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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,657 records · Page 92
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DOE OSTI2019

Excited-State Dynamics of a CsPbBr 3 Nanocrystal Terminated with Binary Ligands: Sparse Density of States with Giant Spin–Orbit Coupling Suppresses Carrier Cooling

Fully inorganic lead halide perovskite nanocrystals (NCs) are of interest for photovoltaic and light-emitting devices due to optoelectronic properties that can be tuned/optimized via halide composition, surface passivation, doping, and confinement. Compared to bulk materials, certain excited-state properties in NCs can be adjusted by electronic confinement effects such as suppressed hot carrier cooling and enhanced radiative recombination. In this paper, we use spinor Kohn–Sham orbitals (SKSOs) with spin–orbit coupling (SOC) interaction as a basis to compute excited-state dissipative dynamics simulations on a fully passivated CsPbBr 3 NC atomistic model. Redfield theory in the density matrix formalism is used to describe electron–phonon interactions which drive hot carrier cooling and nonradiative recombination ( k nonrad ). Radiative recombination ( k rad ) is calculated through oscillator strengths using SKSO basis. From k rad and k rad + k nonrad , we compute a theoretical photoluminescence quantum yield (PLQY) of 53%. Computed rates of hot carrier cooling ( k cooling ≈ 10 –1 1/ps) compare favorably with what has been reported in the literature. Interestingly, we observe that hot electron cooling slows down near the band edge, which we attribute to large SOC in the conduction band combined with strong confinement, which creates subgaps above the band edge. This slow carrier cooling could potentially impact hot carrier extraction before complete thermalization in photovoltaics (PVs). Implications of this work suggest that strong/intermediate confined APbX 3 NCs are better suited to applications in PVs due to slower carrier cooling near the conduction band edge, while intermediate/weak confined NCs are more appropriate for light-emitting applications, such as LEDs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Isolation and Study of Ruthenium–Cobalt Oxo Cubanes Bearing a High-Valent, Terminal Ru V –Oxo with Significant Oxyl Radical Character

High-valent Ru V -oxo intermediates have long been proposed in catalytic oxidation chemistry, but investigations into their electronic and chemical properties have been limited due to their reactive nature and rarity. The incorporation of Ru into the [Co 3 O 4 ] subcluster via the single-step assembly reaction of Co II (OAc) 2 (H 2 O) 4 (OAc = acetate), perruthenate (RuO 4 - ), and pyridine (py) yielded an unprecedented Ru(O)Co 3 (μ 3 -O) 4 (OAc) 4 (py) 3 cubane featuring an isolable, yet reactive, RuV-oxo moiety. EPR, ENDOR, and DFT studies reveal a valence-localized [Ru V (S = 1/2)Co III 3(S = 0)O 4 ] configuration and non-negligible covalency in the cubane core. Significant oxyl radical character in the Ru V -oxo unit is experimentally demonstrated by radical coupling reactions between the oxo cubane and both 2,4,6-tri-tert-butylphenoxyl and trityl radicals. The oxo cubane oxidizes organic substrates and, notably, reacts with water to form an isolable μ-oxo bis-cubane complex [(py) 3 (OAc) 4 Co 3 (μ 3 -O) 4 Ru]-O-[RuCo 3 (μ 3 -O) 4 (OAc) 4 (py) 3 ]. Redox activity of the Ru V -oxo fragment is easily tuned by the electron-donating ability of the distal pyridyl ligand set at the Co sites demonstrating strong electronic communication throughout the entire cubane cluster. Natural bond orbital calculations reveal cooperative orbital interactions of the [Co 3 O 4 ] unit in supporting the Ru V -oxo moiety via a strong π-electron donation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Discovery and Mechanistic Studies of Facile N-Terminal Cα–C Bond Cleavages in the Dissociation of Tyrosine-Containing Peptide Radical Cations

Gas phase fragmentations of protein and peptide (M) ions in a mass spectrometer—induced by, for example, electron-capture dissociation1-2 and electron-transfer dissociation3-422 —form the foundation for top-down amino acid sequencing approaches for the rapid identification of protein components in complex biological samples. During these processes, protonated protein and peptide radicals ([M + nH]•(n – 1)+)5–8 are generated; their fragmentations are governed largely by the properties of the unpaired electron. Because of their importance in modern bioanalytical chemistry, considerable attention has been drawn recently toward understanding the radical cation chemistry behind the fragmentations of these odd-electron biomolecular ions in the gas phase.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2024

Allosteric control of dynamin-related protein 1 through a disordered C-terminal Short Linear Motif

Abstract The mechanochemical GTPase dynamin-related protein 1 (Drp1) catalyzes mitochondrial and peroxisomal fission, but the regulatory mechanisms remain ambiguous. Here we find that a conserved, intrinsically disordered, six-residue Short Linear Motif at the extreme Drp1 C-terminus, named CT-SLiM, constitutes a critical allosteric site that controls Drp1 structure and function in vitro and in vivo. Extension of the CT-SLiM by non-native residues, or its interaction with the protein partner GIPC-1, constrains Drp1 subunit conformational dynamics, alters self-assembly properties, and limits cooperative GTP hydrolysis, surprisingly leading to the fission of model membranes in vitro. In vivo, the involvement of the native CT-SLiM is critical for productive mitochondrial and peroxisomal fission, as both deletion and non-native extension of the CT-SLiM severely impair their progression. Thus, contrary to prevailing models, Drp1-catalyzed membrane fission relies on allosteric communication mediated by the CT-SLiM, deceleration of GTPase activity, and coupled changes in subunit architecture and assembly-disassembly dynamics.

Science & Technology - Other Topics↗