The Triplet and Radical Species of Haematoporphyrin and Some of Its Derivatives

Abstract

Abstract— Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin, and three 0‐acyl compounds derived from it (the monoacetate, the diacetate and the disuccinate). After 347 nm irradiation in water containing 2% Triton X‐100, haematoporphyrin forms the triplet state (φT= 0.92) and photoionises monophotonically (φI= 0.03). For the O‐acyl derivatives, φT approaches unity and photoionisation is reduced. In acetone the triplet yield of all four compounds are close to unity. The difference and corrected spectra for the triplet species are presented and decay rates (k1˜104s‐1) and oxygen quenching constants (kQ˜1.5times109M‐1s‐1) for the triplet state have been measured. The difference and corrected spectra for the semi‐reduced species in methanol and semi‐oxidised species in aqueous Triton X‐100 are presented. The photophysical characteristics in fluid solution of haematoporphyrin and its 0‐acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins.

Enhancement of meta-tetrahydroxyphenylchlorin-sensitized photodynamic treatment on human tumor xenografts using a water-soluble vitamin E analogue, Trolox

“…The slow absorbance growth was assigned to the reduction of the mTHPC triplet state leading to the mTHPC anion radical (mTHPC •-, step 4; Fig.4). The observed spectral properties are very similar to these of porphyrin or chlorophyll radicals (Bonnett et al, 1983;Neta et al, 1979). The rate constant for the reaction between Trolox and 3 mTHPC, k r , is given by the slope of the linear plots shown in Figure 5b.…”

“…The sum of contributions of the 1 O 2 -and Trolox-mediated pathways is not 100% due to natural decay of the triplet state (step 2). (Bonnett et al, 1983;Brault et al, 1988), triplet formation at this wavelength was characterized by a small absorbance increase that decayed subsequently according to step 2 (Fig. 5).…”

Controlled targeting of different subcellular sites by porphyrins in tumour-bearing mice

“…Furthermore, the possibility exists to target different subcellular sites by selecting the porphyrin to be transported. This should not cause large modifications of the intrinsic efficiency of the photosensitisation process, since most free base porphyrins display similar photophysical properties, including the ability to generate the cytotoxic agent 102 (Bonnett et al, 1980(Bonnett et al, , 1983Reddi et al, 1983). On the other hand, the preferential localisation of porphyrins in given subcellular structures can affect the type of photodamaged targets, hence the mechanism and kinetics of cell necrosis (Brun et al, 1981;Sandberg & Romslo, 1981).…”

Steady-state and time-resolved spectroscopic studies of photodynamic sensitizers: Porphyrins and phthalocyanines

“…The formation of T1 for various porphyrins has been studied by laser flash photolysis and pulse radiolysis [25,26]. In nitrogen-saturated solutions, the porphyrin triplet state generally has a lifetime of several hundred microseconds [25,27]. For any given porphyrin this value is only slightly affected by the nature of the solvent.…”