Spectroscopic Studies of Water‐Soluble Porphyrins with Protein Encapsulated in Bis(2‐ethylhexyl)sulfosuccinate (AOT) Reverse Micelles: Aggregation versus Complexation

Abstract

We have investigated the interaction of two water-soluble free-base porphyrins (negatively charged meso-tetrakis(p-sulfonatophenyl)porphyrin sodium salt (TSPP) and positively charged meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMpyP)) with two drug-carrier proteins (human serum albumin (HSA) and beta-lactoglobulin (betaLG)) in bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane/water reverse micelles (RM) by using steady-state and transient-state fluorescence spectroscopy. TSPP exhibited a complex pattern of aggregation on varying the RM size and pH in the absence of the protein: at low omega0 (the ratio of water concentration to AOT concentration, the emission of H-aggregates prevails under acidic or neutral "pH(ext)" conditions. Upon formation of the water-pool, J-aggregates and monomeric diacid species dominate at low "pH(ext)" but only monomer is detected at neutral "pH(ext)". The aggregation number increases with omega0 and the presence of the protein does not seem to contribute to further growth of the aggregate. The presence of protein leads to H-deaggregation but promotes J-aggregation up to a certain protein/porphyrin ratio above which, complexation with the monomer bound to a hydrophobic site of the protein prevails. The effective complex binding constants are smaller than in free aqueous solution; this indicates a weaker binding in these RM probably due to some conformational changes imposed by encapsulation. Only a weak quenching of TMpyP fluorescence is detected due to the presence of protein in contrast to the negative porphyrin.

Spectral properties of tetraanionic porphyrin in formamide colloids of layered double hydroxides

“…Apparently the band at longer wavelength was due to low emission from molecular aggregates. This is in agreement with similar changes observed for the systems based on TPPS in micelles [23]. The low emission band, red-shifted with respect to that for monomers, was assigned to the H-aggregates.…”

Translational and Rotational Motions of Albumin Sensed by a Non-Covalent Associated Porphyrin Under Physiological and Acidic Conditions: A Fluorescence Correlation Spectroscopy and Time Resolved Anisotropy Study

“…Moreover, under acidic conditions TSPP is prevalently present in solution as a zwitterion. This has proved to contribute decisively to the formation of highly ordered molecular aggregates of the porphyrin at relatively low [TSPP] induced by different polymeric templates [12][13][14] including albumins [11,15]. These aggregates of J-type are particularly interesting in view of their possible applications in nonlinear optics, nanometer-sized photoconductors, and light harvesting systems and contributed also for the relevance of the studies carried on at pH=2.…”

J-aggregation of a sulfonated amphiphilic porphyrin at the air–water interface as a function of pH

“…This band has been assigned either as an H-aggregate or to the splitting of the Soret band [17,58]. In the case of TPPS 4 porphyrin [29], similar behavior to the (OD) 3 TPPS 3 porphyrin is exhibited, that is, DR < 1.…”

“…It was reported that the J-aggregation of the TPPS 4 could be promoted in the presence of template agents such as surfactants [14,16,17], proteins [18], dendrimers [19] and helical polyacetylene [20] and polysaccharide [21], as well as at different medium, as the air-water interface [22][23][24], and liquid-liquid interface [25].…”