Fluorescent Probe Solubilization in the Headgroup and Core Regions of Micelles:  Fluorescence Lifetime and Orientational Relaxation Measurements

Abstract

Experimental results demonstrate that the fluorescent probes 2-(N-hexadecylamino)-naphthalene-6-sulfonate (HANS) and 2-(N-decylamino)-naphthalene-6-sulfonate (DANS) are solubilized in two distinct regions, that is, the headgroup and core, within micelles of cetyltrimethylammoniumbromide (CTAB), tetradecyltrimethylammoniumbromide (TTAB), dodecyltrimethylammoniumbromide (DTAB), cetyltrimethylammoniumchloride (CTAC), and tetradecyltrimethylammoniumchloride (TTAC). The fluorescence lifetime decays for both chromophores are biexponential in all the different micelles. The population associated with the shorter lifetime (τ 1 = 4-5 ns) is located in the Stern layer, where reduction of the fluorescence lifetime occurs because of quenching induced by the bromide counterions. The second population of chromophores is located in the hydrocarbon core region of the micelle. In this environment the chromophores have a considerably longer lifetime (τ 2 = 19-20 ns) because there is no significant quenching by bromide counterions. Evidence of water penetration places them fairly close to the core-Stern layer interface. Time-dependent fluorescence anisotropy is analyzed in terms of these two populations. The measurements show that the orientational relaxation of the probes in the hydrocarbon core region is considerably slower than orientational relaxation in the Stern layer. When the lifetime measurements and the orientational relaxation measurements are combined, the partitioning of the chromophores in the core and headgroup regions of the micelles can be determined.

Study of Ligand Substitution Reactions at Pentacyanoferrates(II) in Aqueous Salt and Micellar Solutions

“…In this regard two opposing factors can be operative. On one hand, it is known that the ionic concentration in the Stern layer of ionic micelles is high (3-5 mol dm −3 (21)) and this should cause a diminution in the rates of the two processes studied (see Table 1). On the other hand, the polarity of the layer sorrounding the cationic micelles is different from that of pure water (22).…”

Photophysics and rotational relaxation dynamics of a β-carboline based fluorophore in cationic alkyltrimethylammonium bromide micelles

“…Rotational diffusion of two ionic lipophilic fluorophores in alcohol and in SDS, CTAB, and TX-100 micellar environments was reported by Quitevis et al and the study has presented a detailed picture of the structural and dynamical aspects of the probes in micelle-water interfaces [22]. Study of the effect of hydrophobic chain length of surfactants on the dynamical behavior of a fluorophore was started rather recently [19][20][21]. Chakrabarty et al have reported the effect of varying chain length as well as head group of cationic surfactants on the rotational relaxation of coumarin 480 in micellar and mixed micellar environments [19].…”

“…Dynamic behavior includes the rotational and/or tumbling motion of the bound fluorophore within the microheterogeneous environments on the picosecond/nanosecond time scale [3,19]. Development of pico-and femtosecond lasers has enabled the researchers to directly probe into the ultrafast relaxation processes in micellar environments by time-resolved fluorescence depolarization techniques [8,14,[19][20][21]. Dutt characterized various components of rotational motion of two structurally similar dyes in Triton X-100 (TX-100) micelle, where the growth of the micelle was induced by the addition of sodium chloride [3].…”

“…Chakrabarty et al have reported the effect of varying chain length as well as head group of cationic surfactants on the rotational relaxation of coumarin 480 in micellar and mixed micellar environments [19]. Orientational relaxation studies of two biologically important dyes in alkyltrimethylammonium bromide (nTAB) and their chloride analogs (nTAC) have been studied by Fayer's group and they have determined the partition coefficients of the dyes that are distributed in two different domains of the micelles [20]. In one of our recent studies, we have shown the structural switchover of a proton transfer fluorophore, norharmane (NHM) in nTAB micelles, and the study demonstrates that chain length of the cationic surfactant plays an important role in promoting a specific prototropic form of the fluorophore [7].…”

Characterization of the kinetics of phospholipase C activity toward mixed micelles of sodium deoxycholate and dimyristoylphosphatidylcholine

“…(i) fluorescence quenching is diffusion controlled and as such the quenching rate constant, k q , determined from the fits to the quenched decay curve is given by the bimolecular collision rate between probe and quencher, (ii) the larger the size of the micelle, the smaller is the probe-quencher encounter rate; thus k q is inversely proportional to micelle size and has been observed to be so in all TRFQ experiments [20][21][22][23][24][25]. This is proven besides being intuitive.…”