The solution properties of Mn-hydroxo and Mn-methoxy complexes featuring N amide-containing ligands were investigated using H NMR spectroscopy. TheH NMR spectrum for one of these complexes, the previously reported [Mn(OH)(dpaq)](OTf) (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino- N-quinolin-8-yl-acetamidate) shows hyperfine-shifted signals, as expected for this S = 2 Mn-hydroxo adduct. However, the H NMR spectrum of [Mn(OH)(dpaq)](OTf) also shows a large number of proton resonances in the diamagnetic region, suggesting the presence of multiple species in CDCN solution. The majority of the signals in the diamagnetic region disappear when a small amount of water is added to a CHCN solution of [Mn(OH)(dpaq)](OTf). Electronic absorption and Mn K-edge X-ray absorption experiments support the formulation of this diamagnetic species as the μ-oxodimanganese(III,III) complex [Mn(μ-O)(dpaq))]. On the basis of these observations, we propose that the dissolution of [Mn(OH)(dpaq)](OTf) in CDCN results in the formation of mononuclear Mn-hydroxo and dinuclear μ-oxodimanganese(III,III) species that are in equilibrium. The addition of a small amount of water is sufficient to shift this equilibrium in favor of the Mn-hydroxo adduct. Surprisingly, electronic absorption experiments show that the conversion of [Mn(μ-O)(dpaq))] to [Mn(OH)(dpaq)] by added water is relatively slow. Because this dimer to monomer conversion is slower than TEMPOH oxidation by [Mn(OH)(dpaq)], the previously observed TEMPOH oxidation rates for [Mn(OH)(dpaq)] reflected both processes. Here, we report the bona fide TEMPOH oxidation rate for [Mn(OH)(dpaq)], which is significantly faster than previously reported. H NMR spectra are also reported for the related [Mn(OMe)(dpaq)] and [Mn(OH)(dpaq)] complexes. These spectra only show hyperfine-shifted signals, suggesting the presence of only mononuclear Mn-methoxy and Mn-hydroxo species in solution. Measurements of T relaxation times and proton peak integrations for [Mn(OMe)(dpaq)] provide preliminary assignments for H NMR resonances.
A series of manganese(II) and oxomanganese(IV) complexes supported by neutral, pentadentate ligands with varied equatorial ligand-field strength (N3pyQ, N2py2I, and N4pyMe2) were synthesized and then characterized using structural and spectroscopic methods. On the basis of electronic absorption spectroscopy, the [MnIV(O)(N4pyMe2)]2+ complex has the weakest equatorial ligand field among a set of similar MnIV-oxo species. In contrast, [MnIV(O)(N2py2I)]2+ shows the strongest equatorial ligand-field strength for this same series. We examined the influence of these changes in electronic structure on the reactivity of the oxomanganese(IV) complexes using hydrocarbons and thioanisole as substrates. The [MnIV(O)(N3pyQ)]2+ complex, which contains one quinoline and three pyridine donors in the equatorial plane, ranks among the fastest MnIV-oxo complexes in C–H bond and thioanisole oxidation. While a weak equatorial ligand field has been associated with high reactivity, the [MnIV(O)(N4pyMe2)]2+ complex is only a modest oxidant. Buried volume plots suggest that steric factors dampen the reactivity of this complex. Trends in reactivity were examined using density functional theory (DFT)-computed bond dissociation free energies (BDFEs) of the MnIIIO–H and MnIV O bonds. We observe an excellent correlation between MnIVO BDFEs and rates of thioanisole oxidation, but more scatter is observed between hydrocarbon oxidation rates and the MnIIIO–H BDFEs.
During the COVID-19 pandemic, members of the African American Medical Librarians Alliance (AAMLA) Caucus of the Medical Library Association formed a weekly virtual forum known as the “Chat & Chew.” The purpose of these weekly check-ins was to build community and provide support amidst a series of unprecedented health crises adversely affecting Black Americans, including the coronavirus pandemic and the long-standing issue of police killings and brutality. In coming together for these weekly check-ins, group participants benefited by actively practicing self-care and exchanging ideas and information with colleagues across the country. Each gathering incorporated various presentations and discussions, including topics related to self-care and wellness, microaggressions and stigmatization in the workplace, virtual technologies, plant care, book discussions, and opportunities to engage in diversity, equity, and inclusion work. This chapter provides successes for member engagement and best practices that made the program sustainable throughout 2020 and beyond.
When I think of Beverly Murphy, AHIP, FMLA, three words come to mind: Bold, Brave, Brilliant. In every action that Beverly has undertaken as a health sciences librarian, she has demonstrated an innate ability to just “Be.” Being bold, brave, and brilliant is just what she will need to be as the Medical Library Association’s first African-American president since the association’s founding in 1898.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.