Thermodynamic and kinetic studies on interaction of some transition metal ions with tryptophan

Amino acid of tryptophan (Trp) was chosen as a drug. A systematic approach was made to study its interaction with some transition metal ions, and qualitatively and quantitatively examine the thermodynamic and kinetic phenomena on this model drug. To accomplish these tasks, the stability constants of Trp complexes with Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Pb(II) at temperatures of 25, 30, 35, and 40 °C were determined potentiometrically, utilizing modified Bjerrum’s method. Potentiometric titrations were carried out in water, and water:dioxane mixture (50:50, v:v). Our findings showed that the stability constants of the complexes increased as the dioxane content was raised or temperature was elevated. The negative values of ΔG° are indication of spontaneity of the processes. ΔH° values are positive, conveying the complex formation is an endothermic process and ΔS° values are positive contributing more to spontaneity, causing reaction favoring and disordering. The variations of natural logarithm of the stability constants versus 1/T are linear leading to evaluation of the stability constant of the complexes at any temperature. Moreover, kinetic study gave rise to estimation of rate constant and activation energy for each complex formation process. It was concluded that the order of increasing stability of the complexes is: kf Co(II)-Trp » kf Zn(II)-Trp < kf Pb(II)-Trp < kf Ni(II)-Trp < kf Cu(II)-Trp < kf Fe (III)- Trp. Furthermore the activation energy values for the aforementioned complexes in water-dioxane mixture obeyed the following trend Ea Zn(II)-trp < Ea Fe(III)-Trp < Ea Ni(II)-trp < Ea Co(II)-trp <Ea Cu(II)-trp <Ea Pb(II)-trp

Binary Complexes of Aspartic Acid with Some Metal Ions in Aqueous Solution and Water-dioxane Mixtures

The reaction between amino acids and metal ions has been used as a model for transferring the metallic ions to body tissues. How stable these complexes are formed is our concern. The stability constants of the complexes between L-aspartic acid (Asp) and Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Ce(III) metal ions were determined by potentiometric titrations in aqueous solution and in 25-75%(v/v) of water-dioxane mixtures(I = 0.1 M, NaNO3) at 15, 20, 25, 35, and 45°C.The observed increasing stability order for the corresponding complexes in water and water-dioxane mixtures were as follows: Kf Cd (II)-Asp< Kf Zn (II)-Asp < Kf Co (II)-Asp< Kf Ni (II)-Asp < Kf Ce(III)-Asp< Kf Cu(II)-Asp Mixed solvents such as water-dioxane provide a better model for in vivo reactions. It was observed that with increase in the percentage of dioxane, the stability constants were elevated. The results showed that the reactions were exothermic and spontaneous

Density estimation of normal alkanes from the statistical-thermodynamic perturbation theory based equation of state

591-594An analytical equation of state (EoS) proposed by Ihm-Song-Mason (ISM) is employed to calculate the density of normal alkanes from methane to decane. The best available values of the Lennard-Jones (12,6) parameters have been used to evaluate the second virial coefficient of the EoS for each compound. The second virial coefficient is not very sensitive to the feature of the intermolecular potential. The remaining parameters in the EoS depend only on the repulsive part of the potential. Consequently, they are insensitive to the details of the interaction potential. The calculated second virial coefficients in conjunction with other temperature-dependent parameters of the EoS are employed to predict the density of all alkanes (C1-C10). There is a good agreement comparison between the experimental values of density and the calculated values from ISM EoS for all of the compounds