Formamide Water Research Articles

Temperature dependence of the pair interaction between hydrophobic and hydrophilic solutes: A calorimetric study

The enthalpies of tetraethyl- and tetrabutylammonium bromides solution in water and highly aqueous water–formamide (FA) mixtures were measured at 277.15, 288.15, 313.15, 319.15 and 328.15 K. The standard enthalpies of solution are obtained and compared with previously determined values at 298.15 K. Heat capacities of solution were computed. Enthalpic and heat capacity coefficients of solute–FA pair interactions were calculated. The heat capacity of methylene group interaction with FA was found to be negative, whereas the heat capacity of bromide ion–FA interaction appeared to be positive. The free energy and entropic coefficients of tetrabutylammonium bromide–FA interaction coefficients were estimated and compared with those for other non-electrolytes. It has been found that the interaction between two hydrophobic species is the entropic origin which is in agreement with classical models of hydrophobic interaction. In contrast, the interaction of tetrabutylammonium bromide with FA is the enthalpic origin, it being repulsive at all temperatures studied.

The Effect of Different Surface Modification Agents on the Dispersion of Nano-Hydroxyapatite (n-HA) Crystallites

The surface of synthetic calcium hydroxyapatite (HA, Ca10(PO4)6(OH)2) was modified through combining freeze-drying, solvent replacement and surface modification methods in an effort to obtain the deaggregative n-HA crystallites. Three surface modification agents: Polyethylene glycol (PEG, Mw: 6000), poly(propyl oxide)-poly (ethyl oxide)-co-poly(propyl oxide)(Pluronic F-127, Mw: 12,000) and poly(d, l-lactide)-co-poly (ethylene glycol) (PELA, Mw: 20,000)were selected. The dispersion of the modified n-HA was characterized by sedimentation time in distilled water, acetone and dimethyl formamide (DMF). The results indicate that the three surface modification agents influence the dispersion of n-HA crystallites in various solvent based on different mechanisms. Transmission electron microscopy (TEM) observation shows that the dried and acetone-replacement powders are composed of needle-like HA crystallites isolated individually. The chosen solvents have a profound effect on the sedimentation time. In distilled water, the dispersion of as-synthesized n-HA crystallites is increased greater by F127 than by PEG. After freeze-drying, the two n-HA particles show homogeneous dispersion in acetone. The colloid stability of freeze-dried HA/PEG, solution-replaced HA/F127 and solution-replaced HA/PELA in DMF were improved significantly. The suspensions remained stable after 30 days with only a blue transparent sol being observed.

BSSE‐corrected geometry and harmonic and anharmonic vibrational frequencies of formamide–water and formamide–formamide dimers

AbstractThe basis set superposition error (BSSE) influence in the geometry structure, interaction energies, and intermolecular harmonic and anharmonic vibrational frequencies of cyclic formamide–formamide and formamide–water dimers have been studied using different basis sets (6‐31G, 6‐31G**, 6‐31++G**, D95V, D95V**, and D95V++**). The a posteriori “counterpoise” (CP) correction scheme has been compared with the a priori “chemical Hamiltonian approach” (CHA) both at the Hartree–Fock (HF) and second‐order Møller–Plesset many‐body perturbation (MP2) levels of theory. The effect of BSSE on geometrical parameters, interaction energies, and intermolecular harmonic vibrational frequencies are discussed and compared with the existing experimental data. As expected, the BSSE‐free CP and CHA interaction energies usually show less deep minima than those obtained from the uncorrected methods at both the HF and MP2 levels. Focusing on the correlated level, the amount of BSSE in the intermolecular interaction energies is much larger than that at the HF level, and this effect is also conserved in the values of the force constants and harmonic vibrational frequencies. All these results clearly indicate the importance of the proper BSSE‐free correlation treatment with the well‐defined basis functions. At the same time, the results show a good agreement between the a priori CHA and a posteriori CP correction scheme; this agreement is remarkable in the case of large and well‐balanced basis sets. The anharmonic frequency correction values also show an important BSSE dependence, especially for hydrogen bond stretching and for low frequencies belonging to the intermolecular normal modes. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Activity coefficients of NaF in aqueous mixtures with ɛ-increasing co-solvent: formamide–water mixtures at 298.15 K

The electromotive force E, of the cell containing the ion-selective electrodes Na-ISE | NaF( m), formamide ( Y), H 2O(100 − Y) | F-ISE has been measured at 298.15 K as a percentage of the weight of the amide in the mixed solvent. The percentage ( Y) was varied from 0 to 90% in 10-unit steps, and the molality of the electrolyte ( m) from approximately 0.005 to saturation. The corresponding standard electromotive forces, E 0 (molal scale), were determined using traditional methods of extrapolation (Debye–Hückel and Pitzer equations). The results obtained by application of both equations show experimental errors of the same sort as those for this type of measurements. Once the E 0 was obtained, we determined the mean ionic activity coefficients for NaF, the transfer free energy from water to the water–formamide mixture, and the NaF primary hydration number. The variation of these parameters, with the composition of this ɛ-increasing solvent, is discussed in comparison with that previously obtained for the ɛ-decreasing methanol–water and ethanol–water systems, in terms of both ion–solvent and ion–ion interactions and of the effect of the medium dielectric constant change.

Membrane electrode sensitive to a cationic surfactant in aquo-organic media

An electrode originally sensitive to dodecyltrimethylammonium ions (DTA +) was proven to be sensitive to tetradecyltrimethylammonium ions (TTA +) and was used for determination of critical micelle concentration of tetradecyltrimethylammonium bromide (TTAB) in water. Moreover the response of the electrode was tested in presence of non-aqueous polar solvents i.e. dimethyl formamide (DMF) and dimethyl sulphoxide (DMSO) in water and was observed to be Nernstian within the concentration range studied (up to 40% v/v of DMF and DMSO). The validity of this electrode, for electrochemical measurements, was checked by comparing the critical micelle concentration values of TTAB obtained by using the electrode, with those obtained by conductivity measurements in mixed polar solvents. The effect of solvent on the micellization of TTAB has been discussed.

Calculation of the electronic spectra of molecules in solution and on surfaces

An approach is presented to calculate the electronic spectra of molecules in solution or adsorbed on surfaces. Through limiting electronic excitations to include only those between orbitals localized on the solute or adsorbant, large computational savings are achieved with minimal additional error. This approach has been implemented within time-dependent density functional theory and single excitation configuration interaction. Calculations of the electronic spectrum of formamide in water and carbon monoxide on the Ni(1 1 1) surface illustrate the method.

Activity coefficients of NaF in aqueous mixtures with ε-increasing co-solvent: ethylene carbonate–water mixtures at 298.15 K

The electromotive force, E, of the cell containing two ion-selective electrodes (ISE), Na-ISE|NaF( m),EC( Y),H 2O(100− Y)|F-ISE has been measured at a temperature of 298.15 K as a function of the weight percentage Y of ethylene carbonate (EC) in a mixed solvent. The Y was varied between 0 and 60 wt.% in 10-unit steps and the molality of the electrolyte ( m) was between ca. 0.005 and saturation. The values of the standard electromotive force, E 0 (molal scale), were determined using routine methods of extrapolation (Debye–Hückel and Pitzer equations) and also using a chemical model in order to account for the possible formation of ion pairs (Na +F −) 0. The results obtained produced good internal consistency, within the normal limits of experimental error encountered in these types of measurement. Once E 0 was determined, the mean ionic activity coefficients for NaF, the free energy of transfer from the water to the EC–water mixture, and the primary NaF hydration number were calculated. The variation of these magnitudes with the composition of the mixture with ε-increasing co-solvent is discussed in comparison with those previously obtained with formamide–water, as well as for those from ε-decreasing methanol–water and ethanol–water systems in terms of the ion–solvent and ion–ion interactions and their changes with the properties of the medium.

Density functional theory study of formamide–formamidic acid tautomerization

AbstractThe mechanism of tautomerization reaction of formamide–formamidic acid in gas phase and in water has been completely investigated in the present study using, density functional theory (DFT) and the second‐order Møller–Plesset perturbation (MP2) method. Large basis sets 6‐311++G(d,p) have been employed to determine the equilibrium structure and vibrational frequencies. Activation energy of the non‐water F → FA reaction is 202.9 kJ/mol at B3LYP/6‐311++G(d,p) level. Extensions to situations in which tautomerization is assisted by neighboring solvent molecule(s) are considered. If a single H2O molecule is considered, three stable structures and transition states of formamide–water complexes are found. If the water locates between the HN group and the CO moiety, the activation energy decreases to 94.5 kJ/mol. If the water locates in other positions, it can cause the activation energy to increase to 2–4 kJ/mol. When two intimate H2O molecules locate between the HN group and the CO moiety, the activation energy decreases to 89.3 kJ/mol. Intimate solvent participation is thus found much more strongly affecting the activation energy than the overall thermodynamics in this case. Finally, the solution phase studies are also carried out using the Onsager reaction field model, with a range of dielectric constants from 2 to 80 at the B3LYP/6‐311++G(d,p) level. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

A new infrared spectroscopy technique for structural studies of mass-selected neutral polar complexes without chromophore

We report gas-phase experimental and theoretical results on the configurations of weakly-bound neutral polar complexes without chromophores: the water dimer and the formamide–water complex. Experimental data are obtained by combining infrared (IR) absorption spectroscopy, in the 2800–3800 cm−1 domain, with the Rydberg electron transfer (RET) technique leading to dipole-bound anion (DBA) formation. In the absence of IR excitation, RET to neutral complexes with a given total dipole moment, and thus a given molecular structure, leads to DBAs which are observed without any possible fragmentation. In the presence of the IR laser, prior to ionisation, resonant IR absorption of intramolecular vibrations of the parent neutral complexes can either induce the breaking of the weak intermolecular bonds (vibrational predissociation of the neutral) or the fast departure of the excess electron after RET (autodetachment of the DBA). Anion signal depletion, monitored at the parent mass, is then a signature of resonant IR absorption from mass- and structure-selected neutral complexes. The validity of the present experimental method and of different types of quantum chemistry calculations is discussed by comparison between calculated harmonic or anharmonic frequencies, the present experimental gas-phase IR spectra, and previous experimental data on these two test-case hydrogen-bonded complexes.

Apparent Molar Volumes of Sodium Methylbenzoates in N, N-Dimethyl Formamide–Water Mixtures at 298.15 K

Densities of sodium methylbenzoate (o-, m-, p-) have been measured in dimethyl formamide (DMF)-water mixtures at 298.15 K with an oscillating-tube densimeter. From these densities, apparent molar volumes of sodium methylbenzoates in DMF-H 2 O mixtures have been calculated and partial molar volumes at infinite dilution have been evaluated. Substituent and solvent effects on the transfer volumes of each isomer from water to DMF-H 2 O mixed solvents have also been obtained. The results are explained in terms of solvent-solvent and solute-solvent interactions.

Synthesis of titania hollow microspheres using non-aqueous emulsions

Hollow titania microspheres ranging from 100 nm to a few micrometres in diameter were synthesized by a novel method using surfactant-stabilized non-aqueous emulsion droplets. Well-defined micron-sized hollow spheres with amorphous titania walls typically 50 nm thick were prepared by addition of water to formamide dispersions of hexadecane droplets containing titanium ethoxide. In contrast, addition of titanium ethoxide to formamide–water droplets dispersed in hexadecane produced hollow spheres of amorphous titania only 100 nm in diameter. In both cases, hydrolysis/condensation reactions at the formamide/oil interface gave rise to intact shells that could have uses as low density pigments, dyes, self-repairing coatings, photoactive storage/release agents, as well as compartmentalized structures in nanotechnology.

Geometry optimization of molecules in solution: Joint use of the mean field approximation and the free-energy gradient method

The average solvent electrostatic potential/molecular dynamics (ASEP/MD) and the free-energy gradient methods are applied together with the multidimensional geometry optimization of molecules in solution. The systems studied were formamide in aqueous solution and water and methanol in liquid phase. The solute molecules were described through ab initio quantum mechanics methods (density dunctional theory or Møller–Plesset second order perturbation theory) while the solvent structure was obtained from Molecular Dynamics calculations. The method is very efficient; the increase in computation time is minimal with respect to previous ASEP/MD versions that worked at a fixed geometry. Despite the use of the mean field approximation in the calculation of the solvent reaction potential the agreement with previous theoretical calculations was satisfactory. Large changes were observed in the solute charge distribution induced by the solvent, and the solute polarization was accompanied by an increase in the solvent structure around the solute.

Thermodynamics and Micellar Properties of Tetradecyltrimethylammonium Bromide in Formamide–Water Mixtures

The effect of formamide on the micellization of tetradecyltrimethylammonium bromide has been investigated by conductance and fluorescence probe experiments. The critical micelle concentration and the degree of counterion dissociation of micelles were obtained from conductance measurements in the temperature range of 20 to 40°C. It was found that these two parameters increase with both temperature and formamide content in the solvent system. The thermodynamic parameters of micellization were estimated using the equilibrium model of micelle formation. The standard free energy of micellization was found to be negative in all cases and becomes less negative as the formamide content in the mixed solvent increases, but it is roughly independent of temperature. Although the entropic contribution was found to be larger than the enthalpy one, in particular at lower temperatures, an enthalpy–entropy compensation effect was observed for all systems. Micellar aggregation numbers were determined by the static quenching method, using pyrene as a probe and cetylpyridinium chloride as a quencher. The observed decrease in the micelle aggregation number, which is controlled by the increase in the surface area per headgroup, was attributed to an enhanced solvation in formamide rich solvent mixtures. Changes in the pyrene 1:3 ratio index, indicating a more polar environment, are consistent with an increased micellar solvation. Fluorescence polarization of both coumarin 6 and fluorescein are indicative of a decrease in microviscosity with cosolvent addition. The data on fluorescence anisotropy of coumarin 6 were analyzed using the wobbling in cone model. Data indicated the formation of micelles with a less ordered structure as the formamide increases in the solvent system.

Growth and characteristics of the [formula omitted] NaCl crystal surface grown from solution

The morphology of {1 1 1} faces grown from water–formamide solutions as well as from pure water solutions was investigated. Surface patterns were examined ex situ and in situ using bright field and differential interference contrast optical microscopy and ex situ atomic force microscopy. It was shown that formamide and urea stabilize the {1 1 1} NaCl faces, whereas larger homologous molecules do not. For the {1 1 1} NaCl crystals growing from water–formamide solutions, it was observed that growth proceeds by monomolecular, stabilized layers of height d {1 1 1} , with most probably Na + ions on top of Cl − ions. Steps originate from spiral-dislocation growth as well as from 2D nucleation starting from the edges of the crystal. Atomic resolution imaging of NaCl {1 1 1} showed no surface reconstruction. The {1 1 1} surfaces grown from pure water solutions showed developing of shallow growth hillocks with rounded tops. It is presumed that these hillocks are related to dislocation outcrops and growth proceeds close to the roughening temperature. Growth pits develop after a longer period of {1 1 1} surface growth in water solution. Their formation is explained by the presence of a semipermeable particle at the pit bottom, which locally retards the fast {1 1 1} growth.

Photophysical and light scattering studies on the aggregation behaviour of Triton X-100 in formamide—water mixed solvents

Micelle formation and structure of the non-ionic surfactant p-tert-octyl-phenoxy (9.5) polyethylene ether (Triton X-100) in mixed solvents consisting of water and formamide have been investigated. Changes in the critical micelle concentration of the surfactant upon the addition of formamide were examined by using the pyrene 1:3 ratio method. The observed increase in the critical micelle concentration was attributed to a rise in the solubility of the surfactant as the formamide content increased in the solvent system. Micelle structure parameters were obtained as a function of the co-solvent concentration by using combined static and dynamic light scattering measurements. It was found that the decrease in the micelle size, produced by the addition of formamide, is mainly due to a reduction in the mean aggregation number rather than to changes in the magnitude of the whole solvation of micelles. This fact was also supported by the observed trend in the partial specific volume of the TX-100 micelles, obtained by complementary density measurements. However, the postulated changes in the composition of the solvation layer of micelles were supported by the rise in both the surface area per head group and the cloud point of the surfactant. From the photophysical response of different fluorescent probes incorporated in the micellar phase, we obtained information on the changes in the microstructure of Triton X-100 micelles upon the addition of formamide. The pyrene 1:3 ratio index revealed an increasing micropolarity as the formamide content increases in the solvent system. On the other hand, studies based on both fluorescence polarization of coumarin 6 and intermolecular pyrene excimer formation have shown that the microviscosity of Triton X-100 decreases with the presence of co-solvent. These results were interpreted on the basis of considerable contact of the co-solvent with the inner region of the micelles.

Oxidative behavior and relative reactivities of some unsaturated compounds towards hexachloroiridate(IV) in perchloric acid medium

AbstractThe kinetics of the oxidation of styrene, cinnamic acid, and some of their substituted derivatives by hexachloroiridate(IV) in dimethyl formamide–water mixtures and in the presence of perchloric acid have been investigated. The reactions appear to proceed via the formation of an unstable intermediate 1:1 complex between iridium(IV) and the substrate, followed by the decomposition of the complex in the rate‐determining step. Correlation with σ yielded ρ values of −4.0 and −3.5 which suggests the formation of a cationic intermediate in the rate‐determining step of the reaction. Subsequent cleavage of the carbon–carbon bond yielded the product aldehydes. Thermodynamic and activation parameters associated with the equilibrium and the rate‐determining steps were also evaluated. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 411–417, 2002

Viscosities and Volumes of Dilute Solutions of Formamide in Water + Acetonitrile and for Formamide and N,N-Dimethylformamide in Methanol + Acetonitrile Mixed Solvents: Viscosity B-Coefficients, Activation Free Energies for Viscous Flow, and Partial Molar Volumes

The viscosity B-coefficients and partial molar volumes have been measured for N,N-dimethylformamide and formamide in methanol + acetonitrile solvent systems and for N,N-dimethylformamide in water + acetonitrile mixed solvents. These data are used to calculate the solute contribution to the activation free energy for viscous flow, Δμ≠13, for these systems. It is found that the Δμ≠13 values are simply related to the corresponding enthalpies of transfer.

Interaction energies of van der Waals and hydrogen bonded systems calculated using density functional theory: Assessing the PW91 model

The performance of density functional theory using the Perdew and Wang’s exchange and correlation functionals (PW91) functional for the prediction of intermolecular interaction energies is evaluated based on calculations on the neon, argon, methane, ethylene, and benzene dimers, as well as on 12 hydrogen bonded complexes (water, methanol, formic acid, hydrogen fluoride, ammonia, formamide dimers and water–methanol, water–dimethyl ether, water–formaldehyde, hydrogen cyanide–hydrogen fluoride, water–ammonia, water–formamide complexes). The results were compared with those obtained from Becke’s exchange and Lee, Yang, and Parr’s correlation functionals (BLYP), Becke’s 3 parameter functional combined with Lee, Yang, and Parr’s correlation functional (B3LYP), second order Mo/ller–Plesset perturbation (MP2), and coupled cluster calculations with single and double substitutions and with non-iterative triple corrections [CCSD(T)] calculations. The calculated interaction energies show that the PW91 functional performs much better than the BLYP or B3LYP functionals. The error in the computed binding energies of the hydrogen bonded complexes is 20% in the worst case. The most demanding cases are the systems with large dispersion contributions to the binding energy, such as the benzene dimer. In contrast to the BLYP and B3LYP functionals which fail to account for dispersion, the PW91 functional at least partly recovers the attraction. The basis set dependence of the PW91 functionals is relatively small in contrast to the MP2 and CCSD(T) methods. Despite its occasional difficulties with dispersion interaction, the PW91 functional may be a viable alternative to the ab initio methods, certainly in situations where large complexes are being studied.

Effect of water on the formamide-intercalation of kaolinite

The molecular structures of low defect kaolinite completely intercalated with formamide and formamide–water mixtures have been determined using a combination of X-ray diffraction, thermoanalytical techniques, DRIFT and Raman spectroscopy. Expansion of the kaolinite to 10.09 Å was observed with subtle differences whether the kaolinite was expanded with formamide or formamide–water mixtures. Thermal analysis showed that greater amounts of formamide could be intercalated into the kaolinite in the presence of water. New infrared bands were observed for the formamide intercalated kaolinites at 3648, 3630 and 3606 cm −1. These bands are attributed to the hydroxyl stretching frequencies of the inner surface hydroxyls hydrogen bonded to formamide with water, formamide and interlamellar water. Bands were observed at similar positions in the Raman spectrum. At liquid nitrogen temperature, the 3630 cm −1 Raman band separated into two bands at 3633 and 3625 cm −1. DRIFT spectra showed the hydroxyl deformation mode at 905 cm −1. Changes in the molecular structure of the formamide are observed through both the NH stretching vibrations and the amide 1 and 2 bands. Upon intercalation of kaolinite with formamide, bands are observed at 3460, 3344, 3248 and 3167 cm −1 attributed to the NH stretching vibration of the NH involved with hydrogen bonded to the oxygens of the kaolinite siloxane surface. In the DRIFT spectra of the formamide intercalated kaolinites bands are observed at 1700 and 1671 cm −1 and are attributed to the amide 1 and amide 2 vibrations.

Calculations of Activation Entropies of Chemical Reactions in Solution

The elucidation of the role of entropic effects in enzyme catalysis is a problem of practical and fundamental interest. In order to address this problem it is essential to develop simulation methods capable of evaluating the entropic contribution, (ΔS⧧)‘, of the reacting fragments to the total activation entropy, ΔS⧧. In fact, the general ability to evaluate activation entropies of chemical reactions in solution has long been a challenge to computational chemists. The present work develops and examines a method for evaluation of (ΔS⧧)‘ and ΔS⧧. This method introduces a thermodynamic cycle that considers the transformation between the reactants state (RS) and the transition state (TS) in two paths. In the first path the reacting fragments are constrained to move along a single reaction coordinate while in the second path they are allowed to move also in the subspace perpendicular to the reaction coordinate. The difference between the activation barriers that correspond to the two paths provides the desired −T(ΔS⧧)‘. The cycle also involves two steps where a Cartesian restraint that fixes the reacting fragments in the RS and TS is released. The free energies, ΔG‘'s, associated with these restraint release steps are used to complete the thermodynamic cycle and to provide the actual estimate of (ΔS⧧)‘. This estimate is optimized by using different initial conditions and by selecting the smallest value of |ΔG‘|. The solvent contributions to the activation entropy are evaluated using a newly developed version of the Langevin dipole model. The potential surfaces used in the present work are obtained by the empirical valence bond (EVB) method. This method provides analytical yet reliable potential surfaces that reflect properly the motions of the reacting fragments and the coupling between these motions and the solvent polarization. The analytical representation of the EVB surfaces allows us to perform the extensive sampling necessary in order to obtain converging results. Our method is examined by evaluating the activation entropy for the hydrolysis of formamide in water. It is found that the calculated activation entropies reach convergence in a reasonable computer time and that the agreement between the calculated and observed results is reasonable. This method can be easily implemented in studies of enzymatic reactions and helps in assessing the importance of entropic effects in enzyme catalysis.