More Like this

1. Temperature-Dependent Spin-Driven Dimerization Determines the Ultrafast Dynamics of a Copper(II)-Bound Tripyrrindione Radical

   https://doi.org/10.1021/acs.jpclett.3c02726  

   Kumar, Anshu; Thompson, Benjamin; Gautam, Ritika; Tomat, Elisa; Huxter, Vanessa (December 2023, The Journal of Physical Chemistry Letters)

   Radicals and other open-shell molecules play a central role in chemical transformations and redox chemistry. While radicals are often highly reactive, stable radical systems are desirable for a range of potential applications, ranging from materials chemistry and catalysis to spintronics and quantum information. Here we investigate the ultrafast properties of a stable radical system with temperature-dependent spin-tunable properties. This radical complex, Cu(II) hexaethyl tripyrrin-1,14-dione, accommodates unpaired electrons localized on both the copper metal center and the tripyrrolic ligand. The unusual combination of two unpaired electrons and high stability in this radical molecule enable switchable temperature-dependent spin coupling. Two-dimensional electronic spectroscopy measurements of Cu(II) hexaethyl tripyrrin-1,14-dione were collected at room temperature and at 77 K. At room temperature, the molecules are present as monomers and have short picosecond lifetimes. At 77 K, the molecules are present in a dimer form mediated by ferromagnetic and antiferromagnetic coupling. This reversible spin-driven dimerization changes the optical properties of the system, generating long-lived excitonic states. 

   more » « less
2. Multicenter interactions and ligand field effects in platinum( ii ) tripyrrindione radicals

   https://doi.org/10.1039/D3DT00894K  

   Tomat, Elisa; Curtis, Clayton J.; Astashkin, Andrei V.; Conradie, Jeanet; Ghosh, Abhik (May 2023, Dalton Transactions)

   The tripyrrin-1,14-dione biopyrrin, which shares the scaffold of several naturally occurring heme metabolites, is a redox-active platform for metal coordination. We report the synthesis of square planar platinum( ii ) tripyrrindiones, in which the biopyrrin binds as a tridentate radical and the fourth coordination position is occupied by either aqua or tert -butyl isocyanide ligands. These complexes are stable through chromatographic purification and exposure to air. Electron paramagnetic resonance (EPR) data and density functional theory (DFT) analysis confirm that the spin density is located predominantly on the tripyrrindione ligand. Pancake bonding in solution between the Pt( ii ) tripyrrindione radicals leads to the formation of diamagnetic π dimers at low temperatures. The identity of the monodentate ligand ( i.e. , aqua vs . isocyanide) affects both the thermodynamic parameters of dimerization and the tripyrrindione-based redox processes in these complexes. Isolation and structural characterization of the oxidized complexes revealed stacking of the diamagnetic tripyrrindiones in the solid state as well as a metallophilic Pt( ii )−Pt( ii ) contact in the case of the aqua complex. Overall, the properties of Pt( ii ) tripyrrindiones, including redox potentials and intermolecular interactions in solution and in the solid state, are modulated through easily accessible changes in the redox state of the biopyrrin ligand or the nature of the monodentate ligand. 

   more » « less
3. Gold Tripyrrindione: Redox Chemistry and Reactivity with Dichloromethane

   https://doi.org/10.1021/acs.inorgchem.4c02903  

   Curtis, Clayton J; Habenšus, Iva; Conradie, Jeanet; Bardin, Andrey A; Nannenga, Brent L; Ghosh, Abhik; Tomat, Elisa (September 2024, Inorganic Chemistry)

   The identification of ligands that stabilize Au(III) centers has led to the isolation of complexes for applications in catalysis, gold-based therapeutics, and functional materials. Herein, we report the coordination of gold by tripyrrin-1,14-dione, a linear tripyrrole with the scaffold of naturally occurring metabolites of porphyrin-based protein cofactors (e.g., heme). Tripyrrindione H3TD2 binds Au(III) as a trianionic tridentate ligand to form square planar complex [Au(TD2)(H2O)], which features an adventitious aqua ligand. Two reversible ligand-based oxidations of this complex allow access to the other known redox states of the tripyrrindione framework. Conversely, (spectro)electrochemical measurements and DFT analysis indicate that the reduction of the complex is likely metal-based. The chemical reduction of [Au(TD2)(H2O)] leads to a reactive species that utilizes dichloromethane in the formation of a cyclometalated organo-Au(III) complex. Both the aqua and the organometallic Au(III) complexes were characterized in the solid state by microcrystal electron diffraction (MicroED) methods, which were critical for the analysis of the microcrystalline sample of the organo-gold species. Overall, this study illustrates the synthesis of Au(III) tripyrrindione as well as its redox profile and reactivity leading to gold alkylation chemistry. 

   more » « less
4. Primary amines as ligands and linkers in complexes of tripyrrindione radicals

   https://doi.org/10.1142/S1088424623501109  

   Habenšus, Iva; Ghavam, Ameen; Curtis, Clayton J.; Astashkin, Andrei V.; Tomat, Elisa (July 2023, Journal of Porphyrins and Phthalocyanines)

   Biopyrrin pigments, which result from the degradation of heme in biological settings, feature three or two pyrrole rings and characteristic pyrrolin-2-one termini. These scaffolds serve as redox-active ligands and electron reservoirs in coordination compounds. Tripyrrin-1,14-dione coordinates divalent transition metals as a dianionic ligand hosting a delocalized radical. Herein, we report the synthesis and characterization of palladium(II) and platinum(II) tripyrrindione complexes featuring a primary amine (i.e., aniline, tert-butylamine, 1,2-ethylenediamine) at the fourth coordination site within square planar geometries. Interligand hydrogen-bonding interactions are observed between the coordinated amine and the carbonyl groups on the tripyrrindione scaffold. Notably, 1,2-ethylenediamine is employed to link two Pt(II) tripyrrindione complexes. As revealed by optical absorption and electron paramagnetic resonance (EPR) spectroscopy, all resulting complexes present ligand-based radicals that are stable at room temperature and when exposed to air. Spin pairing through multicenter interactions leads to [Formula: see text]-dimerization of the tripyrrindione radicals and a decrease in the EPR signal at low temperatures. Electrochemical measurements indicate that the ligand system undergoes quasi-reversible one-electron oxidation and reduction, thus confirming the ability of tripyrrindione to form square planar complexes in three different redox states. 

   more » « less
5. Somatosensory changes associated with motor skill learning

   https://doi.org/10.1152/jn.00497.2019  

   Mirdamadi, Jasmine Lauren; Block, Hannah J (January 2020, Journal of Neurophysiology)

   Trial-and-error motor adaptation has been linked to somatosensory plasticity and shifts in proprioception (limb position sense). The role of sensory processing in motor skill learning is less understood. Unlike adaptation, skill learning involves the acquisition of new movement patterns in the absence of perturbation, with performance limited by the speed-accuracy tradeoff. We investigated somatosensory changes during motor skill learning at the behavioral and neurophysiological level. Twenty-eight healthy young adults practiced a maze-tracing task, guiding a robotic manipulandum through an irregular 2D track featuring several abrupt turns. Practice occurred on days 1 and 2. Skill was assessed before practice on day 1 and again on day 3, with learning indicated by a shift in the speed-accuracy function between these assessments. Proprioceptive function was quantified with a passive two-alternative forced choice task. In a subset of 15 participants, we measured short latency afferent inhibition (SAI) to index somatosensory projections to motor cortex. We found that motor practice enhanced the speed-accuracy skill function (F 4,108 = 32.15, p < 0.001) and was associated with improved proprioceptive sensitivity at retention (t 22 = 24.75, p = 0.0031). Further, SAI increased after training (F 1,14 = 5.41, p = 0.036). Interestingly, individuals with larger increases in SAI, reflecting enhanced somatosensory afference to motor cortex, demonstrated larger improvements in motor skill learning. These findings suggest that SAI may be an important functional mechanism for some aspect of motor skill learning. Further research is needed to test what parameters (task complexity, practice time, etc) are specifically linked to somatosensory function. 

   more » « less