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Cooperative Recognition of a Copper Cation and Anion by a Calix[4]arene Substituted at the Lower Rim by a β‐Amino‐α,β‐Unsaturated Ketone
Author(s) -
Senthilvelan Annamalai,
Ho I.Ting,
Chang KaiChi,
Lee GeneHsiang,
Liu YiHung,
Chung WenSheng
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200802654
Subject(s) - chemistry , titration , fluorescence , cationic polymerization , metal ions in aqueous solution , metal , copper , molecule , medicinal chemistry , crystallography , stereochemistry , inorganic chemistry , polymer chemistry , organic chemistry , physics , quantum mechanics
Abstract Chemodosimeter : Upon titration with Cu II , the fluorescence of 1 showed strong fluorescence enhancement because the metal ion helps to lock the conformation of the fluorophores. Cu II was reduced to Cu I by the free phenolic OH group of 1 , the phenol was then oxidised by Cu II and assisted in the trapping of Cu I . Ditopic behaviour was observed for 1⋅ Cu I , which showed further enhancement of its fluorescence intensity upon complexation with anions (as depicted, A − =CH 3 COO − or F − ).We report herein a new ditopic calix[4]arene receptor 25,27‐bis‐{[4‐amino‐4‐(1‐naphthyl)‐2‐oxo‐3‐butenyl]oxy}‐26,28‐dihydroxycalix[4]arene ( 2 ) for the simultaneous complexation of anionic and cationic species. The host molecule 25,27‐bis{[3‐(1‐naphthyl)‐5‐isoxazolyl]methoxy}‐26,28‐dihydroxycalix[4]arene ( 1 ) was synthesised first and was followed by a [Mo(CO) 6 ]‐mediated ring‐opening reaction to give the target receptor 2 . The binding properties of ligands 1 and 2 towards metal ions in CH 3 CN were investigated by UV/Vis and fluorescence spectroscopies. The results showed that both ligands 1 and 2 were highly selective for Cu II ions. Upon titration with Cu II , the fluorescence of 1 was severely quenched, whereas 2 showed strong fluorescence enhancement because the metal ions help to lock the conformation of the fluorophores. During the complexation of 2 with Cu II , the Cu II was reduced to Cu I by the free phenolic OH of 2 , whereas the phenol was oxidised by Cu II , after which it assisted in the trapping of Cu I . Ditopic behaviour was observed for the complex 2⋅ Cu I , which showed further enhancement of its fluorescence intensity upon complexation with anions such as acetate or fluoride.