Search

The short-lived paramagnetic particles formed during the UV irradiation of nonsteroidal anti-inflammatory drug - ketoprofen (KP) have been investigated using chemically induced dynamic nuclear polarization (CIDNP). This study answers the questions about the nature of paramagnetic particles which can be responsible for KP phototoxic effects. Phototoxic side effects of NSAIDs, according modern point of view, are associated with the action of free radicals, however, there is insufficient information regarding the nature of the radical species. In contrast, most ketoprofen photodegradation schemes include carbanion as a precursor of products. CIDNP effects analysis has shown that all the major products of KP photodegradation can form via radical pairs (RPs) involving benzyl (2′), ketyl (3′) and CO2H or CO2− free radicals and solvated electron. Radical ways of KP photodegradation include: decarboxylation via RP with benzyl radical formation (I) in non-aqueous solution and both, (I) and photoreduction with formation of ketyl radicals in the presence of water. Moreover, it was found that the photoinduced radical decarboxylation of KP represents a reversible process.

Nanosecond laser flash photolysis (XeCl, 308 nm), optical spectroscopy, fluorescence, and time-resolved chemically induced nuclear polarization (CIDNP) were used to determine photophysical and photochemical processes for 5-sulfosalicylic acid dianion (HSSA2−) in aqueous solutions and frozen matrices. The triplet–triplet absorption (TTA) band with a maximum at 470 nm was recorded under excitation in the region of the long-wave absorption band of dianion (λmax=300 nm). For high laser pulse intensities, a two-quantum formation of an aquated electron is observed. CIDNP in solutions and flash photolysis in frozen matrices, with preliminary excitation to populate T1 state, indicate that photoionization occurs during absorption of a second quantum by an excited singlet S1 state. The spectral and kinetic characteristics of the excited states of dianion and aquated electron were determined.