Water Encapsulation in a Polyoxapolyaza Macrobicyclic Compound

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• 作者：Pedro Mateus ; Rita Delgado ; Patrick Groves ; Sara R. R. Campos ; Ant贸nio M. Baptista ; Paula Brand茫o ; V铆tor F茅lix
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：August 17, 2012
• 年：2012
• 卷：77
• 期：16
• 页码：6816-6824
• 全文大小：432K
• 年卷期：v.77,no.16(August 17, 2012)
• ISSN：1520-6904

文摘

A new heteroditopic macrobicyclic compound (t₂pN₅O₃) containing two separate polyoxa and polyaza compartments was synthesized in good yield through a [1 + 1] 鈥渢ripod鈥搕ripod coupling鈥?strategy. The X-ray crystal structure of H₃t₂pN₅O₃³⁺ revealed the presence of one encapsulated water molecule accepting two hydrogen bonds from two protonated secondary amines and donating a hydrogen bond to one amino group. The acid鈥揵ase behavior of the compound was studied by potentiometry at 298.2 K in aqueous solution and at ionic strength 0.10 M in KCl. The results revealed unusual protonation behavior, namely a surprisingly low fourth protonation constant contrary to what was expected for the compound. ¹H NMR and DOSY experiments, as well as molecular modeling studies, showed that the water encapsulation and the conformation observed in the solid state are retained in solution. The strong binding of the encapsulated water molecule, reinforced by the cooperative occurrence of a trifurcated hydrogen bond at the polyether compartment of the macrobicycle, account for the very low log K₄^H value obtained.