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Synthesis of Lanthanide (III) Macrocyclic Schiff Base Complexes Containing Pyridine and their Decomposition in Aqueous Solution

Azizi, Zahra | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39436 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Mohammadi Boghaei, Davar
  7. Abstract:
  8. This study involved the synthesis, structural characterization and studies of gadolinium (III) hexaaza macrocyclic Schiff base complexes containing pyridine head and their decomposition in aqueous solution.There are many applications of lanthanide(III) macrocyclic complexes as medicine and in the biological systems, as magnetic resonance imaging (MRI) agents, and etc.These applications require that the Gd(III) complexes be resistant to gadolinium ion release under physiological conditions.
    We considered planer macrocyclic ligands as a means to obtain highly stable complexes of Gd(III). Symmetric [2+2] Schiff base macrocyclic derived from 2,6-diacetylpyridine with amines would exhibit rigidity. Furthermore, incorporation of pyridine rings in the macrocyclic framework would increase the stereo chemical rigidity and binding ability to wards Gd(III) cation, a property often associated with an increase in the thermodynamic stability of the complexes. We synthesized three hexaaza macrocycle Schiff base complexes of gadolinium, containing pyridine head by a template condensation [2+2] of 2, 6- diacetylpyridine with 1, 2-diaminoethane, Gd(L1)(NO3)3(H2O)6, (1) L1: C22H26N6, 1, 3-diaminopropane, Gd(L2) (NO3)3(H2O)4(MeOH)2, (2) L2: C24H30N6, and L-lysinemonohydrochloride, Gd(L3)(NO3) (H2O)2(MeOH)2, (3) L3: C30H36N6O4, that gives complexes of the hexadentate nitrogen donor macrocycle. In these syntheses, the metal ion is a template agent. These complexes were characterized by IR and UV-visible spectroscopy and elemental analysis. Decomposition of the macrocyclic Gd(III) Schiff base complexes in aqueous solution has been studied. These complexes decompose by hydrolysis of the imine bonds. This study was followed by UV-visible spectroscopy and we have measured rate constant for decomposition which first-order rate constants were k = 5×10-7 s-1(1), k = 5×10-7s-1(2), and k = 4×10-7 s-1(3). We have studied decomposition of the complexes in the presence of EDTA, as a competing ligand by UV-visible spectroscopy and the rate constants have been measured. Pseudo-First-order rate constants were k = 2×10-5 s-1(1), k = 1×10-6 s-1(2) and k = 2×10-5 s-1(3) respectively
  9. Keywords:
  10. Macrocylic Schiff Base ; Macrocylic Schiff Base Complexe ; Lanthanide Complexe ; 2,6-Diacetyl Pyridine ; Hexa Aza Macrocycle

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