Computational examination on monomeric,dimeric, trimeric structural and vibrational interactions,AIM, Hirshfeld,IGM and oxygenated solvent effect on optical properties for pyridine N-oxide

This work reports DFT (Density functional theory) and topological examination by means of AIM (Atom in molecule) theory, Laplacian electron density (ED), Electron –Localization function (ELF) and Hirshfeld surface were executed monomer, dimer and trimer structure of PNO molecule. These structures were optimized and Structural parameters like bond – length and Angles are compared by using B3LYP/6-311G++(d,p) basis set. Computed vibrational – frequencies and corresponding PED (Potential energy – Distribution) were also compared. Polarizability, Dipole moment and the electronic properties were calculated for all three cases of PNO molecule. Hirshfeld surface investigation has been executed to achieve the C–H?O/N–O?H type of hydrogen -bond intermolecular interactions. Moreover, Reactive site, inter/intra interactions are calculated, the optical behaviors for monomer structure of PNO were investigate by using UV–Vis spectroscopy in oxygenated solvents.     

NMR structure of the peptidyl transferase RNA inhibitor antibiotic amicetin

In this communication, we report the solution state NMR structure determination of the peptidyl transferase RNA inhibitor antibiotic amicetin. We have successfully characterised the NMR spectrum of amicetin using a range of homo- and heteronuclear NMR techniques. Using experimental ROE-based distance and 1H--1H scalar coupling derived dihedral angle geometrical constraints as input into the three-dimensional structure determination protocol, we have generated an energy-minimised average structure of the antibiotic. Amicetin adopts a stable well-folded conformation in solution, mediated by a network of hydrogen bonds caused by proton donor and acceptor groups at either end of the molecule. The NMR structure of amicetin shows that the cytosine moiety occupies the critical turn position within the fold, which may be structurally significant for interaction with peptidyl transferase ribosomal RNA. The structure is distinctly different from the published X-ray crystal structure of amicetin in which it adopts a linear, extended chain-like conformation with a number of intermolecular hydrogen bonds. In addition to structure, we have probed the dynamics of amicetin in solution and have observed retarded exchange of the amide proton involved in folding. We have also characterised the ionisation properties of amicetin by carrying out NMR pH titration and measuring the pKa of the primary and tertiary amino groups, 7.27 and 7.52, respectively, which are in agreement with the reported values in literature. Solving the NMR structure of amicetin provides a valuable opportunity to determine the structure of its complex with RNA in solution state.     

Morphology studies of polyaniline lengthy nanofibers formed via dimers copolymerization approach

In this paper, two different aniline dimers, N-phenyl-1,2-phenylenediamine (2-PPD) and N-phenyl-1,4-phenylenediamine (4-PPD) were used as starting monomers in polyaniline (PANI) synthesis. It was found that 2-PPD dimer alone produced only an amorphous PANI oligomer with a flaky morphology, while the 4-PPD provided either linear nanofiber or a spaghetti-like hollow nanofiber structures comprising of worm-like fibril subunits. By adjusting the molar fed ratio of 4-PPD to 2-PPD in the copolymerization, long PANI nanofibers with length up to tens of microns, bundled together by single PANI fibrils with diameter ca. 3-5 nm, was formed. A possible formation mechanism was proposed taking account of the reactivity difference at positions 4 and 2 on the 4-PPD and 2-PPD, respectively.     

Symmetric and asymmetric ent-kaurane dimers isolated from Isodon japonicus

Bisjaponins A (1) and B (2), two new dimeric ent-kaurane diterpenoids connected with a rare four-membered carbon ring, which was formed by [2+2] reaction, were isolated from the aerial parts of Isodon japonicus. Their structures were elucidated by the analysis of spectroscopic evidence including extensive 2D NMR and MS data. Both the compounds were inactive for their cytotoxicity against human tumor cell lines, K562 and HepG2.     

Bifurcation in two-dimensional neural network model with delay

A kind of 2-dimensional neural network model with delay is considered. By analyzing the distribution of the roots of the characteristic equation associated with the model, a bifurcation diagram was drawn in an appropriate parameter plane. It is found that a line is a pitchfork bifurcation curve. Further more, the stability of each fixed point and existence of Hopf bifurcation were obtained. Finally, the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions were determined by using the normal form method and centre manifold theory. Foundation item: the National Natural Science, Foundation of China (19831030) Biography: WEI Jun-jie, Professor, Doctor, E-mail: weijj@hit.edu.cn     

Cooper对质心定向运动速度的研究

研究了稳恒超导电流密度 j=ensνs中 ,νS在产生磁场方面的作用 ;指出超导抗磁性起源的物理本质是 ,νSC(T)很大 (约为 1 0 3 - 1 0 4 ms- 1) ,νSC(0 )的上限是 0 K时电子 Fermi速度 (数量级为1 0 5ms- 1) ;并说明了 London穿透深度的物理意义。指出 L ondon穿透深度是产生拆对磁场 Hc(T)所要求的 Jc(T)分布的最小线度。     

New solutions of classical problems in rigid body dynamics

The equations of motion of a rigid body acted upon by general conservative potential and gyroscopic forces were reduced by Yehia to a single second-order differential equation. The reduced equation was used successfully in the study of stability of certain simple motions of the body. In the present work we use the reduced equation to construct a new particular solution of the dynamics of a rigid body about a fixed point in the approximate field of a far Newtonian centre of attraction. Using a transformation to a rotating frame we also construct a new solution of the problem of motion of a multiconnected rigid body in an ideal incompressible fluid. It turns out that the solutions obtained generalize a known solution of the simplest problem of motion of a heavy rigid body about a fixed point due to Dokshevich.     

含自旋轨道角动量耦合的耦合簇理论研究Zn2和Cd2二聚物的结构和光谱常数

在二分量相对论有效势和与之匹配的基组aug-cc-pvnz-pp (n=Q, 5)的基础上, 结合电子相关能的完备基组外推和四阶多项式拟合, 我们用含自旋轨道角动量耦合的耦合簇方法研究了Zn₂和Cd₂的结构和光谱常数. 尽管Zn₂和Cd₂的自旋轨道角动量耦合效应不及Hg₂的明显, 但还是把自旋轨道角动量耦合放在耦合簇迭代计算中, 以获得更加合理的理论结果. 通过比较, 理论结果与最新发表的实验结果或其他课题组的理论结果吻合得较好, 因此我们的理论计算将有助于丰富对Zn₂和Cd₂光谱性质的认识.     

对称变截面平面曲杆的单元刚度矩阵

本以一种新的思路和做法对变截面曲杆进行单元分析,直接把变截面曲杆作为单元,采用弹性中心法导出了单元刚度矩阵通用公式,确定了截面按余弦规律变化时,轴线分别为圆弧形、抛物线形、半椭圆形平面曲杆的单元刚度矩阵精确式,供结构设计参考使用。     

Fixed points of nonexpansive mappings on star-shaped subsets of a convex metric space

In this paper, we give some characteristic properties of star-shaped sets which include a subset of a convex metric space. Using the characteristic properties, we discuss the existence problems of fixed points of nonexpansive type mappings on star-shaped subsets of convex metric spaces, which generalize the recent results obtained by Ding Xie-ping, Beg and Azam. Finally, we give an example which shows that our generalizations are essential.