Think / Make / Think (Exhibition Catalogue)

This exhibition featured the work of current professors in the University of Tennessee School of Art. Exhibiting faculty were: Joshua Bienko, Emily Bivens, Sally Brogden, Jason S. Brown, Paul Harrill, Paul Lee, Sarah Lowe, Beauvais Lyons, Frank Martin, Althea Murphy-Price, John Powers, Deborah Shmerler, Jered Sprecher, Cary Staples, Claire Stigliani, David Wilson, Karla Wozniak, Koichi Yamamoto, and Sam Yates

Heterometallic Second-Row Transition Metal Chain Compounds in Two Charge States: Syntheses, Properties, and Electronic Structures of [Mo–Mo–Ru]^6+/7+ Chains

Reaction of Mo₂(dpa)₄ (dpa = 2,2′-dipyridylamido) with ¹/₂ equiv of [Ru­(CO)₃Cl₂]₂ in molten naphthalene at 250 °C provides facile access to the first all-second-row transition metal heterometallic chain compound, MoMoRu­(dpa)₄Cl₂ (<b>1</b>). The one-electron oxidized compound [MoMoRu­(dpa)₄Cl₂]­(OTf) (<b>2</b>) is synthesized by reaction of <b>1</b> with FeCp₂(OTf). X-ray crystallography reveals a contraction of the Mo–Ru bond distance from 2.38 Å in <b>1</b> to 2.30 Å in <b>2</b>, and an elongation of the Mo–Mo bond distance from 2.12 Å in <b>1</b> to 2.21 Å in <b>2</b>. The short Mo–Ru bond distances indicate significant electron delocalization along the Mo–Mo–Ru chain, which is quantified by density functional theory (DFT) calculations. Molecular orbital analyses of both compounds based on DFT results reveal full delocalization of the orbitals of σ and π symmetry for both compounds. Additionally, δ orbital delocalization is observed in <b>2</b>

Heterometallic Multiple Bonding: Delocalized Three-Center σ and π Bonding in Chains of 4d and 5d Transition Metals

Heterotrimetallic compounds Mo₂Ru­(dpa)₄Cl₂ (<b>1</b>) and W₂Ru­(dpa)₄Cl₂ (<b>2</b>) are prepared by reactions of M₂(dpa)₄ (M = Mo or W; dpa = 2,2′-dipyridylamide) with [Ru­(CO)₃Cl₂]₂. Crystallographic studies reveal short Mo–Ru and W–Ru distances, 2.38 Å (<b>1</b>) and 2.39 Å (<b>2</b>), suggestive of delocalized Mo–Mo–Ru and W–W–Ru bonding. In contrast to the σ bonding found in the corresponding iron compounds, density functional theory calculations reveal both a three-center/two-electron σ bond and two three-center/four-electron π bonds in the M–M–Ru compounds

Deposition Efficacy of Natural and Synthetic Antioxidants on Fabrics

Pine bark extracts were tested as valid natural alternatives to common phenolic antioxidants to be deposited onto solid matrices. An analytical method for determining both deposition-efficacy and maintenance of antioxidant activity on fabrics surfaces was developed and successfully applied to phenolic antioxidants and pine tannins onto cotton fabric samples. Accumulated data suggest that common phenolic antioxidants and tannin contribute to an elevated antioxidant activity on fabric. A known source of odour is autoxidation of residual sebum on fabric, leading to the generation of malodourous compounds. Therefore, antioxidants hold the promise for mitigating malodour on fabrics, a top unmet consumer need around the globe

Assessing Metal-Metal Multiple Bonds in Cr-Cr, Mo-Mo, and W-W Compounds and a Hypothetical U-U Compound: A Quantum Chemical Study Comparing DFT and Multireference Methods

To gain insights into the trends in metal–metal multiple bonding among the Group 6 elements, density functional theory has been employed in combination with multiconfigurational methods (CASSCF and CASPT2) to investigate a selection of bimetallic, multiply bonded compounds. For the compound [Ar-MM-Ar] (Ar=2,6-(C6H5)2-C6H3, M=Cr, Mo, W) the effect of the Ar ligand on the M2 core has been compared with the analogous [Ph-MM-Ph] (Ph=phenyl, M=Cr, Mo, W) compounds. A set of [M2(dpa)4] (dpa=2,2′-dipyridylamide, M=Cr, Mo, W, U) compounds has also been investigated. All of the compounds studied here show important multiconfigurational behavior. For the Mo2 and W2 compounds, the σ2π4δ2 configuration dominates the ground-state wavefunction, contributing at least 75 %. The Cr2 compounds show a more nuanced electronic structure, with many configurations contributing to the ground state. For the Cr, Mo, and W compounds the electronic absorption spectra have been studied, combining density functional theory and multireference methods to make absorption feature assignments. In all cases, the main features observed in the visible spectra may be assigned as charge-transfer bands. For all compounds investigated the Mayer bond order (MBO) and the effective bond order (EBO) were calculated by density functional theory and CASSCF methods, respectively. The MBO and EBO values share a similar trend toward higher values at shorter normalized metal–metal bond lengths

High content analysis to determine cytotoxicity of the antimicrobial peptide, melittin and selected structural analogs

Antimicrobial peptides (AMPs) are naturally occurring entities with potential as pharmaceutical candidates and/or food additives. They are present in many organisms including bacteria, insects, fish and mammals. While their antimicrobial activity is equipotent with many commercial antibiotics, current limitations are poor pharmacokinetics, stability and potential toxicology issues. Most elicit antimicrobial action via perturbation of bacterial membranes. Consequently, associated cytotoxicity in human cells is reflected by their capacity to lyse erythrocytes. However, more rigorous toxicological assessment of AMPs is required in order to predict potential failure at a later stage of development.Wedescribe a high-content analysis (HCA) screening protocol recently established for determination and prediction of safety in pharmaceutical drug discovery. HCA is a powerful, multi-parameter bioanalytical tool that amalgamates the actions of fluorescence microscopy with automated cell analysis software in order to understand multiple changes in cellular health. We describe the application of HCA in assessing cytotoxicity of the cytolytic-helical peptide, melittin, and selected structural analogs. The data shows that structural modification of melittin reduces its cytotoxic action and that HCA is suitable for rapidly identifying cytotoxicity.Irish Research Council for Science, Engineering and TechnologyScience Foundation IrelandMerrion PharmaceuticalsNYP: http://www.sciencedirect.com/science/article/pii/S0196978111002300 - AV 11/07/201

Oxidative Stretching of Metal–Metal Bonds to Their Limits

Oxidation of quadruply bonded Cr₂(dpa)₄, Mo₂(dpa)₄, MoW­(dpa)₄, and W₂(dpa)₄ (dpa = 2,2′-dipyridylamido) with 2 equiv of silver­(I) triflate or ferrocenium triflate results in the formation of the two-electron-oxidized products [Cr₂(dpa)₄]²⁺ (<b>1</b>), [Mo₂(dpa)₄]²⁺ (<b>2</b>), [MoW­(dpa)₄]²⁺ (<b>3</b>), and [W₂(dpa)₄]²⁺ (<b>4</b>). Additional two-electron oxidation and oxygen atom transfer by <i>m</i>-chloroperoxybenzoic acid results in the formation of the corresponding metal–oxo compounds [Mo₂O­(dpa)₄]²⁺ (<b>5</b>), [WMoO­(dpa)₄]²⁺ (<b>6</b>), and [W₂O­(dpa)₄]²⁺ (<b>7</b>), which feature an unusual linear M···MO structure. Crystallographic studies of the two-electron-oxidized products <b>2</b>, <b>3</b>, and <b>4</b>, which have the appropriate number of orbitals and electrons to form metal–metal triple bonds, show bond distances much longer (by >0.5 Å) than those in established triply bonded compounds, but these compounds are nonetheless diamagnetic. In contrast, the Cr–Cr bond is completely severed in <b>1</b>, and the resulting two isolated Cr³⁺ magnetic centers couple antiferromagnetically with <i>J</i>/<i>k</i>_B= −108(3) K [−75(2) cm^–1], as determined by modeling of the temperature dependence of the magnetic susceptibility. Density functional theory (DFT) and multiconfigurational methods (CASSCF/CASPT2) provide support for “stretched” and weak metal–metal triple bonds in <b>2</b>, <b>3</b>, and <b>4</b>. The metal–metal distances in the metal–oxo compounds <b>5</b>, <b>6</b>, and <b>7</b> are elongated beyond the single-bond covalent radii of the metal atoms. DFT and CASSCF/CASPT2 calculations suggest that the metal atoms have minimal interaction; the electronic structure of these complexes is used to rationalize their multielectron redox reactivity