1,721,015 research outputs found
Structural organization in a methanol:ethylammonium nitrate (1:4) mixture: A joint X-ray/Neutron diffraction and computational study
No full textThe molecular organization and dynamics of a binary mixture of a Protic Ionic Liquid (PIL), Ethylammonium Nitrate (EAN), and methanol (χEAN = 0.8) have been investigated by means of X-ray/Neutron Scattering with the support of classical Molecular Dynamics simulations. While at low EAN concentration, as some of us previously have reported (Russina, O. et al., 2014) [1], mesoscopic segregation occurs, in the present study the two components are fully miscible at mesoscopic level and no clustering is observed. The low alcohol's concentration does not lead to strong effects on the PIL's structure; on the other hand methanol's environment is substantially different than in the neat state. Enhanced interactions of EAN with alcohol lead to a loss of methanol-methanol correlations. Structural, dynamical and thermodynamical analysis on the computational model shows that the strongest and most probable hydrogen bond interactions of methanol occur with the nitrate anion, while its methyl group has an aliphatic interaction with EAN's terminal carbon and behaves like a pseudo hydrogen bond donor
Ionic Liquids and Neutron Scattering
No full textIonic liquids represent an exciting class of compounds that are composed solely of ionic species and are liquid below 100°C. They are attracting great attention as environmentally responsible solvent media, and as such, they are the focus of a profusion of research activities. Aiming at relating their appealing macroscopic properties, in terms of micro- and mesoscopic features, neutron scattering techniques have been successfully applied in the last decade to explore these compounds. In this contribution, an overview of fundamental structural (over the spatial scale ranging from angstrom to several nanometers) and dynamic (across the window from fraction of picosecond to several nanosecond) studies are accounted for, aiming at revealing the contribution that neutron scattering can provide in complementing and extending the level of understanding so far reached
Liquid structure of a water-based, hydrophobic and natural deep eutectic solvent: The case of thymol-water. A Molecular Dynamics study
Full text linkThe structural organization of the first example of a water-based, type V, hydrophobic, natural deep eutectic solvent (DES) is investigated in this work, exploiting the synergy of X-ray scattering and compu- tational techniques. The stoichiometric mixture of thymol:water (4.8:1) has been recently reported to behave as a DES, with a melting point at 6 C, well below the one foreseen for the ideal liquid mixture. Our study provides an atomistic insight into the structural correlations in this system, highlighting the major role played by hydrogen bonding (HB) correlations in affecting morphology as well as the solid– liquid equilibrium. Thymol engages HB-mediated interactions with both thymol and water molecules: evidences of conventional HB interactions involving the hydroxyl group are found, together with indica- tions of p HAO hydrogen bonding correlations with both thymol and water. Overall, in the mixture, thymol is involved in a larger number of HB interactions than in its neat liquid state. Such a strong inter- ference of water into thymol structural organization strongly hinders the development of HB-mediated thymol hexamers that is the structural leitmotif in crystalline thymol. On the other hand, only 30 % of the present water molecule can engage into correlations with at least another water molecule, thus pre- venting the formation of an extended HB network among water molecules that would result incompat- ible with the otherwise hydrophobic environment. Evidences of mesoscopic organization are observed experimentally and confirmed by simulations: these are related to the clustering of thymol hydroxyl groups with water molecules, leading to the formation on polar nano-pools embedded into the apolar matrix. This new solvent extends the range of water based, type V, hydrophobic DES, and represents an additional contribution to the development of sustainable technologies, with appealing properties
Structural Features of β-Cyclodextrin Solvation in the Deep Eutectic Solvent, Reline
Full text linkThe inherently amphiphilic nature of native cyclodextrins (CDs) determines their peculiar molecular encapsulation features, enabling applications such as targeted drug nanodelivery, aroma protection, etc. On the contrary, it may also lead to poor solubility in water and other organic solvents and to potentially detrimental flocking in these media, thus posing limitations to more extensive usage. Here we use small angle X-ray scattering to show that deep eutectic solvent reline (1:2 choline chloride:urea) succeeds in dissolving large amounts of β-CD (at least 800 mg/mL, compared with the solubility in water of 18 mg/mL), without aggregation phenomena occurring. At the microscopic level, molecular dynamics simulations highlight the complex interplay of hydrogen bonding-mediated hydrophilic interactions and hydrophobic force mitigation occurring between β-CD and reline components, leading to energetically favorable β-CD solvation. The possibility of achieving very high concentration conditions for unaggregated β-CD in an environmentally responsible media, such as reline, can open the way to new, so far unpredictable applications, addressing multiple societal challenges
Solubility and solvation features of native cyclodextrins in 1-ethyl-3-methylimidazolium acetate
No full textThe comprehension of the mechanism entailing efficient solvation of cyclodextrins (CD) by green solvents is of great relevance to boost environmentally sustainable usages of smart supramolecular systems. Here, 1-ethyl-3-methylimidazolium acetate, an ecofriendly ionic liquid (IL), is considered as an excellent solvent for native CDs. This IL efficiently dissolves up to 40 wt.% β- and γ-CD already at ambient temperature and X-ray scattering indicates that CDs do not tend to detrimental flocculation under these drastic concentration conditions. Simulation techniques reveal the intimate mechanism of CD solvation by the ionic species: while the strong hydrogen bonding acceptor acetate anion interacts with CD's hydroxyl groups, the imidazolium cation efficiently solvates the hydrophobic CD walls via dispersive interactions, thus hampering CD's hydrophobic driven flocking. Overall the amphiphilic nature of the proposed IL provides an excellent solvation environment for CDs, through the synergic action of its components
Experimental and Computational investigation of room temperature ionic liquids and their binary mixtures.
No full textRoom Temperature Ionic Liquids (RTILs) are an exciting novel class of materials, whose interest stems from their environmentally sustainable performances in several applications. They are composed solely by ionic species with a melting point lower than 100°C. Their negligible vapour pressure and high thermal and electrochemical stability make them very appealing for many applications, including (bio-) catalysis, separation, synthesis, electrochemistry, lubrication. This wide spectrum of applications reflects the complexity of their chemical-physical properties. This complexity is the consequence of the delicate balance between long range coulombic and short range dispersive interactions in these materials.
Our group is involved in the exploration of structural and dynamic properties of RTILs and their mixtures with molecular compounds (e.g. water, alcohols, polymers etc), using an integrated experimental and computational approach.
Making use of Large Scale Facilities (synchrotron and reactor sources) we explore the morphological organization and the relaxation processes in these systems. These experimental data are complemented with in-house X-ray and spectroscopic tools. The experimental results are being rationalised by High Performance Computing (HPC) at facilities such as CASPUR and CINECA, modelling the morphology and the dynamics in these systems using both ab initio and classical Molecular Dynamics techniques. As a consequence of the long spatial and temporal correlations in these systems, HPC is required.
In this presentation, we will highlight some of the recent results that we obtained on both structure and dynamics in RTILs by a joint use of experimental and HP computational approaches
Short/Medium-to-Long Range Order correlations in Room Temperature Ionic Liquids.
No full textOur group is presently working on a new, attractive class of materials, namely room temperature ionic liquids (RTILs): they are composed solely of ionic species that, because of their chemical architecture, have melting point below ambient temperature.
These systems are attracting great attention because of their low vapour pressure and other properties that make them green replacements for the noxious organic volatile solvents.
Recently we investigated a peculiar set of RTILs that is characterized by an alkaline metal as the cation (Na, Li, K) and a complex anion (Figure 1). Their interest lies in the fact that so far alkali metals were not known to be able to lead to low-melting salts. The Kunz group [1,2], which we are collaborating with on this topic, proposed two models for their morphology: the alkali metal can be either coordinated by a crown of ether-oxygen atoms (belonging to the chain) or by the chelating carboxy (CO2-) group.
Synchrotron high energy X-ray diffraction (HEXRD) measurements were collected on the Na-RTIL at ambient temperature. Similarly to other RTILs, this system shows a distinct low-Q peak that fingerprints the existence of an enhanced long range order over the spatial scale of several nm. [3] MD calculations were developed for this system at 500 K. The calculated diffraction pattern is in good agreement with the experimental data, thus validating our potential. MD-derived pair distribution functions (pdf ́s) indicate a strong coordination between the carboxy-group oxygen and the Na atoms. A much weaker correlation exists between the ether-oxygen and the Na. These observations support the structural scenario where the Na is coordinated by chelating carboxy rather than the ether groups, thus forming well-defined carboxy-coordinated sodium clusters.
A more detailed analysis allows detecting that the low Q peak is the fingerprint of the structural correlation between the mentioned clusters that are kept at fairly well defined distance by the ether chains that are separating them.
Accordingly on the basis of a comparison between HEXRD and simulation data, we propose a structural scenario where short-to-medium range interactions-driven clusters (carboxy-coordinated sodium ones) are able to induce the occurrence of long range order, showing up as a low-Q peak in the diffraction pattern.
[1] Kunz et al., Chem. Eur. J., 15, 1341 (2009); PCCP 12, 14341 (2010)
[2] Russina et al., JPCB 111, 4641 (2007
On the nature of nm-scale heterogeneities in ionic liquids
No full textThe issue of nanoscale structural heterogeneities has gained a great relevance in the last few years. Due to the intrinsic amphiphilic nature of conventional room temperature ionic liquids, such as alkyl-imidazolium-based salts, a self-assemblying scenario characterises the morphology of this important class of materials. This phenomenon has huge implications and several applicative features as relevant as solvation performances, catalysis and separation are expected to be affected by this occurrence.
In agreement with the early findings by MD simulation groups, we highlighted the existence of X-ray as well as neutron diffraction features that represent the fingerprint of the existence of structural correlations over a spatial scale as large as few nm in the bulk liquid state of a large class of ionic liquids.
We will present new results on novel classes of materials including alkyl- morpholinium and DABCO based ionic liquids, that further support the view of nm scale structural organization in ionic liquids. These results will be discussed in view of the recent arguments raised by other experimental groups.
Furthermore the consequences of this structural organization onto the relaxation processes occurring over the nsec temporal scale will be discussed, in view of the new Neutron Spin Echo data that we collected on deuterated salts as a function of the alkyl chain length. Indications of the existence of a complex dynamic behaviour as a consequence of structural segregation will be presented.
This experimental study provides information that validate recent MD simulations from a number of computational groups. We will also stress the importance of a joined experimental-computational approach in the investigation of these complex material systems
Structure of a binary mixture of ethylammonium nitrate and methanol
No full textWe report a joint experimental (X-ray and neutron diffraction) and computational study on a binary mixture of ethylammonium nitrate (EAN), a protic ionic liquid, and methanol, the shortest alcohol. These two amphiphilic compounds are also characterized by the existence of an extended hydrogen bonding network in their neat states. We explore how these similar compounds structurally organize at the micro- and mesoscopic levels when mixed in a homogeneous state. The study demonstrates that the mixture is organized similarly to neat EAN, where the polar versus apolar dualism of the ionic liquid determines the segregation of alkyl tails into domains embedded into the ionic, percolating matrix. Methanol, due to the strong hydrogen bond with the nitrate anion, tends to intrude into this polar network, merging at EAN’s polar–apolar interface. Further studies are proposed to rationalize the emerging mesoscopic density fluctuations that develop when approaching methanol-rich conditions
Structural organization in a methanol:ethylammonium nitrate (1:4) mixture: a joint X-ray/Neutron diffraction and computational study
No full textThe molecular organization and dynamics of a binary mixture of a Protic Ionic Liquid (PIL), Ethylammonium Nitrate (EAN), and methanol (χEAN = 0.8) have been investigated by means of X-ray/Neutron Scattering with the support of classical Molecular Dynamics simulations. While at low EAN concentration, as some of us previously have reported (Russina, O. et al., 2014) [1], mesoscopic segregation occurs, in the present study the two components are fully miscible at mesoscopic level and no clustering is observed. The low alcohol's concentration does not lead to strong effects on the PIL's structure; on the other hand methanol's environment is substantially different than in the neat state. Enhanced interactions of EAN with alcohol lead to a loss of methanol–methanol correlations. Structural, dynamical and thermodynamical analysis on the computational model shows that the strongest and most probable hydrogen bond interactions of methanol occur with the nitrate anion, while its methyl group has an aliphatic interaction with EAN's terminal carbon and behaves like a pseudo hydrogen bond donor
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