Values Of Complexation Constants Research Articles

Synthesis, Characterization and Biological Application of Pyrazolo[1,5-a]pyrimidine Based Organometallic Re(I) Complexes

The neutral rhenium(I) complexes (I-VI) of type [ReCl(CO)3Ln-] where L1 = 7-phenyl-5-(pyridin-2-yl)pyrazolo[1,5-a]pyrimidine, L2 = 7-(4-bromophenyl)-5-(pyridin-2-yl)pyrazolo[1,5-a]pyrimi- dine, L3 = 7-(4-chlorophenyl)-5-(pyridin-2-yl)pyrazolo[1,5-a]pyrimidine, L4 = 7-(2-chlorophenyl) -5-(pyridin-2-yl)pyrazolo[1,5-a]pyrimidine, L5 = 7-(4-methoxyphenyl)-5-(pyridin-2-yl)pyrazolo [1,5-a]pyrimidine, L6 = 5-(pyridin-2-yl)-7-(p-tolyl)pyrazolo[1,5-a]pyrimidine were synthesized and characterized by 13C-APT, 1H-NMR, IR, electronic spectra, magnetic moment and conductance measurement. The anti-proliferative activity on HCT116 cells by MTT assay suggests potent cytotoxic nature of complexes, even some complexes have better activity than standard drug cisplatin, oxaliplatin, and carboplatin. The complexes found to have better antimicrobial activity compare to pyrazolo pyrimidine ligands. The theoretical study of compounds-DNA interactions was examined by molecular docking as a supportive tool to the experimental data, which suggests the groove mode of binding. The values of docking energy for compounds-DNA interaction were found in the range of -230.31 to -288.34 kJ/mol. The intrinsic binding constant values of complexes (1.1-3.5×105 M-1) were found higher than the ligands (0.32-1.8×105 M-1).

Thermodynamic equilibrium constants for important isosaccharinate reactions: A review

Isosaccharinic acid is a cellulose degradation product that can form in low-level nuclear waste repositories and is known to form strong complexes with many elements, including actinides, disposed of in these repositories. We 1) reviewed the available data for deprotonation and lactonisation constants of isosaccharinic acid, and the isosaccharinate binding constants for Ca, Fe(III), Th, U(IV), U(VI), Np(IV), Pu(IV), and Am(III), 2) summarized complexation constant values for predicting actinide behavior in geologic repositories in the presence of isosaccharinate, and 3) outlined additional studies to acquire reliable thermodynamic data where the available data are inadequate.

Fluorescence Quenching Determination of Uranium (VI) Binding Properties by Two Functional Proteins: Acetylcholinesterase (AChE) and Vitellogenin (Vtg).

The interactions between uranium and two functional proteins (AChE and Vtg) were investigated using fluorescence quenching measurements. The combined use of a microplate spectrofluorometer and logarithmic additions of uranium into protein solutions allowed us to define the fluorescence quenching over a wide range of [U]/[Pi] ratios (from 1 to 3235) at physiologically relevant conditions of pH. Results showed that fluorescence from the two functional proteins was quenched by UO2 (2+). Stoichiometry reactions, fluorescence quenching mechanisms and complexing properties of proteins, i.e. binding constants and binding sites densities, were determined using classic fluorescence quenching methods and curve-fitting software (PROSECE). It was demonstrated that in our test conditions, the protein complexation by uranium could be simulated by two specific sites (L1 and L2). The obtained complexation constant values are log K1 = 5.7 (±1.0), log K2 = 4.9 (±1.1); L1 = 83 (±2), L2 = 2220 (±150) for U(VI) - Vtg and log K1 = 8.1 (±0.9), log K2 = 6.6 (±0.5), L1 = 115 (±16), L2 = 530 (±23) for U(VI)-AChE (Li is expressed in mol/mol of protein).

Determination of thermodynamic values of acidic dissociation constants and complexation constants of profens and their utilization for optimization of separation conditions by Simul 5 Complex

In this paper we determine acid dissociation constants, limiting ionic mobilities, complexation constants with β-cyclodextrin or heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, and mobilities of resulting complexes of profens, using capillary zone electrophoresis and affinity capillary electrophoresis. Complexation parameters are determined for both neutral and fully charged forms of profens and further corrected for actual ionic strength and variable viscosity in order to obtain thermodynamic values of complexation constants. The accuracy of obtained complexation parameters is verified by multidimensional nonlinear regression of affinity capillary electrophoretic data, which provides the acid dissociation and complexation parameters within one set of measurements, and by NMR technique. A good agreement among all discussed methods was obtained. Determined complexation parameters were used as input parameters for simulations of electrophoretic separation of profens by Simul 5 Complex. An excellent agreement of experimental and simulated results was achieved in terms of positions, shapes, and amplitudes of analyte peaks, confirming the applicability of Simul 5 Complex to complex systems, and accuracy of obtained physical–chemical constants. Simultaneously, we were able to demonstrate the influence of electromigration dispersion on the separation efficiency, which is not possible using the common theoretical approaches, and predict the electromigration order reversals of profen peaks. We have shown that determined acid dissociation and complexation parameters in combination with tool Simul 5 Complex software can be used for optimization of separation conditions in capillary electrophoresis.

Electrochemical assessment of water|ionic liquid biphasic systems towards cesium extraction from nuclear waste

A room temperature ionic liquid (IL) composed of a quaternary alkylphosphonium (trihexyltetradecylphosphonium, P66614+) and tetrakis(pentafluorophenyl)borate anion (TB−) was employed within a water|P66614TB (w|P66614TB or w|IL) biphasic system to evaluate cesium ion extraction in comparison to that with a traditional water|organic solvent (w|o) combination. 137Cs is a major contributor to the radioactivity of spent nuclear fuel as it leaves the reactor, and its extraction efficiency is therefore of considerable importance. The extraction was facilitated by the ligand octyl(phenyl)-N,N′-diisobutylcarbamoylphosphine oxide (CMPO) used in TRans-Uranium EXtraction processes and investigated through well established liquid|liquid electrochemistry. This study gave access to the metal ion to ligand (1:n) stoichiometry and overall complexation constant, β, of the interfacial complexation reaction which were determined to be 1:3 and 1.6×1011 at the w|P66614TB interface while the study at w|o elicited an n equal to 1 with β equal to 86.5. Through a straightforward relationship, these complexation constant values were converted to distribution coefficients, δα, with the ligand concentrations studied for comparison to other studies present in the literature; the w|o and w|IL systems gave δα of 2 and 8.2×107, respectively, indicating a higher overall extraction efficiency for the latter. For the w|o system, the metal ion-ligand stoichiometries were confirmed through isotopic distribution analysis of mass spectra obtained by the direct injection of an emulsified water–organic solvent mixture into an electron spray ionization mass spectrometer.

Determinations of Uranium(VI) Binding Properties with some Metalloproteins (Transferrin, Albumin, Metallothionein and Ferritin) by Fluorescence Quenching

The interactions between uranium and four metalloproteins (Apo-HTf, HSA, MT and Apo-EqSF) were investigated using fluorescence quenching measurements. The combined use of a microplate spectrofluorometer and logarithmic additions of uranium into protein solutions allowed us to define the fluorescence quenching over a wide range of [U]/[Pi] ratios (from 0.05 to 1150) at physiologically relevant conditions of pH. Results showed that fluorescence from the four metalloproteins was quenched by UO(2)(2+). Stoichiometry reactions, fluorescence quenching mechanisms and complexing properties of metalloproteins, i.e. binding constants and binding sites densities, were determined using classic fluorescence quenching methods and curve-fitting software (PROSECE). It was demonstrated that in our test conditions, the metalloprotein complexation by uranium could be simulated by two specific sites (L(1) and L(2)). Results showed that the U(VI)-Apo-HTf complexation constant values (log K(1)=7.7, log K(2)=4.6) were slightly higher than those observed for U(VI)-HSA complex (log K(1)=6.1, log K(2)=4.8), U(VI)-MT complex (log K(1)=6.5, log K(2)=5.6) and U(VI)-Apo-EqsF complex (log K(1)=5.3, log K(2)=3.9). PROSECE fitting studies also showed that the complexing capacities of each protein were different: 550 moles of U(VI) are complexed by Apo-EqSF while only 28, 10 and 5 moles of U(VI) are complexed by Apo-HTf, HSA and MT, respectively.

Complexation of Pinosylvin, an Analogue of Resveratrol with High Antifungal and Antimicrobial Activity, by Different Types of Cyclodextrins

The complexation of pinosylvin, a potent antimicrobial and antifungal stilbenoid, by cyclodextrins (CDs) is described for first time in this work. Steady-state fluorescence was used to demonstrate that natural (alpha-, beta-, and gamma-CD) and modified (HP-beta-CD, methyl-beta-CD, and ethyl-beta-CD) CDs are able to complex pinosylvin following a 1:1 stoichiometry. However, substantial differences in the strength of the complexation exist between the CDs tested. Although among natural CDs the interaction of pinosylvin with beta-CD was more efficient than with alpha- and gamma-CD, the results show that the complexation constants (K(F)) were higher for all of the modified CDs than for natural CDs, the highest K(F) being that determined for HP-beta-CD-pinosylvin complexes (12112 +/- 761 M(-1)). Moreover, deprotonation of the hydroxyl group of pinosylvin led to a sharp fall in the K(F) values with respect to those observed for the complexes formed between the protonated structure of this stilbenoid and the CDs. Moreover, a pK(a) value is reported for the first time for pinosylvin. Furthermore, when the temperature of the system was increased, a significant drop was observed in the complexation constant values. From these K(F) values and to throw light on the mechanism of pinosylvin affinity for HP-beta-CD, three thermodynamic parameters, DeltaH degrees , DeltaS degrees , and DeltaG degrees , were calculated. The results show that the complexation of pinosylvin by HP-beta-CD is a spontaneous and exothermic process with negative values for entropy changes. Finally, to gain information on the effect of the structure of different compounds belonging to the stilbenoid family on the K(F) values, the complexation of other molecules such as (E)-resveratrol and pterostilbene was studied and compared with the results obtained for the HP-beta-CD-pinosylvin complexes.

Thermodynamic Model for ThO2(am) Solubility in Alkaline Silica Solutions

No thermodynamic data for Th complexes with aqueous Si are available. To obtain such data, extensive studies on ThO2(am) solubility were carried out as functions of: (1) a wide range of aqueous silica concentrations (0.0004 to 0.14 mol⋅L−1) at fixed pH values of about 10, 11, 12, and 13; and (2) and variable pH (ranging from 10 to 13.3) at fixed aqueous Si concentrations of about 0.006 mol⋅L−1 or 0.018 mol⋅L−1. The samples were equilibrated over long periods (ranging up to 487 days), and the data showed that steady-state concentrations were reached in 10. The data were interpreted using both the Pitzer and SIT models, and required only the inclusion of one mixed-hydroxy-silica complex of Th [Th(OH)3(H3SiO4) 3 2− ]. Both models provided similar complexation constant values for the formation of this species. Density functional theory calculations predict complexes of this stoichiometry, having six-fold coordination of the Th cation, to be structurally stable. Predictions based on the fitted value of log 10 K 0=−18.5±0.7 for the ThO2(am) solubility reaction involving Th(OH)3(H3SiO4) 3 2− [ThO2(am)+3H4SiO4+H2O↔Th(OH)3(H3SiO4) 3 2− +2H+], along with the thermodynamic data for aqueous Si species reported in the literature, agreed closely with the extensive experimental data and showed that under alkaline conditions aqueous Si makes very strong complexes with Th.

Preparation and Characterization of the Inclusion Complex of Chlorpyrifos in Cyclodextrins To Improve Insecticide Formulations

The chemical control of crops by organophosphate insecticide treatment is usually limited because the insecticides do not maintain their efficiency for long periods for several reasons, including environmental conditions or rapid degradation of the active ingredient. Chlorpyrifos is an organophosphate insecticide used worldwide to control a variety of soil insects and arthropods in a wide range of crops. It is easily soluble in organic solvents but shows poor water solubility. The inclusion of chrorpyrifos in cyclodextrins (CDs) improves its water solubility, bioavailability, and insecticidal activity and helps prevent overdosing, leading to more cost-effective and more environmentally friendly agricultural practices. Solubility studies of chlorpyrifos in the presence of different types of CDs show G2-beta-CDs to be the most effective CDs in the complexation process, giving 1:2 complexes, with complexation constant (Kc) values of 12.34 +/- 3.1 M(-1) for K1 and 3895 +/- 183 M(-1) for K2. These complexation constant values were corroborated by applying a fluorimetric method.

Metal Ion Distribution Between Water and River Sediment: Speciation Model and Spectroscopic Validation

Natural sediments show sequestering properties that can lead to a process of self-purification of aquatic environment from metal pollution. The study of the interaction between metal ions and sediment particles enhances what is known about the distribution and bioavailability of heavy metals in natural systems. Our contribution concerns the characterisation of the sequestering ability of a River Po sediment with regard to calcium(II), magnesium(II), cadmium(II), nickel(II) and copper(II), in fixed experimental conditions, through pH-metric and spectrometric measurements. A batch titration procedure was adopted and, in each solution, after equilibration, both pH and pM (M = Ca(II), Mg(II), Cd(II), Ni(II), Cu(II)) (via Inductively Coupled Plasma - Optical Emission Spectroscopy, ICP-OES) values were measured. The experimental data were first processed with a specific software to evaluate the concentration and protonation constants of the sediment ligand site(s). The speciation model was then assessed, together with the values of complexation constants, for the different sediment/metal cation systems. In order to better characterise the copper(II)-sediment interaction and to obtain more information about the nature of ligand site(s) involved, EPR (Electronic Paramagnetic Resonance) measurements were also made on the dry sediment before and after reaction with copper(II) ions.

Effect of hydroxypropyl beta cyclodextrin complexation on aqueous solubility, stability, and corneal permeation of acyl ester prodrugs of ganciclovir.

The purpose of the study was to investigate the effect of hydroxypropyl beta cyclodextrin (HPbetaCD) on aqueous solubility, stability, and in vitro corneal permeation of acyl ester prodrugs of ganciclovir (GCV). Aqueous solubility and stability of acyl ester prodrugs of Ganciclovir (GCV) were evaluated in pH 7.4 isotonic phosphate buffer solution (IPBS) in the presence and absence of HPbetaCD. Butyryl cholinesterase-mediated enzymatic hydrolysis of the GCV prodrugs was studied using various percentage w/v HPbetaCD. In vitro corneal permeation of GCV and its prodrugs (with and without 5% HPbetaCD) across isolated rabbit cornea was studied using side-by-side diffusion cells. HPbetaCD-prodrug complexation was of the A(L) type with values for complexation constants ranging between 12 and 108 M(-1). Considerable improvement in chemical and enzymatic stability of the GCV prodrugs was observed in the presence of HPbetaCD. The stabilizing effect of HPbetaCD was found to depend on the degree of complexation and the degradation rate of prodrug within the complex. Five percent w/v HPbetaCD was found to enhance the corneal permeation of only the most lipophilic prodrug GCV dibutyrate (2.5-fold compared with 0% HPbetaCD). All other prodrugs showed little or no difference in transport in the presence of 5% w/v HPbetaCD. Agitation in the donor chamber largely influenced the transport kinetics of GCV dibutyrate across cornea. Results indicate the presence of an unstirred aqueous diffusion layer at the corneal surface that restricts the transport of the highly lipophilic GCV dibutyrate prodrug. HPbetaCD improves corneal permeation by solubilizing the hydrophobic prodrug and delivering it across the mucin layer at the corneal surface.

LiBr · 2H2O Crystallization Inhibition in the Presence of Additives

Experiments have been performed to measure the effect of additives on the crystallization temperature of concentrated LiBr solutions cooled at a rate of 20°C/h. The measured crystallization temperatures correspond not to the temperatures of equilibrium solubility but to the critical temperature for heterogeneous nucleation of the hydrated LiBr salt on the glass wall of the test tube containing the sample solution. Various additives at concentrations from 250 to 1500 ppm have been investigated. Some soluble additives further decreased the experimental crystallization temperature by as much as 13°C, corresponding to 22°C below the equilibrium solubility. Large decreases in the crystallization temperature can be correlated with large values of complexation constants of the additive for either the Li+ or the Br− ion in solution. Solution complexation, however, is not sufficient to explain the magnitude of the decrease in the crystallization temperature. The only phenomenon capable of quantitatively explaining the magnitude of the decrease in the crystallization temperature is the change in the crystal/solution interfacial energy due to adsorption of the additive on the surface of the prenucleation embryos. A quantitative model of the crystal/solution interfacial energy due to adsorption has been developed using both the Langmuir and Gibbs adsorption equations, allowing the quantitative prediction of crystallization temperatures with additive concentration.

Capillary electrophoretic study of the complexation of nucleotides with magnesium and calcium ions

The complexation equilibrium between nucleotides (ATP, ADP) and inorganic cations (Mg2+, Ca2+) has been studied by capillary electrophoresis. The equilibrium constant and the stoichiometry of nucleotide-inorganic cation complexes can be deduced from the dependence of the electrophoretic mobility of each nucleotide on the negative logarithm of the inorganic cation concentration. The experimental values of complexation constants determined by CE compare favorably with those in the literature. As expected, Mg2+ forms more stable complexes with ATP (logK=2.30 and 4.10 at pH 5 and 8, respectively) than with ADP (logK=1.92 and 3.15 at pH 5 and 8, respectively). In the pH range 4–8, the stoichiometry of ADP-Mg2+ and ADP-Ca2+ complexes is always 1∶1 whereas that of the complexes between these cations and ATP depends on pH-hence ATP-Mg2+ and ATP-Ca2+ complexes have 1∶1 stoichiometry at pH 5 and 1∶2 at pH 8.

New phenol-containing bis(azacrown ether)s: synthesis and complexing properties

A simple synthesis of phenol-containing bis(azacrown ethers) by the treatment of N-methoxymethyl-substituted azacrowns with phenols has been elaborated. Temperature conditions have been found for selectively introducing into one phenolic ring both one and two monoazacrown ether substituents. New symmetric 14a–e and asymmetric 15 phenol-bridged bis(azacrown ether)s exhibited strong complexation abilities towards both alkali and especially alkaline-earth metal cations. All measurements have been carried out using the pH-metric titration technique. Complexation constant values in neutral (K1) and in alkaline (K2) media are in the order: monocyclic 1b–d K1. These results show participation of phenolic ions in the complex formation process. In an alkaline medium, bis(azacrown ether)s 14b, 14e and 14d showed high selectivity towards Li+, Ba+2 and Sr+2, respectively.

Crowns in alkali alkoxide-conjugate acid solutions: A remarkably low propensity to complex formation

Complexing ability of the macrocyclic polyethers 18-crown-6, 15-crown-5 and 12-crown-4 has been investigated ebulliometrically in the homologous series of 0.6 molal ROM-ROH solutions (M = K, Na, Li; R = H, CH3, C2H5, n-C3H7, i-C3H7, t-C4H9). The values of complexation constants have been estimated in all the 54 crown-ROM combinations and the effects of cation, crown-cavity size and solvent have been examined. Two intriguing facts emerged from a comparison of the new results with the pertinent literature data. Firstly, it was found that the cation-crown cavity-complex stability variation in the ROM-ROH series disagrees with the well-known principle of steric match, the propensity of crowns to complexation decreasing in most instances in the order 15-crown-5 > 12-crown-4 > 18-crown-6 for the potassium and 12-crown-4 > 15-crown-5 > 18-crown-6 for the sodium alkoxide. An energetical preference of 2 : 1 over 1 : 1 crown-ROM complexes is presumably the responsible factor. Secondly, and even more importantly, it was found that complexation constants obtained in this study are strikingly small, the values for complexation of potassium and sodium alkoxides with 18-crown-6 being smaller by 3-7 power of ten than those which were previously obtained for the alkali ions, at lower concentrations. Evidence is provided that the difference does not originate from ion-pairing but from the operation of some effect which so far escaped notice.

Evaluation of stability constants of complexes from irreversible polarographic waves

A general equation of the totally irreversible complex reduction polarographic wave is derived by a simple method. The partial derivatives of this equation (at constant ligand concentration, constant potential and constant relative current) are useful for determination of the electrode mechanism. The mechanism developed considerably simplifies the general equation. A possibility of obtaining the values of complexation constants from the half-wave potential differences for two main types of electrode mechanism is discussed. The effect of the ψ 2 potential in the electrode double layer is also discussed.