The efficacy of surfactant mixtures of Pluronic ® F127 and Tween 80 at overall concentration in the micromolar range and molar ratio 1:1, 1:10, and 10:1 in inhibiting aggregation of the photosensitizer meso-tetraphenyl chlorin disulphonate (TPCS 2a ) was investigated in aqueous media at pH 2.9 by means of steady-state absorption and fluorescence emission spectroscopy as well as time-resolved fluorescence analysis. Corresponding experiments were performed at pH 7.4 in the absence of surfactants to determine the spectroscopic properties of a monomeric sample. Aggregation resulted in a red shift of the Soret absorption band and in substantial fluorescence quenching. The fluorescence lifetime of TPCS 2a was a particularly sensitive indicator of the aggregation state, as the monomer at pH 7.4 decayed with a ∼ 10 ns time constant, while aggregation resulted in subnanosecond decay. The critical micelle concentration (CMC) of the surfactant mixtures was determined spectrophotometrically in the presence of TPCS 2a . The ability of the surfactant mixtures to prevent aggregation at acidic pH was evaluated at overall surfactant concentration below and above CMC. Solubilization of TPCS 2a in Pluronic ® F127/Tween 80 mixtures prevented aggregation of the photosensitizer at overall surfactant concentrations much lower than those needed for both pure Pluronic ® F127 and pure Tween 80.
Solubilization of the chlorin TPCS 2a in the presence of Pluronic ® F127/Tween 80 mixtures
CUCCATO, NICOLA;Nardo L.;
2019-01-01
Abstract
The efficacy of surfactant mixtures of Pluronic ® F127 and Tween 80 at overall concentration in the micromolar range and molar ratio 1:1, 1:10, and 10:1 in inhibiting aggregation of the photosensitizer meso-tetraphenyl chlorin disulphonate (TPCS 2a ) was investigated in aqueous media at pH 2.9 by means of steady-state absorption and fluorescence emission spectroscopy as well as time-resolved fluorescence analysis. Corresponding experiments were performed at pH 7.4 in the absence of surfactants to determine the spectroscopic properties of a monomeric sample. Aggregation resulted in a red shift of the Soret absorption band and in substantial fluorescence quenching. The fluorescence lifetime of TPCS 2a was a particularly sensitive indicator of the aggregation state, as the monomer at pH 7.4 decayed with a ∼ 10 ns time constant, while aggregation resulted in subnanosecond decay. The critical micelle concentration (CMC) of the surfactant mixtures was determined spectrophotometrically in the presence of TPCS 2a . The ability of the surfactant mixtures to prevent aggregation at acidic pH was evaluated at overall surfactant concentration below and above CMC. Solubilization of TPCS 2a in Pluronic ® F127/Tween 80 mixtures prevented aggregation of the photosensitizer at overall surfactant concentrations much lower than those needed for both pure Pluronic ® F127 and pure Tween 80.
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