The spherical macrotricyclic cryptand tetramine "C24" (1) displays remarkable protonation behaviour. It undergoes protonation in four successive steps for which pKa values of 11.17±0.05, 10.28±0.04, 6.00±0.06 and 3.08±0.08 have been determined at 298 K. The unusually close values for the first two protonations provide evidence for the encapsulation of a water molecule serving as effector for the second protonation, which is consistent with earlier observations that the exchange of protons bound in the diprotonated species with solvent protons is unusually slow and that 17 O NMR spectra show the presence of an oxygen centre in the same species quite distinct from that of solvent water. Encapsulation of water is also observed in the solid state in the picrate salt of the triprotonated form of 1 and has been characterised by means of X-ray structural determination.

中文翻译：

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球形大三环四胺的质子化：水包裹体，变构作用和协同作用。

球形大三环隐孢子虫四胺“ C24”（1）表现出显着的质子化行为。它在四个连续的步骤中经历了质子化，在298 K下确定了pKa值分别为11.17±0.05、10.28±0.04、6.00±0.06和3.08±0.08。前两个质子的异常接近的值提供了包裹a的证据。水分子作为第二次质子化的效应子，这与先前的观察结果一致，即与质子结合的双质子化物质中质子的交换异常缓慢，并且17 O NMR光谱显示相同物种中氧中心的存在不同于溶剂水。