Chapter 18
Effect of Oxygen-Containing Functional Groups on Protein Stability in Ionic Liquid Solutions
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Megan B. Turner , John D. Holbrey , Scott K. Spear , Marc L. Pusey, and Robin D. Rogers 3
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Center for Green Manufacturing and Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487 NASA Marshall Space Flight Center, Huntsville, A L 35812 3
The ability of functionalized ionic liquids (ILs) to provide an environment of increased stability for biomolecules has been studied. Serum albumin is an inexpensive, widely available protein that contributes to the overall colloid osmotic blood pressure within the vascular system (1). Albumin is used in the present study as a marker of biomolecular stability in the presence of various ILs in a range of concentrations. The incorporation of hydroxyl functionality into the metJiylimidazolium-based cation leads to increased protein stability detected by fluorescence spectroscopy and circular dichroic (CD) spectrometry.
© 2005 American Chemical Society
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In Ionic Liquids IIIB: Fundamentals, Progress, Challenges, and Opportunities; Rogers, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.
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Introduction Ionic liquids (ILs) are a class of solvents generally composed of large, complex organic cations associated with inorganic anions that are liquids below 100 °C. The most extensively studied ILs are systems derived from 1,3dialkylimidazolium, tetraalkylammonium, tetraalkylphosphonium, and N alkylpyridinium cations (2). Derivitization of the cations can include the addition of alkyl chains, introduction of branching and/or chirality, fluorination, or addition of specific active functions. Common anions that allow for the formation of low melting ILs are typically charge diffuse, and can range from simple inorganic anions such as chloride (CI), bromide (Br), and iodide (Γ), through larger pseudo-spherical polyatomic anions including hexafluorophosphate [PF ]" and tetrafluoroborate [BF ]* to larger, flexible fluorinated examples such as bis(trifluoromethanesulfonyl)amide [(CF S0 )N]\ The anionic component of the ionic liquid typically controls the reactivity of the solvent with water, coordinating ability, and hydrophobicity (2). Anions can also contain chiral components or be catalytically active, i.e. carboranes, polytungstate, or tetrachloroaluminate anions (5). Manipulation of the rheological properties of an IL system can be preformed either by; (i) functionalization and/or cation/anion substitution or (ii) through mixing of cation/anionpairs. Τ he ability to design the solvent system to support and/or enhance reactions makes the use of ILs in chemical reactions an intriguing alternative to conventional solvents (4). Interest in ILs can be attributed to the unique combination of qualities inherent to these materials. First, the liquids are entirely ionic in nature making them conducting materials that can be used in a number of electrochemical applications including, battery production and metal deposition (5). In fact, ILs were first designed to be used in the electrochemical field to exploit this feature. Second, in most cases ILs exhibit a wide range of liquid character while possessing negligible measurable vapor pressure making them an attractive replacement for volatile organic solvents (
