20 research outputs found
Proton transfer and esterification reactions in EMIMOAc-based acidic ionic liquids
Acetate-based ionic liquids (such as 1-ethyl-3-methylimidazolium acetate, EMIMOAc) have potential applications for CO2 absorption and electrochemical reduction, chemical separations and extractions, and Fischer esterification of alcohols, amines, and starch. Both strong and weak organic acids can be dissolved in EMIMOAc and yield interesting proton-rich acidic ionic liquid solutions. We have used GCMS vapor pressure measurements, spectroscopic methods, calorimetry, and viscosity/conductivity measurements to investigate the properties and reactions of various acids dissolved in EMIMOAc. Unique proton transfer and esterification reactions are observed in many of these acidic solutions with carboxylic acids or sulfonic acids as solutes. Some acids react with the acetate anion to produce acetic acid, which provides a measure of acid strength in ionic liquid solvents. In addition, we observed an esterification reaction that might involve the imidazolium cation and the acetate anion to yield methyl acetate
Synergistic interactions of ionic liquids and antimicrobials improve drug efficacy.
Combinations of ionic liquids (ILs) with antimicrobial compounds have been shown to produce synergistic activities in model liposomes. In this study, imidazolium chloride-based ILs with alkyl tail length variations are combined with commercially available, small-molecule antimicrobials to examine the potential for combinatorial and synergistic antimicrobial effects on P. aeruginosa, E. coli, S. aureus, and S. cerevisiae. The effects of these treatments in a human cell culture model indicate the cytotoxic limits of ILs paired with antimicrobials. The analysis of these ILs demonstrates that the length of the alkyl chain on the IL molecule is proportional to both antimicrobial activity and cytotoxicity. Moreover, the ILs which exhibit synergy with small-molecule antibiotics appear to be acting in a membrane permeabilizing manner. Collectively, results from these experiments demonstrate an increase in antimicrobial efficacy with specific IL + antimicrobial combinations on microbial cultures while maintaining low cytotoxicity in a mammalian cell culture model
Conductivity, Viscosity, Spectroscopic Properties of Organic Sulfonic Acid solutions in Ionic Liquids
Sulfonic acids in ionic liquids (ILs) are used as catalysts, electrolytes, and solutions for metal extraction. The sulfonic acid ionization states and the solution acid/base properties are critical for these applications. Methane sulfonic acid (MSA) and camphor sulfonic acid (CSA) are dissolved in several IL solutions with and without bis(trifluoromethanesulfonyl)imine (HTFSI). The solutions demonstrated higher conductivities and lower viscosities. Through calorimetry and temperature-dependent conductivity analysis, we found that adding MSA to the IL solution may change both the ion migration activation energy and the number of āfreeā charge carriers. However, no significant acid ionization or proton transfer was observed in the IL solutions. Raman and IR spectroscopy with computational simulations suggest that the HTFSI forms dimers in the solutions with an N-H-N ābridgedā structure, while MSA does not perturb this hydrogen ion solvation structure in the IL solutions. CSA has a lower solubility in the ILs and reduced the IL solution conductivity. However, in IL solutions containing 0.4 M or higher concentration of HTFSI, CSA addition increased the conductivity at low CSA concentrations and reduced it at high concentrations, which may indicate a synergistic effect
The spectroscopy of jet-cooled porphyrins: an insight into the vibronic structure of the Q band
We will present resonant two-photon ionization spectra for meso-tetraphenylporphyrin, H2TPP, measured under isolated conditions. The polycrystalline compound was vaporized, in vacuo, using both thermal and laser desorption, and seeded into a supersonic expansion of an inert-carrier gas. The molecules remain largely intact in the gaseous phase. However, the two techniques for vaporizing H2TPP give different internal temperatures for the isolated substrate, with greater vibrational cooling achieved using laser desorption. A comparison of the peak positions and intensities in the resonant two-photon ionization spectra of thermal- and laser-desorbed molecules provides an insight into the vibrational structure of the Q band. In particular, the greater contribution made by electronic transitions originating from higher vibrational levels in the ground state of H2TPP is emphasized. We conclude that vibronic coupling in the ground electronic state plays an important role in a quantum-mechanical interpretation of the Q band
Double-resonance spectroscopy of the jet-cooled free base and Cu(II) complex of protoporphyrin IX
The excited-state dynamics of porphyrins, and related compounds, impact on their applications as photosensitizers for tumor-targeting drugs and solar cells. Many researchers have examined the influence of non-planar distortions in the ground-state geometry on the properties of photoexcited states. We have identified the added importance of conformational changes in the excited state, relative to the initial geometry, on the resulting decay pathways. The ground-state structure and photodynamics of free-base and Cu(II) complexes of protoporphyrin IX, laser desorbed into a cold supersonic expansion, have been investigated using infrared ion-dip spectroscopy combined with density-functional theory calculations. The vibrational bands associated with the NāH stretching mode of the free base are broader in the first electronically excited state, accessed via the Q band of protoporphyrin IX, than the corresponding bands in the ground-electronic state. This is attributed to rapid intersystem crossing in the excited state promoted by extension of the NāH bonds. Our calculations show that the stretching modes are highly anharmonic, which suggests the likelihood that other conformational changes are also taking place in the excited state
Heme Dissociation from Myoglobin in the Presence of the Zwitterionic Detergent <i>N</i>,<i>N</i>-Dimethyl-<i>N</i>-Dodecylglycine Betaine: Effects of Ionic Liquids
We have investigated myoglobin protein denaturation using the zwitterionic detergent Empigen BB (EBB, N,N-Dimethyl-N-dodecylglycine betaine). A combination of absorbance, fluorescence, and circular dichroism spectroscopic measurements elucidated the protein denaturation and heme dissociation from myoglobin. The results indicated that Empigen BB was not able to fully denature the myoglobin structure, but apparently can induce the dissociation of the heme group from the protein. This provides a way to estimate the heme binding free energy, ΔGdissociation. As ionic liquids (ILs) have been shown to perturb the myoglobin protein, we have investigated the effects of the ILs 1-butyl-3-methylimidazolium chloride (BMICl), 1-ethyl-3-methylimidazolium acetate (EMIAc), and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) in aqueous solution on the ΔGdissociation values. Absorbance experiments show the ILs had minimal effect on ΔGdissociation values when compared to controls. Fluorescence and circular dichroism data confirm the ILs have no effect on heme dissociation, demonstrating that low concentrations ILs do not impact the heme dissociation from the protein and do not significantly denature myoglobin on their own or in combination with EBB. These results provide important data for future studies of the mechanism of IL-mediated protein stabilization/destabilization and biocompatibility studies
Quantitative Evaluation of Myoglobin Unfolding in the Presence of Guanidinium Hydrochloride and Ionic Liquids in Solution
The
use of ionic liquids in biochemical and biophysical applications has
increased dramatically in recent years due to their interesting properties.
We report results of a thermodynamic characterization of the chaotrope-induced
denaturation of equine myoglobin in two different ionic liquid aqueous
environments using a combined absorption/fluorescence spectroscopic
approach. Denaturation by guanidinium hydrochloride was monitored
by loss of heme absorptivity and limited unfolding structural information
was obtained from FoĢrster resonance energy transfer experiments.
Results show that myoglobin unfolding is generally unchanged in the
presence of ethylmethylimidazolium acetate (EMIAc) in aqueous solution
up to 150 mM concentration but is facilitated by butylmethylimidazolium
boron tetrafluoride (BMIBF<sub>4</sub>) in solution. The presence
of 150 mM BMIBF<sub>4</sub> alone does not induce unfolding but destabilizes
the structure as observed by a decrease in threshold denaturant concentration
for unfolding and an 80% decrease in the magnitude of Ī<i>G</i><sub>unfolding</sub> from 44 kJ/mol in the absence of BMIBF<sub>4</sub> to 8 kJ/mol in the presence of 150 mM BMIBF<sub>4</sub>.
Thus, the BMIBF<sub>4</sub> significantly destabilizes the myoglobin
structure while the EMIAc does not, likely due to differences in anion
interaction capabilities. This is confirmed with control studies using
NaAc and LiBF<sub>4</sub> solutions. EMIAc may be chosen as cosolvent
additive with minimal effects on protein structure while BMIBF<sub>4</sub> may be used as a supplement in protein folding experiments,
potentially allowing access to proteins which have been traditionally
difficult to denature as well as designing ionic liquids to match
protein characteristics