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    STUDIA CHEMIA - Issue no. 2 / 2013  
         
  Article:   EQUILIBRIUM AND THERMODYNAMIC STUDY OF COMPLEXES OF THALLIUM WITH URACIL AT DIFFERENT TEMPERATURES AND CONSTANT IONIC STRENGTH.

Authors:  . 		 
       
         
  Abstract:   In aqueous solution, the protonation equilibria of uracil and their complex formation with thallium(I) ion were investigated using a combination of potentiometric and spectrophotometric methods at different temptatures (283.15, 288.15, 293.15, 298.15, 303.15 and 308.15) K and constant ionic strength (0.1mol dm-3 sodium perchlorate). A careful and accurate method based on chemometrical concepts was used in order to determine stability constants. For this purpose, spectral titration data were used and the spectra were recorded in the range (200-500 nm). The stability constants of thallium(I) ion with all the heterocyclic bases were calculated at various temperatures by means of computer fitting of the pH-absorbance data with appropriate mass balance equations. The computer program equispec was used to extract the desired information from the spectral data. The outputs of the fitting processes were protonation and stability constants, spectral profiles of pure forms, distribution diagrams, and other factor analysis data. The composition of the formed complexes were determined and it was shown that thallium(I) forms a mononuclar 1:1 species with the uracil, of the type TlL in the pH range of study (1.0-12.4), where L represents each heterocyclic base. Finally, The effect of temprature on the protonation and stability constants were studied and thermodynamic functions such as change in enthalpy (ΔH), change in entropy (ΔS) and change in gibbs energy (ΔG) have been obtained for the complexes of thallium(I) ion with the heterocyclic bases from the stability constants values and their temperature dependence. 

Key words: Equispec, Thallium(I) complexe, Uracil, Temperature, Constant ionic strengh.
 
         
     
         
         
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