engleski

Acid-Base Properties Of Manganese Tetra(Ethylpyridyl)Porphyrins

In recent years there has been a considerable interest in manganese porphyrins due to their unique electronic properties which allow them to function as sodium dismutase (SOD) mimetics. Accessibility of several oxidation states of manganese enables removal of reactive oxygen and nitrogen species, such as superoxide and peroxynitrite, and consequently facilitates relief of oxidative stress. Investigated manganese tetra(ortho-ethylpyridyl) porphyrin MnIIITE-2- PyP5+ and manganese tetra(meta-ethylpyridyl) porphyrin MnIIITE-3-PyP5+ (Figure 1) have the formal reduction potential close to the potential of the SOD enzyme itself and excellent in vitro and in vivo SOD-like activity [ , ]. In aqueous solution, manganoporphyrins coordinate two axial water molecules, and they can undergo up to two ionization steps in the alkaline pH range. Data in the literature with respect to these ionization reactions are diverse, both in the methods and in the results. The equilibrium spectrophotometric measurements reveal that in the basic aqueous solution three forms of MnIII- and MnII-porphyrins coexist in equilibrium. The equilibrium constants obtained by the spectrophotometric pH titrations exhibit small standard deviations confirming the reliability of the measurements. The deprotonation sites in meta-complexes are slightly more basic than in ortho- ones. It is also interesting to note that the first pKa values for both MnIITE-2- PyP and MnIITE-3-PyP, are smaller than the analogous pKa values obtained for MnIII analogues.

Mn porphirins; disociation konstants

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