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1.
J Am Chem Soc ; 2020 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-32573220

RESUMO

This work represents an important step in the quest to make heteromultimetallic molecules featuring specific metal types and complicated metal ratios. The rational design, synthesis, and characterization of a complex heterotrimetallic single-source molecular precursor for the next generation sodium-ion battery cathode material, Na2Mn2FeO6, is described. A unique pentametallic platform [MnII(ptac)3-Na-MnIII(acac)3-Na-MnII(ptac)3] (1) was derived from the known polymeric structure of [NaMnII(acac)3]∞, through a series of elaborate design procedures, such as mixed-ligand, unsymmetric ligand, and mixed-valent approaches. Importantly, the application of those techniques results in a molecule with distinctively different transition metal positions in terms of ligand environment and oxidation states. An isovalent substitution of FeIII for the central MnIII ion forms the target heterotrimetallic precursor [MnII(ptac)3-Na-FeIII(acac)3-Na-MnII(ptac)3] (3) with an appropriate metal ratio of Na:Mn:Fe = 2:2:1. The arrangement of metal ions and ligands in this pentametallic assembly was confirmed by single crystal X-ray investigation. The unambiguous assignment of the positions and oxidation states of the Periodic Table neighbors Fe and Mn in 3 has been achieved by a combination of investigative techniques that include synchrotron resonant diffraction, X-ray multiwavelength anomalous diffraction, X-ray fluorescence spectroscopy, Mössbauer spectroscopy, and gas-phase DART mass spectrometry. The heterotrimetallic single-source precursor 3 was shown to exhibit a clean decomposition pattern yielding the phase-pure P2-Na2Mn2FeO6 quaternary oxide with high uniformity of metal ion distribution as confirmed by electron microscopy.

2.
Biochemistry ; 59(15): 1474-1481, 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-32233423

RESUMO

The CRISPR-Cas12a nuclease shreds short single-stranded DNA (ssDNA) substrates indiscriminately through trans-cleavage upon activation with a specific target DNA. This shredding activity offered the potential for development of ssDNA-templated probes with fluorescent dye (F) and quencher (Q) labels. However, the formulations of double-stranded DNA (dsDNA)-templated fluorescent probes have not been reported possibly due to unknown (or limited) activity of Cas12a against short dsDNAs. The ssDNA probes have been shown to be powerful for diagnostic applications; however, limiting the probe selections to short ssDNAs could be restrictive from an application and probe diversification standpoint. Here, we report a dsDNA substrate (probe-full) for probing Cas12a trans-cleavage activity upon target detection. A diverse set of Cas12a substrates with alternating dsDNA character were designed and studied using fluorescence spectroscopy. We have observed that probe-full without any nick displayed trans-cleavage performance that was better than that of the form that contains a nick. Different experimental conditions of salt concentration, target concentration, and mismatch tolerance were examined to evaluate the probe performance. The activity of Cas12a was programmed for a dsDNA frame copied from a tobacco curly shoot virus (TCSV) or hepatitis B virus (HepBV) genome by using crRNA against TCSV or HepBV, respectively. While on-target activity offered detection of as little as 10 pM dsDNA target, off-target activity was not observed even at 1 nM control DNAs. This study demonstrates that trans-cleavage of Cas12a is not limited to ssDNA substrates, and Cas12a-based diagnostics can be extended to dsDNA substrates.

3.
Chemistry ; 2020 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-32297999

RESUMO

FeSb2 exhibits a colossal Seebeck coefficient ( S ) and a record-breaking high thermoelectric power factor. It also has an atypical shift from diamagnetism to paramagnetism with increasing temperature, and the fine details of its electron correlation effects have been widely discussed. The extraordinary physical properties must be rooted in the nature of the chemical bonding, and indeed, the chemical bonding in this archetypical marcasite structure has been heavily debated on a theoretical basis since the 1960s. The two prevalent models for describing the bonding interactions in FeSb2 are based on either ligand-field stabilization of Fe or a network structure of Sb hosting Fe ions. However, neither model can account for the observed properties of FeSb2 . Herein, an experimental electron density study is reported, which is based on analysis of synchrotron X-ray diffraction data measured at 15 K on a minute single crystal to limit systematic errors. The analysis is supplemented with density functional theory calculations in the experimental geometry. The experimental data are at variance with both the additional single-electron Sb-Sb bond implied by the covalent model, and the large formal charge and expected d-orbital splitting advocated by the ionic model. The structure is best described as an extended covalent network in agreement with expectations based on electronegativity differences.

4.
Angew Chem Int Ed Engl ; 59(24): 9624-9630, 2020 Jun 08.
Artigo em Inglês | MEDLINE | ID: mdl-32166883

RESUMO

A known trinuclear structure was used to design the heterobimetallic mixed-valent, mixed-ligand molecule [CoII (hfac)3 -Na-CoIII (acac)3 ] (1). This was used as a template structure to develop heterotrimetallic molecules [CoII (hfac)3 -Na-FeIII (acac)3 ] (2) and [NiII (hfac)3 -Na-CoIII (acac)3 ] (3) via isovalent site-specific substitution at either of the cobalt positions. Diffraction methods, synchrotron resonant diffraction, and multiple-wavelength anomalous diffraction were applied beyond simple structural investigation to provide an unambiguous assignment of the positions and oxidation states for the periodic table neighbors in the heterometallic assemblies. Molecules of 2 and 3 are true heterotrimetallic rather than a statistical mixture of two heterobimetallic counterparts. Trinuclear platform 1 exhibits flexibility in accommodating a variety of di- and trivalent metals, which can be further utilized in the design of molecular precursors for the NaMM'O4 functional oxide materials.

5.
J Phys Chem A ; 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32009390

RESUMO

We demonstrate a strongly thresholded response in cyclotrimethylene trinitramine (RDX) when it is cylindrically shocked using a novel waveguide geometry. Using ultrafast single-shot multi-frame imaging, we demonstrate that <100 µm diameter single crystals of RDX embedded in a polymer host deform along preferential planes for >100 ns after the shock first arrives in the crystal. We use in situ imaging and time-resolved photoemission to demonstrate that short-lived chemistry occurs with complex deformation pathways. Using scanning electron microscopy and ultra-small-angle X-ray scattering, we demonstrate that the shock-induced dynamics leave behind porous crystals, with pore shapes and sizes that change significantly with shock pressure. A threshold pressure of ∼12 GPa at the center of convergence separated the single-mode planar crystal deformations from the chemistry-coupled multi-plane dynamics at higher pressures. Our observations indicate preferential directions for deformation in our cylindrically shocked system, despite the applied stress along many different crystallographic planes.

6.
J Am Chem Soc ; 142(4): 2031-2041, 2020 Jan 29.
Artigo em Inglês | MEDLINE | ID: mdl-31894979

RESUMO

Three novel unconventional clathrates with unprecedented III-V semiconducting frameworks have been synthesized: Cs8In27Sb19, Cs8Ga27Sb19, and Rb8Ga27Sb19. These clathrates represent the first examples of tetrel-free clathrates that are completely composed of main group elements. All title compounds crystallize in an ordered superstructure of clathrate-I in the Ia3̅ space group (No. 206; Z = 8). In the clathrate framework, a full ordering of {Ga or In} and Sb is observed by a combination of high-resolution synchrotron single-crystal and powder X-ray diffraction techniques. Density functional theory (DFT) calculations show that all three clathrates are energetically stable with relaxed lattice constants matching the experimental data. Due to the complexity of the crystal structure composed of heavy elements, the reported clathrates exhibit ultralow thermal conductivities of less than 1 W·m-1·K-1 at room temperature. All compounds are predicted and experimentally confirmed to be narrow-bandgap p-type semiconductors with high Seebeck thermopower values, up to 250 µV·K-1 at 300 K for Cs8In27Sb19. The latter compound shows carrier concentrations and mobilities, 1.42 × 1015 cm-3 and 880 cm2 ·V-1·s-1, which are on par with the values for parent binary InSb, one of the best electronic semiconductors. The high hole carrier mobility is uncommon for complex bulk materials and a highly desirable trait, opening ways to design semiconducting materials based on tunable III-V clathrates.

7.
Nat Chem ; 12(2): 186-192, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31792386

RESUMO

Competitive water adsorption can have a significant impact on metal-organic framework performance properties, ranging from occupying active sites in catalytic reactions to co-adsorbing at the most favourable adsorption sites in gas separation and storage applications. In this study, we investigate, for a metal-organic framework that is stable after moisture exposure, what are the reversible, loading-dependent structural changes that occur during water adsorption. Herein, a combination of in situ synchrotron powder and single-crystal diffraction, infrared spectroscopy and molecular modelling analysis was used to understand the important role of loading-dependent water effects in a water stable metal-organic framework. Through this analysis, insights into changes in crystallographic lattice parameters, water siting information and water-induced defect structure as a response to water loading were obtained. This work shows that, even in stable metal-organic frameworks that maintain their porosity and crystallinity after moisture exposure, important molecular-level structural changes can still occur during water adsorption due to guest-host interactions such as water-induced bond rearrangements.

8.
J Synchrotron Radiat ; 26(Pt 6): 1929-1935, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31721736

RESUMO

X-ray irradiation has been extensively used in recent years as a fabrication step for nanoparticles and nanoparticle systems. A variant of this technique, continuous-flow X-ray irradiation, has recently been developed, and offers three important advantages: precise control of the irradiation dose, elimination of convection effects in the precursor solution, and suitability for large-scale production. Here, the use of this method to fabricate Au nano-meshes of interest as transparent and flexible electrodes for optoelectronics is reported. The study includes extensive characterization of the synthesis parameters and of the product properties, with rather encouraging results.

9.
Front Neurol ; 10: 1114, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31695670

RESUMO

Non-motor symptoms of Parkinson's disease (PD) have been receiving increasing attention. Approximately half of patients with PD have experience PD-related pain. We investigated the effect and mechanism of acupuncture in patients with PD who have pain. PD patients with pain were divided into acupuncture group and control group. Nine patients completed acupuncture treatment; seven patients who received only an analgesic agent underwent resting-state functional magnetic resonance imaging (rs-fMRI) twice. fMRI was performed to evaluate the functional connectivity of the brain regions. After treatment, a decrease in total scores on the King's Parkinson's Disease Pain Scale (KPPS) and Unified Parkinson's Disease Rating Scale was observed in the acupuncture group (-46.2 and -21.6%, respectively). In the acupuncture group, increased connectivity was observed in four connections, one in the left hemisphere between the middle temporal gyrus (MTG) and precentral gyrus, and three in the right hemisphere between the postcentral gyrus and precentral gyrus, supramarginal gyrus and precentral gyrus, and MTG and insular cortex. A significant correlation was noted between the changes in functional connectivity and KPPS. The involved connection was between the left middle frontal gyrus and the right precentral gyrus (R = -0.698, P = 0.037). Acupuncture could relieve pain in PD patients by modulating brain regions related to both sensory-discriminative and emotional aspects. The present study might increase the confidence of users that acupuncture is an effective and safe analgesic tool that can relieve PD-related pain.

10.
J Phys Condens Matter ; 32(13): 135802, 2019 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-31778991

RESUMO

The crystal structures and phase relationships of Tb1-x Dy x Co2 alloys with 0 ⩽ x ⩽ 1 were investigated by synchrotron-based high-resolution x-ray powder diffraction. Three different crystal structures are observed in the system: all the compositions show cubic structure with space group [Formula: see text] at temperatures above the Curie temperature T C; the Tb-rich side sample shows a rhombohedral structure with space group [Formula: see text] and the Dy-rich side sample has a tetragonal [Formula: see text] space group. In situ measurements on the intermediate compound Tb0.3Dy0.7Co2 show a rhombohedral to tetragonal structural transition, and the two phases coexist from 99 K to 111 K, where the so-called magnetic morphotropic phase boundary (MPB) is found. The coexisting phases are believed to induce the anomalous magnetostrictive effect in the MPB regime.

12.
Cell Res ; 29(11): 927-941, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31520064

RESUMO

Over 150 types of RNA modifications are identified in RNA molecules. Transcriptome profiling is one of the key steps in decoding the epitranscriptomic panorama of these chemical modifications and their potential functions. N7-methylguanosine (m7G) is one of the most abundant modifications present in tRNA, rRNA and mRNA 5'cap, and has critical roles in regulating RNA processing, metabolism and function. Besides its presence at the cap position in mRNAs, m7G is also identified in internal mRNA regions. However, its transcriptome-wide distribution and dynamic regulation within internal mRNA regions remain unknown. Here, we have established m7G individual-nucleotide-resolution cross-linking and immunoprecipitation with sequencing (m7G miCLIP-seq) to specifically detect internal mRNA m7G modification. Using this approach, we revealed that m7G is enriched at the 5'UTR region and AG-rich contexts, a feature that is well-conserved across different human/mouse cell lines and mouse tissues. Strikingly, the internal m7G modification is dynamically regulated under both H2O2 and heat shock treatments, with remarkable accumulations in the CDS and 3'UTR regions, and functions in promoting mRNA translation efficiency. Consistently, a PCNA 3'UTR minigene reporter harboring the native m7G modification site displays both enriched m7G modification and increased mRNA translation upon H2O2 treatment compared to the m7G site-mutated minigene reporter (G to A). Taken together, our findings unravel the dynamic profiles of internal mRNA m7G methylome and highlight m7G as a novel epitranscriptomic marker with regulatory roles in translation.

13.
Chemistry ; 25(69): 15846-15857, 2019 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-31529652

RESUMO

Large separations between ground and excited magnetic states in single-molecule magnets (SMMs) are desirable to reduce the likelihood of spin reversal in the molecules. Spin-phonon coupling is a process leading to magnetic relaxation. Both the reversal and coupling, making SMMs lose magnetic moments, are undesirable. However, direct determination of large magnetic states separations (>45 cm-1 ) is challenging, and few detailed investigations of the spin-phonon coupling have been conducted. The magnetic separation in [Co(12-crown-4)2 ](I3 )2 (12-crown-4) (1) is determined and its spin-phonon coupling is probed by inelastic neutron scattering (INS) and far-IR spectroscopy. INS, using oriented single crystals, shows a magnetic transition at 49.4(1.0) cm-1 . Far-IR reveals that the magnetic transition and nearby phonons are coupled, a rarely observed phenomenon, with spin-phonon coupling constants of 1.7-2.5 cm-1 . The current work spectroscopically determines the ground-excited magnetic states separation in an SMM and quantifies its spin-phonon coupling, shedding light on the process causing magnetic relaxation.

14.
J Am Chem Soc ; 141(41): 16232-16236, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31550138

RESUMO

The fleeting lifetimes of reactive intermediates in C-H functionalization chemistry often prevent their direct characterization. For example, the critical nitrenoid intermediates that mediate Rh2-catalyzed C-H amination have eluded characterization for more than 40 years. In the absence of structural characterization of these species, methodological development is often computationally guided. Here we report the first X-ray crystal structure of a reactive Rh2 nitrenoid, enabled by N2 elimination from an organic azide ligand within a single-crystal matrix. The resulting high-resolution structure displays metrical parameters consistent with a triplet nitrene complex of Rh2. The demonstration of facile access to reactive metal nitrenoids within a crystalline matrix provides a platform for structural characterization of the transient species at the heart of C-H functionalization.

15.
J Am Chem Soc ; 141(41): 16217-16221, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31509710

RESUMO

A series of stellated metallosupramolecular architectures have been assembled through three-component integrative self-sorting. Building on the complementary ligand pairing, the initial attempts to synthesize the hexagram complex from a combination of X-shaped tetrakis- and V-shaped bis-terpyridine ligands, and CdII ions, resulted in an unprecedented mixture of stellated octanuclear and dodecanuclear metallocages, which were further isolated by column chromatography. To overcome the unexpected obstacle, the multivalent ligand design along with spontaneous heteroleptic complexation was applied to realization of the one-pot synthesis of the intricate topology. A centrally situated triangle served as a prop for quantitative formation of the six-pointed stellated complex. Notably, in the absence of the triangular prop, a four-pointed star was produced.

16.
Opt Express ; 27(16): A1308-A1323, 2019 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-31510595

RESUMO

A simulation scheme was developed to explore the light distribution of full-color micron-scale light-emitting diode (LED) arrays. The influences of substrate thickness, patterning, and cutting angle of the substrate on several important features, such as light field pattern, light extraction efficiency, and color variation, were evaluated numerically. An experiment was conducted; the results were consistent with simulation results for a 225 × 125 µm2 miniLED and those for an 80 × 80 µm2 microLED. Based on the simulation results, the light extraction efficiency of LED devices with a substrate increases by 67.75% over the extraction efficiency of those without a substrate. The light extraction efficiency of LED devices with a substrate increases by 113.55% when an additional patterned design is used on green and blue chips. The calculated large angle Δu'v' can be as low as 0.015 for miniLED devices.

17.
Front Cell Neurosci ; 13: 370, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31474834

RESUMO

LIS1 is the main causative gene for lissencephaly, while MeCP2 is the main causative gene for Rett syndrome, both of which are neurodevelopmental diseases. Here we report nuclear functions for LIS1 and identify previously unrecognized physical and genetic interactions between the products of these two genes in the cell nucleus, that has implications on MeCP2 organization, neuronal gene expression and mouse behavior. Reduced LIS1 levels affect the association of MeCP2 with chromatin. Transcriptome analysis of primary cortical neurons derived from wild type, Lis1±, MeCP2-/y, or double mutants mice revealed a large overlap in the differentially expressed (DE) genes between the various mutants. Overall, our findings provide insights on molecular mechanisms involved in the neurodevelopmental disorders lissencephaly and Rett syndrome caused by dysfunction of LIS1 and MeCP2, respectively.

18.
J Am Chem Soc ; 141(36): 14443-14450, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31431009

RESUMO

The corrole unit from the porphyrinoid family represents one of the most important ligands in the field of coordination chemistry, which creates a unique environment allowing for the observation of unusual electronic states of bound metal cations and has shown great promise in various applications. Nevertheless, studies that directly and systematically introduce these motifs in porous crystalline materials for targeting further functionalizations are still lacking. Herein, we report for the first time the construction of two robust corrole-based metal-organic frameworks (MOFs), M6(µ3-O)4(µ3-OH)4(OH)3(H2O)3(H3TCPC)3 (M = Zr for Corrole-MOF-1 and M = Hf for Corrole-MOF-2, H3TCPC = 5,10,15-tris(p-carboxylphenyl)corrole), which are assembled by a custom-designed C2ν-symmetric corrolic tricarboxylate ligand and the unprecedented D3d-symmetric 9-connected Zr6/Hf6 clusters. The resultant frameworks feature a rare (3,9)-connected gfy net and exhibit high chemical stability in aqueous solutions within a wide range of pH values. Furthermore, we successfully prepared the cationic Corrole-MOF-1(Fe) from the iron corrole ligand, which can serve as an efficient heterogeneous catalyst for [4 + 2] hetero-Diels-Alder reactions between unactivated aldehydes and a simple diene, outperforming both the homogeneous counterpart and the porphyrinic MOF counterpart.

19.
Nat Commun ; 10(1): 3443, 2019 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-31371724

RESUMO

Self-assembly of twelve pentatopic tectons, which have complementary edges or can be linked using either digonal or trigonal connectors, represents the optimal synthetic strategy to achieve spherical objects, such as chemical capsids. This process requires conditions that secure uninterrupted equilibria of binding and self-correction en route to the global energy minimum. Here we report the synthesis of a highly soluble, deca-heterosubstituted corannulene that bears five terpyridine ligands. Spontaneous self-assembly of twelve such tectons with 30 cadmium(II) cations produces a giant icosahedral capsid as a thermodynamically stable single product in high yield. Nuclear magnetic resonance (NMR) methods, mass spectrometry analyses, small-angle X-ray scattering, transmission electron microscopy, and atomic force microscopy indicate that this spherical capsid has an external diameter of nearly 6 nm and shell thickness of 1 nm, in agreement with molecular modeling. NMR and liquid chromatography evidences imply that chiral self-sorting complexation generates a racemic mixture of homochiral capsids.


Assuntos
Proteínas do Capsídeo/metabolismo , Capsídeo/química , Hidrocarbonetos Policíclicos Aromáticos/metabolismo , Montagem de Vírus/fisiologia , Antraquinonas , Cádmio/metabolismo , Modelos Moleculares , Termodinâmica
20.
Chemistry ; 25(59): 13547-13565, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31381207

RESUMO

A solution, solid-state, and computational study is reported of polycyclic aromatic hydrocarbon PAH/PAH(CF3 )n donor/acceptor (D/A) charge-transfer complexes that involve six PAH(CF3 )n acceptors with known gas-phase electron affinities that range from 2.11(2) to 2.805(15) eV and four PAH donors, including seven CT co-crystal X-ray structures that exhibit hexagonal arrays of mixed π-stacks with 1/1, 1/2, or 2/1 D/A stoichiometries (PAH=anthracene, azulene, coronene, perylene, pyrene, triphenylene; n=5, 6). These are the first D/A CT complexes with PAH(CF3 )n acceptors to be studied in detail. The nine D/A combinations were chosen to allow several structural and electronic comparisons to be made, providing new insights about controlling D/A interactions and the structures of CT co-crystals. The comparisons include, among others, CT complexes of the same PAH(CF3 )n acceptor with four PAH donors and CT complexes of the same donor with four PAH(CF3 )n acceptors. All nine CT complexes exhibit charge-transfer bands in solution with λmax between 467 and 600 nm. A plot of E(λmax ) versus [IE(donor)-EA(acceptor)] for the nine CT complexes studied is linear with a slope of 0.72±0.03 eV eV-1 . This plot is the first of its kind for CT complexes with structurally related donors and acceptors for which precise experimental gas-phase IEs and EAs are known. It demonstrates that conclusions based on the common assumption that the slope of a CT E(λmax ) versus [IE-EA] plot is unity may be incorrect in at least some cases and should be reconsidered.

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