Fluorescence decay measurements micellization

Static fluorescence quenching has been used to measure the mean aggregation number of surfactant-related systems [27-29]. This method was originally developed by Turro and Yekta for anionic surfactant micelles [30]. This method works well without significant errors when kjk1 and no quencher redistribution has taken place. On the other hand, fluorescence-decay experiment, namely, time-resolved fluorescence quenching (TRFQ), has been extensively used to determine the micelle aggregation number in a surfactant system. The reader is referred to the review [24] on this subject. 

Fig. 11 Relative fluorescence decays of naphthalene tags. Fda(0/Fd(0 vs. time t. Fda(0 is the fluorescence from the double-tagged micelles and FcCO is the decay measured in a virtually identical micellar system formed by chains of almost the same length of both blocks tagged only by naphthalene in between the blocks in a 1,4-dioxane-watermixlraes with 5,20, and 100 vol % water, respectively (curves 1, 2, and 3). Adapted with permission frran Macromolecules 35, 2002, 9497-9505, flgure 7, [178]. Copyright 2002. American Chemical Society...

For quite some time, there have been indications for a phase-separation in the shell of polyelectrolyte block copolymer micelles. Electrophoretic mobility measurements on PS-PMAc [50] indicated that a part of the shell exhibits a considerable higher ionic strength than the surrounding medium. This had been corroborated by fluorescence studies on PS-PMAc [51-53] and PS-P2VP-heteroarm star polymers [54]. According to the steady-state fluorescence and anisotropy decays of fluorophores attached to the ends of the PMAc-blocks, a certain fraction of the fluorophores (probably those on the blocks that were folded back to the core/shell interface) monitored a lower polarity of the environment. Their mobility was substantially restricted. It thus seemed as if the polyelectrolyte corona was phase separated into a dense interior part and a dilute outer part. Further experimental evidence for the existence of a dense interior corona domain has been found in an NMR/SANS-study on poly(methylmethacrylate-fr-acrylic acid) (PMMA-PAAc) micelles [55]. 

A spectroscopic investigation of the formation of THF-Cu"Cl2 complexes has been described, and irradiation of [Cu(Dto)2] (Dto = dithiooxalate) has been found to induce an intramolecular Dto Cu two-electron transfer with cleavage of the C-C bond in the Dto ligand and the formation of SCO. The kinetics of photo-oxidation of pyrene by Cu" in SDS micelles have been measured, but oxidants such as Eu" and Hg do not produce pyrene cations. A non-exponential decay of fluorescence is observed, and this is interpreted in terms of a model due to Tachiya which restricts the numbers of quenchers in a micelle. Transient Cu"-alkyl species are formed on flash photolysis of Cu -bis(amino-acid) complexes such as those of serine and valine, and pseudo first order rate constants for the decay of the transients have been obtained. 

H -tetramethylbenzidine in anionic-cationic mixed micelles has been studied in detail by ESR . The photochemistry of the semi-oxidised forms of eosin Y and rose bengal have been investigated in colloidal solutions. Relevant to the fluorescence of proteins is a study of fluorescence quenching of indolic compounds by amino-acids in SOS, CTAB, and CTAC micelles O Rate constants for proton transfer of several hydroxyaromatic compounds have been measured in a variety of surfactant solutions. Photoprotolytic dissociation does not require exit of the reactant molecules from the micelles. Micellar solutions can be used to improve the fluorescence determination of 2-naphthol by inhibiting proton transfer or proton inducing reactions z2. jpe decay of the radical pair composed of diphenylphosphonyl and 2,4,6-trimethyl benzoyl radicals in SDS is affected by magnetic... 

The steady-state fluorescence of p-naphthol in water (Figure 41) consists of two emission bands, 350 nm (4>OH ) and 410 nm (< >0 ). Once adsorbed on Brij 58 micelles (4 mg/ml), the emission band of is not observed any more, indicating that the emitter molecules are adsorbed and immerse their hydroxyl in the hydrophobic phase of the micelle. Time-resolved fluorescence reveals that this is not precisely so. The fluorescence at A >435 nm has a fast rise time, much faster than that measured for (3-naphthol in water, and a decay time characteristic for the... 

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