scholarly journals Enzyme Kinetics of Organic Contaminant Oxygenations

2020 ◽  
Vol 74 (3) ◽  
pp. 108-114
Author(s):  
Charlotte E. Bopp ◽  
Hans-Peter E. Kohler ◽  
Thomas B. Hofstetter

Enzymatic oxygenations initiate biodegradation processes of many organic soil and water contaminants. Even though many biochemical aspects of oxygenation reactions are well-known, quantifying rates of oxidative contaminant removal as well as the extent of oxygenation remains a major challenge. Because enzymes use different strategies to activate O2, reactions leading to substrate oxygenation are not necessarily limiting the rate of contaminant removal. Moreover, oxygenases react along unproductive pathways without substrate metabolism leading to O2 uncoupling. Here, we identify the critical features of the catalytic cycles of selected oxygenases that determine rates and extents of biodegradation. We focus most specifically on Rieske dioxygenases, a subfamily of mononuclear non-heme ferrous iron oxygenases, because of their ability to hydroxylate unactivated aromatic structures and thus initiate the transformation of the most persistent organic contaminants. We illustrate that the rate-determining steps in their catalytic cycles range from O2 activation to substrate hydroxylation, depending on the extent of O–O cleavage that is required for generating the reactive Fe-oxygen species. The extent of O2 uncoupling, on the other hand, is highly substrate-specific and potentially modulated by adaptive responses to oxidative stress. Understanding the kinetic mechanisms of oxygenases will be key to assess organic contaminant biotransformation quantitatively.

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Ahed H. Zyoud ◽  
Fedaa Saleh ◽  
Muath H. Helal ◽  
Ramzi Shawahna ◽  
Hikmat S. Hilal

Pharmaceutical wastes are emerging as water contaminants. Like other organic contaminants, it is necessary to find safe and economic methods to remove them from the water. In this work, anthocyanin was used as a natural dye sensitizer for the wide band gap nanosize rutile TiO2. The TiO2/Anthocyanin particles were supported on activated carbon particle surfaces. The resulting composite, which was prepared and characterized by different methods, was then used as a catalyst in the photodegradation of phenazopyridine (a model pharmaceutical contaminant) under a solar simulated light. Depending on experimental conditions, up to 90% of the contaminant was mineralized leaving no new organic products in the reaction mixture. The results show the feasibility of using the activated carbon-supported TiO2/Anthocyanin photocatalyst for pharmaceutical contaminant removal in water. The natural dye anthocyanin readily sensitized the TiO2 to visible light. The unsupported TiO2, with its nanosize particles, was not easy to recover by simple separation methods, while the activated carbon-supported catalyst was easily isolated by decantation after reaction cessation. Moreover, the recovered AC/TiO2 catalyst could also be regenerated by adding fresh anthocyanin sensitizer after recovery for further reuse. Keeping the contaminant molecules closer to the catalytic sites by adsorption, the support also enhanced the efficiency of photocatalyst.


Proceedings ◽  
2019 ◽  
Vol 29 (1) ◽  
pp. 27
Author(s):  
Leslie F. Petrik ◽  
Jimoh Tijani ◽  
Akhona Gura ◽  
Emile S. Massima Mouele ◽  
Mihaela Dinu ◽  
...  

The occurrence of persistent organic contaminants. [...]


2021 ◽  
Vol 2 (1) ◽  
pp. 100296
Author(s):  
Long Chen ◽  
Akram N. Alshawabkeh ◽  
Shayan Hojabri ◽  
Meng Sun ◽  
Guiyin Xu ◽  
...  

2016 ◽  
Vol 2 (1) ◽  
pp. 213-222 ◽  
Author(s):  
Judy Blackbeard ◽  
James Lloyd ◽  
Mirela Magyar ◽  
John Mieog ◽  
Karl G. Linden ◽  
...  

The 350 ML per d Eastern Treatment Plant (ETP) tertiary facility produces “Class A” water for the city of Melbourne, Australia, which is used for irrigation, dual reticulation and fire fighting.


2013 ◽  
Vol 807-809 ◽  
pp. 486-489
Author(s):  
Tong Zhou Liu ◽  
Pin Hua Rao

An investigation on the effects of humic acid (representing NOM) on TCE (a typical organic contaminant) removal by Fe0in batch settings was carried out. Inhibitory effects of humic acid on Fe0towards TCE removal were observed. At early stage of the experiments, humic acid might partition with TCE, and the adsorption or deposition of humic acid onto Fe0surface would further facilitated TCE immobilization. Once the reduction reactive sites on Fe0surfaces were covered by accumulated humic acid and the partition of TCE to humic acid became saturated, TCE removal in Fe0was observed retarded.


2019 ◽  
Vol 150 ◽  
pp. 140-152 ◽  
Author(s):  
Katherine T. Peter ◽  
Skuyler Herzog ◽  
Zhenyu Tian ◽  
Christopher Wu ◽  
John E. McCray ◽  
...  

2019 ◽  
Vol 361 ◽  
pp. 111-122 ◽  
Author(s):  
Kristin M. Blum ◽  
Christine Gallampois ◽  
Patrik L. Andersson ◽  
Gunno Renman ◽  
Agnieszka Renman ◽  
...  

Author(s):  
А.К. ГОРЕЛКИНА ◽  
И.В. ТИМОЩУК ◽  
Н.С. БАГДОНАС

Изучена стойкость нутриентов молокосырья – белков, лактозы, витаминов С и группы В, используемого в производстве сывороточных напитков в присутствии приоритетных органических контаминантов – трихлорэтилена, хлороформа и дихлорэтана, которые обладают токсическим и канцерогенным действием и образуются при хлорировании в процессе водоподготовки в воде, применяемой для производства восстановленных и рекомбинированных молочных продуктов. Содержание белков, лактозы в восстановленной сыворотке определяли методом рефрактометрии; водорастворимых витаминов – методом капиллярного электрофореза; хлороформа, трихлорэтилена и дихлорэтана – методом газожидкостной хроматографии. Установлено, что хлороформ в воде не оказывает влияния на сохранность лактозы, белков и витаминов при приготовлении восстановленной сыворотки. Отмечено снижение содержания белков сыворотки, приготовленной на воде в присутствии трихлорэтилена и дихлорэтана, на 11%, лактозы – на 32% в сравнении с контрольными образцами, произведенными на воде без органических контаминантов. Содержание витаминов в восстановленной молочной сыворотке в присутствии трихлорэтилена снизилось: С – на 19%, В1 – на 28%, В2 – на 53%, В6 – на 8%; для дихлорэтана содержание витаминов снизилось: С – на 17%, В1 – на 36%, В2 – на 38%, В6 – на 36% в сравнении с контрольными образцами без органических примесей. Теоретически обоснован механизм взаимодействия белков, лактозы, витаминов восстановленной сыворотки с трихлорэтиленом и дихлорэтаном. Предложено для предотвращения снижения качества готового продукта воду, используемую для производства сывороточных напитков, подвергать дополнительной очистке от галогенорганических контаминантов. The stability of milk raw materials’ nutrients – proteins, lactose, vitamins C and B used in the production of whey beverages in the presence of priority organic contaminants – trichloroethylene, chloroform and dichloroethane, which have a toxic and carcinogenic effect and are formed during chlorination during water treatment in water used for the production of reduced and recombined dairy products was studied. The content of proteins and lactose in the reduced serum was determined by refractometry; water-soluble vitamins – by capillary electrophoresis; chloroform, trichloroethylene and dichloroethane – by gas-liquid chromatography. It was found that chloroform in water does not affect the safety of lactose, proteins and vitamins in the preparation of reduced whey. There was a decrease in the content of serum proteins prepared in water in the presence of trichloroethylene and dichloroethane by 11%, and lactose – by 32% in comparison with control samples produced in water without organic contaminants. Vitamin C content in the recovered whey in the presence of trichloroethylene has declined by 19%, vitamin B1 – 28%, vitamin B2 – 53%, vitamin B6 – 8%; for dichloroethane content of vitamin C decreased by 17%, vitamin B1 – 36%, vitamin B2 – 38%, vitamin B6 – 36% in comparison with control samples without organic impurity. The mechanism of interaction of proteins, lactose, and reduced serum vitamins with trichloroethylene and dichloroethane is theoretically justified. Therefore, to prevent a decrease in the quality of the finished product, the water used for the production of whey beverages must first be subjected to additional purification from organohalogen contaminants.


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