Photophysical and Photochemical Studies of 2-Phenylbenzimidazole and UVB Sunscreen 2-Phenylbenzimidazole-5-sulfonic Acid¶

Abstract

The sunscreen agent 2-phenylbenzimidazole-5-sulfonic acid (PBSA) and its parent 2-phenylbenzimidazole (PBI) cause DNA photodamage via both Type-I and Type-II mechanisms when UVB irradiated. We have studied the photophysical and photochemical properties of these compounds and their ability to photogenerate reactive oxygen species including free radicals. PBI and PBSA exhibit both oxidizing and reducing properties in their excited state. The absorption and fluorescence properties of PBSA depend strongly upon pH, and hence the photochemistry of PBSA was studied in both neutral and alkaline solutions. PBSA showed strong oxidizing properties when UV irradiated in neutral aqueous solution (pH 7.4) in the presence of cysteine, glutathione and azide, as evidenced by the detection of the corresponding S-cysteinyl, glutathiyl and azidyl radicals with the aid of the spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO). However, when an aqueous anaerobic solution (pH 10) of PBSA and either nitromethane (NM) or 4-nitrobenzoic acid (4-NBA) were irradiated, the corresponding nitro anion radicals were observed. This finding suggests that both NM and 4-NBA are reduced by direct electron transfer from the excited state PBSA. During UV irradiation of an aerobic solution of PBSA, O2*- and *OH radical were generated and trapped by DMPO. Further, PBI (in ethanol) and PBSA (in ethylene glycol : water 2: 1 mixture) showed low temperature (77 K) phosphorescence (lambdamax = 443, 476 and 509 nm) and also an electron paramagnetic resonance half-field transition (deltaMs = +/-2), which is evidence for a triplet state. This triplet produced singlet oxygen (1O2) with quantum yields 0.07 and 0.04 in MeCN for PBI and PBSA, respectively. These studies demonstrate that UV irradiation of PBSA and PBI generates a variety of free radicals and active oxygen species that may be involved in the photodamage of DNA.

Clotrimazole Scaffold as an Innovative Pharmacophore Towards Potent Antimalarial Agents: Design, Synthesis, and Biological and Structure–Activity Relationship Studies

“…On the other hand, the piperazine nitrogen is protonated at the FV pH but is unable to generate a radical through a conjugation-mediated electron transfer. Accordingly, 4o was found to be more potent than 4p but slightly less potent than 2 because its benzimidazole ring is able to chelate iron and to generate free radicals 21 but is less protonated at FV pH than imidazole. This finding further supports our design hypothesis.…”

Photodegradation of the azole fungicide fluconazole in aqueous solution under UV-254: Kinetics, mechanistic investigations and toxicity evaluation

“…In fact, UV-254 photodegradation has been investigated for the removal of some emerging contaminants such as PPCPs (Benitez et al, 2013;Canonica et al, 2008;Liu et al, 2011;Marotta et al, 2013). In addition, reactive oxygen species (ROS) including singlet oxygen ( 1 O 2 ), superoxide anion radical ðO À$ 2 Þ and even stronger oxidant hydroxyl radical ( OH) can be photogenerated by certain PPCPs (Agrawal et al, 2007;Chen et al, 2008;Ge et al, 2010;Inbaraj et al, 2002), indicating that photodegradation could be a promising technology for the removal of emerging contaminants like fluconazole. However, there has been no photodegradation report available for fluconazole.…”

Sunscreen enhancement of UV-induced reactive oxygen species in the skin

“…To date the study of the effects of photoprotection molecules upon ROS production has been limited to a small number of solution-phase and in vitro experiments. Para-aminobenzoic acid (PABA) and 2-phenylbenzimidazle-5-sulfonic acid (PBSA) induce both 1 O 2 and thymine-dimer formation, although the two have not been definitely correlated [8][9][10][11][12][13][14]. Solution-phase studies found that octylmethoxycinnamate (OMC), octocrylene (OC), and PABA all produce 1 O 2 in phosphate-buffered saline (PBS) [8,13].…”