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Photolytic and photocatalytic degradation of the pharmaceutical memantine

Memantine is a N-methyl-D-aspartate receptor antagonist used for the treatment of moderate to severe confusion (dementia) related Alzheimer's disease, movement disorders [1]. It is initially approved by FDA in 2013. In 2013, 44 million people worldwide were living with Alzheimer's disease, and it is estimated that this number will double every 20 years [2]. Once in the organism, memantine is poorly metabolised, and the most (57- 82%) of the administered dose is excreted unchanged in urine [3]. In view of this, it is reasonable to expect that memantine will end up in wastewater, and without proper treatment, in environmental waters. However, only scare literature reported on the detection of memantine in wastewater effluents [4] and the environment [5]. The reason may be that most scientists have been focused on pharmaceuticals such as sulfonamides, fluoroquinolones, macrolides, etc., whose occurrence in the environment is now well- studied. The aim of this study was to evaluate photolytic and photocatalytic degradation of memantine. Ultraviolet (UV) lamps with a peak wavelength of 254 nm and 365 nm were used as source of light. TiO2 in a form of a nanostructured film deposited on borosilicate glass wall of the reactor was used for photocatalytic experiments, and reactor without TiO2 film was used for photolytic experiments. Process degradation efficiencies and evaluation of kinetic constants were based on the results of HPLC-MS/MS analyses, which also enable identification and monitoring of memantine degradation products. Photodegradation of memantine followed pseudo-first-order kinetics. The half-life of photocatalytic degradation at 365 nm was much higher (43.6 min) than half-life obtained at 254 nm (3.9 min). The chemical structures of five detected photodegradation products were suggested based on mass spectra. The acute toxicity of the reaction mixture during the degradation experiment was evaluated by monitoring the inhibition of the luminescence of Vibrio fischeri bacteria. The results showed that memantine and its photodegradation products were not toxic to Vibrio fischeri.

memantine ; photolysis ; photocatalysis

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