potentials are obtained by direct inversion of experimental measurements of low density binary mixture viscosity and diffusion coefficients In those cases where these data extend to sufficiently low temperatures to enable the potential well depth e/k to be determined, the values obtained for this parameter are Kr-Xe 220 ± 5 K, Ar-Xe 170 ± 5 K, Ar-Kr 165 ± 10 K, Ne-Xe 70 ± 5 K, Ne-Kr 60 +10 -5 K, Ne-Ar 60 ± 5 K For the systems He-Xe, He-Kr, He-Ar and He-Ne only the repulsive branch of the potential energy function is obtained For all systems the potentials are shown to reproduce well other macroscopic data not used in their construction The agreement with thermal diffusion data is particularly encouraging The independent determination of this wide range of potentials provides a direct test of both the hypothesis that they are conformal and the validity of parameter mixing rules Signifi
TL;DR: In this paper, an intermolecular potential function describing the interaction between two rigid HF molecules has been obtained by fitting to the ab initio potential energy surface of Yarkony et al.
Abstract: An intermolecular potential function describing the interaction between two rigid HF molecules has been obtained by fitting to the ab initio potential energy surface of Yarkony et al. [J. Chem. Phys. 60, 855 (1974)]. In addition, allowance is made for the spherically averaged intermolecular dispersion interaction. The potential function so derived has been used in a molecular dynamics simulation of liquid HF at a temperature of T=278 K and a volume of 20 cm3 mol−1. Results for the radial distribution functions and the diffusion coefficient are presented.
01 Jan 1978
TL;DR: In this article, a critical review of vibrational data, their assignments, and force field constants of polyethylene and the related homologous series of n-alkanes are presented.
Abstract: : The results of a critical review of vibrational data, their assignments, and force field constants of polyethylene and the related homologous series of n-alkanes are presented. The vibrational frequencies derived from Raman spectroscopy, infrared spectroscopy, and neutron inelastic scattering were collected from the literature. We have reviewed the vibrational band assignments starting from the comprehensive treatment of the n-alkanes by Schachtschneider and Snyder and including subsequent reassignments. Theoretical calculations of the vibrational frequencies were reviewed with emphasis on the various models used for molecular structure and force fields. Lattice dynamical calculations of polyethylene were performed using a valence force field for intramolecular interactions and a force field derived from a nonbonded atom-atom potential function for intermolecular interactions. The molecular and lattice structural parameters were taken from x-ray and neutron diffraction studies of polyethylene and selected n-alkanes. A refinement procedure was carried out by the method of least squares on intramolecular force field constants and on parameters of a phenomenological nonbonded atom-atom potential energy function. The resulting force field constants and associated standard deviations are presented. (Author)
TL;DR: In this article, the intermolecular structure of liquid n-butane is studied with an application of the RISM integral equation, and it is found that the pair correlations between atoms in different nbutane molecules do depend upon the nature of the intramolecular trans-gauche conformational equilibrium.
Abstract: In this article the intermolecular structure of liquid n‐butane is studied with an application of the RISM integral equation. It is found that the pair correlations between atoms in different n‐butane molecules do depend upon the nature of the intramolecular trans–gauche conformational equilibrium. An incorrect picture of the liquid structure is obtained if it is assumed that the fluid is composed only of trans conformers—the species most favored energetically. The local packing of CH3 and CH2 groups in the liquid is discussed. Particular attention is focused on the prediction of the Chandler–Pratt theory, which says that steric effects produce a solvent shift in conformational equilibria in liquid n‐butane. It is shown that x‐ray diffraction experiments can provide a direct probe of this phenomenon.
TL;DR: In this article, the total vapour pressure of the systems hydrogen bromide + xenon and hydrogen Bromide+ hydrogen chloride was measured as a function of composition at 195.42 K. The results were used to estimate the excess Gibbs function GE.
Abstract: The total vapour pressure of the systems hydrogen bromide + xenon and hydrogen bromide + hydrogen chloride have been measured as a function of composition at 195.42 K. The results have been used to estimate the excess Gibbs function GE. The volume of mixing VE has been determined for each system at 195.42 K. The HBr + Xe system departs considerably from ideal behaviour, while HBr + HCl is only slightly nonideal. Neither system exhibits an azeotrope at the temperature studied. These results, together with similar data reported previously for the HCl + Xe system (J.C.S. Faraday I, 1975, 71, 1372), are compared with theoretical calculations based on perturbation theory for liquids of nonspherical molecules. Agreement is good for all three systems. The results show that both dipolar and quadrupolar forces for the HCl and HBr molecules have a large effect on the phase diagram, while other types of anisotropic intermolecular forces (overlap, dispersion, induction) appear to have a considerably smaller effect.
TL;DR: In this article, a pair-potential energy function for all the unlike interactions of the monatomic gases was derived by direct inversion of experimental measurements of low density binary mixture viscosity and diffusion coefficients.
Abstract: Intermolecular pair-potential energy functions are given for all the unlike interactions of the monatomic gases. The potentials are obtained by direct inversion of experimental measurements of low density binary mixture viscosity and diffusion coefficients. In those cases where these data extend to sufficiently low temperatures to enable the potential well depth e/k to be determined, the values obtained for this parameter are Kr-Xe 220 ± 5 K, Ar-Xe 170 ± 5 K, Ar-Kr 165 ± 10 K, Ne-Xe 70 ± 5 K, Ne-Kr 60 +10 -5 K, Ne-Ar 60 ± 5 K. For the systems He-Xe, He-Kr, He-Ar and He-Ne only the repulsive branch of the potential energy function is obtained. For all systems the potentials are shown to reproduce well other macroscopic data not used in their construction. The agreement with thermal diffusion data is particularly encouraging. The independent determination of this wide range of potentials provides a direct test of both the hypothesis that they are conformal and the validity of parameter mixing rules. Signifi...
TL;DR: In this article, a model for the ammonia dimer with Coulombic and dispersion interactions for asymptotically large intermolecular separations is presented, where the second virial coefficient of the gas together with the known structure and binding energy of the solid is used to constrain the parameters of short range interatomic interactions.
Abstract: Model interatomic potential energy functions are presented for the ammonia dimer (NH3)2 which have the correct Coulombic and dispersion interactions for asymptotically large intermolecular separations Existing data for the second virial coefficient of the gas together with the known structure and binding energy of the solid are used to constrain the parameters of the short range interatomic interactions Finally, new experimental results for the differential collision cross section of NH3+NH3 are used to test the proposed potential energy functions
TL;DR: It is shown, albeit heuristically, that this type of environment may be represented with the combined effect of a reaction field and an inhomogeneous external electric field acting over the site system, this latter being provided by the main chain dipolar peptide residues.