IGF2BP2-modified circular RNA circCHD7 promotes endometrial cancer progression via stabilizing PDGFRB and activating JAK/STAT signaling pathway.

Circular RNAs (circRNAs) represent a class of covalently closed, single-stranded RNAs and have been linked to cancer progression. N6-methyladenosine (m6A) methylation is a ubiquitous RNA modification in cancer cells. Increasing evidence suggests that m6A can mediate the effects of circRNAs in cancer biology. In contrast, the post-transcriptional systems of m6A and circRNA in the progression of endometrial cancer (EC) remain obscure. The current study identified a novel circRNA with m6A modification, hsa_circ_0084582 (circCHD7), which was upregulated in EC tissues. Functionally, circCHD7 was found to promote the proliferation of EC cells. Mechanistically, circCHD7 interacted with insulin-like growth factor 2 mRNA-binding protein (IGF2BP2) to amplify its enrichment. Moreover, circCHD7 increased the mRNA stability of platelet-derived growth factor receptor beta (PDGFRB) in an m6A-dependent manner, thereby enhancing its expression. In addition, the circCHD7/IGF2BP2/PDGFRB axis activated the JAK/STAT signaling pathway and promoted EC cell proliferation. In conclusion, these findings provide new insights into the regulation of circRNA-mediated m6A modification, and the new "circCHD7-PDGFRB" model of regulation offers new perspectives on circCHD7 as a potential target for EC therapy.

Mechanistic Aspects of Photodegradation of Deoxynucleosides Induced by Triplet State of Effluent Organic Matter.

Excited triplet states of wastewater effluent organic matter (3EfOM*) are known as important photo-oxidants in the degradation of extracellular antibiotic resistance genes (eArGs) in sunlit waters. In this work, we further found that 3EfOM* showed highly selective reactivity toward 2'-deoxyguanosine (dG) sites within eArGs in irradiated EfOM solutions at pH 7.0, while it showed no photosensitizing capacity toward 2'-deoxyadenosine, 2'-deoxythymidine, and 2'-deoxycytidine (the basic structures of eArGs). The 3EfOM* contributed to the photooxidation of dG primarily via one-electron transfer mechanism, with second-order reaction rate constants of (1.58-1.74) × 108 M-1 s-1, forming the oxidation intermediates of dG (dG(-H)•). The formed dG(-H)• could play a significant role in hole hopping and damage throughout eArGs. Using the four deoxynucleosides as probes, the upper limit for the reduction potential of 3EfOM* is estimated to be between 1.47 and 1.94 VNHE. Compared to EfOM, the role of the triplet state of terrestrially natural organic matter (3NOM*) in dG photooxidation was minor (∼15%) mainly due to the rapid reverse reactions of dG(-H)• by the antioxidant moieties of NOM. This study advances our understanding of the difference in the photosensitizing capacity and electron donating capacity between NOM and EfOM and the photodegradation mechanism of eArGs induced by 3EfOM*.

lncRNA UCA1 promotes tumor progression by targeting SMARCD3 in cervical cancer.

Long noncoding RNA urothelial carcinoma associated 1 (UCA1) has been identified as a key molecule in human cancers. However, its functional implications remain unspecified in the context of cervical cancer (CC). This research aims to identify the regulatory mechanism of UCA1 in CC. UCA1 was identified through microarray and confirmed through a quantitative real-time polymerase chain reaction. Proteins that bind with UCA1 were recognized using RNA pull-down assays along with RNA immunoprecipitation. Ubiquitination assays and coimmunoprecipitation were performed to explore the molecular mechanisms of the SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily d, member 3 (SMARCD3) downregulated in CC. The effects of UCA1 and SMARCD3 on the progression of CC were investigated through gain- and loss-of-function assays and xenograft tumor formation in vivo. In this study, UCA1 was found to be upregulated in CC cells as well as in human plasma exosomes for the first time. Functional studies indicated that UCA1 promotes CC progression. Mechanically, UCA1 downregulated the SMARCD3 protein stabilization by promoting SMARCD3 ubiquitination. Taken together, we revealed that the UCA1/SMARCD3 axis promoted CC progression, which could provide a new therapeutic target for CC.

Triplet Photochemistry of Effluent Organic Matter in Degradation of Extracellular Antibiotic Resistance Genes.

Wastewater effluent is a major source of extracellular antibiotic resistance genes (eArGs) in the aquatic environment, a threat to human health and biosecurity. However, little is known about the extent to which organic matter in the wastewater effluent (EfOM) might contribute to photosensitized oxidation of eArGs. Triplet states of EfOM were found to dominate the degradation of eArGs (accounting for up to 85%). Photo-oxidation proceeded mainly via proton-coupled electron transfer reactions. They broke plasmid strands and damaged bases. O2•- was also involved, and it coupled with the reactions' intermediate radicals of eArGs. The second-order reaction rates of blaTEM-1 and tet-A segments (209-216 bps) with the triplet state of 4-carboxybenzophenone were calculated to be (2.61-2.75) × 108 M-1 s-1. Besides as photosensitizers, the antioxidant moieties in EfOM also acted as quenchers to revert intermediate radicals back to their original forms, reducing the rate of photodegradation. However, the terrestrial origin natural organic matter was unable to photosensitize because it formed less triplets, especially high-energy triplets, so its inhibitory effects predominated. This study advances our understanding of the role of EfOM in the photo-oxidation of eArGs and the difference between EfOM and terrestrial-origin natural organic matter.

Assessing the Use of Probes and Quenchers for Understanding the Reactive Species in Advanced Oxidation Processes.

Advanced oxidation processes (AOPs) are increasingly applied in water and wastewater treatment. Understanding the role of reactive species using probes and quenchers is one of the main requirements for good process design. However, much fundamental kinetic data for the reactions of probes and quenchers with reactive species is lacking, probably leading to inappropriate probe and quencher selection and dosing. In this work, second-order rate constants for over 150 reactions of probes and quenchers with reactive species such as •OH, SO4•-, and Cl• and chemical oxidants such as free chlorine and persulfate were determined. Some previously ill-quantified reactions (e.g., furfuryl alcohol and methyl phenyl sulfoxide reactions with certain chemical oxidants, nitrobenzene and 1,4-dioxane reactions with certain halogen radicals) were found to be kinetically favorable. The selection of specific probes can be guided by the improved kinetic database. The criteria for properly choosing dosages of probes and quenchers were proposed along with a procedure for quantifying reactive species free of interference from probe addition. The limitations of probe and quencher approaches were explicated, and possible solutions (e.g., the combination with other tools) were proposed. Overall, the kinetic database and protocols provided in this work benefit future research in understanding the radical chemistry in AOPs as well as other radical-involved processes.

Reactions of neonicotinoids with peroxydisulfate: The generation of neonicotinoid anion radicals and activation pathway to form sulfate radicals.

To activate persulfate to generate reactive species such as sulfate radical (SO4•-) for micropollutants abatement, external energy or chemicals are often needed. In this study, a novel SO4•- formation pathway was reported during the oxidation of neonicotinoids by peroxydisulfate (S2O82-, PDS) without any other chemical additions. Thiamethoxam (TMX) was used as a representative neonicotinoid and SO4•- was the dominant specie contributing to its degradation during PDS oxidation at neutral pH. TMX anion radical (TMX•-) was found to activate PDS to generate SO4•- with the second-order reaction rate constant determined to be (1.44 ± 0.47)× 106 M-1s-1 at pH 7.0 by using laser flash photolysis. TMX•- was generated from the TMX reactions with superoxide radical (O2•-), which was formed from the hydrolysis of PDS. This indirect PDS activation pathway via anion radicals was also applicable to other neonicotinoids. The formation rates of SO4•- were found to negatively linearly correlated with Egap (LUMO-HOMO). The DFT calculations indicated the energy barrier of anion radicals to activate PDS was greatly reduced compared to the parent neonicotinoids. The pathway of anion radicals' activation of PDS to form SO4•- improved the understanding of PDS oxidation chemistry and provided some guidance to enhance oxidation efficiency in field applications.

Ultra-sensitive biosensor based on CRISPR-Cas12a and Endo IV coupled DNA hybridization reaction for uracil DNA glycosylase detection and intracellular imaging.

As an essential biomarker associated with various diseases, Uracil-DNA Glycosylase (UDG) detection is vital for disease diagnosis, treatment selection, and prognosis assessment. In recent years, the signal amplification effect of the CRISPR-Cas12a trans-cleaved single-stranded DNA probe has provided an available strategy for constructing highly sensitive biosensors. However, its superior trans-cleavage activity has become a "double-edged sword" for building biosensors that can amplify the target signal while also amplifying the leakage signal, causing out of control. Therefore, the construction of structurally simple, extremely low-background, highly sensitive CRISPR-Cas12a-based biosensors is an urgent bottleneck problem in the field. Here, we applied CRISPR-Cas12a with a DNA hybridization reaction to develop a simple, rapid, low background, and highly sensitive method for UDG activity detection. It has no PAM restriction and the detection limit is as low as 2.5 × 10-6 U/mL. As far as we know, this method is one of the most sensitive methods for UDG detection. We also used this system to analyze UDG activity in tumor cells (LOD: 1 cell/uL) and to evaluate the ability to screen for UDG inhibitors. Furthermore, we verified the possibility of intracellular UDG activity imaging by transfecting the biosensors to the cells. We believe this novel sensor has good clinical application prospects and will effectively broaden the application space of CRISPR-Cas12a.

Gene signature and prognostic value of ubiquitination-related genes in endometrial cancer.

Protein ubiquitination is closely related to tumor occurrence and development. The specific role of ubiquitination in endometrial cancer remains largely unclear. Therefore, we constructed a novel endometrial cancer prognostic model based on ubiquitination-related genes. We extracted the expression matrices of ubiquitination-related genes from the Cancer Genome Atlas database, upon which we performed univariate Cox regression and least absolute shrinkage and selection operator (LASSO) regression analyses to obtain 22 ubiquitination-related genes for the construction of the prognostic model. Survival, regression, clinical correlation, and principal component analyses were performed to assess the performance of the model. Drug sensitivity analysis was performed based on these ubiquitination-related genes. Finally, a prognostic nomogram was constructed based on the prognostic model to quantify patient outcomes. Survival, regression, clinical correlation, and principal component analyses revealed that the performance of the prognostic model was satisfactory. Drug sensitivity analysis provided a potential direction for the treatment of endometrial cancer. The prognostic nomogram could be used to effectively estimate the survival rate of patients with endometrial cancer. In summary, we constructed a new endometrial cancer prognostic model and identified 5 differentially expressed, prognosis-associated, ubiquitination-related genes. These 5 genes are potential diagnostic and treatment targets for endometrial cancer.

A sensitive and specific nano-vehicle based on self-amplified dual-input synthetic gene circuit for intracellular imaging and treatment.

Synthetic genetic circuits (SGCs) that sense multiple biomarkers and respond intelligently provide a powerful tool for intracellular biosensing. The SGC is usually loaded into the nanoscale liposomes to build functional intracellular nano-vehicles, widely applied in diagnosing and treating diseases. However, because the system needs to identify multiple targets to activate, the sensitivity will be inevitably reduced though the specificity is improved, leading to false-negative results in diagnosis and low killing dosage in treatment. Such compromise between specificity and sensitivity has been a bottleneck problem for the field. We innovatively invented the self-amplified dual-input (SADI) SGC@liposome nano-vehicle and broke the bottleneck problem above. It provides multiple sites for regulating sensitivity at both coarse and fine levels, allowing researchers to conveniently balance the sensitivity and specificity according to the application and instrumental setups. In recognizing ovarian cancer cells, the nano-vehicle could enhance the sensitivity by nearly 10-fold, and the specificity remained at high levels of 16-fold. We also changed the output fluorescent signal to output effectors such as apoptosis regulator (BAX) and proliferation-inhibiting protein (p21) and demonstrated the application range. Furthermore, we verified the generality of the system by applying it to target different cells. We believe it will provide a convenient and powerful tool for biosensors and targeted therapy.

CircRAPGEF5 interacts with RBFOX2 to confer ferroptosis resistance by modulating alternative splicing of TFRC in endometrial cancer.

Endometrial cancer (EC) is one of the most common gynecological cancers. Ferroptosis is a newly identified form of cell death characterized by iron-dependent lipid peroxide accumulation. Circular RNAs (circRNAs) have emerged as critical regulators for cancer development. However, circRNA-mediated modulation of ferroptosis in EC is yet to be clarified. In this study, we found that circRAPGEF5 expression was elevated in EC tissues compared to the normal endometrial tissues. In vitro and in vivo functional analysis demonstrated that circRAPGEF5 facilitates rapid proliferation of EC cells. RNA binding protein fox-1 homolog 2 (RBFOX2), a splicing regulator, was identified as the protein interacts with circRAPGEF5. Further studies revealed that circRAPGEF5 can bind to the Fox-1 C-terminal domain of RBFOX2 and induces specific exon exclusion of TFRC through obstructing the binding of RBFOX2 to pre-mRNA. As a result, elevated levels of circRAPGEF5 lead to ferroptosis resistance via the decreased labile iron pool and attenuated lipid peroxide production in EC cells. Additionally, a series of gain- and loss-of-function experiments demonstrated that knocking down or overexpressing RBFOX2 reversed the effects of knocking down or overexpressing circRAPGEF5 in EC cells. Finally, it is revealed that circRAPGEF5 promote the formation of TFRC with exon-4 skipping and confer ferroptosis resistance in EC cells through the interaction with RBFOX2. Collectively, these findings provide new insight into the molecular mechanism in which circRNAs mediate mediates ferroptosis via modulating alternative splicing, and circRAPGEF5/RBFOX2 splicing axis could be a promising therapeutic target for treating EC.

The Progress of the Specific and Rapid Genetic Detection Methods for Ovarian Cancer Diagnosis and Treatment.

Cancer is a public health problem that threatens human health. Due to the lack of specific and rapid diagnosis and treatment methods, the 5-year survival rate of patients has not been effectively improved in the past 10 years. Abnormal gene expression is closely related to the occurrence and development of cancer. Cancer diagnosis and treatment methods based on genetic testing have received extensive attention in recent years. It is essential to explore specific and rapid cancer genetic testing methods. Taking ovarian cancer as an example, we reviewed the progress of specific and rapid nucleic acid detection methods related to cancer risk assessment, low-abundance mutation detection, and methylation detection, to provide new strategies and ideas for related research.

Quantification of the diverse inhibitory effects of dissolved organic matter on transformation of micropollutants in UV/persulfate treatment.

Dissolved organic matter (DOM), ubiquitous in natural waters, is known to inhibit the degradation of micropollutants in the advanced oxidation processes such as the UV/peroxydisulfate process. However, the quantitative understanding of the inhibitory pathways is missing. In this study, guanosine, aniline and catechol belonging to amines, purines and phenols were first investigated due to their resistance to UV irradiation at 254 nm and similar reactivity with SO4•- and HO•, respectively. The presence of 0.5 mgC L-1 Suwannee River NOM (SRNOM) inhibited their degradation rates by 72.9%, 54.5%, and 32.4%, respectively, despite their similar degradation rates in the absence of SRNOM. The results highlight the importance of reverse reduction of oxidation intermediates to the parent compound by antioxidant moieties in SRNOM besides the inner filtering and radical scavenging effects. The three inhibitory pathways were quantified for 34 common micropollutants. In the presence of 0.5 mgC L-1 SRNOM, inner filtering effect was found to contribute less than 2.8% of the inhibitory percentages (IP). Radical scavenging effects contribute between 10.7% and 38.9% and compounds having lower reactivity with SO4•- (< 4.0 × 109 M-1 s-1) tended to be inhibited more strongly. The IP of reverse reduction effects of SRNOM varied significantly from none up to 70.8%. It was linearly related with a micropollutant's reduction potential. Purines and amines generally exhibited more pronounced reverse reduction inhibition than phenols. The results of this study provide guidance on improving the elimination efficiency of micropollutants.

Bromine Radical (Br• and Br2•-) Reactivity with Dissolved Organic Matter and Brominated Organic Byproduct Formation.

Dissolved organic matter (DOM) is a major scavenger of bromine radicals (e.g., Br• and Br2•-) in sunlit surface waters and during oxidative processes used in water treatment. However, the literature lacks quantitative measurements of reaction rate constants between bromine radicals and DOM and lacks information on the extent to which these reactions form brominated organic byproducts. Based on transient kinetic analysis with different fractions and sources of DOM, we determined reaction rate constants for DOM with Br• ranging from <5.0 × 107 to (4.2 ± 1.3) × 108 MC-1 s-1, which are comparable with those of HO• but higher than those with Br2•- (k = (9.0 ± 2.0) × 104 to (12.4 ± 2.1) × 105 MC-1 s-1). Br• and Br2•- attack the aromatic and antioxidant moieties of DOM via the electron transfer mechanism, resulting in Br- release with minimal substitution of bromine into DOM. For example, the total organic bromine was less than 0.25 µM (as Br) at environmentally relevant bromine radicals' exposures of ∼10-9 M·s. The results give robust evidence that the scavenging of bromine radicals by DOM is a crucial step to prevent inorganic bromine radical chemistry from producing free bromine (HOBr/OBr-) and subsequent brominated byproducts.

Role of Antioxidant Moieties in the Quenching of a Purine Radical by Dissolved Organic Matter.

Dissolved organic matter (DOM) has been known to inhibit the degradation of trace organic contaminants (TrOCs) in advanced oxidation processes but quantitative understanding is lacking. Adenine (ADN) was selected as a model TrOC due to the wide occurrence of purine groups in TrOCs and the well-documented transient spectra of its intermediate radicals. ADN degradation in the presence of DOM during UV/peroxydisulfate treatment was quantified using steady-state photochemical experiments, time-resolved spectroscopy, and kinetic modeling. The inhibitory effects of DOM were found to include competing for photons, scavenging SO4•- and HO•, and also converting intermediate ADN radicals (ADN(-H)•) back into ADN. Half of the ADN(-H)• were reduced back to ADN in the presence of about 0.2 mgC L-1 of DOM. The quenching rate constants of ADN(-H)• by the 10 tested DOM isolates were in the range of (0.39-1.18) × 107 MC-1 s-1. They showed a positive linear relationship with the total antioxidant capacity of DOM. The laser flash photolysis results of the low-molecular-weight analogues of redox-active moieties further supported the dominant role of antioxidant moieties in DOM in the quenching of ADN(-H)•. The diverse roles of DOM should be considered in predicting the abatement of TrOCs in advanced oxidation processes.

Redox-Active Moieties in Dissolved Organic Matter Accelerate the Degradation of Nitroimidazoles in SO4•--Based Oxidation.

The presence of dissolved organic matter (DOM) is known to inhibit the degradation of trace organic contaminants (TrOCs) in SO4•--based advanced oxidation processes (AOPs) due to filtering of the photochemically active light and radical scavenging effects. This study revealed an unexpected contribution for DOM in the degradation of nitroimidazoles (NZs) in the UV/persulfate AOP. The apparent second-order rate constants of NZs with SO4•- increased by 2.05 to 4.77 times in the presence of different DOMs. The increments were linearly related to the total electron capacity of DOM. Quinone and polyphenol moieties were found to play a dominant role. The reactive species generated from SO4•-'s oxidation of DOM, including semiquinone radical (SQ•-) and superoxide (O2•-), were found to react with NZs via Michael addition and O2•- addition. The second-order rate constants of tinidazole with SQ•- is determined to be (5.69 ± 0.59) × 106 M-1 s-1 by laser flash photolysis. Reactive species potentially generated from DOM may be considered in designing processes for the abatement of different types of TrOCs.

Rate Constants and Mechanisms for Reactions of Bromine Radicals with Trace Organic Contaminants.

Bromine radicals can pose great impacts on the photochemical transformation of trace organic contaminants in natural and engineered waters. However, the reaction kinetics and mechanisms involved are barely known. In this work, second-order reaction rate constants with Br• and Br2•- were determined for 70 common trace organic contaminants and for 17 model compounds using laser flash photolysis and steady-state competition kinetics. The kBr• values ranged from <108 to (2.86 ± 0.31) × 1010 M-1 s-1 and the kBr2•- values from <105 to (1.18 ± 0.09) × 109 M-1 s-1 at pH 7.0. Six quantitative structure-activity relationships were developed, which allow predicting additional unknown kBr• and kBr2•- values. Single-electron transfer was shown to be a favored pathway for the reactions of Br• and Br2•- with trace organic contaminants, and this was supported by transient spectroscopy and quantum chemical calculations. This study is essential in advancing the scientific understanding of halogen radical-involved chemistry in contaminant transformation.

Prediction of Photolysis Kinetics of Viral Genomes under UV254 Irradiation to Estimate Virus Infectivity Loss.

UV254 irradiation disinfection is a commonly used method to inactivate pathogenic viruses in water and wastewater treatment. Model prediction method can serve as a pre-screening tool to quickly estimate the effectiveness of UV254 irradiation on emerging or unculturable viruses. In this study, an improved prediction model was applied to estimate UV254 photolysis kinetics of viral genomes (kpred, genome) based on the genome sequences and their photoreactivity and to correlate with the experimental virus infectivity loss kinetics (kexp, infectivity). The UV254 inactivation data of 102 viruses (including 2 dsRNA, 65 ssRNA, 33 dsDNA and 2 ssDNA viruses) were collected from the published experimental data with kexp, infectivity ranging from 0.016 to 3.49 cm2 mJ-1. The model had fairly good performance in predicting the virus susceptibility to UV254 irradiation except dsRNA viruses (Pearson's correlation coefficient = 0.64) and 70% of kpred, genome fell in the range of 1/2 to 2 times of kexp, infectivity. The positive deviation of the model often occurred for photoresistant viruses with low kexp, infectivity less than 0.20 cm2 mJ-1 (e.g., Adenovirus, Papovaviridae and Retroviridae). We also applied this model to predict the UV254 inactivation rate of SARS-CoV-2 (kpred, genome = 3.168 cm2 mJ-1) and a UV dose of 3 mJ cm-2 seemed to be able to achieve a 2-log removal by conservative calculation using 1/2kpred, genome value. This prediction method can be used as a prescreening tool to assess the effectiveness of UV254 irradiation for emerging/unculturable viruses in water or wastewater treatment.

Molecular characterization of transformation and halogenation of natural organic matter during the UV/chlorine AOP using FT-ICR mass spectrometry.

UV/chlorine process, as an emerging advanced oxidation process (AOP), was effective for removing micro-pollutants via various reactive radicals, but it also led to the changes of natural organic matter (NOM) and formation of disinfection byproducts (DBPs). By using negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), the transformation of Suwannee River NOM (SRNOM) and the formation of chlorinated DBPs (Cl-DBPs) in the UV/chlorine AOP and subsequent post-chlorination were tracked and compared with dark chlorination. In comparison to dark chlorination, the involvement of ClO•, Cl•, and HO• in the UV/chlorine AOP promoted the transformation of NOM by removing the compounds owning higher aromaticity (AImod) value and DBE (double-bond equivalence)/C ratio and causing the decrease in the proportion of aromatic compounds. Meanwhile, more compounds which contained only C, H, O, N atoms (CHON) were observed after the UV/chlorine AOP compared with dark chlorination via photolysis of organic chloramines or radical reactions. A total of 833 compounds contained C, H, O, Cl atoms (CHOCl) were observed after the UV/chlorine AOP, higher than 789 CHOCl compounds in dark chlorination, and one-chlorine-containing components were the dominant species. The different products from chlorine substitution reactions (SR) and addition reactions (AR) suggested that SR often occurred in the precursors owning higher H/C ratio and AR often occurred in the precursors owning higher aromaticity. Post-chlorination further caused the cleavages of NOM structures into small molecular weight compounds, removed CHON compounds and enhanced the formation of Cl-DBPs. The results provide information about NOM transformation and Cl-DBPs formation at molecular levels in the UV/chlorine AOP.

The role of chlorine oxide radical (ClO•) in the degradation of polychoro-1,3-butadienes in UV/chlorine treatment: kinetics and mechanisms.

Polychoro-1,3-butadienes (CBDs) were widely found in aqueous environment and resistant to conventional water treatment. In this study, the abatement of CBDs during UV/chlorine treatment was investigated. In comparison to UV irradiation alone, free chlorine addition brought benefits for the reduction of tetra-CBDs (TCBDs), but to lesser extent for penta-CBDs (PCBDs), and virtually no benefit for hexa-CBD (HCBD). At a UV dose of 128 mJ cm-2 and a chlorine dose of 10 mg L-1, about 71.7-97.8% CBDs were degraded by UV/chlorine treatment within 10 min. UV irradiation contributed 32.8%-97.6%, HO• contributed 2.6%-14.4%, and reactive chlorine species (RCS) contributed less than 0.5%-42.3% to CBDs degradation. The percentages of RCS contribution generally followed the order of TCBDs (except (Z,Z)-1,2,3,4-TCBD) > PCBDs > HCBD. The chlorine oxide radical (ClO•) was the dominant RCS contributing to the degradation of CBDs. The second-order reaction rate constants of ClO• with CBDs ( [Formula: see text] ) were at âˆ¼ 107 M-1s-1 except (Z,Z)-1,2,3,4-TCBD and HCBD (<106 M-1s-1). [Formula: see text] generally decreased with increasing numbers of chlorine atoms and was also affected by the positions of chlorine atoms in CBDs. A distinct reaction pathway of ClO•, with (Z)-1,1,2,3,4-PCBD as a representative CBD, was proposed. Photoisomers of CBDs from Z or E configuration were observed at lower concentrations in UV/chlorine treatment than under UV irradiation alone due to the radical-involved oxidation, but more organic acids including oxalic acid were observed. In a natural water sample, UV/chlorine treatment also exhibited a good performance in abatement of TCBDs and PCBDs, but not in abatement of HCBD.

Coexposure Degradation of Purine Derivatives in the Sulfate Radical-Mediated Oxidation Process.

Purines are the most widely occurring heterocyclic-N compounds. The degradation behaviors of purine derivatives, theophylline (TPL) and adenine (ADN) as representatives, in both single-component and mixture systems during UV/peroxydisulfate (PDS) treatment were explored. In the mixture system when the concentrations of SO4•- and HO• were reduced by more than half in comparison to a single-component system, the observed first-order rate constant of TPL was reduced by 11%, whereas ADN degradation was almost completely inhibited. An ADN "revert" pathway, that is, back transformation of ADN(-H)• to ADN by TPL via single electron-transfer reactions, was found. The second-order rate constant of ADN(-H)• with TPL was determined to be (1.94 ± 0.21) × 108 M-1 s-1. A kinetic model was developed, which successfully quantifies the contribution of each reaction pathway at various target compound concentrations. In the copresence of 0.1 µM TPL, 58% ADN (3.0 µM) was reduced back to ADN at the PDS dose of 290 µM. The ADN revert pathway's effectiveness is governed by the relative reduction potentials of the reactants. Purines and phenols with lower reduction potentials are able to react via the ADN revert pathway. These findings improve the understanding of the removal of mixture pollutants from real water media in advanced oxidation processes.