Solutions Of Polar Molecules Research Articles

A new technique for the determination of the polarizability anisotropy of intramolecular charge transfer molecules

We present an original set-up for the determination of the polarizability anisotropy Δα of polar molecules in solution. The technique is based on electric field-induced ellipsometry measurements and the analysis takes into account the contributions of the orientational birefringence and the electro-optic Pockels effect to the total refractive index change of the studied solutions.

Attractive potential effect on the self-diffusion coefficients of a solitary water molecule in organic solvents

H 1 -Fourier-transform pulsed field-gradient spin-echo NMR method is applied at 30 °C to measure the self-diffusion coefficients of water, acetonitrile, and benzene in dilute organic solutions of carbon tetrachloride, benzene, chloroform, dichloromethane, acetonitrile, acetone, and water. The dependence of the translational friction coefficients ζT of the apolar solute molecule, benzene, on solvent viscosity η is linear as predicted by the simple hydrodynamic theory. The η dependence of ζT of the polar solute molecule, acetonitrile, is linear, though the slope is different in apolar and polar solvents. The η dependence of ζT of the hydrogen-bonding solute molecule, water, is nonlinear and dependent on the strength of the solvent as a proton acceptor. The breakdown of the hydrodynamic theory is discussed in terms of the attractive part of the solute–solvent interaction. The role of the attractive interaction is illustrated through a linear relationship between the proton chemical shift of water and the residual friction coefficient, which is defined by removing the repulsive component from the overall translational friction coefficient.

Theory of solvent effects on electronic absorption spectra of rodlike or disklike solute molecules: Frequency shifts

A theory, which has been advanced by the author and his co-workers, for frequency shifts of electronic absorption spectra of a nonpolar rodlike molecule in dilute nonpolar and polar solutions is extended so that it is applicable to a polar rodlike solute molecule and a nonpolar or polar disklike solute molecule. The theory takes into account higher-order multipole moments (in addition to a dipole) of the solute molecule, and its solution-phase polarizabilities are properly taken into account. Furthermore, it explains how the dispersive interaction is altered by the presence of permanent dipoles of the solvent.

Classical electrostatics in biology and chemistry.

A major revival in the use of classical electrostatics as an approach to the study of charged and polar molecules in aqueous solution has been made possible through the development of fast numerical and computational methods to solve the Poisson-Boltzmann equation for solute molecules that have complex shapes and charge distributions. Graphical visualization of the calculated electrostatic potentials generated by proteins and nucleic acids has revealed insights into the role of electrostatic interactions in a wide range of biological phenomena. Classical electrostatics has also proved to be successful quantitative tool yielding accurate descriptions of electrical potentials, diffusion limited processes, pH-dependent properties of proteins, ionic strength-dependent phenomena, and the solvation free energies of organic molecules.

Solvation thermodynamics of polar molecules in aqueous solution by the XRISM method

The aqueous solvation free energies and the average solute-solvent interaction energies of a diverse set of organic molecules were calculated by the XRISM (extended reference interaction-site model) method for two related potential-energy functions based upon the optimized potentials for liquid simulation (OPLS) parameter set. The results are compared with available data obtained from experimental and other theoretical methods. The XRISM method with the given potential-energy function parameter sets produces reasonable free-energy values for a number of molecules but not for all of the molecules studied. For some molecules, the results were also quite sensitive to the potential-energy function parameters used

Fluorescent molecules as probes for the characterization of mineral oils degradation processes

In this work we study the spectroscopic behaviour of certain organic polar molecules in solution versus their surrounding environment, resolving their fluorescence spectra into some of their emission bands. The results obtained are applied to the characterization of the degradation process in mineral oils. In particular, data obtained for Vestan oil with N-methylindole as polar probe are presented.

Three-dimensional lattice model of TIP4P water molecules and of polar monomeric and dimeric solute molecules against a charged wall

A three-dimensional lattice model of TIP4P water molecules in the presence of polar monomeric and dimeric solute molecules against a charged wall is described. The statistical-mechanical treatment of this model is carried out on the basis of a generalization of Barker's self-consistent field theory (J.A. Barker, J. Chem. Phys., 44 (1966) 4212), without introducing adjustable parameters to account for the behaviour of interfacial water molecules. The adsorption isotherms calculated for a dimeric solute consisting of a polar “head” and a non-polar “tail” compare favourably with the experimental behaviour of simple monofunctional aliphatic compounds on mercury from aqueous solutions.

On the correlation factor of pure polar fluids whose molecules dimerize to nonpolar dimers

The dipolar correlation of pure polar fluids whose molecules undergo dimerization, resulting in the formation of nonpolar ring dimers and polar monomers in statistical equilibrium, has been studied. Such a system has been treated as a solution of polar molecules (monomers) in an apolar solvent (dimers). This approach allowed us to introduce a new parameter that accounts for the correlation among polar monomers, besides the well known Kirkwood-Frohlich correlation factor. A relation between the two correlation factors, involving the degree of association, has been established. The above summarized model was applied to the case of five monocarboxylic fatty acids: propionic, n-butyric, n-valeric, caprylic, and pelargonic. On going from high to low molecular mass terms the room temperature static dielectric constant of the considered series of acids increases together with the degree of association, obtained from adiabatic compressibility data on the hypothesis that only dimerization occurs. This behaviour of...

Relationship between energy gap time correlation and fluorescence stokes shift correlation functions in solvation dynamics

The relationship between the energy gap time correlation function (EGTCF), measured in optical lineshape experiments, for a charged particle in a polar liquid, and the time correlation function obtained from time-dependent fluorescence Stokes shift measurements is explored. We show that if the distortion of the host solvent by the polar solute molecule is neglected, then both provide the same dynamical information. In the presence of a sizeable solvent distortion, emission and absorption lineshapes and Stokes shift measurements are all influenced differently by the solvent dynamics.

Force constants of solvent polarization fluctuations: Softening at intermediate wave vectors

A microscopic calculation of the wave vector (k) dependent force constant [K(k)] of solvent polarization fluctuations in a dipolar liquid is presented. We find that the force constant of the pure liquid undergoes a pronounced softening at intermediate wave vectors (kσ≂2π, where σ is the solvent molecular diameter). An analysis of the modification of the solvent polarization force constant because of the presence of a polar solute molecule is also presented. In agreement with the calculation of Carter and Hynes, we find that this modificaton is a nonlinear effect. In the present density-functional theory, the contribution of the solute enters through the space- and orientation-dependent triplet direct correlation function. We use the convolution approximation of the triplet direct correlation function to derive an analytic expression for the solute-induced contribution to both free energy and force constant. A preliminary numerical calculation shows that the long-wavelength (k→0) force constant increases because of the presence of the solute, which is in agreement with Carter and Hynes and also with Kakitani and Mataga. The significance of these results in charge transfer processes in a dipolar liquid is discussed.

Dynamics of Solvation and Charge Transfer Reactions in Dipolar Liquids

The effects of solvent and solvent dynamics on chemical reactions, especially on charge transfer processes, have long been a subject of great importance in physical chemistry. In the past, attention was focused pri­ marily on equilibrium solvent effects, such as the effect of solvent polarity on the reaction potential surface. Tn recent years it has become clear that in many fast reactions solvent dynamics can play a direct role and can affect both the rate and the outcome of a reaction profoundly. Thus, an understanding of the time-dependent response of a polar solvent to a changing charge distribution in a polar solute molecule is essential to understand the role of solvent in many important chemical and biological processes in liquids. Such understanding can be achieved by studying the dynamics of solvation of a newly created ion or of an instantaneously changed dipole in a polar liquid. This subject has undergone a renaissance in recent years because of the availability of ultra-short laser pulses that make it possible to study solvation dynamics directly with a time resolution hitherto impossible. An understanding of the details of solvent response to a sudden change in the charge distribution of a polar solute probe molecule is beginning to emerge. Experimental studies on the dynamics of solvation are usually carried out by instantaneously creating a charged species inside a polar solvent and subsequently monitoring the emission/absorption spectrum of this

Theoretical Treatment of Solvent Effects on the Frequency Shifts of Fluorescence Spectra

Abstract A theoretical expression for the solvent fluorescence spectral shifts of a neutral solute molecule has been developed by following the same treatment as in Abe’s expression for solvent absorption spectral shifts (Bull. Chem. Soc. Jpn., 54, 327 (1981); 58, 3415 (1985)). Compared with all previous applicable expressions being applied to only polar solute molecules, the present expression has the advantage that it can be applied to not only the polar solute molecules but also nonpolar solute molecules. The polarizabilities of the ground and excited states concerning fluorescence are treated as being different from the corresponding values concerning absorption. Applications to nonpolar solute molecules are successfully presented.

1H nuclear magnetic resonance and molecular orbital studies of the structure and internal rotations in ethylbenzene

Rather extensive geometry-optimized computations at the STO-3G, 4-21G, 4-31G, and 6-31G levels of abinitio molecular orbital theory suggest that the fourfold component of the barrier to internal rotation about the Csp2—Csp3 bond in ethylbenzene amounts to about 20% of the twofold component. The 1H nuclear magnetic resonance spectral parameters, extracted by complete analyses of the spectra arising from the ten protons, are reported for ethylbenzene in acetone-d6, CCl4, CS2, and perfluoromethylcyclohexane solutions. The long-range proton–proton spin–spin coupling constants demonstrate that the internal barrier is insensitive to the polarity of the solvent, in contrast to polar solute molecules such as benzyl fluoride. The coupling constants do not support a dependence of the internal barrier on the internal pressure of the solvent.

Current technological challenges in capillary supercritical fluid chromatography

AbstractIn cases where high efficiency is required to resolve complex mixtures of either thermally labile or nonvolatile organic compounds, capillary supercritical fluid chromatography may be the most desirable analytical method. While great strides in this new technology have been made over the last few years, several problem areas are requiring increased attention. These include sample introduction systems, pressure reduction at the end of the column, column stability in various supercritical mobile phases, and migration of polar solute molecules. This paper describes the state‐of‐the‐art in capillary SFC with emphasis on the progress made and future needs in the solutions to these specific problems.

Solvent Effects on the nπ* and ππ* Absorption Intensities of Some Organic Molecules

Abstract Recently proposed experimental and theoretical expressions for the molecular electronic oscillator strength in a solution (J. Chem. Phys., 83, 1546 (1985)) have been succesfully applied to the spectral data of some nonpolar and polar organic molecules (benzoquinones, ketones, nitroalkanes, β-carotene, and substituted benzenes). In an application of the theoretical expression, the transition moment of a nonpolar solute molecule in various solvents was assumed to be approximately constant, while that of a polar solute molecule was developed on the assumptions of a first-order perturbation of the wave function and a Block–Walker reaction field. The ratio of the oscillator strength in a solution to that either in a vapor or a specified solvent was computed from both experimental data and theoretically from the transition moments. The results of the two computational modes are, generally, in good agreement for the range of compounds studied.

Far-infrared spectra of strongly polar molecules in solid solution: Acetone and nitromethane

Both acetone and nitromethane suspended in a solid gas matrix form exclusively antiparallel dimers (point group C 2 h ) which exhibit two ir-active intermolecular vibrations in the spectral interval between 90 and 130 cm −1. The intermolecular interactions are predominantly dipoledipole forces, with some evidence for a slight contribution of hydrogen bonding between methyl and nitro groups of the two constituents of the nitromethane dimer. Apart from characteristic isotope shifts of the band positions on deuteration, an extraordinary intensity increase is observed for one of the far-ir bands when the acetone dimer is deuterated. This effect is explained by considering the free volume which is required by the respective intermolecular normal vibration in relation to the restricted cage dimensions. In addition to the dimer bands which appear at sufficiently high concentrations and after annealing the matrix, monomer absorptions occur which must be assigned to collision-induced translational and rotational motions of perfectly isolated monomer molecules with respect to the solid cage of the matrix.

Electrohydrodynamic effects in dielectric relaxation

We consider a polar molecule immersed in a fluid and study several effects of electrohydrodynamic coupling. The molecule performs oscillatory rotational motion and is subjected to an oscillatory applied electric field. A resistance matrix relates the torque on the molecule and its external dipole moment to the angular velocity and the field. We show that electrohydrodynamic coupling leads to a frequency dependence of the resistance matrix. We study the consequences for the effective dielectric constant of a dilute solution of polar molecules. We also develop a self-consistent theory of the dielectric constant of a polar fluid which at zero frequency leads to a modification of a formula proposed by Fatuzzo and Mason and by Nee and Zwanzig.

Performance of a fast atom bombardment source on a quadrupole mass spectrometer

A saddle field fast atom bombardment gun was installed on a quadrupole mass spectrometer and its performance evaluated. Only some minor modifications to a standard gas chromatography mass spectrometry system were required to accommodate this source. Using xenon as the bombarding atom, measurements were made with respect to sensitivity, background effects, sample type, calibration of the data system and other parameters pertinent to the operation of a fast atom bombardment source on a quadrupole system. The simplicity of operation and its unique ability to produce gaseous ionic species from highly polar molecules in solution make it an ideal complement to other mass spectrometric ionizing devices.

Far Infrared Spectra of Strongly Polar Molecules in Solid Solution. III. Cyanoacetylene, Cyanogen Chloride, and Propionitrile

AbstractThe spectral range around and below 100 cm−1 yields information on the intermolecular motion of molecules. In solid rare gas matrices aprotic molecules such as cyanogen chloride and propionitrile behave similarly to acetonitrile, which has previously been studied. All of these compounds are trapped in the matrix both as monomers and as antiparallel dimers, each of which exhibits a characteristic absorption spectrum uniquely related to intermolecular motions. H‐bonding compounds such as cyanoacetylene or hydrogen cyanide may be present in a solid rare gas matrix in the form of at least three different species: (a) isolated monomer molecules, (b) linear dimers, and (c) chainlike multimers. Each of these three species provides a characteristic far IR absorption pattern, which is, again, uniquely related to intermolecular motions.

Solute-solvent interaction in liquids

The infrared absorption spectra of HCl and DCl in dilute CCl4 have been recorded over a range of temperatures. The band shapes have been analysed using the method of moments, allowing both the rms torque and rms force acting on the solute to be determined as functions of temperature. It is shown that rotation-translation coupling makes a significant contribution to the dynamics of these polar molecules in solution.