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Selective Colorimetric Detection of Hg 2+ and Mg 2+ with Crown Ether Substituted N ‐Aryl‐9‐aminobenzo[ b ]quinolizinium Derivatives
Author(s) -
Tian Maoqun,
Ihmels Heiko
Publication year - 2011
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/ejoc.201100329
Subject(s) - chemistry , substituent , ether , deprotonation , aryl , amide , medicinal chemistry , conjugate , acceptor , metal , metal ions in aqueous solution , ion , stereochemistry , organic chemistry , alkyl , physics , condensed matter physics , mathematical analysis , mathematics
1,4‐Dioxa‐7,13‐dithia‐10‐azacyclopentadecane (AT 2 15C5) or 1,4,7,10‐tetraoxa‐13‐azacyclopentadecane (A15C5) were attached as metal‐ion‐binding receptor units at the ortho or para positions of the 9‐amino‐ N ‐phenylbenzo[ b ]quinolizinium chromophore. The addition of Hg 2+ or Mg 2+ to the para isomers of the AT 2 15C5–quinolizinium or A15C5–quinolizinium conjugate, respectively, led to a blueshift of the absorption maxima of each compound because of the reduced donor ability of the complexed amino group. In contrast, the addition of Hg 2+ to a solution of the ortho ‐AT 2 15C5–quinolizinium conjugate in H 2 O/MeOH mixtures induced a significant redshift (ca. 50 nm) of the absorption maximum and enabled the photometric discrimination between Hg 2+ and competing thiophilic cations, such as Ag + or Pb 2+ , because the latter, as well as other competing metal ions, did not induce such an effect. It is proposed that the Hg 2+ ‐induced redshift originates from the complexation of Hg 2+ by the thiaazacrown ether followed by deprotonation of the secondary 9‐amino substituent of the aminobenzoquinolizinium unit. The resulting amide functionality increases the donor–acceptor interplay leading to the redshifted absorption and also coordinates to Hg 2+ to form a lariat ether type complex. A similar effect was observed upon the addition of Mg 2+ to the 9‐amino‐ N ‐phenylbenzo[ b ]quinolizinium derivative with the A15C5 unit in the ortho position; however, this effect was only operative in aprotic solvents, e.g. CH 3 CN, and with less than 1 mol‐equiv. of Mg 2+ .