Complexation of metal cations with acyclic and macrocyclic nucleobase derivatives containing uracil and 2-thiocytosine units linked by polymethylene spacers was studied. The investigated compounds have demonstrated high extraction selectivity for the Ag + ion over a large number of competitive cations (Na + , Ca 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ ). The structure and composition of Ag + complexes have been investigated by a variety of physical-chemical methods. The crystal structures of three Ag + complexes with 2-thiocytosine have been established by X-ray analysis. To refine the composition of the complexes formed in solution, the self-diffusion coefficients have been determined by NMR spectroscopy. For the estimation of the most reliable complex structures, the combined analysis of NMR data and DFT calculations was successfully applied. It was shown that the tendency of 2-thiocytosine moieties to form N1-nitrogen coordinated complexes and the presence of a polymethylene spacer between amine groups in the pyrimidinophanes provides the formation of Ag + mediated duplex-type multi-component complexes.the elucidating the receptor properties of pyrimidinophanes and their acyclic counterparts.Herein, we represent new results obtained for the binding properties of pyrimidine derivatives and the structures of their Ag + complexes. Competitive extraction, X-ray crystallography, the combined analysis of NMR data and DFT calculations were used. Eventually, various models of the complex structures were discussed and compared.
Results and discussion
Competitive solvent extraction of metal cationsWe have previously estimated the extraction ability of pyrimidine derivatives L1, L3, L4, L5a,b towards s-(Li + , Na + , K + , Cs + , Ca 2+ ), d-(Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ ) and f-(La 3+ , Gd 3+ , Lu 3+ ) metal ions by the noncompetitive extraction method which demonstrated a high affinity of the investigated compounds towards Ag + ion. 12 The extraction selectivity (S) for the Ag + ion relative to the other studied metal ions in the case of macrocycle L5b reached the value S z 50. These excellent results proved stimulating to proceed with our investigations. A competitive solvent extraction of the metal cations for L1, L3, L4 and L5a,b ligands has been carried out in the water-chloroform system. The concentrations of picric acid and metal cations (Na + , Ca + , Co 2+ , Ni + , Cu 2+ , Zn 2+ , Ag + and Cd 2+ ) in the aqueous phase were identical in all the experiments. The extraction percentages are summarized in Fig. 1.The results obtained have apparently demonstrated the good selectivity of the Ag + ion recovery revealed by these ligands in the presence of a wide range of metal ions in the solution. For example, the extraction ratio Ag + /Me n+ values determined for the compound L5b were up to $53, that agree with the data obtained for noncompetitive extraction selectivity. It has been This journal is
