Search results for " complex"
showing 10 items of 3391 documents
Complex formation equilibria between the acetazolamide ((5-acetamido-1,3,4-thiadiazole)-2-sulphonamide), a potent inhibitor of carbonicanhydrase, and…
1990
Abstract The stability constants for the equilibrium of complexation between acetazolamide and the divalent metal ions copper(II), nickel(II), zinc(II), and cobalt(II) have been determined by potentiometry both in water and in water-ethanol 50 vol. % solutions in 0.15 mol dm −3 NaNO 3 at 25°C. This mixed solvent has been used in order to obtain higher concentrations of acetazolamide in solution. For copper(II) and nickel(II), the binuclear species [Cu 2 (Acm) 2 ] and [Ni 2 (Acm) 3 ] 2− are detected in both solvents together with hydroxo species. The values of the stability constants are always higher in the mixed solvent than in water. For cobalt(II) and zinc(II), while in aqueous solution …
Speciation of low molecular weight ligands in natural fluids: protonation constants and association of open chain polyamines with the major component…
2000
Abstract The interaction of five open chain polyamines (ethylenediamine (en), diethylenetriamine (dien), trietylenetetramine (trien), tetraethylenepentamine (tetren), spermine (sper)) with the major components of seawater was studied potentiometrically at 25°C, in an artificial seawater (containing Na+, K+, Mg2+, Ca2+, Cl− and SO42−) at different salinities (5–45‰). Potentiometric data were interpreted in terms of both the apparent protonation constants of polyamines and the formation constants of complexes formed by unprotonated or protonated amines and the cation and the anion of seawater (the inorganic content of seawater being considered as a single 1:1 salt). Some empirical relationshi…
Single Molecule Spectroscopy of Oriented Recombinant Trimeric Light Harvesting Complexes of Higher Plants
2002
The bleaching dynamics of reconstituted single light-harvesting chlorophyll a/b investigated. The complexes containing one histidine6 tag per monomeric subunit were immobilised predominantly in a defined orientation with their symmetry axis perpendicular to a Ni-ion-containing surface allowing for the first time the examination of single LHCIIb in an aqueous environment. Most complexes exhibit photobleaching in one step, indicating coupling between the monomeric subunits leading to an energy transfer between adjacent subunits. Differences in bleaching behaviour between these and previous observations with single LHCIIb are discussed.
Spectroscopic study of molecular associations between riboflavin and some (dihydro) β-carboline derivatives
1993
Abstract The spectrophotometric and thermodynamic properties of molecular complexes of riboflavin (RFN) with some dihydro β-carboline derivatives have been investigated by using electronic absorption and fluorescence spectroscopic methods in aqueous solution. The molecular associations have been examined by means of eletronic absorption spectra, since in each, a new charge transfer-like band has been located, and also by observing the variation of the fluorescence emission of RFN on the solutions. The formation constants for the molecular complexes were determined from absorption data, using the Forster—Hammick—Wardley method. The quenching phenomenon observed in RFN fluorescence is related…
DFT computational study on Fe(III)-N,N′-ethylene-bis(salicylideneiminato) derivatives
2005
DFT calculations, at unrestricted B3LYP level, have been performed on the structures of three iron(III) complexes, Fe(Salen)Cl, [Fe(Salen)]+ and [Fe(Salen)OH2]+, where Salen is the anion of Schiff base ligand N,N′-ethylene-bis (salicylideneimine), considering the spin multiplicity (S) values 2, 4 and 6. The results obtained have been compared with the available structural an magnetic experimental data, allowing us to conclude that a stable form of the FeIII(Salen) complex in aqueous solution should be characterized by an energy stabilization of the S=4 compared to the S=6 state.
Uranium(VI) sequestration by polyacrylic and fulvic acids in aqueous solution
2011
Stability data on the formation of dioxouranium(VI) species with polyacrylic (PAA) and fulvic acids (FA) are reported with the aim to define quantitatively the sequestering capacity of these high molecular weight synthetic and naturally occurring ligands toward uranium(VI), in aqueous solution. Investigations were carried out at t = 25 °C in NaCl medium at different ionic strengths and in absence of supporting electrolyte for uranyl–fulvate (\( {{\text{UO}}_{2}}^{2+} \)–FA) and uranyl–polyacrylate (\( {{\text{UO}}_{ 2}}^{ 2+ } \)–PAA, PAA MW 2 kDa) systems, respectively. The experimental data are consistent with the following speciation models for the two systems investigated: (i) UO2(FA1),…
Ti(iv)-amino triphenolate complexes as effective catalysts for sulfoxidation
2010
C 3 -symmetric Ti (IV) amino triphenolate complexes efficiently catalyze, without previous activation and in excellent yields, the oxidation of sulfides at room temperature, using both CHP and the more environment friendly aqueous hydrogen peroxide as terminal oxidants, with catalyst loadings down to 0.01%. The Ti(IV) catalysts and the intermediate Ti(IV)-peroxo complexes have been characterized in solution by 1H NMR and ESI-MS techniques and via density functional studies.
Machine learning for rapid mapping of archaeological structures made of dry stones – Example of burial monuments from the Khirgisuur culture, Mongoli…
2020
11 pages; International audience; The present study proposes a workflow to extract from orthomosaics the enormous amount of dry stones used by past societies to construct funeral complexes in the Mongolian steppes. Several different machine learning algorithms for binary pixel classification (i.e. stone vs non-stone) were evaluated. Input features were extracted from high-resolution orthomosaics and digital elevation models (both derived from aerial imaging). Comparative analysis used two colour spaces (RGB and HSV), texture features (contrast, homogeneity and entropy raster maps), and the topographic position index, combined with nine supervised learning algorithms (nearest centroid, naive…
Social differentiation and land use at an Early Iron Age “princely seat”: bioarchaeological investigations at the Glauberg (Germany)
2014
Excavations at the late Hallstatt/early La Tene (6th–4th century BC) “princely seat” of the Glauberg (Hesse, Germany) revealed exceptionally furnished graves in monumental mounds, simple inhumations in associated ditches and non-normative burials of up to eight individuals in conical storage pits. The study presented here addresses bioarchaeological characteristics of these burials and their implications for social differentiation and the sphere of influence of the “princely seat”. It includes osteological, aDNA, and multi-isotope analyses of 27 human individuals and faunal remains. One of the outstandingly rich graves (tumulus 1/grave 1) contained the skeleton of a young man (the “prince”)…
Ivory in the Chalcolithic enclosure of Perdigões (South Portugal): the social role of an exotic raw material
2015
AbstractThis article discusses the social role played by ivory and ivory articles in the Perdigoes enclosures (South Portugal) during the Chalcolithic (third millennium bc), in the context of the emergence and development of social complexity on the Iberian Peninsula. Perdigoes is a Portuguese prehistoric site with some of the highest concentrations of ivory objects known in Iberia and with the greatest variety. The contexts, almost exclusively funerary, are discussed along with the results of provenance studies. Comparing the different contexts and the categories of objects made of ivory makes it possible to distinguishing a variety of active social dimensions (such as individual status, g…