关键词: 化学位移, 环流, ATP(5′-三磷酸腺苷), [ATP-Mg^2＋]复合物, pH

Abstract: The chemical shifts induced by the ring current was calculated for H1′ and H2′ of ATP with different torsion angle χ (O4′－C1′－N9－C4) based on the method of Johnson and Bovey. The chemical shift of H1′ showed relatively strong dependence on the χ angle, which reflected fine conformation changes with pH. By comparing the calculated results with the experimental data, it is shown that in the pH range (1～10) studied in this paper and in the presence of Mg2＋,the torsion angle χ of ATP varies in the small range from 230° to 360°.As the pH of the solution is decreased, the conformation of the ATP molecule changes from trans to cis through -gauche form. At lower pH, the ATP molecule is more likely to take the cis conformation, while at higher pH, the trans conformation is more stable. This supports the conclusion that N1 binds the metal ion at lower pH while the binding site becomes N7 when pH is neutral. In the discussion, the change of the ring current strength induced by pH variation was also taken into account.

Key words: Chemical shift, Ring current, ATP (Adenosine 5′-triphosphate), [ATP-Mg^2＋] complex, pH