Time-resolved fluorescence depolarization of rhodamine B and octadecylrhodamine B in Triton X-100 micelles and Aerosol OT reversed micelles.

J. Phys. Chem. 92 (1988) 759-765
Source: OAI
  • [Show abstract] [Hide abstract]
    ABSTRACT: The peculiarities of the structure of the fluorescent dye N,N'-di-n-octadecylrhodamine advantage its using as an interfacial acid–base probe in aqueous micellar solution of colloidal surfactants. Two long hydrocarbon tails of the dye provide similar orientation of both cation and zwitterion on the micelle/water interface, with the ionizing group COOH exposed to the Stern region in all the systems studied. Further, the charge type of the acid–base couple, A+B±, ensures similar values of the ‘intrinsic’ contribution, pK, to the ‘apparent’ pK value in micelles of different surfactants. This makes the indicator suitable for determination of electrical surface potentials, Ψ. The pKs have been obtained in cationic, anionic, zwitterionic, and nonionic surfactant systems, at various salt background. In total 17 systems were studied. At bulk counterion concentration of ca. 0.05 M, the pK values vary from 2.14 ± 0.07 in n–C18H37N(CH3)Cl– micelles to 5.48 ± 0.06 in n–C16H33OSONa+ micelles. The Ψ values, corresponding to the Stern region of micelles, have been evaluated as Ψ = 59.16 pK–pK for T = 298.15 K. The pK parameter was equated to the average value of 4.23 in nonionic surfactants (4.12–4.32, depending on the surfactant type). For cetyltrimethylammonium bromide and sodium n-dodecylsulfate micelles, the Ψ values (±(7–11) mV) appeared to be +118 mV and at bulk Br− concentration 0.019 M and −76 mV at bulk Na+ concentration 0.020 M, respectively. This satisfactorily agrees with the theoretical values +111 and −84 mV, estimated using the Oshima, Healy, and White equation for these well-defined colloidal systems. Finally, not only absorption, but also fluorescence spectra display the same response to changes in bulk pH. Copyright © 2007 John Wiley & Sons, Ltd.
    Journal of Physical Organic Chemistry 04/2007; 20(5):332 - 344. · 1.58 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Abstract Fluorescence, excitation and absorption spectra of octadecylrhodamine B (ORB) have been observed in solutions of water, methanol, ethanol and other simple alcohols. A remarkable increase in the ORB fluorescence intensity occurs when the probe is transferred from water to the alcohols. This effect is ascribed to the release of ORB fluorescent monomers from nonfluorescent multimers, which exist predominantly in water. The dependence of the fluorescence intensity on the composition of water-alcohol binary solvent systems shows that hydrophobic interactions play an important role in the monomer = multimer equilibrium of ORB in these solutions. The fluorescence lifetimes of ORB in the alcohols are also reported.
    Photochemistry and Photobiology 01/2008; 60(6):563 - 566. · 2.29 Impact Factor
  • Shikizai Kyokaishi 01/2010; 83(2):66-75.