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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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Zirconium Metal–Organic Frameworks Assembled from Pd and Pt P N N N P Pincer Complexes: Synthesis, Postsynthetic Modification, and Lewis Acid Catalysis
Abstract not provided
Tuning the Metabolic Stability of Visual Cycle Modulators through Modification of an RPE65 Recognition Motif
Not provided.
Novel Modes of Inhibition of Wild-Type Isocitrate Dehydrogenase 1 (IDH1): Direct Covalent Modification of His315
IDH1 plays a critical role in a number of metabolic processes and serves as a key source of cytosolic NADPH under conditions of cellular stress. However, few inhibitors of wild-type IDH1 have been reported. Furthermore we present the discovery and biochemical characterization of two novel inhibitors of wild-type IDH1. In addition, we present the first ligand-bound crystallographic characterization of these novel small molecule IDH1 binding pockets. Importantly, the NADPH competitive α,β-unsaturated enone 1 makes a unique covalent linkage through active site H315. As few small molecules have been shown to covalently react with histidine residues, these data support the potential utility of an underutilized strategy for reversible covalent small molecule design.
Can Excited State Electronic Coherence Be Tuned via Molecular Structural Modification? A First-Principles Quantum Electronic Dynamics Study of Pyrazolate-Bridged Pt(II) Dimers
Materials and molecular systems exhibiting long-lived electronic coherence can facilitate coherent transport, opening the door to efficient charge and energy transport beyond traditional methods. Recently, signatures of a possible coherent, recurrent electronic motion were identified in femtosecond pump-probe spectroscopy experiments on a binuclear platinum complex, where a persistent periodic beating in the transient absorption signal’s anisotropy was observed. In this study, we investigate the excitonic dynamics that underlie the suspected electronic coherence for a series of binuclear platinum complexes exhibiting a range of interplatinum distances. Results suggest that the long-lived coherence can only result when competitive electronic couplings are in balance. At longer Pt-Pt distances, the electronic couplings between the two halves of the binuclear system weaken, and exciton localization and recombination is favored on short time scales. For short Pt-Pt distances, electronic couplings between the states in the coherent superposition are stronger than the coupling with other excitonic states, leading to long-lived coherence.
Modification of a Carbon Nanobelt with Actinides Th–Am: A Density Functional Theory Study
Not provided.
Electronic Structure Modification of Rectangular Phosphorene Quantum Dots Via Edge Passivation
Phosphorene is an elemental two-dimensional material that shows great promise as a metal-free photocatalyst owing to its high carrier mobility and direct band gap. Doping and edge functionalization of phosphorene can be exploited to tune its band gap and alter other properties. Herein, the electronic properties of a series of edge-passivated monolayer phosphorene quantum dots are investigated using an array of functional groups (OH, SH, NH 2 , SCH 3 , OCN, CN, and Cl) that are known to have electron-donating or electron-withdrawing capabilities. By employing density functional theory calculations, we demonstrate that edge functionalization can perturbatively shift the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energy levels while simultaneously preserving the geometric structure and other favorable properties of pristine phosphorene. We use the average overall electrostatic potential of these systems to successfully predict the relative positioning of the HOMO and LUMO energy levels while presenting qualitative explanations on potential jumps introduced by the dipole layers formed due to edge functionalization. Furthermore, our results suggest that selective functionalization permits considerable control over the band edge positions, which could be utilized for applications in energy and optoelectronic devices.
Electrical and magnetic properties modification in heavy ion irradiated nanograin NixCo(3-x)O4 films
Reactively sputtered NixCo(3-x)O4 films (x = 1.5, 1.0, and 0.75) were grown and subsequently irradiated with 5.5 MeV Si+ ions to investigate effects of lattice-site and charge state distribution. Films were characterized before and after irradiation by x-ray diffraction, x-ray photoemission spectroscopy, Rutherford backscattering spectroscopy, electric resistivity measurements, and temperature-dependent AC and DC magnetometry. Results indicate that ion irradiation induces oxygen loss, partial reduction of nickel, and an increase in both low temperature ferrimagnetism and room temperature conductivity. Frequency dependent AC magnetic susceptibility measurements indicate a spin-glass like transition at low temperature which moves to higher temperature after irradiation. Significance of the charge transfer for magnetism and conduction in a mixed spinel with Co2+, Co3+, Ni2+, and Ni3+ in tetrahedral and octahedral sites is discussed.
Strain-Mediated Modification of Phagraphene Dirac Cones
We present a first-principles study on the electronic and dynamical properties of phagraphene [Nano Lett., 2015, 15 (9), pp 6182]. This carbon allotrope exhibits a square unit cell, Dirac cones, and robustness against uniaxial deformation. By analyzing the contribution of each carbon atom orbital in the formation of the electronic states, we conclude that only the pz orbitals of eight out of the twenty atoms in the square unit cell are responsible of the formation of the nano-structure Dirac cones. Spatial symmetry breaking of the underlying honeycomb-like network upon shear stress application leads to a band gap opening. The analysis of the phonon spectra demonstrates that the dynamical stability of phagraphene is guaranteed for small distortion angles. Phagraphene is identified here as the first all-C graphitic monolayer with Dirac cones modifiable by a small and realistic physical deformation. The analysis and conclusions of this study can be applied to other monolayered materials exhibiting Dirac cones in square lattices.
Proposed modification of the graphene analogue Ni3(HITP)2 to yield a semiconducting material.
Abstract not provided.
Surface Modification of Indium–Tin Oxide with Functionalized Perylene Diimides: Characterization of Orientation, Electron-Transfer Kinetics and Electronic Structure
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Metal Chelating Polymer Thin Films by Surface-Initiated ROMP and Modification
Not provided.
Luminescent InP Quantum Dots with Tunable Emission by Post-Synthetic Modification with Lewis Acids
Abstract not provided
Response to Extreme Temperatures of Mesoporous Silica MCM-41: Porous Structure Transformation Simulation and Modification of Gas Adsorption Properties
In this paper, molecular dynamics (MD) and Monte Carlo (MC) simulations were applied together for the first time to reveal the porous structure transformation mechanisms of mesoporous silica MCM-41 subjected to temperatures up to 2885 K. Silica was experimentally characterized to inform the models and enable prediction of changes in gas adsorption/separation properties. MD simulations suggest that the pore closure process is activated by a collective diffusion of matrix atoms into the porous region, accompanied by bond reformation at the surface. Degradation is kinetically limited, such that complete pore closure is postponed at high heating rates. We experimentally observe decreased gas adsorption with increasing temperature in mesoporous silica heated at fixed rates, due to pore closure and structural degradation consistent with simulation predictions. Applying the Kissinger equation, we find a strong correlation between the simulated pore collapse temperatures and the experimental values which implies an activation energy of 416 ± 17 kJ/mol for pore closure. MC simulations give the adsorption and selectivity for thermally treated MCM-41, for N 2 , Ar, Kr, and Xe at room temperature within the 1–10 000 kPa pressure range. Relative to pristine MCM-41, we observe that increased surface roughness due to decreasing pore size amplifies the difference of the absolute adsorption amount differently for different adsorbate molecules. In particular, we find that adsorption of strongly interacting molecules can be enhanced in the low-pressure region while adsorption of weakly interacting molecules is inhibited. Finally, this then results in higher selectivity in binary mixture adsorption in mesoporous silica.
Longitudinally Controlled Modification of Cylindrical and Conical Track-Etched Poly(ethylene terephthalate) Pores Using an Electrochemically Assisted Click Reaction
Not Available
Proof of Tacticity of Stereoregular ROMP Polymers through Post Polymerization Modification
Partial bromination or epoxidation has been used to confirm the tacticities of several stereoregular polymers made through ROMP methods with well-defined Mo or W initiators. Tacticities were proven for cis,isotactic and cis,syndiotactic poly(norbornene), poly(3-methyl-3-phenylcyclopropene), and poly( endo,anti -tetracyclododecene). Various limitations can stop application of these proofs in general to stereoregular polymers prepared through ROMP.
High Dielectric Constant Semiconducting Poly(3-alkylthiophene)s from Side Chain Modification with Polar Sulfinyl and Sulfonyl Groups
In this paper, there is growing interest in designing and developing high dielectric constant (ε r ) organic semiconductors because they have the potential to further enhance device performance by promoting exciton dissociation, reducing bimolecular charge carrier recombination, and potentially enhancing charge carrier mobility via charge screening. In this study, a new class of semiconducting polymers with high ε r , i.e., sulfinylated and sulfonylated poly(3-alkylthiophene)s (P3ATs), were synthesized. Because of efficient rotation of highly polar methylsulfinyl and methylsulfonyl side groups (i.e., orientational polarization), high ε r values were achieved for these functionalized P3ATs based on an accurate capacitance measurement using a gold/semiconducting polymer/SiO 2 /n-doped Si configuration. For example, the ε r at megahertz and room temperature increased from 3.75 for the regioregular poly(3-hexylthiophene) (P3HT) to 7.4 for the sulfinylated and 8.1–9.3 for sulfonylated P3AT polymers. These values are among the highest ε r reported for conjugated polymers so far. Grazing-incident wide-angle X-ray diffraction results showed that these polar groups decreased the crystallinity for the polythiophene backbones and interfered with the π–π stacking in the crystalline structure. Consequently, their optical properties, including UV–vis absorption and fluorescence, changed in thin films. From this study, the sulfinylated polymer may be promising to provide a balance between high ε r and preserving favorable polythiophene π–π stacking structure for device applications.