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A New Macrocyclic Polylactam‐Type Neutral Receptor for Anions − Structural Aspects of Anion Recognition
Author(s) -
Szumna Agnieszka,
Jurczak Janusz
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(200111)2001:21<4031::aid-ejoc4031>3.0.co;2-9
Subject(s) - chemistry , hydrogen bond , denticity , titration , selectivity , amide , crystallography , stoichiometry , carboxylate , molecule , ligand (biochemistry) , crystal structure , stereochemistry , inorganic chemistry , receptor , organic chemistry , biochemistry , catalysis
A macrocyclic ligand containing four amide functionalities was synthesised and its complexes with various anions (F − , Cl − , AcO − , H 2 PO 4 − , and p ‐NO 2 C 6 H 4 O − ) were investigated in solution and in the solid state. NMR titration experiments (carried out in [D 6 ]DMSO), X‐ray studies and electrospray mass spectrometry (ESI MS) were employed for determination of stoichiometry and selectivity. The results in solution indicated predominant formation of 1:1 complexes for all anions studied. However, the existence of a 2:1 complex of 1 with bidentate AcO − anion as a minor species was also detected. X‐ray crystal structure determination provided evidence that the Cl − anion is too bulky to be included in the cavity of the 18‐membered tetralactam ring [ K ass (Cl − ; DMSO) = 65 M −1 ], but that F − fits well [ K ass (F − ; DMSO) = 830 M −1 ]. The binding mode of AcO − anion consists of formation of four hydrogen bonds to only one of the carboxylate oxygen atoms (employing the syn ‐ anti lone pairs of AcO − ). The selectivity of the receptor towards AcO − anion [ K ass (AcO − ; DMSO) = 2640 M −1 ] is discussed in terms of a favourable arrangement of hydrogen‐bond donors. The limited extent of formation of a 2:1 ( 1 /AcO − ) complex is attributed to unfavourable interactions between two receptor molecules.