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Htet Y.,Clemson University | Tennyson A.G.,Clemson University | Tennyson A.G.,Center for Optical Materials Science and Engineering Technologies anderson
Chemical Science | Year: 2016

Metalloenzymes that normally perform catalytic antioxidant or radical-degrading functions, as well as small-molecule complexes that mimic them, can also exert pro-oxidant or radical-forming effects depending on the identity of the terminal reductant. Because nitroxyl radicals function as redox active cocatalysts in the aerobic oxidation of alcohols, we hypothesized that catalytic radical reduction could be achieved via the oxidation of biologically-relevant alcohols. Herein we report an organoruthenium complex (Ru1) that catalyzed reduction of 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonate) radical monoanion (ABTS-) to ABTS2- in phosphate buffered saline (pH 7.4) using MeOH, EtOH, i-PrOH, serine, threonine, glucose, arabinose, methyl lactate or dimethyl malate as the terminal reductant. Replacing either the C-H or O-H groups of a -CHOH- moiety resulted in the loss of ABTS- reducing ability. Moreover, in conjunction with an alcohol terminal reductant, Ru1 was able to inhibit the oxidation of ABTS2- by H2O2 and horseradish peroxidase, even after multiple successive challenges with excess H2O2 or ABTS-. Collectively, these results demonstrate that Ru1 inhibits the oxidative formation of and catalyzes the reduction of radicals in aqueous solution via oxidation of biologically-relevant alcohols. © The Royal Society of Chemistry 2016.

Duniho T.L.,Clemson University | Laughlin B.J.,Clemson University | Buelt A.A.,Clemson University | Baker W.F.,Clemson University | And 3 more authors.
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2014

A series of eight poly(p-phenylene vinylene) (PPV) and poly(p-phenylene ethynylene) (PPE) (P1-P8) derivatives were tested for their ability to detect the nitroaromatic explosive 2,4,6-trinitrotoluene (TNT) and its model compound 2,6-dinitrotoluene (DNT). The polymers P1-P8 represent five structural classes that have not been examined for nitroaromatic sensing. These new motifs include PPE derivatives with a main-chain m-terphenyl unit (P1) or oxacyclophane canopy-like structure (P2) and PPV derivatives with 2,6-mesitylenephenylene repeats (P3 and P4), 9,9-dialkyl-1,4-fluorenylene repeats (P5 and P6), or m-phenylene units that periodically disrupt π-conjugation along the backbone of the polymer (P7 and P8). The time-dependent photoluminescent response of films to TNT and DNT and the solution-phase Stern-Volmer quenching constants for both TNT and DNT were determined. The results are rationalized in terms of side-chain sterics and π-system electronics and are discussed relative to known conjugated polymers. © 2014 Wiley Periodicals, Inc.

Mangalum A.,Clemson University | Mangalum A.,Center for Optical Materials Science and Engineering Technologies anderson | Hardin R.A.,Clemson University | McMillen C.D.,Clemson University | And 2 more authors.
Inorganica Chimica Acta | Year: 2015

To construct the framework for a chelating, anionic benzimidazole-based N-heterocyclic carbene (NHC) ligand (1-), N-(3,5-dimethylphenyl)benzimidazole was reacted with 2-bromoacetic acid to yield the corresponding benzimidazolium [1H2][Br]. Double deprotonation followed by metallation of [1H2][Br] with Ag2O produced the Ag-NHC complex [Ag(1)]n (2), which exhibited good solubility in organic solvents despite its multinuclear nature. Crystallographic analysis of 2 revealed a dodecametallic structure (n = 12) comprising mononuclear [Ag(1)] and dinuclear [Ag2(1)2] subunits, the latter of which featured close AgAg contacts. Transmetallation of 1- from Ag to Ru via the reaction of [RuCl(η6-cymene)(μ-Cl)]2 with 2 afforded the Ru-NHC complex [RuCl(1)(η6-cymene)] (3), which demonstrated catalytic activity for transfer hydrogenation of CO, CN and CC bonds using isopropanol as the H2 source. © 2014 Elsevier B.V.

Mangalum A.,Clemson University | Mangalum A.,Center for Optical Materials Science and Engineering Technologies anderson | Htet Y.,Clemson University | Roe D.A.,Clemson University | And 3 more authors.
Inorganica Chimica Acta | Year: 2015

A chelating benzimidazolylidene-carboxylate ligand (1) was transferred from [Ag(1)] to [RuCl2(dmso)4] to afford trans(C)-[Ru(1)2(bpy)] (2), but all attempts to incorporate 1 into cis(Cl)-[RuCl2(bpy)2] were unsuccessful. Alternatively, reaction of [RuCl(1)(η6-cymene)] (3) with bpy and AgOTf successfully produced [Ru(1)(bpy)2][OTf] (4). Methylation of 2 and 4 with MeOTf yielded trans(C)-[Ru(1-Me)2(bpy)][OTf]2 (5) and [Ru(1-Me)(bpy)2][OTf]2 (6), accompanied by a +2 and +1 increase in net charge, respectively. Cyclic voltammetry indicated that the increase in Ru(II)/Ru(III) oxidation potential from 2 to 5 was twice the increase from 4 to 6. UV-Vis spectroscopy also revealed that transitions in 5 occurred at higher energy than in 2 by double the difference between 6 and 4. Crystallographic analysis demonstrated that the coordination environment of Ru did not differ significantly between 2 and 5, suggesting that the observed shifts in oxidation potentials and absorption wavelengths are not due to changes in coordination chemistry or formal oxidation state. Collectively, these results show that 5 and 6 feature Ru centers more electron deficient than those in 2 and 4, respectively, by amounts linearly proportional to the difference in net charge. © 2015 Elsevier B.V. All rights reserved.

Laughlin B.J.,Clemson University | Laughlin B.J.,Center for Optical Materials Science and Engineering Technologies anderson | Htet Y.,Clemson University | He S.,Clemson University | And 8 more authors.
European Polymer Journal | Year: 2015

A debromination-chain polymerization-debromination (DPD) route to poly(p-phenylene vinylene) (PPV) derivatives is reported. In contrast to existing chain polymerization routes for the preparation of PPV derivatives, this route takes advantage of a symmetric monomer to preclude head-to-head or tail-to-tail coupling that ultimately leads to alkyne or alkyl defects in the polymer chain. Mechanistic studies were performed and revealed that the DPD route can be carried out with the desirable intermediacy of a soluble, isolable polymer precursor. Unsubstituted PPV, poly(p-(2,5-dihexyloxyphenylene)vinylene) and a PPV derivative with a sterically encumbering side chain were all readily prepared by the new DPD route. © 2015 Elsevier Ltd. All rights reserved.

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