Kevin N. West
University of South Alabama
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Featured researches published by Kevin N. West.
Angewandte Chemie | 2010
Samuel M. Murray; Richard A. O'Brien; Kaila M. Mattson; Christopher Ceccarelli; Richard E. Sykora; Kevin N. West; James H. Davis
Proposed by Singer and Nicolson in 1972, the fluid-mosaic model holds that the phospholipid bilayer is a dynamic twodimensional solvent milieu. Its proper function is closely tied to its “fluidity”, and that is often quantified by reference to the melting point, Tm (increased fluidity corresponds to a lower Tm value). The fluid-mosaic model is highly evocative of the emerging picture of nanoscale structuring in ionic liquids (ILs), and just as the function of phospholipid bilayers is tied to the Tm value, so too is the utility of ILs. Whereas the former often have low Tm values despite being composed of charged species with long aliphatic appendages, the fluidity of ILs generally decreases when progressively longer aliphatic appendages are used. It is a challenge to design imidazolium ILs (the most common IL class) that incorporate progressively more lipophilic structural elements while keeping their melting points below room temperature (Figure 1). Indeed, the Tm values of these ILs begin to rise dramatically once an appended Nalkyl group exceeds seven carbon atoms in length. Herein we report that by using an approach modeled on homeoviscous adaptation (HVA), ILs with very long alkyl appendages and very low Tm values can be prepared. This discovery may have significant implications for IL use in enzymatic catalysis, lubricants, heat-transfer fluids, and gas storage and separation, among other applications. Widely accepted as a mechanism by which the melting temperature of cell membranes is modulated, HVA is the incorporation into cell membranes of phospholipids with “kinked” tail structures. It is argued that the packing efficiency of the collective membrane hydrophobic components is diminished by the presence of these phospholipids and that increased fluidity results. A comparison of the Tm value of distearoylphosphatidylcholine with that of dioleylphosphatidylcholine provides a dramatic example of how much impact this seemingly trivial difference can have. The former, with its linear, saturated C18 tails has a Tm value of 58 8C; the latter, with its “kinked” C18 tails (each of which incorporates a cis-alkenyl group), has a Tm value of 22 8C. This effect is also at the heart of the Tm difference between the solid triacyl glycerols called fats, and those that are liquid at room temperature known as oils. In both instances, the effect is probably entropic in nature, as in the case of anthracene (“linear”, Tm = 217 8C) and phenanthrene (“kinked”, Tm = 99 8C). Accordingly, we hypothesized that ILs with long, unsaturated, aliphatic tail structures would, like the corresponding phospholipids, have significantly lower Tm values than their counterparts with saturated appendages. To test the validity of our hypothesis by measuring their Tm values, we prepared a series of lipid-inspired ILs in a threestep process from high-purity (99 + %) fatty-alcohol mesylates, 1-methylimidazole, NaI, and NaTf2N. [12] Each of the ILs (Scheme 1) had a long alkyl appendage identical to that in a natural fatty acid. Compounds 1, 3, and 8 feature fully saturated C16, C18, and C20 side chains, respectively, and their Figure 1. Influence of alkyl-chain length on Tm in N-alkyl N-methylimidazolium salts and the corresponding n-alkanes. The graph includes data from the literature and newly synthesized ionic liquids.
RSC Advances | 2013
Arsalan Mirjafari; Lam N. Pham; John R. McCabe; Niloufar Mobarrez; E. Alan Salter; Andrzej Wierzbicki; Kevin N. West; Richard E. Sykora; James H. Davis
ILs of dications with linked protic and aprotic centres have been prepared. They have rich H-bonding and a Bronsted acid–base character like small ΔpKa protic ILs, but very low apparent vapour pressures, more akin to aprotic ILs.
Angewandte Chemie | 2014
Li Chen; Genevieve E. Mullen; Myriam Le Roch; Cody G. Cassity; Nicolas Gouault; Henry Y. Fadamiro; Robert E. Barletta; Richard A. O'Brien; Richard E. Sykora; Alexandra C. Stenson; Kevin N. West; Howard E. Horne; Jeffrey M. Hendrich; Kang Rui Xiang; James H. Davis
The practical utility of ionic liquids (ILs) makes the absence (heretofore) of reported examples from nature quite puzzling, given the facility with which nature produces many other types of exotic but utilitarian substances. In that vein, we report here the identification and characterization of a naturally occurring protic IL. It can be formed during confrontations between the ants S. invicta and N. fulva. After being sprayed with alkaloid-based S. invicta venom, N. fulva detoxifies by grooming with its own venom, formic acid. The mixture is a viscous liquid manifestly different from either of the constituents. Further, we find that the change results as a consequence of formic acid protonation of the N centers of the S. invicta venom alkaloids. The resulting mixed-cation ammonium formate milieu has properties consistent with its classification as a protic IL.
RSC Advances | 2013
Richard A. O'Brien; Christy Wheeler West; Brian E. Hollingsworth; Alexandra C. Stenson; Codey B. Henderson; Arsalan Mirjafari; Niloufar Mobarrez; Kevin N. West; Kaila M. Mattson; E. Alan Salter; Andrzej Wierzbicki; James H. Davis
A simple approach for the preparation of symmetrical quaternary ammonium bromides employing thiol–ene click chemistry is used to synthesize tetra(4-thiaalkyl)ammonium bromides. This approach allows the incorporation of a variety of alkyl moieties onto the nitrogen center with a one-step synthesis involving easy work-up, no side reactions and environmentally friendly reagents. To elucidate information regarding the behaviour of this novel class of compounds, comparisons to tetraalkylammonium analogues have been made. These include melting points, activity as phase-transfer catalysts, and conformational predictions from computational modelling. All results are consistent in indicating stronger bonding between the quaternary cation and the anion for the salts with 4-thiaalkyl chains as compared to those with n-alkyl chains.
RSC Advances | 2017
Benjamin Siu; Cody G. Cassity; Adela Benchea; Taylor Hamby; Jeffrey M. Hendrich; Katie J. Strickland; Andrzej Wierzbicki; Richard E. Sykora; E. Alan Salter; Richard A. O'Brien; Kevin N. West; James H. Davis
Select triarylsulfonium salts constitute ionic liquids with outstanding long-term, high-temperature aerobic stability (no mass loss in 90 days at 300 °C in air), making them among the most thermally stable organic materials known. A detailed analysis of their thermophysical properties reveals that lowering melting points in these salts by increasing ion size or lowering ion symmetry cannot be assumed, but remains an iterative process.
New Journal of Chemistry | 2017
Adela Benchea; Benjamin Siu; Mohammad Soltani; JaMichael H. McCants; E. Alan Salter; Andrzej Wierzbicki; Kevin N. West; James H. Davis
The stability of fourteen different PPN+ salts has been studied in 96 hour tests, in air, at temperatures of 200 °C, 250 °C, and 300 °C. The results have enabled generation of a ranking of their stabilities, and by extension, that of their anionic components. This data should prove especially useful in ongoing efforts to formulate ionic liquids for high-temperature applications.
New Journal of Chemistry | 2017
A. Shay Thigpen; Stephen T. Nestor; Richard A. O'Brien; Samuel Minkowicz; Yinghong Sheng; James H. Davis; Kevin N. West; Arsalan Mirjafari
A series of ionic liquids containing 3- and 4-picolinium cations appended to thioether side chain moieties was constructed via the thiol–ene “click” reaction. Their structure–property relationships were comprehensively investigated by studying the temperature transition region (melting points and glass transition temperatures) and heat capacity and the experimental results were fully supported by theoretical studies. The synthesized ionic liquids are melted below 20.2 °C. Also, the impact of varying chain length, type of cations (picolinium vs. imidazolium) and the position of methyl group on the ring on their thermal and thermophysical properties were explored. According to the collected data, the glass transition temperature values of the picolinium-based ionic liquids with odd-number chains is lower than the even-number ones, which shows that the even-number moieties have more organized structures. And the miscibility of selected ionic liquids in water (polar) and heptane (nonpolar) solvents were quantified.
Journal of Physical Chemistry B | 2016
Thai L. Y. Huynh; Kaitlyn Poiroux; Richard A. O’Brien; Kevin N. West; James H. Davis; Christy Wheeler West
Quaternary ammonium salts are widely used in consumer products and industrial processes, where their instability at elevated temperatures limits their range of applications. In this work, the thermal behavior of a new class of quaternary ammonium salts was investigated using differential scanning calorimetry. These salts contain a sulfur atom in each chain at the fourth position from the central nitrogen and are thus termed thiaquats. The temperatures at which these salts melt and thermally degrade were determined, and enthalpies and entropies of fusion were evaluated. Their melting points increase with chain lengths, in contrast to the behavior of traditional quaternary ammonium salts. Furthermore, they exhibit enthalpies and entropies of fusion significantly lower than corresponding tetraalkyl analogues. These trends provide physical insight into the molecular-level behavior of these salts, suggesting that they do not fully dissociate upon melting. The thiaquats also exhibit thermal stability to markedly higher temperatures than traditional quaternary ammonium bromides, a phenomenon that can be explained in by strong pairing between the quaternary cation and bromide anion, which inhibits possible decomposition mechanisms. This enhanced thermal stability may enable applications of these salts in processes where traditional salts are not viable, such as phase-transfer-catalyzed systems performed at elevated temperatures.
Industrial & Engineering Chemistry Research | 2004
Kevin N. West; Jason P. Hallett; Rebecca S. Jones; David Bush; Charles L. Liotta; Charles A. Eckert
Journal of Power Sources | 2010
Vyjayanthi Alagharu; Srinivas Palanki; Kevin N. West