New insights into chloromethyl-oxirane and chloromethyl-thiirane in liquid and solid phase from low-temperature infrared spectroscopy and ab initio modeling.

A detailed study of the conformational landscape of chloromethyl-oxirane and chloromethyl-thiirane is here reported. The equilibrium of the three different conformers of the two molecules was assessed, using a joint approach of experimental and theoretical methods. High quality infrared spectroscopy measurements of the liquid and of the crystalline phases were interpreted with the aid of ab initio Molecular Dynamics (AIMD) simulations, anharmonic frequencies and free energy calculations, obtaining a very good reproduction of the experimental data. The modulation of the conformational equilibrium upon the addition of polar and non-polar solvents was computationally evaluated and results found a confirmation in experimental measures.

Nanoscale organization in the fluorinated room temperature ionic liquid: Tetraethyl ammonium (trifluoromethanesulfonyl)(nonafluorobutylsulfonyl)imide.

Fluorinated Room Temperature Ionic Liquids (FRTILs) are a branch of ionic liquids that is the object of growing interest for a wide range of potential applications, due to the synergic combination of specifically ionic features and those properties that stem from fluorous tails. So far limited experimental work exists on the micro- and mesoscopic structural organization in this class of compounds. Such a work is however necessary to fully understand morphological details at atomistic level that would have strong implications in terms of bulk properties. Here we use the synergy between X-ray and neutron scattering together with molecular dynamics simulations to access structural details of a technologically relevant FRTIL that is characterised by an anion bearing a long enough fluorinated tail to develop specific morphological features. In particular, we find the first experimental evidence that in FRTILs bearing an asymmetric bis(perfluoroalkyl)sulfonyl-imide anion, fluorous side chains tend to be spatially segregated into nm-scale spatial heterogeneities. This feature together with the well-established micro-segregation of side alkyl chains in conventional RTILs leads to the concept of triphilic ILs, whose technological applications are yet to be fully developed.

Water and hexane in an ionic liquid: computational evidence of association under high pressure.

High pressures may strongly affect the mesoscopic structure of some ionic liquids. In particular, the so called sponge-like structure is gradually destroyed when an increasing pressure is applied. Here we show how a polar solute, an apolar solute or a mixture thereof behave in the ionic liquid trihexyl, tetradecylphosphonium bis (trifluoromethyl-sulfonyl) imide when the pressure is raised up to 10 kbar. Our calculations clearly show an association between molecules that would not interact in ordinary conditions.

Structural and vibrational study of 2-MethoxyEthylAmmonium Nitrate (2-OMeEAN): Interpretation of experimental results with ab initio molecular dynamics.

In this work we report an analysis of the bulk phase of 2-methoxyethylammonium nitrate based on ab initio molecular dynamics. The structural and dynamical features of the ionic liquid have been characterized and the computational findings have been compared with the experimental X-ray diffraction patterns, with infrared spectroscopy data, and with the results obtained from molecular dynamics simulations. The experimental infrared spectrum was interpreted with the support of calculated vibrational density of states as well as harmonic frequency calculations of selected gas phase clusters. Particular attention was addressed to the high frequency region of the cation (ω > 2000 cm(-1)), where the vibrational motions involve the NH3+ group responsible for hydrogen bond formation, and to the frequency range 1200-1400 cm(-1) where the antisymmetric stretching mode (ν3) of nitrate is found. Its multiple absorption lines in the liquid arise from the removal of the degeneracy present in the D3h symmetry of the isolated ion. Our ab initio molecular dynamics leads to a rationalization of the frequency shifts and splittings, which are inextricably related to the structural modifications induced by a hydrogen bonding environment. The DFT calculations lead to an inhomogeneous environment.

Pressure-induced mesoscopic disorder in protic ionic liquids: first computational study.

It has been recently shown that pressure may affect the mesoscopic heterogeneity in aprotic ionic liquids, owing to the long alkyl chain folding on itself. Here we explore protic ionic liquids, using classical molecular dynamics. These compounds have shorter and stiffer alkyl chains, harder to fold. We observed that high pressure affects the mesoscopic structure of the studied chemicals and, indeed, the effect may be ascribed to chain folding.

Interaction and dynamics of ionic liquids based on choline and amino acid anions.

The combination of amino acid anions with the choline cation gives origin to a new and potentially important class of organic ionic liquids that might represent a viable and bio-compatible alternative with respect to the traditional ones. We present here a detailed study of the bulk phase of the prototype system composed of the simplest amino acid (alanine) anion and the choline cation, based on ab initio and classical molecular dynamics. Theoretical findings have been validated by comparing with accurate experimental X-ray diffraction data and infrared spectra. We find that hydrogen bonding (HB) features in these systems are crucial in establishing their local geometric structure. We have also found that these HBs once formed are persistent and that the proton resides exclusively on the choline cation. In addition, we show that a classical force field description for this particular ionic liquid can be accurately performed by using a slightly modified version of the generalized AMBER force field.

The structural organization of N-methyl-2-pyrrolidone + water mixtures: a densitometry, x-ray diffraction, and molecular dynamics study.

A combined approach of molecular dynamics simulations, wide angle X-ray scattering experiments, and density measurements was employed to study the structural properties of N-methyl-2-pyrrolidone (NMP) + water mixtures over the whole concentration range. Remarkably, a very good agreement between computed and experimental densities and diffraction patterns was achieved, especially if the effect of the mixture composition on NMP charges is taken into account. Analysis of the intermolecular organization, as revealed by the radial and spatial distribution functions of relevant solvent atoms, nicely explained the density maximum observed experimentally.

Amino acid anions in organic ionic compounds. An ab initio study of selected ion pairs.

The combination of amino acids in their deprotonated and thus anionic form with a choline cation gives origin to a new and potentially important class of organic ionic compounds. A series of such neutral ion pairs has been investigated by first principle methods. The results reveal intriguing structural motives as well as regular patterns in the charge distribution and predict a number of vibrational and optical properties that could guide the experimental investigation of these compounds. The replacement of choline with its phosphocholine analogue causes the spontaneous reciprocal neutralization of cations and anions, taking place through the transfer of a proton between the two ions. Systems of this kind, therefore, provide a wide and easily accessible playground to probe the ionic/polar transition in organic systems, while the easy transfer of H(+) among neutral and ionic species points to their potential application as proton conductors. The analysis of the ab initio data highlights similarities as well as discrepancies from the rigid-ions force-field picture and suggests directions for the improvement of empirical models.

FTIR spectra and density functional theory P.E.D. assignments of oxiranes in Ar matrix at 12 K.

The FTIR spectra of a series of oxiranes were studied in Ar matrix at 12K. The interpretation of the spectra was accomplished on the basis of density functional theory calculations employing the 6-311++G(3df,3pd) basis set with the B3LYP functional. Potential energy distribution was carried out for each molecule employing the B3LYP/6-311++G(3df,3pd) force field and a non-redundant definition of internal coordinates. The study of the FTIR spectra led to the reassignment of some vibrational modes of the molecules. The FTIR spectrum of trifluoroepoxypropane measured in Ar matrix and its assignment is reported for the first time.