Circular DNA by “Bis‐Click” Ligation: Template‐Independent Intramolecular Circularization of Oligonucleotides with Terminal Alkynyl Groups Utilizing Bifunctional Azides

A highly effective and convenient “bis‐click” strategy was developed for the template‐independent circularization of single‐stranded oligonucleotides by employing copper(I)‐assisted azide–alkyne cycloaddition. Terminal triple bonds were incorporated at both ends of linear oligonucleotides. Alkynylated 7‐deaza‐2′‐deoxyadenosine and 2′‐deoxyuridine residues with different side chains were used in solid‐phase synthesis with phosphoramidite chemistry. The bis‐click ligation of linear 9‐ to 36‐mer oligonucleotides with 1,4‐bis(azidomethyl)benzene afforded circular DNA in a simple and selective way; azido modification of the oligonucleotide was not necessary. Short ethynyl side chains were compatible with the circularization of longer oligonucleotides, whereas octadiynyl residues were used for short 9‐mers. Compared with linear duplexes, circular bis‐click constructs exhibit a significantly increased duplex stability over their linear counterparts. The intramolecular bis‐click ligation protocol is not limited to DNA, but may also be suitable for the construction of other macrocycles, such as circular RNAs, peptides, or polysaccharides.     

Pyrrolo‐dC Metal‐Mediated Base Pairs in the Reverse Watson–Crick Double Helix: Enhanced Stability of Parallel DNA and Impact of 6‐Pyridinyl Residues on Fluorescence and Silver‐Ion Binding

Reverse Watson–Crick DNA with parallel‐strand orientation (ps DNA) has been constructed. Pyrrolo‐dC (PyrdC) nucleosides with phenyl and pyridinyl residues linked to the 6 position of the pyrrolo[2,3‐d]pyrimidine base have been incorporated in 12‐ and 25‐mer oligonucleotide duplexes and utilized as silver‐ion binding sites. Thermal‐stability studies on the parallel DNA strands demonstrated extremely strong silver‐ion binding and strongly enhanced duplex stability. Stoichiometric UV and fluorescence titration experiments verified that a single ^2pyPyrdC–^2pyPyrdC pair captures two silver ions in ps DNA. A structure for the PyrdC silver‐ion base pair that aligns 7‐deazapurine bases head‐to‐tail instead of head‐to‐head, as suggested for canonical DNA, is proposed. The silver DNA double helix represents the first example of a ps DNA structure built up of bidentate and tridentate reverse Watson–Crick base pairs stabilized by a dinuclear silver‐mediated PyrdC pair.     

Combining the biased and unbiased sampling strategy into one convenient free energy calculation method

Constructing a free energy landscape for a large molecule is difficult. One has to use either a high temperature or a strong driving force to enhance the sampling on the free energy barriers. In this work, we propose a mixed method that combines these two kinds of acceleration strategies into one simulation. First, it applies an adaptive biasing potential to some replicas of the molecule. These replicas are particularly accelerated in a collective variable space. Second, it places some unbiased and exchangeable replicas at various temperature levels. These replicas generate unbiased sampling data in the canonical ensemble. To improve the sampling efficiency, biased replicas transfer their state variables to the unbiased replicas after equilibrium by Monte Carlo trial moves. In comparison to previous integrated methods, it is more convenient for users. It does not need an initial reference biasing potential to guide the sampling of the molecule. And it is also unnecessary to insert many replicas for the requirement of passing the free energy barriers. The free energy calculation is accomplished in a single stage. It samples the data as fast as a biased simulation and it processes the data as simple as an unbiased simulation. The method provides a minimalist approach to the construction of the free energy landscape. © 2019 Wiley Periodicals, Inc.     

Resin‐Derived Ni3S2/Carbon Nanocomposite for Advanced Rechargeable Aqueous Zn‐Based Batteries

The exploration of high‐energy and stable cathode materials is highly desirable and challenging for the development of advanced Zn‐based batteries. In this work, a facile pyrolysis method is reported to synthetize Ni₃S₂/carbon nanocomposite as high‐performance cathode by employing ion exchange resin as a precursor. Attributing to the abundant active sites and enhanced conductivity from well binding between Ni₃S₂ and carbon, a markedly high capacity of 234.3 mA h g^?1 is obtained for this Ni₃S₂/carbon at a high current density of 6.9 A g^?1. Moreover, a Zn‐based battery is demonstrated by using the Ni₃S₂/carbon as a cathode and Zn plate as an anode, which delivers a maximum power density of 58.6 kW kg^?1, together with a peak energy density of 356 W h kg^?1 and 93.7% capacity retention after 5000 charging–discharging cycles. This simple synthetic strategy to achieve robust Ni‐based composite electrodes may open up new opportunities to design other transition metal–based electrodes for energy storage applications.     

Structural refinement of the high-pressure phase of aluminum trihydroxide: in-situ high-pressure angle dispersive synchrotron X-ray diffraction and theoretical studies

In-situ high-pressure synchrotron angle-dispersive X-ray diffraction for gibbsite (aluminum trihydroxide) was performed at room temperature up to 20 GPa. A pressure-induced phase transition was observed at 2.6 GPa. The new high-pressure phase can be recovered at ambient pressure. Rietveld refinement shows that the new phase of Al(OH)(3) has an orthorhombic structure, spacegroup Pbca, and the lattice parameters at ambient condition are a = 868.57(5) pm, b = 505.21(4) pm, c = 949.54(6) pm, V = 416.67(6) x 10(6) pm(3) with Z = 8. The compressibility of gibbsite and the high-pressure polymorph was analyzed, and their bulk moduli were estimated as 49.8 +/- 1.8 and 81.0 +/- 5.2 GPa, respectively. First-principles calculations of the high-pressure phase were performed to determine the hydrogen positions and to confirm the structural stability of the new phase.     

结构可靠度的虚拟变量算法

从与结构失效函数有关随机变量均值和协方差的确定性特征出发 ,提出了准确计算结构可靠度的一种虚拟变量算法。使用虚拟变量算法时 ,只需给出失效函数就能正确算出结构的可靠度。由于无需人工确定失效函数的偏导数 ,计算较为简单 ,当失效函数形式复杂、与失效函数有关随机变量较多时 ,可使计算效率得到显著提高     

Cleavable bimetallic-organic polymers for ROS mediated cascaded cancer therapy under the guidance of MRI through tumor hypoxia relief strategy

Despite recent advances in tumor treatment, reactive oxygen species(ROS)-mediated therapy, such as photodynamic therapy(PDT) and chemical dynamic therapy(CDT), remains challenging mainly due to hypoxia in tumor microenviroment. Relieving the hypoxia of tumor tissue has been considered as an attractive strategy for enhancing efficacy of ROS-based cancer treatment.Herein, one cascaded platform was developed to overcome tumor hypoxia and synergistically enhance the effect of ROSmediated therapy. This platform is based on cleavable bimetallic metal organic polymers(DOX@Fe/Mn-THPPTK-PEG). As an efficient Fenton-like material, it could not only produce cytotoxic ·OH by catalyzing the decomposition of intracellular H_2O_2, but also generate O_2 to alleviate tumor hypoxia. In addition, the DOX-loaded metal organic polymers(MOPs could be disrupted after being exposed to laser irradiation or/and treated with H_2O_2, and then release the DOX for chemotherapy. Overall, 3 therapies(hypoxia-relieved PDT, photo-enhanced CDT, and ROS-mediated chemotherapy) could be achieved simultaneously by such a smart platform. Furthermore, T_1-weighted MRI imaging ability of the MOPs could be greatly improved under H_2O_2 treatment.Therefore, total four robust functions were realized in a simple platform. These findings demonstrate great clinical potentials of the MOPs for cancer theranostics.     

1,7‐Dideaza‐2′‐deoxy‐6‐nitronebularine: a pyrrolo[2,3‐b]pyridine nucleoside with an intramolecular hydrogen bond stabilizing the syn conformation

The title compound [systematic name: 1‐(2‐deoxy‐β‐D‐erythro‐pentofuranosyl)‐4‐nitro‐1H‐pyrrolo[2,3‐b]pyridine], C₁₂H₁₃N₃O₅, forms an intramolecular hydrogen bond between the pyridine N atom as acceptor and the 5′‐hydroxy group of the sugar residue as donor. Consequently, the N‐glycosylic bond exhibits a syn conformation, with a χ torsion angle of 61.6 (2)°, and the pentofuranosyl residue adopts a C2′‐endo envelope conformation (²E, S‐type), with P = 162.1 (1)° and τ_m = 36.2 (1)°. The orientation of the exocyclic C4′—C5′ bond is +sc (gauche, gauche), with a torsion angle γ = 49.1 (2)°. The title nucleoside forms an ordered and stacked three‐dimensional network. The pyrrole ring of one layer faces the pyridine ring of an adjacent layer. Additionally, intermolecular O—H...O and C—H...O hydrogen bonds stabilize the crystal structure.     

A flame‐retardant DOPO‐MgAl‐LDH was prepared and applied in poly (methyl methacrylate) resin

A novel inorganic and organic composite flame retardant (9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide [DOPO]–layered double hydroxide [LDH]) was synthesized via grafting DOPO with organic‐modified Mg/Al‐LDH, which was introduced into poly (methyl methacrylate) (PMMA) resin to prepare the flame‐retardant PMMA composites. Thermogravimetric analyzer (TGA) showed that the T_‐50% of DOPO‐LDH/PMMA composites enhanced by about 20°C, and with the 20% flame retardant, the residual char content can be increased by 39.8% in the air atmosphere compared with LDH/PMMA composites. In the UL‐94 and the limiting oxygen index (LOI) tests, it can be found that compared with LDH/PMMA composites, the LOI value of DOPO‐LDH/PMMA composites were raised evidently with the increased flame retardants, and the droplet combustion was greatly improved. These results could be ascribed to the action of DOPO free‐radical, catalytic charring of polymer and the effect of LDH physical barrier. Moreover, the novel DOPO‐LDH not only given PMMA a good flame‐retardant property and thermal stability, but also have higher visible light transmittance, ultraviolet‐shielding effect, and low loss of mechanical properties, which could further facilitate the wide application of inorganic environment‐friendly flame retardants in general resins and engineering resins and broaden the application of polymers.