Zhaolang5735

To reveal the relation of guest dynamics within the structure H clathrate hydrate and its macroscopic physical properties, experimental and computational works have been conducted on the system of fluoromethane (HFC-41) and pinacolone coexisting with water. The phase boundaries of the hydrate formed from HFC-41 and pinacolone within the pressure range of (0.25-2.48) MPa and the temperature range of (277-293) K were measured. The equilibrium hydrate formation pressure incorporating HFC-41 was lowered by adding the pinacolone as a large guest molecule compound to form a sH phase compared to the HFC-41 single hydrate. find more Powder X-ray diffraction measurements confirmed the formation of the structure H hydrate with the HFC-41 and pinacolone binary hydrate. The lattice constants of the sH hydrate were also measured to see the effect of the help guest molecular size, which showed a different trend from that of the previous studies of sH pinacolone hydrates. Molecular dynamics simulations of the binary sH phase indicate weak hydrogen bonding of the pinacolone molecules with the water in the cages in the phase with HFC-41. The oblate HFC-41 molecules showed strong orientational preference to the equatorial planes of the D' cages, which may explain some of the trends in the behavior of this phase.The interaction between α-synuclein (α-syn) and synaptic vesicles (SVs) plays an important role in the life cycle of α-syn, and a disruption of it could lead to numerous neurodegenerative diseases. The N-terminal of α-syn (first 15 residues) has been shown to recapitulate the association dynamics of α-syn to the bilayer in various studies. This manuscript presents an extensive all-atom molecular dynamics studies (close to 100 μs) of the interaction between the N-terminal of α-syn and a lipid bilayer that mimics the SV under physiological conditions. The research demonstrates α-syn's overwhelming binding preference to the outer leaflet of the SV, which carries a net negative charge as compared to the neutral inner leaflet. Further structural analysis reveals that the Coulombic interaction between the positively charged residues of α-syn and the negatively charged lipid surface is the driving force of the binding, but has a potential of hindering the configurational change of α-syn. In addition, metadynamics simulations are carried out to investigate the folding of the N-terminal of α-syn in the presence and absence of the lipid bilayer, and the result confirms that the α-syn/membrane association facilitates protein folding.Indole and indoline rings are important pharmacophoric scaffolds found in marketed drugs, agrochemicals, and biologically active molecules. The [2 + 2] cycloaddition reaction is a versatile strategy for constructing architecturally interesting, sp3-rich cyclobutane-fused scaffolds with potential applications in drug discovery programs. A general platform for visible-light mediated intermolecular [2 + 2] cycloaddition of indoles with alkenes has been realized. A substrate-based screening approach led to the discovery of tert-butyloxycarbonyl (Boc)-protected indole-2-carboxyesters as suitable motifs for the intermolecular [2 + 2] cycloaddition reaction. Significantly, the reaction proceeds in good yield with a wide variety of both activated and unactivated alkenes, including those containing free amines and alcohols, and the transformation exhibits excellent regio- and diastereoselectivity. Moreover, the scope of the indole substrate is very broad, extending to previously unexplored azaindole heterocycles that collectively afford fused cyclobutane containing scaffolds that offer unique properties with functional handles and vectors suitable for further derivatization. DFT computational studies provide insights into the mechanism of this [2 + 2] cycloaddition, which is initiated by a triplet-triplet energy transfer process. The photocatalytic reaction was successfully performed on a 100 g scale to provide the dihydroindole analog.Defects are closely related to the optical properties and metal-to-insulator phase transition in SmNiO3 (SNO) and therefore play an important role in their applications. In this paper, the intrinsic point defects were studied in both stoichiometric and nonstoichiometric SNO by first-principles calculations. In stoichiometric SNO, the Schottky defects composed of nominally charged Sm, Ni, and O vacancies are the most stable existence. In nonstoichiometric SNO, excess Sm2O3 (or Sm) creates the formation of O vacancies and Ni vacancies and SmNi antisite defects, while NiSm antisite defects form in an excess Ni2O3 (or Ni and NiO) environment. Oxygen vacancies affect electronic structures by introducing additional electrons, leading to the formation of an occupied Ni-O state in SNO. Moreover, the calculations of optical properties show that the O vacancies increase the transmittance in the visible light region, while the Ni interstitials decrease transmittance within visible light and infrared light regions. This work provides a coherent picture of native point defects and optical properties in SNO, which have implications for the current experimental work on rare-earth nickelates compounds.Hydrogenated carbon nitride is synthesized by polymerization of 1,5-naphthyridine, a nitrogen-containing heteroaromatic compound, under high-pressure and high-temperature conditions. The polymerization progressed significantly at temperatures above 573 K at 0.5 GPa and above 623 K at 1.5 GPa. The reaction temperature was relatively lower than that observed for pure naphthalene, suggesting that the reaction temperature is considerably lowered when nitrogen atoms exist in the aromatic ring structure. The polymerization reaction largely progresses without significant change in the N/C ratio. Three types of dimerization are identified; naphthylation, exact dimerization, and dimerization with hydrogenation as determined from the gas chromatograph-mass spectrometry analysis of soluble products. Infrared spectra suggest that hydrogenation products were likely to be formed with sp3 carbon and NH bonding. Solid-state 13C nuclear magnetic resonance reveals that the sp3/sp2 ratio is 0.14 in both the insoluble solids synthesized at 0.5 and 1.5 GPa. Not only the dimers but also soluble heavier oligomers and insoluble polymers formed through more extensive polymerization. The major reaction mechanism of 1,5-Nap was common to both the 0.5 and 1.5 GPa experiments, although the required reaction temperature increased with increasing pressure and aromatic rings preferentially remained at the higher pressure.As demonstrated in previous spectroscopic studies of 1,3-dioxole [ J. Am. Chem. Soc., 1993, 115, 12132-12136] and 1,3-benzodioxole [ J. Am. Chem. Soc., 1999, 121, 5056-5062], analysis of the ring-puckering potential energy function (PEF) of a "pseudo-four-membered ring" molecule can provide insight into understanding the magnitude of the anomeric effect. In the present study, high-level CCSD/cc-pVTZ and somewhat lower-level MP2/cc-pVTZ ab initio computations have been utilized to calculate the PEFs for 1,3-dioxole and 1,3-benzodioxole and 10 related molecules containing sulfur and selenium atoms and possessing the anomeric effect. The potential energy parameters derived for the PEFs directly provide a comparison of the relative magnitudes of the anomeric effect for molecules possessing OCO, OCS, OCSe, SCS, SCSe, and SeCSe linkages. The torsional potential energies produced by the anomeric effect for these linkages were estimated to range from 5.97 to 1.91 kcal/mol. The ab initio calculations also yielded the structural parameters, barriers to planarity, and ring-puckering angles for each of the 12 molecules studied. Based on the refined structural parameters for 1,3-dioxole and 1,3-benzodioxole, improved PEFs for these molecules were also calculated. The calculations also support the conclusion that the relatively low barrier to planarity of 1,3-benzodioxole results from competitive interactions between its benzene ring and the oxygen atom p orbitals.Ynamides, though relatively more stable than ynamines, are still moisture-sensitive and prone to hydration especially under acidic and heating conditions. Here we report an environmentally benign, robust protocol to synthesize sulfonamide-based ynamides and arylynamines via Sonogashira coupling reactions in water, using a readily available quaternary ammonium salt as the surfactant.Clathrate hydrates of natural gases are important backup energy sources. It is thus of great significance to explore the nucleation process of hydrates. Hydrate clusters are building blocks of crystalline hydrates and represent the initial stage of hydrate nucleation. Using dispersion-corrected density functional theory (DFT-D) combined with machine learning, herein, we systematically investigate the evolution of stabilities and nuclear magnetic resonance (NMR) chemical shifts of amorphous precursors from monocage clusters CH4(H2O) n (n = 16-24) to decacage clusters (CH4)10(H2O) n (n = 121-125). Compared with planelike configurations, the close-packed structures formed by the water-cage clusters are energetically favorable. The 512 cages are dominant, and the emerging amorphous precursors may be part of sII hydrates at the initial stage of nucleation. Based on our data set, the possible initial fusion pathways for water-cage clusters are proposed. In addition, the 13C NMR chemical shifts for encapsulated methane molecules also showed regular changes during the fusion of water-cage clusters. Machine learning can reproduce the DFT-D results well, providing a structure-energy-property landscape that could be used to predict the energy and NMR chemical shifts of such multicages with more water molecules. These theoretical results present vital insights into the hydrate nucleation from a unique perspective.A strategy toward epitope-selective functionalized nanoparticles is introduced in the following ultrasmall gold nanoparticles (diameter of the metallic core about 2 nm) were functionalized with molecular tweezers that selectively attach lysine and arginine residues on protein surfaces. Between 11 and 30 tweezer molecules were covalently attached to the surface of each nanoparticle by copper-catalyzed azide alkyne cycloaddition (CuAAC), giving multiavid agents to target proteins. The nanoparticles were characterized by high-resolution transmission electron microscopy, differential centrifugal sedimentation, and 1H NMR spectroscopy (diffusion-ordered spectroscopy, DOSY, and surface composition). The interaction of these nanoparticles with the model proteins hPin1 (WW domain; hPin1-WW) and Survivin was probed by NMR titration and by isothermal titration calorimetry (ITC). The binding to the WW domain of hPin1 occurred with a KD of 41 ± 2 μM, as shown by ITC. The nanoparticle-conjugated tweezers targeted cationic amino acids on the surface of hPin1-WW in the following order N-terminus (G) ≈ R17 > R14 ≈ R21 > K13 > R36 > K6, as shown by NMR spectroscopy. Nanoparticle recognition of the larger protein Survivin was even more efficient and occurred with a KD of 8 ± 1 μM, as shown by ITC. We conclude that ultrasmall nanoparticles can act as versatile carriers for artificial protein ligands and strengthen their interaction with the complementary patches on the protein surface.