Micelle pyrene

Pyrene carboxaldehyde and a series of pyrene carboxylic acids were found useful as fluorescence probes in describing the constitution of inverted micelles of certain calcium alkarylsulfonates in hydrocarbon media. 1-Pyrene carboxaldehyde is a convenient probe for studying the particle sizes of micelles in the region of lOOA. A series of graded probes, pyrene carboxylic acids with varying alkyl chain length, have been used to determine internal fluidity and micro-polarity as a function of distance from the polar core of these Inverted micelles. Pyrene exclmer to monomer fluorescence intensity ratio and fluorescene lifetime provided the means of measurement of internal fluidity and micropolarity, respectively. 

Radiolysis and Rdated Tedmiques.—Solvated electrons are the primary product of pulse radiolysis, and react with micellated pyrene with a rate constant of 10 s , the corresponding reaction with nitropyrene being twice as rapid. 

Other solubilization and partitioning phenomena are important, both within the context of microemulsions and in the absence of added immiscible solvent. In regular micellar solutions, micelles promote the solubility of many compounds otherwise insoluble in water. The amount of chemical component solubilized in a micellar solution will, typically, be much smaller than can be accommodated in microemulsion fonnation, such as when only a few molecules per micelle are solubilized. Such limited solubilization is nevertheless quite useful. The incoriDoration of minor quantities of pyrene and related optical probes into micelles are a key to the use of fluorescence depolarization in quantifying micellar aggregation numbers and micellar microviscosities [48]. Micellar solubilization makes it possible to measure acid-base or electrochemical properties of compounds otherwise insoluble in aqueous solution. Micellar solubilization facilitates micellar catalysis (see section C2.3.10) and emulsion polymerization (see section C2.3.12). On the other hand, there are untoward effects of micellar solubilization in practical applications of surfactants. Wlren one has a multiphase... 

Kalyanasundaram K, Thomas JK (1997) Solvent-dependent fluorescence of pyrene-3-car-boxaldehyde and its applications in the estimation of polarity at micelle-water interfaces. J Phys Chem 81 2176-2180... 

The evidence accumulated in the literature suggests that the structure of surfactant adsorbed layers is, in some respects, analogous to that of surfactant micelles. Fluorescence probing techniques - e.g., pyrene and dinaphtylpropane (DNP) fluorescence probes are used to investigate the structure of adsorbed layer of a surfactant - give information on the polarity of the microenvironment in the adsorbed... 

A popular method for the determination of micellar aggregation numbers is based on self-quenching of pyrene by excimer formation within micelles (see Box 4.2). 

Pyrene has been used to investigate the extent of water penetration into micelles and to accurately determine critical micellar concentrations (Kalyanasundaram, 1987). Polarity studies of silica or alumina surfaces have also been reported. In lipid vesicles, measurement of the ratio Ii/Iui provides a simple tool for determination of phase transition temperatures and also the effect of cholesterol addition. 

Kalyanasundaran K. and Thomas J. K. (1977a) Solvent-Dependent Fluorescence of Pyrene-3-Carboxaldehyde and its Applications in the Estimation of Polarity at Micelle-Water Interfaces,/. Phys. Chem. 81, 2176-2180. 

This may not be the full answer as the photoinduced electron exchange between pyrene, P, and dimethylaniline, D, on CTAB micelles and other CTAB structures, etc.,... 

Keywords Fluorescence probing Hemimicelle Micellar fluidity Micelle Organized assemblies in solution and interfaces Polarity parameter Pyrene... 

The photophysics of formation of pyrene monomer and excimer can be represented as shown in Scheme 1. In sufficiently dilute systems, when there is no micelle... 

The appearance of the excimer peak has been attributed to the formation of a premicelle or nascent micelle aggregate, which because of its small size and hydrophobic nature allows the solubilized excited pyrene to interact with the ground-state pyrene to form an excimer. The peak vanishes in the plateau due to the difficulties for the ground-state pyrene to encounter the excited species in the relatively large microdomain of the micelle. This observation led Sahoo et al. [123] to propose a step-wise formation for the micelles (Scheme 2, Fig. 16)... 

Initially, this mechanism was proposed on the basis of results obtained for zeta potential and flotation (Fig. 29). The formation of the hydrophobic aggregates at the interface was confirmed after the advent of the fluorescence probing technique. The adsorption isotherm is determined in the presence of pyrene as the fluorescent probe and the emission spectra of pyrene in both supernatant and slurries were analyzed after adsorption. The h/h of pyrene in solutions of SDS containing 0.1 M NaCl and in the slurry are shown in Figs. 30 and 31. In solution, the ratio remains at around 0.6 till the CMC (as determined by surface tension measurement) is attained. Above CMC, the value becomes 1.0 due to the solubilization of pyrene in micelles. In... 

Fig. 36 Schematic diagram of surfactant-adsorption on silica surface as monomer, hemimicelle, and at surfactant concentration above CMC where pyrene is bound to micelle...

Zhang et al. [135] have studied the physicochemical behavior of mixtures of -dodecyl-/l-D-maltoside with anionic, cationic and nonionic surfactants in aqueous solutions. To acquire information on the property of mixed micelles, the characteristic change of pyrene with changes in polarity was monitored. The polarity parameter at low concentrations was found to be 0.5-0.6. 

Fig. 45 Schematic representation of solubilization of pyrene in hydrophobic patches of a menger micelle, the exposure of the hydrophobic tail to water results in formation of hydrophobic patches at the micellar surface...

Fig. 46 Pyrene monomer and excimer decay profiles in SDS micellar solutions [SDS] = 8.2 X 10 kmolm , [NaCl] = 10 kmolm , CMC = 1.5 x 10" kmolm", pyrene levels are indicated as the ratio of micellized SDS to added pyrene emission monitored at 383 nm for monomer and 480 nm for excimer. (A) Monomer emission for SDS/Py = 2160, (B) monomer emission for SDS/Py 108 (C) excimer emission for SDS/Py = 108...

Characterization of Inverted Micelles of Calcium Alkarylsulfonates by Some Pyrene Fluorescence Probes... 

Much remains to be learned, however, regarding the limits of applicability of the fluorescence probe technique to aggregates in non-polar media. A number of obvious experiments are conspicuous by their absence from the published literature. For example, 1-pyrene carboxaldehyde is a well known probe which has been used to measure the microscopic polarity of sodium dodecyl sulfate micelles in aqueous medium (5) there is, however, no account of its use in non-polar media. 

In order to test further the applicability of 1-pyrene carboxaldehyde as a fluorescent probe, we applied Keh and Valeur s method (4) to determine average micellar sizes of sulfonate A and B micelles. This method is based on the assumption that the motion of a probe molecule is coupled to that of the micelle, and that the micellar hydrodynamic volumes are the same in two apolar solvents of different viscosities. For our purposes, time averaged anisotropies of these systems were measured in two n-alkanes hexane and nonane. The fluorescence lifetime of 1-pyrene carboxaldehyde with the two sulfonates in both these solvents was found to be approximately 5 ns. The micellar sizes (diameter) calculated for sulfonates A and B were 53 5A and 82 lOA, respectively. Since these micelles possesed solid polar cores, they were probably more tightly bound than typical inverted micelles such as those of aerosol OT. Hence, it was expected that the probe molecules would not perturb the micelles to an extent which would substantially affect the micellar sizes measured. 

Lateral Mobility(Fluidity) of Sulfonate A and B Micelles. The ratio of excimer to monomer fluorescence intensity of pyrene had previously been used to measure the fluidity of biological membranes (8). The ease of excimer formation was correlated with the fluidity of the membrane. The same principle may be applied to the measurement of fluidity in inverted micelles. To this end, we used three pyrene carboxylic acid probes of varying chain length PVA, PNA and... 

Figure 2. Unconvoluted anisotropy decays of 1-pyrene car ox-aldehyde in sulfonate micelles (a) sulfonate A (5 x 10 M)/ heptane (7 ns), (b) Sulfonate B (5 x 10 M /heptane (28 ns). The cmc of sulfonate A is less than 10 °M, while that of sulfonate B is "infinitely" dilute.

Polarity Variation in Sulfonate Micelles. Other workers have established a correlation between the fluorescence lifetime of pyrene in solution and the polarity of the solvent medium (9). Polar media quench the excited electronic state of pyrene and hence shorten its fluorescence lifetime. We applied this principle to measure the polarity variation within the micelles of sulfonates A and B. 

Pyrene Carboxaldehyde in Calcium Alkarylsulfonates. Our work shows that 1-pyrene carboxaldehyde as a fluorescent probe for the sulfonate systems behaves very much the same as rhodamine B (1 ) and anillnonaphthalene sulfonate (2), whose fluorescence intensities in hydrocarbon media are enhanced in the presence of inverted micelles. However, the intensity Increase observed with AOT was considerably less than that observed with the sulfonates. It is speculated that... 

Figure 5. Plots of the fluorescence lifetime of pyrene as a function of distance from the polar core of the micelles of sulfonates A and B in heptane solutions.

The internal rotational relaxation times of 1-pyrene carboxaldehyde in sulfonate systems may offer some indication of the extent of probe binding to the inverted micelle. In the absence of any background fluorescence interference to the time-dependent anisotropy decay profile, the internal rotational relaxation time should correlate with the strength of binding with the polar material in the polar core. However, spectral interference from the aromatic moieties of sulfonates is substantial, so that the values of internal rotational relaxation time can only be used for qualitative comparison. 

Lateral Mobility in Alkarylsulfonate Micelles. In order to make a valid comparison of fluidity between sulfonates A and B, the micellar sizes should be comparable. This condition is required so that equal population of pyrene moieties between the two sulfonate systems can be assumed. Alternatively, the requirements might be met if they have equal aggregation numbers. If the above-mentioned (See Section A under "Results") assumptions regarding polar core composition are reasonable, the condition for equal probe population between the two sulfonate micelles can still be reasonably approximated. 

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