Dipole Moment Of Solvent Research Articles

Kinetics and Mechanism of Unimolecular Heterolysis of Framework Compounds: XVII. Solvation Effects in Dehydrobromination of tert-Butyl Bromide, 1-Bromo-1-Methylcyclohexane, and 2-Bromo-2-methyladamantane in Dipolar Aprotic Solvents

Dehydrobromination rate of tert-butyl bromide, 1-bromo-1-methylcyclohexane, and 2-bromo-2-methyladamantane grows with increasing polarity and dipole moment of solvents. No correlation was found between rate constants of the process and electrophilicity or ionizing power of the solvents. The observed solvation effects are due mainly to dispersion interactions.

Badania odpornosci blon z wulkanizatow kauczuku butylowego na przenikanie mieszanin rozpuszczalnikow organicznych

The results of investigations of the resistance of membranes (0.2 mm thickness) of butyl rubber vulcanizates to permeation by organic solvents (as individuals or binary mixtures) commonly used in paint and varnish manufacture (Fig. 1) were presented. Normalized value of membrane' breakthrough time for the substance used (Table 1) has been taken as a resistance criterion. The results of permeation by mixtures of acetone/toluene or toluene/n-butyl acetate show that breakthrough time of individual solvents significantly differ from break-through time of the same solvents in mixtures in various compositions. It was found increasing part of toluene (showing very short breakthrough time) accelerates permeation of the other component i.e. shortens measured breakthrough time. However, mixtures of ethyl acetate/n-butyl acetate, independently on the composition, do not show significant differences in breakthrough time values of individual solvents and their mixtures. The results of tests were interpreted on the basis of dipole moments of solvents, their molecules' spatial dimensions and generalized three-dimensional solubility parameters.

Transient cavities and the excess chemical potentials of hard-spheroid solutes in dipolar hard-sphere solvents

Monte Carlo computer simulations are used to study transient cavities and the solvation of hard-spheroid solutes in dipolar hard-sphere solvents. The probability distribution of spheroidal cavities in the solvent is shown to be well described by a Gaussian function, and the variations of fit parameters with cavity elongation and solvent properties are analyzed. The excess chemical potentials of hard-spheroid solutes with aspect ratios x in the range of 15< or =x< or =5, and with volumes between 1 and 20 times that of a solvent molecule, are presented. It is shown that for a given molecular volume and solvent dipole moment (or temperature) a spherical solute has the lowest excess chemical potential and hence the highest solubility, while a prolate solute with aspect ratio x should be more soluble than an oblate solute with aspect ratio 1x. For a given solute molecule, the excess chemical potential increases with increasing temperature; this same trend can be observed in hydrophobic solvation. A scaled-particle theory based on the solvent equation of state and a fitted solute-solvent interfacial tension shows excellent agreement with the simulation results over the whole range of solute elongations and volumes considered. An information-theoretic model based on the solvent density and radial distribution function is less successful, being accurate only for small solute volumes and low solvent densities.

Intramolecular charge transfer effects on 3-aminobenzoic acid

Effect of solvents, buffer solutions of different pH and β-cyclodextrin on the absorption and fluorescence spectra of 3-aminobenzoic acid (3ABA) have been investigated. The solid inclusion complex of 3ABA with β-CD is discussed by UV–Vis, fluorimetry, semiempirical quantum calculations (AM1), FT-IR, 1H NMR and Scanning Electron Microscope (SEM). The thermodynamic parameters (Δ H, Δ G and Δ S) of the inclusion process are also determined. The experimental results indicated that the inclusion processes is an exothermic and spontaneous. The large Stokes shift emission in solvents with 3ABA are correlated with different solvent polarity scales suggest that, 3ABA molecule is more polar in the S 1 state. Solvent, β-CD studies and excited state dipole moment values confirms that the presence of intramolecular charge transfer (ICT) in 3ABA. Acidity constants for different prototropic equilibria of 3ABA in the S 0 and S 1 states are calculated. β-Cyclodextrin studies shows that 3ABA forms a 1:1 inclusion complex with β-CD. β-CD studies suggest COOH group present in non-polar part and amino group present in hydrophilic part of the β-CD cavity. A mechanism is proposed to explain the inclusion process.

Mesoscopic Simulation of Adsorption of Peptides in a Hydrophobic Chromatography System

Mesoscopic simulations using Langevin dipoles on a lattice for the solvent and calculated partial charges for the solute have been used to estimate free energies of adsorption from data on reversed-phase chromatography on nine protected peptides covering a wide range of structures. There is a single parameter, the effective solvent dipole moment, that is fit to data for one peptide and used to predict properties of the other eight peptides. Good agreement of adsorption chemical potentials, including order of chromatographic retention times, is found for calculations that are Boltzmann-averaged over a set of orientations. In addition, the results suggest that there are preferential orientations for each peptide at the model hydrophobic chromatographic surface. Estimation methods for adsorption based on molecular descriptors and hydrophobicity scales are shown to be unreliable for these systems. With refinements and extensions, this simulation method should be applicable to solvents containing salt, such as in hydrophobic interaction chromatography, and to larger solutes including proteins.

CHARMM fluctuating charge force field for proteins: II protein/solvent properties from molecular dynamics simulations using a nonadditive electrostatic model.

A fluctuating charge (FQ) force field is applied to molecular dynamics simulations for six small proteins in explicit polarizable solvent represented by the TIP4P-FQ potential. The proteins include 1FSV, 1ENH, 1PGB, 1VII, 1H8K, and 1CRN, representing both helical and beta-sheet secondary structural elements. Constant pressure and temperature (NPT) molecular dynamics simulations are performed on time scales of several nanoseconds, the longest simulations yet reported using explicitly polarizable all-atom empirical potentials (for both solvent and protein) in the condensed phase. In terms of structure, the FQ force field allows deviations from native structure up to 2.5 A (with a range of 1.0 to 2.5 A). This is commensurate to the performance of the CHARMM22 nonpolarizable model and other currently existing polarizable models. Importantly, secondary structural elements maintain native structure in general to within 1 A (both helix and beta-strands), again in good agreement with the nonpolarizable case. In qualitative agreement with QM/MM ab initio dynamics on crambin (Liu et al. Proteins 2001, 44, 484), there is a sequence dependence of average condensed phase atomic charge for all proteins, a dependence one would anticipate considering the differing chemical environments around individual atoms; this is a subtle quantum mechanical feature captured in the FQ model but absent in current state-of-the-art nonpolarizable models. Furthermore, there is a mutual polarization of solvent and protein in the condensed phase. Solvent dipole moment distributions within the first and second solvation shells around the protein display a shift towards higher dipole moments (increases on the order of 0.2-0.3 Debye) relative to the bulk; protein polarization is manifested via the enhanced condensed phase charges of typical polar atoms such as backbone carbonyl oxygens, amide nitrogens, and amide hydrogens. Finally, to enlarge the sample set of proteins, gas-phase minimizations and 1 ps constant temperature simulations are performed on various-sized proteins to compare to earlier work by Kaminsky et al. (J Comp Chem 2002, 23, 1515). The present work establishes the feasibility of applying a fully polarizable force field for protein simulations and demonstrates the approach employed in extending the CHARMM force field to include these effects.

Effects of molecular weight, solvent and substrate on the dewetting morphology of polystyrene films

Surface morphology of polystyrene (PS) films on different substrates by spin-coating before and after annealing was observed using atomic force microscopy (AFM). The effects of polymer molecular weight, substrates, solvents, and annealing conditions on the morphology of the films were investigated. Before annealing, the grain height decreases, and simultaneously the grain diameter increases with molecular weight (Mw) within the measured molecular weight. After annealing, the situation is opposite, i.e., the grain height increases while the grain diameter decreases with Mw. Furthermore, after annealing the smaller surface roughness (Ra) was obtained. It was also found that film surface roughness (Ra) depends on the vapor pressure and dipole moment of different used solvents as well as the substrates. The experimental results show that when the used solvents have similar dipole moment but different vapor pressure, the Ra of PS film decreased with the decreasing vapor pressure of solvents whether on silicon or on mica. And when the used solvents have close vapor pressure but different dipole moment, the Ra decreased with the increasing of solvent dipole moments on both substrates.

Solvent reorganization energy of electron-transfer reactions in polar solvents.

A microscopic theory of solvent reorganization energy in polar molecular solvents is developed. The theory represents the solvent response as a combination of the density and polarization fluctuations of the solvent given in terms of the density and polarization structure factors. A fully analytical formulation of the theory is provided for a solute of arbitrary shape with an arbitrary distribution of charge. A good agreement between the analytical procedure and the results of Monte Carlo simulations of model systems is achieved. The reorganization energy splits into the contributions from density fluctuations and polarization fluctuations. The polarization part is dominated by longitudinal polarization response. The density part is inversely proportional to temperature. The dependence of the solvent reorganization energy on the solvent dipole moment and refractive index is discussed.

On the validity of dielectric continuum models in application to solvation in molecular solvents

We report Monte Carlo simulations of solvation of a point dipole in dipolar–quadrupolar solvents of varying dipole moment and axial quadrupole. The simulations are carried out to test the prediction of dielectric solvation models of a monotonic increase of the absolute value of the solvation chemical potential |μp| with the solvent dielectric constant ε. Dielectric constants are obtained from pure liquid simulations carried out for each solvent used in solvation simulations. A raising dependence of |μp| on ε, in qualitative agreement with dielectric solvation models, is seen when the solvent dipole moment is varied at constant solvent quadrupole. An increase in the axial quadrupole at constant solvent dipole reduces the dielectric constant at the same time leading to higher |μp| values. The simulations and dielectric models thus give the opposite dependence on the solvent quadrupole for any solvent dipole. We also show that for solvation in dipolar–quadrupolar solvents the saturation limit |μp|→const at ε≫1 predicted by linear response dielectric continuum models actually occurs in the range of nonlinear solvation.

Kinetics of Silver Electrocrystallization in Nonaqueous Solutions

The effect of the solvent nature on the silver electroreduction and electrooxidation, including the initial electrocrystallization stage, is studied. Basic kinetic parameters of the process are determined. With increasing donor number of the solvent, which defines its capability for solvating cations, the rate constant of the electrochemical reaction decreases and the silver nucleation overvoltage increases. With increasing dipole moment of the solvent, which defines its adsorption properties, the surface energy of the silver nucleation decreases. The effect of the solvent on the silver electroreduction reveals itself through its solvation and adsorption properties.

Decomposition of 2-isopropylnaphthalenehydroperoxide into 2-naphthol and acetone: reactor operation parameters

Reactor operation parameters for the liquid-phase acid-catalyzed decomposition of 2-isopropylnaphthalenehydroperoxide (2-IPNHP) were investigated to produce simultaneously 2-naphthol and acetone with a high yield. The 2-naphthol and acetone are produced from 2-IPNHP by ionic reactions, nevertheless, dimethyl-2-naphthylcarbinol (DMNC) and 2-acetonaphthone (AN) formations through radical reactions cannot be avoided because of the induced decomposition effects but can be decreased. The decomposition of 2-IPNHP was carried out in the presence of two different aprotic solvents of low dielectric (DE) constant, i.e. 2-isopropylnapthalene (IPN) and acetone (AC), and the protogenic solvent acetic acid (AcOH), with two different oxyacid catalysts, i.e. HClO 4 and H 2SO 4. The production rate of 2-naphthol increases with the increase in the dipole moment (DM) of aprotic solvents. The increase in the initial 2-IPNHP concentration increases 2-IPNHP decomposition and 2-naphthol production rates. 2-Naphthol production rate decreases and the radical by-product AN formation rate increases with increasing temperature. The presence of the impurities DMNC and AN of the reactant mixture and a radical scavenger in the decomposition reaction medium decreased the 2-naphthol production rate. A 70% yield of 2-naphthol was obtained in the presence of IPN by 0.047 mol dm −3 HClO 4 with the initial concentrations of 1.155 mol dm −3 2-IPNHP, 0.470 mol dm −3 DMNC and 0.011 mol dm −3 AN at T=22 °C and N=1000 rpm. The reaction rate equations for the decomposition reaction of 2-IPNHP and production of 2-naphthol are also presented.

Microsolvation of small anions by aromatic molecules: An exploratory study

This work was motivated by the experimental finding that the O2−/benzene interaction energy is unexpectedly large. To further explore the interactions of small anions with aromatic molecules, anion photoelectron spectroscopy was utilized to measure interaction strengths of the seed anions, O2− and NO−, complexed with several aromatic molecules, including benzene, naphthalene, pyridine, and pyrimidine. As in the case of O2−(benzene), the anion(aromatic)1 binding energies for the other complexes studied were also higher than one might have anticipated. In addition, the interaction energy of O2− complexed with a given aromatic molecule was, in every case studied, higher (by a factor of ∼1.5) than that of NO− complexed with the same aromatic. While the dependence of interaction strengths on solvent dipole moments and/or polarizabilities implied a substantial electrostatic component to the binding in these complexes, differences in the binding of O2− and NO− with these aromatic molecules showed that there is a distinct covalent aspect to the interaction as well. A significant portion of this interaction was attributed to the fact that O2− and NO− are both open-shell anions that are interacting with closed-shell aromatic molecules. In the accompanying paper [J. Chem. Phys. 116, 9672 (2002)] calculations on O2−(benzene)1 by Jalbout and Adamowicz shed additional light on the nature of small anion–aromatic molecule interactions. Last, results are also presented comparing the interaction energies of several multisolvent, anion–molecule complexes.

Role of dipole moment of solvents in formation and stabilization of the TICT states in Coumarin 445 under nitrogen laser excitation

In this paper we report the observation of dual Amplified Spontaneous Emission (ASE) from solutions of 7-ethylamino-4-methyl coumarin dye (Coumarin 445) in certain solvents such as n-butyl acetate, dioxane etc. when pumped by high power nitrogen laser. The two ASE bands appear to be from two different excited species (ICT and TICT conformation) one of which is the precursor of the other. The spectral characteristics of dye Coumarin 445 depend upon the solvent environment. The TICT coumarin photoisomers, which form exciplexes with the solvent molecules, have enough gain to produce amplified spontaneous emission even when there is apparently no detectable fluorescence. The behaviour of this dye in the excited state is studied by measuring the small signal gain and variation of the gain slope with temperature in different solvents. It is observed that polarity of the solvent plays a more dominant role in formation and stabilization of TICT states.

Molecular Dynamics of Carbohydrate Aqueous Solutions. Dielectric Relaxation as a Function of Glucose and Fructose Concentration

At some solute concentrations c between 1 and 5.4 mol/L, the complex (electric) permittivity of aqueous solutions of d-glucose and d-fructose has been determined as a function of frequency υ between 300 kHz and 40 GHz. The permittivity spectrum of the 5.4 mol/L d-fructose solution has been measured at six temperatures between 10 and 35 °C, and the other spectra have been taken at 25 °C. All dielectric spectra revealed one dispersion/dielectric loss region, which indicated a rather homogeneous relaxation of the solute and solvent dipole moments. Analytically, the measured spectra were represented by the Cole−Cole relaxation spectral function, which corresponds with a continuous, symmetrically bell shaped relaxation time distribution. The parameters of the spectral function are discussed to show that the monosaccharides exhibit unusual hydration properties. Particularly, when treated in terms of a wait-and-switch model of dipole reorientation, the principal dielectric relaxation time is indicative of the ex...

Analysis of dipolarity/polarisability parameter, π*, for a range of supercritical fluids

The dipolarity/polarisability parameter, π*, of Kamlet and Taft can be used to characterise the solvent properties of supercritical fluids and hence its correlation to more readily available parameters is important for predictive purposes. Almost perfect correlations are demonstrated between the π* parameter and the cohesive energy density parameter, δH2, as a function of solvent type, temperature and pressure. Correlation is also observed between π* and solvent dipole moment at constant reduced density. It is shown that the Gibbs energy of dissociation data can be modelled using δH2 and π* parameters.

Electron Transfer in Aromatic Solvents: The Importance of Quadrupolar Interactions

Molecular solvation calculations are performed on a donor−bridge−acceptor (DBA) molecule in polar and nonpolar environments. A strictly dipolar treatment of solvation reproduces experimental values of the reaction free energy, ΔrG, determined in nondipolar and weakly dipolar aromatic solvents but does not simultaneously predict accurate values of ΔrG in highly dipolar solvents. By contrast, a solvation model that includes contributions from solvent dipole and quadrupole moments (J. Chem. Phys. 1999, 111, 36301) reproduces ΔrG values over a large polarity range. The reliability of the predicted ΔrG and solvent reorganization energies, λo, are assessed through fitting experimental rate data. The fits display good agreement with the experimental data and the donor−acceptor electronic couplings derived via these analyses agree with prior determinations. The availability of a model that generates reasonable predictions of ΔrG and λo allows a first exploration of the temperature dependence of solvent mediated electronic coupling.

Structure of NaI ion pairs in water clusters

The structural properties of the thermodynamically stable NaI salt ion pairs in water clusters have been investigated by means of Monte Carlo simulations with model potentials. Attention was also paid to the structure of single ion–water Na +(H 2O) n and I −(H 2O) n clusters, which are found to be non-spherically symmetric at room temperature. In agreement with earlier studies, I −(H 2O) n clusters exhibit surface structures, with the “hydrophobic” iodide ion sitting at the surface of a water network, while room-temperature Na +(H 2O) n clusters exhibit a solvation shell structure, where solvent molecules beyond the first solvation shell tend to accumulate on one side of the cluster instead of forming a spherical droplet. Both “contact” ion pairs (CIP) and solvent-separated ion pairs (SSIP) are found to have surface structures for the smaller clusters while both interior and surface structures may exist at room temperature for cluster size of 32. A remarkable feature of the ion pair cluster structural properties is that they are very much akin to those for individual ion–water clusters, especially for SSIPs, and some insight into the ion pair cluster structures can thus be gained from single ion–water cluster structures. We propose that the (small) extent of solvent–solvent hydrogen bonding and the magnitude of the (large) solvent dipole moments in the clusters can be used to illustrate the extent of the perturbation introduced by the ions or the ion pairs in the solvent environments. In contrast to the ion pair free energetics investigated in previous work, ion–water and salt-water cluster structural properties are rather insensitive to the choice of model potentials, whether one employs non-polarizable optimized potentials for liquid simulations (OPLS) such as TIP4P/OPLS or polarizable optimized potentials for cluster simulations. The structure of NaI(H 2O) n CIP and SSIP clusters have implications for the NaI(H 2O) n cluster photodissociation dynamics. The large solvent dipole moments obtained for NaI(H 2O) n clusters are indicative of increasingly larger local solvent dipoles in the clusters, which may then grow large enough to dipole-bind an electron upon cluster photoexcitation. Photoexcitation of the larger clusters might then proceed via a different route than it does for the small clusters and isolated NaI possibly involving a charge-transfer-to-solvent excited state akin to that of I −(H 2O) n clusters. For the NaI photodissociation pathway, the surface structure of the small NaI(H 2O) n clusters may imply a slow change in the reaction dynamics with cluster size.

Experimental evaluation of (LE) and (TICT) states dipole moments of 9,9′-Bianthryl, 10-Bromo-9,9′-Bianthryl and 10-Cyano-9,9′-Bianthryl

Abstract A comparative study on the solvation induced intramolecular charge transfer in the excited state has been made for 9,9′-Bianthryl (BA), 10-Bromo-9,9′-Bianthryl (BABr) and 10-Cyano-9,9′-Bianthryl (BACN) by fluorescence measurement at room temperature. The study of this fluorescence in liquid solutions shows a strong dependence of Stokes shift versus the dipole moment of the solvents. Experimental results show an important dipole moment variation between ground and TICT (Twisted Intramolecular Charge Transfer) states, whereas this variation between ground and LE (locally excited) states is very weak, when the hydrogen atom in position 10 of (BA) is substituted by a bromine or cyano group respectively.

Phototransformation of Alkanethiol-derivatized Noble Metal Nanoparticle

Abstract Photon-initiated shape transformation of n-alkanethiol-derivatized noble metal nanoparticles has been studied with variations of metal, alkanethiol, and solvent. Silver nanoparticles undergo fragmentation upon irradiation while gold ones barely do. Silver/gold composite particles follow the case of silver with a reduced efficiency. The efficiency decreases as alkanethiol length or solvent dipole moment increases. Following the conduction of thermalized photon energy, alkanethiol can dissociate in a period of heat dissipation, and some of dethiolated particles fragment within the recombination time. Prior to the thermal conduction, shape transformation via melt and vaporization also occurs for both metals but this effect is less apparent for silver because of more notable fragmentation followed. The difference in the transformation of two metals is ascribed to the differences in work function, oxidation potential, atomization enthalpy, and particle size. Smaller fragmentation efficiency with more polar solvent or longer alkanethiol is attributed mainly to relatively smaller dissociation rate compared with heat dissipation rate.

Solvent–catalyst interactions in the decomposition process of 2-isopropylnaphthalenehydroperoxide into 2-naphthol and acetone

Decomposition of 2-isopropylnaphthalenehydroperoxide (2-IPNHP) proceeds through either ionic or radical reaction mechanism. 2-Naphthol and acetone are produced by ionic reactions, however, dimethyl-2-naphthylcarbinol and 2-acetonaphthone productions through radical reactions cannot be avoided because of induced decomposition effects. In this work, we performed the acid-catalysed decomposition of 2-IPNHP for 2-naphthol and acetone production in the presence of eight different solvents and three different acid catalysts. The results were discussed in combination with the ionic reaction mechanism to evaluate the solvent–catalyst interactions. Dodecane, isopropylnaphthalene, propyl acetate, acetone (aprotic solvents of low dielectric constant); acetonitrile, nitrobenzene (NB) (aprotic solvents of high dielectric constant), acetic acid (AcOH) (protogenic solvent) and methyl alcohol (MeOH) (amphiprotic solvent) were used separately with oxyacids HClO 4 and H 2SO 4, and hydroacid HCl. 2-IPNHP decomposition and 2-naphthol production rates increased with increasing dipole moment of aprotic solvents. The highest reaction rates were obtained in the protogenic solvent AcOH and in the aprotic solvent NB where the reactions in the amphiprotic solvent MeOH resulted in the lowest reaction rates. In addition to characters of the solvent and catalyst of the decomposition medium, the composition of the reactant mixture also affected the reaction mechanism and decomposition yield. According to the experimental results, AcOH and HClO 4 are the favourable solvent and catalyst for 2-naphthol production, respectively. 61% yield of 2-naphthol was achieved in the presence of AcOH by 0.114 mol dm −3 HClO 4 with the medium concentrations of 1.078 mol dm −3 2-IPNHP, 0.222 mol dm −3 DMNC, 8.680×10 −3 mol dm −3 AN and 0.255 mol dm −3 H 2O 2.