9 research outputs found
Investigation of phosphines as potential host materials in blue dye-doped organic light emitting devices
Currently, the most efficient organic light emitting devices (OLEDs) are based on dye-doped OLEDs. The major obstacle has been developing a host material for blue OLEDs that has sufficiently high energy of emission (\u3c380nm) to facilitate energy transfer to the dye. Previous studies of bis(diphenylphosphino)-E-Stilbene (P-STIL) suggested that tertiary aromatic diphosphines (TAPs) may be suitable candidates. Therefore, the P-containing materials, 4,4\u27-bis(naphthylphenylphosphino)biphenyl (alpha-P-NPD) and 4,4\u27-bis(diphenylphosphino)biphenyl (P-DDB) were synthesized and the photophysical properties were evaluated and compared to P-STIL. The TAPs were shown to be sensitive to air oxidation both in solution and the solid state and that the origin of the high energy emission of P-STIL was from the oxide. Furthermore, all TAPs were shown to exhibit dual emission, which may result from different structural geometries about the P-atom in the excited state. Theses studies conclusively demonstrate that TAPs are not suitable as host materials fro blue dye-doped OLEDs, but the fully oxidized materials, which are more stable and emit at higher energy may be better candidates
Chemical derivatization of classes of metabolites in biological systems for detection by NMR with enhanced sensitivity and resolution
NMR spectroscopy is one of the two most important analytical tools used in metabolic profiling of biological systems due to its reproducibility and ability to provide spectroscopic information on a broad range of metabolites. 1H NMR analysis of complex biological samples combined with multivariate data analysis provides a well-established approach for a wide range of applications in metabolomics. In this dissertation, nuclei such as 13C and 31P are explored for improved NMR-based metabolic profiling. 13C NMR is not highly utilized in metabolomics due to issues of poor sensitivity and low natural abundance. The wide chemical shift range and reduced J-coupling are attractive features despite the low sensitivity. In a novel approach, this study demonstrates that chemical derivatization using 13C labeled reagents used to enhance the sensitivity and resolution of selected classes of metabolites in complex biological fluids. Amine containing metabolites were selectively detected from a complex mixture by derivatizing the metabolites with 13C labeled acetic anhydride. 1-D 13C and 2-D HSQC spectra of biological samples after reaction with 13C enriched acetic anhydride can be obtained in less than 10 min, and these spectra show dramatically improved sensitivity (âŒ100 fold) and resolution. This method was used in analyzing trace amounts of amino acids in serum and urine from patients diagnosed with inborn errors of metabolism and in tissue extracts. The 31P nucleus has a higher natural abundance and wider chemical shift range than the 13C NMR. Chemical derivatization of labile hydrogens in hydroxyl and carboxylic acid functionalities with 2-chloro-4,4,5,5-tetramethyldioxaphospholane ensured a good spectral separation upon derivatization as the products appeared in a different chemical environment and thus provided higher sensitivity and resolution. The derivatization procedure was fast, required minimal sample preparation, and was reproducible and cost effective. 31P labeling was then successfully utilized for analyzing lipophilic compounds with labile hydrogens in human serum. In sum, application of enhanced detection of metabolites in pathological tissue and biofluids by appropriate chemical derivatization methodologies provides a convenient and sensitive method for the qualitative and quantitative analysis of various classes of metabolites that may have good diagnostic utility and for the study of pathophysiology in various diseases
Physical Properties and CO<sub>2</sub> Reaction Pathway of 1âEthyl-3-Methylimidazolium Ionic Liquids with Aprotic Heterocyclic Anions
Ionic liquids (ILs) with aprotic
heterocyclic anions (AHA) are
attractive candidates for CO<sub>2</sub> capture technologies. In
this study, a series of AHA ILs with 1-ethyl-3-methylimidazolium ([emim]<sup>+</sup>) cations were synthesized, and their physical properties
(density, viscosity, and ionic conductivity) were measured. In addition,
CO<sub>2</sub> solubility in each IL was determined at room temperature
using a volumetric method at pressures between 0 and 1 bar. The AHAs
are basic anions that are capable of reacting stoichiometrically with
CO<sub>2</sub> to form carbamate species. An interesting CO<sub>2</sub> uptake isotherm behavior was observed, and this may be attributed
to a parallel, equilibrium proton exchange process between the imidazolium
cation and the basic AHA in the presence of CO<sub>2</sub>, followed
by the formation of âtransientâ carbene species that
react rapidly with CO<sub>2</sub>. The presence of the imidazolium-carboxylate
species and carbamate anion species was verified using <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy. While the reaction between
CO<sub>2</sub> and the proposed transient carbene resulted in cation-CO<sub>2</sub> binding that is stronger than the anion-CO<sub>2</sub> reaction,
the reactions of the imidazolium AHA ILs were fully reversible upon
regeneration at 80 °C with nitrogen purging. The presence of
water decreased the CO<sub>2</sub> uptake due to the inhibiting effect
of the neutral species (protonated form of AHA) that is formed
SolidâLiquid Equilibria Measurements of Mixtures of Lithium Bis(trifluoromethanesulfonyl)imide with Varying Alkyl Chain Length Ammonium Bis(trifluoromethanesulfonyl)imide Ionic Liquids
Ionic
liquid (IL)âmetal mixtures are potential solvents
for a variety of applications, including metal electrodeposition,
electrolytes for batteries, catalysis, and for separations processes
involving liquidâliquid extraction. The solubility of a metal
in an IL is fundamentally important to selecting an appropriate IL
for a potential process; however, relatively few measurements have
been reported in the literature. The solidâliquid equilibria
of binary mixtures of lithium bisÂ(trifluoromethanesulfonyl)Âimide and
three ammonium bisÂ(trifluoromethanesulfonyl)Âimide ILs are investigated.
Measurements are made through two different methods. A visual method
allows direct observation of the phase behavior between room temperature
and 373 K and a differential calorimetry method provides solidâliquid
equilibria information up to 623 K. The activity coefficients of the
solid in the liquid are calculated from the measured phase equilibria
and the pure component physical properties. The mutual solubilities
of lithium bisÂ(trifluoromethanesulfonyl)Âimide and hexadecyl-trimethylammonium
bisÂ(trifluoromethanesulfonyl)Âimide are found to be higher than expected
given the long alkyl chain length of the IL cation
Effect of Cation on Physical Properties and CO<sub>2</sub> Solubility for Phosphonium-Based Ionic Liquids with 2âCyanopyrrolide Anions
A series of tetraalkylphosphonium
2-cyanopyrrolide ([P<sub><i>nnnn</i></sub>]Â[2-CNPyr]) ionic
liquids (ILs) were prepared
to investigate the effect of cation size on physical properties and
CO<sub>2</sub> 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 [P<sub><i>nnnn</i></sub>]Â[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 CO<sub>2</sub> 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 CO<sub>2</sub> capture reaction,
the [P<sub><i>nnnn</i></sub>]Â[2-CNPyr] ILs with shorter
alkyl chains on the cations exhibited slightly stronger CO<sub>2</sub> 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
Excess Enthalpy of Monoethanolamine + Ionic Liquid Mixtures: How Good are COSMO-RS Predictions?
Mixtures
of ionic liquids (ILs) and molecular amines have been
suggested for CO<sub>2</sub> capture applications. The basic idea
is to replace water, which volatilizes in the amine regeneration step
and increases the parasitic energy load, with a nonvolatile ionic
liquid solvent. To fully understand the thermodynamics of these systems,
here experimental excess enthalpies for binary mixtures of monoethanolamine
(MEA) and two ILs: 1-hexyl-3-methylimidazolium bisÂ(trifluoromethylsulfonyl)Âimide,
[hmim]Â[NTf<sub>2</sub>], and 1-(2-hydroxyethyl)-3-methylimidazolium
bisÂ(trifluoromethylsulfonyl)Âimide, [OHemim]Â[NTf<sub>2</sub>], were
obtained by calorimetry, using a Setaram C80 calorimeter, over the
whole range of compositions at 313.15 K. Since it is the temperature
derivative of the Gibbs energy, enthalpy is a sensitive measure of
intermolecular interactions. MEA + [hmim]Â[NTf<sub>2</sub>] is endothermic
and MEA + [OHemim]Â[NTf<sub>2</sub>] is exothermic. The reliability
of COSMO-RS to predict the excess enthalpy of the (MEA+IL) systems
was tested based on the implementation of two different molecular
models to define the structure of the IL: the IL as separate cation
and anion [C+A] and the IL as a bonded single specie [CA]. Quantum-chemical
calculations were performed to gain additional insight into the intermolecular
interactions between the components of the mixture. For MEA + [hmim]Â[NTf<sub>2</sub>] both the [C+A] and [CA] models predict endothermic behavior,
but the [CA] model is in better agreement with the experimental results.
For MEA + [OHemim]Â[NTf<sub>2</sub>] the [C+A] model provides the best
match to the experimental exothermic results. However, what is really
surprising is that two different conformations of the cationâanion
pair with nearly identical energies in the [CA] model result in completely
different (exothermic vs endothermic) predictions of the excess enthalpy.
Nonetheless, the results do show that the influence of the structure
of the IL on the thermodynamic behavior of the mixture (endothermic
vs exothermic) can be attributed to hydrogen bonding between the cation
and the MEA molecule. However, this study highlights the importance
of carefully selecting the molecular model and conformation in order
to obtain even qualitatively correct predictions with COSMO-RS. The
fact that even very slightly different conformations of the IL can
drastically change the thermodynamic estimations using COSMO-RS is
of significant concern. Overall, we believe the present work provides
a better understanding of the behavior of mixtures involving amines
and ILs, which is an important aspect to consider when evaluating
the use of such solvent mixtures in CO<sub>2</sub> capture technologies
Phase-Change Ionic Liquids for Postcombustion CO<sub>2</sub> Capture
Phase-change ionic liquids, or PCILs,
are salts that are solids
at normal flue gas processing temperatures (e.g., 40â80 °C)
and that react stoichiometrically and reversibly with CO<sub>2</sub> (one mole of CO<sub>2</sub> for every mole of salt at typical postcombustion
flue gas conditions) to form a liquid. Thus, the melting point of
the PCILâCO<sub>2</sub> complex is below that of the pure PCIL.
A new concept for CO<sub>2</sub> separation technology that uses this
key property of PCILs offers the potential to significantly reduce
parasitic energy losses incurred from postcombustion CO<sub>2</sub> capture by utilizing the heat of fusion (Î<i>H</i><sub>fus</sub>) to provide part of the heat needed to release CO<sub>2</sub> 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<sub>2</sub> 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<sub>2</sub> solubility, physical
properties, phase transition behavior, and water uptake for tetraethylphosphonium
benzimidazolide ([P<sub>2222</sub>]Â[BnIm]). The process based on [P<sub>2222</sub>]Â[BnIm] has the potential to reduce the amount of energy
required for the CO<sub>2</sub> capture process substantially compared
to the current technology that employs aqueous monoethanolamine (MEA)
solvents