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Hydrogen‐Bonded Complexes of Carboxylate Anions and Dextrins in an Aprotic Polar Solvent
Author(s) -
Kano Koji,
Tanaka Norihiro,
Negi Shigeru
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200110)2001:19<3689::aid-ejoc3689>3.0.co;2-o
Subject(s) - chemistry , hydrogen bond , carboxylate , solvent , aqueous solution , hydrogen , vicinal , nuclear magnetic resonance spectroscopy , solvent effects , inorganic chemistry , molecule , medicinal chemistry , stereochemistry , organic chemistry
Complexation of p ‐methylbenzoate ( p ‐CH 3 C 6 H 4 CO 2 − ) and alkanoate anions (C n CO 2 − ) with cyclodextrins (CDs) and acyclic dextrins (G n s) through hydrogen bonding in an aprotic polar solvent, [D 6 ]DMSO, has been studied by means of 1 H NMR spectroscopy. Although undissociated p ‐methylbenzoic acid, p ‐CH 3 C 6 H 4 CO 2 H, does not interact with dextrins, p ‐CH 3 C 6 H 4 CO 2 − binds through hydrogen‐bonding interactions with fairly large binding constants ( K ) both to native CDs such as α‐, β‐, and γ‐CDs and to G n s. Similar complexation was observed with C n CO 2 − anions. The K values are related to the basicity of the carboxylate anions. 1 H NMR spectroscopy shows that the CO 2 − group of the guest interacts with the secondary OH groups at the vicinal 2‐ and 3‐positions of the dextrins, while the primary OH groups do not participate at all. Formation of the hydrogen‐bonded complex of β‐CD and p ‐CH 3 C 6 H 4 CO 2 − is an entropically favorable process. Addition of a small amount of D 2 O suppresses the formation of the hydrogen‐bonded complexes, suggesting that hydrogen‐bonding interactions between simple hosts possessing dense OH groups as hydrogen‐bond donors and guests with CO 2 − groups as hydrogen‐bond acceptors hardly occur in aqueous solution.