Search results for "Constants"
showing 10 items of 150 documents
Chemical speciation of organic matter in natural waters. Interaction of nucleotide 5′ mono-, di- and triphosphates with major components of seawater
2004
AbstractThe interactions of nucleotide 5’ mono-, di- and triphosphates in a multicomponent ionic medium simulating the macro-composition of seawater (Na+, K+, Ca2+, Mg2+, Cl-, SO42-, Synthetic Sea Water, SSW) have been investigated at different ionic strengths and at T= 25°C. A chemical speciation model, according to which all the internal interactions between the components of the ionic medium are taken into account, was applied to determine the effective formation constants of species in the nucleotide-seawater system. The results were compared to protonation parameters calculated from single electrolyte systems. A simpler model (SSW considered as a single salt BA, with Bz+ and Az-), repr…
Equilibrium studies in natural fluids: interactions of -PO43−, -P2O74−and -P3O105−with the major constituents of sea water
1998
AbstractThe interaction of PiO(i+2)−(3i+1) (i = 1,2,3) with the major components of seawater has been studied potentiometrically, at 25°C, in an artificial seawater (Na+, K, Ca2+, Mg2+, Cl− and SO42−) at different salinities (5—45%o). Apparent protonation constants have been calculated, from potentiometric data, and estimated, using an appropriate complex formation model. Formation constants of complexes formed by phosphates and the cation of seawater (the inorganic content of seawater being considered as a single 1:1 salt) have been determined. The comparison between experimental and estimated results showed that a suitable complexation model can be used with a fairly good accuracy in pred…
Calorimetric investigation of the complex formation between surfactants and α-, β- and γ-cyclodextrins
1992
Abstract A calorimetric technique has been used to study complex formation between α-, β- and γ-cyclodextrins (αCD, βCD and γCD) and some surfactants (sodium dodecylsulphate (SDS), hexadecyl trimethylammonium bromide (CTAB) and p-(1,1,3,3-tetramethylbutyl) phenoxypoly(oxyethyleneglycol) (Triton X-100)). The experimental data indicate that some complexes (SDS-αCD, SDS-βCD and CTAB-αCD) are very stable and allow direct determination of their stoichiometry and molar enthalpy of complex formation. Those for other complexes closely fit a model based on an equilibrium reaction between surfactant, cyclodextrin and a single complex. According to the model, data analysis allows determination of the …
Binding properties of mono-(6-deoxy-6-amino)-β-cyclodextrin towards p-nitroaniline derivatives: a polarimetric study
2009
Abstract Polarimetry was used in order to investigate the formation of supramolecular complexes between mono-6-amino-β-cyclodextrin and various p-nitroaniline derivatives at two different pH values. Comparison with the behaviour of native β-cyclodextrin gave us the opportunity to consider the effect exerted by the presence of charged groups, having different solvation requirements, on the binding equilibrium. Data offer some support to the hypothesis of ‘dynamic co-inclusion’ of solvent molecules within the host–guest complex.
Study on the synthesis of novel 5-substituted 2-[2-(pyridyl)ethenyl]-1,3,4-oxadiazoles and their acid–base interactions
2014
Abstract A series of novel 5-substituted 2-[2-(pyridyl)ethenyl]-1,3,4-oxadiazoles were efficiently synthesized by cyclocondensation of the appropriate 3-(pyridyl)acrylohydrazides with triethyl orthoesters in the presence of glacial acetic acid. The products were identified by means of spectroscopic methods and their pKA ionization constants were determined. The influence of substituents on the basicity of the pyridine system has been discussed. Graphical Abstract
Polymer supported synthesis of mixed ligand complexes
2003
A series of novel polymer-supported mixed ligand complexes were synthesized and studied. Two percent divinyl benzene (DVB)-crosslinked polystyrene supports were synthesized by the suspension copolymerization technique. An ethylene diamine group was anchored onto the support and the corresponding copper complexes were prepared. The ligating functions like phthalate, acetate, and oxalate groups were introduced, and mixed ligands complexes were synthesized. The resultant polymer supported mixed ligand complexes were characterized by UV-Vis, IR, and EPR methods. The stability constants dictate the formation of these complexes on polymer support. Spectral results gave information about the struc…
Cyclic Analogs of Desferrioxamine E Siderophore for 68Ga Nuclear Imaging: Coordination Chemistry and Biological Activity in Staphylococcus aureus
2021
As multidrug-resistant bacteria are an emerging problem and threat to humanity, novel strategies for treatment and diagnostics are actively sought. We aim to utilize siderophores, iron-specific strong chelating agents produced by microbes, as gallium ion carriers for diagnosis, applying that Fe(III) can be successfully replaced by Ga(III) without losing biological properties of the investigated complex, which allows molecular imaging by positron emission tomography (PET). Here, we report synthesis, full solution chemistry, thermodynamic characterization, and the preliminary biological evaluation of biomimetic derivatives (FOX) of desferrioxamine E (FOXE) siderophore, radiolabeled with 68Ga …
Complexation of phosphine ligands with peracetylated β-cyclodextrin in supercritical carbon dioxide: spectroscopic determination of equilibrium const…
2007
The interaction between peracetylated beta-cyclodextrin and several triphenyl phosphine derivatives was studied in supercritical carbon dioxide (scCO2) by UV-visible spectroscopy. The equilibrium constant for a 1:1 complexation reaction was obtained from titration spectra and calculated using two established mathematical models. The values of the equilibrium constants are 1-3 orders of magnitude smaller than those obtained in aqueous solution with analogous phosphines. This is likely due to the absence in scCO2 of the hydrophobic effect, which is replaced by a corresponding, but weaker, CO2-phobic effect. The largest value of Kf was found for complexes of diphenyl(4-adamantylphenyl)phosphin…
Review: Solution equilibria of ternary complexes formed from copper(II), aliphatic amines, and bioligands
2014
This review provides a summary of the coordination chemistry of ligands in the ternary system: copper(II)–aliphatic amine–bioligand, where amine = ethylenediamine – En, diethylenetriamine – Dien, or N, N, N′, N″, N″-pentamethyldiethylenetriamine – Me5dien, and bioligand = selected amino acid, aminohydroxamic acid, or aminophosphonic acid, in aqueous solution. We would like to show the specific interactions of copper(II) in ternary systems in the context of complex equilibria chemistry.
A Novel Zeolite-Induced Population of a Planar Viologen Conformation. New Viologen Charge Transfer Complexes and Alkene/Viologen/Zeolite Arrays
2004
A rare example of a novel zeolite-induced conformational change and a mechanism for this process are suggested in order to rationalize an unexpected spontaneous intrazeolite reduction observed during preparation of a new viologen (MQ2+)-doped zeolite (NaY). In addition, the formations of six new alkene/viologen/ zeolite charge transfer (CT) arrays using NaMQY and the previously reported NaMVY are also reported. The binding constants between MQ2+ and MV2+ and 2,3-dimethyl-2-butene (TME) were determined using the Benesi-Hildebrand approach, and the stabilities of these CT complexes are compared to their intrazeolite analogue.