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Structure of Hydrated Gibbsite and Brucite Edge Surfaces: DFT Results and Further Development of the ClayFF Classical Force Field with Metal–O–H Angle Bending Terms
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Tuning the Oxidation State, Nuclearity, and Chemistry of Uranium Hydrides with Phenylsilane and Temperature: The Case of the Classic Uranium(III) Hydride Complex [(C 5 Me 5 ) 2 U(μ-H)] 2
Here, this work demonstrates that the oxidation state and chemistry of uranium hydrides can be tuned with temperature and the stoichiometry of phenylsilane. The trivalent uranium hydride [(C 5 Me 5 ) 2 U–H] x (5) was found to be comprised of an equilibrium mixture of U(III) hydrides in solution at ambient temperature. A single U(III) species can be selectively prepared by treating (C 5 Me5)2UMe2 (4) with 2 equiv of phenylsilane at 50 °C. The U(III) system is a potent reducing agent and displayed chemistry distinct from the U(IV) system [(C 5 Me 5 ) 2 U(H)(μ-H)] 2 (2), which was harnessed to prepare a variety of organometallic complexes, including (C 5 Me 5 ) 2 U(dmpe)(H) (6), and the novel uranium(IV) metallacyclopentadiene complex (C 5 Me 5 ) 2 U(C 4 Me 4 ) (11).
Functional AdoMet Isosteres Resistant to Classical AdoMet Degradation Pathways
S-adenosyl-L-methionine (AdoMet) is an essential enzyme cosubstrate in fundamental biology with an expanding range of biocatalytic and therapeutic applications. We report the design, synthesis and evaluation of stable, functional AdoMet isosteres that are resistant to the primary contributors to AdoMet degradation (depurination, intramolecular cyclization and sulfonium epimerization). Corresponding biochemical and structural studies demonstrate the AdoMet surrogates to serve as competent enzyme cosubstrates and to bind a prototypical class I model methyltransferase (DnrK) in a manner nearly identical to AdoMet. Given this conservation in function and molecular recognition, the isosteres presented are anticipated to serve as useful surrogates in other AdoMet-dependent processes and may also be resistant to, and/or potentially even inhibit, other therapeutically relevant AdoMet-dependent metabolic transformations (such as the validated drug target AdoMet decarboxylase). This work also highlights the ability of the prototypical class I model methyltransferase DnrK to accept non-native surrogate acceptors as an enabling feature of a new high-throughput methyltransferase assay.
Molecular-Level Insights into the NMR Relaxivity of Gadobutrol Using Quantum and Classical Molecular Simulations
MRI is an indispensable diagnostic tool in modern medicine; however, understanding the molecular-level processes governing NMR relaxation of water in the presence of MRI contrast agents remains a challenge, hindering the molecular-guided development of more effective contrast agents. By using quantum-based polarizable force fields, the first-of-its-kind molecular dynamics (MD) simulations of Gadobutrol are reported where the 1 H NMR longitudinal relaxivity r 1 of the aqueous phase is determined without any adjustable parameters. The MD simulations of r 1 dispersion (i.e., frequency dependence) show good agreement with measurements at frequencies of interest in clinical MRI. Importantly, the simulations reveal key insights into the molecular level processes leading to r 1 dispersion by decomposing the NMR dipole–dipole autocorrelation function G(t) into a discrete set of molecular modes, analogous to the eigenmodes of a quantum harmonic oscillator. The molecular modes reveal important aspects of the underlying mechanisms governing r 1 , such as its multiexponential nature and the importance of the second eigenmodal decay. By simply analyzing the MD trajectories on a parameter-free approach, the Gadobutrol simulations show that the outer-shell water contributes ∼50% of the total relaxivity r 1 compared to the inner-shell water, in contrast to simulations of (nonchelated) gadolinium-aqua where the outer shell contributes only ∼15% of r 1 . The deviation between simulations and measurements of r 1 below clinical MRI frequencies is used to determine the low-frequency electron-spin relaxation time for Gadobutrol, in good agreement with independent studies.
The Temperature Dependent Photoswitching of a Classic Diarylethene Monitored by in Situ X-ray Diffraction
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Structural basis for the context-specific action of the classic peptidyl transferase inhibitor chlor
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Exceptional points in classical spin dynamics
Abstract Non-conservative physical systems admit a special kind of spectral degeneracy, known as exceptional point (EP), at which eigenvalues and eigenvectors of the corresponding non-Hermitian Hamiltonian coalesce. Dynamical parametric encircling of the EP can lead to non-adiabatic evolution associated with a state flip, a sharp transition between the resonant modes. Physical consequences of the dynamical encircling of EPs in open dissipative systems have been explored in optics and photonics. Building on the recent progress in understanding the parity-time ( $${\mathscr{P}}{\mathscr{T}}$$ P T )-symmetric dynamics in spin systems, we use topological properties of EPs to implement chiral non-reciprocal transmission of a spin through the material with non-uniform magnetization, like helical magnet. We consider an exemplary system, spin-torque-driven single spin described by the time-dependent non-Hermitian Hamiltonian. We show that encircling individual EPs in a parameter space results in non-reciprocal spin dynamics and find the range of optimal protocol parameters for high-efficiency asymmetric spin filter based on this effect. Our findings offer a platform for non-reciprocal spin devices for spintronics and magnonics.
Hybrid classical and quantum computing for enhanced glioma tumor classification using TCGA data
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Identifying the chemical and structural irreversibility in LiNi 0.8 Co 0.15 Al 0.05 O 2 – a model compound for classical layered intercalation
In this work, we extracted 95% of the electrochemically available Li from LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) by galvanostatically charging the NCA/MCMB full cell to 4.7 V. Joint powder X-ray and neutron diffraction (XRD & ND) studies were undertaken for NCA at highly charged states at the first cycle, and discharged states at different cycles. The results indicate that the bulk structure of NCA maintains the O3 structure up to the extraction of 0.90 Li per formula unit. In addition, we found that the transition metal layer becomes more disordered along the c-axis than along the a- and b-axes upon charging. This anisotropic disorder starts to develop no later than 4.3 V on charge and continues to grow until the end of charge. As Li is re-inserted during discharge, the structure that resembles the pristine NCA is recovered. The irreversible loss of Li and the migration of Ni to the Li layer have been quantified by the joint XRD and ND refinement and the results were further verified by solid state 7 Li NMR and magnetic measurements. Thus, our work clearly demonstrates that the NCA bulk retains a robust, single phase O3 structure throughout the wide delithiation range (up to 0.9 Li per formula unit of NCA) and is suitable for higher energy density usage with proper modifications.