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Polymethine cyanine dyes in β ‐cyclodextrin solution: multiple equilibria and chemical oxidation
Author(s) -
Barros Teresa C.,
Toma Sergio H.,
Toma Henrique E.,
Bastos Erick L.,
Baptista Mauricio S.
Publication year - 2010
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1692
Subject(s) - chemistry , cyanine , reaction rate constant , oxidizing agent , photochemistry , reactivity (psychology) , cyclic voltammetry , cyclodextrin , hydrogen peroxide , absorption spectroscopy , stoichiometry , absorption (acoustics) , electrochemistry , fluorescence , inorganic chemistry , kinetics , organic chemistry , medicine , physics , alternative medicine , electrode , pathology , quantum mechanics , acoustics
Absorption and fluorescence spectroscopy, electrochemical techniques, and semiempirical calculations were employed to characterize the multiple complexation equilibria between two polymethine cyanine dyes (IR‐786 and Indocyanine green‐ICG, S) and β ‐cyclodextrin ( β ‐CD, L), as well as the chemical reactivity of the complexed and uncomplexed species against the oxidizing agents hypochlorite (HC) and hydrogen peroxide (HP). IR‐786 dimerization is favored with the increase in β ‐CD concentration in the form of (SL) 2 complexes. In the case of ICG, free dimers (D) and SL complexes are favored. Both IR‐786 and ICG react and discolor in the presence of HC and HP. For IR‐786, the reaction with HP and HC proceeds with observed rate constants of 10 −3 and 0.28 s −1 and second‐order rate constants ( k 2 ) of ∼10 −3 and 10 4 M −1 s −1 , respectively. The intermediate species observed in the bleaching reactions of IR‐786 and ICG were shown, by cyclic voltammetry and VIS absorption, to result from one electron oxidation. IR‐786 complexed with β ‐CD is protected against bleaching in the presence of HP and HC by factors of 20 and 4, respectively. This protection was not observed in ICG complexes. Superdelocalizability profile of both dyes and frontier orbital analysis indicates that β ‐CD does not protect ICG from oxidation by HP or HC, whereas the 2:2 IR‐786/ β ‐Cd complex is able to avoid the oxidation of IR‐786. We concluded that the decrease in the chemical reactivity of the dyes against oxidant agents in the presence of β ‐CD is due to the formation of (SL) 2 complexes. Copyright © 2010 John Wiley & Sons, Ltd.