Photodegradation of antibiotic 5-sulfaminouracil in the presence of vitamin B2: a kinetic study.

OBJECTIVE: This paper studies the kinetics and mechanism of the sensitized photodegradation of 5-sulfaminouracil (SFU). This compound is a synthetic bacteriostatic belonging to the sulfa drugs, usually detected in surface water and effluent wastewater. METHODS: SFU interacts with electronically excited singlet and triplet states of riboflavin (Rf), (1)Rf* and (3)Rf*, respectively. The rate constants for these processes were determined in MeOH-H2O by stationary fluorescence spectroscopy (for kQ(1)) and by laser flash photolysis (for kQ(3)). RESULTS: SFU is photodegraded by visible light irradiation in the presence of the natural sensitizer (Rf). In competitive processes, (3)Rf* generates the reactive oxygen species superoxide radical anion (O2(•-)) and singlet molecular oxygen [O2((1)Δg)], which are involved in SFU photodegradation. In aqueous solutions, where SFU adopts different forms depending on the pH of the medium, the participation of O2((1)Δg) is predominant. Therefore, the O2((1)Δg)-mediated mechanism was evaluated at pHs 7 and 12, employing perinaphthenone as a synthetic photosensitizer. DISCUSSION: The results indicate that SFU is photodegraded through a relatively efficient process in a neutral environment, whereas it is quickly degraded in alkaline media. This is attributed to the ionization of the sulfamino- group, a substituent in the uracil molecule that exerts an activating power on the molecule. Thus, sensitized photodegradation may be an important tool to reduce the environmental impact of SFU.

Solvent effect on the UV/Vis absorption and fluorescence spectroscopic properties of berberine.

Spectral and photophysical properties of the alkaloid berberine (B) were studied in solvents with different solvent parameters, using UV/Vis absorption, emission and excitation spectroscopy. The absorption and emission maxima were found to be between 421-431 nm and 514-555 nm, respectively, leading to Stokes' shifts between 4099 and 5735 cm(-1). The fluorescence quantum yields varied between 10(-2)-10(-4), depending on the solvent. Different solvent scales have been used to study the solvatochromism of B. Linear solvation energy relationships (LSER) proposed by Kamlet-Taft suggest that B is a molecule attractive as a probe for solvent polarity and hydrogen bonding properties.