Dependency of the photocatalytic and photochemical decomposition of per- and polyfluoroalkyl substances (PFAS) on their chain lengths, functional groups, and structural properties

This study reports the removal of per- and polyfluoroalkyl substances (PFAS) in water using various photocatalytic and photochemical processes. PFAS were chosen, based on chain lengths, functional groups, and structural properties: 4 perfluorocarboxylic acids (PFCAs) including perfluorooctanoic acid (PFOA), 3 perfluorosulfonic acids (PFSAs) including perfluorooctanesulfonic acid (PFOS), hexafluoropropylene oxide dimer (GenX), and 6:2 fluorotelomer sulfonate (6:2 FTS), and investigated dependency of the photocatalytic decomposition of PFAS on their properties. Oxidants and reductants were introduced to study the photochemical decomposition of PFAS, and reactive species and reaction byproducts were identified to elucidate the decomposition mechanism of PFAS. Some notable findings include long chain PFCAs (95% in 48 h) and 6:2 FTS (100%) were removed via chemical decomposition in TiO2/UVC while GenX (37%), long chain PFSAs (60%), short chain PFSAs (0–10%) and short chain PFCAs (5–18%) were removed via physical adsorption. Sulfate radicals generated with persulfate (PS) played an important role in decomposing PFCAs (60–90%). Sulfite activated by UVC worked for defluorination of PFOA (75%) and PFOS (80%). PFOA was removed faster by UVC/sulfite > UVC/TiO2/sulfite ≈ UVC/TiO2/PS ≥ UVC/PS > UVC/TiO2 while PFOS was removed faster by UVC/sulfite ≫ UVC/TiO2/sulfite ≈ UVC/TiO2/PS ≈ UVC/TiO2 ≫ UVC/PS. Susceptibility of PFAS to the chemical reactions could be explained with their properties and the reactive species produced in each system.

Total Synthesis of C-8 Hydroxyl Substituted Lomefloxacin as the Photolysis Impurity

Objective: Photochemical decomposition of lomefloxacin (Lom) is supposed to result in the generation of C-8 substituted impurity and accompanied fluoride. The existence and amount of C-8 hydroxyl substituted Lom could be proposed as the marker to the stability and process consistency. The specific C-8 hydroxyl substituent impurity (1-ethyl-6-fluoro-8-hydroxy-7-(3-methylpiperazin-1-yl )-4-oxo-1,4-dihydroquinoline-3-carboxylic acid) was designed and synthesized to be available. Method: 2,4,5-trifluoro-3-methoxybenzoic acid as the initial reactant was subjected to a series of seven-step reactions, such as acylation, condensation with trans N,N-dimethylamino ethyl acrylate, N-ethylation, cyclization, hydrolysis, condensation with piperazine and acidification. The resultant substance was then purified using HPLC and C18 solid-phase extraction. The structure of C-8 hydroxyl substituted Lom was identified with 1H-NMR, 13C-NMR and HRMS spectroscopes, as well as the purity was determined by HPLC. Conclusion: C-8 hydroxyl substituted Lom was successfully synthesized and purified with purity more than 96%. This photolysis impurity offers an alternative for not only further generic Lom active pharmaceutical ingredient development involved in quality control and consistency evaluation, but also research for the mechanism underlying Lom-induced photosensitivity.

PHOTOCHEMICAL DEGRADATION OF PHENOL WITH THE PARTICIPATION OF TiO2 NANOPARTICLES AND ETHYL-3,3,5,5-TETRACIANO-2-HYDROXIDE-2-METIL-4,6-DIPHENYL CYCLOHEXANE CARBOXYLATE

The photochemical decomposition of phenol with the participation of TiO2 nano-particles and ethyl-3,3,5,5-tetraciano-2-hydroxide-2-metil-4,6-diphenyl cyclohexane carboxylate by UV spectroscopy was studied for the first time. It has been shown, that UV irradiation of this mixture during 1 hour brings to 52% decomposition of phenol

Photosensitivity Reactions Induced by Photochemical Degradation of Drugs

Photochemical degradation of drugs can lead to degradation products with potential toxic or allergizing effects for the human body. A significant amount of work has been carried out over the past few decades to clarify the molecular mechanism of photosensitizing processes observed after the administration of certain drugs and exposure to light. There is a close relation between the photosensitizer effect of a drug and its chemical structure. Compounds possessing certain moieties and functional groups in their molecular structure, like aromatic chromophore systems or photo-dissociable bonds that can form free radicals, and consequently are susceptible to have light-induced adverse effects. Photoionization, photodissociation, photoaddition and photoisomerization are the main chemical processes, which can occur during the photochemical decomposition of a pharmaceutical compound. The current study is a short review describing photochemical degradation of certain pharmaceuticals, presenting specific examples from various pharmaceutical classes for the different types of decomposition mechanisms. In vivo methods and clinical tests available for the investigation of photosensitizing reactions are also discussed.

Pulse Рhotochemical Decomposition of Phenol in Wastewater

Photochemical decomposition of phenol with a concentration of 5 to 24 mg/L using hydrogen peroxide and ultraviolet irradiation (UV/H2O2) was studied. Xenon flash lamp was chosen as a radiation source. It emits high-intensity continuous-spectrum radiation in a wide wavelength range from 200 to 1000 nm. The effect of the initial concentration of hydrogen peroxide and the source average radiation power on the phenol destruction rate were studied. An extremum in the dependence of the phenol decomposition rate constant on the initial concentration of hydrogen peroxide was found. Kinetic model of the process based on the obtained data was developed. It was tested by predicting phenol destruction rate with the different process parameters and gave good accuracy.