Evaluation of Stoichiometry, Stability Constants and Gibbs Free Energies of Acetaminophen-Zn (II) complex at Different Temperatures

Acetaminophen also known as paracetamol, is a drug used in the treatment of pain and fever. It is essentially used for the relief of mild to moderate pain. The presence of phenol and carbonyl oxygen atom enables acetaminophen to behave as a bidentate ligand. The stoichiometry, stability constants and Gibbs free energies of acetaminophen-Zn (II) were determined colorimetrically at 25 and 40 oC using continuous variation and mole ratio methods. The formation of Zn (II) complex with acetaminophen was studied colorimetrically at an absorption maximum of 630 nm at different temperatures. The data showed that Zn (II) and acetaminophen combine in the molar ratio of 1:1 at pH 7.4 with ionic strength maintained using 0.1M KNO3. Calculated stability constants values were 2.70 x 103 and 2.20 x 103 using continuous variation method and 7.21 x 103 and 7.21 x 103 using mole ratio methods at 25 and 40 oC respectively. Calculated ΔGƟ for the complex were - 1.96 x 104 and -1.98 x 104 J using continuous variation method and -2.2 x 104 J and - 2.31 x 104 J using mole ratio method at 25 and 40 oC respectively. The stability constant and Gibbs free energy results suggested that acetaminophen used in the study is a good chelating agent and can be an efficient antidote in the therapy of Zn (II) overload or poisoning. Keywords: Acetaminophen, Zinc, complex, stability constant, Gibbs free energy.

Colorimetric Determination of Stability Constant of Sulfamethoxazole-Cu(II) Complex at Different Temperatures by Continuous Variation Method

Sulfamethoxazole is an antibiotic that is used for the treatment of bacterial infections such as prostatitis, bronchitis and urinary tract infections. It is effective against gram negative and gram positive bacteria. Classical equation has been used in the calculation of stability constant of SulfamethoxazoleCu(II) complex depending on the theoretical explanation of the stoichiometry. The formation of Cu(II) complex with sulfamethoxazole was studied colorimetrically at an absorption maximum of 430 nm at 25, 30, 35 and 40 oC. The data showed that Cu(II) and sulfamethoxazole combine in the molar ratio of 1:2 at pH 7.4 with ionic strength maintained using 0.1M KNO3. Calculated stability constants values were 4.02 x 106 , 2.93 x 106 , 1.37 x 106 and 9.21 x 105 using continuous variation method. Calculated ∆GƟ for the complex were -3.77 x 104 , -3.75 x 104 , -3.62 x 104 and - 3.57 x 104 . The stoichiometry, stability constant and Gibbs free energy results suggested that sulfamethoxazole used in the study is a good chelating agent and can be an efficient antidote in the therapy of Cu(II) overload or poisoning

Determination of Stability Constants and Thermodynamic parameters of Cefotaxime –Fe(III) Complex at Different Temperatures

Cefotaxime, a β-lactam antibiotic, has a structure which enables it to act as a chelating agent. The formation of Fe(III) complex with cefotaxime has been studied colorimetrically at an absorption maximum of 480 nm at different temperatures. The data showed that Fe(III) and cefotaxime combine in the molar ratio of 1:1 at pH 7.4 with ionic strength maintained using 0.1M KNO3. The stability constants of the complex were calculated to be 1.56 - 1.90 x 104 by continuous variation method and 1.34 - 1.71 x 104 by mole ratio method at 25 and 40 oC respectively. ∆HƟ values for the complex were calculated to be -1.02 x 104 and -1.05 x 104 J by continuous variation method and mole ratio method respectively. ∆GƟ of the complex were calculated to be -2.44 – (-2.51) x 104 J by continuous variation method and -2.41- (- 2.48) x 104 J by mole ratio method at 25 and 40 oC. ∆SƟ of the complex were calculated to be 2.44 - 2.51 x 104 J/K by continuous variation method and -2.41 -2.48) x 104 J/K by mole ratio method at 25 and 40 oC respectively. Cefotaxime is a good chelating agent and can be an efficient antidote in the therapy of copper overload or poisoning.

1H-NMR Study of Famotidine and Nizatidine Complexes with b-cyclodextrin

The aim of this study was to obtain and to characterize some inclusion complexes of famotidine and nizatidine with b-cyclodextrin (b-CD) in solution. The formation of famotidine- and nizatidine - b-CD complexes were evaluated by means of 1H-NMR spectroscopy. Thereafter, the stoichiometry and association constants of the complexes obtained were calculated via a continuous variation method by using the chemical shifts of specific protons from both host and guest molecules. The association constants calculated are 179.6 M--1for famotidine - b-cyclodextrin complex, and 74.9 M-1 for nizatidine - b-cyclodextrin complex, at 295 K. Due to their better stability, these complexes could be use as oral pharmaceutical preparations with better taste compared with that of free drugs.

Spectrophotometric Determination of Cu2+ Metal Ions via Complex Formation with Carboxylated Tris(2-aminoethyl)amine

An aminopolycarboxylic acid chelating agent; tris(2-aminoethyl)aminehexaacetic acid (TAHA) was prepared and characterized. TAHA formed stable complexes with Cu(II) ions and other metal ions at pH 10. The complexation behavior was studied by spectrophotometry at the complex maximum wavelength. Mixtures of Cu(II) and other metal ions (M2+; Ca2+, Co2+, Ni2+, Cd2+)were titrated with TAHA at pH 10. The stoichiometry of ligand - to - metal was found to be 1:1. The stability constant of Cu(II)–TAHA complex was determined to be 1.86×105 by using the continuous variation method. Beer’s law was obeyed over the concentration range 3.0×10–4 M – 1.2×10–2 M for Cu(II) solution. The results of the quantitative determination of Cu(II) gave LOD and LOQ values of 7.285×10–6 M and 2.428×10–5 M respectively. The percent relative standard deviation (%RSD) for five replicate samples was found to be 1.088% and 4.804% for Cu(II) concentrations of 1.2×10–2 M and 3.0×10–4 M respectively.

FORMULA ESTABLISHMENT OF COLORLESS Pb(II) COMPLEX WITH N-BENZOYL-N-PHENYL HYDROXYLAMINE (BPA) USING ATOMIC ABSORPTION SPECTROSCOPY

A new method for determination of stoichiometry of colorless complexes by using atomic absorption spectrophotometric technique in continuous variation method and slope ratio method was described here. This method can be used in same manner as that of mole ratio method and slope ratio method. In this method atomic absorption spectroscopy was used instead of UV-Vis spectrophotometry. Atomic absorption spectrophotometric technique is superior to UV-Vis spectrophotometry as it can be applied to colorless soluble complexes. Pb(II) and n-benzoyl-n-phenyl hydroxylamine react to form colorless complex at pH 6.5, which can be easily determined by this method. It was found that Pb(II) forms 1:2 complex with n-benzoyl-n-phenyl hydroxylamine and is quantitatively extracted back to aqueous solution for AAS analysis.

SPECTROPHOTOMETRIC STUDY ON THE FORMATION AND ANALYTICAL APPLICATION OF THE RHODIUM (III) CHELATE WITH 2-THIOXO-4-THIAZOLIDINONE

The paper presents a spectrophotometric study of the binary system Rh(III)-2-thioxo-4-thiazolidinone. The formation conditions and the analytical application of the formed complex for spectrophotometric determination of Rh(III) were studied. The composition of the Rh(III) chelate with this particular ligand was determined by the continuous variation method, its instability constant being Kinst = 1,61·10-8 mol2L-2.