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Protonation of a Spherical Macrotricyclic Tetramine: Water Inclusion, Allosteric Effect, and Cooperativity
Author(s) -
Graf Ernest,
Harrowfield Jack,
Kintzinger JeanPierre,
Lehn JeanMarie,
Le Moigne Jacques,
Rissanen Kari
Publication year - 2018
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201700557
Subject(s) - protonation , chemistry , tetramine , picrate , cryptand , solvent , molecule , cooperativity , affinities , computational chemistry , inorganic chemistry , crystallography , stereochemistry , ion , organic chemistry , biochemistry
The spherical macrotricyclic cryptand tetramine “C24” ( 1 ) displays remarkable protonation behaviour. It undergoes protonation in four successive steps for which p K a 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.