Dielectric Constant Of Medium Research Articles

Carrier mediated ion transport through artificial liquid membranes in relation to thermodynamic and structural properties of membrane macromolecules

A study has been made of the carrier mechanism of the migration of cations through a non-aqueous liquid membrane. The liquid membrane is a layer of a solution of an amphipatic polyacid—the alternate copolymer of maleic acid and hexadecyl vinyl ether—in N-octanol. The membrane separates two aqueous solutions containing a mixture of electrolytes NaCl and CaCl 2 at varying pH. A description of the thermodynamic and structural properties of the polymer in N-octanol is given. Flux measurements of cations across the membrane are reported for symmetrical situations (unidirectional fluxes) and in the case of asymmetry when the acid and salt concentrations in the aqueous phase were different. In the latter case, incongruent fluxes of sodium ions are found and the mechanism of countertransport is analyzed quantitatively on the basis of the thermodynamic data relating to the affinities of the polymeric acid sites towards alkali and alkaline-earth metal ions in the low dielectric constant medium.

Investigation of the active site of papain with fluorescent probes.

7-Chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD chloride) and 7-(2'-hydroxyethylthio)-NBD (obtained from NBD chloride and mercaptoethanol) undergo a reversible spectral change in alkaline solution that depends respectively on a single apparent pK(a) 9.76 (at 25 degrees C) and 8.81 (at 32 degrees C). In acid solution however no spectral change was observed. NBD chloride reacts slowly with papain at pH7, but the rate of inhibition increases at lower pH and depends on an apparent pK(a) of 3.7 (at 35 degrees C), which has been tentatively assigned to the carboxyl group of aspartic acid-158. The spectral properties of NBD-papain indicate that the thiol group of cysteine-25 is the site of reaction. The intensity of the fluorescence-emission spectrum of NBD-papain depends on a single pK(a) of 4.2 (at 26.7 degrees C). The intensity of the fluorescence-emission spectrum of the mixed disulphide formed from papain and 7-(2'-mercaptoethylamino)-NBD (obtained from NBD chloride and cysteamine) depended on a single pK(a) of 3.94 in water and 3.89 in aq. 19.2% (v/v) dioxan (at 27 degrees C). This small change to lower pK(a) value in a medium of lower dielectric constant is characteristic of a cationic acid. The only acid of this type in the active-site region is the conjugate acid of histidine-159.

A Study of Solute–Solvent Interaction in Solvents of Medium Dielectric Constant from the Apparent Molal Volume Data. I

Abstract A study of the apparent molal volume (φv) of some common salts and the tetraalkylammonium iodides in DMSO has been reported in this communication. All the salts studied here, including those containing the larger R4N+ ions, have a positive slope in the φv vs. \sqrtC curves, indicating a strong ionic interaction, apparently due to the medium dielectric constant of the solvent. This dielectric constant also promotes ion-association at higher concentrations and thus mutual penetration of the R4N+ ions is prevented. As a result, no negative slope in the φv vs. \sqrtC curves of the larger R4N-iodides is observed in this solvent. The effect of temperature on the limiting apparent molal volume, φ°, reveals that the ion-solvent interaction is comparatively stronger in the non-hydrogen bonded solvents like DMSO and DMF than that in strongly hydrogen-bonded solvents like NMA and NMP. Addition of a CH2-group to each of the four R-chains of the R4N+ ion increases its volume by about 70 ml per mole in DMSO, DMF, and NMA.

Analysis of interdigitated thin film capacitors

A thorough analysis is made of geometrical effects on the capacity and dissipation factor of gold and thermally anodized tantalum interdigitated thin film capacitors. These capacitors are realized by deposition of a thin film conductor over a substrate with a medium dielectric constant. A series of evaluation tests under several environmental conditions and for both the deposited layers is given, together with a report of the behavioural analysis of the parameters which characterize the capacitors at different working frequencies. Examples of applications at both high and low frequencies with considerations about stability for the two types of conductor materials and choice criteria are then presented for the range of values from 1 to 30 pF, which are those in practical use.

Electrostatics of Diffuse Anisotropic Interfaces. III. Point Charge and Dipole Image Potentials for Air-Water and Metal-Water Interfaces

Within the framework of macroscopic continuum theory, the point charge and point dipole image potentials in the presence of a diffuse dielectric interface are calculated. We consider the cases of both short and long range diffuseness for air-water interfaces. In the first category we propose a model profile for which the charge image potential is devoid of singularities and is an integral over elementary functions. The calculated image potential goes through a maximum and minimum as the charge is taken from the high to the low dielectric constant medium. The heights of the maximum and minimum may be estimated in terms of a physical cutoff, characteristic of the gradient of the dielectric constant, D, in the diffuse region, using the crude model of an abrupt interface. For a diffuse layer, the very large but finite electrostatic barrier for an ion is determined by the ratio of a distance characteristic of the bulk electrolyte and a distance characteristic of the maximum gradient of D. The image potential for a point dipole, normal or tangential to the diffuse interface, is exhibited in the repulsive region, for the long range diffuse interface. For metal-water interfaces, encountered in electrochemistry, the effects of diffuseness of the inner region, adjacent to the metal, are examined. One effect of diffuseness is to remove singularities in the image potential and to increase it in the relevant part of the inner region. The other effect is to decrease the effective attractive interaction between charges. For both the air-water and metal-water interfaces, the limitations of the commonly used constant dielectric profile are discussed.

Conformation of polymer analogs in solution. X‐ray scattering from ethylene oxide oligomers carrying iodine atoms at the chain ends

AbstractThe angular dependence of X‐ray scattering intensities of solutions of diiodobenzenes was compared with that of iodobenzene solutions containing the same concentration of iodine atoms. The data yielded interiodine distances of 3.6, 5.9, and 6.9 Å for the ortho, meta, and para isomers, respectively, in good agreement with the known values of 3.52, 5.92, and 6.84 Å. The same method was applied to a study of inter‐iodine separations in ICH2CH2(OCH2CH2)nI (n = 1, 2, 3) using CH3CH2OCH2CH2I as the monoiodo analog. Experimental limitations preclude detailed interpretation of the data in terms of a probability distribution of the end‐to‐end distances of these model compounds. The intramolecular inter‐iodine distances were characterized by the first minimum and the first maximum of the scattering function i(s) = ΔĪcorr/f, where ΔĪ is the difference in the scattering intensity from solutions of the diiodo and monoiodo compounds corrected for polarization, fI is the form factor of iodine and s = 4π sin Θ/λ, 2Θ is the scattering angle and λ the wavelength of the X‐rays. The molecular chains of all three oligomers were significantly more expanded in m‐xylene than in ethanol, the difference increasing with increasing chain length. A conformational analysis was carried out for ICH2CH2OCH2CH2I choosing the energies for conformational transition so as to yield a conformational distribution with the observed average square dipole moment and scattering function in non‐polar media. The contraction of the molecule in ethanol is much larger than can be accounted for by the reduction in the COULOMBic energy of dipole interaction in a medium of higher dielectric constant.

The Effect of Pressure on the Rate of the Acid-catalyzed Hydration of Propylene

Abstract In order to confirm whether a water molecule (or molecules) is held in a protonated activated complex by electrostatic interaction or by a partial valence bond, the pressure dependency of the activation volume, ΔV\ewq, for the hydration of propylene was measured at 180°C. The pressure effect on the rate of the hydration of propylene was studied in such dilute sulfuric acid solutions of a 0.0000108 mole fraction (0.00060n under S.T.P.) that the dielectric constant, D, and the density of pure water could be replaced for those of the reacting solution. The absolute value of the ΔV\ewq decreases steeply from 19 ml/mol at 300 kg/cm2 to 4 ml/mol at 5000 kg/cm2. The activation energies and entropies, obtained from the temperature dependency of the reaction rate, are 22.7 kcal/mol and −16.6 e.u./mol respectively at 1000 kg/cm2 and 21.9 kcal/mol and −17.0 e.u./mol respectively at 3000 kg/cm2. The ΔV\ewq is approximately proportional to the −∂D⁄D2∂p value, (D: dielectric constant of medium; p: pressure), which follows from the Krichevski equation; hence, it was concluded that the contraction of water around an activated complex by electrostatic interaction contributes to the ΔV\ewq and that a water molecule (or molecules) is held in the activated complex by electrostatic interaction. The case of a water molecule being held by a partial valence bond was discussed in terms of the molar volumes of the reactants.

Synchronization of gas-laser modes during modulation of the dielectric constant of the medium

In a calculation of the regions in which the modes of a gas laser are synchronized during modulation of the dielectric constant of the laser medium, two synchronization regions are found. The synchronization band in one of them is much higher than that in the other. The calculated results are confirmed experimentally, and it is shown that when the modes are synchronized the fluctuations in the radiation intensity are 20–30 dB below their level in the absence of synchronization.

Kinetics of the trypsin-catalyzed hydrolysis and ethanolysis of l-lysine methyl ester

1. 1. The reaction of l-lysine methyl ester (LME) and trypsin in aqueous ethanol yields in the first place methanol, lysine and l-lysine ethyl ester (LEE). LEE is then acted upon by trypsin to give lysine and ethanol. Hence, kinetics are complex and involve 4 rate constants and 2 equilibrium constants. 2. 2. An attempt was made to determine Michaelis constant ( K m ) and catalytic rate constant ( K cat ) for the first reaction, i.e. trypsin-catalyzed cleavage of LME, by analyzing the composition of reaction mixtures at early stages in order to have a ratio LEE:LME as small as possible. 3. 3. At pH 6.5 the reaction follows Michaelis kinetics, but at pH 8.5 double reciprocal plots become curved suggesting activation by excess substrate. Apparently the number of substante molecules bound per enzyme molecule increase as dielectric constant decreases. 4. 4. The value of k eat for the overall reaction increases as alcohol concentration increases. This effect may be ascribed mainly to an enhanced alcoholysis. The ratio of deacylation constants k 4:k 3 (alcohol:water) is also modified by a change of the medium dielectric constant. From the results presented here the suggestion is possible that the principal effect of lowering the dielectric constant is to increase the rate of acylation with respect to that of dissociation of Michaelis complex.

Magnetic nonequivalence in asymmetric phosphorus compounds

The nuclear magnetic resonance (n.m.r.) spectra of seven compounds of the type (CH3)P(O)(SCH2SR)(OR′) have been examined as a function of solvent. The resonance pattern of the methylene protons, SCH2S, is strongly solvent dependent. In solvents of low dielectric constant, the methylene protons are magnetically nonequivalent and are observed as the AB part of an ABX spin system, where X is the phosphorus atom. In high dielectric constant medium (DMSO d6) only a well-resolved doublet is obtained indicating magnetic equivalence. When R′ = CH(CH3)2, nonequivalent methyl groups which show analogous solvent effects are observed.Eight compounds of the type (CH3)P(O)(OCH(CH3)2)(X) have been studied. The chemical shift between the magnetically nonequivalent isopropyl methyl groups does not correlate with any simple property of X.

Dielectric diffusion--a new cross phenomenon.

When an electric field interacts with a medium of inhomogeneous dielectric constant, there is a flow of matter in the direction of increasing dielectric constant. The process may be relevant to the study of biological membranes.

Proton Magnetic Resonance of Dimethyl Phthalates

We have studied the high-resolution proton magnetic resonance spectra of the ring protons in dimethyl phthalate, dimethyl isophthalate, and dimethyl terephthalate. The proton chemical shifts were determined relative to benzene in a series of solvents of widely varying dielectric constant, with both species at infinite dilution. This effectively removes the solvent van der Waals contribution to the observed shifts, and the remaining shifts are in accord with Buckingham's theory of dielectric reaction fields. Extrapolation to a medium of unit dielectric constant was performed in order to obtain chemical shifts typical of isolated molecules. These values were then approximately corrected for intramolecular electric and magnetic fields. For the two nearly planar molecules, the corrected values were correlated with pi-electronic charge densities obtained by Hückel molecular-orbital calculations. The failure of this correlation in the case of dimethyl phthalate can be attributed to the large deviations from planarity due to extreme steric hindrance.

Theoretische Behandlung der Solvatochromie polarer Farbstoffe am Beispiel des Pyridinium-cyclopentadien-ylids und Pyridinium-N-phenol-betains

The solvent effects on the electronic spectra of two polar organic dyes: pyridinium-cyclopentadien-ylid (I) and pyridinium-N-phenol-betain (II) are predicted and shown to be in agreement with experimental results. The solvatochromic behavior of the dyes is related to a medium of dielectric constant 2 and not as it is usually done to a vacuum. This method leads to the problem of calculating the dipole moments and molecular polarizabilities of the ground state and the excited states of the dye molecules in a medium of dielectric constant 2. Procedures for calculating these molecular constants are given.

π-Elektronen-Dipolmoment eines Pyridinium-N-phenol-betains

The ground state dipole moment of the π-electrons of 2.4.6-triphenyl-N- [3.5-di-tert-butyl-4-hydroxy-phenyl] -pyridinium-betain I, a highly solvatochromic substance, was determined by measuring the dielectric constant of a dilute solution and calculating first the dipole moment of the whole system (σ- and π-electrons) using the method of HALVERSTADT and KUMLER. The dipole moment of the π-electrons was then calculated, asuming the π-electron dipole to be imbedded in a spherical medium of dielectric constant 2. The value calculated by this method was compared with the π-electron dipole moment directly obtained from the dielectric constant of the dilute solution using a method of H. KUHN. This method is based on the assumption that a π-electron of a dissolved molecule sees the σ-electrons of the molecule and of the surrounding solvent, a saturated hydrocarbon, as a continuous uniform medium of dielectric constant 2. Thus the π-electron dipole of the solute molecule is regarded as being imbedded in a continuous medium of dielectric constant 2. It was found that the values of the π-electron dipole moments determined by the two methods agree well. Furthermore these experimental values agree with a theoretical value obtained in the case of N- [4-hydroxy-phenyl] -pyridinium-betain II using the one dimensional electron gas method including electron repulsion. The order of magnitude of the π-electron dipole moment of I clearly shows that the ground state of this molecule is highly polar.

Conductivity of graham salt solutions in media of different dielectric constants

Conductivities of Graham Salt solutions in dioxane-water and acetone-water mixtures have been measured and a plot of reciprocal of the dielectric constant of the medium against the logarithm of equivalent conductivity is found to be linear in all cases studied. The phenomenon is explained on the basis of the ideas of Fuoss on association of polyions with counterions.

Generalized Plots of Mode Patterns in a Cylindrical Dielectric Waveguide Applied to Retinal Cones

Generalized curves are presented which describe the characteristics of the 12 lowest cutoff-frequency modes of an electromagnetic wave propagating down an infinite lossless dielectric rod, surrounded by an infinite Iossless medium of lower dielectric constant. These curves were developed by a computer study particularly to analyze the optical mode patterns generated within the photosensitive portions of the cones of the retina. However, they should also be particularly useful in the study of fiber optics and dielectric microwave antennas.

The Ionic Strength Function for Strong Electrolytes in Anhydrous Acetic Acid

As an adjunct to the Debye-Hiickel theory, this function permits the direct calculation of the mean activity coefficient of an electrolyte at solute concentrations within the range 0.0 to nearly 0.1 M. The ionic strength concept has been applied to electrolytes dissolved in nonaqueous solvents, including water-containing binary systems and one-component solvents, having dielectric constants well below that of water. Because of the ionic association of strong electrolytes in low dielectric constant media, the simple Debye-Hiickel limiting law expressed in terms of does not apply. However, this theoretical restriction has been overcome in some instances by viewing such electrolyte-nonaqueous solvent systems as being analogous to concentrated aqueous solutions that require the more general Debye-Hiickel equation(5). Attempts were made to test the Debye-Hiickel theory in several early investigations on the anhydrous acetic acid solvent system. In each case the ionic strength was computed directly from equation 1. The acid-base indicator studies by Conant and Werner(3) included plots of pK for the

Upper and Lower Bounds for Ground-State Second-Order Perturbation Energy

The first-order perturbation equation, using the Dalgarno—Lewis formulation, is arranged in a form analogous to the Poisson equation for the electrostatic potential produced by a charge distribution in a medium of variable dielectric constant. Thus, the Thomson and Dirichlet variational principles of electrostatics can be used to obtain approximate solutions to the first-order perturbation equation for systems in either the ground state or the lowest energy state of a given symmetry. The Thomson principle provides a useful lower bound to the second-order perturbation energy. The Dirichlet principle is derivable from the Rayleigh—Ritz or Hylleraas principles and gives an upper bound to the second-order energy. For excited states, the Sinanoğlu principle provides the upper bound. By optimizing the scaling of the trial perturbed wavefunction, the Hylleraas principle is presented in a somewhat improved form. As an example, the polarizability of atomic hydrogen is used to illustrate both the Thomson and Dirichlet principles and to place upper and lower bounds on the polarizability.

Proton Chemical Shifts and Pi-Electron Distributions in the Hydroxy-Benzenes

The proton magnetic resonance spectra of phenol, hydroquinone, catechol, resorcinol, and pyrogallol have been studied, and the chemical shifts of the aromatic protons relative to benzene determined. The chemical shifts for the isolated molecules were obtained by making measurements in two solvents and extrapolating to a medium of unit dielectric constant. The electric fields at the protons from the C–O and O–H bond dipoles were calculated, and their contributions to the proton chemical shifts were removed by employing the approximate relation derived by Buckingham. It was assumed that the remaining parts of the chemical shifts were due to changes in the pi-electron distributions. Hückel molecular orbital calculations were performed, and it was shown that the corrected chemical shifts, δi, can be expressed in the form δi=aqi+a′qi′+a′′qi′′,where qi is the excess number of pi electrons on the ith carbon atom, qi′ is the sum of those on the two adjacent carbon atoms, and qi″ is the sum of those on any oxygen atoms ortho to the ith proton. The constants a, a′, and a″ were evaluated by fitting the chemical-shift data with a least-squares procedure. The derived constants depended sensitively on the values chosen for the necessary Coulomb and resonance integrals. It was not possible to conclude whether sigma inductive effects should be included or not, so it is suggested that they be omitted for the time being. By requiring reasonable values for the constants, i.e., a≅7, a′≅1, and a″≅0 ppm/electron and searching for closest agreement between calculated and observed chemical shifts, it was possible to choose as the most appropriate molecular orbital parameters, αO=αC+0.75 βCC, and βCO=1.0 βCC.

Coagulation of ferric oxide sol by organic solvents

The coagulation of ferric oxide sol by several organic solvents, such as ethyl alcohol, has been studied. It has been observed that the coagulation takes place when the dielectric constant of medium is lowered to a certain critical value for coagulation by the addition of any organic solvent. The lowering of dielectric constant of medium is accompanied by the contraction of electrical double layer around sol particle, which leads to coagulation.