title: Photochemical and Nonphotochemical Transformations of Cysteine with Dissolved Organic Matter.
abstract: Cysteine (Cys) plays numerous key roles in the biogeochemistry of natural waters. Despite its importance, a full assessment of Cys abiotic transformation kinetics, products and pathways under environmental conditions has not been conducted. This study is a mechanistic evaluation of the photochemical and nonphotochemical (dark) transformations of Cys in solutions containing chromophoric dissolved organic matter (CDOM). The results show that Cys underwent abiotic transformations under both dark and irradiated conditions. Under dark conditions, the transformation rates of Cys were moderate and were highly pH- and temperature-dependent. Under UVA or natural sunlight irradiations, Cys transformation rates were enhanced by up to two orders of magnitude compared to rates under dark conditions. Product analysis indicated cystine and cysteine sulfinic acid were the major photooxidation products. In addition, this study provides an assessment of the contributions of singlet oxygen, hydroxyl radical, hydrogen peroxide, and triplet dissolved organic matter to the CDOM-sensitized photochemical oxidation of Cys. The results suggest that another unknown pathway was dominant in the CDOM-sensitized photodegradation of Cys, which will require further study to identify.
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science, ETH Zurich , 8092 Zurich, Switzerland.
authors.forename: Chiheng
authors.initials: C
authors.lastname: Chu
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science, ETH Zurich , 8092 Zurich, Switzerland.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Erickson
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science, ETH Zurich , 8092 Zurich, Switzerland.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Lundeen
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science, ETH Zurich , 8092 Zurich, Switzerland.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Stamatelatos
authors.affiliation: Department of Chemistry, Seattle University , Seattle, Washington 98122, United States.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Alaimo
authors.affiliation: Department of Chemistry, Seattle University , Seattle, Washington 98122, United States.
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Latch
authors.affiliation: Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science, ETH Zurich , 8092 Zurich, Switzerland.
authors.forename: Kristopher
authors.initials: K
authors.lastname: McNeill
mesh_terms: D003545:Cysteine; D007700:Kinetics; D055668:Photochemical Processes; D010782:Photolysis; D012996:Solutions; D013472:Sunlight; D014874:Water Pollutants, Chemical
chemical_list: D012996:Solutions; D014874:Water Pollutants, Chemical; D003545:Cysteine