Cleavage Of Azo Bond Research Articles

Harnessing Chlorella vulgaris for the phycoremediation of azo dye: A comprehensive analysis of metabolic responses and antioxidant system

This study investigates the phycoremediation potential of microalgae Chlorella vulgaris in the degradation of Direct green 6 (DG6), a synthetic azo dye commonly used in the textile industry, which poses significant environmental and health risks due to its toxic and carcinogenic properties. Over 50 days of treatment, we analyzed the effects of varying concentrations of DG6 on the biodegradation capabilities of C. vulgaris with the characterization of growth and antioxidant parameters. The findings demonstrate that C. vulgaris reduced DG6 levels significantly (p < 0.05) at higher temperatures (40 °C) compared to other environmental ambient temperatures. Within the acidic range pH < 7 progressive removal efficiency was observed within 25 days in consistency with the enhanced growth indices of biomass concentration (Xm), productivity (Px), specific growth rate (μm), and doubling time (td) at the higher concentration of 60 mg L−1. Induction of both enzymatic and non-enzymatic antioxidant activities were quantified for superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), azoreductase, and laccase, as well as changes in the total ascorbate pool (AsA + DHA) and ferric reducing antioxidant power (FRAP). Furthermore, the underlying biodegradation mechanisms were elucidated by identifying the reductive cleavage of azo bonds by azoreductase and breakdown by peroxidases and laccase. These molecular by-products were identified using gas chromatography–mass spectrometry (GC–MS), which shed light on the metabolic pathways involved in DG6 biodegradation. This study underscores the effectiveness of C. vulgaris as a sustainable, low-cost solution for the bioremediation of azo-dye-polluted water. This study lays the groundwork for further exploration into the genetic and metabolic adaptations of algae under complex organic pollutant stress, with potential implications for ecophysiology, biotic interactions, and evolutionary biology.

In Situ Utilization of Electron-Enhanced Degradation of Azo Dyes in a Constructed Wetland–Microbial Fuel Cell Coupling System

In this study, a constructed wetland was coupled with a microbial fuel cell to establish a coupled system known as the constructed wetland–microbial fuel cell (CW–MFC), utilized for the treatment of X-3B azo dye wastewater at varying concentrations. Experimental results indicated that the anodic region made the primary contributions to the discoloration of azo dyes and COD removal, with a contribution rate of 60.9–75.8% for COD removal and 57.8–83.0% for the effectiveness of discoloration. Additionally, the role of plants in the constructed wetland area could achieve the removal of small molecular substances and further discoloration. In comparison to open-circuit conditions, under closed-circuit conditions the CW–MFC effectively degraded X-3B azo dye wastewater. Under an external resistance of 2000 Ω, a maximum COD removal rate of 60.0% and a maximum discoloration rate of 85.8% were achieved for X-3B azo dye at a concentration of 100 mg/L. Improvements in the treatment efficiency of X-3B dye wastewater were achieved by altering the external resistance. Under an external resistance of 100 Ω and an influent concentration of X-3B of 800 mg/L, the COD removal rate reached 78.6%, and the decolorization rate reached 85.2%. At this point, the CW–MFC exhibited a maximum power density of 0.024 W/m3 and an internal resistance of 99.5 Ω. Spectral analysis and GC–MS results demonstrated the effective degradation of azo dyes within the system, indicating azo bond cleavage and the generation of numerous small molecular substances. Microbial analysis revealed the enrichment of electrogenic microorganisms under low external resistance conditions, where Geobacter and Trichococcus were dominant bacterial genera under an external resistance of 100 Ω, playing crucial roles in power generation and azo dye degradation within the system.

Development of a hypoxia-activated red-emission fluorescent probe for in vivo tumor microenvironment imaging and anti-tumor therapy.

Hypoxia, a significant feature of the tumor microenvironment, is closely associated with tumor growth, metastasis, and drug resistance. In the field of tumor microenvironment analysis, accurately imaging and quantifying hypoxia - a critical factor associated with tumor progression, metastasis, and resistance to therapy - remains a significant challenge. Herein, a hypoxia-activated red-emission fluorescent probe, ODP, for in vivo imaging of hypoxia in the tumor microenvironment is presented. Among various imaging methods, optical imaging is particularly convenient due to its rapid response and high sensitivity. The ODP probe specifically targets nitroreductase (AzoR), an enzyme highly expressed in hypoxic cells, playing a vital role by catalyzing the cleavage of azo bonds. The optical properties of ODP exhibited excellent performance in terms of fluorescence enhancement, fluorescence lifetime (0.81 ns), and detection limit (0.86 µM) in response to SDT. Cell imaging experiments showed that ODP could effectively detect and image intracellular hypoxia and the imaging capability of ODP was studied under various conditions including cell migration, antioxidant treatment, and different incubation times. Through comprehensive in vitro and in vivo experiments, including cellular imaging and mouse tumor models, this work demonstrates the efficacy of ODP in accurately detecting and imaging hypoxia. Moreover, ODP's potential in inducing apoptosis in cancer cells offers a promising avenue for integrating diagnostic and therapeutic strategies in cancer treatment. This innovative approach not only contributes to the understanding and assessment of tumor hypoxia but also opens new possibilities for targeted cancer therapy.

Decolorization of acid orange 7 in moving bed biofilm reactor packed with polyhydroxyalkanoate/activated carbon

Moving bed biofilm reactor (MBBR) using various carrier medium has been widely employed in wastewater treatment. This study aimed to investigate the feasibility of polyhydroxyalkanoate (PHA) and activated carbon (AC) composite (PHA/AC) as biofilm carrier to enhance MBBR treatment of azo dye acid orange 7 (AO7). Each PHA/AC carrier had a height of 0.40 cm and a cylindrical diameter of 1.25 cm. The biofilm on PHA/AC carrier was characterized using microscopic and chemical analysis. AO7 decolorization efficiency and kinetics were evaluated. The incorporation of AC in PHA was found to promote biofilm growth. Mature biofilm of 2075 ± 79.30 μm was successfully formed on PHA/AC carrier. Compared to a control reactor, the MBBR with 5 % (v/v) PHA/AC exhibited improved decolorization, with decolorization efficiency and first-order rate constant, kAO7, increasing from 78.2 % and 9.90 × 10−4 min−1 to 95.0 % and 1.70 × 10−3 min−1, respectively. The enhancement of decolorization in MBBR was attributed to the presence of anoxic zone within the biofilm that favored the azo bond cleavage. Batch studies on the effects of suspended activated sludge (AS) and biofilm amounts showed an additive effect on decolorization efficiency when combined. The combined suspended AS and biofilm also resulted a 3–4 folds increase in kAO7 value compared to AS alone. The results indicate that PHA/AC was an effective carrier and its biofilm exhibited high decolorizing ability for AO7. The enhancement provided by the PHA/AC biofilm makes it advantageous for developing efficient and environmentally-friendly wastewater treatment systems with compact design and minimal sludge production.

Theoretical Design and Synthesis of Caged Compounds Using X-Ray-Triggered Azo Bond Cleavage.

Caged compounds are frequently used in life science research. However, the light used to activate them is commonly absorbed and scattered by biological materials, limiting their use to basic research in cells or small animals. In contrast, hard X-rays exhibit high bio-permeability due to the difficulty of interacting with biological molecules. With the main goal of developing X-ray activatable caged compounds, azo compounds are designed and synthesized with a positive charge and long π-conjugated system to increase the reaction efficiency with hydrated electrons. The azo bonds in the designed compounds are selectively cleaved by X-ray, and the fluorescent substance Diethyl Rhodamine is released. Based on the results of experiments and quantum chemical calculations, azo bond cleavage is assumed to occur via a two-step process: a two-electron reduction of the azo bond followed by N─N bond cleavage. Cellular experiments also demonstrate that the azo bonds can be cleaved intracellularly. Thus, caged compounds that can be activated by an azo bond cleavage reaction promoted by X-ray are successfully generated.

Nature-Inspired Photocatalytic Azo Bond Cleavage with Red Light.

The emerging field of photoredox catalysis in mammalian cells enables spatiotemporal regulation of a wealth of biological processes. However, the selective cleavage of stable covalent bonds driven by low-energy visible light remains a great challenge. Herein, we report that red light excitation of a commercially available dye, abbreviated NMB+, leads to catalytic cleavage of stable azo bonds in both aqueous solutions and hypoxic cells and hence a means to photodeliver drugs or functional molecules. Detailed mechanistic studies reveal that azo bond cleavage is triggered by a previously unknown consecutive two-photon process. The first photon generates a triplet excited state, 3NMB+*, that is reductively quenched by an electron donor to generate a protonated NMBH•+. The NMBH•+ undergoes a disproportionation reaction that yields the initial NMB+ and two-electron-reduced NMBH (i.e., leuco-NMB, abbreviated as LNMB). Interestingly, LNMB forms a charge transfer complex with all four azo substrates that possess an intense absorption band in the red region. A second red photon induces electron transfer from LNMB to the azo substrate, resulting in azo bond cleavage. The charge transfer complex mediated two-photon catalytic mechanism reported herein is reminiscent of the flavin-dependent natural photoenzyme that catalyzes bond cleavage reactions with high-energy photons. The red-light-driven photocatalytic strategy offers a new approach to bioorthogonal azo bond cleavage for photodelivery of drugs or functional molecules.

Cationic and anionic cross-assisted synergistic photocatalytic removal of binary organic dye mixture using Ni-doped perovskite oxide

Organic dyes present in industrial wastewater are the major contributor to water pollution, which harm human health and the environment. Photocatalytic dye degradation is an effective strategy for water remediation by converting these organic dyes waste into non-harmful by-products. Therefore, in this study, Ni-doped LaFeO3 (NLFO) perovskite nanoparticles were extensively explored for photocatalytic degradation of cationic and anionic dyes and their mixture. The NLFO nanoparticles were successfully synthesized by surfactant assisted hydrothermal method under controlled Ni doping. The X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) revealed the variation in size (40–70 nm) of orthorhombic crystalline LFO nanoparticles with Ni doping and hence the size of microspheres (0.78. to 1.78 μm). The kinetic studies revealed that the LaFe0·6Ni0·4O3 performed well by providing degradation efficiency of 99.2% in 210 min, 99.1% in 100 min, and 98.4% in 70 min for Crystal Violet (CV), Congo Red (CR), and their mixture with rate constant of 0.019, 0.039, and 0.055 min−1 respectively. The radical scavenger tests indicated the synergetic contributions of O2− and •OH− active radicals in faster degradation of CV and CR dye mixture. The stepwise fragmentation of dye molecule during the photocatalytic degradation identified from the LCMS indicates the degradation of CV dye through de-alkylation and benzene ring breaking, whereas azo bond cleavage and oxidation lead to low molecular weight intermediates for CR dye, which all together helped to degrade their dye mixture (50 mg L−1 and 100 mg L−1) in significantly lesser time (70 min). Overall, the Ni-doped LFO microsphere consisting of nanoparticles acts as a superior catalyst for the more efficient and faster degradation of binary dye mixture.

Application of Hydrogen-Based Denitrification: Simultaneous Removal of Nitrate and Reactive Black 5 Dye from Textile Wastewater Containing Organic Matter

In this study, a hydrogen-based denitrification (HD) reactor was used to investigate the simultaneous treatment of nitrogen and decolorization in textile wastewater contaminated with organic matter. The reactor operated in two phases: without and with organic matter. Despite the short hydraulic retention time, the HD system successfully removed all pollutants, including nitrate, nitrite, reactive black-5 dye and chemical oxygen demand. The unhindered treatment efficiency for nitrogen and decolorization in the presence of organic pollutants was observed. With the addition of organic matter, the nitrogen removal efficiency increased slightly from 85% to 90–100%, and the decolorization rate doubled from 25% to 50–60%. Organic matter played a crucial role in stimulating heterotrophic bacteria during biological denitrification and acted as a carbon source facilitating biological denitrification and azo bond cleavage during dye degradation. Despite the generation of toxic byproducts and changes in the dominant microbial community, the treatment efficiency remained stable and improved. This approach offers a promising solution for enhancing treatment efficiency in textile wastewater, providing a cost-effective and environmentally friendly option for developing countries to treat wastewater before discharge.

A Review of Environmental Impact of Azo Dyes

Green plants are one of nature’s factories, fixing inorganic chemicals into organic compounds through photosynthesis and other reactions. Microbes are one of the nature’s most effective tools, converting organic materials—dead plants and animals—into inorganic forms through decomposition and mineralization. Together, green plants and microbes are responsible for maintaining a balance between the organic and inorganic worlds, but pollutants, such as synthetic dyes, can upset this balance. Compared with synthetic dyes, natural dyes are safer and more environmentally friendly, but they are also costlier and more difficult to apply, so they are not viable in most commercial applications. Azo dyes are low cost and have high intensity and color fastness, so they are the most frequently used class of synthetic dyes. The main threats related to the dumping of untreated azo dyes into the environment come from their primary byproducts––aromatic amines––which result from the cleavage of the central azo bonds, and which have been classified as significant carcinogenic compounds, representing a great risk to humans as well as the environment. To address this threat, the degradation of synthetic azo dyes is showing promise as an approach to treating azo-dye wastewater. In this review, the classification of azo dyes and their color mechanism is presented first, and then an overview of the research on their environmental impacts is provided, including their effects on biochemical and chemical oxygen demand, water ecosystems, plants, and crops. Finally, the legislation and guidelines on azo dyes and their byproducts are discussed. Keywords: azo dyes; climate change; biochemical oxygen demand; chemical oxygen demand; aromatic amines

Mechanistic insights on enzyme mediated-metabolite cascade during decolourization of Reactive Blue 13 using novel microbial consortium

Understanding the role of oxido-reductase enzymes followed by deciphering the functional genes and their corresponding proteins are crucial for the speculation of molecular mechanism for azo dye degradation. In the present study, decolourization efficiency of developed microbial consortium was tested using 100 mgL−1 reactive blue 13 (RB13) and the results showed ∼92.67% decolourization of RB13 at 48 h of incubation. The fourier-transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC-MS) analysis were performed to identify the metabolites formed during RB13 degradation, followed by hypothesizing the metabolic pathway. The GC-MS analysis showed formation of 1,4-dihydronaphthalen-1-ol and 1,3,5-triazin-2-amine as the final degraded compounds after enzymatic breakdown of RB13 dye. The activity of different oxido-reductase enzymes was determined, and the results showed that NADH DCIP reductase and azo reductase had higher activity than other enzymes. It clearly indicated the degradation was initiated with the enzymatic cleavage of azo bond of RB13. Further, the functional genes were annotated against the database of clusters of orthologous groups (COGs) and kyoto encyclopedia of genes and genomes (KEGG). It provided valuable information about the role of crucial functional genes and their corresponding proteins correlated with dominant bacterial species in degradation of RB13. Hence, the present research is the first systematic study that correlated the formation of degradation compounds with the functional genes/enzymes and their corresponding bacterial species responsible for RB13 degradation.

Bacterial enzymes for azo dye degradation: an insight

Azo dye has a massive marketplace in various industries, biological laboratories and clinics. A significant drawback is the excessive flush-off of azo dyes and their intermediate products are that they pollute the environment. Several environmental bacteria degrade azo dye under certain specific ecological conditions. Decolourisation by different bacteria occurs under aerobic, anoxic and anaerobic conditions. Bacterial genera such as Pseudomonas, Bacillus and Rhodococcus are used for the rapid decolourisation of azo dyes. Bacterial enzymes play an essential role in the degradation of azo dyes by cleavage of azo bonds (-N=N-). It is degraded by both oxidative and reductive enzymes including azo reductase, laccase, lignin peroxidase, NADH-DCIP reductase, malachite green reductase, polyphenol oxidase (tyrosinase), veratrol alcohol oxidase. This review describes the role and mechanism of these enzymes in the degradation of azo dyes.

Degradation of Diazo Congo Red Dye by Using Synthesized Poly-Ferric-Silicate-Sulphate through Co-Polymerization Process.

The ability of poly-ferric-silicate-sulphate (PFSS) synthesized via a co-polymerization process has been applied for the removal of diazo Congo red dye. A novel degradation pathway of diazo Congo red dye by using PFSS is proposed based on LC-MS analysis. Diazo Congo red dye was successfully removed using synthesized PFSS at lower coagulant dosages and a wider pH range, i.e., 9 mg/L from pH 5 to 7, 11 mg/L at pH 9, and 50 mg/L at pH 11. The azo bond cleavage was verified by the UV-Vis spectra of diazo Congo red-loaded PFSS and FTIR spectra which showed disappearance of the peak at 1584 cm-1 for -N=N- stretching vibrations. The synchronized results of UV-Vis spectra, FTIR, and the LC-MS analysis in this study confirmed the significance of the Si and Fe bond in PFSS towards the degradation of diazo Congo red dye. The successfully synthesized PFSS coagulant was characterized by FTIR, SEM, TEM, and HRTEM analysis. From this analysis, it was proven that PFSS is a polycrystalline material which is favorable for the coagulation-flocculation process. Based on all these findings, it was established that synthesized PFSS can be employed as a highly efficient polymeric coagulant for the removal of dye from wastewater.

Nano-sphere RuO2 embedded in MOF-derived carbon arrays as a dual-matrix anode for cost-effective electrochemical wastewater treatment

The electrodes' activity, surface area and cost hinder the deployment of electrochemical wastewater treatment. Using an economical microfiber-based carbon felt (CF) substrate, we design RuO2 nanospheres confined by CoxO cooperated carbon nanoarrays (RuO2-CoxO@TCF) to augment noble metal utilization and thus reduce the catalyst cost. RuO2-CoxO@TCF anode with vertical diffusion channels exhibits rapid generation ability of oxidizing species particularity in the presence of Cl− ions, which play a crucial role in azo bond cleavage and benzene ring chlorination of methyl orange. As a result, the catalyst shows 99.5 % color removal and ∼ 70 % mineralization efficiency at a concentration of 60 ppm. In synthetic dyeing wastewater, RuO2-CoxO@TCF delivers a stable total organic carbon (TOC) removal throughout ten cycling tests. Moreover, the electricity consumption of RuO2-CoxO@TCF is far below the reference anode, showing great promise for dye degradation and remediation of industrial wastewater.

Activated peroxydisulfate by sorghum straw-based biochar for enhanced tartrazine degradation: Roles of adsorption and radical/nonradical processes

Biochar obtained from biomass waste through pyrolysis has significant potential in wastewater treatment due to its large specific surface area and multi-functional active sites. In current study, sorghum straw (SS) was pyrolyzed to prepare various biochar under nitrogen atmosphere. Adsorption kinetics of prepared biochar toward tartrazine (TTZ) was systematically investigated, and the biochar was also characterized by using multiple techniques to explore the contribution of physicochemical properties to adsorption. Then, the biochar with optimum TTZ adsorption performance, was also applied as a catalyst for peroxydisulfate (PDS) activation to degrade TTZ. Factors including PDS concentration, solution pH, and reaction temperature were examined. The optimized degradation rate constant of TTZ (1.1627 min−1) was achieved under the conditions at 2 mM PDS, pH of 3, and 23 °C. In addition, the free radical trapping experiments and EPR spectra revealed that the reactive substances of electron (e−), 1O2, SO4•−, O2•−, and •OH contributed to TTZ degradation. Density Functional Theory (DFT) also concluded that the atoms C(6), O(12), N(16), N(17), C(18) and N(22) in TTZ molecule showed larger f0 values which are vulnerable to radical attack. Therefore, the synergistic mechanism embodying adsorption and radical/non-radical processes were proposed. Besides, the degradation pathways of TTZ were identified with the aid of HPLC/MS technique, indicating that multiple reaction processes containing the symmetrical cleavage of azo bonds, the asymmetrical cleavage of C–N, desulfonation, and benzene-like structure cracking were involved. Therefore, this study provides a simple and effective catalytic system for TTZ degradation, and also realizes the resource utilization of solid waste.

Resource utilization of agricultural waste: Converting peanut shell into an efficient catalyst in persulfate activation for degradation of organic pollutant.

Agricultural waste was characterized by large quantity and low degree of resource utilization. The peanut shell waste was converted into value-added biochar to alleviate the pollution of dyeing wastewater, which caters to the concept of resource recovery and sustainable utilization. In this work, peroxydisulfate (PDS) could be efficiently activated by biochar obtained by pyrolysis at 700°C (BC) and Acid Orange 7 (AO7) was rapidly eliminated with 96% removal ratio in 10min. Meanwhile, BC catalyst performed good stability and reusability. In addition, remarkable removal performance within 40min (>94%) could be achieved in a wide range of pH (3.0-11.0). Through series characterizations, it was found that 700°C was the critical pyrolysis temperature to prepare material with excellent property mainly attributing to large specific surface area (SSA), followed by high defect structure and rich C-O. It was speculated that radical pathway mainly especially surface-bounded radicals (SO4•-、•OH、O2-•) worked in the degradation of AO7. Specifically, abundant and typical oxygen-containing functional groups (OFGs) and defect structure catalytic sites of BC enhanced PDS activation. In addition, various radicals participated the whole degradation processes, such as the cleavage of azo bond (-NN-), hydroxylation, deamination and desulfurization.

Spectral Studies of Azo Dye Degradation Using Selected Biofertilizer: Pseudomonas Fluorescens

Azo dyes are the azo colorants with about 70% dyestuff. Azo dyes persist in the environment for years and are toxic to human life. In the present study, it was attempted to decolorize the selected azodye by three selected biofertilizers: Rhizobium sp., Azospirillum sp. and Pseudomonas fluorescens whereas also to prove biofertlizer’s degradation property. Initially decolorization of 10% azo dye of silk dyeing effluent was biotreated with above mentioned biofertilizers at 37 °C separately as preliminary studies. It was found that preliminarily decolorization of azo dye with Pseudomonas fluorescens with 85% followed by Azospirillum sp. with 74%. Based on this, the percentage decolorization was evaluated for various concentrations of 25, 50, 75 and 100% of azo dye of silk dyeing effluent under static conditions with glucose as carbon source. The percentage decolorization was found to be 91% in 5 days with 25% effluent by Pseudomonas fluorescens reduced to 68% with crude azo dye effluent which had positive influence on the growth of bacterium in the 0.002g glucose as carbon source as growth rate was increased along with decolorization. In contrast the least percentage decolorization was analyzed as 23% in 5 days with 25% effluent by Rhizobium sp. whereas reduced drastically to 11% with 100% effluent. This indicated the dilution is more needed for the better decolorization. The cleavage of azo bond was confirmed through spectral studies such as UV and in HPLC chromatogram of silk dyeing raw industrial bio-treated azo dye Silk dyeing effluent. Microbial growth has utilized and decolorized the dye wastewater shows its biodegradation potential. The high decolorization ability was observed in Pseudomonas fluorescens compared to Azospirillum sp., and Rhizobium sp., as biofertilizer to convert toxic azo dyes into nontoxic compounds reducing the contaminants will prove dual purpose of usage of biofertilizers in the environment.&#x0D;

Cell-Free Protein Synthesis for the Screening of Novel Azoreductases and Their Preferred Electron Donor.

Azoreductases are potent biocatalysts for the cleavage of azo bonds. Various gene sequences coding for potential azoreductases are available in databases, but many of their gene products are still uncharacterized. To avoid the laborious heterologous expression in a host organism, we developed a screening approach involving cell‐free protein synthesis (CFPS) combined with a colorimetric activity assay, which allows the parallel screening of putative azoreductases in a short time. First, we evaluated different CFPS systems and optimized the synthesis conditions of a model azoreductase. With the findings obtained, 10 azoreductases, half of them undescribed so far, were screened for their ability to degrade the azo dye methyl red. All novel enzymes catalyzed the degradation of methyl red and can therefore be referred to as azoreductases. In addition, all enzymes degraded the more complex and bulkier azo dye Brilliant Black and four of them also showed the ability to reduce p‐benzoquinone. NADH was the preferred electron donor for the most enzymes, although the synthetic nicotinamide co‐substrate analogue 1‐benzyl‐1,4‐dihydronicotinamide (BNAH) was also accepted by all active azoreductases. This screening approach allows accelerated identification of potential biocatalysts for various applications.

Novel Near‐Infrared Fluorescent Nanoprobe Synthesized by the RAFT‐Mediated PISA Strategy for Hypoxia‐Triggered Tumor Imaging and Azoreductase‐Responsive Drug Release

AbstractDrug carriers and visual tracking play an important role in accurate and efficient drug delivery systems for targeted drug therapy. Polymerization‐induced self‐assembly (PISA), a powerful strategy for the fabrication of stimuli‐responsive polymeric nanoparticles has been a focus over the past decade due to its promising applications in biomedical fields such as targeted drug delivery and fluorescent nanoprobes used for tumor imaging. Herein, hypoxia‐responsive near‐infrared (NIR) fluorescent nanoprobes of amphiphilic block copolymers (PPEGMA14‐ADP‐Azo‐PBzMAx) are reported, the first example synthesized by RAFT‐mediated PISA strategy in situ to realize synchronous drug release and cell imaging. First, a series of nanoparticles with different morphologies and sizes, including spheres and vesicles, are synthesized by the PISA strategy using PPEGMA14‐ADP‐Azo‐CDPA as macro‐RAFT agents link with near‐infrared Aza‐BODIPY fluorogen and azobenzene groups. Hypoxia‐triggered dissociation of the nanoprobes and NIR fluorescence emission is then observed because of the cleavage of azo bonds. Meanwhile, the in situ DOX‐loaded nanoprobes by the PISA demonstrate synchronous drug release and NIR fluorescence enhancement against mouse colon cancer cells (CT26) under hypoxia (1% O2) compared with under normoxia (16% O2).

Biodegradation, Decolorization, and Detoxification of Di-Azo Dye Direct Red 81 by Halotolerant, Alkali-Thermo-Tolerant Bacterial Mixed Cultures.

Azo dyes impact the environment and deserve attention due to their widespread use in textile and tanning industries and challenging degradation. The high temperature, pH, and salinity used in these industries render industrial effluent decolorization and detoxification a challenging process. An enrichment technique was employed to screen for cost-effective biodegraders of Direct Red 81 (DR81) as a model for diazo dye recalcitrant to degradation. Our results showed that three mixed bacterial cultures achieved ≥80% decolorization within 8 h of 40 mg/L dye in a minimal salt medium with 0.1% yeast extract (MSM-Y) and real wastewater. Moreover, these mixed cultures showed ≥70% decolorization within 24 h when challenged with dye up to 600 mg/L in real wastewater and tolerated temperatures up to 60 °C, pH 10, and 5% salinity in MSM-Y. Azoreductase was the main contributor to DR81 decolorization based on crude oxidative and reductive enzymatic activity of cell-free supernatants and was stable at a wide range of pH and temperatures. Molecular identification of azoreductase genes suggested multiple AzoR genes per mixed culture with a possible novel azoreductase gene. Metabolite analysis using hyphenated techniques suggested two reductive pathways for DR81 biodegradation involving symmetric and asymmetric azo-bond cleavage. The DR81 metabolites were non-toxic to Artemia salina nauplii and Lepidium sativum seeds. This study provided evidence for DR81 degradation using robust stress-tolerant mixed cultures with potential use in azo dye wastewater treatment.

Biodegradation of methyl red dye by a novel actinobacterium Zhihengliuella sp. ISTPL4: Kinetic studies, isotherm and biodegradation pathway

Among azo dyes, methyl red dye is mutagenic and its persistence causes serious impacts on the environment and human health. The current study is the first report of methyl red dye degradation by an actinobacterium, Zhihengliuella sp. ISTPL4. Strain showed 98.87% of 500 mg/L methyl red dye degradation within 12 h. Optimization of the efficient decolorization by the strain, Quadratic regression model analysis was done by using R software. The kinetic studies revealed the biosorption of dye and explained by Freundlich isotherm model where maximum adsorption was observed (0.99) followed by a pseudo second order reaction. N,N -dimethyl-p-phenylaminediamine (DMPD), and 2-aminobenzoic acid (2-ABA) were detected as key metabolites. Whole genome sequencing analysis showed the presence of azoreductase enzyme. FTIR analysis showed the reductive cleavage of the methyl red azo bond. Furthermore, the degradation pathway of methyl red has been proposed. With these results, we propose a novel application of Zhihengliuella sp. ISTPL4 in methyl red dye degradation at higher concentration.