Phosphates, Phosphonates, Nucleosides, and Nucleotides

Most of this section will be devoted to summarizing information relating to the stability constants reported for complexes of this group of Ca2+-binding ligands. However, we shall precede this main part with a short mention of a few relevant structures. Other properties of calcium phosphates and phosphonates will be mentioned in Sections VIII.B.4 and VIII.D below. An overall view of complexes of nucleosides, nucleotides, and nucleic acids is available (670). 

Stability constants for Ca2+ complexes of several inorganic phosphate ligands have been given in Table V (Section II.C.l above), for Ca2+ complexes of glucose-1-phosphate and glycerol-1-phosphate (log]0 A — 2.5, 1.4 respectively) in Sections V.B.2. For 

There has been much discussion of complexes between M2+ cations and nucleoside phosphates, which ligands can in principle 

Stability Constants (LogU)K, at 298 K and I = 0.1M) for Phosphate, Phospho-nate, Nucleoside, and Nucleotide Complexes of Selected M2+ Cations 

MePO2- or PME2- (Table XIX), but the open closed equilibrium lies very much on the side of the chelated form of the complex (87% for the Ca2+ complex - compare 15% for [Ca(atp)]2 and just 7% for [Ca(amp)] (695)). The availability of stability constants both for methylphosphonate and for benzimidazole (a purine model) complexes means that the chelate effect for complexes of (1H-benzimidazol-2-yl-methyl)phosphonate can be discussed without the usual complications, such as the differences between ethane-1,2-diamine and two ammonia or two methylamine ligands and disparities between units (704). 

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