Abstract
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)Hx(diamine) type are formed. In the (Glu)H2(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 ML…L′ type complexes are formed. However, in the ternary systems only the heteroligand complexes Cu(Glu)(diamine) and Cu(Glu)(diamine)(OH) are observed.
Highlights
L-Glutamic acid is an amino acid present in many food products either in its free form or in peptides and proteins
An inversion effect was found to take place in (Glu)H2(tn) adduct, in which the first deprotonated amine group from the diamine acts as a negative center of interaction with a protonated amine group from the amino acid
No inversion effect was found in the system with Put, similar to the system Asp–Put [37], which is related to the differences in the protonation constants of the two polyamines
Summary
L-Glutamic acid is an amino acid present in many food products either in its free form or in peptides and proteins This amino acid is found throughout the mammalian brain and participates in many metabolic pathways [1, 2]. Protonated PAs are aliphatic cations with multiple functions and are essential for life They are implicated in a variety of cellular processes, e.g. in embryonic development, chromatin organization, mRNA translation, ribosome biogenesis, cell growth and proliferation, programmed cell death, influence the transcriptional and translational stages of protein synthesis, stabilize membranes, modulate neurophysiological functions and may act as intracellular messengers. Acid–PA systems [35,36,37], presents the results of studies focused on Glu–diamine systems and relevant ternary systems with Cu(II) ions present in human cells [38, 39]
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