Micelles phosphorescence

Emission spectra Phosphorescence Differential phase Surfactant enhancement (micelles, etc.)... 

Finally, and apart from the importance of micelles in the solubilization of chemical species, mention should also be made of their intervention in the displacement of equilibria and in the modification of kinetics of reactions, as well as in the alteration of physicochemical parameters of certain ions and molecules that affect electrochemical measurements, processes of visible-ultraviolet radiation, fluorescence and phosphorescence emission, flame emission, and plasma spectroscopy, or in processes of extraction, thin-layer chromatography, or high-performance liquid chromatography [2-4, 29-33],... 

The uses of micelles in chemical analysis are rapidly increasing (Hinze, 1979). Analytical reactions are carried out typically on a small scale and are based on spectrophotometry. At the same time, undesired side reactions can cause major problems, especially when the analytical procedure depends on reactions which are relatively slow and require high temperatures, exotic solvents or high reagent concentrations for completion. Micelles can suppress undesired reactions as well as speed desired ones and they also solubilize reagents which are sparingly soluble in water. In addition it is often possible to make phosphorescence measurements at room temperature in the presence of surfactants which enormously increases the utility of this very sensitive method of detection. 

Phosphorescence can also be detected when the phosphor is incorporated into an ionic micelle. Deoxygenation is still required either by degassing with nitrogen or by the addition of sodium sulphite. Micellestabilized room-temperature phosphorescence (MS RTP) promises to be a useful analytical tool for determining a wide variety of compounds such as pesticides and polyaromatic hydrocarbons. 

Inorganic ions, such as Tl+, Ag+, etc., can be incorporated as counterions on anion micelles containing the excited triplet. Spin orbit coupling ensues and enhanced phosphorescence is observed. The spin orbit coupling reaction is too inefficient to be observed in homogeneous media. 

Photoinduced electron transfer from eosin and ethyl eosin to Fe(CN)g in AOT/heptane-RMs was studied and the Hfe time of the redox products in reverse micellar system was found to increase by about 300-fold compared to conventional photosystem [335]. The authors have presented a kinetic model for overall photochemical process. Kang et al. [336] reported photoinduced electron transfer from (alkoxyphenyl) triphenylporphyrines to water pool in RMs. Sarkar et al. [337] demonstrated the intramolecular excited state proton transfer and dual luminescence behavior of 3-hydroxyflavone in RMs. In combination with chemiluminescence, RMs were employed to determine gold in aqueous solutions of industrial samples containing silver alloy [338, 339]. Xie et al. [340] studied the a-naphthyl acetic acid sensitized room temperature phosphorescence of biacetyl in AOT-RMs. The intensity of phosphorescence was observed to be about 13 times higher than that seen in aqueous SDS micelles. 

Fig. 25. (A) DELFIA (Dissociation Enhanced Lanthanide Fluoro-ImmunoAssay) system. This heterogeneous immunoassay system uses a primary antibody bound to a solid support, to which a variable amount of unlabeled antigen is bound. The secondary antibody is labeled with a non-phospho-rescent lanthanide chelate, which becomes phosphorescent after dissociation from the antibody, due to the addition of an enhancement solution [which typically contains a mixture of sensitizer (typically a (1-diketonate) and micelle inducing surfactant (5). (B) Heterogeneous fluoroimmunoassay using a secondary antibody directly labeled with a phosphorescent lanthanide chelate.

Phosphorescence is most easily attained in a solid state rather than in the liquid state. In solid-state dissipation of energy by virtue of collision is minimised and time to the excited state increased. This result in increase in probability of inter system crossing and consequently to phosphorescent. Solid like rigidity and phosphorescence can also be attained by absorption of molecule on a surface or by using a Micelle to stabilise the molecules. 

If we estimate the time required for S-T mixing and recombination for a radical pair to be 100 ns( and the lifetime of the plvaloyl radical at 31°C to be v6 ps(i5., we can estimate the rate constant for the exit of t-butyl/plvaloyl radicals from HDTCl micelles to be on the order of 10 -10 sec . This Is nicely In line with exit rates of small phosphorescent probe molecules from similar micelle systems. 

The rates of diffusion of solutes and surfactants in and out of micelles have been measured using photophysical techniques. The most commonly used method is to measure the deactivation of excited states of the probe by added quenchers, which are only soluble in the aqueous phase. The measurement of either the decrease in emission intensity or a shortening of the emission lifetime of the probe can be employed to determine exit and entrance rates out of and into micelles 7d). The ability of an added quencher to deactivate an excited state is determined by the relative locations and rates of diffusion of the quenchers and excited states. Incorporation of either the quencher or excited state into a surfactant allows one to determine the rates of diffusion of surfactants. Because of the large dynamic range available with fluorescent and phosphorescent probes (Fig. 3), rates as fast as... 

When anionic micelles are employed the counter ions can often have a profound effect upon the photophysical processes of micellised compounds. Thus if the counter ion is a heavy atom, e.g. silver, intersystem crossing can become highly efficient and make it possible for phosphorescence to be readily detected at room temperature (Kalyanasundaram et al., 1977 Humphry-Baker et al., 1978). If, on the other hand, the counter ion does not interfere with photophysical processes, high triplet yields can be observed, e.g. for N-methyl-phenothiazine (Moroi et al., 1979a), zinc(II) tetrasulphophthalo-cyanine (Darwent, 1980), because the high likelihood of single occupancy of micelles precludes triplet-triplet annihilation. 

In room temperature phosphorescence, the triplet state of the analyte can be protected by being incorporated into a surfactant aggregate called a micelle. In aqueous solutions the aggregate has a nonpolar core due to repulsion of the polar head groups. The opposite occurs in nonpolar solvents. 

The properties of reverse micelles are of considerable interest at the present time. Amongst photochemical studies reported in this area are the behaviour of indole alkanoic acids and tryptamine in sodium dioctyl succinate, fluorescence and phosphorescence studies of A0T/H20/alkane systems using a variety of probes, photoionization of alkylphenothiazine sulphonates in reversed micelles, and interfacial interaction of probes with AOT inverted micelles. ... 

Observations of the room temperature phosphorescence of polycyclic aromatic hydrocarbons in micelles, which stabilize the triplet states by reduction of quenching, indicate that measurement of phosphorescence lifetimes can be a useful analytical parameter . Room temperature phosphorescence and delayed fluorescence have been shown to occur with triplet states of a wide variety of organic molecules in silica sol-gel glasses . ... 

Benzo-fused pyridinium systems also undergo the reaction and a new example, the photocyclisation of (153) to (154) in the presence of iodine, has been published. The quantum efficiency of photocyclisation of l,2-jbis-(a-naphthyl)ethylene to dihydropicene has been examined in micelles and the cyclisation of [5]-helicene (155) to dihydrobenzperylene (156) has been carried out at 4K (156) was characterised by its fluorescence and phosphorescence emission. The effect of different substituents on the photocyclisation of the symmetrically tetra-substituted stilbene (157) has been probed. 

Phosphorescence was employed to study the dynamics of polycyclic aromatic hydrocarbons with SDS micelles [62]. Equation (25) was applied with the assumption that k i, is negligible. In the case of 1-bromonaphthalene, the val-... 

Room-temperature phosphorescence in solution has been observed in organized media containing micelles. With miceltcs. the analyte is incorporated into the core of the micelle, which serves to protect the triplet stale. Cyclodexlrin molecules, which are... 

The anomalous activity characteristics have been attributed to conformational changes of the solubilized enzyme [49], but more recent spectroscopic studies seem to indicate that this is not the main cause. Solubilization of an enzyme into microemulsion droplets does not normally lead to major conformational alterations, as indicated, e.g., by fluorescence and phosphorescence spectral investigations [28,50]. The situation is complex, however, and it has been shown by circular dichroism (CD) measurements that the influence of the oil/water interface on enzyme conformation may vary even between enzymes belonging to the same class [51]. In the case of human pancreatic lipase, the conformation of the polypeptide chain is hardly altered after the enzyme is transferred from a bulk aqueous solution to the microenvironment of reverse micelles. Conversely, the CD spectra of the lipases from... 

In June 1986, Berthod started a sabbatical stay at the Department of Chemistry at the University of Florida with Prof J. D. Winefordner to study the hyphenation of laser spectroscopy with LC [9]. In December 1986, Dr. Garcia-Alvarez-Coque joined Winefordner s research group to investigate room-temperature phosphorescence in micellar media [10]. The exchange of ideas between both Berthod and Garcia Alvarez-Coque inspired their collaboration on fluorescence in microemulsions and reversed micelles [11]. 

In recent years, there has been a rapid growth in the number of publications that report the use of surfactant monomers or micelles to improve the analytical perfommice of various spectroscopic (UV-visible spectrophotometry, fluorimetry, phosphorimetry, chemiluminescence and atomic spectroscopy), and electrochemical (especially amperometry) methods [1]. The unique properties of surfactants have been recognized as being very helpful to overcome many problems associated with the use of organic solvents in these methods. Surfactant-modified procedures yield sensitivity and/or selectivity improvements in determinations commonly performed in homogeneous solution, whereas certain analytic methods (such as room-temperature phosphorescence in solution) can be exclusively conducted in organized media. 

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