Ionic liquids (ILs) with aprotic heterocyclic anions, or AHAs, can bind CO2 with reaction enthalpies that are suitable for gas separations and without suffering large viscosity increases. In the present work, we have synthesized ILs bearing an alkyl-phosphonium cation with indazolide, imidazolide, pyrrolide, pyrazolide and triazolide-based anions that span a wide range of predicted reaction enthalpies with CO2. Each AHA-based IL was characterized by NMR spectroscopy and their physical properties (viscosity, glass transition, and thermal decomposition temperature) determined. In addition, the influence of substituent groups on the reaction enthalpy was investigated by measuring the CO2 solubility in each IL at pressures between 0 and 1 bar at 22 °C using a volumetric method. The isotherm-derived enthalpies range between -37 and -54 kJ mol(-1) of CO2, and these values are in good agreement with computed enthalpies of gas-phase IL-CO2 reaction products from molecular electronic structure calculations. The AHA ILs show no substantial increase in viscosity when fully saturated with CO2 at 1 bar. Phase splitting and compositional analysis of one of the IL/H2O and IL/H2O/CO2 systems conclude that protonation of the 2-cyanopyrrolide anion is improbable, and this result was confirmed by the equimolar CO2 absorption in the presence of water. Taking advantage of the tunable binding energy and absence of viscosity increase after the reaction with CO2, AHA ILs are promising candidates for efficient and environmental-friendly absorbents in postcombustion CO2 capture.

A series of tetraalkylphosphonium 2-cyanopyrrolide ([Pnnnn][2-CNPyr]) ionic liquids (ILs) were prepared to investigate the effect of cation size on physical properties and CO2 solubility. Each IL was synthesized in our laboratory and characterized by NMR spectroscopy. Their physical properties, including density, viscosity, and ionic conductivity, were determined as a function of temperature and fit to empirical equations. The density gradually increased with decreasing cation size, while the viscosity decreased noticeably. In addition, the [Pnnnn][2-CNPyr] ILs with large cations exhibited relatively low degrees of ionicity based on analysis of the Walden plots. This implies the presence of extensive ion pairing or formation of aggregates resulting from van der Waals interactions between the long hydrocarbon substituents. The CO2 solubility in each IL was measured at 22 °C using a volumetric method. While the anion is typically known to be predominantly responsible for the CO2 capture reaction, the [Pnnnn][2-CNPyr] ILs with shorter alkyl chains on the cations exhibited slightly stronger CO2 binding ability than the ILs with longer alkyl chains. We attribute this to the difference in entropy of reaction, as well as the variation in the relative degree of ionicity.

Phase-change ionic liquids, or PCILs, are salts that are solids at normal flue gas processing temperatures (e.g., 40− 80 °C) and that react stoichiometrically and reversibly with CO 2 (one mole of CO 2 for every mole of salt at typical postcombustion flue gas conditions) to form a liquid. Thus, the melting point of the PCIL−CO 2 complex is below that of the pure PCIL. A new concept for CO 2 separation technology that uses this key property of PCILs offers the potential to significantly reduce parasitic energy losses incurred from postcombustion CO 2 capture by utilizing the heat of fusion (ΔH fus ) to provide part of the heat needed to release CO 2 from the absorbent. In addition, the phase transition yields almost a step-change absorption isotherm, so only a small pressure or temperature swing is required between the absorber and the stripper. Utilizing aprotic heterocyclic anions (AHAs), the enthalpy of reaction with CO 2 can be readily tuned, and the physical properties, such as melting point, can be adjusted by modifying the alkyl chain length of the tetra-alkylphosphonium cation. Here, we present data for four tetrabutylphosphonium salts that exhibit PCIL behavior, as well as detailed measurements of the CO 2 solubility, physical properties, phase transition behavior, and water uptake for tetraethylphosphonium benzimidazolide ([P 2222 ][BnIm]). The process based on [P 2222 ][BnIm] has the potential to reduce the amount of energy required for the CO 2 capture process substantially compared to the current technology that employs aqueous monoethanolamine (MEA) solvents.

We report a chemical derivatization method that selects a class of metabolites from a complex mixture and enhances their detection by 13 C NMR. Acetylation of amines directly in aqueous medium with 1,1 -13 C2 acetic anhydride is a simple method that creates a high sensitivity and quantitative label in complex biofluids with minimal sample pretreatment. Detection using either 1D or 2D 13 C NMR experiments produces highly resolved spectra with improved sensitivity. Experiments to identify and compare amino acids and related metabolites in normal human urine and serum samples as well as in urine from patients with the inborn errors of metabolism tyrosinemia type II, argininosuccinic aciduria, homocystinuria, and phenylketonuria demonstrate the method. The use of metabolite derivatization and 13 C NMR spectroscopy produces data suitable for metabolite profiling analysis of biofluids on a time scale that allows routine use. Extension of this approach to enhance the NMR detection of other classes of metabolites has also been accomplished. The improved detection of low-concentration metabolites shown here creates opportunities to improve the understanding of the biological processes and develop improved disease detection methodologies.carbon-13 ͉ inborn errors of metabolism ͉ metabolite profiling ͉ metabolomics ͉ metabonomics T he metabolic profile in biofluids represents a snapshot of ongoing biological processes in the human body. The presence of a particular metabolite, panel of metabolites, or a certain ratio of metabolites can indicate normal homeostasis, a response to biological stress, or even a specific disease state. Conventional medical diagnostic methods are typically based on the selective detection of a single or a few biochemical parameters that are associated with a given disease. A major challenge in the present practice of clinical medicine is the lack of suitable biomarkers and bioanalytical technologies for earlier detection of numerous diseases. Metabolic profiling or metabolomics, defined as the analysis of multiple biofluid metabolites in parallel, holds the promise of earlier disease detection and improved understanding of systems biology (1-3). Early indications of this potential have been reported for the detection of several diseases, including inborn errors of metabolism, cardiovascular diseases, and cancer (4-7).NMR and mass spectrometry are the two most often used analytical methods for metabolite profiling because of their high resolution and rich data content (8)(9)(10)(11)(12)(13)(14). Although mass spectrometry is the more sensitive technique, NMR provides broad coverage of the metabolome by detecting all of the (hydrogencontaining) metabolites present in the biofluid simultaneously, with excellent reproducibility and only limited sample pretreatment. Thus, for example, many classic inborn errors of metabolism (IEM) can be diagnosed by the use of 1 H NMR spectroscopy of body fluids (15-17). Several of the IEM are associated with the accumulation of amino acids as metabolites in serum an...

We show that phosphonium azolide ionic liquids of interest for CO2 capture applications react with CO2 both through the normal anion channel and, at elevated temperatures, through a previously unrecognized cation channel. The reaction is caused by an interaction between the anion and cation that allows proton transfer, and involves a phosphonium ylide intermediate. The cation reaction can be mitigated by using ammonium rather than phosphonium cations. Thus, phosphonium and ammonium cations paired with aprotic heterocyclic anions (AHAs) react with CO2 through different mechanisms at elevated temperatures. This work shows that careful consideration of both physical properties and chemical reactivity of ILs based on AHA anions is needed when designing ionic liquids for CO2 separations.