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Sum frequency generation (SFG) spectroscopy is a nonlinear vibrational spectroscopic technique used in the study of interfaces, due to its unique ability to distinguish surface molecules that have preferential ordering compared to the isotropic bulk. Here, a series of alkyltrioctylphosphonium chloride ionic liquids, systematically varied by cation structure, were characterized at the air-liquid interface by SFG. The effect on surface structure resulting from molecular variation (i.e., addition of cyano- and methoxy-functional groups) of the cation alkyl chain was investigated. SFG spectra in the C—H stretching region (2750–3100 cm−1) for [P8 8 8 n][Cl], where n = 4, 5, 8, 10, 12, or 14, showed characteristic changes as the alkyl chain length was increased. Spectral profiles for n = 4, 5, 8, or 10 appeared similar; however, when the fourth alkyl chain was sufficiently long (as in the case of n = 12 or n = 14), abrupt changes occurred in the spectra. Molecular dynamics (MD) simulation of a slab of each ionic liquid (with n = 8, 10, or 12) confirmed gauche defects, with enhancement for the long alkyl chain and an abrupt increase of gauche occurrence from n = 8 to n = 10. A comparison of the tilt angle distribution from the simulation and the SFG analysis show a broad distribution of angles. Using experimental SFG spectra in conjunction with MD simulations, a comprehensive molecular picture at the surface of this unique class of liquids is presented. [ABSTRACT FROM AUTHOR]

It has been widely recognized that although ionic liquids should be colorless, they are frequently not. Colored samples appear to be pure by most analytical techniques (e.g., NMR spectroscopy, mass spectrometry, HPLC, and ion chromatography), and there have been many attempts to identify the source of color in our own laboratories and others--after 20 years the best that can be said is that the impurities are at a very low level (probably parts per billion) with very high molar extinction coefficients. In this paper, we do not identify these impurities but describe a practical method for removing them for spectrochemical applications. We clearly note that the method is not 'green', but we anticipate that it will only be applied to the small volumes of ionic liquids required for fundamental spectroscopic studies in academia but not in industrial processes.

Author(s): Martyn J. Earle [1]; José M.S.S. Esperança [2]; Manuela A. Gilea [1]; José N. Canongia Lopes [2]; Luís P.N. Rebelo (corresponding author) [2]; Joseph W. Magee [3]; Kenneth R. [...]

Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim] [PF6]), 1-hexyl-3-methylimidazolium chloride ([C6mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C4mim] [PF6]), and binary mixtures thereof, are assigned using ab initio MP2 calculations. The vibrational analysis of the binary system reveal that the changes in hydrogen bonding to the ring hydrogen atoms do not have any detectable effect on the 50:50 distribution of the two conformers.

The nature of various types of interactions prevailing in solutions of potassium thiocyanate (KCNS), ammonium thiocyanate (NH4CNS), sodium nitrate(NaNO3), and ammonium nitrate (NH4NO3) in 2-methoxyethanol from precise measurements on electrical conductivity and Fourier transform infrared spectral (FTIR) measurements is reported. Results indicate that all of the electrolytes are found to exist essentially as solvent-separated dimers or both in 2-methoxyethanol solutions.

Studies done on the preferred gas-phase conformations of a series of deprotonated and protonated mononucleotides by ion mobility experiments and theoretical modeling calculations is reported. Density Functional Theory (DFT) calculations indicate that the most energetically favored sites for protonation are N3 on dAMP, N7 on dGMP, N3 on dCMP, and the phosphate group on dTMP.

Molecular dynamics (MD) simulation and normal-mode analysis (NMA) are used to study the thermodynamic properties of bovine pancreatic trypsin inhibitor (BPTI) hydrated by up to 1600 water molecules. Results indicate that the coefficient of thermal conductivity may well be 50% or so larger than that computed with normal modes.

Isothermal-isobaric Monte Carlo molecular simulation is used to measure the vapor-phase fugacity coefficients and equation of state of three fixed-charge models of water that are SPC/E, MSPC/E, and TIP3P. Findings reveal that the model show significant deviation from ideal-gas behavior, considerably more than seen experimentally, and a second-order virial treatment does not fully characterize the behavior.

Studies done on liquid-liquid phase splitting in ternary mixtures that contain a room-temperature ionic liquid and an alcohol aqueous solution -namely, [bmim][PF6] + ethanol + water and [bmim] [NTf2] + 2-methypropanol + water using a He-Ne laser light-scattering method is reported. It was found that both ternary mixtures exhibit a very pronounced water-alcohol co-solvent effect.

The study states that the laser flash photolysis (LFP) of nine - azidoanthracene produces singlet 9 - anthrylnitrene ((super 1) AN) with transient absorption maxima at 331, 344 and 412 nm. The study observes an agreement with calculation that indicates that the conversion of (super 1) A to A2 is endothermic by 23 kcal/mol.

The one-electron reduction of oxygen was investigated by cyclic voltammetry at a gold microdise electrode in the RTILs, 1-ethyl-3-methylimidazotium bis ((trifluoromethyl) sulfonyl) imide ([EMIM][(Tf)(sub 2)]) and hexyltriethylammonium bis ((trifluoromethyl) sulfonyl) imide ([N (sub 6222][N (Tf)(sub 20]). The study results of the higher viscosity of [N (sub 6222][N (Tf)(sub 2)] in comparison to [EMIM][N (Tf)(sub 2)] due to the structural differences in cationic component.

The paper of the Dunhuang Diamond Sutra - the world's oldest, dated, printed book - is dyed yellow with an extract believed to contain the alkaloid berberine as the principal colorant. Unambiguous identification of the dye used on this unique book is essential for its conservation. We have developed here a simple, rapid, high-performance liquid chromatography method that gives excellent separation of the protoberberine alkaloids and allows the unambiguous detection of berberine in dyes extracted from tiny fragments of ancient papers. Examination of 25 ancient papers contemporary with the Dunhuang Diamond Sutra revealed the presence not only of berberine but also the previously unsuspected yellow compounds, palmatine and jatrorrhizine.

Cyclic voltammetry and electronic absorption spectroscopy help characterize the chloride complexes from the metal-metal bonded (Ta6Cl12)z+ in acetonitrile and in acidic AlCl3-1-methyl-3-ethylimidazolium chloride. Substitution of (AlCl4)- for labile chlorides on the ((Ta6Cl12)Cl6)(6-z)- generates a species of the type ((Ta6Cl12)Cl(y)(AlCl4)6y)(6-z)-. The influence of solvents on the reduction potentials of these complexes is discussed.

Spectroscopic and electrochemical studies probe into the structure and stability of chloride clusters from {Nb6Cl12}(z+) cores (z = 1-4) dissolved in the molten salt AlCl3-MeEtimCl. The basic melt yields four (Nb6Cl12)Cl6 anions. The z(5-) anion decomposes on electrolytic reduction while the z(1-) anion is reduced to the z(3-) anion. The acidic melt yields stable z(2+-4+) cationic clusters. The mass-transport controlled redox reactions of {Nb6Cl12}(2+/3+) and {Nb6Cl12}(3+/4+) are in contrast with quasireversible reactions in dichloromethane of their phosphine cousins. The positive voltage shift on going from basic to acidic melt indicates displacement by AlCl4(-) of unstable chloride ions in the {Nb6Cl12} chloride clusters.