Rico E. Del Sesto

The large scale synthesis of pure imidazolium and pyrrolidinium ionic liquids

Ionic liquids are being employed in almost all areas of chemistry and materials, yet there are inherent issues which arise if the utmost care is not taken in the preparation and purification of these materials. They are not easily synthesized and purified using the existing methods. We describe a reliable method for producing large quantities of high quality ionic liquids. Additionally, we show that imidazoliums are not ‘special’ due to their ‘inherently fluorescent’ nature, that spectroscopically clean imidazoliums are attainable, and most classes of ionic liquids do exhibit fluorescent backgrounds when extreme care is not taken during their synthesis and purification.

Exceptionally Long (≥2.9 Å) C−C Bonds between [TCNE]− Ions: Two‐Electron, Four‐Center π*–π* C−C Bonding in π‐[TCNE]22−

Attractive interaction with the cation overcomes the electrostatic repulsion between two tetracyanoethylene radical anions, [TCNE].- , and leads to the formation of a diamagnetic dimer [TCNE]22- , for example, in [K(glyme)]2 [TCNE]2 . The bonding is described as two-electron, four-center bonding arising from π*-π* overlap. Crystallographic as well as spectroscopic (IR and UV/Vis) features of this bonding are observed.

Exceptionally long (> 2.9 Å) CC bonding interactions in π-[TCNE]22-Dimers: Two-electron four-center cation-mediated CC bonding interactions involving π* electrons

Three groups of singlet ground state [TCNE](2) (2-) (TCNE=tetracyanoethylene) dimers with characteristic intradimer CC separations (r) and dihedral angles (d) [i.e., group S(t) (r approximately 1.6 A; d=180 degrees ), L(t) (r approximately 3.5 A; d=180 degrees ), and L(c) (r approximately 2.9 A; d= approximately 0 degrees ); notation: S/L: short/long bond length; subscript t/c: trans/cis, respectively] are experimentally characterized. The S(t) group is comprised of sigma-dimers of [TCNE](.-) and octacyanobutanediide, [C(4)(CN)(8)](2-), which have a typical, albeit long, sp(3)-sp(3) sigma bond (r approximately 1.6 A) between each [TCNE](.-) moiety and characteristic nu(CN), nu(CC), and delta(CCN) IR absorptions. The L groups are structurally characterized as pi-dimers of [TCNE](.-) that are either eclipsed with r approximately 2.9 A (L(c)) and the nitriles bend away from the nominal TCNE plane away from the center of the dimer by 5.0 degrees (approximately sp(2.17)) or are noneclipsed with r approximately 3.5 A (L(t)) and the nitriles bend toward the center of the dimer by 1.9 degrees ( approximately sp(2.06)). Ab initio computations on isolated dimers were used to study the formation and stability of these exceptionally long CC (> or =2.9 A) bonding interactions as well as the process of pi-[TCNE](2) (2-) dimer formation for the L(c) and L(t) groups. The results of these computational studies show that the ground-state potential curve is that of a closed-shell/open-shell singlet, depending on the distance. The short S(t) group (r approximately 1.6 A) of dimers in this surface are true minimum-energy structures; however, the L(t) and L(c) groups are unstable, although two different nonphysical minima are found when imposing a double occupancy of the orbitals. These minima are metastable relative to dissociation into the isolated [TCNE](.-) units. Consequently, the existence of dimer dianions in crystals is due to cation.[TCNE](-) interactions, which provide the electrostatic stabilization necessary to overcome the intradimer electrostatic repulsion. This cation-mediated pi*-pi* [TCNE](-).[TCNE](-) interaction complies with Paulings definition of a chemical bond. This bonding interaction involves the pi* orbitals of each fragment, and arise from the overlap of the b(2g) SOMO on each of the two [TCNE](.-)s to form a filled b(2u) [TCNE](2) (2-) orbital. Although a pi dimer typically forms, if the fragments are close enough a sigma dimer can form. Due to the presence of cation-mediated intradimer CC bonding interactions the L(c) group of pi-[TCNE](2) (2-) dimers exhibits experimentally observable nu(CN) IR absorptions at 2191+/-2 (m), 2173+/-3 (s), and 2162+/-3 cm(-1) (s) and nu(CC) at 1364+/-3 cm(-1) (s) as well as a new UV-Vis feature in the range of 15 000 to 18 200 cm(-1) (549 to 667 nm) and averaging 16 825+/-1180 cm(-1) (594 nm) assigned to the predicted new intradimer (1)A(1g) --> (1)B(1u) transition and is purple on reflected light. Upon cooling to 77 K in 2-methyl tetrahydrofuran, this new band occurs at 18 940 cm(-1) (528 nm) for [[Et(4)N](+)](2)[TCNE](2) (2-), and the yellow solution turns deep red. Group L(t) is characterized by nu(CN) absorptions at 2215+/-2, 2197+/-3, and 2180+/-4 cm(-1) and nu(CC) at 1209+/-9 cm(-1) (w), while group S(T) has nu(CN) bands at 2215+/-4, 2157+/-3, and 2107+/-4 cm(-1) and nu(CC) at 1385+/-1 cm(-1) (vs).

Ionic liquids as a class of materials for transdermal delivery and pathogen neutralization

Significance Effective treatment of skin-based bacterial biofilms has been identified as a serious and unmet medical need. Biofilm-protected bacteria account for ∼80% of bacterial infections in humans and are 50–1,000 times more resistant to antibiotics than their planktonic counterparts. Biofilms in skin are further protected by the outermost layer of skin, the stratum corneum, which serves as a natural barrier to most therapeutics. Here, we present compelling evidence for exploiting ionic liquids (ILs) as an arsenal of materials both in a concerted effort to combat antibiotic-resistant bacterial biofilms in skin as well as for topical transdermal drug delivery. Our comprehensive strategy resulted in the identification of ILs that are effective at disrupting biofilms, neutralizing pathogens, and enhancing delivery of antibiotic into skin. Moreover, ILs did not show skin irritation that is typically associated with topical formulations. Biofilm-protected microbial infections in skin are a serious health risk that remains to be adequately addressed. The lack of progress in developing effective treatment strategies is largely due to the transport barriers posed by the stratum corneum of the skin and the biofilm. In this work, we report on the use of Ionic Liquids (ILs) for biofilm disruption and enhanced antibiotic delivery across skin layers. We outline the syntheses of ILs, analysis of relevant physicochemical properties, and subsequent neutralization effects on two biofilm-forming pathogens: Pseudomonas aeruginosa and Salmonella enterica. Further, the ILs were also examined for cytotoxicity, skin irritation, delivery of antibiotics through the skin, and treatment of biofilms in a wound model. Of the materials examined, choline-geranate emerged as a multipurpose IL with excellent antimicrobial activity, minimal toxicity to epithelial cells as well as skin, and effective permeation enhancement for drug delivery. Specifically, choline-geranate was comparable with, or more effective than, bleach treatment against established biofilms of S. enterica and P. aeruginosa, respectively. In addition, choline-geranate increased delivery of cefadroxil, an antibiotic, by >16-fold into the deep tissue layers of the skin without inducing skin irritation. The in vivo efficacy of choline-geranate was validated using a biofilm-infected wound model (>95% bacterial death after 2-h treatment). This work establishes the use of ILs for simultaneous enhancement of topical drug delivery and antibiotic activity.

Improved Hydrogen Release from Ammonia–Borane with ZIF-8

The promotion for hydrogen release from ammonia-borane (AB) was observed in the presence of ZIF-8. Even at concentrations of ZIF-8 as low as 0.25 mol %, a reduction of the onset temperature for dehydrogenation accompanies an increase in both the rate and amount of hydrogen released from AB.

On the existence of long C–C bonds between pairs of anions which repel: when and why? A test case on the [TCNE]22− dimers found in ionic crystals

Many of the Cm[TCNE]n (C = cation) salts have intradimer C–C interactions in the range of 2.9 to 3.5 A and show the electronic fingerprints associated with C–C bond formation (IR and UV spectra, magnetic properties, structural changes), despite the fact that two [TCNE]˙− anions should repel each other due to purely Coulombic considerations. Herein, we analyze these pairwise interactions in detail for a particular crystal in which such a C–C bond is found, to understand when and why these bonds are formed in a general case.

Evaluation of ionic liquids on phototrophic microbes and their use in biofuel extraction and isolation

Multiple ionic liquids (ILs) were assessed for their ability to extract branched, unsaturated hydrocarbons from an aqueous medium. In addition, IL cytotoxicity studies were performed on two phototrophic microbes, Synechocystis sp. PCC6803 and Botryococcus braunii var Showa. The optimum IL for use in an isoprenoid hydrocarbon extraction may vary based on the biological source of the isoprenoids. Our results suggest that ionic liquids have the potential to serve as novel biocompatible milking agents for extracting high-value chemicals from the microbes, with toxicity to both species minimized by considerations of ionic liquid structure and hydrophobicity.

Tetraalkylphosphonium-based ionic liquids for a single-step dye extraction/MALDI MS analysis platform.

Room temperature ionic liquids, or RTILs, based on tetraalkylphosphonium (PR(4)(+)) cations were used as the basis of a platform that enables separation of dyes from textiles, extraction of dyes from aqueous solution, and identification of the dyes by MALDI-MS in a single experimental step for forensic purposes. Ionic liquids were formed with PR(4)(+) cations and ferulate (FA), α-cyano-4-hydroxycinnamate (CHCA), and 2,5-dihydroxybenzoate (DHB) anions. The use of tetraalkylphosphonium-based ionic liquids in MALDI-MS allowed detection of small molecule dyes without addition of a traditional solid MALDI matrix.

Large-scale synthesis of CexLa1−xF3 nanocomposite scintillator materials

Transparent nanocomposites have been developed which consist of nanocrystals embedded in an organic matrix. The materials are comprised of up to 60% by volume of 7–13 nm crystals of the phosphor CexLa1−xF3, and are greater than 70% transparent in the visible region at a thickness of 1 cm. Consistencies of the nanocomposites range from a solid polymer to a wax to a liquid, depending on the workup conditions of the nanoparticle synthesis. These transparent nanophosphor composite materials have potential applications in radiation detection as scintillators, as well as in other areas such as imaging and lighting, and can be produced on large scales up to near-kilogram quantities at near ambient conditions, much lower in temperature than typical nanoparticle syntheses.

Luminescence in CeIV polyoxometalate [Ce(W5O18)2]8-: a combined experimental and theoretical study

Herein we describe the unique luminescent behavior observed in [Ce(IV)(W(5)O(18))(2)](8-) clusters and examine the photophysical properties using density functional theory.