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On the Signalling Pathways and Cu II ‐Mediated Anion Indication of N ‐ meso ‐Substituted Heptamethine Cyanine Dyes
Author(s) -
Descalzo Ana B.,
Rurack Knut
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.200802087
Subject(s) - cyanine , chemistry , cyclam , protonation , bathochromic shift , photochemistry , chromophore , metal ions in aqueous solution , moiety , aqueous solution , ion , metal , stereochemistry , organic chemistry , physics , quantum mechanics , fluorescence
Join or attack : meso ‐Cyclam‐substituted heptamethine cyanine dye 1 responds very differently to the presence of metal ions and protons. Whereas the former are embraced in a host–guest complex, the latter attack the cyanine π system (see picture). In the presence of Cu II , 1 selectively forms near‐infrared absorbing aggregates in buffered solution that allow the determination of citrate by using colourimetry.Three mid‐chain rigidified heptamethine cyanine dyes substituted with dimethylamino or cyclam groups at the meso position of the polymethine chain have been prepared and studied both experimentally and theoretically with respect to their spectroscopic response toward protons and various metal ions. Despite a potentially rich conformational ground‐state chemistry, the spectroscopic studies revealed that the behaviour of the dyes is in agreement with Kuhn's classic polymethine dye theory. Coordination of metal ions and protonation of the alkyl amino groups in the cyclam moiety accordingly lead to moderate bathochromic shifts in absorption and reduced Stokes shifts. In contrast, protonation of the dimethylamino‐substituted derivatives occurs at the polymethine chain, transforming the heptamethine into a trimethine‐type chromophore with concomitant gigantic spectral blueshifts. In the presence of Cu II in buffered aqueous solution, the cyclam‐substituted dye selectively forms near‐infrared absorbing aggregates. The latter allow the determination of citrate under realistic conditions by changes in absorption at wavelengths greater than 800 nm, which results from a disruption of the aggregates when citrate binds to Cu II . The copper ions thus act as mediators in a signalling reaction that constitutes a colourimetric displacement assay.