Shubha Pandey

Fluorescent Probe Studies of Polarity and Solvation within Room Temperature Ionic Liquids: A Review

Ionic liquids display an array of useful and sometimes unconventional, solvent features and have attracted considerable interest in the field of green chemistry for the potential they hold to significantly reduce environmental emissions. Some of these points have a bearing on the chemical reactivity of these systems and have also generated interest in the physical and theoretical aspects of solvation in ionic liquids. This review presents an introduction to the field of ionic liquids, followed by discussion of investigations into the solvation properties of neat ionic liquids or mixed systems including ionic liquids as a major or minor component. The ionic liquid based multicomponent systems discussed are composed of other solvents, other ionic liquids, carbon dioxide, surfactants or surfactant solutions. Although we clearly focus on fluorescence spectroscopy as a tool to illuminate ionic liquid systems, the issues discussed herein are of general relevance to discussions of polarity and solvent effects in ionic liquids. Transient solvation measurements carried out by means of time-resolved fluorescence measurements are particularly powerful for their ability to parameterize the kinetics of the solvation process in ionic liquids and are discussed as well.

Ionic Liquid-Based Optical and Electrochemical Carbon Dioxide Sensors.

Due to their unusual physicochemical properties (e.g., high thermal stability, low volatility, high intrinsic conductivity, wide electrochemical windows and good solvating ability), ionic liquids have shown immense application potential in many research areas. Applications of ionic liquid in developing various sensors, especially for the sensing of biomolecules, such as nucleic acids, proteins and enzymes, gas sensing and sensing of various important ions, among other chemosensing platforms, are currently being explored by researchers worldwide. The use of ionic liquids for the detection of carbon dioxide (CO2) gas is currently a major topic of research due to the associated importance of this gas with daily human life. This review focuses on the application of ionic liquids in optical and electrochemical CO2 sensors. The design, mechanism, sensitivity and detection limit of each type of sensor are highlighted in this review.

Ionic liquids containing fluorinated β-diketonate anions: synthesis, characterization and potential applications

Ionic liquids (ILs) sporting anions comprising the β-diketonate functionality were prepared, fully characterized via ESI-MS, FTIR, and 1H/13C NMR, and tested in multiple scenarios. We present eight new salts based on four different β-diketonate anions, each coupled with the choline or tetrabutylphosphonium cation. The thermal stabilities and transitions of these β-diketonate salts were explored using DSC and TGA. Seven of the compounds displayed melting points at or below 100 °C and hence formally qualify as ILs. The inherent binding capability of the β-diketonate moiety made possible a task-specific IL amenable to lanthanide recognition. For example, coordination with Eu3+ was accompanied by a striking three order-of-magnitude intensification of luminescence (‘turn-on’). Additionally, these ILs display prominent acidochromism. That is, the intense visible color of β-diketonate ILs is modulated in the presence of an acid source, permitting the visual transduction of local pH changes. Utility for carbon capture was also considered, however, these ILs were essentially incapable of binding CO2. Computational studies were better able to elucidate this behavior, revealing that the association of CO2 with the β-diketonate anion is thermodynamically unfavored and sterically hindered. Despite this negative result for CO2 capture, these newly introduced β-diketonate ILs show interesting and useful physicochemical properties applicable to a number of future applications.

Fluorescein prototropism within poly(ethylene glycol)s and their aqueous mixtures.

Depending on the solubilizing milieu and conditions, fluorescein may exist in one or more of its many prototropic forms [cationic, neutral (zwitterionic, quinoid, and lactone), monoanionic (phenolate and carboxylate), and dianionic]. Fluorescein prototropism is investigated in liquid poly(ethylene glycol)s (PEGs) of different average molecular weight (MW) and their aqueous mixtures using UV-vis absorbance along with static and time-resolved fluorescence spectroscopic techniques. Information regarding various prototropic forms of fluorescein in up to 30 wt % different average MW PEG-added aqueous buffers at varying pH reveals that addition of PEG causes lactonization of fluorescein in the milieu; higher the average MW of PEG, the more the lactonization is. Neat PEG200, PEG400, and PEG600 are found to support the dianionic form of fluorescein, while PEG1000 supports the neutral lactonized form. It is demonstrated that various prototropic forms of fluorescein may be generated within PEGs by addition of adequate amounts of acidic aqueous buffer. Significant bathochromic shift in absorbance and fluorescence band maxima of dianionic fluorescein as concentration of PEG200 is increased correlates well with hydrogen bond accepting basicity, hydrogen bond donating acidity, and dipolarity/polarizability of the aqueous PEG200 mixture. Interestingly, fluorescence emission from the cationic form of fluorescein is observed from dilute aqueous acidic media in the presence of high concentration of PEG200, whereas the fluorescence emission from cation in the absence of PEG200 is observed only from aqueous solutions of very high acidity (>5 M [H(+)]). Excited-state intensity decay is also used to support this outcome. It is proposed that, in the presence of a small amount of acid in PEG200, a highly acidic water-rich solvation microenvironment is formed around fluorescein, which converts its dianionic form to cationic form and considerably hinders the rapid deprotonation of the excited state of the cationic form.

Binding of the ionic liquid cation 1-alkyl-3-methylimidazolium to p-tetranitrocalix[4]arene probed by fluorescent indicator displacement

AbstractAcridine orange (AO) was used as a fluorescent probe molecule to study the encapsulation of an alkylimidazolium cation from a water-soluble ionic liquid (IL) within two cavitand species, p-tetranitrocalix[4]arene (1) and calix[4]resorcinarene (2), both in alkaline aqueous media. The addition of IL to the preformed [1⋅AO] adduct resulted in significantly increased fluorescence due to the expulsion of AO from the inclusion complex to the aqueous phase by competitive recognition of the 1-alkyl-3-methylimidazolium cation ([Cnmim]+, n = 4 and 6) by 1. Conversely, the fluorescence signal dropped upon the addition of IL to the [2⋅AO] host–guest complex due to unfavorable binding between [Cnmim]+ and 2. The formation of these postulated adducts is corroborated using ab initio calculations, which also provide evidence for the location of [bmim]+ at the lower external rim of [2⋅AO], providing an explanation for the observed luminescence quenching in the latter case. These results point to a number of different paths for exploration, ranging from the fluorescence monitoring of IL contamination in groundwater to the “daisy chaining” of macrocyles toward supramolecular ionic networks. They also broadly encourage the exploration of ILs in host–guest-based optical and mass spectrometric sensory systems. FigureThe acridine orange (AO) adduct with the p-tetranitrocalix[4]arene cavitand (1) displays fluorescence turn-on when challenged with the 1-butyl-3-methylimidazolium ([bmim]+) cation in aqueous media due to expulsion of AO from the inclusion complex to the aqueous phase by competitive recognition of [bmim]+.

A novel dansyl-appended bile acid receptor for preferential recognition of Hg2+

We have designed and synthesized a novel dansyl appended bile acid chemosensor using click chemistry. The chemosensor shows selective and efficient recognition of Hg2+ ions by forming a 1:1 complex with Hg2+ with a binding constant of 3.3 × 104 M−1. The limit of detection for Hg2+ was estimated to be 2 μM.

Synthesis and properties of L-valine based chiral long alkyl chain appended 1,2,3-triazolium ionic liquids

The increasing importance of ionic liquids (ILs) in various strata of chemical sciences is largely due to the fact that modification in the architecture of the cation and/or the anion imparts favorable and specific properties to an IL. Consequently, there is a need to develop new ILs with different functionalities. A series of L-valine based alkyl chain-appended 1,2,3-triazolium ILs (alkyl = hexyl, octyl, dodecyl, cetyl and octadecyl) with iodide and hexafluorophosphate anions, respectively, are synthesized and characterized. These new ILs show optical activity and hence are termed chiral ILs (CILs). All ten CILs are room temperature ILs (RTILs) as their melting points, obtained from differential scanning calorimetry (DSC), are found to be below ambient temperature. Thermogravimetric analysis indicates these CILs to have adequate thermal stability. The longer alkyl chain containing CILs exhibit facile self-aggregation when dissolved in ethanol. There is a hint of pre-micellar aggregation by short alkyl chain possessing CILs along with the long alkyl chain containing ones. These CILs demonstrate weak absorbance and emission of UV-Vis radiation and hence can be considered ideal solvents for photochemical applications. These CILs, consisting of different functionalities, possess interesting properties and have potential to be used in many areas of chemistry.

Applications of ionic liquids in biphasic separation: Aqueous biphasic systems and liquid–liquid equilibria

Ionic liquids (ILs) have been receiving much attention in many fields of analytical chemistry because of their various interesting properties which distinguish them from volatile organic compounds. They offer both directional and non-directional forces towards a solute molecule and therefore act as excellent solvents for a wide range of polar and non-polar compounds. Because of the presence of various possible interactions, ILs easily undergo biphasic separation with water and other less polar/non-polar organic solvents. Their ability to create biphasic splitting makes them a promising candidate for liquid-liquid separation processes, such as aqueous biphasic systems and liquid-liquid equilibria. Various aspects of ILs in these separation methods are discussed in view of the origin of physical forces responsible for the biphasic interactions, the effect of structural components, temperature, pressure, pH and additives. The specific advantages of using ILs in aqueous biphasic systems and liquid-liquid equilibria in binary and ternary systems are discussed with a view to defining their future role in separation processes by giving major emphasis on developing non-toxic ILs with physical and solution properties tailored to the needs of specific sample preparation techniques.

Applications of Ionic Liquids in Spectroscopy

Ionic liquid has emerged as intriguing modern material in science and technology. In order to understand and explore the unique and interesting properties of ionic liquids, various spectroscopic techniques offer a key role. In return, ionic liquids, due to their unique molecular architecture and properties, have helped enhance capabilities and potential applications of most spectroscopic techniques. Recent advances and developments in the research field associating ionic liquids and various modern spectroscopic techniques are outlined. The importance of ionic liquids in modern spectroscopy and the importance of various spectroscopic techniques in understanding ionic liquids are presented.

A Study of Effect of Progesterone on Epididymis in Albino Rats

Abstract Progesterone, an anti androgen compound that recently receiving attention for potential use as male contraceptive and for other medical purposes, such as treatment of prostate diseases. In the present study adult male albino rats were administered the progesterone for 15 &; 30 days and the histology and fine structures of the epididymis were studied. After treatments for 15 and 30 days sperms were found to greatly reduce in number from lumen of caput epididymis, middle segment and cauda epididymis, of severely affected specimen. The epithelium was tall and the light cells were large and distended with many dense bodies resembling lysosome (Loving &; Flickinger 1976)1. The lumen was filled with scanty sperm and debris, which appears to be derived from germ cells. It is suggested that the light cells of epididymal epithelium may have a role in clearing the lumen in which they are particularly large and numerous. The aim of present study is to determine the effect of progesterone on the structure of target cells of epididymis normally stimulated by androgens and further correlate the findings in light of previous studies, to draw the significant conclusion. The study showed that the progesterone have intense inhibitory effect on the epididymis. The degenerative histological findings are found in form of reduce number of spermatozoa, debris of cell mass &; reduce epithelial cells height. These changes may have an important role in the anti fertility effect of progesterone.