Excess Polarizability Research Articles

Comparison of in vitro membrane permeabilities of diverse environmental chemicals with in silico predictions

The parallel artificial membrane permeability assay (PAMPA) is widely used for estimating biomembrane permeabilities of experimental drugs in pharmaceutical research. However, there are few reports of studies using PAMPA to measure membrane permeabilities of chemicals of environmental concern (CECs) outside the pharmaceutical domain, many of which differ substantially from drugs in their physicochemical properties. We applied PAMPA methods simulating gastrointestinal (PAMPA-GIT) and blood-brain barrier (PAMPA-BBB) membranes under consistent conditions to 51 CECs, including some pharmaceuticals. A backward stepwise multivariate linear regression was implemented to explore the correlation between the differences of measured permeabilities from PAMPA-GIT and PAMPA-BBB and Abraham solute descriptors. In addition, a previously reported in silico model was evaluated by comparing predicted and measured permeability results. PAMPA-GIT and PAMPA-BBB experimental permeability results agreed relatively well. The backward stepwise multivariate linear regression identified excess molar refraction and polarizability to be significant at the 0.10 level in predicting the differences between PAMPA-GIT and PAMPA-BBB. The in silico model performed well – with predicted permeability of most compounds within two-fold of experimentally measured values. We found that CECs pose experimental challenges to the PAMPA method in terms of having lower solubility and lower stability compared to most drugs.

Hybrid quantum-classical polarizability model for single molecule biosensing.

Optical whispering gallery mode biosensors are able to detect single molecules through effects of their polarizability. We address the factors that affect the polarizability of amino acids, which are the building blocks of life, via electronic structure theory. Amino acids are detected in aqueous environments, where their polarizability is different compared to the gasphase due to solvent effects. Solvent effects include structural changes, protonation and the local field enhancement through the solvent (water). We analyse the impact of these effects and find that all contribute to an increased effective polarizability in the solvent. We also address the excess polarizability relative to the displaced water cavity and develop a hybrid quantum-classical model that is in good agreement with self-consistent calculations. We apply our model to calculate the excess polarizability of 20 proteinogenic amino acids and determine the minimum resolution required to distinguish the different molecules and their ionised conformers based on their polarizability.

Performance evaluation and prediction of activated carbon for VOCs via experiments and LFER methods

Due to the diversity and fluidity of volatile organic compounds (VOCs), it is difficult to conduct experimental studies on activated carbon (AC) used to capture VOCs in industry. Therefore, predicting the adsorption capacity of AC for VOCs is of great significance for evaluating the adsorption performance of AC and developing its promising applications. Herein, based on the experimental data of dynamic adsorption, the poly parameter linear free energy relationship (pp-LFER) model was developed to quantify the interactions between VOCs and AC. Through the dynamic adsorption curves of 25 VOCs on a fixed bed packed with the AC, the partition coefficient (PC) and adsorption capacity (q) of AC for VOCs were calculated, and the pp-LFER equations used to predict them were established. For the PC values, the pp-LFER model consists of the excess molar refractive index (E), molar polarizability (S), hydrogen-bond acidity (A), and logarithmic hexadecane-air partition coefficient (L), and the R2 of it was 0.86. For the ln q values, the developed model can predict it in R2 of 0.83, and the increased adsorption capacity was predominantly attributed to the dispersive interaction (lL). Finally, the internal and external validation results confirmed that the developed models have reliability, robustness, and predictability.

Ultra-sensitive DNAzyme-based optofluidic biosensor with liquid crystal-Au nanoparticle hybrid amplification for molecular detection

Due to the specific cofactor dependence and the potent catalytic capability, DNAzymes have shown great promise in the application of biosensors. However, it poses significant challenges for researchers to enhance the sensitivities of DNAzyme-based biosensing platforms. In this work, an ultra-sensitive, label-free, and quick-responsive DNAzyme biosensor is developed based on whispering gallery mode (WGM) optofluidic resonator with a hybrid amplification from liquid crystals (LCs) and Au nanoparticles (AuNPs). When a DNAzyme is cleaved by biotargets, the event of DNA hybridization is triggered and will result in the orientation transition of LC molecules (in the resonator core). According to the quadruple amplification from the disturbance of AuNPs, the excess polarizability of adhering biomolecules, the orientation variation of LC molecules, and the WGM resonance, the spectral wavelength shift can be employed as the sensing parameter to indicate the information of biotarget. L-histidine molecules are applied as the analyte. An ultra-low detection limit at a sub-femtomole level (~ 5 × 10−16 M) has been achieved using this highly-selective biosensor, which is eight orders of magnitude lower compared to the reported LC-based L-histidine sensor. In addition to L-histidine, this proposed optofluidic scheme with LC-AuNP hybrid amplification can also extend the applicability of DNAzyme-based biosensors for the detection of various molecules.

Dispersion forces in inhomogeneous planarly layered media: A one-dimensional model for effective polarizabilities

Dispersion forces such as van der Waals forces between two microscopic particles, the Casimir-Polder forces between a particle and a macroscopic object, or the Casimir force between two dielectric objects are well studied in vacuum. However, in realistic situations the interacting objects are often embedded in an environmental medium. Such a solvent influences the induced dipole interaction. With the framework of macroscopic quantum electrodynamics, these interactions are mediated via an exchange of virtual photons. Via this method the impact of a homogeneous solvent medium can be expressed as local-field corrections leading to excess polarizabilities which have previously been derived for hard boundary conditions. In order to develop a more realistic description, we investigate a one-dimensional analog system illustrating the influence of a continuous dielectric profile.

Time Dependent- Density Functional Theory calculations on frequency-dependent photophysical properties of 2, 3-diphenylcyclopropenone

Time Dependent Density Functional Theory (TD-DFT/B3LYP/6-31G*) calculations have been performed on the optimized structure of 2, 3-diphenylcyclopropenone (DPCP) in the UV region of the spectra; giving energies, oscillator strength, dipole moment, µ and polarizability, α in solvents of different polarities. The study was also extended to the number of transitions, frontier orbital energy gaps (ELUMO - EHOMO) analysis of this strained ring donor–acceptor (D-A) molecular system to calculate its ionization potential (I), electron affinity (EA) and global hardness (η) in the solvent of choice. This aids in understanding the relationship between the structure and properties of this molecule.TD-DFT/B3LYP/6-31G* calculation results, when compared with the reported experimental studies results of the solvatochromic shift properties of this molecule, showed ten excited singlet states for DPCP in the UV region. This indicates minimum overlap of the electronic transition bands computationally. The increased ΔELUMO-HOMO (4.09 - 4.31eV), I and ƞ, the lower dipole moments and polarizability values as solvent polarity increased, suggests high stability of this compound in polar solvents. The excess polarizabilities obtained for its singlet excited states show that the excited state of this compound is more polar than its ground state, and that, the molecule is chemically active.

Commentary on “Studies on molar volume, dielectric properties and refractive indices of cyanex 923 + benzene/xylene at 300 K”

Redlich-Kister equation coefficients reported by Satpathy and coworkers [J. Mol. Liq. 222 (2016) 383–389] for binary benzene+cyanex 923 and xylene+cyanex 923 are found to be inconsistent with the graphs of the experimental excess molar volumes, excess molar polarizabilities and excess molar refractions. Values calculated from the reported Redlich-Kister equation coefficients differ significantly from the measured experimental data.

Thermodynamics of amide + amine mixtures. 3. Relative permittivities of N,N-dimethylformamide + N-propylpropan-1-amine, + N-butylbutan-1-amine, + butan-1-amine, or + hexan-1-amine systems at several temperatures

Relative permittivities at 1MHz, εr, and at (293.15–303.15)K, are reported for the binary systems N,N-dimethylformamide (DMF)+N-propylpropan-1-amine (DPA), +N-butylbutan-1-amine (DBA), +butan-1-amine (BA) or +hexan-1-amine (HxA). The values of the excess relative permittivities, εrE, have also been determined for these solutions. The measurements were realized by means of a precision impedance analyser 4294A, to which a 16452A cell connected using a 16048G test lead, all of them from Agilent. The εrE values are large and negative, and diminish when the size of the amine increases along a homologous series, which has been ascribed mainly to the rupture of interactions between like molecules along mixing. Calculations on excess molar orientational polarizabilities support this conclusion, indicating a dominant contribution to εrE from the orientational polarizability of the molecules in the mixture. The analysis of excess relative Kirkwood correlation factors shows that the correlation between dipoles is effectively decreased along the mixing process.

In Silico Stark Effect: Determination of Excited-State Polarizabilities of Squaraine Dyes.

The static electric polarizabilities (α) of a quadrupolar squaraine dye are investigated in silico, either as the excess polarizability, i.e., the change from the ground to the lowest excited state, Δα, or as those of the two states separately, depending on the approach. The polarizabilities are worked out by making use of the energy and dipole moment Taylor expansions as a function of the electric field (E), in which α is represented by the quadratic and linear terms, respectively, and also by means of the linear response approach. Dipoles and energies are computed at a few values of the electric field, with different strategies that consider the geometry of the molecule either frozen in the ground state or relaxed at each E value. From a physical standpoint, the most appropriate approach to describing the molecular polarizability depends on the processes in which the molecule is involved: for example, fluorescence methods provide information about relaxed excited states, and absorption methods are used to determine the polarizability changes of excited states frozen in the ground-state conformation. We show that the excited-state polarizability does not strongly differ from the ground-state polarizability when the field is applied along the main axis of the squaraine. In contrast, remarkable differences are found when the field is applied perpendicular to the molecular plane due to a large geometrical distortion of the molecular backbone.

Static polarizability effects on counterion distributions near charged dielectric surfaces: A coarse-grained Molecular Dynamics study employing the Drude model

Coarse-grained implicit solvent Molecular Dynamics (MD) simulations have been used to investigate the structure of the vicinal layer of polarizable counterions close to a charged interface. The classical Drude oscillator model was implemented to describe the static excess polarizability of the ions. The electrostatic layer correction with image charges (ELCIC) method was used to include the effects of the dielectric discontinuity between the aqueous solution and the bounding interfaces for the calculation of the electrostatic interactions. Cases with one or two charged bounding interfaces were investigated. The counterion density profile in the vicinity of the interfaces with different surface charge values was found to depend on the ionic polarizability. Ionic polarization effects are found to be relevant for ions with high excess polarizability near surfaces with high surface charge.

Measuring Size, Size Distribution, and Polydispersity of Water-in-Oil Microemulsion Droplets using Fluorescence Correlation Spectroscopy: Comparison to Dynamic Light Scattering.

Water-in-oil microemulsion droplets (MEDs) are thermodynamically stable supramolecular structures formed in a mixture of water and oil, stabilized by surfactant layer. Here we use fluorescence correlation spectroscopy (FCS) to measure the diffusion, and the size, size distribution, and polydispersity of MEDs prepared in ternary mixtures of water/oil/sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in heptane, isooctane, and nonane at (near) single droplet level. We compare FCS data directly to dynamic light scattering (DLS) data, which shows that the optical matching point (OMP) conditions of MEDs in different oils (where excess optical polarizability of droplets vanish) severely influence DLS data, while FCS extracts the accurate size, size distribution, and polydispersity of AOT-MEDs in all three oils. This suggests that extreme precaution must be taken in acquiring and explaining DLS data of MEDs in solution. FCS data show nearly identical W0-dependent (peak) size variations of AOT-MEDs in all three oils, though a subtle increase in (average) polydispersity of droplets is observed with increase in carbon chain length of oils. Establishing the accuracy of FCS data for AOT-MEDs, we further apply FCS to measure the size parameters of MEDs prepared in a quaternary mixture of water/oil/cetyltrimethylammonium bromide (CTAB)/1-butanol in hexane, heptane, and isooctane. Unlike AOT-MEDs, FCS data show substantial effect of added cosurfactant (1-butanol) and external oil on size, size distribution and polydispersity of quaternary CTAB-MEDs. Analysis of size distributions reveals large variation of polydispersity which possibly indicates the existence of larger shape heterogeneity, together with size heterogeneity, of CTAB-MEDs compared to AOT-MEDs in solution.

Electric properties of the low-lying excited states of benzonitrile: geometry relaxation and solvent effects

Accurate calculations of the dipole moment and the polarizability for the ground and two lowest singlet and triplet excited states of benzonitrile (BN) have been performed by a variety of wave function and density functional theory (DFT) methods. Changes in molecular properties upon the electron excitation strongly depend on the character of an excited state. The vertical dipole moment change and the excess polarizability for the 11B state are smaller than those for the 21A state. In order to estimate adiabatic excited-state properties, corresponding relaxed geometries have been obtained using the PBE0 functional with the aug-cc-pVTZ basis set. The excited-state property values obtained with the long-range exchange corrected DFT methods are in general closer to the coupled cluster (CC) results, although the hybrid DFTs also provide reasonable predictions. Our CCSD adiabatic excess dipole moment value for the 11B state equal to 0.11 D is in excellent agreement with the experimental value. The 21A state appears to be more sensitive to selected method due to an important role of double-excitation effects. Solvent effects on dipole moment and polarizability of BN molecule in its ground and excited states were evaluated using both LR and cLR methods combined with the (TD-)CAMB3LYP/POL approach.

Molecular Radius, Molar Refraction, Polarizability and Internal Pressure Studies on THP + 1-Hexanol at Different Temperatures – Molecular Interactions

Molar refraction (Rm), molecular radii (r), polarizability (α) and internal pressure (πi) values determined from the refractive index data for the binary liquid mixture of Tetrahydropyran (THP) with 1-hexanol have been measured at five temperatures (T=298.15, 303.15, 308.15, 313.15 and 318.15 K). The measured data utilized to evaluate the excess molar refraction (Rm E ), excess molecular radii (r E ), excess polarizability (α E ) and excess internal pressure (πi E ) along with their Redlich-Kister co-efficient and standard error values of the mixed solvents. The results show existence of weak molecular interaction in the mixture.

Mechanisms of Photogeneration and Relaxation of Excitons and Mobile Carriers in Anatase TiO2

We studied the temperature dependence of photophysical products on UV excitation of smooth dense anatase TiO2 with frequency- and time-resolved microwave conductance measurements. At 100 K, we observed the subnanosecond formation of microsecond-lived self-trapped excitons (STEs) with a 65% quantum yield, irrespective of the UV excitation wavelength. The remaining 35% photoexcitations results in mobile conduction band electrons (eCB–); the yield of eCB– gradually increases up to about 100% at 300 K. The complex mobility of eCB– is independent of temperature between 100 and 300 K. We explain the temperature-dependent quantum yield of eCB– by the thermally activated escape of the electron from its positive counter charge. At low temperature, the Coulomb attraction causes the electron to remain at short distance from the hole forming a neutral pair. This pair stabilizes by inducing a relaxation of the surrounding lattice resulting in a self-trapped exciton. The excess polarizability volume of each STE is foun...

Investigation on some thermophysical properties of poly(ethylene glycol) binary mixtures at different temperatures

Densities ρ and viscosities η for the binary mixtures of poly(ethylene glycol)+water,+1,2-ethanediol,+1,3-propanediol,+1,4-butanediol over the entire concentration range were determined at temperatures (298.15 to 308.15)K with 5K interval. The experimental data were used to calculate the excess molar volume VmE, coefficient of thermal expansion α, excess coefficient of thermal expansion αE, excess Gibbs free energy of activation ΔG∗E, and other activation parameters (i.e., ΔG∗,ΔH∗,ΔS∗). The values of excess properties were fitted to Redlich–Kister polynomial equation to estimate the binary coefficients. The excess refractive index nE and electronic polarizability αe of PEG+water binary mixtures were also determined from the experimental values of refractive indices. The viscosity data were correlated with Grunberg–Nissan and Tamura–Kurata equations. Moreover, the Prigogine–Flory–Patterson theory has been used to correlate the excess molar volumes of the studied mixtures.

The effect of intermolecular interactions on the electric dipole polarizabilities of nucleic acid base complexes

In this Letter, we report on the interaction-induced electric dipole polarizabilities of 70 Watson–Crick B-DNA pairs (27 adenine–thymine and 43 guanine-cytosine complexes) and 38 structures of cytosine dimer in stacked alignment. In the case of hydrogen-bonded Watson–Crick base pairs the electrostatic as well as the induction and exchange-induction interactions, increase the average polarizability of the studied complexes, whereas the exchange-repulsion effects have the opposite effect and consistently diminish this property. On the other hand, in the case of the studied cytosine dimers in stacked alignment the dominant electrostatic contribution has generally much larger magnitude and the opposite sign, resulting in a significant reduction of the average polarizability of these complexes. As a part of this model study, we also assess the performance of recently developed LPol-ds reduced-size polarized basis set. Although being much smaller than the aug-cc-pVTZ set, the LPol-ds performs equally well as far as the excess polarizabilities of the studied hydrogen-bonded complexes are concerned.

Dipole moment and polarizability of the low-lying excited states of uracil

Accurate TDDFT calculations of the dipole moment μ and components of the dipole polarizability α for the ground and lowest excited states of uracil have been performed with a variety of functionals. It has been found that the functionals with corrected asymptotic behavior like LC-BLYP, ωB97XD, and CAM-B3LYP yield more consistent and reliable data than standard hybrid ones. The results of the TDDFT calculations agree well with more elaborate and expensive linear response CCSD calculations. Excess polarizability Δα for the singlet states is larger than for the triplet states.

Volumetric and steric properties of hydroxamic acids in ethanol at different temperatures

Physical properties, such as density, ρ and refractive index, n of two hydroxamic acids (N-Phenylbenzo, C6H5NOH·C6H5CO and N-o-tolylbenzo, o-CH3·C6H4NOH·C6H5CO) have been measured in ethanol as a function of concentration at T=(298.15, 303.15, and 308.15)K. The apparent molar volume, Vϕ, apparent molar volume at infinite dilution, Vϕ0 and the slope, SV∗ are calculated from the experimental value of density, ρ by applying the Masson’s equation. The apparent molar expansibility at infinite dilution, ϕE0, molar volume, V and the excess molar volume, VE are also computed. The refractive index, n, data have been used to calculate the steric parameters viz. molar refraction, RM, excess refractive index, nE, excess molar refraction, RME and polarizability, α of these molecules. The results obtained have been qualitatively used to interpret the solute–solute and solute–solvent interactions between hydroxamic acids and ethanol.

Electric-Field-Induced Perfect Anti-Nematic Order in Isotropic Aqueous Suspensions of a Natural Beidellite Clay

We study the electric-field-induced birefringence and orientational order in the isotropic phase of aqueous suspensions of exfoliated natural beidellite clay particles, thin (L = 0.65 nm) flat charged sheets with high aspect ratio, D/L ≈ 300. Our electric birefringence experiment is optimized for aqueous suspensions of colloidal particles, with a high frequency a.c. electric field, ν ≈ 1 MHz, applied by two external electrodes to a thin flat sample, sealed in an optical capillary. In isotropic and biphasic samples, we observed strong field-induced birefringence Δn(E), saturating at moderate E(sat) field to a plateau Δn(sat) proportional to the volume fraction ϕ. The field-induced order parameter S(E) is negative and saturates to S(sat) = -0.5 above E(sat). This corresponds to a perfect "anti-nematic" order, i.e. the normals of the beidellite particles are perpendicular to the field, without any preferred azimuthal direction. The measured specific excess polarizability ΔA(sp) is among the highest data reported for other strongly anisometric dielectric and metal particles. We explain the high ΔA(sp) value with the strong induced polarization of the electric double layer of counterions at the charged particle/electrolyte interface. The estimated equivalent conductivity of the beidellite particle K(eq) = 2 K(σ)/L is several orders of magnitude larger than the bulk conductivity of the electrolyte K(e), resulting in a metal-like behavior of the beidellite disks under field. In the isotropic regions of biphasic nematic/isotropic samples, the excess polarizability is further enhanced by an order of magnitude, indicating collective reorientation of the particles. We propose that this enhancement might be due to pretransitional fluctuations of the spontaneous nematic order S(N) of the colloidal suspension and/or formation of chains of particles, with antinematic order of the beidellite disks in the chains.

Combination of high-performance refractometry and infrared spectroscopy as a probe for chemically induced gelation and vitrification of epoxies

A combination of infrared spectroscopy and high-performance refractometry was used to investigate the chemically induced sol–gel and glass transition during the polymerization of epoxies. Representations of the refractive index versus chemical conversion reveal an interesting insight into the optical properties accompanying gelation and vitrification. Whereas the electronic polarizability of the liquid state of small average molecular mass and the glassy state is dominated by the mass density, an unexpected excess polarizability observed during the gelation is attributed to cooperative dipole–dipole interactions.