Journal
JOURNAL OF SOLUTION CHEMISTRY
Volume 43, Issue 12, Pages 2144-2162Publisher
SPRINGER/PLENUM PUBLISHERS
DOI: 10.1007/s10953-014-0269-x
Keywords
Copper(II); L-Glutamic acid; Diamines; Molecular complexes; Inversion effect; Mixed complexes
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Binary and ternary complexes of copper(II) with l-glutamic acid (Glu) and diamines 1,3-diaminopropane and 1,4-diaminobutane, putrescine (tn, Put), as well as adducts formed in the metal-free systems, have been investigated in aqueous solutions. The types of complexes formed and their overall stability constants were established on the basis of computer analysis of potentiometric results. The reaction centers and the modes of interaction were identified on the basis of spectroscopic studies (NMR, Vis and EPR). In the ligands studied the interaction centers are the oxygen atoms from carboxyl groups, nitrogen atom from the amine group of glutamic acid and the nitrogen atoms from amine groups of the diamines. The centers of noncovalent interaction in the adducts that formed in the metal-free systems are also potential sites of metal ion coordination, which is important in biological systems. In the Glu-diamine systems, molecular complexes of the (Glu)H-x(diamine) type are formed. In the (Glu)H-2(tn) adduct, in contrast to the corresponding complex with Put, an inversion effect was observed in which the first deprotonated amine group of tn became a negative reaction center and interacted with the protonated amine groups from Glu. Depending on the pH, the amine groups from the diamine can be either a positive or a negative center of interaction. In the Cu(Glu)(2) species the first molecule of Glu takes part in metallation through all functional groups, whereas the second molecule makes a glycine-like coordination with the Cu(II) ions that is only through two functional groups. According to the results, introduction of Cu(II) ions into metal-free systems (Glu-diamine) changes the character of interactions between the bioligands in the complexes that form in Cu(II)-Glu-diamine systems and no MLaEuro broken vertical bar L' type complexes are formed. However, in the ternary systems only the heteroligand complexes Cu(Glu)(diamine) and Cu(Glu)(diamine)(OH) are observed.
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