1,721,097 research outputs found
Choline-amino acid ionic liquids: past and recent achievements about the structure and properties of these really “green” chemicals
No full textThe structure of choline-amino acid ionic liquids, atoxic task-specific solvents composed of materials originated from renewable feedstocks, is reviewed in this letter. The varied and strong interactions that these liquids are capable of establishing are largely dependent on their structure, and confer them outstanding solvating properties with respect to a large number of different solutes. Among the experimental methods capable of yielding structural insight, the Energy Dispersive version of X-Ray diffraction, that uses the Bremsstrahlung radiation of the X-Ray tube, is a technique very well suited to investigate these liquid systems. The diffraction spectra of five choline-amino acid ionic liquids, recently measured, are reported and discussed; in particular, the presence or absence of the medium-range order prepeak is related to the presence of polar groups within the amino acid sidechain, that destroy the hydrophobic interactions between aliphatic chains. In the final section, a recent example of choline-amino acid ionic liquids as for ancient papers preservation, and two other interesting results are discussed at the end
Higher fullerenes: Compositional analysis by EDXD and molecular dynamics
Full text linkA carbon soot of higher fullerenes was studied by Energy Dispersive X-ray Diffraction (EDXD) aiming at
defining the overall structure as accurately as possible to define the overall structure, without lengthy separation and
purification procedures. EDXD pattern was compared with model curves obtained for single homogeneous fullerenes
already crystallized and for the hypothesized C180. All fullerenes contribute to the overall experimental curve to different
extents, with C96 giving the best agreement. The presence of even higher fullerenes is very likely, since the hypothesized
C180 gives a very good match as well
Water and hexane in an ionic liquid: Computational evidence of association under high pressure
No full textHigh 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
Brominated carbon black: An EDXD study
Full text linkAn energy dispersive X-Ray study of pure and brominated carbon black was carried out. The analysis of the
diffraction patterns reveals that the low bromine load (ca.1% mol) is trapped into the structure, without significantly
modifying it. This allows the application of the difference methods, widely tested for electrolyte solutions, inorganic
matrices containing metals and isomorphic substitutions
A study of cyclohexane, piperidine and morpholine with X-ray diffraction and molecular simulations
No full textDetection of heavy metals in water using graphene oxide quantum dots: an experimental and theoretical study
Full text linkIn this work, we investigate by ab initio calculations and optical experiments the sensitivity
of graphene quantum dots in their use as devices to measure the presence, and concentration, of
heavy metals in water. We demonstrate that the quenching or enhancement in the optical response
(absorption, emission) depends on the metallic ion considered. In particular, two cases of opposite
behaviour are considered in detail: Cd2+, where we observe an increase in the emission optical
response for increasing concentration, and Pb2+ whose emission spectra, vice versa, are quenched
along the concentration rise. The experimental trends reported comply nicely with the different
hydration patterns suggested by the models that are also capable of reproducing the minor quenching/
enhancing effects observed in other ions. We envisage that quantum dots of graphene may be
routinely used as cheap detectors to measure the degree of poisoning ions in water
Pressure-induced mesoscopic disorder in protic ionic liquids: First computational study
No full textIt 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
Does High Pressure Induce Structural Reorganization in Linear Alcohols? A Computational Answer
No full textWe present an exhaustive computational study on the effect of high pressure on normal alcohols with alkyl chains with lengths of three-to-eight carbon atoms. 1-Propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol were studied by using classical molecular dynamics simulations and applying pressures in the range of 1 to 104 bar. The results of our calculations show that high-pressure values affect the structure significantly. In particular, we have observed a marked difference in behavior for alcohols with chain lengths below six and those with more than six or seven carbon atoms, with hexanol and heptanol being boundary cases. We have named the model with the most shrunk alkyl chains as the Asclepius form inspired by the Rod of Asclepius, the universally known symbol of medicine, in which a snake is coiled around a rod
Nanoscale Density Fluctuations in Ionic Liquid Binary Mixtures with Nonamphiphilic Compounds: First Experimental Evidence
No full textA complex mesoscopic organization is observed in systems containing ethylammonium nitrate (EAN) and two nonamphiphilic compounds, using wide and small angle X-ray scattering and molecular dynamics simulations. The macroscopically homogeneous mixtures exhibit a separation where an ionic liquid-rich region is percolating a molecular liquid-rich one, but no unmixing is observed. This effect was already reported in EAN-alcohol mixtures, but the models proposed so far cannot explain this behavior for a nonamphiphilic compound
FTIR spectra and density functional theory P.E.D. assignments of oxiranes in Ar matrix at 12 K Spectrochim. Acta A: Mol. Biomol. Spectrosc. (vol 120, pg 558, 2014)
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