Investigations of binding sites and stability of complexes formed in ternary Cu(II)/adenosine or cytidine/putrescine systems

Biocoordination reactions in copper(II) ions and phosphocholine systems including pyrimidine nucleosides and nucleotides

The complexation reactions of phosphocholine and pyrimidine nucleosides as well as nucleotides with copper(II) ions were studied in the water system. Using potentiometric methods and computer calculations, the stability constants of the species were determined. Using spectroscopic methods such as UV-vis, EPR, ¹³C NMR, ³¹P NMR, FT-IR and CD, the coordination mode was established for complexes created in pH range 2.5-11.0. These studies will lead to a better understanding the role of copper(II) ions in living organisms and explain the interactions between them and the studied bioligands. The differences and similarities between nucleosides and nucleotides in the studied systems were also described, which testify to the significant influence of phosphate groups on the processes of metal ion complexation and interactions between ligands.

Computer analysis of potentiometric data of complexes formation in the solution

The determination of equilibrium constants is an important process for many branches of chemistry. In this review we provide the readers with a discussion on computer methods which have been applied for elaboration of potentiometric experimental data generated during complexes formation in solution. The review describes both: general basis of modeling tools and examples of the use of calculated stability constants.

Stability and Solution Structure of Binary and Ternary Cu(II) Complexes with l-Glutamic Acid and Diamines as Well as Adducts in Metal-Free Systems in Aqueous Solution

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)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.

Coordination Reactions and Noncovalent Interactions of Polyamines with Nucleotides in Binary Systems and with Nucleotides and Copper(II) Ion in Ternary Systems

Interactions of nucleotides (AMP, CMP) and 1,2-diaminopropane (tn-1) or 2-methyl-1,2-diaminopropane (tn-2) in metal-free systems as well as in the systems including copper(II) ions were studied. The composition and overall stability constants of the complexes formed were determined by the potentiometric method, whereas the interaction centres and coordination sites were identified by spectroscopic methods. It was found that phosphate groups of nucleotides and the protonated amine groups of polyamines are the centres of interaction. The differences in the interactions with the polyamines which act as models of biogenic amines are impacted by the presence of lateral chains (methylene groups) in tn-1 and tn-2. In the ternary systems with Cu(II) ions, the heteroligand complexes are mainly of the ML⋯L' type, in which the protonated polyamine is engaged in noncovalent interactions with the anchoring Cu(II)-nucleotide complex. The complexes formed in the Cu/NMP)/tn-1 system are more stable than those formed in the system with tn-2. The mode of coordination in the complex is realised mainly through the phosphate groups of the nucleotide with involvement of the endocyclic nitrogen atoms in a manner which depends upon the steric conditions and in particular on the number of the methylene groups in the polyamine molecule.

Complexes of Cu(II) ions and noncovalent interactions in systems with L-aspartic acid and cytidine-5'-monophosphate

Interactions between aspartic acid (Asp) and cytidine-5-monophosphate (CMP) in metal-free systems as well as the coordination of Cu(II) ions with the above ligands were studied. The composition and overall stability constants of the species formed in those systems were determined by the potentiometric method, and the interaction centres in the ligands were identified by the spectral methods UV-Vis, EPR, NMR, and IR. In metal-free systems, the formation of adducts, in which each ligand has both positive and negative reaction centres, was established. The main reaction centres in Asp are the oxygen atoms of carboxyl groups and the nitrogen atom of the amine group, while the main reaction centre in CMP at low pH is the N(3) atom. With increasing pH, the efficiency of the phosphate group of the nucleotide in the interactions significantly increases, and the efficiency of carboxyl groups in Asp decreases. The noncovalent reaction centres in the ligands are simultaneously the potential sites of metal-ion coordination. The mode of coordination in the complexes formed in the ternary systems was established. The sites of coordination depend clearly on the solution pH. In the molecular complexes ML⋯L, metallation involves the oxygen atoms of the carboxyl groups of the amino acid, while the protonated nucleotide is in the outer coordination sphere and interacts noncovalently with the anchoring CuH_x(Asp) species. The influence of the metal ions on the weak interactions between the biomolecules was established.

Complexation of thallium(I) with adenosine 5'-monophosphate in aqueous methanol solutions

The formation constants of the species formed in the systems H+ + thallium(I) + AMP and H+ + AMP have been determined in aqueous solutions of methanol at 25 degrees C and constant ionic strength 0.1 mol dm(-3) sodium perchlorate, using spectrophotometric and potentiometric techniques. Thallium(I) forms two mononuclear 1:1 complexes with AMP of the type TlHL and TlL- in the pH range of study (1-11), where L2- represents the fully dissociated ligand. The formation constants in various media were analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlation of the formation constants, beta111, and beta101, versus alpha (hydrogen-bond donor acidity), beta (hydrogen-bond accepter basicity), and for pi* (dipolarity/polarizability) are relatively poor in all solutions, but multi-parameter correlation represents significant improvement with regard to the single-parameter models. Finally, the results are discussed in terms of the effect of the solvent on complexation.

Interaction centres of purine nucleotides: adenosine-5'-diphosphate and adenosine-5'-triphosphate in their reactions with tetramines and Cu(II) ions

The interactions between the nucleotides: adenosine-5'-diphosphate (ADP) and adenosine-5'-triphosphate (ATP) with spermine (Spm) and 1,11-diamine-4,8-diazaundecane (3,3,3-tet), as well as Cu(II) ions are studied. In the metal-free systems nucleotide-polyamine molecular complexes have been found to form, in which the interaction centres are the nitrogen atoms of the purine ring N(1) and N(7), oxygen atoms of the phosphate group of the nucleotide (for 3,3,3-tet) and protonated nitrogen atoms of the polyamine. Significant differences in the mode of metallation between the systems with Spm and 3,3,3-tet have been established. In the systems with Spm, the main products are protonated species with [N(7),O] chromophore and the nitrogen N(1) is involved in the intramolecular interaction additionally stabilising the complex. In the systems with 3,3,3-tet the formation of metal-ligand-ligand (MLL) species has been observed, in which the oxygen atoms from the phosphate group and the nitrogen atoms from the polyamine are involved in the metallation, while the N(1) and N(7) atoms from the purine ring of the nucleotide remain outside the inner coordination sphere of the copper ion. The main centre of metallation in the nucleotide, both with Spm and 3,3,3-tet, is the phosphate group of the nucleotide.

Copper(II) complexes with uridine, uridine 5'-monophosphate, spermidine, or spermine in aqueous solution

Molecular complexes of the types (Urd)H(x)(PA) and (UMP)H(x)(PA) are formed in the uridine (Urd) or uridine 5'-monophosphate (UMP) plus spermidine or spermine systems, as shown by the results of equilibrium and spectral studies. Overall stability constants of the adducts and equilibrium constants of their formation have been determined. An increase in the efficiency of the reaction between the bioligands is observed with increasing length of the polyamine. The pH range of adduct formation is found to coincide with that in which the polyamine is protonated while uridine or its monophosphate is deprotonated. The -NH(x)(+) groups from PA and the N(3) atom of the purine base as well as phosphate groups from the nucleotides have been identified as the significant centres of non-covalent interactions. Compared to cytidine, the pH range of Urd adduct formation is shifted significantly higher due to differences in the protonation constants of the endocyclic N(3) donor atoms of particular nucleosides. Overall stability constants of the Cu(II) complexes with uridine and uridine 5'-monophosphate in ternary systems with spermidine or spermine have been determined. It has been found from spectral data that in the Cu(II) ternary complexes with nucleosides and polyamines the reaction of metallation involves mainly N(3) atoms from the pyrimidine bases, as well as the amine groups of PA. This unexpected type of interaction has been evidenced in the coordination mode of the complexes forming in the Cu-UMP systems including spermidine or spermine. Results of spectral and equilibrium studies indicate that the phosphate groups taking part in metallation are at the same time involved in non-covalent interaction with the protonated polyamine.

Investigation of the ternary D-myo-inositol 1,2,6-tris(phosphate)-spermine-Zn2+ system in solution

Interactions of Ins(1,2,6)P3 (IP), with spermine (Spm) and zinc cations have been studied by potentiometric and 31P NMR titrations. In the 4-11 pH range, two IPSpmZn2H3 and IPSpmZn2H mixed complexes are formed which are largely predominant with respect to the binary species. According to 31P NMR titration it is likely that one of the zinc cations preferably binds phosphates P1 and P6. The adduct formation between Ins(1,2,6)P3 and spermine seems also favourable to the formation of the mixed complexes. The occurrence of ternary complexes involving inositol-phosphates, biogenic amines, and metallic cations may be of relevance in the regulation of biological processes.

Mixed-ligand complexes of copper(II) ions with AMP and CMP in the systems with polyamines and non-covalent interaction between bioligands

The occurrence of non-covalent interactions and formation of molecular complexes between adenosine 5'-monophosphate (AMP) or cytidine 5'-monophosphate (CMP) and the polyamines, putrescine, 1,7-diamino-4-azaheptane (3,3-tri), spermidine and 1,11-diamino-4,8-diazaundecane (3,3,3-tet), were detected in metal-free systems. The stoichiometric composition of the adducts and their stability constants were determined on the basis of computer analysis of the titration data, taking into account the fact that the acid-base properties of the system change as a result of these interactions. Spectral analysis allowed an identification of the interaction centers in the adducts as protonated amine groups of polyamines, phosphate groups as well as nitrogen atoms of high electron density from nucleotides. Unexpectedly, no participation of the phosphate group from AMP in the formation of molecular complexes with tetramine-3,3,3-tet was detected. The stoichiometric composition and stability constants of mixed-ligand complexes in the systems of Cu(II) with AMP or CMP and polyamines were obtained. Analysis of the results of equilibrium studies and 13C, 31PNMR, UV-Vis, IR and EPR data permitted determination of the mode of coordination. In the systems with metal ions, the formation of molecular complexes Cu(CMP)H4(3,3-tri) was found, apart from heteroligand complexes of the MLL' and MLL'Hx type. In protonated complexes the occurrence of non-covalent interactions leading to stabilization of the coordination compounds was observed. The differences in the character of coordination biogenic amines and their biologically inactive analogs were identified.