1-Pyrene carboxaldehyde micelles

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. 

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. 

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... 

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. 

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. 

Quendiii of Exdted States.—Much research has been adapted from early observations that micelles could drastically alter the fluorescence lifetime of pyrene and the efficiency of excimer formation. The various mechanisms of excited-state transformation have been reviewed. " The polarity of the micellar surface may be estimated from the fluorescence spectrum of pyrene 2-carboxaldehyde " giving rise to the conclusion that sodium laurylsulphate (e=45) has a more polar surface than cetyltrimethylammonium bromide (e = 18). The fluidity of the site of solubilization may be estimated from fluorescence polarization " in surfactants of general structure (104). The Si... 

The interaction of cationic fluorocarbon and hydrocarbon surfactants was studied by Tamori et al. [145]. The mixed cmc of diethanolheptadecafluoro-2-2-undecanolammonium chloride and dodecyltrimethylammonium chloride was determined by electric conductivity measurements. Partition coefficients of alcohols (methanol and C4F7H2OH) and a fluorescent probe (pyrene-3-carboxaldehyde) between micelles and the bulk aqueous phase were determined. The data interpreted by a regular solution theory fitted an interaction parameter /3 = 1, indicating a much smaller repulsive interaction between the two cationic surfactants than that between an anionic fiuorinated surfactant and an anionic hydrocarbon-type surfactant. The weak repulsion between the two cationic surfactants was explained by a large difference in their cmc values. 

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