alexa Stability and structure of binary and ternary complexes of α-lipoate and lipoate derivatives with Mn2+, Cu2+, and Zn2+ in solution
Pharmaceutical Sciences

Pharmaceutical Sciences

Journal of Pharmacological Reports

Author(s): Helmut Sigel, Bernhard Prijs, Donald Bruce Mccormick, Jason CH Shih

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The stabilities of the 1:1 complexes of Mn2+, Cu2+, and Zn2+ with lipoate and its chainshortened catabolites, viz., bisnorlipoate and tetranorlipoate, were studied by potentiometric titrations in water containing 50% dioxane (I = 0.1, NaClO4; 25 °C). A comparison of the stabilities of these complexes with those of simple carboxylates reveals that the catabolite complexes formed with Cu2+ and Zn2+ are more stable than expected from only the basicity of the carboxylate groups. This is evidence that chelates involving the disulfide group are formed. The stability of all Mn2+ complexes is determined by the basicity of the carboxylate groups. The same pattern of stability holds for the mixed-ligand complexes formed by Cu2+ or Zn2+, 2,2′-bipyridyl, and lipoate or one of its derivatives. It is evident that the disulfide group of the 1,2-dithiolane moiety can participate in the formation of binary and ternary complexes. The somewhat less-pronounced coordinating properties of the 1,2-dithiolane moiety compared with the tetrahydrothiophene moiety are discussed. It is apparent that the electron density at S(1) and S(2) in the dithiolane moiety of lipoate is not equivalent: S(1) is favored over S(2) in electrophilic reactions; possible biological implications are indicated.

This article was published in Arch Biochem Biophys and referenced in Journal of Pharmacological Reports

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