碱金属醇盐甲醇羰基化催化剂活性研究

利用红外、气相色谱、色谱－质谱联用方法对甲醇羰基化反应过程中甲醇钾和甲醇钠催化剂的失活情况进行了研究。结果表明：在本研究条件下,甲醇钠（甲醇钾）催化剂活性在保持一段时间的稳定后,随反应时间的继续延长逐渐降低。导致催化剂活性降低的主要原因是甲醇钠（甲醇钾）可以直接与产物甲酸甲酯反应形成甲酸钠（甲酸钾）和二甲醚。甲酸钠对甲醇羰基化反应也具有一定的催化作用,但其活性远远低于甲醇钠。降低瓜在温度可以减缓催     

H2,HF分子的基态势能函数

通过二次组态相互作用方法QCISD计算了H2，HF分子基态的平衡结构、振动频率和离解能．并使用基组6-311＋＋G（3df，3pd）对H2分子，HF分子基态进行了单点能扫描计算，采用最小二乘法拟合标准Murrell—Sorbie函数得到了相应的势能函数和与该基组相对应的光谱常数（ωe，ωe,χe，βe，ae），计算结果与实验数据吻合．     

Synthesis of (3S,5R)-carbapenam-3-carboxylic acid and its role in carbapenem biosynthesis and the stereoinversion problem

(5R)-Carbapenem-3-carboxylic acid is the simplest structurally among the naturally occurring carbapenem beta-lactam antibiotics. It is the produced from (3S,5S)-carbapenam-3-carboxylic acid utilizing a remarkable stereoinversion/desaturation process by CarC (carbapenem synthase), an alpha-ketoglutarate dependent non-heme iron oxygenase. In this communication, we demonstrate for the first time that the epimeric (3S,5R)-carbapenam-3-carboxylic acid is an intermediate in the overall catalytic cycle to the carbapenem antibiotic. The role of alpha-ketoglutarate in the stereoinversion and desaturation processes is also examined.     

He-N2碰撞体系散射截面的理论研究

本文运用量子化学从头计算MP2方法6-311 G(3df,2p)基组,计算了He-N2相互作用的势能,拟合出He原子与N2分子相互作用的各向异性势函数,其势函数参数:势能球平均势阱位置、势阱深度、势能零点位置与通过散射实验数据分析的ESMSV(Exponential-Spline-Morse-Spline-Van der waals)势比较吻合.然后,用公认精确度高的密耦方法计算了He原子与N2分子碰撞体系的总微分截面、弹性微分截面、转动激发的非弹性微分截面和积分截面,计算结果与实验数据符合得较好.     

闭通道对氦氢碰撞激发分波截面影响的研究

采用精确度较高的密耦近似方法计算了不同能量下的氯原子与氢分子碰撞体系的振转激发分波截面.在计算时依次考虑了入射通道中耦合态的数目为开通道数加上1个闭通道数,2个闭通道数,3个闭通道数,直到7个闭通道数的情况.结果表明:在研究氦氢碰撞体系的弹性碰撞、纯转动激发时,可以只考虑1个闭通道的影响,但在研究振转激发分波截面时,至少要考虑5个闭通道,才能得到比较准确的计算结果.     

Computational Simulation of HIV Protease Inhibitors to the Main Protease (Mpro) of SARS-CoV-2: Implications for COVID-19 Drugs Design

SARS-CoV-2 is highly homologous to SARS-CoV. To date, the main protease (Mpro) of SARS-CoV-2 is regarded as an important drug target for the treatment of Coronavirus Disease 2019 (COVID-19). Some experiments confirmed that several HIV protease inhibitors present the inhibitory effects on the replication of SARS-CoV-2 by inhibiting Mpro. However, the mechanism of action has still not been studied very clearly. In this work, the interaction mechanism of four HIV protease inhibitors Darunavir (DRV), Lopinavir (LPV), Nelfinavir (NFV), and Ritonavire (RTV) targeting SARS-CoV-2 Mpro was explored by applying docking, molecular dynamics (MD) simulations, and MM–GBSA methods using the broad-spectrum antiviral drug Ribavirin (RBV) as the negative and nonspecific control. Our results revealed that LPV, RTV, and NFV have higher binding affinities with Mpro, and they all interact with catalytic residues His41 and the other two key amino acids Met49 and Met165. Pharmacophore model analysis further revealed that the aromatic ring, hydrogen bond donor, and hydrophobic group are the essential infrastructure of Mpro inhibitors. Overall, this study applied computational simulation methods to study the interaction mechanism of HIV-1 protease inhibitors with SARS-CoV-2 Mpro, and the findings provide useful insights for the development of novel anti-SARS-CoV-2 agents for the treatment of COVID-19.     

The Critical Curves of the Random Pinning and Copolymer Models at Weak Coupling

We study random pinning and copolymer models, when the return distribution of the underlying renewal process has a polynomial tail with finite mean. We compute the asymptotic behavior of the critical curves of the models in the weak coupling regime, showing that it is universal. This proves a conjecture of Bolthausen, den Hollander and Opoku for copolymer models (Bolthausen et al., in Ann Probab, 2012), which we also extend to pinning models.     

Two highly stable and selective solid phase microextraction fibers coated with crown ether functionalized ionic liquids by different sol–gel reaction approaches

In this work, two novel crown ether functionalized ionic liquid (FIL)-based solid phase microextraction (SPME) fibers were prepared by sol–gel technology using the synthesized 1-(trimethoxysily)propyl 3-(6′-oxo-benzo-15-crown-5 hexyl) imidazolium bis(trifluoromethanesulphonyl)imide ([TMSP(Benzo15C5)HIM][N(SO₂CF₃)₂]) and 1-allyl-3-(6′-oxo-benzo-15-crown-5 hexyl) imidazolium bis(trifluoromethanesulphonyl)imide ([A(Benzo15C5)HIM][N(SO₂CF₃)₂]) as selective stationary phases. Owing to the introduction of trimethoxysilypropyl to the imidazole cation, the [TMSP(Benzo15C5)HIM][N(SO₂CF₃)₂] could be chemically bonded to the formed sol–gel silica substrate through the hydrolysis and polycondensation reaction. Similarly, the [A(Benzo15C5)HIM][N(SO₂CF₃)₂] was able to participate in the formation of the organic–inorganic copolymer coatings through the free radical crosslinking reaction. These two fibers were determined to have “bubble-like” surface characteristics analogous to a previously prepared [A(Benzo15C5)HIM][PF₆]-based fiber. Their thermal stabilities were much higher than that of the [A(Benzo15C5)HIM][PF₆]-based coating. They were capable of withstanding temperatures as high as 400 °C without evident loss of the crown ether FILs. They also had strong solvent, acid and alkali resistance, good coating preparation reproducibility and high selectivity for medium polar to polar compounds. The high selectivity of these two fibers could be attributed to the strong ion-dipole, hydrogen bonding and π–π interactions provided by the synergetic effect of ILs and benzo-15-crown-5 functionalities. Moreover, the selectivity of these two fibers was rather different although the structures of these two crown ether FILs were very similar. This is maybe because the relative contents of the crown ether FILs chemically bonded to the organic–inorganic copolymer coatings were quite different when prepared by different sol–gel reaction approaches.     

Subdiffusivity of a Random Walk Among a Poisson System of Moving Traps on $\mathbb {Z}$

We consider a random walk among a Poisson system of moving traps on \(\mathbb {Z}\). In earlier work (Drewitz et al. Springer Proc. Math. 11, 119-158 2012), the quenched and annealed survival probabilities of this random walk have been investigated. Here we study the path of the random walk conditioned on survival up to time t in the annealed case and show that it is subdiffusive. As a by-product, we obtain an upper bound on the number of so-called thin points of a one-dimensional random walk, as well as a bound on the total volume of the holes in the random walk’s range.     

Ferroelectric phase transitions of the 0.32PIN-0.345PMN-0.335PT single crystals studied by temperature-dependent Raman spectroscopy,dielectric and ferroelectric performance

The ferroelectric phase transition characteristics of the 0.32Pb(In_1/2Nb_1/2)O₃-0.345Pb(Mg_1/3Nb_2/3)O₃-0.335PbTiO₃ (0.32PIN-0.345PMN-0.335PT) single crystals were studied by the temperature-dependent Raman spectroscopy and some electrical properties. Ferroelectric monoclinic phase was confirmed at room temperature by the numbers of the Raman modes. Successive ferroelectric phase transitions, i.e. ferroelectric monoclinic phase to ferroelectric tetragonal phase transition (FE_M-FE_T) and ferroelectric tetragonal phase to paraelectric cubic phase transition (FE_T-P_C), are evidenced by the anomalies of Raman modes line width, peaks intensity and their ratios around T_M-T and T_C/T_m temperatures. The temperature dependent permittivity derivative ξ = d?/dT not only provides further evidence of the successive ferroelectric phase transitions, but also demonstrates the second-order transition characteristic of the FE_M-FE_T phase transition and the first-order transition feature of the FE_T-P_C phase transition. The FE_M-FE_T phase transition is also confirmed by the abnormal narrowing of the P-E loops, decrease of the P_r and E_c values, and extremums of the pyroelectric performance.