title: Water encapsulation in a polyoxapolyaza macrobicyclic compound.
abstract: A new heteroditopic macrobicyclic compound (t(2)pN(5)O(3)) containing two separate polyoxa and polyaza compartments was synthesized in good yield through a [1 + 1] "tripod-tripod coupling" strategy. The X-ray crystal structure of H(3)t(2)pN(5)O(3)(3+) 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-base 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. (1)H 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 K(4)(H) value obtained.
authors: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
authors: Pedro
authors: P
authors: Mateus
authors: Rita
authors: R
authors: Delgado
authors: Patrick
authors: P
authors: Groves
authors: Sara R R
authors: SR
authors: Campos
authors: António M
authors: AM
authors: Baptista
authors: Paula
authors: P
authors: Brandão
authors: Vítor
authors: V
authors: Félix
mesh_terms: D053961:Azabicyclo Compounds / Q000138:chemical synthesis*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000737:chemistry; D011199:Potentiometry; D011522:Protons; D012996:Solutions; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D053961:Azabicyclo Compounds; D011522:Protons; D012996:Solutions; D014867:Water; D011189:Potassium Chloride