TY - JOUR

T1 - A kinetic study of the photolysis of sulfamethoxazole with special emphasis on the photoisomer

AU - Palm, Wolf Ulrich

AU - Schmidt, Nicola

AU - Stahn, Marcel

AU - Grimme, Stefan

N1 - Publisher Copyright: © 2022, The Author(s). This study was financially supported by the Lower Saxony Water Management, Coastal Defence, and Nature Conservation Agency (NLWKN) and the Environmental Ministry of Lower Saxony under grant no. 54711/1552-72/2019-2.5.

PY - 2023/3/1

Y1 - 2023/3/1

N2 - Abstract: The previously not studied photochemical degradation of sulfamethoxazole (SMX) to the isomer of SMX (ISO) was measured via a polychromatic (Xe) and a monochromatic (Hg) light source and accompanied by quantum chemical DFT calculations. In addition to the pKa=7.0±0.1 of ISO, tautomer-dependent properties such as the KOW were measured and theoretically confirmed by DFT. The kinetics in solutions below and above the p Ka= 5.6 of SMX were studied for the available and quantifiable products SMX, ISO, 3-amino-5-methylisoxazole (AMI), 2-amino-5-methyloxazole (AMO), and sulfanilic acid (SUA). The quantum yields of the neutral (Φ N) and anionic Φ A) forms of SMX (Φ A= 0.03 ± 0.001 , Φ N= 0.15 ± 0.01) and ISO (Φ A= 0.05 ± 0.01 and Φ N= 0.06 ± 0.02) were found to be wavelength-independent. In a competitive reaction to the formation of ISO from SMX, the degradation product TP271 is formed. Various proposed structures for TP271 described in the literature have been studied quantum mechanically and can be excluded for thermodynamic reasons. In real samples in a northern German surface water in summer 2021 mean concentrations of SMX were found in the range of 120 ng/L. In agreement with the pH-dependent yields, concentrations of ISO were low in the range of 8 ng/L. Graphical abstract: [Figure not available: see fulltext.]

AB - Abstract: The previously not studied photochemical degradation of sulfamethoxazole (SMX) to the isomer of SMX (ISO) was measured via a polychromatic (Xe) and a monochromatic (Hg) light source and accompanied by quantum chemical DFT calculations. In addition to the pKa=7.0±0.1 of ISO, tautomer-dependent properties such as the KOW were measured and theoretically confirmed by DFT. The kinetics in solutions below and above the p Ka= 5.6 of SMX were studied for the available and quantifiable products SMX, ISO, 3-amino-5-methylisoxazole (AMI), 2-amino-5-methyloxazole (AMO), and sulfanilic acid (SUA). The quantum yields of the neutral (Φ N) and anionic Φ A) forms of SMX (Φ A= 0.03 ± 0.001 , Φ N= 0.15 ± 0.01) and ISO (Φ A= 0.05 ± 0.01 and Φ N= 0.06 ± 0.02) were found to be wavelength-independent. In a competitive reaction to the formation of ISO from SMX, the degradation product TP271 is formed. Various proposed structures for TP271 described in the literature have been studied quantum mechanically and can be excluded for thermodynamic reasons. In real samples in a northern German surface water in summer 2021 mean concentrations of SMX were found in the range of 120 ng/L. In agreement with the pH-dependent yields, concentrations of ISO were low in the range of 8 ng/L. Graphical abstract: [Figure not available: see fulltext.]

KW - DFT

KW - Kinetics

KW - Quantum chemistry

KW - Quantum yields

KW - Surface water

KW - Biology

UR - http://www.scopus.com/inward/record.url?scp=85143338671&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/0067d872-dff4-3758-9ed5-64831c454ad7/

U2 - 10.1007/s43630-022-00340-x

DO - 10.1007/s43630-022-00340-x

M3 - Journal articles

C2 - 36471235

AN - SCOPUS:85143338671

VL - 22

SP - 615

EP - 630

JO - Photochemical and Photobiological Sciences

JF - Photochemical and Photobiological Sciences

SN - 1474-905X

IS - 3

ER -