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We showed that in simulation 1, regions with small β-barrels are populated, indicating the chance of spontaneous formation of domains resembling channel-like structures. These structural domains are alternative to those more representative of mature fibrils (simulation 2), the latter showing a stable bundle of C-termini that is not sampled in simulation 1. Moreover, trimer of Aβ(1-42) can form internal pores that are large enough to be accessed by water molecules and Ca2+ ions.In this study, we address the long-standing issue-arising prominently from conceptual density functional theory (CDFT)-of the relative importance of electrostatic, i.e., "hard-hard", versus spin-pairing, i.e., "soft-soft", interactions in determining regiochemical preferences. We do so from a valence bond (VB) perspective and demonstrate that VB theory readily enables a clear-cut resolution of both of these contributions to the bond formation/breaking process. Our calculations indicate that appropriate local reactivity descriptors can be used to gauge the magnitude of both interactions individually, e.g., Fukui functions or HOMO/LUMO orbitals for the spin-pairing/(frontier) orbital interactions and molecular electrostatic potentials (and/or partial charges) for the electrostatic interactions. In contrast to previous reports, we find that protonation reactions cannot generally be classified as either charge- or frontier orbital-controlled; instead, our results indicate that these two bonding contributions generally interplay in more subtle patterns, only giving the impression of a clear-cut dichotomy. Finally, we demonstrate that important covalent, i.e., spin pairing, reactivity modes can be missed when only a single spin-pairing/orbital interaction descriptor is considered. This study constitutes an important step in the unification of CDFT and VB theory.We examine the effect of equilibration methodology and sampling on ab initio molecular dynamics (AIMD) simulations of systems of common solvents and salts found in lithium-oxygen batteries. We compare two equilibration methods (1) using an AIMD temperature ramp and (2) using a classical MD simulation followed by a short AIMD simulation both at the target simulation temperature of 300 K. We also compare two different classical all-atom force fields PCFF+ and OPLS. By comparing the simulated association/dissociation behavior of lithium salts in different solvents with the experimental behavior, we find that equilibration with the classical force field that produces more physically accurate behavior in the classical MD simulations, namely, OPLS, also results in more physically accurate behavior in the AIMD runs compared to equilibration with PCFF+ or with the AIMD temperature ramp. Equilibration with OPLS outperforms even the pure AIMD equilibration because the classical MD equilibration is much longer than the AIMD equilibration (nanosecond vs picosecond timescales). These longer classical simulations allow the systems to find a more physically accurate initial configuration, and in the short simulation times available for the AIMD production runs, the initial configuration has a large impact on the system behavior. We also demonstrate the importance of averaging coordination number over multiple starting configurations and Li+ ions, as the majority of Li+ ions do not undergo a single association or dissociation event even in an ∼40 ps long simulation and thus do not sample a statistically significant portion of the phase space. These results show the importance of both equilibration method and sufficient independent sampling for extracting experimentally relevant quantities from AIMD simulations.An efficient synthesis of β-methylsulfonylated N-heterocycles via FeCl3-catalyzed C(sp3)-H dehydrogenation and C(sp2)-H methylsulfonylation of inactivated cyclic amines with the promotion and participation of inorganic sodium metabisulfite and dicumyl peroxide (DCP) has been developed. Notably, bifunctional DCP acted not only as an oxidant to promote the dehydrogenation but also as a methyl radical to participate in the sulfone formation. With this protocol, a number of β-methylsulfonylated tetrahydropyridines, tetrahydroazepines, and pyrroles were obtained in a facile one-pot manner.The three-dimensional structures and shapes of biomolecules provide essential information about their interactions and functions. Unfortunately, the computational cost of biomolecular shape representation is an active challenge which increases rapidly as the number of atoms increase. Recent developments in sparse representation and deep learning have shown significant improvements in terms of time and space. A sparse representation of molecular shape is also useful in various other applications, such as molecular structure alignment, docking, and coarse-grained molecular modeling. We have developed an ellipsoid radial basis function neural network (ERBFNN) and an algorithm for sparsely representing molecular shape. click here To evaluate a sparse representation model of molecular shape, the Gaussian density map of the molecule is approximated using ERBFNN with a relatively small number of neurons. The deep learning models were trained by optimizing a nonlinear loss function with L1 regularization. Experimental results reveal that our algorithm can represent the original molecular shape with a relatively higher accuracy and fewer scale of ERBFNN. Our network in principle is applicable to the multiresolution sparse representation of molecular shape and coarse-grained molecular modeling. Executable files are available at https//github.com/SGUI-LSEC/SparseGaussianMolecule. The program was implemented in PyTorch and was run on Linux.A phenotypic high-throughput screen identified a benzamide small molecule with activity against small cell lung cancer cells. A "clickable" benzamide probe was designed that irreversibly bound a single 50 kDa cellular protein, identified by mass spectrometry as β-tubulin. Moreover, the anti-cancer potency of a series of benzamide analogs strongly correlated with probe competition, indicating that β-tubulin was the functional target. Additional evidence suggested that benzamides covalently modified Cys239 within the colchicine binding site. Consistent with this mechanism, benzamides impaired growth of microtubules formed with β-tubulin harboring Cys239, but not β3 tubulin encoding Ser239. We therefore designed an aldehyde-containing analog capable of trapping Ser239 in β3 tubulin, presumably as a hemiacetal. Using a forward genetics strategy, we identified benzamide-resistant cell lines harboring a Thr238Ala mutation in β-tubulin sufficient to induce compound resistance. The disclosed chemical probes are useful to identify other colchicine site binders, a frequent target of structurally diverse small molecules.
Website: https://www.selleckchem.com/products/GDC-0449.html
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