Patrick S. Barber

A Water-Soluble Pybox Derivative and Its Highly Luminescent Lanthanide Ion Complexes

A new water-soluble Pybox ligand, 1, has been synthesized and found to crystallize in the monoclinic P2(1)/n space group with unit cell parameters a = 6.0936(1) Å, b = 20.5265(4) Å, c = 12.0548(2) Å, and β = 90.614(1)°. In the crystal, a water molecule is bound through hydrogen-bonding interactions to the nitrogen atoms of the oxazoline rings. This ligand was used to complex a variety of lanthanide ions, opening up new avenues for luminescence and catalysis in aqueous environment. These complexes are highly luminescent in aqueous solutions, in acetonitrile, and in the solid state. Aqueous quantum yields are high at 30.4% for Eu(III), 26.4% for Tb(III), 0.32% for Yb(III), and 0.11% for Nd(III). Er(III) did not luminesce in water, but an emission efficiency of 0.20% could be measured in D(2)O. Aqueous emission lifetimes were also determined for the visible emitting lanthanide ions and are 1.61 ms for Eu(III) and 1.78 ms for Tb(III). Comparing emission lifetimes in deuterated and nondeuterated water indicates that no water molecules are coordinated to the metal ion. Speciation studies show that three species form successively in solution and the log β values are 5.3, 9.6, and 13.8 for Eu(III) and 5.3, 9.2, and 12.7 for Tb(III) for 1:1, 2:1, and 3:1 ligand to metal ratios, respectively.

Para-Derivatized Pybox Ligands As Sensitizers in Highly Luminescent Ln(III) Complexes

New complexes of pyridine-bis(oxazoline) derivatized with -H, -OMe, and -Br at the para position of the pyridine ring with Eu(III) and Tb(III) have been isolated. These are highly luminescent in the solid state, regardless of the ligand-to-metal ratio. Several of the metal complexes were isolated and characterized by single crystal X-ray diffraction, showing the rich diversity of structures that can be obtained with this family of ligands. [Eu(PyboxOMe)(3)](NO(3))(3)·3CH(2)Cl(2), 1, crystallizes in the monoclinic space group P2(1)/n and has the cell parameters a = 14.3699(10) Å, b = 13.4059(9) Å, c = 25.8766(18) Å, β = 95.367(1)°, and V = 4963.1(6) Å(3). The isostructural [Tb(PyboxOMe)(3)](NO(3))(3)·3CH(2)Cl(2), 2, crystallizes with the parameters a = 14.4845(16) Å, b = 13.2998(15) Å, c = 25.890(3) Å, β = 94.918(2)°, and V = 4969.1(10) Å(3). 3, a 1:1 complex with the formula [Eu(PyboxBr)(NO(3))(3)(H(2)O)], crystallizes in the monoclinic P2(1)/c space group with a = 11.649(2) Å, b = 8.3914(17) Å, c = 20.320(4) Å, β = 100.25(3)°, and V = 1954.5(7) Å(3). 4, a product of the reaction of PyboxBr with Tb(NO(3))(3), is [Tb(PyboxBr)(2)(η(2)-NO(3))(η(1)-NO(3)](2)[Tb(NO(3))(5)]·5H(2)O. It crystallizes in the monoclinic space group P2(1) with a = 15.612(3) Å, b = 14.330(3) Å, c = 16.271(3) Å, β = 92.58(3)°, and V = 3636.5(13) Å(3). [Tb(Pybox)(3)](CF(3)SO(3))(3)·3CH(2)CN, 5, crystallizes in the triclinic space group P1̅ with a = 12.3478(2) Å, b = 15.0017(2) Å, c = 16.1476(4) Å, α = 100.252(1)°, β = 100.943(1)°, γ = 113.049(1)°, and V = 2594.80(8) Å(3). Finally, compound 6, [Tb(Pybox)(2)(NO(3))(H(2)O)](NO(3))(2)·CH(3)OH, crystallizes in the triclinic P1̅ space group with a = 9.7791(2) Å, b = 10.1722(2) Å, c = 15.3368(3) Å, α = 83.753(1)°, β = 78.307(1)°, γ = 85.630(1)°, and V = 1482.33(5) Å(3). In solution, the existence of 3:1, 2:1, and 1:1 species can be observed through absorption and luminescence speciation measurements as well as NMR spectroscopy. The stability constants in acetonitrile, as an average obtained from absorption and emission titrations, are log β(11) = 5.4, log β(12) = 8.8, and log β(13) = 12.8 with Eu(III) and log β(11) = 4.5, log β(12) = 8.4, and log β(13) = 11.7 for the Tb(III) species with PyboxOMe. Pybox displayed stability constants log β(11) = 3.6, log β(12) = 9.1, and log β(13) = 12.0 with Eu(III) and log β(11) = 3.7, log β(12) = 9.3, and log β(13) = 12.2 for the Tb(III) species. Finally, PyboxBr yielded log β(11) = 7.1, log β(12) = 12.2, and log β(13) = 15.5 for the Eu(III) species and log β(11) = 6.2, log β(12) = 11.0, and log β(13) = 15.4 with Tb(III). Photophysical characterization was performed in all cases on solutions with 3:1 ligand-to-metal ion stoichiometry and allowed determination of quantum yields and lifetimes of emission for PyboxOMe of 23.5 ± 1.6% and 1.54 ± 0.04 ms for Eu(III) and 21.4 ± 3.6% and 1.88 ± 0.04 ms for Tb(III). For Pybox these values were 25.6 ± 1.1% and 1.49 ± 0.04 ms for Eu(III) and 23.2 ± 2.1% and 0.44 ± 0.01 ms for Tb(III) and for PyboxBr they were 35.8 ± 1.6% and 1.46 ± 0.03 ms for Eu(III) and 23.3 ± 1.3% and a double lifetime of 0.79 ± 0.05/0.07 ± 0.01 ms for Tb(III). A linear relationship between the triplet level energies and the Hammett σ constants was found. Lifetime measurements in methanol as well as the NMR data in both methanol and acetonitrile indicate that all complexes are stable in the 3:1 stoichiometry in solution and that there is no solvent coordination to the metal ion.

Highly selective extraction of the uranyl ion with hydrophobic amidoxime-functionalized ionic liquids via η2 coordination

Hydrophobic, amidoxime-functionalized ionic liquids selectively extract UO22+ from aqueous solution via η2 coordination as demonstrated here with extraction, spectroscopic, and crystallographic studies which prove the amidoxime-uranyl coordination mode and extraction mechanism.

Drug specific, tuning of an ionic liquid's hydrophilic–lipophilic balance to improve water solubility of poorly soluble active pharmaceutical ingredients

Amphotericin B and itraconazole were used to demonstrate that ionic liquids can be designed or chosen to provide tunable hydrophilicity in one ion and lipophilicity in the other allowing one to match the structural requirements needed to solubilize poorly water soluble active pharmaceutical ingredients. These liquid, amphiphilic excipients could be used as both drug delivery systems and solubilization agents to improve the aqueous solubility of many drugs. The solubility in deionized water, simulated gastric fluid, simulated intestinal fluid, and phosphate buffer solution was greatly improved over current methods for drug delivery by utilizing designed ionic liquids as excipients.

Surface modification of ionic liquid-spun chitin fibers for the extraction of uranium from seawater: seeking the strength of chitin and the chemical functionality of chitosan

Chitin fibers, prepared by extracting chitin directly from shrimp shell waste and dry-jet wet spinning from the resulting ionic liquid (1-ethyl-3-methylimidazolium acetate) solution in a one-pot process, were surface modified by taking advantage of the insolubility of chitin in common solvents (e.g., water, organics). In this proof of concept example, the chitin fiber surfaces were first deacetylated using aqueous NaOH to make available the primary amine (the functional group of chitosan) on the surface. Further treatment of the fibers allowed for the task-specific tailoring of the functionality (here we appended amidoxime for the extraction of aqueous uranyl ions from seawater). Compositional analysis and physical property measurements (e.g., tensile strength and thermal decomposition) of the fibers before and after surface modification indicated minimal change to the bulk material; however, spectroscopy and sorption studies of uranyl ions from aqueous solution demonstrated surface modification. The lower cost, one-pot process used in this study resulted in weak and brittle fibers, suggesting that additional purification of the chitin before pulling fibers will greatly improve the strength and utility of the resulting material. Overall, a platform has been developed for the surface modification of chitin fibers that provides both the physical properties of chitin and the functional properties of chitosan, resulting in an advanced material from a biorenewable resource with reduced chemical input.

Coagulation of Chitin and Cellulose from 1‐Ethyl‐3‐methylimidazolium Acetate Ionic‐Liquid Solutions Using Carbon Dioxide

Chemisorption of carbon dioxide by 1-ethyl-3-methylimidazolium acetate ([C2 mim][OAc]) provides a route to coagulate chitin and cellulose from [C2 mim][OAc] solutions without the use of high-boiling antisolvents (e.g., water or ethanol). The use of CO2 chemisorption as an alternative coagulating process has the potential to provide an economical and energy-efficient method for recycling the ionic liquid.

Prodrug ionic liquids: functionalizing neutral active pharmaceutical ingredients to take advantage of the ionic liquid form

Neutral, non- or not easily-ionizable active pharmaceutical ingredients can take advantage of the unique property sets of ionic liquids by functionalization with hydrolyzable, charged (or ionizable) groups in the preparation of ionic liquid prodrugs as demonstrated here with the synthesis, characterization, and hydrolysis of cationic acetaminophen prodrugs paired with the docusate anion.

Nonaborane and Decaborane Cluster Anions Can Enhance the Ignition Delay in Hypergolic Ionic Liquids and Induce Hypergolicity in Molecular Solvents

The dissolution of nido-decaborane, B10H14, in ionic liquids that are hypergolic (fuels that spontaneously ignite upon contact with an appropriate oxidizer), 1-butyl-3-methylimidazolium dicyanamide, 1-methyl-4-amino-1,2,4-triazolium dicyanamide, and 1-allyl-3-methylimidazolium dicyanamide, led to the in situ generation of a nonaborane cluster anion, [B9H14](-), and reductions in ignition delays for the ionic liquids suggesting salts of borane anions could enhance hypergolic properties of ionic liquids. To explore these results, four salts based on [B10H13](-) and [B9H14](-), triethylammonium nido-decaborane, tetraethylammonium nido-decaborane, 1-ethyl-3-methylimidazolium arachno-nonaborane, and N-butyl-N-methyl-pyrrolidinium arachano-nonaborane were synthesized from nido-decaborane by reaction of triethylamine or tetraethylammonium hydroxide with nido-decaborane in the case of salts containing the decaborane anion or via metathesis reactions between sodium nonaborane (Na[B9H14]) and the corresponding organic chloride in the case of the salts containing the nonaborane anion. These borane cluster anion salts form stable solutions in some combustible polar aprotic solvents such as tetrahydrofuran and ethyl acetate and trigger hypergolic reactivity of these solutions. Solutions of these salts in polar protic solvents are not hypergolic.

Synthesis and molecular recognition studies of pyrrole sulfonamides

We report the synthesis and characterization of the pyrrole sulfonamide as a new class of potential molecular receptors, including conformational analysis and molecular recognition studies for four pyrrole sulfonamide derivatives.

A “green” industrial revolution: Using chitin towards transformative technologies

Even with the high costs of environmental exposure controls, as well as the chance of control failures, options for industries wanting to implement sustainability through frameworks such as green chemistry are not yet cost-effective. We foresee a “green” industrial revolution through the use of transformative technologies that provide cost-effective and sustainable products which could lead to new business opportunities. Through example, we promote the use of natural and abundant biopolymers such as chitin, combined with the solvating power of ionic liquids (ILs), as a transformative technology to develop industries that are overall better and more cost-effective than current practices. The use of shellfish waste as a source of chitin for a variety of applications, including high-value medical applications, represents a total byproduct utilization concept with realistic implications in crustacean processing industries.