1, 4-Pyrone Effects on O-H Bond Dissociation Energies of Catechols in Flavonoids: A Density Functional Theory Study

In recent years, there has been growing interest in selecting efficient antioxidants with low toxicity to reduce the damage of free radicals. Among these antioxidants, flavonoids have been paid much attention, owing to their excellent antioxidative and pharmacological activities1. Up to now, many efforts have been given to summarize the structure-activity relationships (SAR) for flavonoids. It has been widely accepted that two structural factors are critical for flavonoids to enhance the…     

Synthesis and Structure of a Novel Layered Zincophosphate Zn4P3O11(OH)·3C3N2H4 with Organic Amine Acting as Ligand

A novel two-dimensional zinc phosphate Zn₄P₃O₁₁(OH)·3CN₂H₄ in which the structure-directing organic amine acts as a ligand has been synthesized hydrothermally. The structure was solved by single-crystal X-ray diffraction analysis. Crystal data: triclinic, space group P1? (No. 2) with lattice parameters a=9.5663(15) Å, b=9.8530(16) Å, c=12.3658(19) Å, α= 77.495(4)°, β=77.893(4)°, γ=68.175(3)°, V=1045.6(3) Å3, Z=2, R₁[I>2σ(I)]=0.0309, and wR₂[I>2σ(I)]=0.0809. Interestingly the structure involves a network of ZnO₄, PO₄, PO₃(OH), and the unusual ZnO₃N and ZnO₂N₂ tetrahedra with shared vertices. There are 10-membered rings in the layers, in which the structure-directing imidazole molecules reside. The other amine molecules protrude from the Zn centers and occupy spaces between the layers.     

Porphyrazines with annulated diazepine rings. 2. Alternative synthetic route to tetrakis-2,3-(5,7-diphenyl-1,4-diazepino)porphyrazines: new metal complexes, general physicochemical data, ultraviolet-visible linear and optical limiting behavior, and electrochemical and spectroelectrochemical properties

Following a previous report on the synthesis and physicochemical characterization of a novel class of porphyrazines carrying peripherally annulated seven-membered rings, i.e., tetrakis-2,3-(5,7-diphenyl-1,4-diazepino)porphyrazine [Ph(8)DzPzH(2)].4H(2)O and its metal derivatives [Ph(8)DzPzM].xH(2)O (x = 2-7, M = Mg(II)(H(2)O), Cu(II), and Zn(II)), a new more convenient procedure is reported here, allowing the preparation in high yields of the Li(I) and Na(I) derivatives of formulas [Ph(8)DzPzLi(2)].5H(2)O and [Ph(8)DzPzNa(2)].6H(2)O, which can be directly converted into other metal derivatives under mild conditions (room temperature) and in good yields. The series studied has been extended to include the Mn(II) and Co(II) complexes also reported here for the first time. Physicochemical characterization of the new "diazepinoporphyrazines" was based on fast atom bombardment (FAB) mass spectrometry and X-ray powder patterns, infrared (IR), electron paramagnetic resonance (EPR), and room-temperature magnetic susceptibility measurements. A detailed discussion of the UV-vis spectra emphasizes the role played by the external diazepine rings in electron delocalization through their tautomeric or protonated forms present in neutral, basic, and acidic media. The nonlinear optical effect of optical limiting for the different species [M = 2H, Mg(II)(H(2)O), Mn(II), Co(II), Cu(II), and Zn(II)] has also been measured. It has been observed that the extent of the optical limiting depends on the specific M center. The observed nonlinear optical features are analyzed and discussed in terms of the electronic and magnetic properties exhibited by some of the metal ions and taking into account the model of the excited-state absorption in which the nature of M determines the kinetics of formation of the highly absorbing state of the specific complex examined. As evidenced by the detailed electrochemical and spectroelectrochemical study carried out on this new class of macrocycles, one of the most important aspects is the facilitated electron delocalization for the oxidized and reduced species allowed by a 1H-6Htautomerism taking place on the peripheral diazepine rings.     

Convergence of Solutions of the Landau Equations in the Collisionless Limit

This paper addresses the question: when the frequency of collisions vanishes, will the solutions of the Landau system converge to the solutions of the Vlasov system? We give a positive answer to the question for solutions satisfying certain regularity conditions. © 1997 by B. G. Teubner Stuttgart–John Wiley & Sons Ltd. Math. Meth. Appl. Sci., Vol. 20, 679–688 (1997).     

钛—(Ⅳ)氯磺酚S一聚乙烯醇显色体系的研究

本文研究了聚乙烯醇存在下,钛(Ⅳ)—氯磺酚S的显色反应,提出了用于硅酸盐矿中测微量钛的分光光度法。     

含苯并15-冠-5的酚醛型和缩醛型聚合物冠醚的合成及其络合与催化性能

合成了两种新聚合物冠醚,研究了它们对钠、钾离子络合容量和催化性能.     

Solvation studies of electrospray ions—method and early results

Experiments are described in which bare (completely desolvated) ions are separated from their source gas and mixed with a bath gas of any desired temperature and precisely controlled composition. The resulting mixture of ions and bath gas is transported by free jet expansion into a vacuum system for mass analysis to reveal the extent to which the ions have formed adducts with other species in the bath gas. Because the ions are separated from their source gas or vapor before they are mixed with the bath gas, the compositions of the bath gas and source gas are completely independent. Thus, one can examine solvation or adduction by any desired species contained in the bath gas without any interference from other species that might be present in the source gas. Reported here are results obtained on the solvation of electrospray ions of a small peptide, leucine-enkephalin, by water and several alkanols. One provocative finding is that a substantial fraction of ions thought to be singly charged monomers turned out to be doubly charged dimers.     

The reaction of heteroaroyl‐substituted heterocyclic ketene aminals with 2,3,4,6‐tetra‐O‐acetyl‐β‐D‐glucopyranosyl azide

The reaction of heteroaroyl‐substituted heterocyclic ketene aminals with 2,3,4,6‐tetra‐O‐acetyl‐β‐D ‐glucopyranosyl azide was investigated and a series of potential bioactive compounds, 1‐glucopyranosyl‐4‐heterocyclic‐5‐heteroaryl‐1,2,3‐triazoles, were obtained in good yields. Both the reaction rate and the yield were strongly affected by the heteroaryl and heterocyclic groups. In order to improve their water solubility, the deprotection of 1‐glucopyranosyl‐4‐heterocyclic‐5‐heteroaryl‐1,2,3‐triazole was carried out. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:242–247, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10023     

RIBLL中的TOF测量

描述了一种为兰州放射性核束流线(AIBLL)研制的时间拾取装置.次级束引起闪烁薄膜发光,椭球面镜聚焦,光电倍增管读出,CAMACTDC记录次级束的飞行时间.其时间分辨可以达到140ps,计数率可以达到10⁸pps.