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298 results on '"Hirakawa, Kazutaka"'

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

Author

Hirakawa, Kazutaka, Yoshida, Mami, Hirano, Toru, Nakazaki, Jotaro, and Segawa, Hiroshi

Subjects
*CHARGE exchange, *REACTIVE oxygen species, *PORPHYRINS, *GIBBS' free energy, *PHOTODYNAMIC therapy, *ENERGY transfer
Abstract

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. [ABSTRACT FROM AUTHOR]

Published
2022
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48. Electron Transfer-Supported Photodynamic Therapy

Author

Hirakawa, Kazutaka

Subjects
Medical
Abstract

Photodynamic therapy (PDT) is a less-invasive treatment of cancer and precancerous lesions. Porphyrin derivatives have been used and studied as the photosensitizers for PDT. In general, the biomacromolecules oxidation by singlet oxygen, which is produced through energy transfer from the photoexcited photosensitizers to oxygen molecules, is an important mechanism of PDT. However, the traditional PDT effect may be restricted, because tumors are in a hypoxic condition and in certain cases, PDT enhances hypoxia via vascular damage. To solve this problem, the electron transfer-mediated oxidation of biomolecules has been proposed as the PDT mechanism. Specifically, porphyrin phosphorus(V) complexes demonstrate relatively strong photooxidative activity in protein damage through electron transfer. Furthermore, other photosensitizers, e.g., cationic free-base porphyrins, can oxidize biomolecules through electron transfer. The electron transfer-supported PDT may play the important roles in hypoxia cancer therapy. Furthermore, the electron transfer-supported mechanism may contribute to antimicrobial PDT. In this chapter, recent topics about the biomolecules photooxidation by electron transfer-supported mechanism are reviewed.

Published
2019

50. Biomolecules Oxidation by Hydrogen Peroxide and Singlet Oxygen

Author

Hirakawa, Kazutaka

Subjects
Science / Life Sciences / Cell Biology
Abstract

Hydrogen peroxide (H2O2) and singlet oxygen (1O2) are important reactive oxygen species (ROS) for biological and medicinal fields. Oxidation processes of chemical materials by molecular oxygen are important H2O2 source, whereas photochemical reaction is important for 1O2 production. Reactivity and biomolecule damage by these ROS depend on the surrounding conditions and targeting molecules. In this chapter, production mechanisms of H2O2 and 1O2, biomolecule oxidation by these ROS, their detection methods, and production control of 1O2 are briefly reviewed.

Published
2018

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