文摘
The acidity constants of the (N7)H+ sites of inosylyl(3′→5′)inosine (IpI−) were estimated and those of its (N1)H sites were measured by potentiometric pH titrations in aqueous solution (25 °C; I = 0.1 M, NaNO3). The same method was used for the determination of the stability constants of the 1:1 complexes formed between Mg2+, Co2+, Ni2+, Zn2+, or Cd2+ (= M2+) and (IpI − H)2− and, in the case of Mg2+, also of (IpI − 2H)3−. The stability constants of the M(IpI)+ complexes were estimated. The acidity constants of H(inosine)+ and the stability constants of the M(Ino)2+ and M(Ino − H)+ complexes were taken from the literature. The comparison of these and related data allows the conclusion that, in the M(IpI − H) species, chelates are formed; most likely they are preferably of an N7/N7 type. For the metal ions Co2+, Ni2+, Zn2+, or Cd2+, the formation degrees of the chelates are on the order of 60−80%; no chelates could be detected for the Mg(IpI − H) complexes. It is noteworthy that the (N1)H deprotonation, which leads to the M(IpI − H) species, occurs in all M(IpI)+ complexes in the physiological pH range of about 7.5 or even below.