Thermodynamic Parameters Of Complexation Research Articles

Partially Sulfated Pillar[5]arenes: Synthesis and Molecular Recognition Properties

We report the synthesis and characterization of sulfated pillar[5]arene hosts (P5S2 – P5S10) that differ in the number of sulfate substituents. All five P5Sn hosts display high solubility in water (73 – 131 mM) and do not undergo significant self‐association according to 1H NMR dilution experiments. The x‐ray crystal structures of P5S6, P5S6•Me6HDA, P5S8•Me6HDA, and P5S10•Me6HDA reveal one intracavity molecule of Me6HDA and several external molecules of Me6HDA which form a network of close methonium•••sulfate interactions. The thermodynamic parameters of complexation between P5Sn and the panel of guests was measured by direct or competitive isothermal titration calorimetry. We find that the binding free energy toward a guest becomes more negative as the number of sulfate substituents increase. Conversely, the binding free energy of a specific sulfated pillar[5]arene toward a homologous series of guests becomes more negative as the number of NMe groups increases. The ability to tune the host•guest affinity by changing the number of sulfate substituents will be valuable in supramolecular polymers, separation materials, and latching applications.

Patterns of interaction between peptides of various structures and pyrimidine nucleic bases in a buffered saline medium according to the analysis of thermodynamic parameters

Complexation of cytosine, uracil and thymine with the dipeptides glycyl-glycine, glycyl-l-phenylalanine, alanyl-l-glutamine and with the tripeptide γ-l-glutamyl-l-cysteinyl-glycine in a buffered saline has been studied using dissolution calorimetry. The values of the reaction constant, the change in Gibbs energy, enthalpy, and entropy have been found (log Kr, ΔrG, ΔrH, TΔrS). By analyzing the obtained data together with previous results for other peptides, it was found that peptides bind to pyrimidine nucleic bases in a solution in several important patterns. No pattern depending on the charge of the peptide is observed in the obtained thermodynamic values, which indicates a minor role of electrostatic interaction in their binding by the nucleic base. The effect of the structure of the peptide and the nucleobase on the thermodynamic parameters of complexation is manifested in the fine balance of the enthalpy and entropy factors of the process. The Gibbs energy of complexation depends on the number of potential H-bonding sites of the peptide, which shows the major contribution of H-bonding between the reagents. The reduction in the favorable entropy factor is responsible for the tendency of negative ΔrG values to decrease with increasing number of sites. It was found that positive values of entropy change during complex formation increase with increasing hydrophobicity index of the peptide, which is interpreted within the framework of the overlapping hydration sphere model. Strengthening the hydrophobic properties of the nucleic base from uracil to thymine due to the additional CH3 group slightly changes the enthalpy and entropy of the process of binding the +AlaGln− zwitterion but significantly affects the thermodynamic parameters of binding the anion of peptide +/−GluCysGly−.

A Comprehensive Study of Gemfibrozil Complexation with β-Cyclodextrins in Aqueous Solution Using Different Analytical Techniques

Gemfibrozil (GEM) is a hypolipidemic agent, which is effective in reducing serum cholesterol and triglyceride levels. Complexation of GEM with native β-cyclodextrin (β-CD) and with the derivatives hydroxypropyl-β- and randomly methylated β-CD (HPβ-CD and Meβ-CD) was studied in aqueous solution of pH 2.8 and 7.0. The stability constants were determined by spectrofluorimetry, 1H-NMR spectroscopy and solubility assays. Considering the well-known difficulties to obtain similar stability constants by different techniques, the agreement of the values obtained supports the reliability of the results presented. The advantages and drawbacks of each analytical technique for the study of inclusion complexation were discussed as well. In addition, the thermodynamic parameters of complexation, enthalpy (ΔH) and entropy (ΔS), were determined and related to the type of molecular interactions that take place between GEM and the different cyclodextrins. Finally, solid dispersions were prepared by co-evaporation, kneading, vacuum desiccation, and coprecipitation, and complexation was evaluated by X-ray diffraction.

Determination of Stability Constant of The Complexes of Metal Ion Fe(III), Mn(II) And Cr(III) With Some Substituted 2-Oxo-2H-Chromene-3-Carbohydrazide Derivatives at 0.1 M Ionic Strength at 42oC

Proton ligand and metal ligand stability constant are measured for Fe(III) and 1, 2-dihydroxy benzene and 1, 5-disulphonic acid complexes . Determination of stability constant of substituted of pyrazoles with rare earth metals form complexes are reported . Effect of temperature on formation constants of 2 acetylpyridine(N benzoyl)glycine hydrazone with lanthanide(III) ions at different ionic strengths are reported. Irving and Rossotti, Herson and Gilbert , Wilkins and Lewis and Rossotti and Rossotti have determined stability constant by Bjerrum-Calvin titration technique . Kabadi , Jahagirdar and Narwade have determined pK values of salicylaldehyde, salicylic acid and sulphonic acid respectively by similar procedure. The metal ligand stability constant of some β-diketones are reported . Stability constants have investigated for some substituted pyrazolines, isoxalline and diketone . The method most frequently applied for study of complex equilibria is pH-metric titration technique . Stepwise formation of mononuclear binary complexes is described by set of equilibrium constants. For pH-metric measurements an electrode must be selected. According to Bjerrum, Martell and Calvin , the formation of complex MLN is stepwise process and one has to deal with a series of equilibria of the type: Irving and Rossotti, Herson and Gilbert , Wilkins and Lewis and Rossotti and Rossotti have determined stability constant by Calvin-Bjerrum titration technique . The value of nA,n, pK, log K1 and log K2 are evaluated by Irving and Rossotti's equation. The stability constant and thermodynamic parameters of complexes containing lighter lanthanides , copper(II) , calcium and magnesium are reported. It is also important in environmental studies , medicinal and industrial chemistry . Effects of transition metal on stability constant of complexes have studied by pH metric method . Bendi , Janrao and Ramteke have studied stability constant of ligands with lanthanide metals complexes.The present work involves pH metric study of substituted 2-oxo-2H-chromene-3-carbohydrazide derivatives with metal ions Fe(III), Mn(II), Cr(III) and Ti(III) at temperature42oC. The Bjerrum-Calvin titration technique as modified by Irving and Rossotti has been employed in the present study. The following three sets of titrations are carried out in sequence.

Synthesis, structural characterization and nematicidal studies of some new N2O2 Schiff base metal complexes

ABSTRACT. Cobalt(II), copper(II), yttrium(III), zirconium(IV), lanthanum(III) and uranium(VI) complexes of 1,4-di(2-hydroxybenzylidene)thiosemicarbazide (H2L) were prepared and characterized. The proposed structures were determined from their elemental analyses, molar conductivities, magnetic moment, IR, Proton NMR, UV-Vis., mass spectra, X-ray diffraction and thermal analyses measurements. The high conductance data supply evidence for the electrolytic nature of the complexes. The changes in the selected bands in IR of Schiff base ligand upon coordination showed that Schiff base exhibits as a neutral tetradentate manner with oxygen and nitrogen donor sites. The complexes are thermally steady at room temperature and break up to two or three steps. The kinetic and thermodynamic parameters of complexes have been determined by using Coats-Redfern and Horowitz-Metzeger methods at n=1 and n≠1 and values suggest more ordered activated complex formation. The calculated bond length and force constant, F(U=O), in the uranyl complex are 1.744 Å and 664.886 Nm-1. The nematicidal activity of free Schiff base and all complexes were investigated and showed a low inhibition percentage (%I) of complexes compared with H2L.
 
 KEY WORDS: Schiff base, IR, Thermal, XRD, Nematicidal activity
 
 Bull. Chem. Soc. Ethiop. 2021, 35(2), 315-335.
 DOI: https://dx.doi.org/10.4314/bcse.v35i2.8

Synthesis, Characterization and Thermogravimetric Study of Some Metal Complexes of Selenazone Ligand Nanoparticles Analogue of Dithizone

A new method for preparing 1,5-diphenylselenocarbazone (selenazone) nanoparticles and their complexes with Pb2+, Cd2+, Co2+, and Ni2+ has been performed using hot methanol solvent. The ligand and its complexes were characterized using FT-IR, UV-Vis, 1H-NMR, 13C-NMR, X-ray powder diffraction (XRD), EI-mass spectrometry, scanning electron microscopy (SEM), HG and flame-atomic absorption spectrophotometer, thermal analysis (TG/DTA), and molar conductance measurements. The molar conductance measurements in all complexes were recorded low values in DMSO, indicating that all the metal complexes were non-electrolytes except the nickel complex that possessed an electrolytic nature. Kinetic and thermodynamic parameters of complexes (A, E, ∆H, ∆S, and ∆G) have been computed using three kinetic models of Coast-Redfern, Broido, and Horowitz-Metzger, that illustrated the decomposition reactions in all steps were nonspontaneous. Thermogravimetric analyses (TG/DTA) were consistent with the atomic spectroscopy data proving that the geometry shape of all the complexes was octahedral.

Synthesis and intensive characterization for novel Zn(II), Pd(II), Cr(III) and VO(II)-Schiff base complexes; DNA-interaction, DFT, drug-likeness and molecular docking studies

A novel bioactive series was synthesized from Zn(II), Pd(II), Cr(III) and VO(II) ions with a new Schiff base derivative (HNP) [HNP = 1-(Pyrimidin-2-yliminomethyl)-naphthalen-2-ol]. The proposed structures were defined from elemental analysis, molar conductivity, magnetic moment, IR, 1H NMR, UV-Vis, and TGA. Based on analytical and spectroscopic data, suitable geometry has been suggested for all complexes. The HNP ligand acts as a tri-dentate via NNO donors towards the metal ions inside octahedral geometry with Cr(III), square pyramidal with VO(II), tetrahedral with Zn2+ and square planner with Pd2+ ion. The kinetic and thermodynamic parameters of complexes have been determined by using Coats-Redfern method and their values suggested that the activated complexes were more ordered. The binding efficiency of the investigated complexes with calf thymus DNA (ctDNA), was examined by using different methods and the binding feature was suggested to be electrostatic, intercalation, or replacement mode. Moreover, in-vitro antimicrobial and anticancer potency of the compounds were evaluated. The new complexes showed an effective impact on decreasing cell viability of breast carcinoma cells (MCF-7) in a concentration-dependent manner. In-vitro antioxidant activity of all compounds was investigated and the results showed appreciated free radical scavenging activity of Pd(II) complex. Furthermore, Molecular docking inspection has been carried out to explain the binding affinity of the tested compounds towards breast cancer cell-protein (PDB: 3hb5)

Conductance studies on complex formation of nano Cu(NO3)2.2.5H2O with 4,6-diacetylresorcinol in mixed solvents

The different complexation thermodynamic parameters for example, formation constants (Kf), free energies of formation (∆Gf), enthalpies of formation (∆Hf) and entropies of formation (∆Sf) for nano copper nitrate hemi pentahydrate (Cu(NO3)2.2.5H2O) with 4,6-diacetylresorcinol as a ligand in pure DMF and in mixed solvents of DMF and water are calculated at different temperatures, 293.15, 303.15, 313.15 and 323.15 K by using conductance measurements. By drawing the relation between molar conductance and ratio of metal to ligand, the figures indicate the formation of two types of complexes with M:L ratios 1:2 and 1:1 stoichiometric complexes.

Two DNA binding modes of a zinc-metronidazole and biological evaluation as a potent anti-cancer agent

A complex of metronidazole (MTZ) with zinc ion was synthesized and characterized by UV-Vis, Fourier transform infrared (FT-IR), 1H-NMR, X-ray crystallography and thermal gravimetric-differential thermal analysis (TG-DTA). The cytotoxicity effect of the synthesized complex investigated over SKNMC, A549, MCF-7, and MCDK cell lines and the results have shown that it has high cytotoxic potential over cancer cell lines. In order to clarify the mechanism of cell cytotoxicity, the oxidative stress and binding of the complex to the calf thymus-DNA studied by evaluating the intrinsic binding constant and defining thermodynamic parameters of complex over the DNA accompanying with in silico molecular modeling method. For this purpose, the complex optimized at the B3LYP/LANL2DZ level and docked over the DNA structure. The results revealed that the metronidazole-zinc complex interacted with DNA via hydrogen binding and electrostatic interaction to the minor groove region and phosphate backbone of DNA, respectively.

Experimental and Theoretical Study of the Complexation of Cesium and Thallium Cations by a Water-Soluble Cryptophane

Cs (cesium) and Tl (thallium) are known to be very toxic for the environment and human health. Thus, the synthesis of molecular receptors aimed at extracting these two elements from the environment is strongly desired. In this Article, we report the synthesis of the two enantiomers of cryptophane-223(OH)$_7$ (1) and the study of their interaction with cesium and thallium cations in basic aqueous solutions. These two complexes have been studied by $^{133}$Cs and $^{205}$Tl NMR spectroscopy to reveal the complexation of the two metallic cations and by chiroptical techniques (electronic and vibrational circular dichroism) to provide valuable information about the conformational changes occurring during the binding process. The thermodynamic parameters of complexation K, $\Delta $$H^0$ and $\Delta $$S^0$ obtained from titration experiments reveal a strong interaction between 1 and the two cations under a large range of experimental conditions. A decomposition of the total binding energy, performed by DFT calculations, allows us to characterize the nature of the interactions existing between the cage-molecule and these two cations. These calculations also reveal the importance of the spin-orbit coupling for predicting correctly the large frequency difference between the free Tl$^+$ and Tl$^+$@1 NMR signals and to understand its origin. In addition to the development of a methodology enabling detailed understanding of the host-guest interaction, this study indicates a very pronounced selectivity of this cage-molecule towards both Cs$^+$ and Tl$^+$ cations in various experimental conditions.

Six-coordinate nitrosyl complex of Co-meso-tetra-p-tolylporphyrin with a trans-1-methylimidazole ligand

Electron absorption and Fourier-transform IR spectroscopy was used to determine that the reaction of 1-methylimidazole (1-MeIm) with a nitrosyl complex of meso-tetra-p-tolylporphyrinate cobalt (Co(TTP)(NO)) at 210—240 K led to the formation of the six-coordinate complex (1-MeIm)Co(TTP)(NO), which was stable at low temperatures both in the solid state and in a solution of toluene. Based on the temperature dependence of the equilibrium constants, the thermodynamic parameters of complexation were calculated, which indicated a weak binding of the 1-methylimidazole ligand with the Co-porphyrin nitrosyl complex.

STUDY OF INCLUSION COMPLEXES OF 2-HYDROXYPROPYL-β-CYCLODEXTRIN WITH BIOLOGICALLY ACTIVE SALINAZIDE AND VANILIN ISONIAZIDE

Complexation of 2-hydroxypropyl-β-cyclodextrin with salinazide and vanillin isoniazide possessing broncholytic and antitubercular activity was studied by the UV-spectroscopy method in a phosphate buffer solution (рН 7.4).The solubilizing effect of cyclodextrin was studied by the phase diagram method which consisted in quantitatively determining the solubility of biologically active compounds in a buffer solution containing different concentrations of cyclodextrin. The addition of cyclodextrin to a solution leads to a significant increase in the optical density of the compounds under study and in a shift in the wavelength of peak maximum indicating the formation of inclusion complexes. It was determined that the presence 2-hydroxypropyl-β-cyclodextrin in the amount of 0.09 mol kg-1 results in the 13-time solubility increase for salinazide and the 9-time solubility growth for vanillin isoniazide. Linear increase in the solubility of compounds with the addition of cyclodextrin confirms the formation of inclusion complexes compounds I, II with cyclodextrin of stoichiometric composition of 1:1. The temperature dependencies of solubility for the test compounds at different concentrations of cyclodextrin in a buffer solution were obtained. It has found that the solubility of the compounds in the presence of cyclodextrin increases with the temperature rises. Stability constants and thermodynamic parameters of complexation were calculated. Vanillin isoniazide has a lower stability constant than salinazide which is explained by the presence in its structure of methoxy group creating steric hindrance for deeper penetration of this substance into the macrocyclic cavity of the cyclodextrin. It is concluded that the process of formation of complexes is exothermic and enthalpy was determined. The results of this study showed the possibility of using 2-hydroxypropyl-β-cyclodextrin for significant increase in the solubility of the compounds, which improves their bioavailability.For citation:Ol’khovich M.V., Sharapova A.V., Blokhina S.V., Trostin A.N. Study of inclusion complexes of 2-hydroxypropyl-β-cyclodextrin with biologically active salinazide and vanilin isoniazide Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 4. P. 68-74.

COMPARISON OF ? CYCLODEXTRIN AND SULFA DERIVATIVES COMPLEX THERMODYNAMIC PARAMETERS OBTAINED EXPERIMENTALLY AND COMPUTER SOFTWARE

The aim of study was to investigate the drug and Cyclodextrin complex thermodynamic parameters comparison between validated experimental and Computer aided software. This study shows the ease of predicting the free energy change, Change of enthalpy and change of entropy is much more as compare to that of experimental and software methods. Experimentally determined thermodynamic quantities for drugs are taken from the literature. As a result we found that computer aided software provides ease of predicting the thermodynamic parameters in simple manner and in lesser time. But, for all these drugs three thermodynamic parameters predicted were not found similar to those calculated experimentally by classical thermodynamic equation.

Interaction of alkali, alkaline earth and transition metal ions with a ketocyanine dye: A comparative electronic spectroscopic study

Interaction of a dye which is structurally similar to a ketocyanine dye with metal ions (alkali, alkaline earth and transition metal) has been studied by monitoring the electronic absorption, steady state and time resolved fluorescence parameters of the dye. The dye (S0 state) forms a 1:1 complex with cations as indicated by the appearance of a new band at a longer wavelength. Equilibrium constant and other thermodynamic parameters for complexation have been determined. The interaction between the dye and the cation is mostly electrostatic in nature. Spectroscopic results have been supplemented by DFT calculation. For very low concentration of cations, where complexation is insignificant, the absorption band of the dye undergoes a slight blue shift. Enhancement of fluorescence intensity has been observed in the same concentration range. Both phenomena have been explained in terms of formation of a weak association complex where one/more cation replace equivalent solvent molecules in the cybotatic region around the dye. The binding constant of the weak association complex involving cation and the dye (S1 state) has been determined and has been found to depend on the charge-to-size ratio of the cations. Measurement of fluorescence lifetime of the dye indicates that the association complex is slowly decaying relative to solvated dye. At higher concentration of metal ions, however, fluorescence of the dye is quenched by the metal ions. A red shift of fluorescence maximum has also been observed in this concentration range.

Quantitative correlations relating the interaction of Zn(II)-tetraphenylporphine and horseradish peroxidase with amines

Reactions ofnucleophilic substitution and enzymatic processes with participation of metal-porphyrins (MP) are considered from the point of view of Zn-tetraphenylporphin (Zn-TPhP) coordination with corresponding ligand/nucleophyl/substrate/base. Linear correlations perform between kinetic parameters of process of coordination of Zn-TPhP in chloroform (constants of stability) and reactions of nucleophilic substitution both in aqueous and organic solvents with participation ofpyridines, N-oxides ofpyridines, anilines, primary amines and oxidation of anilines by horseradish peroxidase in aqueous solutions (rate constants). Thermodynamic parameters of complexation and nucleophilic substitution mutually correlate linearly in the case of pyridines, anilines and primary amines.

Interaction of thorium(iv) with nitrate in aqueous solution: medium effect or weak complexation?

Microcalorimetric titrations were performed to study the Th(IV)/nitrate interaction in aqueous solution. The results show the formation of a weak mononuclear complex of Th(IV) with nitrate and allow the determination of the complexation thermodynamic parameters at 298 K and ionic strength 1.0 mol dm(-3). The reaction is endothermic and entropy driven. Data and comparison with similar actinide(IV) complexes allow to confirm the inner-sphere nature of the Th(NO(3))(3+) complex.

Complex Formation of Tetraphenylporphyrinatozinc(II) and Nucleophilic Substitution Reactions with Pyridines and Pyridine N-Oxides

Thermodynamic parameters of complexation of tetraphenylporphyrinatozinc(II) with pyridines in chloroform at 273–313 K are linearly related to the corresponding shifts of their absorption maxima in the electronic spectra, logarithms of the stability constants of the complexes, pKa values of the ligands in water, and Hammett substituent constants σ provided that steric factors are absent. Linear correlations also exist between thermodynamic and kinetic parameters of some nucleophilic substitution reactions and complex formation of tetraphenylporphyrinatozinc(II) with pyridines and pyridine N-oxides.

Determination of the binding constants of modafinil enantiomers with sulfated β‐cyclodextrin chiral selector by capillary electrophoresis using three different linear plotting methods

Binding constants for the enantiomers of modafinil with the negatively charged chiral selector sulfated-β-CD (S-β-CD) using CE technique is presented. The calculations of the binding constants employing three different linearization plots (double reciprocal, X-reciprocal and Y-reciprocal) were performed from the electrophoretic mobility values of modafinil enantiomers at different concentrations of S-β-CD in the BGE. The highest inclusion affinity of the modafinil enantiomers were observed for the S-enantiomer-S-β-CD complex, in agreement with the computational calculations performed previously. Binding constants for each enantiomer-S-β-CD complex at different temperatures, as well as thermodynamic parameters for binding, were calculated. Host-guest binding constants using the double reciprocal fit showed better linearity (r(2)>0.99) at all temperatures studied (15-30°C) and compared with the other two fit methods. The linear van't Hoff (15-30°C) plot obtained indicated that the thermodynamic parameters of complexation were temperature dependent for the enantiomers.

ChemInform Abstract: Modeling of Ion Complexation and Extraction Using Substructural Molecular Fragments.

A substructural molecular fragment (SMF) method has been developed to model the relationships between the structure of organic molecules and their thermodynamic parameters of complexation or extraction. The method is based on the splitting of a molecule into fragments, and on calculations of their contributions to a given property. It uses two types of fragments: atom/bond sequences and “augmented atoms” (atoms with their nearest neighbors). The SMF approach is tested on physical properties of C2−C9 alkanes (boiling point, molar volume, molar refraction, heat of vaporization, surface tension, melting point, critical temperature, and critical pressures) and on octanol/water partition coefficients. Then, it is applied to the assessment of (i) complexation stability constants of alkali cations with crown ethers and phosphoryl-containing podands, and of β-cyclodextrins with mono- and 1,4-disubstituted benzenes, and (ii) solvent extraction constants for the complexes of uranyl cation by phosphoryl-containing ...

Novel phosphorylated calixarenes for the recognition of f-elements

The binding properties of three series of phosphorylated calixarene derivatives bearing phosphine oxide or phosphonate groups either at the wide or the narrow rims have been investigated towards some representative lanthanide and actinide ions using several approaches: (i) liquid–liquid extraction of europium, americium, thorium and uranyl ions from nitric acid solutions into the two diluents m-nitrobenzotrifluoride (m-NBTF) or dichloromethane; (ii) complexation in single media (methanol and acetonitrile) followed by UV-spectrophotometric and isoperibolic (micro)calorimetric titrations (ITC). The latter technique was found to be very useful for the determination of the stoichiometries of the complexes formed, in particular when the complexation did not induce significant spectral changes. It also provided a full thermodynamic characterization of these new systems. The influence of some structural features of the ligands as the nature of the substituents and the condensation degree of the calixarene moiety, on the distribution coefficients and on the complexation thermodynamic parameters has been established.