ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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, Mg2+ or Zn2+, and L-tryptophanate, 2,2′-bipyridyl (bipy), or 1,10-phenanthroline (phen) have been estimated by 1H-NMR. shift measurements in D2O (I = 0.1M, NaNO3; 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 KABA = 28.2 ± 4.7, 8.1 ± 2.6, 8.8 ± 1.8, and ∼ 1 (M-1), respectively (D2O; I = 0.1 M, NaNO3; 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(trp)(ATP)(trp) = 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.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19790620605
