Anirban Mondal

Quantitative prediction of physical properties of imidazolium based room temperature ionic liquids through determination of condensed phase site charges: a refined force field.

Quantitative prediction of physical properties of room temperature ionic liquids through nonpolarizable force field based molecular dynamics simulations is a challenging task. The challenge lies in the fact that mean ion charges in the condensed phase can be less than unity due to polarization and charge transfer effects whose magnitude cannot be fully captured through quantum chemical calculations conducted in the gas phase. The present work employed the density-derived electrostatic and chemical (DDEC/c3) charge partitioning method to calculate site charges of ions using electronic charge densities obtained from periodic density functional theory (DFT) calculations of their crystalline phases. The total ion charges obtained thus range between -0.6e for chloride and -0.8e for the PF6 ion. The mean value of the ion charges obtained from DFT calculations of an ionic liquid closely matches that obtained from the corresponding crystal thus confirming the suitability of using crystal site charges in simulations of liquids. These partial charges were deployed within the well-established force field developed by Lopes et al., and consequently, parameters of its nonbonded and torsional interactions were refined to ensure that they reproduced quantum potential energy scans for ion pairs in the gas phase. The refined force field was employed in simulations of seven ionic liquids with six different anions. Nearly quantitative agreement with experimental measurements was obtained for the density, surface tension, enthalpy of vaporization, and ion diffusion coefficients.

Dissolution of Cellulose in Room Temperature Ionic Liquids: Anion Dependence

The dissolution of cellulosic biomass in room temperature ionic liquids (RTILs) is studied through free energy calculations of its monomer, viz., cellobiose, within a molecular dynamics simulation approach. The solvation free energy (SFE) of cellobiose in ionic liquids containing any of seven different anions has been calculated. The ranking of these liquids based on SFE compares well with experimental data on the solubility of cellulose. The dissolution is shown to be enthalpically dominated, which is correlated with the strength of intermolecular hydrogen bonding between cellobiose and the anions of the IL. Large entropic changes upon solvation in [CF3SO3](-) and [OAc](-) based ionic liquids have been explained in terms of the solvent-aided conformational flexibility of cellobiose.

A Refined All-Atom Potential for Imidazolium-Based Room Temperature Ionic Liquids: Acetate, Dicyanamide, and Thiocyanate Anions.

A refined set of potential parameters for 1-alkyl-3-methylimidazolium based room temperature ionic liquids with anions such as acetate, dicyanamide, and thiocyanate has been obtained. Site charges of ions were derived through the density-derived electrostatic and charge partitioning (DDEC/c3) method utilizing periodic density functional theory calculations of these liquids. Intermolecular structure and dynamics, in particular, the collective quantities predicted by the refined force field, match experimental results quantitatively.

Emergency Otorhinolaryngolocal cases in Medical College, Kolkata-A statistical analysis.

At the round the clock entergency of the Deparment of Otorhinolaryngology, Medical College, Kolkata, different types of cases are managed everyday. The various emergency conditions encountered by us in last four years are gathered and analyzed in this study. The different problems and their modes of management are discussed here.

Universal strategy for Ohmic hole injection into organic semiconductors with high ionization energies

Barrier-free (Ohmic) contacts are a key requirement for efficient organic optoelectronic devices, such as organic light-emitting diodes, solar cells, and field-effect transistors. Here, we propose a simple and robust way of forming an Ohmic hole contact on organic semiconductors with a high ionization energy (IE). The injected hole current from high-work-function metal-oxide electrodes is improved by more than an order of magnitude by using an interlayer for which the sole requirement is that it has a higher IE than the organic semiconductor. Insertion of the interlayer results in electrostatic decoupling of the electrode from the semiconductor and realignment of the Fermi level with the IE of the organic semiconductor. The Ohmic-contact formation is illustrated for a number of material combinations and solves the problem of hole injection into organic semiconductors with a high IE of up to 6 eV.It is shown that Ohmic contacts for the injection of hole carriers into organic semiconductors with high ionization energy can be formed by adding ultrathin interlayers with higher ionization energy.

Vibrational Signatures of Cation–Anion Hydrogen Bonding in Ionic Liquids: A Periodic Density Functional Theory and Molecular Dynamics Study

Hydrogen bonding in alkylammonium based protic ionic liquids was studied using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Normal-mode analysis within the harmonic approximation and power spectra of velocity autocorrelation functions were used as tools to obtain the vibrational spectra in both the gas phase and the crystalline phases of these protic ionic liquids. The hydrogen bond vibrational modes were identified in the 150-240 cm(-1) region of the far-infrared (far-IR) spectra. A blue shift in the far-IR mode was observed with an increasing number of hydrogen-bonding sites on the cation; the exact peak position is modulated by the cation-anion hydrogen bond strength. Sub-100 cm(-1) bands in the far-IR spectrum are assigned to the rattling motion of the anions. Calculated NMR chemical shifts of the acidic protons in the crystalline phase of these salts also exhibit the signature of cation-anion hydrogen bonding.

Molecular Dynamics Investigation of Efficient SO2 Absorption by Anion-Functionalized Ionic Liquids

AbstractIonic liquids are appropriate candidates for the absorption of acid gases such as SO2. Six anion-functionalized ionic liquids with different basicities have been studied for SO2 absorption capacity by employing quantum chemical calculations and molecular dynamics (MD) simulations. Gas phase quantum calculations unveil that the high uptake of SO2 in these ionic liquids originates from the basicity of the anions and the consequent enhanced anion-SO2 interactions. MD simulations of SO2–IL mixtures reveal the crucial role of both cations and anions in SO2 dissolution. Multiple-site interactions of SO2 with the anions have been identified. The calculated solvation free energy substantiates these observations. The order of computed Henry’s law constant values with change in the anion is in fair agreement with experimentally determined SO2 solubility order. Graphical AbstractEfficient absorption of SO2 by anion-functionalized ionic liquids has been studied using quantum mechanical and molecular dynamics simulation methods. Improved absorption capacity at much lower desorption cost has been found to be consequence of SO2-cation interaction via dispersion forces and multiple-site interactions of SO2 with anions.

Occult foreign bodies in the aero digestive tracts in infancy

Foreign body impaction in aero digestive tract in infancy is difficult to diagnose sometimes. In this review of five unusual cases of occult foreign body impaction in aero digestive tract has been presented and their management discussed

Molecular dynamics simulations of ammonium/phosphonium-based protic ionic liquids: influence of alkyl to aryl group

The variation of the center atom in the cation from an N to a P-atom leads to improved physiochemical properties of protic ionic liquids (PILs) which are suitable for electrolyte applications. We present an atomistic simulations study to compare the effect of an alkyl or aryl group on trioctylammonium triflate ([HN(Oct)3][TFO]) and triphenylammonium triflate ([HN(Ph)3][TFO]) with their phosphonium analogues. We have computed the binding energy from quantum chemical calculations and physical properties such as the viscosity and the electrical conductivity of PILs from molecular dynamics simulations. The influence of the aromatic character in PILs is found to be significant to the physical properties. Gas phase quantum chemical calculations on clusters of ion pairs have revealed the presence of C-H/π interactions in aromatic PILs along with hydrogen bonding. The variation in strength of the ion-pair affinities is examined using electric-current correlation and velocity autocorrelation functions. The qualitative differences observed are due to the aromatic rings and change in the central atom of the quaternary cation from an N to a P-atom, substantiated quantitatively by diffusion coefficients and electrical conductivities. The relatively weaker ion-pair interactions and low binding energy (-73.34 kcal mol-1) lead to the highest electrical conductivity in [HP(Ph)3][TFO].

Publisher Correction: Universal strategy for Ohmic hole injection into organic semiconductors with high ionization energies

In the html version of this Article originally published, Paul W. M. Blom and Gert-Jan A. H. Wetzelaer were incorrectly listed as Paul M. W. Blom and Gert-Jan H. A. Wetzelaer, respectively, due to a technical error. This has now been amended in all online versions of the Article.