Lancelot G
Biophys J. 1977 Mar;17(3):243-54. doi: 10.1016/S0006-3495(77)85653-1.
High resolution proton magnetic resonance measurements provide evidence for the formation of hydrogen-bonded complexes between 9-ethyladenine and p-cresol used as a model of tyrosine side chain in CDCl3. We have calculated the sum of the association constants corresponding to the three existing 1:1 complexes: K=6.3+/-0.15. By methylation of the amino group of adenine, we were able to calculate the ratio of the two strongest equilibrium constants K7/K1=1.6+/-0.3. Theoretical computations by the complete neglect of differential overlap (CNDO/2) method indicate that several hydrogen-bonded planar complexes can form between 9-methyladenine and phenol. The computed energy of the complexes with 6-dimethylamino adenine removes some ambiguity concerning the computed ratio of the association constants. Comparison of the calculated energies with free energies experimentally determined in organic solvent shows that despite the competition with CDCl3, which associates with both solute molecules, the preferential order of association is conserved. The small variations of charge density of adenine carbon atoms when complexed with phenol are in agreement with very small chemical shifts observed by 13C-nuclear magnetic resonance.
高分辨率质子磁共振测量结果为9-乙基腺嘌呤与用作酪氨酸侧链模型的对甲酚在CDCl₃中形成氢键复合物提供了证据。我们计算了对应于三种现有1:1复合物的缔合常数之和：K = 6.3±0.15。通过腺嘌呤氨基的甲基化，我们能够计算出两个最强平衡常数的比值K₇/K₁ = 1.6±0.3。采用完全忽略微分重叠（CNDO/2）方法进行的理论计算表明，9-甲基腺嘌呤和苯酚之间可以形成几种氢键平面复合物。用6-二甲基氨基腺嘌呤计算出的复合物能量消除了关于缔合常数计算比值的一些模糊性。将计算出的能量与在有机溶剂中实验测定的自由能进行比较表明，尽管存在与溶质分子都缔合的CDCl₃的竞争，但缔合的优先顺序得以保留。腺嘌呤碳原子与苯酚络合时电荷密度的微小变化与¹³C核磁共振观察到的非常小的化学位移一致。
