The Biphotonic Photoionization of Chlorpromazine During Conventional Flash Photolysis: Spin Trapping Results With 5,5‐dimethyl‐1‐pyrroline‐n‐oxide

Abstract

A novel combination of conventional flash photolysis and electron spin resonance (ESR) spin-trapping has been used to demonstrate that photoionization of chlorpromazine (CPZ), and the concomitant production of hydrated electron, occurs through a stepwise biphotonic mechanism during conventional flash photolysis at wavelengths above 290 nm. The production of hydrated electron in the flash photolysis experiment has been monitored and quantified through the use of the spin trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). The effects of nitrous oxide, varying concentrations of CPZ and DMPO, and a range of flash intensities on the ESR spectra of the observed spin adducts of DMPO are discussed. The use of ESR spin trapping to monitor hydrated electron yields in flash photolysis experiments has the potential to permit the use of a much wider range of flash intensities than is typically possible with conventional optical experiments. Thus, there is a greater possibility of distinguishing between monophotonic and biphotonic processes.

UVA/B-Induced Formation of Free Radicals from Decabromodiphenyl Ether

“…Deca-BDE absorbs readily in the wavelength range passed by a 309 nm filter, but there is no absorbance above ~350 nm (Figure S1). THF, DMF, toluene, and DMPO (λ max = 230 nm, ε 228 = 7.7 × 10 3 M −1 cm −1 ) (28) do not absorb significantly in this range (Figure S1). Thus, the activating wavelength for radical formation from deca-BDE is in the UVA (400-320 nm) to UVB (320-280 nm) range.…”

Excited-state Properties and In Vitro Phototoxicity Studies of Three Phenothiazine Derivatives¶

“…In fact, it decays by a first-order kinetics (likely because of the interaction with a molecule of drug in the ground state); its kinetics was not affected by the presence of molecular oxygen and was sensitized in acetonitrile by chloranil, a well-known electron acceptor in the triplet state (30)(31)(32)(33). This behavior is in agreement with that already reported for similar compounds (34). The spectral and kinetic properties of the transients detected in water are shown in Table 4, together with the absorption coefficients of the cation radicals and the photoionization quantum yields.…”

Photosensitization of Biomolecules by Phenothiazine Derivatives

“…As already reported for CPZ [30][31][32][33], laser flash experiments with these phenothiazines derivatives indicate the occurrence of monophotonic ionization of the substrate, even if a scarce contribution of a biphotonic pathway cannot be excluded, as suggested for CPZ by conventional flash photolysis [35] and the two-color, twopulse excitation method [36] described above.…”

“…Thus phenothiazines photoionization has been clearly demonstrated by several groups using transient absorption spectroscopy or EPR, but controversy remains over the mechanism of photoionization of these compounds. Motten et al [33], Buetner et al [34] and Hall et al [35] in contrast to the previous works proposed a wavelength-dependent photoionization of CPZ and promazine (PMZ) involving stepwise biphotonic photoionization through the triplet state at wavelength> 280 nm and monophotonic photoionization at wavelength <300 nm: this wavelength dependence suggest that the mechanism for cutaneous phototoxicity associated with clinical use of CPZ, which occur at solar wavelength >300 nm does not involve photoionization. More recently Garcia et al [36] in an elegant study using conditions where absorption by singlet or triplet excited states occur selectively have confirmed that photoionization occurs through biphotonic excitation for CPZ and PZ.…”