identification of a reversible EC-mechanism

Bu4N[Fe(CO)3(NO)] displays unique catalytic properties in electron-transfer catalysis such as in allylic substitutions, hydrosilylation, transesterifications, or carbene transfer chemistry. Herein we present a detailed spectroelectrochemical investigation of this complex that unravels an interesting electrochemical–chemical transformation in which two parts of [Fe(CO)3(NO)]− are oxidized and undergo a disproportionation in the presence of CO to [Fe(CO)5] and [Fe(CO)2(NO)2]. Upon re-reduction the former two complexes regenerate [Fe(CO)3(NO)]− to about 85

Valence and spin situations in isomeric [(bpy)Ru(Q′)2]n (Q′ = 3,5-di-tert- butyl-N-aryl-1,2-benzoquinonemonoimine). An experimental and DFT analysis

The article deals with the ruthenium complexes, [(bpy)Ru(Q′)2] (1–3) incorporating two unsymmetrical redox-noninnocent iminoquinone moieties [bpy = 2,2′-bipyridine; Q′ = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, aryl = C6H5 (Q′1), 1; m-Cl2C6H3 (Q′2), 2; m-(OCH3)2C6H3 (Q′3), 3]. 1 and 3 have been preferentially stabilised in the cc-isomeric form while both the ct- and cc-isomeric forms of 2 are isolated [ct: cis and trans and cc: cis and cis with respect to the mutual orientations of O and N donors of two Q′]. The isomeric identities of 1–3 have been authenticated by their single-crystal X-ray structures. The collective consideration of crystallographic and DFT data along with other analytical events reveals that 1–3 exhibit the valence configuration of [(bpy)RuII(Q′Sq)2]. The magnetization studies reveal a ferromagnetic response at 300 K and virtual diamagnetic behaviour at 2 K. DFT calculations on representative 2a and 2b predict that the excited triplet (S = 1) state is lying close to the singlet (S = 0) ground state with singlet–triplet separation of 0.038 eV and 0.075 eV, respectively. In corroboration with the paramagnetic features the complexes exhibit free radical EPR signals with g [similar]2 and 1HNMR spectra with broad aromatic proton signals associated with the Q′ at 300 K. Experimental results in conjunction with the DFT (for representative 2a and 2b) reveal iminoquinone based preferential electron-transfer processes leaving the ruthenium(II) ion mostly as a redox insensitive entity: [(bpy)RuII(Q′Q)2]2+ (12+–32+) [leftrightharpoons] [(bpy)RuII(Q′Sq)(Q′Q)]+ (1+–3+) [leftrightharpoons] [(bpy)RuII(Q′Sq)2] (1–3) [leftrightharpoons] [(bpy)RuII(Q′Sq)(Q′Cat)]−/[(bpy)RuIII(Q′Cat)2]− (1−–3−). The diamagnetic doubly oxidised state, [(bpy)RuII(Q′Q)2]2+ in 12+–32+ has been authenticated further by the crystal structure determination of the representative [(bpy)RuII(Q′3)2](ClO4)2 [3](ClO4)2 as well as by its sharp 1H NMR spectrum. The key electronic transitions in each redox state of 1n–3n have been assigned by TD–DFT calculations on representative 2a and 2b

Expanding the diversity of mycobacteriophages: insights into genome architecture and evolution.

Mycobacteriophages are viruses that infect mycobacterial hosts such as Mycobacterium smegmatis and Mycobacterium tuberculosis. All mycobacteriophages characterized to date are dsDNA tailed phages, and have either siphoviral or myoviral morphotypes. However, their genetic diversity is considerable, and although sixty-two genomes have been sequenced and comparatively analyzed, these likely represent only a small portion of the diversity of the mycobacteriophage population at large. Here we report the isolation, sequencing and comparative genomic analysis of 18 new mycobacteriophages isolated from geographically distinct locations within the United States. Although no clear correlation between location and genome type can be discerned, these genomes expand our knowledge of mycobacteriophage diversity and enhance our understanding of the roles of mobile elements in viral evolution. Expansion of the number of mycobacteriophages grouped within Cluster A provides insights into the basis of immune specificity in these temperate phages, and we also describe a novel example of apparent immunity theft. The isolation and genomic analysis of bacteriophages by freshman college students provides an example of an authentic research experience for novice scientists

The redox series [Ru(bpy)2(L)]n, n = +3, +2, +1, 0, with L = bipyridine, “click” derived pyridyl-triazole or bis-triazole: a combined structural, electrochemical, spectroelectrochemical and DFT investigation

The compounds [Ru(bpy)2(L1)](ClO4)2 (1(ClO4)2), [Ru(bpy)2(L2)](ClO4)2 (2(ClO4)2), [Ru(bpy)2(L3)](ClO4)2 (3(ClO4)2), [Ru(bpy)2(L4)](ClO4)2 (4(ClO4)2), [Ru(bpy)2(L5)](ClO4)2 (5(ClO4)2), and [Ru(bpy)2(L6)](ClO4)26(ClO4)2 (bpy = 2,2′-bipyridine, L1 = 1-(4-isopropyl- phenyl)-4-(2-pyridyl)-1,2,3-triazole, L2 = 1-(4-butoxy- phenyl)-4-(2-pyridyl)-1,2,3-triazole, L3 = 1-(2-trifluoromethyl- phenyl)-4-(2-pyridyl)-1,2,3-triazole, L4 = 4,4′-bis-{1-(2,6-diisopropyl- phenyl)}-1,2,3-triazole, L5 = 4,4′-bis-{(1-phenyl)}-1,2,3-triazole, L6 = 4,4′-bis-{1-(2-trifluoromethyl-phenyl)}-1,2,3-triazole) were synthesized from [Ru(bpy)2(EtOH)2](ClO4)2 and the corresponding “click”-derived pyridyl- triazole or bis-triazole ligands, and characterized by 1H-NMR spectroscopy, elemental analysis, mass spectrometry and X-ray crystallography. Structural analysis showed a distorted octahedral coordination environment about the Ru(II) centers, and shorter Ru–N(triazole) bond distances compared to Ru–N(pyridine) distances in complexes of mixed-donor ligands. All the complexes were subjected to cyclic voltammetric studies, and the results were compared to the well-known [Ru(bpy)3]2+ compound. The oxidation and reduction potentials were found to be largely uninfluenced by ligand changes, with all the investigated complexes showing their oxidation and reduction steps at rather similar potentials. A combined UV-vis-NIR and EPR spectroelectrochemical investigation, together with DFT calculations, was used to determine the site of electron transfer in these complexes. These results provided insights into their electronic structures in the various investigated redox states, showed subtle differences in the spectroscopic signatures of these complexes despite their similar electrochemical properties, and provided clues to the unperturbed redox potentials in these complexes with respect to ligand substitutions. The reduced forms of the complexes display structured absorption bands in the NIR region. Additionally, we also present new synthetic routes for the ligands presented here using Cu-abnormal carbene catalysts

Substituent-Induced Reactivity in Quinonoid-Bridged Dinuclear Complexes: Comparison between the Ruthenium and Osmium Systems

The ligand 2,5-bis­[2-(methylthio)­anilino]-1,4-benzoquinone (<b>L</b>) was used in its doubly deprotonated form to synthesize the complex [{Cl­(η⁶-Cym)­Os}₂(μ<i>-</i>η²:η²-<b>L</b>_<b>‑2H</b>)] (<b>1</b>; Cym = <i>p</i>-cymene = 1-isopropyl-4-methylbenzene). Spectroscopic characterization and elemental analysis confirms the presence of the chloride ligands in <b>1</b>, which indirectly shows that the bridging ligand <b>L</b>_<b>‑2H</b> acts in a bis-bidentate fashion in <b>1</b>, with the thioether substituents on the bridge remaining uncoordinated. Abstraction of the chloride ligands in <b>1</b> by AgBF₄ in CH₃CN leads not only to the release of those chloride ligands but also to a simultaneous substituent-induced release of Cym with the bridging ligand changing its coordination mode to bis-tridentate. In the resulting complex [{(CH₃CN)₃Os}₂(μ-η³:η³-<b>L</b>_<b>‑2H</b>)]²⁺ (<b>2</b>^<b>2+</b>), the thioether groups of <b>L</b>_<b>‑2H</b> are now coordinated to the osmium centers with the bridging ligand coordinating to the metal center in a bis-meridional form. The coordination mode of <b>L</b>_<b>‑2H</b> in <b>2</b>^<b>2+</b> was confirmed by single-crystal X-ray diffraction data. A structural analysis of <b>2</b>^<b>2+</b> reveals localization of double bonds within the “upper” and “lower” parts of the bridging ligand in comparison to bond distances in the free ligand. Additionally, the binding of the bridge to the osmium centers is seen to occur through O^– and neutral imine-type N donors. The complexes <b>1</b> and <b>2</b>^<b>2+</b> were investigated by cyclic voltammetry and UV–vis–near-IR and EPR spectroelectrochemistry. This combined approach was used to unravel the redox-active nature of the ligand <b>L</b>_<b>‑2H</b>, to determine the sites of electron transfer (ligand radical versus mixed valency), and to compare the present systems with their ruthenium analogues <b>3</b> and <b>4</b>^<b>2+</b> (Schweinfurth, D. Inorg. Chem. 2011, 50, 1150). The effect of replacing ruthenium by its higher homologue osmium on the reactivity and the electrochemical and spectroscopic properties were explored, and the differences were deciphered by taking into account the intrinsic dissimilarities between the two homologues. The usefulness of incorporating additional donor substituents on potentially bridging quinonoid ligands was probed in this work

Tuning Ligand Effects and Probing the Inner-Workings of Bond Activation Steps: Generation of Ruthenium Complexes with Tailor-Made Properties

Activating chemical bonds through external triggers and understanding the underlying mechanism are at the heart of developing molecules with catalytic and switchable functions. Thermal, photochemical, and electrochemical bond activation pathways are useful for many chemical reactions. In this Article, a series of Ru^II complexes containing a bidentate and a tripodal ligand were synthesized. Starting from all-pyridine complex <b>1</b>²⁺, the pyridines were stepwise substituted with “click” triazoles (<b>2</b>²⁺–<b>7</b>²⁺). Whereas the thermo- and photoreactivity of <b>1</b>²⁺ are due to steric repulsion within the equatorial plane of the complex, <b>3</b>²⁺–<b>6</b>²⁺ are reactive because of triazoles in axial positions, and <b>4</b>²⁺ shows unprecedented photoreactivity. Complexes that feature neither steric interactions nor axial triazoles (<b>2</b>²⁺ and <b>7</b>²⁺) do not show any reactivity. Furthermore, a redox-triggered conversion mechanism was discovered in <b>1</b>²⁺, <b>3</b>²⁺, and <b>4</b>²⁺. We show here ligand design principles required to convert a completely inert molecule to a reactive one and vice versa, and provide mechanistic insights into their functioning. The results presented here will likely have consequences for developing a future generation of catalysts, sensors, and molecular switches

Tuning Ligand Effects and Probing the Inner-Workings of Bond Activation Steps: Generation of Ruthenium Complexes with Tailor-Made Properties

Activating chemical bonds through external triggers and understanding the underlying mechanism are at the heart of developing molecules with catalytic and switchable functions. Thermal, photochemical, and electrochemical bond activation pathways are useful for many chemical reactions. In this Article, a series of Ru^II complexes containing a bidentate and a tripodal ligand were synthesized. Starting from all-pyridine complex <b>1</b>²⁺, the pyridines were stepwise substituted with “click” triazoles (<b>2</b>²⁺–<b>7</b>²⁺). Whereas the thermo- and photoreactivity of <b>1</b>²⁺ are due to steric repulsion within the equatorial plane of the complex, <b>3</b>²⁺–<b>6</b>²⁺ are reactive because of triazoles in axial positions, and <b>4</b>²⁺ shows unprecedented photoreactivity. Complexes that feature neither steric interactions nor axial triazoles (<b>2</b>²⁺ and <b>7</b>²⁺) do not show any reactivity. Furthermore, a redox-triggered conversion mechanism was discovered in <b>1</b>²⁺, <b>3</b>²⁺, and <b>4</b>²⁺. We show here ligand design principles required to convert a completely inert molecule to a reactive one and vice versa, and provide mechanistic insights into their functioning. The results presented here will likely have consequences for developing a future generation of catalysts, sensors, and molecular switches

Tuning Ligand Effects and Probing the Inner-Workings of Bond Activation Steps: Generation of Ruthenium Complexes with Tailor-Made Properties

Activating chemical bonds through external triggers and understanding the underlying mechanism are at the heart of developing molecules with catalytic and switchable functions. Thermal, photochemical, and electrochemical bond activation pathways are useful for many chemical reactions. In this Article, a series of Ru^II complexes containing a bidentate and a tripodal ligand were synthesized. Starting from all-pyridine complex <b>1</b>²⁺, the pyridines were stepwise substituted with “click” triazoles (<b>2</b>²⁺–<b>7</b>²⁺). Whereas the thermo- and photoreactivity of <b>1</b>²⁺ are due to steric repulsion within the equatorial plane of the complex, <b>3</b>²⁺–<b>6</b>²⁺ are reactive because of triazoles in axial positions, and <b>4</b>²⁺ shows unprecedented photoreactivity. Complexes that feature neither steric interactions nor axial triazoles (<b>2</b>²⁺ and <b>7</b>²⁺) do not show any reactivity. Furthermore, a redox-triggered conversion mechanism was discovered in <b>1</b>²⁺, <b>3</b>²⁺, and <b>4</b>²⁺. We show here ligand design principles required to convert a completely inert molecule to a reactive one and vice versa, and provide mechanistic insights into their functioning. The results presented here will likely have consequences for developing a future generation of catalysts, sensors, and molecular switches