The Number of Water-Water Hydrogen Bonds in Water-Tetrahydrofuran and Water-Acetone Binary Mixtures Determined by Means of X-Ray Scattering

The liquid structures of water-tetrahydrofuran (THF) and water-acetone binary mixtures were investigated by the X-ray scattering method. Comparison of the X-ray scattering data revealed that only one kind of intermolecular water-organic molecule interaction is commonly involved throughout all mole fractions of these liquid mixtures, in addition to the intermolecular water-water and organic molecule-organic molecule interactions, which are present in neat water and organic liquids, respectively. On the basis of this finding, we proposed a new analytical method for studying liquid mixtures. By this method the structural information on the intermolecular water-organic molecule interaction as well as the concentrations of the intermolecular water-water, water-organic molecules, and organic molecule-organic molecule interactions were obtained. Combining the concentrations of the intermolecular water-water interaction with the concentrations of water in the liquid mixtures, the number of water-water hydrogen bonds at various mole fractions was experimentally determined for the first time. From the dependence of the number of water-water hydrogen bonds on the composition of the liquid mixtures, the change of the size of the self-associated water-water clusters was deduced.     

Cobalt(II) chloro complexation in N-methylformamide–N, N-dimethylformamide mixtures

Cobalt(II) chloro complexation has been studied by titration calorimetry and spectrophotometry in solvent mixtures of N-methylformamide (NMF) and N,N-dimethylformamide (DMF). It revealed that a series of mononuclear CoCln_n ^(2–n)+ (n=1–4) complexes are formed in the mixtures of NMF mole fraction x _NMF=0.05 and 0.25, and the CoCl⁺, CoCl₃ ^– and CoCl₄ ^2– complexes in the mixture of x _NMF=0.5, and their formation constants, enthalpies and entropies were obtained. As compared with DMF, the complexation is markedly suppressed in the mixtures, as well as in NMF. The decreasing formation constant of CoCl⁺ with the NMF content is mainly ascribed to the decreasing formation entropy. DMF is aprotic and thus less-structured, whereas NMF is protic to form hydrogen- bonded clusters. In DMF-NMF mixtures, solvent clusters in neat NMF are ruptured to yield new clusters involving DMF, the structure of which depends on the solvent composition. The entropy of formation of CoCl⁺ will be discussed in relation to the liquid structure of DMF, NMF and their mixtures.     

Isotope effects on thermodynamic properties in four binary systems: Water (or heavy water) + dimethylsulfoxide (or N,N-Dimethylformamide) at 25‡C

Excess enthalpy, excess isobaric heat capacity, density, and speed of sound in mixtures of heavy water (D₂O) + dimethylsulfoxide (DMSO), and D₂O + dimethylformamide (DMF) were measured at 25‡C. The same properties of the mixtures of normal water + DMSO, and H₂O + DMF were also measured to estimate isotope effects on the thermodynamic excess functions. Both DMSO and DMF are proton acceptors and thus form hydrogen bonds with water. Large negative excess enthalpies and volumes of mixing and excess isentropic compressibilities show that the hydrogen bonding structures of DMSO and DMF with water are stronger and more compact than those in pure water. The excess heat capacity of DMSO-containing mixtures changes sign from negative to positive with increasing water content. The deviations of the excess properties of D₂O systems from those of H₂O systems indicate that the hydrogen bonding structure with D₂O is stronger and more compact.     

CdSe quantum dots in chiral smectic C matrix: experimental evidence of smectic layer distortion by small and wide angle X-ray scattering and subsequent effect on electro-optical parameters

CdSe quantum dots (QDs) dispersed ferroelectric liquid crystal (FLC) has been subjected to small and wide-angle X-ray scattering and atomic force microscopy to understand the molecular organization in chiral smectic C (SmC*) phase. SAXS indicates that the presence of QDs causes enhancement in the smectic layer separation. The smectic order parameter for neat FLC and FLC–QDs mixtures is obtained in the range of 0.6 to 0.85. Both smectic order parameter and structural tilt are found to be lesser for FLC–QDs mixtures as compared to neat FLC. The insertion of QDs in SmC* matrix causes localized smectic layer distortion in such a way that spontaneous polarization remains almost the same but the electro-optic switching of molecules becomes faster. We have outlined the superiority of FLC–QDs mixtures for electrical energy storage and their suitability in electronic devices.     

Liquid structure and preferential solvation of metal ions in solvent mixtures of N,N-dimethylformamide and N-methylformamide

Raman spectra of aprotic N,N-dimethylformamide (DMF) and protic N-methylformamide (NMF) mixtures containing manganese(II), nickel(II), and zinc(II) perchlorate were obtained, and the individual solvation numbers around the metal ions were determined over the whole range of solvent compositions. Variation profiles of the individual solvation numbers with solvent composition showed no significant difference among the metal systems examined. In all of these metal systems, no preferential solvation occurs in mixtures with DMF mole fraction of x(DMF) < 0.5, whereas DMF preferentially solvates the metal ions at x(DMF) > 0.5. The liquid structure of the mixtures was also studied by means of small-angle neutron scattering (SANS) and low-frequency Raman spectroscopy. SANS experiments demonstrate that DMF molecules do not appreciably self-aggregate in the mixtures over the whole range of solvent composition. Low-frequency Raman spectroscopy suggests that DMF molecules are extensively hydrogen-bonded with NMF in NMF-rich mixtures, whereas NMF molecules extensively self-aggregate in DMF-rich mixtures, although the liquid structure in neat NMF is partly ruptured. The bulk solvent structure in the mixtures thus varies with solvent composition, which plays a decisive role in developing the varying profiles of the individual solvation numbers of metal ions in the solvent mixtures.     

Amide-induced phase separation of hexafluoroisopropanol-water mixtures depending on the hydrophobicity of amides

Amide-induced phase separation of hexafluoro-2-propanol (HFIP)-water mixtures has been investigated to elucidate solvation properties of the mixtures by means of small-angle neutron scattering (SANS), (1)H and (13)C NMR, and molecular dynamics (MD) simulation. The amides included N-methylformamide (NMF), N-methylacetamide (NMA), and N-methylpropionamide (NMP). The phase diagrams of amide-HFIP-water ternary systems at 298 K showed that phase separation occurs in a closed-loop area of compositions as well as an N,N-dimethylformamide (DMF) system previously reported. The phase separation area becomes wider as the hydrophobicity of amides increases in the order of NMF < NMA < DMF < NMP. Thus, the evolution of HFIP clusters around amides due to the hydrophobic interaction gives rise to phase separation of the mixtures. In contrast, the disruption of HFIP clusters causes the recovery of the homogeneity of the ternary systems. The present results showed that HFIP clusters are evolved with increasing amide content to the lower phase separation concentration in the same mechanism among the four amide systems. However, the disruption of HFIP clusters in the NMP and DMF systems with further increasing amide content to the upper phase separation concentration occurs in a different way from those in the NMF and NMA systems.     

Stability constants of zinc halide complexes in DMSO—water and DMF—water mixtures

The overall stability constants of zinc bromide and iodide complexes in DMSO—water and those of zinc chloride, bromide and iodide in DMF—water mixtures have been determined potentiometrically at mole ratios about 0.2–1 for the organic solvents at 25°C and in a 0.5 M ammonium perchlorate ionic medium. The complex formation is much stronger in DMF and its mixtures than in DMSO and the log βs are generally higher in solvent mixtures than those expected from the values measured in the pure components.     

Solvent influence on complex formation between Cd<Superscript>2+</Superscript> and 2-hydroxy-1,4-naphthoquinone in binary mixed nonaqueous solvents at 15–45°C

The complexation reaction of Cd²⁺ cation with 2-hydroxy-1,4-naphthoquinone (HNQ) was studied in acetonitrile (AN), 2-PrOH, ethyl acetate (EtOAc), EtOH, dimethylformamide (DMF) and in binary solutions AN–2-PrOH, AN–DMF, AN–EtOH, and AN–EtOAc using conductometric method at 15–45°C. The conductance data show that the stoichiometry of the Cd²⁺ complex with HNQ in all solvent systems is 1 : 1. In the pure solvents the stability of the complex changes in the order AN > 2-PrOH > EtOH > DMF. The stability of the complex at 25°C in the studied mixtures changes in the following order : AN?EtOAc > AN?2-PrOH > AN?EtOH > AN?DMF. These orders are affected by the nature and composition of the solvent systems and by the temperature. From the temperature dependence data, the thermodynamic functions values (ΔH° and ΔS°) for the complex formation were calculated.     

Tunable clathrates

Investigation of the selectivity of a diol organic host for mixtures of DMF and DMSO, showed the formation of five inclusion compounds in which the stoichiometry varies in discrete steps and is determined by the composition of the liquid guest mixture; the structures of these compounds are described.     

Study of the complex formation between 18C6 crown ether and Tl(+), Pb(2+) and Cd(2+) in binary non-aqueous solvents using differential pulse polarography

Complexation of the Tl(+), Pb(2+) and Cd(2+) ions with macrocyclic ligand 18-crown-6 (18C6) was studied in various binary solvent mixtures of propylencarbonate (PC)/dimethylformamide (DMF) and acetonitrile (AN)/dimethylsulfoxide (DMSO) systems at 22 degrees C using the differential pulse polarographic technique. The stoichiometry of the complexes was found to be 1:1 and the complexation constants increased with decreasing amounts of dimethylsulfoxide and dimethylformamide in these binary systems. In all cases, the variation of the stability constant with composition of the solvents was monotonic and showed good correlation with the inherent solvation ability of the neat solvents which form the mixture. In all of the solvent systems, the selectivity order for 18C6 complexes is Tl(+) > Pb(2+) > Cd(2+).     

Non‐Ideal Behaviour and Solution Interactions in Binary DMSO Solutions

The structure and dynamics of hydrogen‐bonded structures are of significant importance in understanding many binary mixtures. Since self‐diffusion is very sensitive to changes in the molecular weight and shape of the diffusing species, hydrogen‐bonded associated structures in dimethylsulfoxide–methanol (DMSO–MeOH) and DMSO–ethanol (DMSO–EtOH) mixtures are investigated using nuclear magnetic resonance (NMR) diffusion experiments and molecular dynamics (MD) simulations over the entire composition range at 298 K. The self‐diffusion coefficients of DMSO–MeOH and DMSO–EtOH mixtures decrease by up to 15% and 10%, respectively, with DMSO concentration, indicating weaker association as compared to DMSO–water mixtures. The calculated heat of mixing and radial distribution functions reveal that the intermolecular structures of DMSO–MeOH and DMSO–EtOH mixtures do not change on mixing. DMSO–alcohol hydrogen‐bonded dimers are the dominant species in mixtures. Direct comparison of the simulated and experimental data afford greater insights into the structural properties of binary mixtures.     

Thermodynamics of mixtures containing a very strongly polar compound: IV – application of the DISQUAC,UNIFAC and ERAS models to DMSO+ organic solvent systems

Binary mixtures of dimethylsulfoxide (DMSO) with alkane, benzene, toluene 1-alkanol, or 1-alkyne have been investigated in terms of DISQUAC. The corresponding interaction parameters are reported. ERAS parameters for 1-alkanol + DMSO mixtures are also given. ERAS calculations were developed considering DMSO as a not self-associated compound.

DISQUAC represents fairly well a complete set of thermodynamic properties: molar excess enthalpies, molar excess Gibbs energies, vapor–liquid equilibria, natural logarithms of activity coefficients at infinite dilution, or partial molar excess enthalpies at infinite dilution. DISQUAC improves UNIFAC calculations for H ^E . Both models yield similar results for VLE. In addition, DISQUAC also improves, ERAS results for 1-alkanol + DMSO mixtures. This may be due to ERAS cannot represent the strong dipole–dipole interactions present in such solutions.     

Photophysics of phenylpyrrole derivatives and their acetonitrile clusters in the gas phase and in argon matrixes: simulations of structure and reactivity

Recent experiments on the dual fluorescence of phenylpyrrole (PP) and pyrrolobenzonitrile (PBN) in supersonic jets and in cryogenic matrixes are analyzed. The structures of the 1:1 clusters are calculated using ab initio, density functional theory (DFT) and molecular mechanics (MM) methods. In these calculations, the structures of PP and PBN in the ground state and in two possible minima on the charge-transfer excited state are taken from a recent theoretical analysis. The structures of PP and PBN clusters with a larger number of acetonitrile molecules are also calculated using the molecular mechanics method. It is shown that the fact that small PP:AN and PBN:AN clusters do not exhibit any charge-transfer (CT) type emission, whereas for PBN:AN(n) clusters (n > or = 4) CT emission is observed, can be understood on the basis of the calculated structures. The trapping of PP and of PBN in an argon matrix (neat and doped with acetonitrile) is simulated by a molecular dynamics procedure. The observation of locally excited (LE) fluorescence only from PP in neat argon, whereas from argon-trapped PBN both CT and LE emission bands are observed, is readily understood on the basis of these simulations. Moreover, the appearance of CT emission from PP-doped argon matrixes when acetonitrile is added is also explained, as well as the relatively small spectral shift observed upon addition of acetonitrile to PBN-doped argon matrixes.     

Structures of neat and hydrated 1-octanol from computer simulations

Molecular dynamics computer simulations of 1-octanol and its mixtures with water have been performed. The liquid is composed of regions enriched in either hydrocarbons or hydroxyl groups. In neat octanol, the hydroxyl groups form clusters of long, thin chains. Upon the addition of water, the clusters become longer and more spherical, forming a structure that can be described as consisting of "overlapping elongated inverse micelles". The structures of the mixtures obtained at different hydration levels are consistent with those of experimental diffraction studies of water/octanol mixtures and previous computer simulations of neat and water-saturated octanol. The saturation point of the model has been calculated using the cavity-bias particle insertion method. The solubility of water in octanol is slightly too low compared to experimental results, and suggestions for possible improvements to the force field are made.     

Solvent effects on radical copolymerization of acrylonitrile and methyl acrylate: solvent polarity and solvent-monomer interaction

Abstract

New insights for the effects of organic solvent polarities and solvent-monomer interactions on the radical copolymerization for an important copolymer, poly(acrylonitrile-co-methyl acrylate) (PAN-co-MA), were provided in this research. Solvents, dimethylformamide (DMF), dimethylacetamide (DMAc) and dimethyl sulfoxide (DMSO), were used as reaction media. The polarity of these solvents was in the sequence of DMAc?<?DMF?<?DMSO. By studying the reactivity ratios of AN and MA, the triad fractions of the resultant copolymers, the interactions between monomers and solvents, and the compositions of copolymers at various conversions, we concluded that the solvent polarity had minimal influence on the copolymerization of AN and MA, while the solvent-monomer interactions played important roles. The interactions between monomer-monomer, monomer-solvent, and solvent-solvent, were calculated based on quantum chemistry methods. Both theoretical calculations and experimental results suggested that AN and MA in DMSO tended to aggregate locally, while they could be homogeneously dissolved in DMAc and DMF. The interactions between solvent and monomers could cause local monomer concentration variations, or ‘bootstrap’ effect, which is one of the critical factors affecting the copolymerization process of AN and MA and the chemical structures of the resultant polymers.     

Semidilute solution structure of cellulose in an ionic liquid and its mixture with a polar organic co‐solvent studied by small‐angle X‐ray scattering

Structural and thermodynamic properties of cellulose solutions in the ionic liquid 1‐ethyl‐3‐methylimidazolium acetate (EMIMAc) and its binary mixtures with N,N‐dimethyl formamide (DMF) are studied by small‐angle X‐ray scattering (SAXS). These measurements indicate molecular dissolution of the cellulose chains without any significant aggregation. The power–law relationships of the evaluated correlation length and osmotic modulus to concentration exhibit exponents of ?0.76 and 2.06 for EMIMAc and ?0.80 and 2.14 for DMF/EMIMAc solvent mixture, respectively. Thus, these solvents can be considered to be good solvents for cellulose. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55 , 888–894     

The influence of water–organic solvent composition on the morphology and luminescent properties of CdS nanoparticles obtained by chemical precipitation

Cadmium sulfide (CdS) nanoparticles have been obtained by chemical precipitation onto the surface of single-crystalline silicon from an aqueous solution of ammonia, cadmium chloride (CdCl₂), and thiourea, as well as from water–DMSO and water–DMF mixtures with the same concentrations of the reagents. According to data of atomic force microscopy, the samples obtained from the aqueous solution consist of individual nanoparticles and agglomerates thereof with sizes of no larger than 1 µm. Materials obtained from the water–organic mixtures are distinguished by the aggregation of CdS nanoparticles into threadlike chains. The length of the formed curved chains and the size of CdS nanoparticles composing them depend on the nature and amount of an organic component of a mixture. Atomic force microscopy, transmission electron microscopy, and photoluminescence spectroscopy data have shown that the average size of CdS nanoparticles is 2–2.5 nm depending on solvent composition.     

Donor-Acceptor Complexes in Copolymerization. XXVI. Effect of Solvent,Temperature, and Complexing Agent on the Polymerization of Comonomer Charge Transfer Complexes

The copolymerization of styrene with methyl methacrylate (S/MMA = 4/1) or acrylonitrile (S/AN = 1/1) in the presence of ethylaluminum sesquichloride (EASC) yields 1/1 copolymer in toluene or chlorobenzene. In chloroform the S-MMA-EASC polymerization yields 60/40 copolymer while the S-AN-EASC polymerization yields 1/1 copolymer. In the presence of EASC, styrene-α-chloroacrylonitrile yields 1/1 copolymer (DMF or DMSO), S-AN yields 1/1 copolymer (DMSO) or radical copolymer (DMF), S-MMA yields radical copolymer (DMF or DMSO), α-methylstyrene-AN yields radical copolymer (DMSO) or traces of copolymer (DMF), and α-MS-methacrylo-nitrile yields traces of copolymer (DMSO) or no copolymer (DMF). When zinc chloride is used as complexing agent in DMF or DMSO, none of the monomer pairs undergoes polymerization. However, radical catalyzed polymerization of isoprene-AN-ZnCl₂ in DMF yields 1/1 alternating copolymer. The copolymerization of S/MMA in the presence of EASC yields 1/1 alternating copolymer up to 100°C, while the copolymerization of S/AN deviates from 1/1 alternating copolymer above 50°C. The copolymerization of S/MMA deviates from 1/1 copolymer at MMA/EASC mole ratios above 20 while the copolymerization of S/AN deviates from 1/1 copolymer at MMA/EASC ratios above 50.     

The thermochemical characteristics of solution of phenol and benzoic acid in water-dimethylsulfoxide and water-acetonitrile mixtures

The solution of phenol and benzoic acid in water-dimethylsulfoxide (DMSO) and water-acetonitrile (AN) mixtures was studied. As distinct from benzoic acid, the thermodynamic characteristics of solution of phenol sharply change at concentrations corresponding to a change in the character of cluster formation in water-DMSO and water-AN mixtures. Differences in the solvation of phenol and benzoic acid are explained by different mechanisms of the interaction of the solutes with clusters existing in binary mixtures.     

Solvation effect in thermal decomposition of 2,2′-azoisobutyronitrile on the N,N-dimethylformamide/acrylonitrile system

The thermal decomposition rate constant of AIBN (k_d) in N, N-dimethylformamide (DMF)/acrylonitrile (AN) mixtures of various compositions at 60°C is studied. The k_d value is (6.45 ± 0.3) × 10⁻⁴ min⁻¹ for pure DMF and (7.20 ± 0.3) × 10⁻⁴ min⁻¹ for pure acrylonitrile. The k_d values of DMF/AN mixtures were found to be dependent on the mixture composition. This dependence is not a linear function of the monomer mole fraction (x_M), but has a minimum at ca. 70 mol % of AN. The relationship k_d = f(x_M) has been interpreted on the basis of the hypothesis of initiator solvation by monomer AN and solvent DMF. © 1996 John Wiley & Sons, Inc.