On the Position of the Intramolecular Equilibrium between Opened and Aromatic-Ring Stacked Forms in Ternary Complexes Composed of Adenosine 5′-triphosphate, Mg2+ or Zn2+, and L-Tryptophanate, and in Related Ternary Systems
✍ Scribed by Paul R. Mitchell; Bernard Prijs; Helmut Sigel
- Publisher
- John Wiley and Sons
- Year
- 1979
- Tongue
- German
- Weight
- 711 KB
- Volume
- 62
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
The intramolecular and dimensionless equilibrium constant, K′, for the equilibrium between open and aromatic‐ring stacked isomers of ternary complexes formed between adenosine 5′‐triphosphate, inosine 5′‐triphosphate, or uridine 5′‐triphosphate, Mg^2+^ or Zn^2+^, and L‐tryptophanate, 2,2′‐bipyridyl (bipy), or 1,10‐phenanthroline (phen) have been estimated by ^1^H‐NMR. shift measurements in D~2~O (I = 0.1M, NaNO~3~; 27°). The approximate equilibrium constants K′ are ≥ 20, ≥ 20, 1.2, 0.9, 0.7, 0.5, and 0.3 for the ternary complexes Zn (phen) (ATP)^2−^, Mg (phen) (ATP)^2−^, Zn (bipy) (ATP)^2−^, Zn (bipy) (ITP)^2−^, Zn (bipy) (UTP)^2−^, Zn (trp) (ATO) ^3−^, and Mg (trp) (ATP)^3−^, respectively. The percentages of the stacked isomers decrease in the order Zn (phen) (ATP)^2−^ (≥ 95%) ≫ Zn (bipy) (ATP)^2−^ (55%) > Zn (bipy) (ITP)^2−^ (48%) > Zn (bipy) (UTP)^2−^ (∼ 40%), which coincides with the order of stability of the binary metal‐free adducts (phen) (ATP)^4−^ > (bipy) (ATP)^4−^ ≃ (bipy) (ITP)^4−^ > (bipy) (UTP)^4−^; the corresponding stability constants are K = 28.2 ± 4.7, 8.1 ± 2.6, 8.8 ± 1.8, and ∼ 1 (M^−1^), respectively (D~2~O; I = 0.1 M, NaNO~3~; 27°): these series reflect the decreasing size of the aromatic‐ring systems forming the stacks. The indole moiety of tryptophan resembles 2,2′‐bipyridyl rather than 1,10‐phenanthroline and K = 6.2 ± 1.8 M^−1^ for (trp) (ATP)^4−^. Implications with respect to the stability of ternary complexes, and to biological systems are indicated briefly.