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Title: Reversible Redox-Induced Modulation of Sterics in an α-Diimine Ligand Coordinated to Gallium

Abstract

The ability to tune the steric envelope through redox events post-synthetically or in tandem with other chemical processes is a powerful tool that could assist in enabling new catalytic methodologies and understanding potential pitfalls in ligand design. The α-diimine ligand, dmp-BIAN, exhibits the peculiar and previously unreported feature of varying steric profiles depending on oxidation state when paired with a main group element. A study of the factors that give rise to this behaviour as well as its impact on the incorporation of other ligands is performed.

Authors:
 [1];  [1];  [2];  [3]
  1. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. San Francisco State Univ., CA (United States)
  3. Davidson College, Davidson, NC (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1429813
Report Number(s):
SAND-2017-7860J
655658
DOE Contract Number:
AC04-94AL85000
Resource Type:
Program Document
Country of Publication:
United States
Language:
English

Citation Formats

Zarkesh, Ryan A., Foster, Michael E., Ichimura, Andrew S., and Anstey, Mitchell R. Reversible Redox-Induced Modulation of Sterics in an α-Diimine Ligand Coordinated to Gallium. United States: N. p., 2017. Web.
Zarkesh, Ryan A., Foster, Michael E., Ichimura, Andrew S., & Anstey, Mitchell R. Reversible Redox-Induced Modulation of Sterics in an α-Diimine Ligand Coordinated to Gallium. United States.
Zarkesh, Ryan A., Foster, Michael E., Ichimura, Andrew S., and Anstey, Mitchell R. Sat . "Reversible Redox-Induced Modulation of Sterics in an α-Diimine Ligand Coordinated to Gallium". United States. doi:.
@article{osti_1429813,
title = {Reversible Redox-Induced Modulation of Sterics in an α-Diimine Ligand Coordinated to Gallium},
author = {Zarkesh, Ryan A. and Foster, Michael E. and Ichimura, Andrew S. and Anstey, Mitchell R.},
abstractNote = {The ability to tune the steric envelope through redox events post-synthetically or in tandem with other chemical processes is a powerful tool that could assist in enabling new catalytic methodologies and understanding potential pitfalls in ligand design. The α-diimine ligand, dmp-BIAN, exhibits the peculiar and previously unreported feature of varying steric profiles depending on oxidation state when paired with a main group element. A study of the factors that give rise to this behaviour as well as its impact on the incorporation of other ligands is performed.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sat Jul 01 00:00:00 EDT 2017},
month = {Sat Jul 01 00:00:00 EDT 2017}
}

Program Document:
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  • Advantage is taken of oxidation-state-dependent ligand (ammine)/solvent interactions to shift redox potentials and effect redox isomerization in the title complex. In poorly basic solvents, the stable isomeric form is trans-(py)(NH[sub 3])[sub 4]Ru[sup II](NCpy)Ru[sup III](bpy)[sub 2]Cl[sup 4+] (py is pyridine; NCpy is 4-cyanopyridine; bpy is 2,2[prime]-bipyridine). In contrast, in stronger Lewis bases or in a mixture of strong and weak bases (dimethyl sulfoxide + nitromethane), the preferred isomer is trans-(py)(NH[sub 3])[sub 4]Ru[sup III](NCpy)Ru[sup II](bpy)Cl[sup 4+]. Evidence for redox isomerization was obtained, in part, from plots of formal potentials versus solvent Lewis basicity. Confirmatory evidence was obtained from a combination of electrochemicalmore » reaction entropy and resonance Raman spectroscopic experiments. UV-vis-near-IR absorption experiments, however, were not found to be useful in demonstrating isomerization. In a released series of experiments, redox isomerization was also demonstrated based on ammine binding by either a low molecular weight poly(ethylene glycol) species or by a macrocyclic ligand, dibenzo-36-crown-12. Much smaller molar amounts of either the polymer (substoichiometric) or crown (approximately stoichiometic) are required, in comparison to basic solvent (several-fold excess), in order to induce isomerization in nitromethane as the initial solvent. The possible general utility of the redox isomerization concept in time-resolved intramolecular charge-transfer studies and in optical studies of competitive hole- and electron hole- and electron-transfer pathways is mentioned.« less
  • Actinide complexes of the redox-active ligand dpp-BIAN{sup 2-} (dpp-BIAN = bis(2,6-diisopropylphenyl)acenaphthylene), An(dpp-BIAN){sub 2}(THF){sub n} (An = Th, n = 1; An = U, n = 0, 1) have been prepared. Solid-state magnetic and single-crystal X-ray data for U(dpp-BIAN){sub 2}(THF){sub n} show when n = 0, the complex exists in an f{sup 2}-{pi}*{sup 4} configuration; whereas an intramolecular electron transfer occurs for n = 1, resulting in an f{sup 3}-{pi}*{sup 3} ground configuration. The magnetic data also indicate that interconversion between the two forms of the complex is possible, limited only by the ability of THF vapor to penetrate the solidmore » on cooling of the sample. Spectroscopic data indicate the complex exists solely in the f{sup 2}-{pi}*{sup 4} form in solution, evidenced by the appearance of only small changes in the electronic absorption spectra of the U(dpp-BIAN){sub 2} complex on titration with THF and by measurement of the solution magnetic moment m d{sub 8}-tetrahydrofuran using Evans method. Electrochemistry of the complexes is reported, with small differences observed in wave potentials between metals and in the presence of THF. These data represent the first example of a well-defined, reversible intramolecular electron transfer in an f-element complex and the second example of oxidation state change through dative interaction with a metal ion.« less
  • Adaptive responses associated with environmental stressors are critical to cell survival. These involve the modulation of central signaling protein functions through site-specific and enzymatically reversible oxidative modifications of methionines to coordinate cellular metabolism, energy utilization, and calcium signaling. Under conditions when cellular redox and antioxidant defenses are overwhelmed, the selective oxidation of critical methionines within selected protein sensors functions to down-regulate energy metabolism and the further generation of reactive oxygen species (ROS). Mechanistically, these functional changes within protein sensors take advantage of the helix-breaking character of methionine sulfoxide. Thus, depending on either the ecological niche of the organism or themore » cellular milieu of different organ systems, cellular metabolism can be fine-tuned to maintain optimal function in the face of variable amounts of collateral oxidative damage. The sensitivity of several calcium regulatory proteins to oxidative modification provides cellular sensors that link oxidative stress to cellular response and recovery. Calmodulin (CaM) is one such critical calcium regulatory protein, which is functionally sensitive to methionine oxidation. Helix destabilization resulting from the oxidation of either Met{sup 144} or Met{sup 145} results in the nonproductive association between CaM and target proteins. The ability of oxidized CaM to stabilize its target proteins in an inhibited state with an affinity similar to that of native (unoxidized) CaM permits this central regulatory protein to function as a cellular rheostat that down-regulates energy metabolism in response to oxidative stress. Likewise, oxidation of a methionine within a critical switch region of the regulatory protein phospholamban is expected to destabilize the phosphorylationdependent helix formation necessary for the release of enzyme inhibition, resulting in a down-regulation of the Ca-ATPase in response to {beta}-adrenergic signaling in the heart. The important role of the Ca-ATPase in determining the properties of the intracellular calcium transient in muscle highlights the potential role of phospholamban oxidation in cellular stress response. We suggest that under acute conditions, such as inflammation or ischemia, these types of mechanisms ensure minimal nonspecific cellular damage, allowing for rapid restoration of cellular function through repair of oxidized methionines by methionine sulfoxide reductase and degradation pathways after restoration of normal cellular redox conditions.« less
  • No abstract prepared.