Adenine stability constants

Table XIX contains stability constants for complexes of Ca2+ and of several other M2+ ions with a selection of phosphonate and nucleotide ligands (681,687-695). There is considerably more published information, especially on ATP (and, to a lesser extent, ADP and AMP) complexes at various pHs, ionic strengths, and temperatures (229,696,697), and on phosphonates (688) and bisphosphonates (688,698). The metal-ion binding properties of cytidine have been considered in detail in relation to stability constant determinations for its Ca2+ complex and complexes of seven other M2+ cations (232), and for ternary M21 -cytidine-amino acid and -oxalate complexes (699). Stability constant data for Ca2+ complexes of the nucleosides cytidine and uridine, the nucleoside bases adenine, cytosine, uracil, and thymine, and the 5 -monophosphates of adenosine, cytidine, thymidine, and uridine, have been listed along with values for analogous complexes of a wide range of other metal ions (700). Unfortunately comparisons are sometimes precluded by significant differences in experimental conditions.

Thickness of the barrier layer, optimized at 220 nm [133], played a crucial role with respect to the chemosensor sensitivity, selectivity and LOD. So, eventually, the chemosensor architecture comprised a gold-film electrode, sputtered onto a 10-MHz resonator, coated with the poly(bithiophene) barrier layer, which was then overlaid with the MIP film. This architecture enabled selective determination of the amine at the nanomole concentration level. LOD for histamine was 5 nM and the determined stability constant of the MIP-histamine complex, XMn> = 57.0 M 1 [131], compared well with the values obtained with other methods [53, 136, 137]. Moreover, due to the adopted architecture, the dopamine chemosensor could determine this amine with the stability constant for the MIP-dopamine complex, XMip = (44.6 4.0) x 106 M-1 and LOD of 5 nM [133], which is as low as that reached by electroanalytical techniques [138]. The MIP-QCM chemosensor for adenine [132] also featured low, namely 5 nM, LOD and the stability constant determined for the MIP-adenine complex, XMIP = (18 2.4) x 104 M, was as high as that of the MIP-adenine complex prepared by thermo-induced co-polymer-ization [139]. The linear concentration range for determination of these amines extended to at least 100 mM. 

A large number of experimental data including stability constant measurements [11] [12] indicate that, at neutral pH, N(7) of guanine is a better metal-binding site than N(7) of adenine. This observation is also supported by modern quantum-chemical calculations with the inclusion of electron correlation effects which reveal that polarity of the bases and the corresponding basicity of the N(7) site decreases in the order guanine > inosine > adenine > 2-aminoadenine [13]. 

In general the pyrimidines show a much lower reactivity towards the metal ions. Apparently no reaction was observed with uracil while the stability constants of Cu-cytosine are even lower than the lgJCi and gK% values of Cu(NH3)62+ (79). The high stability of the purine metal complexes can be attributed to the binding site at the imidazole residue. There the imino proton competes with the metal ion. Fig. 1 presents a model of the 2 1 complex of Cu-(adenine)%. 

O Sullivan, W. J., and D. D. Perrin The stability constants of metal-adenine nucleotide complexes. Biochemistry 3, 18 (1964). 

Miscellaneous Studies. Kinetic studies of the oxidation of Sn" by Co in perchloric acid and by Mo in hydrochloric acid have been performed, and complexation between Sn " and acetate ions and between Pb " and adenine, " thiourea, and maleate ions has been studied. Stability constants were usually determined. A model has been proposed for the interpretation of tin-119m Mossbauer data for tin(ii) compounds in terms of the distribution of tin valence electrons. The model accounts for the positive signs of the quadrupole coupling constants observed for tin(ii) compounds, and for the variation in the Mossbauer parameters of tris(halogenato)stannate(ii) anions as the cation is changed. ... 

The structure relies crucially on the pairing up of nucleic acid bases between the two chains. Adenine pairs only with thymine via two hydrogen bonds, whereas guanine pairs only with cytosine via three hydrogen bonds. Thus, a bicyclic purine base is always linked with a smaller monocyclic pyrimidine base to allow the constant diameter of the double helix. The double helix is further stabilized by the fact that the base pairs are stacked one on top of each other, allowing hydrophobic interactions... 

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