Spectral characteristics of the aggregation of α,β,γ,δ-tetrakis(p-sulfophenyl)porphyrin in the presence of proteins

With the aid of absorption, fluorescence, and resonance light-scattering measurements, the aggregation of protonated water-soluble porphyrin, alpha,beta,gamma,delta-tetrakis(p-sulfophenyl)porphyrin [H(4)tpps(4)](2-), in the presence of proteins has been characterized. At pH 1.86, proteins dissolved in water can form a positively charged microphase, which can neutralize the negative charges of [H(4)tpps(4)](2-) distributed in it, leading to the J- and H-aggregation of [H(4)tpps(4)](2-). Exciton splitting signals, which are generally associated with the aggregation of porphyrins, as described by molecular-exciton theory, are observed at 436.1 nm on the resonance light-scattering spectra, supporting the porphyrin-porphyrin interactions in the positively charged microphase of proteins. It has been proved that positively charged microphase can protect aggregates of [H(4)tpps(4)](2-) from water dilution and high temperature.