Toshiyuki Takamuku

Liquid Structure of Room-Temperature Ionic Liquid, 1-Ethyl-3-methylimidazolium Bis-(trifluoromethanesulfonyl) Imide

The liquid structure of 1-ethyl-3-methylimidazolium bis-(trifluoromethanesulfonyl) imide (EMI(+)TFSI(-)) has been studied by means of large-angle X-ray scattering (LAXS), (1)H, (13)C, and (19)F NMR, and molecular dynamics (MD) simulations. LAXS measurements show that the ionic liquid is highly structured with intermolecular interactions at around 6, 9, and 15 A. The intermolecular interactions at around 6, 9, and 15 A are ascribed, on the basis of the MD simulation, to the nearest neighbor EMI(+)...TFSI(-) interaction, the EMI(+)...EMI(+) and TFSI(-)...TFSI(-) interactions, and the second neighbor EMI+...TFSI(-) interaction, respectively. The ionic liquid involves two conformers, C(1) (cis) and C(2) (trans), for TFSI(-), and two conformers, planar cis and nonplanar staggered, for EMI(+), and thus the system involves four types of the EMI(+)...TFSI(-) interactions in the liquid state by taking into account the conformers. However, the EMI(+)...TFSI(-) interaction is not largely different for all combinations of the conformers. The same applies alsoto the EMI(+)...EMI(+) and TFSI(-)...TFSI(-) interactions. It is suggested from the 13C NMR that the imidazolium C(2) proton of EMI(+) strongly interacts with the O atom of the -SO(2)(CF(3)) group of TFSI(-). The interaction is not ascribed to hydrogen-bonding, according to the MD simulation. It is shown that the liquid structure is significantly different from the layered crystal structure that involves only the nonplanar staggered EMI(+) and C(1) TFSI(-) conformers.

Experimental evidences for molecular origin of low-Q peak in neutron/x-ray scattering of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ionic liquids.

Short- and long-range liquid structures of [C(n)mIm(+)][TFSA(-)] with n = 2, 4, 6, 8, 10, and 12 have been studied by high-energy x-ray diffraction (HEXRD) and small-angle neutron scattering (SANS) experiments with the aid of MD simulations. Observed x-ray structure factor, S(Q), for the ionic liquids with the alkyl-chain length n > 6 exhibited a characteristic peak in the low-Q range of 0.2-0.4 Å(-1), indicating the heterogeneity of their ionic liquids. SANS profiles I(H)(Q) and I(D)(Q) for the normal and the alkyl group deuterated ionic liquids, respectively, showed significant peaks for n = 10 and 12 without no form factor component for large spherical or spheroidal aggregates like micelles in solution. The peaks for n = 10 and 12 evidently disappeared in the difference SANS profiles ΔI(Q) [=I(D)(Q) - I(H)(Q)], although that for n = 12 slightly remained. This suggests that the long-range correlations originated from the alkyl groups hardly contribute to the low-Q peak intensity in SANS. To reveal molecular origin of the low-Q peak, we introduce here a new function; x-ray structure factor intensity at a given Q as a function of r, S(Q) (peak)(r). The S(Q) (peak)(r) function suggests that the observed low-Q peak intensity depending on n is originated from liquid structures at two r-region of 5-8 and 8-15 Å for all ionic liquids examined except for n = 12. Atomistic MD simulations are consistent with the HEXRD and SANS experiments, and then we discussed the relationship between both variations of low-Q peak and real-space structure with lengthening the alkyl group of the C(n)mIm.

Effect of water on structure of hydrophilic imidazolium-based ionic liquid.

The state of water in room-temperature ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI(+)BF(4)(-)), has been investigated by measurements of absorption and desorption isotherms, attenuated total reflectance infrared (ATR-IR) spectroscopy, and (2)H NMR relaxation method. The absorption enthalpies of water for the ionic liquid were estimated from the absorption isotherms. The enthalpies in the water mole fraction range of x(w) <or= approximately 0.5 are lower than the enthalpy of vaporization for bulk water, but become larger than the value for bulk with increasing mole fraction of absorbed water. The ATR-IR spectra for EMI(+)BF(4)(-)-water solutions in the range of 0.09 <or= x(w) <or= 0.34 have revealed that individual water molecules hydrogen-bonded to the anions predominate in the solutions at x(w) <or= approximately 0.2, while approximately 30% of water molecules are hydrogen-bonded among them in the solutions at x(w) > approximately 0.3. In addition, the activation energies for the rotational motion of a water molecule estimated from the (2)H NMR relaxation rates have indicated that the motion of water molecules in EMI(+)BF(4)(-)-D(2)O solutions gradually becomes freer with increasing water content from x(w) = 0.10 to 0.30, but is retarded again at x(w) = 0.33. Therefore, all the present findings have suggested that the state of water molecules in EMI(+)BF(4)(-) significantly changes at x(w) approximately 0.3. On the other hand, to directly observe the effect of water on structure of EMI(+)BF(4)(-), LAXS experiments have been made on EMI(+)BF(4)(-)-water solutions. It has been suggested that the interactions between the C(2) atom within the imidazolium ring of EMI(+) and BF(4)(-) are strengthened with increasing water content, while those at the C(4) and C(5) atoms weaken. Thus, the present LAXS experiments have clarified the beginning of formation of ion pair in EMI(+)BF(4)(-) by adding water at the molecular level.

Structure and dynamics of 1,4-dioxane-water binary solutions studied by X-ray diffraction, mass spectrometry, and NMR relaxation☆

Abstract The structure of clusters formed in 1,4-dioxane-water binary solutions has been investigated at ambient temperature as a function of 1,4-dioxane concentration by X-ray diffraction for the corresponding solutions and by mass spectroscopy for liquid droplets formed in vacuum from the liquid mixtures by an adiabatic expansion method. The 2H spin-lattice relaxation times of D2O and 1,4-dioxane-d8 molecules in 1,4-dioxane-water binary solutions have also been measured at 30 °C over a whole range of 1,4-dioxane mole fraction. It has been found from the analysis of X-ray radial distribution functions that the number of hydrogen bonds per water and 1,4-dioxane oxygen atom decreases with increasing 1,4-dioxane mole fraction Xdio accompanied by two inflection points at Xdio = ∼-0.1 and ∼0.3: at Xdio ≤ 0.1 the hydrogen-bonded network of water is predominant in the binary solutions, at Xdio ≥ 0.3 the inherent structure of 1,4-dioxane is mostly observed, water molecules probably involved in the structure by hydrogen bonding, and at 0.15 ≤ Xdio ≤ 0.2 both structures of water and 1,4-dioxane are ruptured to form small binary clusters of one or two dioxane and several water molecules. The mass spectra have revealed that at Xdio = 0.01 water clusters Wn (W = water, n = 6 2- 43) are mostly formed, but with increasing Xdio to 0.4 the water clusters are reduced with evolving 1,4-dioxane clusters DmWn (D = 1,4-dioxane, m = 1 – 3, n = 1 – 16). The 2H spin-lattice relaxation data of D2O molecules in the mixtures showed that the rotation of water molecules is gradually retarded with increasing Xdio to −0.3, where the rotation is the slowest, and is then gradually accelerated with further increase in Xdio. The corresponding data of 1,4-dioxane-d8 molecules showed a similar tendency, but the slowest motion observed at Xdio = −0.2. The present microscopic cluster structure and dynamic properties of the mixtures are discussed in connection with the heat of mixing, viscosity, hydrophobic hydration, and clathrate hydrate.

Exposure assessment of organophosphorus and organobromine flame retardants via indoor dust from elementary schools and domestic houses

To assess the exposure of flame retardants (FRs) for school-children, organophosphorus flame retardants and plasticizers (PFRs) and organobromine flame retardants (BFRs) were determined in the indoor dust samples collected from elementary schools and domestic houses in Japan in 2009 and 2010. PFRs were detected in all the dust samples analyzed and the highest concentration of total PFRs was thousand-fold higher than that of BFRs. Among the PFRs, tris(butoxyethyl)phosphate (TBOEP) showed the highest concentration with a median (med.) of 270,000 ng g(-1) dry weight (3700-5,500,000 ng g(-1) dry weight), followed by tris(methylphenyl)phosphate (TMPPs)>triphenyl phosphate (TPHP)=tris(1,3-dichloro-2-propyl)phosphate (TDCIPP)=tris(2-chloroisopropyl)phosphate (TCIPP)=tris(2chloroethyl)phosphate (TCEP)>ethylhexyl diphenyl phosphate (EHDPP). Significantly higher concentrations of TBOEP, tri-n-butyl phosphate (TNBP), TPHP, TMPPs, and total-PFRs were found in dust samples from elementary schools than from domestic houses. It might be due to that higher concentrations of TBOEP (as leveling agent) were detected from the floor polisher/wax products collected in those elementary schools. On the other hand, significantly higher concentrations of TCEP, TCIPPs, and total chloroalkyl-PFRs were found in domestic houses than in elementary schools. Exposure assessments of PFRs via indoor dust from elementary schools and domestic houses were conducted by calculating the hazard quotient (HQ). Among PFRs, HQs for TBOEP exceeded 1 (higher than reference dose: RfD) and its highest value was 1.9. To reduce the intake of TBOEP by school-children, it is recommended that the use of floor polisher/wax containing TBOEP be reduced in schools.

Large-angle X-ray scattering, small-angle neutron scattering, and NMR relaxation studies on mixing states of 1,4-dioxane-water, 1,3-dioxane-water, and tetrahydrofuran-water mixtures

Abstract Aqueous mixtures of cycloethers, 1,4-dioxane (pdio), 1,3-dioxane (mdio), and tetrahydrofuran (THF) have been investigated by using large-angle X-ray scattering (LAXS), small-angle neutron scattering (SANS), and NMR relaxation techniques. The results from the LAXS experiments have revealed that at a microscopic level the structures of the cycloether-water mixtures change with cycloether mole fraction xC (C = pdio, mdio and THF) in a similar way: in the range of xC 1,3-dioxane-water ⪢ 1,4-dioxane-water mixtures. The NMR relaxation data have revealed that the rotational motion of water molecules is most restricted at xC ≈ 0.3, suggesting that the hydrogen bonds among water molecules are most strengthened at this mole fraction. On the basis of the static structures from the microscopic to mesoscopic levels and the dynamic property of water molecules, the effects of the size of cycloether molecules and the position of oxygen atoms in the molecules on the mixing states of the mixtures are discussed.

Clusters of imidazolium-based ionic liquid in benzene solutions.

Cluster formation of 1-dodecyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (C(12)mim(+)TFSA(-)) in benzene solutions was investigated using small-angle neutron scattering (SANS), NMR, attenuated total reflectance infrared (ATR-IR), and large-angle X-ray scattering (LAXS) techniques. The SANS measurements revealed that C(12)mim(+)TFSA(-) is heterogeneously mixed with benzene in the narrow range of benzene mole fraction 0.9 ≤ x(C6D6) ≤ 0.995 with a maximum heterogeneity at x(C6D6) ≈ 0.99. The NMR results suggested that the imidazolium ring is sandwiched between benzene molecules through the cation-π interaction. Moreover, TFSA(-) probably interacts with the imidazolium ring even in the range of x(C6H6) ≥ 0.9. Thus, the imidazolium rings, benzene molecules, and TFSA(-) would form clusters in the C(12)mim(+)TFSA(-)-benzene solutions. The LAXS measurements showed that the distance between the imidazolium ring and benzene is ∼3.8 Å with that between the benzene molecules of ∼7.5 Å. On the basis of these results, we discussed a plausible reason for the liquid-liquid equilibrium of the C(12)mim(+)TFSA(-)-benzene system.

Structure and dynamics of hexafluoroisopropanol-water mixtures by x-ray diffraction, small-angle neutron scattering, NMR spectroscopy, and mass spectrometry

The structure and dynamic properties of aqueous mixtures of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) have been investigated over the whole range of HFIP mole fraction (xHFIP) by large-angle x-ray scattering (LAXS), small-angle reutron scattering (SANS), 19F-, 13C-, and 17O-NMR chemical shifts, 17O-NMR relaxation, and mass spectrometry. The LAXS data have shown that structural transition of solvent clusters takes place at xHFIP∼0.1 from the tetrahedral-like hydrogen bonded network of water at xHFIP⩽∼0.1 to the structure of neat HFIP gradually formed with increasing HFIP concentration in the range of xHFIP⩾0.15. The Ornstein–Zernike plots of the SANS data have revealed a mesoscopic structural feature that the concentration fluctuations become largest at xHFIP∼0.06 with a correlation length of ∼9 A, i.e., maximum in clustering and microhetrogeneities. The 19F and 13C chemical shifts of both CF3 and CH groups of HFIP against xHFIP have shown an inflection point at xHFIP∼0.08, implying that the environment of ...

Liquid Structure of 1-Propanol by Molecular Dynamics Simulations and X-Ray Scattering

Molecular dynamics (MD) simulations and X-ray scattering experiments have been carried out on liquid 1-propanol. The radial distribution functions obtained from these two methods were in good agreement with each other. On the basis of the hydrogen-bond number and the angular correlation functions of the four sequentially hydrogen-bonded O atoms derived from the MD calculation, it was found that the hydrogen-bonded O atoms preferentially form a planar zigzag chain structure, but that the plane undulates like a wave.

An extended Johnson–Furter equation to salting-out phase separation of aqueous solution of water-miscible organic solvents

Abstract The Johnson–Furter equation, which correlates the salt effects on relative volatility changes of components in a binary mixture at presence of salt, is extended to salting-out phase separation phenomenon observed in aqueous solutions of some water-miscible organic solvents. The extended equation quantitatively correlates partitions of components of the ternary mixture, namely, the organic solvent, water, and the salt between the salted-out two phases, and is successfully applied to five ternary mixtures including acetonitrile–H 2 O–LiCl, –NaCl, –KCl, acetone–H 2 O–NaCl, and 2-propanol–H 2 O–NaCl where salting-out phase separation occurs. A molecular mechanism of salting-out phase separation as salt-solvent and solvent–solvent interactions is also discussed by using Kirkwood–Buff solution theory.