Rahul A. Patil

Examination of Selectivities of Thermally Stable Geminal Dicationic Ionic Liquids by Structural Modification

Dicationic ionic liquids (ILs) are widely used as gas chromatography (GC) stationary phases as they show higher thermal stabilities, variety of polarities, and unique selectivities towards certain compounds. An important aspect contributing to them is that they show multiple solvation interactions compared to the traditional GC stationary phases. Dicationic ILs are considered as combination of three structural moieties: (1) cationic head groups; (2) a linkage chain; and (3) the counter anions. Modifications in these structural moieties can alter the chromatographic properties of IL stationary phases. In this study, a series of nine thermally stable IL stationary phases were synthesized by the combination of five different cations, two different linkage chains, and two different anions. Different test mixtures composed of a variety of compounds having different functional groups and polarities were analyzed on these columns. A comparison of the separation patterns of these different compounds on nine different IL columns provided some insights about the effects of structural modifications on the selectivities and polarities of dicationic ILs.

Rapid, effective deprotection of tert-butoxycarbonyl (Boc) amino acids and peptides at high temperatures using a thermally stable ionic liquid

A method for high temperature Boc deprotection of amino acids and peptides in a phosphonium ionic liquid is described. The ionic liquid had low viscosity, high thermal stability and demonstrated a beneficial effect. The study extended the possibility for extraction of water soluble polar organic molecules using ionic liquids. Trace water significantly improved product purity and yield, while only 2 equiv. TFA led to deprotection within 10 min. The trityl group was also deprotected.

Dicationic ionic liquid thermal decomposition pathways

AbstractThe rapid expansion in the study and use of ionic liquids (ILs) is a result of their unique properties including negligible volatility, high thermal stability, and ability to dissolve disparate compounds. However, because ILs have infinitely variable structures (often referred to as “tunability”), these properties can differ considerably. Herein, we focus on the thermal stability of 15 bis-/dicationic ionic liquids. Specifically, their thermal breakdown products are examined to determine the structural linkages, bonds, or atoms most susceptible to thermally induced changes and whether such changes occur before possible volatilization. In most cases, the heteroatom-carbon single bonds were susceptible to thermolytic decomposition. Graphical abstractCapture of dicationic ionic liquid thermal decomposition products for subsequent identification.

Variation of anionic moieties of dicationic ionic liquid GC stationary phases: Effect on stability and selectivity

Dicationic ionic liquids (DILs) are more and more accepted as a new class of high temperature and polar stationary phases for gas chromatography (GC). This study deals with the effect of seven different fluorosulfonyl derivatized anions associated with two dications: 1,3-di(3-methylimidazolium)-2-methylpropane [2mC3(mim)2], and 1,3-di(3-methylimidazolium)-isobutene [i-eneC4(mim)2]. Thermophysical properties of the 14 synthesized DILs were evaluated in terms of melting point, viscosity, and thermal stability. The optimal physicochemical properties of 13 DILs allowed preparing 13 GC capillary columns. Accordingly, the polarity and selectivity of the DILs were evaluated by determining the Rohrschneider-McReynolds constants and the equivalent chain lengths of C18 fatty acid methyl esters (FAMEs). The symmetrical fluoroalkylsulfonyl and the trifluorosulfonate anions seem to produce the most polar DILs. Compared to classical polyethyleneglycol phases, the DILs showed substantially decreased retention of apolar compounds and a much stronger retention of the polar ones. Unique selectivities were observed with unsaturated FAMEs, polyaromatic hydrocarbons, and bacterial specific FAMEs. The two applications presented included a biodiesel and bacterial FAME analyses.

Chiral Liquid Chromatography

Abstract Over the last decade, chiral liquid chromatography has made tremendous advances in selectivity and efficiency. These developments have been beneficial to many scientific disciplines especially in the field of high-throughput research. In this chapter, we review the fundamentals of chiral separations, classes of stationary phases, new particle morphologies, bonding chemistry of chiral selectors and high-efficiency packing procedures. Special detectors for enantiomeric separations are surveyed. The latest developments in chiral chromatography have culminated in sub-second separations of enantiomers. Instrumental considerations to achieve ultrafast enantiomeric separations are discussed. Unique applications of chiral chromatography such as shape selectivity, formation of “Batman” peaks, peak shapes under overloading conditions, and future developments are highlighted.

Chiral Gas Chromatography

Abstract Over the last decade, chiral gas chromatography (GC) has made advances in synthetic chiral stationary phases and applications in advanced GC techniques. These developments have been beneficial to many scientific disciplines especially in the analysis and separation of complex samples. In this chapter, we review commercial and non-commercial chiral GC stationary phases with an emphasis on separation mechanisms and current applications. Chiral GC stationary phases discussed include amino acid, cyclodextrin, cyclofructan, metal organic framework, porous organic cage, and ionic liquid based phases. Topics covered include chiral multi-dimensional GC and the separation of chiral components in essential oils, hydrocarbons, flavors, and fragrances.

Correction to: Branched-chain dicationic ionic liquids for fatty acid methyl ester assessment by gas chromatography

The authors would like to call the reader’s attention to the fact that the original publication included some corrections needed to be addressed.