Juribašić Marina, Bregović Nikola, Stilinović Vladimir, Tomišić Vladislav, Cindrić Marina, Sket Primož, Plavec Janez, Rubčić Mirta, Užarević Krunoslav
Ruđer Bošković Institute, Bijenička 54, Zagreb (Croatia), Fax: (+385) 1-4680-245.
Chemistry. 2014 Dec 22;20(52):17333-45. doi: 10.1002/chem.201403543. Epub 2014 Sep 26.
This work presents a successful application of a recently reported supramolecular strategy for stabilization of metastable tautomers in cocrystals to monocomponent, non-heterocyclic, tautomeric solids. Quantum-chemical computations and solution studies show that the investigated Schiff base molecule, derived from 3-methoxysalicylaldehyde and 2-amino-3-hydroxypyridine (ap), is far more stable as the enol tautomer. In the solid state, however, in all three obtained polymorphic forms it exists solely as the keto tautomer, in each case stabilized by an unexpected hydrogen-bonding pattern. Computations have shown that hydrogen bonding of the investigated Schiff base with suitable molecules shifts the tautomeric equilibrium to the less stable keto form. The extremes to which supramolecular stabilization can lead are demonstrated by the two polymorphs of molecular complexes of the Schiff base with ap. The molecules of both constituents of molecular complexes are present as metastable tautomers (keto anion and protonated pyridine, respectively), which stabilize each other through a very strong hydrogen bond. All the obtained solid forms proved stable in various solid-state and solvent-mediated methods used to establish their relative thermodynamic stabilities and possible interconversion conditions.
这项工作展示了一种最近报道的超分子策略的成功应用，该策略用于在共晶体中将亚稳态互变异构体稳定到单组分、非杂环的互变异构固体中。量子化学计算和溶液研究表明，所研究的由3-甲氧基水杨醛和2-氨基-3-羟基吡啶（ap）衍生的席夫碱分子，作为烯醇互变异构体要稳定得多。然而，在固态中，在所有三种获得的多晶型物中，它仅以酮互变异构体形式存在，在每种情况下都通过一种意想不到的氢键模式得以稳定。计算表明，所研究的席夫碱与合适分子的氢键作用会使互变异构平衡向较不稳定的酮形式移动。席夫碱与ap的分子配合物的两种多晶型物展示了超分子稳定作用所能达到的极端情况。分子配合物的两种组分分子均以亚稳态互变异构体形式存在（分别为酮阴离子和质子化吡啶），它们通过非常强的氢键相互稳定。在用于确定其相对热力学稳定性和可能的相互转化条件的各种固态和溶剂介导方法中，所有获得的固体形式都证明是稳定的。
