Synthesis of Heat-resistant Polymers by Thiol–Ene Reaction of N-Allylmaleimide Copolymers Using Glycoluril Crosslinkers with Rigid Molecular Structures

We carried out the thermal curing of the copolymers of N-allylmaleimide (AMI) and 2-ethylhexyl acrylate (2EHA) using 1,3,4,6-tetra(2-mercaproethyl)glycoluril ( G1 ), 1,3,4,6-tetra(3-mercaptopropyl)glycoluril ( G2 ), 1,3,4,6-tetraallylglycoluril ( G3 ), triallylisocyanurate (TAIC), and pentaerythritol tetrakis(3-mercaptobutyrate) (PEMB) as the crosslinkers. Based on the results for the analysis of thiol–ene reactions monitored by IR spectroscopy, it was confirmed that the curing rate significantly depended on the combination of the used crosslinkers. The insoluble fraction after curing was more than 90% for the systems using the glycoluril crosslinkers, while the conversion of the allyl groups was suppressed due to the rigid structure of these crosslinkers. The heat resistance and the mechanical properties of the crosslinked polymers were investigated by thermogravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, and mechanical tensile tests. For the products cured using the glycoluril crosslinkers, the glass transition temperature (T_g) and the maximum temperature of thermal decomposition (T_max) were 54–59 °C and 395–409 °C, respectively, being higher than those for the cured product prepared with PEMB and TAIC as the conventional crosslinkers. The elasticity (75–139 MPa), the maximum strength (3.0–4.1 MPa), and the adhesion strength (6.7–10.7 MPa) for the polymers cured with the glycoluril crosslinkers, determined by the mechanical tensile and single lap-shear adhesion tests, were higher than those for cured materials produced with PEMB. Thus, the thermal and mechanical properties of the maleimide copolymers were efficiently enhanced by crosslinking using the rigid glycoluril compounds. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 923–931     

In Situ Metal-Assisted Ligand Modification Induces Mn4 Cluster-to-Cluster Transformation: A Crystallography,Mass Spectrometry,and DFT Study

Dehydration of (S,S)-1,2-bis(1H-benzo[d]imidazol-2-yl)ethane-1,2-diol (H₄L) to (Z)-1,2-bis(1H-benzo[d]imidazol-2-yl)ethenol) (H₃L′) was found to be metal-assisted, occurs under solvothermal conditions (H₂O/CH₃OH), and leads to [Mn^II₄(H₃L)₄Cl₂]Cl₂ ⋅ 5 H₂O ⋅ 5 CH₃OH ( Mn₄L₄ ) and [Mn^II₄(H₂L′)₆(μ₃-OH)]Cl ⋅ 4 CH₃OH ⋅ H₂O ( Mn₄L′₆ ), respectively. Their structures were determined by single-crystal XRD. Extensive ESI-MS studies on solutions and solids of the reaction led to the proposal consisting of an initial stepwise assembly of Mn₄L₄ from the reactants via [MnL] and [Mn₂L₂] below 80 °C, and then disassembly to [MnL] and [MnL₂] followed by ligand modification before reassembly to Mn₄L′₆ via [MnL′], [MnL′₂], and [Mn₂L′₃] with increasing solvothermal temperature up to 140 °C. Identification of intermediates [Mn₄L_xL′_6−x] (x=5, 4, 3, 2, 1) in the process further suggested an assembly/disassembly/in situ reaction/reassembly transformation mechanism. These results not only reveal that multiple phase transformations are possible even though they were not realized in the crystalline state, but also help to better understand the complex transformation process between coordination clusters during “black-box” reactions.     

碱金属盐催化1,2,4-三唑与α,β-不饱和酮及二酰亚胺的氮杂Michael反应

发展了一种高效的碱金属盐催化1,2,4-三唑与α,β-不饱和酮及α,β-不饱和二酰亚胺的氮杂Michael加成反应的新方法,以中等到优异的产率得到目标产物.该方法原料易得,底物普适性好,反应条件温和,易实现克级规模的制备.产物容易转化为相应的γ-氨基醇.     

Transition metal complexes of Schiff base ligand based on 4,6-diacetyl resorcinol

Novel Schiff base ligand based on the condensation of 4,6-diacetyl resorcinol with 2-amino-4-methylthiazole in addition to its metal complexes with Cr (III), Mn (II), Fe (III), Co (II), Ni (II), Cu (II), Zn (II) and Cd (II) ions have been synthesized. The structure, electronic properties, and thermal behaviour of Schiff base and its metal complexes have been studied by elemental analysis, mass, ¹H NMR, IR spectra, thermal analysis, and theoretically by density function theory. The ligand acted as mononegative bidentate (NO) ligand and all complexes showed octahedral geometry except Cu (II) showed tetrahedral geometry as indicated from the spectral and magnetic studies. The Cu (II), Zn (II) and Cd (II) complexes were non electrolytes while the rest of the complexes were electrolytes. The antibacterial plus anticancer activities of the parent Schiff base and its metal complexes were screened. In addition, the molecular docking study was performed to explore the possible ways for binding to Crystal Structure of Human Astrovirus capsid protein (5ibv) receptor.     

Reduced graphene oxide supported copper oxide nanocomposites: An efficient heterogeneous and reusable catalyst for the synthesis of ynones, 1,3-diynes and 1,5-benzodiazepines in one-pot under sustainable reaction conditions

A greener and efficient method for the synthesis of ynones and 1,3-diynes using copper oxide nanoparticles (CuONPs) doped reduced graphene oxide (CuO@rGO) catalyst under palladium, ligand and solvent free conditions have been developed. The catalyst was subsequently utilized for the synthesis of biologically active 1,5-benzodiazepines in one pot via sequential addition of acyl chlorides, terminal alkynes and o-phenylenediamines. The methodology initially involves in situ formation of ynones which react with o-phenylenediamines in presence of ethanol to afford a wide variety of benzodiazepines. Mild reaction conditions, good to an excellent yield of the products, cheap and recyclable catalyst make this methodology environmentally benign and sustainable.     

Enhanced electronic and nonlinear optical responses of C24N24 cavernous nitride fullerene by decoration with first row transition metals; A computational investigation

The electronic (energy gap and work function) as well as electrical properties (dipole moment, polarizability, and first hyperpolarizabilities) of the first-row transition metals decorated C₂₄N₂₄ cavernous nitride fullerene were explored using DFT calculations. The transition metals are decorated at N4 cavity of C₂₄N₂₄ fullerene. According to our spin polarized computations, the most stable spin state monotonically increases to sextet for Mn@C₂₄N₂₄ and thereafter dropped off gradually to singlet state for Zn@C₂₄N₂₄ system. The findings demonstrate that transition metals can remarkably decrease the HOMO-LUMO energy gap and work function values up to 63% and 21% of bare C₂₄N₂₄, respectively. As can be seen, when the Sc and Ti metals are located above the N4 cavity of fullerene, systems of enhanced static hyperpolarizabilities (β₀) are delivered. These findings might provide an effective strategy to design high performance eletcro-optical materials based on carbon- nitride fullerene.     

Statistical structure of the velocity field in cavitating flow around a 2D hydrofoil

Transformation of flow turbulence structure with cavitation occurrence, determination of the flow conditions favorable for nucleation of cavitation bubbles, influence of the statistical structure of turbulence on this process and the inverse effect of cavitation on the flow dynamics are challenging problems in modern fluid mechanics. The paper reports on the results of statistical processing of the velocity fields measured by a PIV technique in cavitating flow over a 2D symmetric hydrofoil for four flow conditions, starting from a cavitation-free regime and finishing by unsteady cloud cavitation. We analyze basic information on the statistical structure of velocity fluctuations in the form of histograms and Q-Q diagrams along with profiles of the mean velocity and turbulent kinetic energy. The research reveals that the flow turbulence pattern and distributions of turbulent fluctuations change significantly with the cavitation development. Under unsteady cloud cavitation conditions, the probability density function of the fluctuating velocity has a two-mode distribution, which indicates switching of two alternating flow conditions in a region above the hydrofoil aft part due to periodic passing of cavitation clouds. Behaviors of the mean and most probable velocities unexpectedly appear to be different with a monotonous increase of the incoming flow velocity. This finding must be caused by modification of the skewness coefficient of the fluctuating velocity.     

单斜氧化锆表面水合和脱水的动态模拟

常用的氧化物负载金属催化剂通常在水相中制备，且在使用前常常需要经过煅烧. 因此，氧化物载体表面的水合和脱水过程对于负载型金属催化剂的真实建模至关重要. 通过第一性原理分子动力学模拟，本文考察了温和温度下无水单斜氧化锆(111)表面在显式溶剂水中的演化. 在模拟过程中，所有的双重配位桥位氧位点很快被溶剂水质子化，形成酸性羟基(HO_L)，并在锆原子上留下碱性羟基(HO^*). 这些碱性羟基(HO^*)可以与表面未解离的吸附水分子(H₂O^*$)进行活跃的质子交换，进而在表面自由扩散. 在273 K到373 K的温度范围下，第一性原理分子动力学水相模拟可以得到一种较为确定的、有代表性的平衡水合单斜氧化锆(111)表面，其表面锆原子上覆盖度(θ)为0.75. 随后，为了模拟低于800 K的温和煅烧温度下的表面脱水过程，本文使用密度泛函理论计算了表面水分子的逐步脱附自由能. 通过获得表面的脱水相图，总结了不同煅烧温度下有代表性的、部分水合的单斜氧化锆(111)表面(0.25≤θ<0.75). 这些水合单斜氧化锆(111)表面具有重要的理论意义，可以方便快捷地被应用于氧化锆催化剂及氧化锆负载金属催化剂的真实建模与模拟.     

Stability of Multiplier Ideal Sheaves

Chinese Annals of Mathematics, Series B - In the present article, the authors find and establish stability of multiplier ideal sheaves, which is more general than strong openness.