Search results for "visual_art"

Combretastatin Analogs via Hydration of Stilbene Derivatives

1993

Hydration of the double bond of some stilbene congeners of Picea abies bark by TiCl4·NaBH4 reagent is described. Five racemic 1,2-diphenylethanol derivatives (9–13), structurally related to (R)-(·)-combretastatin [(R)-1], have been obtained and characterized mainly by 13C- and 1H-NMR as well as mass spectrometry. The antileukemic activity of each compound has preliminarily been tested by the mouse leukemia L1210 system. Compound 10 has been synthesized by Friedel-Crafts acylation.

Effect of Processing Conditions on the Degradation and on the Recycling of Polycarbonate

2003

Polycarbonate, like other polycondensation polymers, can be easily recycled without significant loss of properties only with careful drying. Indeed, the presence of humidity strongly decreases the molecular weight of the polymer by hydrolytic chain scission. In this paper, the degradation and the recycling of an extrusion grade polycarbonate sample has been investigated considering mainly the effect of the humidity. Some degradation is observed also for the material reprocessed in dry conditions and due to the thermomechanical stress acting on the melt. The chain scission is strongly reduced if the processing is carried out under nitrogen flow. In these conditions less degradation effects …

Self-organized nanostructures of poly(4-vinylpyridine), polyaniline and polyamides due to metal complexation

2002

Comb-shaped supramolecules are constructed using flexible polymers and semi-rigid conjugated undoped or doped conjugated polymers upon complexing Zinc dodecyl benzene sulphonate, Zn(DBS) 2 . Self-organized nanostructures are formed in the bulk due to competing attractive interactions (coordination or water mediated hydrogen bonding) and repulsive polar/nonpolar interactions, showing characteristic long periods of ca. 30 A.

Mechanical Behavior of Concrete Columns Confined by Laterally Pre-Tensioned FRP

2011

This paper presents the results of an experimental investigation of concrete columns confined by a wound pre-tensioned carbon filament yarn. Yarn winding equipment was developed in the Institute of Polymer Mechanics with the ability to set the desired pre-tension force and thereby producing confined concrete specimens with different initial lateral pressure. It is shown that initial lateral pressure increases the axial stress at which intense internal cracking of the concrete develops.

Bimetallic cyanide-bridged complexes based on the photochromic nitroprusside anion and paramagnetic metal complexes

2001

Abstract Three novel compounds formed by the photochromic nitroprusside anion, [Fe(CN)5NO]2−, and the paramagnetic complexes [Cu(C19H18N6)]2+, [Ni(C6H14N2)2]2+ and [Ni(cyclam)]2+ are reported. The structure of [Cu(C19H18N6)][Fe(CN)5NO] (1) comprises binuclear complexes with a [Fe(CN)5NO]2− anion linked to a [Cu(C19H18N6)]2+ cation. The structure of [Ni(C6H14N2)2][Fe(CN)5NO]·6.5H2O (2) and [Ni(cyclam)][Fe(CN)5NO]·4H2O (3) consists of zigzag chains formed by an alternate array of the paramagnetic cations and [Fe(CN)5NO]2− anions. The three compounds are paramagnets; a fourth compound containing [cis-Ni(en)2]2+ cations and [Fe(CN)5NO]− anions does not show a change in the magnetic properties a…

1990

The determination of average molecular weights and the characterization of molecular weight distributions by the ratio of the weight- to number-average molecular weights Mw/Mn from sedimentation equilibrium in the ultracentrifuge are described. The essential measurement of the density profile of the mixed solvent is conducted according to Munk (Macromolecules15, 500 (1982)). Special evaluation of the polymer band in the equilibrium allowed to deduce from the observed concentration profile Mw and Mn of a series of poly(methyl methacrylate) samples and thus to characterize the molecular weight distribution of the samples.

Copper complexes with dithiocarbamates derived from natural occurring amino acids. Crystal and molecular structure of [Cu(en)(EtOH)(H2O)3][Cu(dtc-pro…

2002

Abstract Reaction of Cu(II) salts with dithiocarbamates derived from the amino acids asparagine, glutamine, serine, threonine and tyrosine leads to reduction of the metallic cation and formation of Cu(I) complexes, whereas reaction with proline dithiocarbamate takes place without reduction, leading to formation of a Cu(II) coordination compound. Simultaneous reaction of proline dithiocarbamate and ethylenediamine with Cu(II) leads to the formation of the mixed complex [Cu(en)(EtOH)(H2O)3][Cu(dtc-pro)2]. In the anion, the Cu(II) centre possesses a D2h local symmetry, coordinated by two bidentate dithiocarbamate ligands, while the Cu(II) centre is in a distorted octahedral coordination in the…

A neutral 2D oxalate-based soluble magnet assembled by hydrogen bonding interactions

2008

Abstract Herein we describe the synthesis, structure and magnetic properties of a novel oxalate-based layered magnetic system: {[Mn(OH2)2(S)2][Mn(S)(OH2)]2[Cr(ox)3]2(18-crown-6)}∞ (S = CH3OH; ox = C 2 O 4 2 - ; 18-crown-6 = C12H24O6) (1). In this case, no cationic templating agent is required to promote the assembling of low-dimensional oxalate-bridged metallic complexes in solution. Instead, strong enough hydrogen bonding interactions are responsible for their packing in the solid state. This magnet is soluble and presents two different types of oxalate bridges: the common bis(bidentate) and the unusual bidentate–monodentate. This structural feature has drastic consequences on the magnetis…

1‑Phenyl-3-(pyrid-2-yl)benzo[e][1,2,4]triazinyl: The First "Blatter Radical" for Coordination Chemistry

2014

A neutral air- and moisture-stable N,N′-chelating radical ligand, 1-phenyl-3-(pyrid-2-yl)benzo[e][1,2,4]triazinyl (1) was synthesized and characterized by electron paramagnetic resonance spectroscopy, X-ray crystallography, and magnetic measurements. Subsequent reaction of 1 with Cu(hfac)2·2H2O (hfac = hexafluoroacetylacetonate) under ambient conditions afforded the coordination complex Cu(1)(hfac)2 in which the radical binds to the metal in a bidentate fashion. Magnetic susceptibility data collected from 1.8 to 300 K indicate a strong ferromagnetic metal-radical interaction in the complex and weak antiferromagnetic radical···radical interactions between the Cu(1)(hfac)2 units. Detailed com…

Copper complexes modelling the interaction between benzolamide and Cu-substituted carbonic anhydrase. Crystal structure of Cu(bz)(NH3)4 complex

1998

New copper benzolamide (H 2 bz, 5-phenylsulfonamide-1,3,4-thiadiazole-2-sulfonamide) complexes with ammonia, diethylentriamine (dien) and dipropylentriamine (dipn) have been prepared. The complex [Cu(bz)(NH 3 ) 4 ] crystallises in the monoclinic space group P 2 1 / n with a = 7.621(3), b = 19.91(5), c = 11.291(3) A, β = 93.17(4)° and Z = 4. The Cu(II) is five-coordinated with an almost regular square pyramidal geometry. The dideprotonated sulfonamide behaves as monodentate ligand interacting with the metal ion through the N atom of the unsubstituted sulfonamide group. In the EPR spectrum, exchange coupling between Cu(II) polyhedra of different orientations in the unit cell is observed. The …