Magnesium and calcium complexes of adenosine 5 triphosphate

A Mg2+ complex, [Mg(HATP)2].[Mg(H2O)6] (Hdpa)212H2O20,21 and a Ca2+ complex, [Ca(HATP)2].[Ca(H2O)6](Hdpa)29H2O20,21 in which Hdpa is proto-

Mol.1

Mol.1

Figure 5.2 Dimeric structure of the Na2H2ATP3H2O complex (Kennard, O. et al., Proc. R. Soc. Lond. A, 1971, 325, 401-436), showing coordination of Nal and Na2 ions with the nucleotide molecules Mol. 1 and Mol. 2. Note the intramolecular N7-Na-O(g-phosphate) chelation in addition to the a,P,g-tridentate chelation to the triphosphate group. The same structure is observed in the Na2H2ATP2H2O complex (Sugawara, Y. et al., J. Am. Chem. Soc., 1991, 113, 5440-5445). Broken lines denote interligand hydrogen bonds.

Figure 5.2 Dimeric structure of the Na2H2ATP3H2O complex (Kennard, O. et al., Proc. R. Soc. Lond. A, 1971, 325, 401-436), showing coordination of Nal and Na2 ions with the nucleotide molecules Mol. 1 and Mol. 2. Note the intramolecular N7-Na-O(g-phosphate) chelation in addition to the a,P,g-tridentate chelation to the triphosphate group. The same structure is observed in the Na2H2ATP2H2O complex (Sugawara, Y. et al., J. Am. Chem. Soc., 1991, 113, 5440-5445). Broken lines denote interligand hydrogen bonds.

nated 2,2'-dipyridylamine (Figure 5.3) have been reported. These complexes are isostructural to each other and the Mg2+ complex is described here.

Figure 5.4 shows the structure of the [Mg(HATP)2]4- structural unit in which the metal ion is located on a twofold axis. The ion is octahedrally bonded to two symmetry-related HATP3- molecules through a-, p-, and g-phosphate oxygens, where the adenine base is protonated at N1 and the triphosphate group is fully deprotonated. No bonding interactions take place between the metal ion and the adenine base. The ATP molecule adopts the usual conformation for nucleotide in the Mg2+ and Ca2+ complexes, that is, anti base, C2'-endo sugar, and gauche-gauche about the C4'-C5' bond (Table 5.4). The triphosphate chain is folded into left-handed helical form and the adenine base is away from the chelate ring — that is, it takes the L-exo configuration (Table 5.2).

These types of structures occur also for 3d divalent metal ions in isomor-phous metal complexes of ATP with the general formula of [M(HATP)2].[M'(H2O)6].(Hdpa)2nH2O, as described next.

Figure 5.3 Chemical structures of aromatic amines, bpy, phen, and dpa.

Figure 5.4 Structure of the [Mg(HATP)2]4- anion,21 showing Mg2+ coordination in which the Mg2+ ion resides on a twofold axis. Note the a,P,g-tridentate chelation to the triphosphate group. The same coordination mode is observed in the corresponding calcium,21 manganese,20 cobalt,20 zinc,24 and cadmium24 complexes.

N6 C6

Figure 5.4 Structure of the [Mg(HATP)2]4- anion,21 showing Mg2+ coordination in which the Mg2+ ion resides on a twofold axis. Note the a,P,g-tridentate chelation to the triphosphate group. The same coordination mode is observed in the corresponding calcium,21 manganese,20 cobalt,20 zinc,24 and cadmium24 complexes.

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