arXiv subjects

Eudes Eterno Fileti

Publications and source records attributed to Eudes Eterno Fileti.

15 recordsLinked to original sources

arXiv2017

Imidazolium Ionic Liquid Mediates Black Phosphorus Exfoliation while Preventing Phosphorene Decomposition

Forthcoming applications in electronics and optoelectronics make phosphorene a subject of vigorous research efforts. Solvent-assisted exfoliation of phosphorene promises affordable delivery in industrial quantities for future applications. We demonstrate, using equilibrium, steered and umbrella sampling molecular dynamics, that the 1-ethyl-3- methylimidazolium tetrafluoroborate [EMIM][BF4] ionic liquid is an excellent solvent for phosphorene exfoliation. The presence of both hydrophobic and hydrophilic moieties, as well as substantial shear viscosity, allows [EMIM][BF4] simultaneously to facilitate separation of phosphorene sheets and to protect them from getting in direct contact with moisture and oxygen. The exfoliation thermodynamics is moderately unfavorable, indicating that an external stimulus is necessary. Unexpectedly, [EMIM][BF4] does not coordinates phosphorene by p-electron stacking with the imidazole ring. Instead, the solvation proceeds via hydrophobic side chains, while polar imidazole rings form an electrostatically stabilized protective layer. The simulations suggest that further efforts in solvent engineering for phosphorene exfoliation should concentrate on use of weakly coordinating ions and grafting groups that promote stronger dispersion interactions, and on elongation of nonpolar chains.

cond-mat.mtrl-sci↗

arXiv2015

Polypeptide A9K at Nanoscale Carbon: Simulation Study

An amphiphilic nature of the surfactant-like peptides is responsible for their propensity to aggregate at the nanoscale. These peptides can be readily used for a non-covalent functionalization of nanoparticles and macromolecules. This work reports an observation of supramolecular ensembles consisting of ultrashort carbon nanotubes (USCNTs), graphene (GR) and A9K polypeptide formed by lysine and arginine. Potential of mean force (PMF) is used as a major descriptor of the CNT-A9K and GR-A9K binding process, supplementing structural data. The phase space sampling is performed by multiple equilibrium molecular dynamics simulations with position restraints, where applicable. Binding in all cases was found to be thermodynamically favorable. Encapsulation in the (10,10) USCNT is particularly favorable. Curvature of external surface does not favor binding. Thus, binding of A9K at GR is stronger than its binding at the outer sidewall of USCNTs. Overall, the presented results favor non-covalent functionalization of nanoscale carbons that are considered interesting in the fields of biomaterials, biosensors, biomedical devices, and drug delivery.

cond-mat.mtrl-sci↗

arXiv2015

Enhanced Stability of the Model Mini-protein in Amino Acid Ionic Liquids and Their Aqueous Solutions

Using molecular dynamics simulations, the structure of model mini-protein was thoroughly characterized in the imidazolium-based amino acid ionic liquids and their aqueous solutions. We report that the mini-protein is more stable when AAIL is added as a cosolvent. Complete substitution of water by organic cations and anions further results in hindered conformational flexibility of the mini-protein. This observation suggests that AAILs are able to defend proteins from thermally induced denaturation. We show by means of radial distributions that the mini-protein is efficiently solvated by both solvents due to agood mutual miscibility. However, amino acid based anions prevail in the first coordination sphere of the mini-protein.

physics.bio-ph↗

arXiv2015

Ionization of Cucurbiturils as a Pathway to More Stable Host-Guest Complexes

Cucurbiturils are particularly interesting to chemists, because these macrocyclic molecules are suitable hosts for an array of neutral and cationic species. It is believed that the host-guest binding originated from hydrophobic interactions and ion-dipole interactions in the case of cationic guests. The fact that an elementary unit of cucurbiturils consists of two fused imidazole rings, which ionize readily, has remained largely unnoticed up to now. This work reports ionized cucurbiturils and their binding to C60 fullerene using versatile electronic-precision description. The methodology is based on density functional theory. We assert that cationization of cucurbiturils fosters C60-cucurbituril binding due to polarization of electron density in C60. Therefore, more stable host-guest complexes can be derived.

cond-mat.mtrl-sci↗

arXiv2015

Can Inorganic Salts Tune Electronic Properties of Graphene?

Electronic properties of graphene quantum dots (GQDs) constitute a subject of intense scientific interest. Being smaller than 20 nm, GQDs contain confined excitons in all dimensions simultaneously. GQDs feature a non-zero band gap and luminesce on excitation. Tuning their electronic structure is an attractive goal with a technological promise. In this work, we apply density functional theory to study an effect of neutral ionic clusters adsorbed on GQD surface. We conclude that both HOMO and LUMO of GQD are very sensitive to the presence of ions and to their distance from the GQD surface. However, the alteration of the band gap itself is modest, as opposed to the case of free ions (recent reports). Our work fosters progress in modulating electronic properties of nanoscale carbonaceous materials.

cond-mat.mtrl-sci↗

arXiv2015

Strong Electronic Polarization of the C60 Fullerene by the Imidazolium-Based Ionic Liquids: Accurate Insights from Born-Oppenheimer Molecular Dynamics Simulations

Fullerenes are known to be polarizable due to the strained carbon-carbon bonds and high surface curvature. Electronic polarization of fullerenes is of steady practical importance, since it leads to non-additive interactions and, therefore, to unexpected phenomena. For the first time, hybrid density functional theory (HDFT) powered Born-Oppenheimer molecular dynamics (BOMD) simulations have been conducted to observe electronic polarization and charge transfer phenomena in the C60 fullerene at finite temperature (350 K). The non-additive phenomena are fostered by the three selected imidazolium-based room-temperature ionic liquids (RTILs). We conclude that although charge transfer appears nearly negligible in these systems, an electronic polarization is indeed significant leading to a systematically positive effective electrostatic charge on the C60 fullerene: +0.14e in [EMIM][Cl], +0.21e in [EMIM][NO3], +0.17e in [EMIM][PF6]. These results are, to certain extent, unexpected providing an inspiration to consider novel C60/RTILs systems. HDFT BOMD provides a powerful tool to investigate electronic effects in RTIL and fullerene containing nuclear-electronic systems.

cond-mat.mtrl-sci↗

arXiv2015

The Force Field for Amino Acid Based Ionic Liquids: Polar Residues

Ionic liquids (ILs) constitute one of the most active fields of research nowadays. Many organic and inorganic molecules can be converted into ions via relatively simple procedures. These ions can be combined into ILs. Amino acid based ILs (AAILs) represent a specific interest due to solubilization of biological species, participation in enzymatic catalysis, and capturing toxic gases. We develop a new force field (FF) for the seven selected AAILs comprising 1-ethyl-3-methylimidazolium cation and amino acid anions with polar residues. The anions were obtained via deprotonation of carboxyl group. We account for peculiar interactions between the anion and the cation by fitting electrostatic potential for an ion pair, in contrast to isolated ions. The van der Waals interactions were transferred from the CHARMM36 FF with minor modifications, as suggested by hybrid density functional theory. Compatibility between our parameters and CHARMM36 parameters is preserved. The developed interaction model fosters computational investigation of ionic liquids.

cond-mat.mtrl-sci↗

arXiv2014

Ionic Clusters vs. Shear Viscosity in Aqueous Amino Acid Ionic Liquids

Aqueous solutions of amino acid ionic liquids (AAILs) are of high importance for applications in protein synthesis and solubilization, enzymatic reactions, templates for synthetic study, etc. This work employs molecular dynamics simulations using our own force field to investigate shear viscosity and cluster compositions of three 1-ethyl-3-methylimidazolium (emim) amino acid salts: [emim][ala], [emim][met], and [emim][trp] solutions (2, 5, 10, 20, 30 mol%) in water at 310 K. We, for the first time, establish simple correlations between cluster composition, on one side, and viscosity, on another side. We argue that knowledge about any of these properties alone is enough to derive insights regarding the missed properties, using the reported correlations. The numerical observations and qualitative correlations are discussed in the context of chemical structure of the amino acid anions, [ala], [met], and [trp]. The reported results will enhance progress in the efficient design and applications of AAILs and their solutions.

cond-mat.mtrl-sci↗

arXiv2014

The Band Gap of Graphene Is Efficiently Tuned by Monovalent Ions

Following recently published study of Prezhdo and coworkers (JPC Letters, 2014, 5, 4129-4133), we report a systematic investigation of how monovalent and divalent ions influence valence electronic structure of graphene. Pure density functional theory is employed to compute electronic energy levels. We show that LUMO of an alkali ion (Li+, Na+) fits between HOMO and LUMO of graphene, in such a way tuning the bottom of the conduction band (i.e. band gap). In turn, Mg2+ shares its orbitals with graphene. The corresponding binding energy is ca. 4 times higher than in the case of alkali ions. The reported insights provide inspiration for engineering electrical properties of the graphene containing systems.

cond-mat.mtrl-sci↗

arXiv2014

Aqueous Solutions of Amino Acid Based Ionic Liquids. Dispersion and Structure

New ionic liquids (ILs) are continuously introduced involving an increasing number of organic and inorganic ions. Amino acid based ILs (AAILs) represent a specific interest due to their natural origin and, allegedly, low cost. We apply our recently developed force field for imidazolium-based AAILs to investigate structure properties in their aqueous solutions via molecular dynamics (MD) simulations. By reporting cluster analysis, radial distribution functions and spatial distribution functions, we argue that AAIL ions are well dispersed in the aqueous media, irrespective of the AAIL content. Aqueous solutions of AAILs exhibit desirable properties as solvents for chemical engineering. The AAILs in relatively dilute aqueous solutions (10 mol% AAIL) exist as ion pairs, while more concentrated solutions feature certain amount of larger ionic aggregates.

cond-mat.mtrl-sci↗

arXiv2014

Exploding Nitromethane in silico, in real time

Nitromethane (NM) is widely applied in chemical technology as a solvent for extraction, cleaning and chemical synthesis. NM was considered safe for a long time, until a railroad tanker car exploded in 1958. We investigate detonation kinetics and reaction mechanisms in a variety of systems consisting of NM, molecular oxygen and water vapor. State-of-the-art reactive molecular dynamics allows us to simulate reactions in time-domain, as they occur in real life. High polarity of the NM molecule is shown to play an important role, driving the first exothermic step of the reaction. Presence of oxygen is important for faster oxidation, whereas its optimal concentration is in agreement with the proposed reaction mechanism. Addition of water (50 mol%) inhibits detonation; however, water does not prevent detonation entirely. The reported results provide important insights for improving applications of NM and preserving safety of industrial processes.

cond-mat.mtrl-sci↗

arXiv2014

Reactive Molecular Dynamics Simulation of a Buckybomb

Abstract. Energetic materials, such as explosives, propellants and pyrotechnics, are widely used in civilian and military applications. Nanoscale explosives represent a special group because of high density of energetic covalent bonds. The reactive molecular dynamics study of nitro-fullerene decomposition reported here provides, for the first time, a detailed chemical mechanism of explosion of a nanoscale carbon material. Upon initial heating, C60(NO2)12 disintegrates, increasing temperature and pressure by thousands of Kelvins and bars within tens of picoseconds. The explosion starts with NO2 group isomerization into C-O-N-O, followed by emission of NO molecules and formation of CO groups on the buckyball surface. NO oxidizes into NO2, and C60 falls apart liberating CO2. At highest temperatures, CO2 gives rise to diatomic carbon. The study shows that the initiation temperature and released energy depend strongly on the chemical composition and density of the material. The established explosion mechanism provides guidelines for control of combustion and detonation on the nanoscale.

cond-mat.mtrl-sci↗

arXiv2014

The Scaled-Charge Additive Force Field for Amino Acid Based Ionic Liquids

Abstract. Ionic liquids (ILs) constitute an emerging field of research. New ILs are continuously introduced involving more and more organic and inorganic ions. Amino acid based ILs (AAILs) represent a specific interest due to their evolutional connection to proteins. We report a new non- polarizable force field (FF) for the eight AAILs comprising 1-ethyl-3-methylimidazolium cation and amino acid anions. The anions were obtained via deprotonation of carboxyl group. Specific cation-anion non-covalent interactions have been taken into account by computing electrostatic potential for ion pairs, in contrast to isolated ions. The van der Waals interactions have been transferred from the CHARMM36 FF with minor modifications. Therefore, compatibility between our parameters and CHARMM36 parameters is preserved. Our FF can be easily implemented using a variety of popular molecular dynamics programs. It will find broad applications in computational investigation of ILs.

cond-mat.mtrl-sci↗

arXiv2013

Does Like Dissolves Like Rule Hold for Fullerene and Ionic Liquids?

Over 150 solvents have been probed to dissolve light fullerenes, but with a quite moderate success. We uncover unusual mutual polarizability of C60 fullerene and selected room-temperature ionic liquids (RTILs), which can be applied in numerous applications, e.g. to significantly promote solubility/miscibility of highly hydrophobic C60 molecule. We report electron density and molecular dynamics analysis supported by the state-of-the-art hybrid density functional theory and empirical simulations with a specifically refined potential. The analysis suggests a workability of the proposed scheme and opens a new direction to obtain well-dispersed fullerene containing systems. A range of common molecular solvents and novel ionic solvents are compared to 1-butyl-3-methylimidazolium tetrafluoroborate.

cond-mat.mtrl-sci↗

arXiv2013

Can Organic Ions Dissolve Fullerenes?

Over 150 solvents have been so far probed to dissolve light fullerenes - with quite moderate success. Based on unusual electronic properties of the C60 fullerene and room-temperature ionic liquids (RTILs), we hereby propose to use their mutual polarizability to significantly promote solubility of C60. We report analysis supported by density functional theory with reliable hybrid functional and large-scale molecular dynamics simulations with specifically tuned empirical potential. The analysis suggests a workability of the proposed mechanism and provides qualitatively new insights into obtaining real fullerene solutions. Our preliminary findings open a wide avenue for engineering specific solvents for fullerenes and, possibly, some other nanoscale carbonaceous structures.

cond-mat.mtrl-sci↗