Spectroscopic, potentiometric and quantum-mechanical studies of S-(-)-nicotine complexes with Cu(II) ion.

Copper(II)-nicotine complexes with chelating perchlorate, nitrate, acetate and formate ligands have been synthesized and characterized in solid state by elemental analysis and FT-IR spectroscopy. Coordination of Cu(II) by nicotine molecule has been also studied in water solution of various pH by potentiometry and spectroscopic (VIS, EPR and NMR) methods. Furthermore, quantum-mechanical calculations helped elucidate the experimental data as they provided some information on the energetic of the possible interaction modes of Cu(II) with nicotine. The studies showed that nicotine acts as a monodentate ligand utilizing for this purpose the pyridine nitrogen atom. In the Cu(II)/Nicotine system the MHL and ML type complexes were formed in 1:1 metal:ligand ratio.

EPR and potentiometric studies of copper(II) binding to nicotinamide adenine dinucleotide (NAD+) in water solution.

Coordination of Cu(II) by nicotinamide adenine dinucleotide (NAD(+)) molecule has been studied in water solutions of various pH by potentiometry and electron paramagnetic resonance (EPR) and electron spin echo (ESE) spectroscopy. Potentiometric results indicate Cu(II) coordination by protonated NAD(+) at low pH and by deprotonated NAD(+) at high pH. At medium pH value (around pH=7) NAD(+) is not able to coordinate Cu(II) ions effectively and mainly the Cu(H(2)O)(6) complexes exist in the studied solution. This has been confirmed by EPR results. Electronic structure of Cu(II)-NAD complex and coordination sites is determined from EPR and ESE measurements in frozen solutions (at 77K and 6K). EPR spectra exclude coordination with nitrogen atoms. Detailed analysis of EPR parameters (g(||)=2.420, g(perpendicular)==2.080, A(||)=-131×10(-4)cm(-1) and A(perpendicular)=8×10(-4)cm(-1)) performed in terms of molecular orbital (MO) theory shows that Cu(II)NAD complex has elongated axial octahedral symmetry with a relatively strong delocalization of unpaired electron density on in-plane and axial ligands. The distortion of octahedron is analyzed using A(||) vs. g(||) diagram for various CuO(x) complexes. Electron spin echo decay modulation excludes the coordination by oxygen atoms of phosphate groups. We postulate a coordination of Cu(II) by two hydroxyl oxygen atoms of two ribose moieties of the NAD molecules and four solvated water molecules both at low and high pH values with larger elongation of the octahedron at higher pH.

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.

Noncovalent interactions and coordination reactions in the systems consisting of copper(II) ions, aspartic acid and diamines.

Interactions of aspartic acid between 1,3-diaminopropane (tn) and 1,4-diaminobutane (Put) 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. The interaction centres and coordination sites were identified by spectroscopic methods. Each of the ligands has both negative and positive interaction centres. In aspartic acid such centres are carboxyl groups and amine group, while in the polyamine molecules - protonated amine groups. The centres are also the potential sites of the coordination of metal ions. Analysis of the logK(e) values of the adducts in the systems with polyamines has shown that the stability of the adducts in the metal-free systems depends on a significant degree on the steric factor that is the length of the polyamine. In some species the inversion effect, hitherto not reported in literature, was found. In the ternary systems including Cu(II) ions, only protonated species are formed, including molecular complexes with intermolecular interactions and metallation through the oxygen atoms of carboxyl groups and amine groups of the amino acid. In the adducts the protonated diamine is in the outer coordination sphere and is involved in noncovalent interactions with the anchoring CuH(Asp) or Cu(Asp) complexes.

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 MLcdots, three dots, centeredL, 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.

Specific type of interactions in the quaternary system of Cu(II), adenosine 5'-triphosphate, 1,11-diamino-4,8-diazaundecane and uridine.

Complexation reactions in the quaternary system Cu/ATP/3,3,3-tet/Urd have been studied. The stability constants of the complexes of the Cu(ATP)(3,3,3-tet)H(x)(Urd) type have been determined by computer analysis of the potentiometric titration. On the basis of the results of spectroscopic as well as equilibrium studies, the mode of interactions has been proposed. Metal ions coordinate phosphate groups of ATP and nitrogen atoms of polyamine. It has been established that in the conditions of the complex Cu(ATP)(3,3,3-tet) formation, uridine introduced into the Cu(II)/ATP/3,3,3-tet ternary system is involved in hydrogen bonding with the endocyclic nitrogen atoms N(1) and N(7) of the ATP purine ring and formation of the adduct Cu(ATP)(3,3,3-tet)H(Urd) is observed. Introduction of metal ions into the system changes substantially the mode of interactions between complementary base pairs relative to that proposed in the Watson and Crick model.