Proton-ligand Stability Constants Research Articles

PH-metric titration technique for the study of metal-complexes of substituted 2- Oxo-2H-Chromene-3-Carbohydrazide derivatives in solution: calculation of stability constants

Background: In coordination chemistry, the stability of complexes is expressed in terms of the formation constant of complexes. In coordination complexes, the temperature is very important. It plays an important role in complex formation reaction. Temperature affects metal-ligand stability constant (log K) and proton-ligand stability constant (pK). The metal ion Mn2+, Co2+, Ni2+, and Cu2+ at different temperatures form complexes with 4-sulfamethoxazoleazo-3-methyl-2-pyrazolin-5-one are reported. The metal-ligand stability constant (logK) and proton-ligand stability constant (pK) of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) with organic ligand n-[2-hydroxy-1-napthalydene]-2-methylanilline at 0.1 M ionic strength in 60% dioxane-water medium is studied. The study of thermodynamic parameters and stability constant of complexes of substituted thiazole Schiff bases with rare earth metal ions in mixed solvent is reported. Objective: The study of coordination compounds and a lot of work has been done on metal-ligand stability constant. The same transition metal ion form complexes with substituted pyrazole for this metal-ligand stability constant are determined. Method: Pointwise Calculation Method Half Integral Method. Result: The values of logK1 and logK2 are determined from the metal-ligand formation curve at formation numbers 0.5 and 1.5. In all cases, logK1 is greater than logK2. The ratio logK1/logK2 is positive and greater than one in all systems. This implies that there is little or no steric hindrance to the addition of the secondary ligand molecules. The difference between logK1 - logK2 is usually positive. If the difference between logK1 and logK2 is less than 2.5, simultaneous formation of 1:1 and 1:2 complexes occurs and if it is more than 2.5, then stepwise complex formation occurs. In the present case, in all systems, it is less than 2.5. This indicates the simultaneous formation of 1:1 and 1:2 complexes takes place. Conclusion: A pH-metric study of Substituted 2-oxo-2H-chromene-3-carbohydrazide derivatives with metal ions Fe(III), and Mn(II) occurs. The graphical representation of the curve shows that the acid + ligand curve is separated from the corresponding acid + ligand + metal curve in this system. The formation of a complex is indicated. Half integral method and pointwise calculation method give nearly similar results. The values of stability constants for all systems indicate that the complexes formed in these processes are stable.

Determination of Stability Constant of Flurosubstituted Chlconemines for its Medicinal Efficiency

The good activity of drug is depending upon its stability constant i.e. proton ligand stability constant and metal ligand stability constant. If the stability constant is fairly very good then it should use as a good and effective medicine .In content to this in present work the proton ligand stability constant and metal ligand stability constant of fluro substituted chalconeimines L5 = 2-Hydroxy naphthalene 4-dimethyl aniline 4- fluro chalconeimine [FN] are studied with highly reactive transition metal like (Cu (II), Co(II),Cr(II) and Fe(III)). The 70% dioxane water solvent system used in the present investigation. The presence of –OH group confirmed by using of 0.1 M ionic strength. The transition metal (Cu (II),Co (II),Cr(II)and Fe(III)) used and the ligand form 1:1 and 1:2 complex with all values of log k1 and log k2 positive.

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.

Potentiometric Studies of Binary and Ternary Complexes of Transition Metal Ions with Ceftriaxone Sodium and Esomeprazole

The present paper deals with potentiometric study for formation of binary (1 : 1) and ternary (1 : 1 : 1) complexes of transition metals Ni(II), Cu(II), Co(II), and Zn(II) with Ceftriaxone Sodium and Esomeprazole in aqua-organic medium. The proton–ligand stability constant and metal–ligand stability constant has been calculated using Calvin–Bjerrum technique. The ionic strength has been maintained by 1.0 M NaClO4 and ternary complexes have been calculated by Thomson–Loraas method to determine log KMXY for all the ternary chelates.

Analysis of Solvent Effect on Formation Constants and Speciation of Cobalt(II), Copper(II) and Lead(II) Complexes of L-Methionine and Uracil

The analysis of coordination of chelating agents to metal ions in the formation of complexes under different experimental conditions provide information on the effects of the conditions on the extent of the coordination of the ligands to the metal ions for potential applications in bioinorganic and environmental Inorganic Chemistry. The effect of solvent on the coordination of L-methionine (primary ligand) and uracil (secondary ligand) to Co(II), Cu(II) and Pb(II) ions in the formation of binary and ternary complexes have been potentiometrically investigated in water and 40% (v/v) ethanol- water media at 27 °C and ionic strength of 0.02 mol dm–3was maintained by using NaNO3. The proton-ligand stability constants and formation constants of the binary and ternary systems were established under the experimental conditions. The formation constants of the ternary complexes were numerically compared with the corresponding binary complexes in terms of Δ log K and percentage relative stabilization (%RS). Speciation of the metal ions, binary and ternary complexes as a function of pH in the solutions was investigated by using HYSS program. The ligands were observed to form more stable ternary complexes than binary complexes. The proton-ligand stability constants the ligands and the formation constants of the metal complexes were found to be higher in 40% (v/v) ethanol-water than water. The distribution of the species revealed a decrease in the metal ion concentrations with increase in the concentrations of the binary and ternary as pH increased. The chelating agents interacted strongly with the metal ions and showed different selectivity towards the metals ions. These properties can be exploited in combating metal poisoning, separating the metals and expounding the bioinorganic chemistry of the metal ions and the ligands.

METAL-LIGAND STABILITY CONSTANTS OF Pr(III) , Nd(III) AND Sm(III) METAL IONS COMPLEXES WITH SOME SUBSTITUTED ISOXAZOLINE pH-METRICALLY

The stepwise stability constant values of substituted isoxazoline with Pr(III), Nd(III), and Sm(III) metal ion have been studied at 0.1M ionic strength pH-Metrically in 70% ethanol-water mixture by Bjerrum method as adopted by Calvin Wilson. The values of proton-ligand stability constant (pK) and metal-ligand stability constant (log K) are calculated and from the data obtained it is observed that metal ions formed 1:1 complexes with ligands L1 and L2 Â using half integral & pointwise calculation method

PH-Metric study of picolinic acid with Cu (II), Co (II) and Fe(II)ions

pH-Metric measurements of picolinic acid were studied with Cu(II), Co (II) and Fe(II)metal ions at 0.2 M ionic strength in water by Irving-Rossotti titration technique for determination of stability constants. 1: 1 complexes were formed in present investigation in between picolinic acid (PA) and Cu (II), Co (II)and Fe(II) metal ions. Values of proton-ligand stability constant (pK) and metal-ligand stability constants log k were evaluate and compared from resultant data.

PH-Metric measurements of azelastine hydrochloride with Cu(II), Co(II) and Fe(II) metal ions

Proton-ligand stability constant, metal-ligand stability constants, pK and log k of azelastine hydrochloride with Cu(II), Co (II) and Fe(II) metal ions were determined by pH-metric technique. Irving-Rossotti titration technique was used for determination of stability constants. 1:1 complexes were formed in present investigation in between azelastine hydrochloride (TH) and Cu (II), Co (II) and Fe (II) metal ions.

Thermodynamic functions of Ni(II) complexes with 5-(2-hydroxyphenyl)-pyrazole derivatives. A potentiometric study

Proton-ligand dissociation constants of five biologically important pyrazole derivatives, viz. [5-(2-hydroxyphenyl)-3-(pyridin-3-yl)-4-benzoyl]-pyrazol (HPPBP), [5-(2-hydroxyphenyl)-3-(3-nitrophenyl)-4-(3-pyridinoyl)]-pyrazol (HPNPPP), [5-(2-hydroxyphenyl)-3-(3-nitrophenyl)-4-benzoyl]-pyrazol (HPNPBP), [5-(2-hydroxyphenyl)-3-phenyl-4-(3-pyridinoyl)]-pyrazol (HPPPP), and [5-(2-hydroxyphenyl)-3-(3-nitrophenyl)-4-(2-furoyl) pyrazol (HPNPFP) and metal ligand stability constants of their Ni(II) complexes in 70% (v/v) dioxane-water and 0.1 M KNO3 were determined at 298.15, 303.15, and 308.15 K by potentiometric method. Thermodynamic functions, such as, free energy change (ΔG ○), enthalpy change (ΔH ○) and entropy (ΔS ○) change for dissociation and complex formation have been estimated form temperature dependence of proton-ligand and metal-ligand stability constants and interpreted in terms of feasibility of these processes.

Stability Constants of Some Biologically Important Pyrazoles and Their Ni2+Complexes in Different Dielectric Constant of Medium

The proton-ligand stability constants of some biologically important new pyrazoles and formation constants of their complexes with Ni(II) were determined at 0.1 mol dm-3ionic strength and at 303.15 K in different dielectric constant of dioxane-water mixture by potentiometric method. The Calvin-Bjerrum's pH-titration technique as used by Irving and Rossotti was used for determination of stability constants. The results enabled to study the electrostatic forces of attraction between metal ion and ligand with changes in dielectric constant of the medium.

Linear free energy relationships for metal–ligand complexation: Bidentate binding to negatively-charged oxygen donor atoms

Stability constants for metal complexation to bidentate ligands containing negatively-charged oxygen donor atoms can be estimated from the following linear free energy relationship (LFER): log K ML = χ OO( α O log K HL,1 + α O log K HL,2) where K ML is the metal–ligand stability constant for a 1:1 complex, K HL,1 and K HL,2 are the proton–ligand stability constants (the ligand p K a values), and α O is the Irving–Rossotti slope. The parameter χ OO is metal specific and has slightly different values for five and six membered chelate rings. LFERs are presented for 21 different metal ions and are accurate to within approximately 0.30 log units in predictions of log K ML values. Ligands selected for use in LFER development include dicarboxylic acids, carboxyphenols, and ortho-diphenols. For ortho-hydroxybenzaldehydes, α-hydroxycarboxylic acids, and α-ketocarboxylic acids, a modification of the LFER where log K HL,2 is set equal to zero is required. The chemical interpretation of χ OO is that it accounts for the extra stability afforded to metal complexes by the chelate effect. Cu–NOM binding constants calculated from the bidentate LFERs are similar in magnitude to those used in WHAM 6. This LFER can be used to make log K ML predictions for small organic molecules. Since natural organic matter (NOM) contains many of the same functional groups (i.e. carboxylic acids, phenols, alcohols), the LFER log K ML predictions shed light on the range of appropriate values for use in modeling metal partitioning in natural systems.

Spectrophotometric and pH-Metric Studies of Ce(III), Dy(III), Gd(III),Yb(III) and Pr(III) Metal Complexes with Rifampicin

The metal-ligand and proton-ligand stability constant of Ce(III), Dy(III), Gd(III),Yb(III) and Pr(III) metals with substituted heterocyclic drug (Rifampicin) were determined at various ionic strength by pH metric titration. NaClO4was used to maintain ionic strength of solution. The results obtained were extrapolated to the zero ionic strength using an equation with one individual parameter. The thermodynamic stability constant of the complexes were also calculated. The formation of complexes has been studied by Job’s method. The results obtained were of stability constants by pH metric method is confirmed by Job’s method.

PH-metric and thermodynamic studies of rare earth metal chelates

Proton ligand stability constants of hydroxybenzoic acid containing nitro group (2-Hydroxy-4-nitrobenzoic acid and 3-Hydroxy-4-nitrobenzoic acid) were determined through Irving-Rossoti pH titration technique. The stability constants of rare earth metal chelates containing 2-Hydroxy-4-nitrobenzoic acid and 3-Hydroxy-4-nitrobenzoic acid as ligands were studied in aqueous medium at different ionic strength (μ=0.01, 0.05 and 0.1 mol/L) and temperatures (298, 308 and 318± 0.1 K). The values of stability constant were evaluated through different computational methods like successive approximation, least square treatment, correction term method, and convergence method. The observed value of thermodynamic parameters (Δ G°, Δ H° and Δ S°) favors the complex formation between metal and ligands. The order of stability constant was found to be Pr(III)<Nd(III)<Sm(III)<Tb(III)<Ho(III)<Er(III) as reported by Stagg and Powell.

Chemical equilibrium studies on some bivalent transition metal chelates of biologically active molecules (drugs)

Stability constants of metal chelates of dicyclomine hydrochloride (dcm), metformin hydrochloride (mfm) drugs with the Co II , Ni II and CU II transition metal ions have been evaluated pH metrically in aqueous solution at 25 C and 0.1 M (NaClO 4 ) fixed ionic strength. Proton ligand stability constant and metal ligand stability constant were determined by Calvin-Bjerrum pH titration techniques as modified by Irving and Rossotti.

Complexation equilibria of ciprofloxacin with proton and metal ions in aqueous-organic mixutres

The proton-ligand stability constants (log K 1 H , log K 2 H ) of ciprofloxacin (CIP) and its metal-ligand stability constants (log K 1 ) in aqueous, acetonitrile-water, alcohol-water, DMSO-water and 1,4-dioxan-water (25 : 75 and 50 : 50% v/v) mixtures have been determined potentiometrically at 25 ± 0.1 °C and 0.1 mol dm -3 (NaCl) ionic strength. Ciprofloxacin formed 1: 1 (M: L) complexes with VO, Cu, Zn, Ni, Mn and Co. In general, the values of log K 1 follow Irving-Williams stability order in each solvent system.

Complexation equilibria of succinylsulfathiazole with VOII, UOII2, CuII, NiII and MnII

The proton-ligand stability constants (log K H 1 , log K H 2 ) of succinylsulfathiazole (SSTZ) and stepwise stability constants (log K 1 , log K 2 ) of its complexes with VO II , UO II 2 , Cu II , Ni II and have been determined potentlometrically in N,N'-dimethylformamlde (DMF)-water and dimethylsulfoxide (DMSO)-water systems [25: 75 and 50: 50 (% v/v)] at 25 ± 0.1 °C and 0.15 M (NaClO 4 ) ionic strength. The values of log K H 1 and log K H 2 as well as log K 1 and log K 2 increase with the increasing DMF or DMSO concentrations. The stability order of the complexes have been found to be VO II > UO II 2 > Cu II > Ni II > Mn II .

Complexation equilibria of sulfisoxazole with proton and some metal ions in aqueous-organic solvents

The proton-ligand stability constant (log K II I i.e. pK a ) of sulfisoxazole in 50: 50 (% v/v) aqueous ethanol and 50: 50 (% v/v) aqueous-dioxane mixtures at different ionic strengths (0.05, 0.10 and 0.15 mol dm -3 ) and its stability constants with some metal ions were determined in 50: 50 (% v/v) aqueous ethanol and aqueous-dioxane mixtures at 25 ± 0.1 °C and 0.15 mol dm -3 (NaClO 4 ) ionic strength. The pK a value decreases with increasing ionic strength of the medium. Based on log β 2 values the stability of the metal complexes follow the order: Mn II < Co II < Ni II < Zn II < Cu II < UO II 2 < VO II in each aqueous-organic mixture.

Proton-ligand stability constants of cefadroxil and stability constants of its metal complexes in aqueous-organic mixtures

Proton-ligand stability constants of cefadroxil and its metal-ligand stability constants with Cu 2+ , Cd 2+ and Co 2+ ions were determined pH-metrically at 30 °C and ionic strength of 0.15 M KCl in aqueous, water-alcohol (75: 25% v/v) and water-dioxane (75: 25% v/v) mixtures. Cefadroxil formed 1: 1 (ML) complexes with Cd 2+ and Co 2+ whereas 1: 2 (ML 2 ) with Cu 2+ in aqueous, water-alcohol (75: 25% v/v) and water-dioxane (75: 25% v/v) mixtures.

Complex formation of some transition metals with thiazole Schiff bases

Proton-ligand stability constants of five Schiff bases, derived from 4-(p-bromophenyl)-2-aminothiazole and R substituted salicylaldehyde (R = H, 5-CH 3 , 4-CH 3 and 5-Br) or 2-hydroxy-l-naphthaldehyde, and formation constants of their transition metal (Co, Ni, Cu and Zn) complexes have been determined pH-metrically at room temperature (25 °C) and at constant ionic strength, 1 = 0.1 M (NaClO 4 ), in 75: 25% (v/v) ethanol-water medium using Calvin-Bjerrum pH-technique as adopted by Irving-Rossotti. The order of stability constants of the complexes has been proposed, which is in accordance with the order suggested by Irving-Williams. The effect of elevated temperature (35 °C and 45 °C) on the determination of formation constants of metal complexes has been studied. Decrease in value of formation constant of the complex with increase in temperature indicates that low temperature is favorable for complex formation. The thermodynamic parameters (AG, ΔH and AS) at different temperatures have been calculated.

Stability constants of 5-carboxyuracil and 5-carboxy-2-thiouracil with some metal ions

The stability constants of metal complexes formed between Cu 2+ , Zn 2+ , Hg 2+ , UO 2+ 2 , VO 2+ , Ni 2+ , Co 2+ and Fe 3+ metal ions with 5-carboxyuracil and 5-carboxy-2-thiouracil were determined by potentiometric titration technique. Calvin-Bjerrum pH titration method us modified by Irving-Rossotti was used to calculate the proton-ligand stability constants (log K H 1 , log K H 2 ) and metal-ligand stability constants (log β n ) values in aqueous, 80: 20% (v/v) water-ethanol and water-DMSO media at 15 °C temperature and constant ionic strength of 0.1 M NaCl. The correlation between log β n values and various parameters relating to ligand as well as metal are discussed. The negative ΔG 0 values indicate that complex formation is spontaneous one.