Photosensitized enzyme deactivation and protein oxidation by axial-substituted phosphorus(V) tetraphenylporphyrins

Photosensitized Protein Damage by DiethyleneglycoxyP(V)tetrakis(p-n-butoxyphenyl)porphyrin Through Electron Transfer: Activity Control Through Self-aggregation and Dissociation

DiethyleneglycoxyP(V)tetrakis(p-n-butoxyphenyl)porphyrin (EGP(V)TBPP) forms a self-aggregation in an aqueous solution, and the photoexcited state of this molecule was effectively deactivated. Association with human serum albumin (HSA), a water-soluble protein, causes dissociation of the self-aggregation, resulting in recovery of the photosensitizer activity of EGP(V)TBPP. Under visible light irradiation, EGP(V)TBPP photosensitized HSA oxidation. The photosensitized singlet oxygen-generating activity of EGP(V)TBPP was confirmed by near-infrared emission measurement. A singlet oxygen quencher, sodium azide, partially inhibited the HSA photodamage; however, the quenching effect was estimated to be 57%. Another 43% of the HSA photodamage could be explained by the electron transfer mechanism. The redox potential of EGP(V)TBPP and the calculated Gibbs energy of electron transfer from tryptophan to photoexcited EGP(V)TBPP demonstrated the possibility of HSA oxidation through electron extraction. Fluorescence lifetime measurements of EGP(V)TBPP verified the electron transfer from HSA. The photosensitizer activity of EGP(V)TBPP can be controlled through an association with biomolecules, such as protein, and the electron transfer-mediated biomolecule photooxidation plays an important role in photodynamic therapy under hypoxia.

The Use of Fluorescent Probes to Detect ROS in Photodynamic Therapy

Photodynamic therapy employs nontoxic dyes called photosensitizers (PS) that are excited by visible light of the correct wavelength to produce a variety of reactive oxygen species (ROS) by an interaction between the long-lived PS triplet states with ambient oxygen. The most important type of ROS in photodynamic therapy (PDT) is singlet oxygen, which is produced by a Type II energy transfer process. On the other hand, superoxide, hydrogen peroxide, and hydroxyl radicals can be produced by a Type I electron transfer process. This chapter describes a set of fluorescent probes that can be used to tease apart these different ROS produced when various PS are illuminated in solution. Singlet oxygen sensor green (SOSG) is used for singlet oxygen, 4-hydroxyphenyl-fluorescein (HPF) for hydroxyl radicals, Amplex Red for hydrogen peroxide, and nitroblue-tetrazolium or XTT for superoxide.

Photoactivated biscarbocyanine dye with two conjugated chromophores: complexes with albumin, photochemical and phototoxic properties

Complexes of photosensitizers with blood proteins play an essential role in their delivery to the cell, as well as in the efficacy of photodynamic therapy. Biscarbocyanine dye non-covalently binds human serum albumin (HSA), the dissociation constant of the dye with albumin being Kd = (1.7 ± 0.1) × 10-5 M. According to time correlated single photon counting (TCSPC) fluorescence lifetime spectroscopy data, two types of complexes with lifetimes of 1.0 ns and 2.5 ns are formed between the dye and HSA. Confocal fluorescence microscopy has unambiguously shown the penetration of biscarbocyanine into endoplasmic reticulum, lysosomes, mitochondria and nuclei of the cells. The dye demonstrates photocytotoxicity towards the colon carcinoma HCT116 cells with IC50 = 0.3 μM. Hydrophobicity of the polymethine chain and the presence of two positive charges on the dye molecule contribute to the effective binding of the dye with HSA and the penetration into cells. These facts allow considering the biscarbocyanine dye as a promising agent for the photodynamic therapy of cancer.

A photochemical and theoretical study of the triplet reactivity of furano- and pyrano-1,4-naphthoquionones towards tyrosine and tryptophan derivatives

The photochemical reactivity of the triplet state of pyrano- and furano-1,4-naphthoquinone derivatives (1 and 2) has been examined employing nanosecond laser flash photolysis. The quinone triplets were efficiently quenched by l-tryptophan methyl ester hydrochloride, l-tyrosine methyl ester hydrochloride, N-acetyl-l-tryptophan methyl ester and N-acetyl-l-tyrosine methyl ester, substituted phenols and indole (k q ∼109 L mol-1 s-1). For all these quenchers new transients were formed in the quenching process. These were assigned to the corresponding radical pairs that resulted from a coupled electron/proton transfer from the phenols, indole, amino acids, or their esters, to the excited state of the quinone. The proton coupled electron transfer (PCET) mechanism is supported by experimental rate constants, isotopic effects and theoretical calculations. The calculations revealed differences between the hydrogen abstraction reactions of phenol and indole substrates. For the latter, the calculations indicate that electron transfer and proton transfer occur as discrete steps.