New insight into transformation of tetracycline in presence of Mn(II): Oxidation versus photolysis

Transformation of chlorobenzene by Mn(III) generated in MnO2/organic acid systems

Chlorobenzene (CB) is a prevalent organic contaminant in water and soil environments. It presents high chemical stability and is resistant to both oxidation and reduction. In this study, we showed that CB was substantially removed by soluble Mn(III) produced during the reductive dissolution of colloidal MnO2 by naturally-occurring organic acids such as formate (FOR), oxalate (OX), and citrate (CIT). The removal rate was dependent on the physicochemical properties of organic acids. With strong electron-donating and coordination ability, OX and CIT promoted MnO2 dissolution and Mn(III) generation compared to FOR, but had adverse effects on the stability and reactivity of Mn(III). As a result, CB removal followed the order: MnO2/CIT > MnO2/FOR > MnO2/OX. Analysis of the transformation products showed that Mn(III) complexes acted as strong electrophiles, attacking the ortho/para carbons of the benzene ring and transforming CB to chlorophenols via an electrophilic substitution mechanism. The theoretical foundation of this proposed reaction mechanism was supplemented by quantum mechanical calculations. Together, the findings of this study provide new insights into the transformation of CB in natural environments and hold the potential to offer a novel strategy for the development of manganese oxide/ligand systems for CB elimination.

Enhanced photolysis of tetracycline by Zn(II): Role of complexation

Zn(II) is a necessary additive during antibiotic production and aquaculture, leading to the coexistence of Zn(II) and antibiotics in aquatic environment, especially in receiving waters of pharmaceutical and aquaculture wastewater. However, the roles of Zn(II) in the photochemical behavior of antibiotics are still not clear, which limits the understanding of the fate of antibiotic in nature. In this study, tetracycline (TC) was selected as typical antibiotic to evaluate the effect of Zn(II) on antibiotic photolysis. The removal of TC was accelerated by 22.75 % with TC:Zn(II) molar ratio at 1:5. The mechanism of Zn(II)-induced TC photolysis was explored via reactive oxygen species (ROS) analysis and density functional theory (DFT) calculation for the first time. Zn(II) could enhance the formation of TC excited states and further produce more singlet oxygen (12.54 % higher than control group) to promote indirect photolysis. Besides, Zn(II) could react with TC via complexation, and the complex was more vulnerable to attack by reactive oxygen species due to more active sites. Furthermore, the structure and toxicity of intermediates were identified with mass spectrometer, T.E.S.T. and ECOSAR software. Zn(II) hardly changed the degradation path of TC, and TC was mainly degraded via ring opening, demethylation, deamidation, and hydrogen abstraction with more toxic intermediates than the parent molecule. This work is significant to better understand the environmental fate of antibiotics, and also provides new insight into wastewater treatment in the pharmaceutical and aquaculture industry.

TET-Yeasate: An engineered yeast whole-cell lysate-based approach for high performance tetracycline degradation

The widespread of tetracycline (TC) residues in anthropogenic and natural environments pose an immediate threat to public health. Herein, we established the TET-Yeasate, an approach based on whole-cell lysate of engineered yeast, to mitigate the TC contamination in environment. The TET-Yeasate is defined as the biological matrix of whole cell lysate from engineered yeast that containing TC-degradative components (Tet(X), NADPH, Mg2+) and protective macromolecules. The TET-Yeasate was able to efficiently eliminate TC residues in tap water (98.8%), lake water (77.6%), livestock sewage (87.3%) and pharmaceutical wastewater (35.3%) without necessity for exogenous addition of expensive cofactors. The TET-Yeasate was further developed into lyophilized form for ease of storage and delivery. The TET-Yeasate in lyophilized form efficiently removed up to 74.6% TC residue within 0.25 h. In addition, the lyophilization confers promising resilience to TET-Yeasate against adverse temperatures and pH by maintaining degradation efficacy of 85.69%-97.83%. The stability test demonstrated that the biomacromolecules in lysate served as natural protectants that exerted extensive protection on TET-Yeasate during the 14-day storage at various conditions. In addition, 5 potential degradation pathways were elaborated based on the intermediate products. Finally, the analysis indicated that TET-Yeasate enjoyed desirable bio- and eco-safety without introduction of hazardous intermediates and spread of resistance genes. To summary, the TET-Yeasate based on whole cell lysate of engineered yeast provides a cost-effective and safe alternative to efficiently remove TC residues in environment, highlighting the great potential of such whole-cell based methods in environmental decontamination.

Transformation of tetracycline by multipurpose Fe-Mn-Cu nano-composite oxide: Dual-synergies and dual-mechanisms

The interaction between tetracycline (TTC) and mixed metallic oxides remains unclear, and even complexation usually is ignored. This study firstly distinguished the triple functions of adsorption, transformation and complexation in presence of Fe-Mn-Cu nano-composite metallic oxide (FMC) on TTC. Rapid adsorption and faint complexation initiated the transformation that dominated the entire reactions at 180 min, which completed TTC removal (up to 99.04%) synergistically within 48 h. Environmental factors (dosage, pH and coexisting ions) had small influence on TTC removal, which primarily depended on the stable transformation characteristics of FMC. Kinetic models incorporating pseudo-second-order kinetics and transformation reaction kinetics demonstrated that the surface sites of FMC promoted electron transfer process through chemical adsorption and electrostatic attraction. ProtoFit program coupled with characterization methods concluded that Cu-OH was the main reaction site of FMC where the protonated surface favored to generate·O₂^-. Meanwhile, three metal ions developed simultaneous mediated transformation reactions on TTC in liquid phase, and·O₂^- induced the production of·OH. The transformed products were subjected to toxicity assessment, which had lost antimicrobial properties toward Escherichia coli. Insights gained from this study can refine the dual mechanisms of multipurpose FMC in solid and liquid phases underlying TTC transformation.

Facile Hydrothermal Synthesis of Cu2MoS4 and FeMoS4 for Efficient Adsorption of Chlortetracycline

Contamination of antibiotics in an aqueous environment has attracted wide attention. Developing high-efficiency adsorbents for antibiotics removal is urgent. In this work, two kinds of ternary transition metal chalcogenides—Cu2MoS4 and FeMoS4 with superior adsorption performance were prepared by a facile hydrothermal synthesis method. The microstructure and physicochemical properties of the adsorbents were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The as-prepared Cu2MoS4 and FeMoS4 were found to have dramatic potential for the adsorption of chlortetracycline (CTC) in an aqueous solution with an extremely high adsorption capacity. The Langmuir maximum adsorption capacity of Cu2MoS4 and FeMoS4 to CTC can reach 1203.81 and 2169.19 mg/g, respectively, which goes far beyond the common adsorbents as reported. Moreover, the adsorption kinetics, thermodynamics as well as adsorption mechanism were examined in detail by a batch of adsorption experiments.