Tuning Electronic Structure To Control Manganese Nitride Activation

Investigation of a series of oxidized nitridomanganese(V) salen complexes with different para ring substituents (R = CF3, tBu, and NMe2) demonstrates that nitride activation is dictated by remote ligand electronics. For R = CF3 and tBu, oxidation affords a Mn(VI) species and nitride activation, with dinitrogen homocoupling accelerated by the more electron-withdrawing CF3 substituent. Employing an electron-donating substituent (R = NMe2) results in a localized ligand radical species that is resistant to N coupling of the nitrides and is stable in solution at both 195 and 298 K

Electronic Structure Description of a Doubly Oxidized Bimetallic Cobalt Complex with Pro-Radical Ligands

The geometric and electronic structure of a doubly oxidized bimetallic Co complex containing two redox-active salen moieties connected via a 1,2-phenylene linker has been investigated and compared to an oxidized monomeric analogue. Both complexes, CoL1 and Co2L2 are oxidized to the mono- and di-cations respectively with AgSbF6 and characterized by X-ray crystallography for the monomer, and Vis-NIR spectroscopy, electron paramagnetic (EPR) spectroscopy, SQUID magnetometry and density functional theory (DFT) calculations for both the monomer and dimer. Both complexes exhibit a water molecule coordinated in the apical position upon oxidation. [CoL1-H2O]+ displays a broad NIR band at 8500 cm-1 (8400 M-1cm-1) which is consistent with recent reports on oxidized Co salen complexes (Kochem, A. et. al., Inorg Chem., 2012, 51, 10557-10571, Kurahashi, T. et. al., Inorg. Chem., 2013, 52, 3908-3919). DFT calculations predict a triplet ground state with significant ligand and metal contributions to the singularly occupied molecular orbital (SOMO). The majority (~75%) of the total spin density is localized on the metal, highlighting both high spin Co(III) and Co(II)L• character in the electronic ground state. Further oxidation of CoL1 to the dication affords a low spin Co(III) phenoxyl radical species. The NIR features for [Co2L2-2H2O]2+ at 8600 cm-1 (17800 M-1cm-1) are doubly intense in comparison to [CoL1-H2O]+ owing to the description of [Co2L2-2H2O]2+ as two non-interacting oxidized Co salen complexes bound via the central phenylene linker. Interestingly, TD-DFT calculations predict two electronic transitions that are 353 cm-1 apart. The NIR spectrum of the analogous Ni complex, [Ni2L2]2+, exhibits two intense transitions (4890 cm-1/26500 M-1cm-1 and 4200 cm-1/21200 M-1cm-1) due to exciton coupling in the excited state. Only one broad band is observed in the NIR spectrum for [Co2L2-2H2O]2+ as a result of the contracted donor and acceptor orbitals and overall CT character

STIS spectroscopy of the emission line gas in the nuclei of nearby FR-I galaxies

We present the results of the analysis of a set of medium resolution spectra, obtained by the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, of the emission line gas present in the nuclei of a complete sample of 21 nearby, early-type galaxies with radio jets (the UGC FR-I Sample). For each galaxy nucleus we present spectroscopic data in the region of H-alpha and the dervived kinematics. We find that in 67% of the nuclei the gas appears to be rotating and, with one exception, the cases where rotation is not seen are either face on or have complex central morphologies. We find that in 62% of the nuclei the fit to the central spectrum is improved by the inclusion of a broad component. The broad components have a mean velocity dispersion of 1349 +/- 345 km\s and are redshifted from the narrow line components (assuming an origin in H-alpha) by 486 +/- 443 km\s.Comment: 119 pages, 26 figures, ApJS Accepted, version with full figures available at http://www.astro.columbia.edu/~jake/pub/fr1datapaper.pd

Disentangling the 1MLCT transition of [Ru(bpy)3]2+ by Stark absorption spectroscopy

金沢大学理工研究域物質化学系The metal-to-ligand charge transfer (MLCT) transition of [Ru(bpy)3]2+ was investigated using Stark absorption spectroscopy, where bpy is the abbreviation of 2,2\u27-bipyridyl ligand. The magnitude and direction of the photoinduced intramolecular charge transfer were precisely determined for the 1MLCT transition of [Ru(bpy)3]2+. The 1MLCT absorption band of [Ru(bpy)3]2+, observed in the 18,000-30,000cm-1 spectral region, is composed of several sub-bands that can be approximated with Gaussian profiles. In particular, three distinct major 1MLCT bands of [Ru(bpy)3]2+ (g4, 21272cm-1; g5, 22026cm-1; g7, 23448cm-1) could be distinguished by the direction of the charge transfer of each transition. The experimentally determined directions of charge transfer showed good agreement with the theoretical prediction by Kober and Meyer. We also re-examined the phosphorescence and the excitation spectra of [Ru(bpy)3]2+. The 1MLCT excited states of the g5 and g7 bands almost completely transform to 3MLCT excited states, and then 40% of the 3MLCT state relaxes to the ground state by emitting phosphorescence. 46% of 1MLCT excited state of the g4 band non-radiatively relaxes to the ground state. These results provide good support for the assignment of the different origins of the g4 and other two Gaussian sub-bands (g5 and g7). © 2017 Elsevier B.V.in Press / Embargo Period 12 month

8-Hydroxyquinoline Schiff-base Compounds as Antioxidants and Modulators of Copper-Mediated Aβ Peptide Aggregation

One of the hallmarks of Alzheimer\u27s disease (AD) in the brain are amyloid-β (Aβ) plaques, and metal ions such as copper(II) and zinc(II) have been shown to play a role in the aggregation and toxicity of the Aβ peptide, the major constituent of these extracellular aggregates. Metal binding agents can promote the disaggregation of Aβ plaques, and have shown promise as AD therapeutics. Herein, we describe the syntheses and characterization of an acetohydrazone (8-H2QH), a thiosemicarbazone (8-H2QT), and a semicarbazone (8-H2QS) derived from 8-hydroxyquinoline. The three compounds are shown to be neutral at pH 7.4, and are potent antioxidants as measured by a Trolox Equivalent Antioxidant Capacity (TEAC) assay. The ligands form complexes with CuII, 8-H2QT in a 1:1 metal:ligand ratio, and 8-H2QH and 8-H2QS in a 1:2 metal:ligand ratio. A preliminary aggregation inhibition assay using the Aβ1–40 peptide showed that 8-H2QS and 8-H2QH inhibit peptide aggregation in the presence of CuII. Native gel electrophoresis/Western blot and TEM images were obtained to give a more detailed picture of the extent and pathways of Aβ aggregation using the more neurotoxic Aβ1 −42 in the presence and absence of CuII, 8-H2QH, 8-H2QS and the drug candidate PBT2. An increase in the formation of oligomeric species is evident in the presence of CuII. However, in the presence of ligands and CuII, the results match those for the peptide alone, suggesting that the ligands function by sequestering CuII and limiting oligomer formation in this assay

Synthesis and Electronic Structure Determination of Uranium(VI) Ligand Radical Complexes

   Pentagonal bipyramidal uranyl complexes of salen ligands, N,N’-bis(3-tert-butyl-(5R)-salicylidene)-1,2-phenylenediamine, in which R = tBu (1a), OMe (1b), and NMe2 (1c), were prepared and the electronic structure of the one-electron oxidized species [1a-c]+ were investigated in solution. The solid-state structures of 1a and 1b were solved by X-ray crystallography, and in the case of 1b an asymmetric UO22+ unit was found due to an intermolecular hydrogen bonding interaction. Electrochemical investigation of 1a-c by cyclic voltammetry showed that each complex exhibited at least one quasi-reversible redox process assigned to the oxidation of the phenolate moieties to phenoxyl radicals. The trend in redox potentials matches the electron-donating ability of the para-phenolate substituents. The electron paramagnetic resonance spectra of cations [1a-c]+ exhibited gav values of 1.997, 1.999, and 1.995, respectively, reflecting the ligand radical character of the oxidized forms, and in addition, spin-orbit coupling to the uranium centre. Chemical oxidation as monitored by ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy afforded the one-electron oxidized species. Weak low energy intra-ligand charge transfer (CT) transitions were observed for [1a-c]+ indicating localization of the ligand radical to form a phenolate / phenoxyl radical species. Further analysis using density functional theory (DFT) calculations predicted a localized phenoxyl radical for [1a-c]+ with a small but significant contribution of the phenylenediamine unit to the spin density. Time-dependent DFT (TD-DFT) calculations provided further insight into the nature of the low energy transitions, predicting both phenolate to phenoxyl intervalence charge transfer (IVCT) and phenylenediamine to phenoxyl CT character. Overall, [1a-c]+ are determined to be relatively localized ligand radical complexes, in which localization is enhanced as the electron donating ability of the para-phenolate substituents is increased (NMe2 > OMe > tBu)

Controlled Radical Polymerization of Vinyl Acetate Mediated by a Bis(imino)pyridine Vanadium Complex

Source type: Prin

Significant benefits of AIP testing and clinical screening in familial isolated and young-onset pituitary tumors

Context Germline mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene are responsible for a subset of familial isolated pituitary adenoma (FIPA) cases and sporadic pituitary neuroendocrine tumors (PitNETs). Objective To compare prospectively diagnosed AIP mutation-positive (AIPmut) PitNET patients with clinically presenting patients and to compare the clinical characteristics of AIPmut and AIPneg PitNET patients. Design 12-year prospective, observational study. Participants & Setting We studied probands and family members of FIPA kindreds and sporadic patients with disease onset ≤18 years or macroadenomas with onset ≤30 years (n = 1477). This was a collaborative study conducted at referral centers for pituitary diseases. Interventions & Outcome AIP testing and clinical screening for pituitary disease. Comparison of characteristics of prospectively diagnosed (n = 22) vs clinically presenting AIPmut PitNET patients (n = 145), and AIPmut (n = 167) vs AIPneg PitNET patients (n = 1310). Results Prospectively diagnosed AIPmut PitNET patients had smaller lesions with less suprasellar extension or cavernous sinus invasion and required fewer treatments with fewer operations and no radiotherapy compared with clinically presenting cases; there were fewer cases with active disease and hypopituitarism at last follow-up. When comparing AIPmut and AIPneg cases, AIPmut patients were more often males, younger, more often had GH excess, pituitary apoplexy, suprasellar extension, and more patients required multimodal therapy, including radiotherapy. AIPmut patients (n = 136) with GH excess were taller than AIPneg counterparts (n = 650). Conclusions Prospectively diagnosed AIPmut patients show better outcomes than clinically presenting cases, demonstrating the benefits of genetic and clinical screening. AIP-related pituitary disease has a wide spectrum ranging from aggressively growing lesions to stable or indolent disease course