Komplexbildung von Nucleinbasen mit Cu²⁺

By means of UV difference spectra, the acidity constants K H HL of the N‐1‐proton in the nucleotides inonine, guanosine, uridine, and thymidine 5′‐triphosphate were measured. The same deprotonation ( K H CuHL ) in the respective Cu 2+ complexes was also determined. The measurement were carried out with and without (Table 1) addition of NaClO 4 (0.1 M). It was found that the influence of the ionic strength is great, possibly due to the formation due to Na + complexes. The difference, Δ pK A = pK H HL – pK H CuHL ∽ 2.0, for the nucleotide systems is of the same order as the respective value 2.2 of the Cu 2+ guanosine system. This indicates a strong interaction between Cu 2+ and the nucleic base in the Cu 2+ ‐nucleotide complexes. From experimental indices and the analogy to the Cu 2+ ‐ATP complex, it is concluded that macrochelates are formed. The acidity constants determined by means of UV difference spectra were confirmed by potentiometric titrations (Table 2). The Cu 2+ ‐nucleoside triphosphates are known to form stable complexes with 2,2′‐bipyridyl. In such ternary complexes, the nucleic base can no longer coordinate to the Cu 2+ . The relatively small Δ pK Bipy/A values (Table 2) are in agreement with this. The hydrolytic tendencies of Cu 2+ bound to the different nucleotides were also estimated (Table 2). The pK H CuL(H2O)x values show that the hydrolytic tendency of the Cu 2+ complexes decreases in the order CTP > ATP > TTP > UTP > ITP ∽ GTP. The influence of the coordination number of the different ligands and also other problems concerning nucleotide complexes were discussed.