Naved I. Malek

Temperature-dependent solvatochromic probe behavior within ionic liquids and (ionic liquid + water) mixtures.

Spectroscopic responses of absorbance probes, betaine dye 33, N,N-diethyl-4-nitroaniline, and 4-nitroaniline, and fluorescence dipolarity probes, pyrene (Py) and pyrene-1-carboxaldehyde (PyCHO) within ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), and aqueous mixtures of [bmim][BF4] are used to assess the changes in important physicochemical properties with temperature in the range 10-90 degrees C. ETN obtained from betaine dye 33, indicating dipolarity/polarizability and/or hydrogen bond donating (HBD) acidity, decreases linearly with increasing temperature within the two ILs. Changes in Kamlet-Taft parameters dipolarity/polarizability (pi*), HBD acidity (alpha), and HB accepting (HBA) basicity (beta) with temperature show interesting trends. While pi* and alpha decrease linearly with increasing temperature within the two ILs, beta appears to be independent of the temperature. Similar to ETNand pi*, the first-to-third band intensity ratio of probe Py also decreases linearly with increasing temperature within the ILs. The lowest energy fluorescence maxima of PyCHO, though it decreases significantly within water as the temperature is increased from 10 to 90 degrees C, it does not change within the two ILs investigated. The temperature dependence of the dipolarity/polarizability as manifested via betaine dye 33 behavior is found to be more within the aqueous mixtures of [bmim][BF4] as compared to that within neat [bmim][BF4] or neat water. The sensitivity of pi* toward temperature increases as IL is added to water and that of alpha decreases. The temperature dependent Py behavior shows no clear-cut trend within aqueous mixtures of [bmim][BF4]; insensitivity of the PyCHO response toward temperature change is reasserted within aqueous IL mixtures. All-in-all, the temperature-dependent behavior of solvatochromic probes within [bmim][PF6], [bmim][BF4], and aqueous mixtures of [bmim][BF4] is found to depend on the identity of the probe.

Visual Evidence for Formation of Water-in-Ionic Liquid Microemulsions

The hygroscopic nature of ILs (even those considered “hydrophobic”), however, renders the characterization of such w/IL microemulsions difficult due to the uncertainties regarding the state of the dispersed water within bulk ILs. [5] Thus, whether the amount of water above the aqueous solubility limit of the hydrophobic IL is simply dispersed within the solution assisted by the surfactant or is helping to form water pools of the w/IL microemulsions is rather difficult to assess. The low but appreciable solubility of water in most hydrophobic ILs further complicates the characterization of w/IL microemulsions. Out of very few investigations relating to the formation of w/IL microemulsions, [4j–m] a surfactant that commonly forms water/oil (w/o) microemulsions, aerosol OT (or AOT), is proposed to form w/IL microemulsions with the IL [C8mim][Tf2N] only in the presence of a cosurfactant 1-hexanol. [4j] Though the formation of w/IL microemulsions using the nonionic surfactants Tween 20 [4k] and Triton X-100 [4l,m] with the hydrophobic IL [bmim][PF6] is reported, the characterization of the proposed microemulsions is either performed using cumbersome techniques with largely inconclusive evidence or is mostly ambiguous and unsatisfactory. The lack of a method that can characterize w/IL microemulsions in a direct, simple, and accurate fashion with concrete evidence is clearly evident. For example, the ternary phase diagrams of such IL/surfactant/ water systems are fairly complicated and ambiguous in nature (usually based on visual inspection), making it difficult to predict whether w/IL microemulsions exist at a given composition. [4k,m] Herein, we present a simple and accurate method that provides clear evidence for the formation of w/IL microemulsions. Our system is composed of the hydrophobic IL 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF6], as the bulk oil phase with triton X-100 (TX-100), which is nonionic, as the surfactant. The presence of w/IL microemulsions is observed visually from the color change associated with Co II in the solution.

A reciprocal binary mixture of protic/aprotic ionic liquids as a deep eutectic solvent: physicochemical behaviour and application towards agarose processing

Apart from structural tuning, the desired properties of ionic liquids (IL) can be achieved through judicious mixing of two or more ionic liquids. Herein we have investigated the alterations in the physicochemical properties of protic/aprotic ILs, (2-hydroxyethylammonium formate/1-butyl-3-methylimidazolium chloride) upon reciprocal binary mixing. Melting point analysis of the mixtures at various mole fractions showed their deep eutectic solvent nature. The variation in physical properties like density, speed of sound, and viscosity have been measured and utilized to derive the volume of mixing, isentropic compressibility, and activation energy of the viscous flow. Unlike the binary mixtures of ILs having common cations or anions, the investigated reciprocal binary mixture showed significant non-ideality, normally desired to take advantage of improved solvent properties. The polarity and ion–ion interactions have been studied through solvatochromic parameters (normalized Reichardts parameter, dipolarity/polarizability, and hydrogen bond donor and acceptor coefficients) derived using solvatochromic probes. The prepared binary mixtures have been utilized for the dissolution of a gelling biopolymer agarose and formation of ionogels. Dissolution of agarose has been correlated with the solvatochromic parameters and the viscoelastic behaviour of ionogels is discussed in light of rheological measurements. The work gives fundamentally useful insights into tuning the properties of ILs for a specific application purpose.

Drug induced micelle-to-vesicle transition in aqueous solutions of cationic surfactants

The effects of the anti-inflammatory drug diclofenac sodium (DS) on the morphology of aqueous micellar aggregates of two ionic liquid-based surfactants (ILBSs), 1-hexadecyl-3-vinylimidazolium bromide, C16VnImBr, 1-hexadecyl-3-methylimidazolium bromide C16MeImBr, and (conventional) cetyltrimethylammonium bromide, C16Me3ABr (Vn, Im, Me, A = vinyl, imidazolium, methyl and ammonium, respectively) were studied at 25 °C. To probe the morphology changes of the formed aggregates, we employed turbidity, viscosity, dynamic light scattering, and transmission electron microscopy. Depending on [DS], the transitions observed were from spherical micelles → worm-like micelles → vesicles. Viscosity data indicated that the first transition occurred at lower [DS] for C16VnImBr compared to C16MeImBr and C16Me3ABr; indicating stronger interaction between (C16VnIm)+ and DS−. Light scattering results revealed that the DS/C16VnImBr system contained larger vesicles, as compared to DS/C16MeImBr and DS/C16Me3ABr. The changes in morphology agree with the expected effects of DS on the packing parameter of the colloidal aggregates.

Molecular interaction study through experimental and theoretical volumetric, transport and refractive properties of N-ethylaniline with aryl and alkyl ethers at several temperatures

Abstract To investigate the molecular interaction study between secondary amine with aryl and alkyl ether, we report densities, speeds of sound, viscosities and refractive indices of N-ethylaniline (NEA) with aryl (anisole, phenetole) and alkyl (tert-butyl methyl ether) ether over the entire composition regime and in the temperature range of 293.15–323.15 K at 5 K intervals. Various excess and transport properties were derived from the experimental data and the excess parameters were fitted to the Redlich–Kister polynomial equation using multiparametric non-linear regression analysis to derive the binary coefficients and to estimate the standard deviation. Molecular interactions between the unlike molecules were analysed through dipole–dipole interactions, cross-association between the components of the mixtures and H-bond formation. Viscosity and refractive index of the mixtures were predicted through several empirical equations and compared with the experimental results. Prigogine–Flory–Patterson statistical theory was used to predict the excess molar volume results.

Interfacial Polymerization of Linear Aromatic Poly(ester amide)s

Linear aromatic poly(ester amide)s (PEAs) have been synthesized by interfacial polycondensation (IPC) of aromatic diamidoacid chloride: 2-{[4-({[2-(chlorocarbonyl) phenyl]amino} carbonyl) benzoyl]amino} benzoyl chloride (2CCBC), with ethylene glycol, bisphenol A, resorcinol, 4,4′-bis(4-hydroxybenzilidine)diaminobenzanilide and 4,4′-bis(4-hydroxy benzilidine)-m-phenylenediamine in chloroform/water system employing phase-transfer-catalyst. The aromatic diamidoacid chloride has been prepared by condensation of terephthaloyl chloride with anthranilic acid. These polymers were characterized by elemental analysis, FTIR, 1H-NMR, solubility studies, intrinsic viscosity and TGA analysis. The polyester-amides so obtained show good thermal stability.

Drug-Induced Micelle-to-Vesicle Transition of a Cationic Gemini Surfactant: Potential Applications in Drug Delivery

An impetus for the sustained interest in the formation of vesicles is their potential application as efficient drug-delivery systems. A simple approach for ionic surfactants is to add a vesicle-inducing drug of opposite charge. In ionic gemini surfactants (GSs) two molecules are covalently linked by a spacer. Regarding drug delivery, GSs are more attractive candidates than their single-chain counterparts because of their high surface activity and the effect on the physicochemical properties of their solutions caused by changing the length of the spacer and inclusion of heteroatoms therein. Herein, the effect of the (anionic) anti-inflammatory drug diclofenac sodium (DS) on the morphology of aqueous micellar aggregates of gemini surfactant hexamethylene-1,6-bis (dodecyldimethylammonium) dibromide (12-6-12) at 25 °C is reported. Several independent techniques are used to demonstrate drug-induced micelle-to-vesicle transition. These include UV/Vis spectrophotometry, dynamic light scattering, TEM, and small-angle neutron scattering. The micelles are transformed into vesicles with increasing [DS]/[12-6-12] molar ratio; precipitation of the catanionic (DS-GS) complex then occurred, followed by partial resuspension of the weakly anionic precipitate. The stability of some of the prepared vesicles at human body temperature shows their potential use in drug delivery.

BIOFUELS FROM COCONUT FAT AND SOYBEAN OIL: MICROWAVE-ASSISTED SYNTHESIS AND GAS CHROMATOGRAPHY/MASS SPECTROMETRY ANALYSIS

We developed a project during an undergraduate course (advanced experimental chemistry) on the microwave-assisted synthesis of biodiesel (BD), via base-catalyzed transesterification of coconut fat (CF) and soybean oil (SO) by ethanol, followed by product analysis by gas chromatography/mass spectrometry. Our goals were to introduce a problem with relevant socio-economic impact (production of BD); to discuss and compare methods for biofuel analysis, and to gain insight into transesterification mechanism as an important example of acyl-transfer reactions. Comparison of both BFs showed clear difference in fatty acid composition; that from CF contains shorter, saturated chains (mainly ethyl dodecanoateand tetradecanoate), whereas biodiesel from SO is essentially composed of longer unsaturated chains (e.g., ethyl oleate and linoleate). The project takes eight hours to complete, is conceptually simple, being suitable for inclusion in the undergraduate science curriculum.

Thermo-Switchable de Novo Ionic Liquid-Based Gelators with Dye-Absorbing and Drug-Encapsulating Characteristics

An ionic liquid-based surfactant with ester functionality self-aggregates in an aqueous medium and forms ionogels at 8.80% (w/v) concentration at physiological pH. The ionogel exhibited a remarkable change in its appearance with temperature from fibrillar opaque to transparent because of the dynamic changes within its supramolecular structure. This gel-to-gel phase transition occurs below the melting point of the solid ionic liquid. The ionogels were investigated using turbidity, differential scanning calorimetry, scanning electron microscopy (SEM), field emission SEM (FE-SEM), inverted microscopy, transmission electron microscopy imaging, Fourier transform infrared spectroscopy, and rheological measurements. The fibrillar opaque ionogel and transparent ionogel were studied for their ability to absorb dyes (methyl orange and crystal violet) and to encapsulate drugs (diclofenac sodium and imatinib mesylate).