Fluorescence of aminofluoresceins as an indicative process allowing one to distinguish between micelles of cationic surfactants and micelle-like aggregates

Abstract

Among the vast set of fluorescein derivatives, the double charged R anions of aminofluoresceins are known to exhibit only low quantum yields of fluorescence, [Formula: see text]. The [Formula: see text] value becomes as high as that of the fluorescein dianion when the lone electron pair of the amino group is involved in a covalent bond. According to Munkholm et al (1990 J. Am. Chem. Soc. 112 2608-12), a much smaller increase in the emission intensity can be observed in the presence of surfactant micelles. However, all these observations refer to aqueous or alcoholic solvents. In this paper, we show that in the non-hydrogen bond donor (or 'aprotic') solvents DMSO and acetone, the quantum yields, φ, of the 4'- (or 5')-aminofluorescein R species amount to 61-67% and approach that of fluorescein (φ = 87%), whereas in water φ is only 0.6-0.8%. In glycerol, a solvent with an extremely high viscosity, the φ value is only 6-10%. We report on the enhancement of the fluorescence of the aminofluorescein dianions as an indicative process, which allows us to distinguish between the micelle-like aggregates of cationic dendrimers of low generation, common spherical surfactant micelles, and surfactant bilayers. Some of these colloidal aggregates partly restore the fluorescence of aminofluoresceins in aqueous media. By contrast, other positively charged micellar-like aggregates do not enhance the quantum yield of aminofluorescein R species. Results for several related systems, such as CTAB-coated SiO particles and reverse microemulsions, are briefly described, and the possible reasons for the observed phenomena are discussed.

Click-based thiol-ene photografting of COOH groups to SiO2 nanoparticles: Strategies comparison

“…Interestingly, the emission band of fluorescein anchored to the nanoparticle presents a remarkable increase in intensity compared to that corresponding to free dye at the same concentration. This was previously reported and attributed to the suppression of the self-quenching effect generated by the free electron pair of the amino group on the fluorophore when it becomes involved in a covalent bond, which results in an increase in quantum fluorescence yield[50]. In addition, the immobilization of fluorescein on the surface of the nanoparticle is verified from fluorescence anisotropy experiments where we obtain an anisotropy of 0.2 at the wavelength of the emission maximum, close to the theoretical value of 0.3(Figure 3Inset) [51].…”

A Dual Fluorescence–Spin Label Probe for Visualization and Quantification of Target Molecules in Tissue by Multiplexed FLIM–EPR Spectroscopy

“…In the next step a fluorescent dye is covalently attached to 4 . In a first trial, 6‐amino‐fluorescein was attached through an amide bond to the carboxylic acid of compound 4 , expecting that the covalent attachment of 6‐aminofluorescein yields a fluorescent conjugate [21] . Unfortunately, neither fluorescence increase upon attachment nor an active spin‐probe were observed (Figure S1).…”

“…In the next step afluorescent dye is covalently attached to 4.I nafirst trial, 6-amino-fluorescein was attached through an amide bond to the carboxylic acid of compound 4,e xpecting that the covalent attachment of 6aminofluorescein yields af luorescent conjugate. [21] Unfortunately,neither fluorescence increase upon attachment nor an active spin-probe were observed (Figure S1). This may be due to quenching effects on the reactions of the PCA radical by the aminofluorescein derivative.For asuccessful fluorescence labeling,weused apiperazine linker between the fluorophore and the spin probe.RhoB was functionalized with piperazine (5)t oa llow stable amide bond formation with the COOH group of lysine and to avoid pH-driven cyclization that forms an on-fluorescent adduct.…”

Aminofluoresceins Versus Fluorescein: Ascertained New Unusual Features of Tautomerism and Dissociation of Hydroxyxanthene Dyes in Solution

“…DMSO and acetonitrile were purified as previously described. 68 The water content was determined by the Karl Fischer potentiometric method (in acetonitrile: 0.007%, in DMSO: 0.016 to 0.06%).…”