Department Environmental Chemistry

Isotope fractionation associated with direct and sensitized photolysis of chloroanilines

Isotope fractionation associated with the photochemical transformation of organic contaminants is not well understood and can arise not only from bond cleavage reactions but also from photophysical processes. 

We are investigating the photolytic dechlorination of 2-Cl-, 3-Cl-, and 4-Cl-aniline as model compound for organic micropollutants that degrade in photochemical processes.

The reaction of each chloroaniline isomer is accompanied by distinctly different and highly variable C and N isotope fractionation due to spin selective isotope effects. The isotope fractionation trends associated with  photolytic dechlorination strongly contrasts dechlorination in thermal reactions and offers new opportunities for fingerprinting photochemical processes in contaminated surface waters.

Reprinted with permission from (Ratti et al, Environ. Sci. Technol. 2015, asap). Copyright (2015) American Chemical Society

Latest publications

Isotope fractionation associated with the biodegradation of 2- and 4-nitrophenols via monooxygenation pathways

Monooxygenation is an important route of nitroaromatic compound (NAC) biodegradation and it is widely found for cometabolic transformations of NACs and other aromatic pollutants. We investigated the C and N isotope fractionation of nitrophenol monooxygenation to complement the characterization of NAC (bio)degradation pathways by compound-specific isotope analysis (CSIA). Because of the large diversity of enzymes catalyzing monooxygenations, we studied the combined C and N isotope fractionation and the corresponding 13C- and 15N-apparent kinetic isotope effects (AKIEs) of four nitrophenol-biodegrading microorganisms (Bacillus spharericus JS905, Pseudomonas sp. 1A, Arthrobacter sp. JS443, Pseudomonas putida B2) in the pH range 6.1–8.6 with resting cells and crude cell extracts. While the extent of C and N isotope fractionation and the AKIE-values varied considerably for the different organisms, the correlated C and N isotope signatures (δ15N vs δ13C) revealed trends, indicative of two distinct monooxygenation pathways involving hydroxy-1,4-benzoquinone or 1,2- and 1,4-benzoquinone intermediates, respectively. The distinction was possible based on larger secondary 15N-AKIEs associated with the benzoquinone pathway. Isotope fractionation was neither masked substantially by nitrophenol speciation nor transport across cell membranes. Only when 4-nitrophenol was biodegraded by Pseudomonas sp. 1A did isotope fractionation become negligible, presumably due to rate-limiting substrate binding steps pertinent to the catalytic cycle of flavin-dependent monooxygenases.
Wijker, R. S.; Kurt, Z.; Spain, J. C.; Bolotin, J.; Zeyer, J.; Hofstetter, T. B. (2013) Isotope fractionation associated with the biodegradation of 2- and 4-nitrophenols via monooxygenation pathways, Environmental Science and Technology, 47(24), 14185-14193, doi:10.1021/es403876u, Institutional Repository