Regulating both the chemo‐ and diastereoselectivity, divergently, of a reaction is highly attractive but extremely challenging. Presented herein is a catalyst‐controlled switch in the chemo‐ and ...diastereodivergent annulation reactions of Morita–Baylis–Hillman carbonates, derived from isatins and 2‐alkylidene‐1H‐indene‐1,3(2H)‐diones, in exclusive α‐regioselectivity. α‐Isocupreine efficiently catalyzed 2+1 reactions to access cyclopropane derivatives, and the diastereodivergent 3+2 annulations were accomplished by employing either a chiral phosphine or a DMAP‐type molecule. All reactions exhibited excellent chemoselectivities, and good to remarkable stereoselectivities were furnished, thus leading to a collection of compounds with skeletal and stereogenic diversity. Moreover, DFT computational calculations elucidated the catalyst‐based switch in mechanism.
Switching it up: The title reactions have been accomplished by employing different chiral Lewis base catalysts, thus resulting in a broad collection of chiral compounds with high structural and stereochemical diversity (see scheme). DFT calculations indicate that the structure of Lewis base plays a key role in controlling the chemo‐ and diastereoselectivity. Boc=tert‐butoxycarbonyl.
We develop a moment QCD sum rule method augmented by fundamental inequalities to study the existence of exotic doubly hidden-charm/bottom tetraquark states made of four heavy quarks. Using the ...compact diquark–antidiquark configuration, we calculate the mass spectra of these tetraquark states. There are 18 hidden-charm ccc¯c¯ tetraquark currents with JPC=0++, 0−+, 0−−, 1++, 1+−, 1−+, 1−−, and 2++. We use them to perform QCD sum rule analyses, and the obtained masses are all higher than the spontaneous dissociation thresholds of two charmonium mesons, which are thus their dominant decay modes. The masses of the corresponding hidden-bottom bbb¯b¯ tetraquarks are all below or very close to the thresholds of the ϒ(1S)ϒ(1S) and ηb(1S)ηb(1S), except one current of JPC=0++. Hence, we suggest to search for the doubly hidden-charm states in the J/ψJ/ψ and ηc(1S)ηc(1S) channels.
Inspired by P(c)(4380) and P(c)(4450) recently observed by LHCb, a QCD sum rule investigation is performed, by which they can be identified as exotic hidden-charm pentaquarks composed of an ...anticharmed meson and a charmed baryon. Our results suggest that P(c)(4380) and P(c)(4450) have quantum numbers J(P)=3/2(-) and 5/2(+), respectively. Furthermore, two extra hidden-charm pentaqurks with configurations D̅Σ(c)(*) and D̅(*)Σ(c)(*) are predicted, which have spin-parity quantum numbers J(P)=3/2(-) and J(P)=5/2(+), respectively. As an important extension, the mass predictions of hidden-bottom pentaquarks are also given. Searches for these partners of P(c)(4380) and P(c)(4450) are especially accessible at future experiments like LHCb and BelleII.
•As of 3 March 2020, COVID-19 has spread rapidly in 46 countries, causing >90 000 confirmed cases and >2946 deaths.•Detection methods for SARS-CoV-2 include RT-qPCR and SHERLOCK technique.•Four ...structural proteins are essential for SARS-CoV-2 assembly and infection, comprising the S, M, E and N proteins.•Pangolin may be a potential intermediate host for SARS-CoV-2.•Antiviral therapy, cellular therapy, immunotherapy and Chinese medicine may be promising therapeutic strategies.
Coronavirus disease 2019 (COVID-19) originated in the city of Wuhan, Hubei Province, Central China, and has spread quickly to 72 countries to date. COVID-19 is caused by a novel coronavirus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) previously provisionally known as 2019 novel coronavirus (2019-nCoV). At present, the newly identified SARS-CoV-2 has caused a large number of deaths with tens of thousands of confirmed cases worldwide, posing a serious threat to public health. However, there are no clinically approved vaccines or specific therapeutic drugs available for COVID-19. Intensive research on the newly emerged SARS-CoV-2 is urgently needed to elucidate the pathogenic mechanisms and epidemiological characteristics and to identify potential drug targets, which will contribute to the development of effective prevention and treatment strategies. Hence, this review will focus on recent progress regarding the structure of SARS-CoV-2 and the characteristics of COVID-19, such as the aetiology, pathogenesis and epidemiological characteristics.
It is observed experimentally that the sign of the Hall resistance can be flipped by a dc electric current in the twisted bilayer graphene (TBG) at 3/4 filling of the fourfold degenerate conduction ...flat bands. The experiment implies a switching of the valley polarization (VP) and topology in TBG. Here we present a theory on the current-induced switching of VP and topology. The presence of current in the bulk causes the redistribution of electron occupation in bands near the Fermi energy, which then deforms and shifts the band dispersion due to the Coulomb interaction. Above a critical current, the original occupied and empty bands can be swapped, resulting in the switching of VP and topology.
We adopt the heavy baryon chiral perturbation theory to calculate the scattering lengths of ϕBcc(*) up to O(p3), where ϕ is the pseudoscalar mesons. The recoil effect and the mass splitting between ...the spin-1/2 and spin-3/2 doubly charmed baryons are included. In order to give the numerical results, we construct the chiral Lagrangians with heavy diquark-antiquark symmetry in a formally covariant approach. Then, we relate the low energy constants of the doubly charmed baryons to those of D(*) mesons. The LECs for the ϕD(*) scattering are estimated in two scenarios, fitting lattice QCD results and using the resonance saturation model. The chiral convergence of the first scenario is not good enough due to the large strange quark mass and the presence of the possible bound states, virtual states, and resonance. The final results for two scenarios are consistent with each other. The interaction for the πΞcc(*)(1/2), KΞcc(*)(0), KΩcc(*)(1/2), ηΞcc(*)(1/2), ηΩcc(*)(0), and K¯Ξcc(*)(0) channels are attractive. The most attractive channel K¯Ξcc(*)(0) may help to form the partner states of the Ds0*(2317) Ds1(2460) in the doubly heavy sector.
Pentaquark and Tetraquark States Liu, Yan-Rui; Chen, Hua-Xing; Chen, Wei ...
Progress in particle and nuclear physics,
July 2019, 2019-07-00, Letnik:
107
Journal Article
Recenzirano
Odprti dostop
The past seventeen years have witnessed tremendous progress on the experimental and theoretical explorations of the multiquark states. The hidden-charm and hidden-bottom multiquark systems were ...reviewed extensively in Ref. 1. In this article, we shall update the experimental and theoretical efforts on the hidden heavy flavor multiquark systems in the past three years. Especially the LHCb collaboration not only confirmed the existence of the hidden-charm pentaquarks but also provided strong evidence of the molecular picture. Besides the well-known XYZ and Pc states, we shall discuss more interesting tetraquark and pentaquark systems either with one, two, three or even four heavy quarks. Some very intriguing states include the fully heavy exotic tetraquark states QQQ̄Q̄ and doubly heavy tetraquark states QQq̄q̄, where Q is a heavy quark. The QQQ̄Q̄ states may be produced at LHC while the QQq̄q̄ system may be searched for at BelleII and LHCb. Moreover, we shall pay special attention to various theoretical schemes such as the chromomagnetic interaction (CMI), constituent quark model, meson exchange model, heavy quark and heavy diquark symmetry, QCD sum rules, Faddeev equation for the three body systems, Skyrme model and the chiral quark-soliton model, and the lattice QCD simulations. We shall emphasize the model-independent predictions of various models which are truly/closely related to Quantum Chromodynamics (QCD). For example, the chromomagnetic interaction arises from the gluon exchange which is fundamental and universal in QCD and responsible for the mixing and mass splitting of the conventional mesons and baryons within the same multiplet. The same CMI mechanism shall also be responsible for the mixing of the different color configurations and mass splittings within the multiplets in the multiquark sector. There have also accumulated many lattice QCD simulations through multiple channel scattering on the lattice in recent years, which provide deep insights into the underlying structure/dynamics of the XYZ states. In terms of the recent Pc states, the lattice simulations of the charmed baryon and anti-charmed meson scattering are badly needed. We shall also discuss some important states which may be searched for at BESIII, BelleII and LHCb in the coming years.
In the framework of one-pion-exchange (OPE) model, we study the hidden-charm and charm-strange molecular pentaquark systems composed of a heavy baryon (Σc,Σc⁎) and a vector meson (K¯⁎,D¯⁎), where the ...S-D mixing effect is considered in our calculation. Our result shows that the ΣcD¯⁎ molecular state with (I=1/2,JP=3/2−) and the Σc⁎D¯⁎ molecular state with (I=1/2,JP=5/2−) exist in the mass range of the observed Pc(4380) and Pc(4450), respectively. Moreover, we predict two other hidden-charm molecular pentaquarks with configurations ΣcD¯⁎(I=3/2,JP=1/2−) and Σc⁎D¯⁎(I=3/2,JP=1/2−) and two charm-strange molecular pentaquarks Pcs(3340) and Pcs(3400) corresponding to the ΣcK¯⁎ configuration with (I=1/2,JP=3/2−) and the Σc⁎K¯⁎ configuration with (I=1/2,JP=5/2−), respectively. Additionally, we also predict some hidden-bottom Σb(⁎)B⁎ and Bc-like Σc(⁎)B⁎/Σb(⁎)D¯⁎ pentaquarks.
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