Reduction of hexavalent chromium using naturally-derived flavonoids

Harnessing the potential of ginkgo biloba extract: Boosting denitrification performance through accelerated electron transfer

Ginkgo biloba extract (GBE) had several effects on the human body as one of the widely used phytopharmaceuticals, but it had no application in microbial enhancement in the environmental field. The study focused on the impact of GBE on denitrification specifically under neutral conditions. At the identified optimal addition ratio of 2% (v/v), the system exhibited a noteworthy increase in nitrate reduction rate (NRR) by 56.34%, elevating from 0.71 to 1.11 mg-N/(L·h). Moreover, the extraction of microbial extracellular polymeric substance (EPS) at this ratio revealed changes in the composition of EPS, the electron exchange capacity (EEC) was enhanced from 87.16 to 140.4 μmol/(g C), and the transfer impedance was reduced within the EPS. The flavin, fulvic acid (FA), and humic acid (HA) provided a π-electron conjugated structure for the denitrification system, enhancing extracellular electron transfer (EET) by stimulating carbon source metabolism. GBE also improved electron transfer system activity (ETSA) from 0.025 to 0.071 μL O2/(g·min·prot) and the content of NADH enhanced by 22.90% while significantly reducing the activation energy (Ea) by 85.6% in the denitrification process. The synergy of improving both intracellular and extracellular electron transfer, along with the reduction of Ea, notably amplified the initiation and reduction rates of the denitrification process. Additionally, GBE demonstrated suitability for denitrification across various pH levels, enhancing microbial resilience in alkaline conditions and promoting survival and proliferation. Overall, these findings open the door to potential applications of GBE as a natural additive in the environmental field to improve the efficiency of denitrification processes, which are essential for nitrogen removal in various environmental contexts.

Reduction of hexavalent chromium using Bacillus safensis isolated from an abandoned mine

The present work focused on the isolation of a bacterial strain multi-resistant to heavy metals with a high potential for reducing hexavalent chromium (Cr(VI)) and studied its Cr(VI) removal performance in immobilized state and the mechanisms involved. Bacterial isolate was identified as Bacillus safensis CCMM B629 (B. safensis), is able to completely reduce 50, 100 and 200 mg/L of Cr(VI) after 24, 48 and 120 h, respectively under optimized conditions of pH 7 and 30°C. The coexistence of nitrates, cadmium and mercury inhibits reduction, while copper and iron significantly improve removal efficiencies. Additionally, the presence of electron donors such as glycerol, glucose and citrate significantly increases bioreduction rate. Cells immobilized in alginate beads successfully reduced Cr(VI) compared to free cells, showing the performance of biobeads in Cr(VI) reduction. Membrane fraction exhibited highest rate of Cr(VI) reduction (65%) compared to other cellular components, indicating that Cr(VI) reduction occurred primarily in cell membrane. Further characterization of Cr(VI) removal by B. safensis cells using scanning electron microscopy and energy-dispersive X-ray (SEM-EDX) analysis showed its ability to reduce and adsorb Cr(VI), confirming that hexavalent chromium was taken up successfully on bacterial cell surfaces. Based on Fourier transform infrared spectroscopy analysis (FTIR), hydroxyl, carboxyl, amide, and phosphoryl functional groups participated in combination with Cr(III). In conclusion, B. safensis is a bacterium with great potential for Cr(VI) removal, and it is a promising and competitive strain for use in bioremediation of Cr(VI) contaminated industrial effluents.

Ecotoxicity study of reduced-Cr(III) generated by Cr(VI) biosorption

Hexavalent chromium (Cr(VI)) is a known carcinogen in living organisms, and many studies have investigated Cr(VI) removal methods. Biosorption, one of the Cr(VI) removal methods, is dominated by chemical binding, ion exchange, physisorption, chelation and oxidation-reduction. Among these mechanisms, Cr(VI) can be removed by nonliving biomass through a redox reaction, which has been recognized as 'adsorption-coupled reduction'. Cr(VI) is reduced to Cr(III) during biosorption, but there are no studies on the property and toxicity of the reduced-Cr(III). In this study, the harmfulness of reduced-Cr(III) was identified through assessment of mobility and toxicity in nature. Pine bark, a low-cost biomass, was used to remove Cr(VI) from aqueous solution. Reduced-Cr(III) was characterized by structural features using X-ray Absorption Near Edge Structure (XANES) spectra, mobility assessed using precipitation, adsorption and soil column test, and toxicity using radish sprouts and water flea. XANES analysis confirmed that reduced-Cr(III) has an unsymmetrical structure, and the reduced-Cr(III) showed low mobility and was virtually non-toxic, and helpful for plant growth. Our findings demonstrate that Cr(VI) biosorption technology using pine bark is a groundbreaking technology for Cr(VI) detoxification.

Nuclear magnetic resonance relaxometry to monitor chromium (VI) reduction by hydrogen peroxide, ascorbic acid, and aluminum powder

The reduction of K₂ Cr₂ O₇ solutions by H₂ O₂ was studied by nuclear magnetic resonance (NMR) relaxometry and UV-vis spectroscopy in HCl/KCl buffer (pH 2), NaCl/glycine/HCl buffer (pH 3), and sodium acetate/acetic acid buffer (pH 4). Because of Cr(III) paramagnetism, 1/T₁ and 1/T₂ of the solutions increase during the reduction of diamagnetic Cr(VI). This increase is proportional to the produced Cr(III) concentration. Using different initial H₂ O₂ concentrations, partially reduced Cr(VI) samples were prepared and studied by T₁ and T₂ relaxometry and by UV-vis spectroscopy. The correlation between the relaxation rates and the concentration of Cr(VI) remaining in the sample, measured by spectroscopy, was excellent. It was possible, thanks to the measurement of T₂ , to study the kinetics of the reduction of K₂ Cr₂ O₇ by H₂ O₂ in the pH 3 and pH 4 buffers. The reduction of Cr(VI) by ascorbic acid was successfully monitored by NMR relaxometry in the pH 2 buffer. The presence of complexing molecules/ions was shown to drastically influence the nuclear magnetic relaxation dispersion profiles of reduced K₂ Cr₂ O₇ solutions: Both relaxation rates are divided by ~5 when citrate or acetate ions are present and by ~3 in the presence of ascorbic acid. Therefore, the comparison of relaxation results obtained in different reaction mixtures must be done carefully. When all the solutions are set to pH 0, which prevents any complexation, the longitudinal and transverse relaxation rates of all samples become comparable. Finally, as a proof of concept for a turbid solution, the kinetics of the reduction of a K₂ Cr₂ O₇ solution by aluminum powder in the pH 2 buffer was successfully monitored.

Fungal Selectivity and Biodegradation Effects by White and Brown Rot Fungi for Wood Biomass Pretreatment

The biodegradation path and mechanism of wood varies depending on diverse fungi and tree species, as fungi possess selectivity in degradation of versatile wood components. This paper aims to clarify the actual and precise selectivity of white and brown rot fungi and the biodegradation effects on different tree species. Softwood (Pinus yunnanensis and Cunninghamia lanceolata) and hardwood (Populus yunnanensis and Hevea brasiliensis) were subjected to a biopretreating process by white rot fungus Trametes versicolor, and brown rot fungi Gloeophyllum trabeum and Rhodonia placenta with various conversion periods. The results showed that the white rot fungus Trametes versicolor had a selective biodegradation in softwood, which preferentially convert wood hemicellulose and lignin, but cellulose was retained selectively. Conversely, Trametes versicolor achieved simultaneous conversion of cellulose, hemicellulose and lignin in hardwood. Both brown rot fungi species preferentially converted carbohydrates, but R. placenta had a selectivity for the conversion of cellulose. In addition, morphological observation showed that the microstructures within wood changed significantly, and the enlarged pores and the improved accessibility could be beneficial for the penetration and accessibility of treating substrates. The research outcomes could serve as fundamental knowhows and offer potentials for effective bioenergy production and bioengineering of bioresources, and provide a reference for further application of fungal biotechnology.

Fagonia indica ameliorates chromium-induced nephrotoxicity: Role of antioxidant activity and pro-inflammatory cytokines in in-vivo renoprotection

Chromium (Cr) is an environmental pollutant, has high redox potential, and can exist in various oxidation states, possibly leading to nephrotoxicity. As a potential treatment option, Fagonia indica (F. indica) is an herb remedy traditionally used as a phytomedicine to cure ailments. However, efficient validation of its protective effect and molecular mechanisms has not yet been established. As such, this study aims to investigate the protective effect of F. indica against Cr-induced nephrotoxicity in Swiss mice. Mice were divided into five groups: group I (negative control), group II (F. indica), group III (potassium dichromate [PDC]-treated), group IV (PDC + saline), and group V (PDC + F. indica). Our results demonstrate that group III exhibited decreases in superoxide dismutase (SOD), glutathione s-transferases (GST), glutathione peroxidase (GSH-Px), catalase (CAT), and thioredoxin peroxidase (TPX) levels. Meanwhile, protein carbonyl (PCO) and malondialdehyde (MDA) levels increased in kidney homogenates, increasing the expression of the pro-inflammatory cytokine interleukin-6 (IL-6). This was followed by elevated NF-κB, blood urea nitrogen (BUN), and creatinine serum levels in group III compared with group I. Moreover, histopathological and immunohistochemical examinations demonstrated severe damage to the renal tubular epithelial cells, as well as marked congestion and expressions of caspase-3 and NF-κB. Further, group V showed an improvement in antioxidant activity parameters and reductions in the IL-6, caspase-3, and NF-κB expressions, followed by significant decreases in NF-κB, BUN, and creatinine serum levels. Furthermore, fewer histopathological disturbances were observed compared with untreated group III. Such alterations may be attributed to the antioxidant and anti-inflammatory effects of F. indica. Therefore, our exploration reveals that F. indica is effective in protecting against Cr-induced nephrotoxicity, and it could be applied in the future to human kidney diseases caused by environmental pollutants.

Effect of Ginkgo biloba leaves on the removal efficiency of Cr(VI) in soil and its underlying mechanism

Cr(VI) is a toxic, teratogenic, and carcinogenic heavy metal element in soil that poses major ecological and human health risks. In this study, microcosm tests combined with X-ray absorption near-edge spectra (XANES) and 16Sr DNA amplification techniques were used to explore the effect of Ginkgo biloba leaves on the removal efficiency of Cr(VI) in soil and its underlying mechanism. Ginkgo biloba leaves had a favorable remediation effect on soil varying in Cr(VI) contamination levels, and the optimal effect was observed when 5% Ginkgo biloba leaves were added. The occurrence state of Cr(VI) in soil before and after the addition of Ginkgo biloba leaves was analyzed by XANES, which revealed that Cr(VI) was fully converted to the more biologically innocuous Cr(III), and the hydroxyl-containing quercetin in Ginkgo biloba leaves was one of the primary components mediating this reduction reaction. The Cr(VI) content was significantly lower in non-sterilized soil than in sterilized soil, suggesting that soil microorganisms play a key role in the remediation process. The addition of Ginkgo biloba leaves decreased the α-diversity and altered the β-diversity of the soil bacterial community. Actinobacteria was the dominant phylum in the soil remediated by Ginkgo biloba leaves; four genera of Cr(VI)-reducing bacteria were also enriched, including Agrococcus, Klebsiella, Streptomyces, and Microbacterium. Functional gene abundances predicted by PICRUST indicated that the expression of glutathione synthesis genes was substantially up-regulated, which might be the main metabolic pathway underlying the mitigation of Cr(VI) toxicity in soil by Cr(VI)-reducing bacteria. In sum, Ginkgo biloba leaves can effectively remove soil Cr(VI) and reduce Cr(VI) to Cr(III) via quercetin in soil, which also functions as a carbon source to drive the production of glutathione via Cr(VI)-reducing bacteria and mitigate Cr(VI) toxicity. The findings of this study elucidate the chemical and microbial mechanisms of Cr(VI) removal in soil by Ginkgo biloba leaves and provide insights that could be used to enhance the remediation of Cr(VI)-contaminated soil.

Metallic nanoparticles for catalytic reduction of toxic hexavalent chromium from aqueous medium: A state-of-the-art review

The ever increasing concentration of toxic and carcinogenic hexavalent chromium (Cr (VI)) in various environmental mediums including water-bodies due to anthropogenic activities with rapid civilization and industrialization have become the major issue throughout the globe during last few decades. Therefore, developing new strategies for the treatment of Cr(VI) contaminated wastewaters are in great demand and have become a topical issue in academia and industry. To date, various techniques have been used for the remediation of Cr(VI) contaminated wastewaters including solvent extraction, adsorption, catalytic reduction, membrane filtration, biological treatment, coagulation, ion exchange and photo-catalytic reduction. Among these methods, the transformation of highly toxic Cr(VI) to benign Cr(III) catalyzed by metallic nanoparticles (M-NPs) with reductant has gained increasing attention in the past few years, and is considered to be an effective approach due to the superior catalytic performance of M-NPs. Thus, it is a timely topic to review this emerging technique for Cr(VI) reduction. Herein, recent development in synthesis of M-NPs based non-supported, supported, mono-, bi- and ternary M-NPs catalysts, their characterization and performance for the reduction of Cr(VI) to Cr(III) are reviewed. The role of supporting host to stabilize the M-NPs and leading to enhance the reduction of Cr(VI) are discussed. The Cr(VI) reduction mechanism, kinetics, and factors affecting the kinetics are overviewed to collect the wealthy kinetics data. Finally, the challenges and perspective in Cr(VI) reduction catalyzed by M-NPs are proposed. We believe that this review will assist the researchers who are working to develop novel M-NPs catalysts for the reduction of Cr(VI).

Simultaneous reduction and sequestration of hexavalent chromium by magnetic β-Cyclodextrin stabilized Fe3S4

In this study, β-Cyclodextrin (CD) modified Fe₃S₄ nanomaterials were synthesized by a one-step facile strategy and investigated for the removal of Cr(VI). The resulted CD-Fe₃S₄ exhibited enhanced removal efficiency toward Cr(VI) than bared Fe₃S₄ with a maximum capacity of 220.26 mg·g^-1 as the molar ratio of CD-to-Fe₃S₄ at 0.2. The effective performance of CD-Fe₃S₄ toward Cr(VI) could well maintain under oxic conditions and a wide pH range of aqueous solution. A high selectivity for Cr(VI) was achieved in the presence of coexisting cations and anions. More significantly, a single treatment step of CD-Fe₃S₄ effectively removed chromium from actual electroplating wastewater to the detection limit of 0.004 mg·L^-1 that far below the WHO limitation of Cr (VI) (<0.05 mg·L^-1) combing with the rapid magnetic separation without adjusting the pH value of wastewater at 7. The effective removal of Cr (VI) by CD-Fe₃S₄ involved a complex process of surface adsorption/reduction, and solution homogenous reduction and subsequent sequestration of Cr(III) achieving the effective removal of aqueous total Cr. The superior Cr (VI) removal capability and facial separation of CD-Fe₃S₄ attained its prominent potential application as an effective material for the Cr(VI) removal.

A Clean Method for Vanadium (V) Reduction with Oxalic Acid

Water pollution deteriorates ecosystems and is a great threat to the environment. The environmental benefits of wastewater treatment are extremely important to minimize pollutants. Here, the oxalic acid used as reductant was used to treat the wastewater which contained high concentration of vanadium (V). Nearly 100% of vanadium was efficiently reduced at selected reaction conditions. The optimization results simulated by response surface methodology (RSM) analysis indicated the parameters all had significant effects on the reduction process, and followed the order: dosage of oxalic acid > reaction temperature > reaction time > initial pH of vanadium-containing wastewater. The reduction behavior analysis indicated that the pseudo first-order kinetics model could describe well the reduction process with Ea = 42.14 kJ/mol, and was described by the equation as followed: −LnC=K0·[pH]0.1016·[n(O)/n(V)]2.4569·[T]2.2588·exp(−42.14/T)·t.

Influence of foliar glutathione and putrescine on metabolism and mineral status of genetically diverse rapeseed cultivars under hexavalent chromium stress

We studied the physio-biochemical involvement of exogenous signaling compounds, glutathione and putrescine (alone and in combination), on three contrasting genotypes (cvs. Shiralee, Rainbow, and Dunkled) of canola (Brassica napus L.) of plants exposed to chromium stress. Seeds were germinated in Cr-contaminated soil (0 and 50 μg/g Cr⁶⁺), and both signaling compounds were applied as a foliar spray to 20-day-old plants. Changes in root, stem, and leaf nitro-oxidative metabolism, endogenous GSH level, secondary metabolites, and mineral nutrients were investigated from 60-day-old plants. Exposure to Cr⁶⁺ increased stem GSH and NO concentrations in all cultivars. Maximum root Cr⁶⁺ bioaccumulation was recorded in cv. Rainbow and the least in cv. Shiralee. Also, Cr⁶⁺ stress decreased number and weight of seeds and pod length. Disturbances in root and shoot mineral profile were evident; however, its magnitude varied in all cultivars. The exogenous GSH improved root and shoot P, Fe, S, and Zn concentrations; however, the effect was cultivar specific. Leaf endogenous GSH was increased by exogenous GSH while NO levels remained unaffected. The GSH application also promoted shoot Cr⁶⁺ bioaccumulation while PUT application caused a recovery in seed number and seed weight. Both PUT and GSH differentially affected tissue-specific secondary metabolite profile. Overall, the exogenous GSH was much more effective in alleviating the Cr⁺⁶ toxicity in canola.

Mechanism and enhancement of Cr(VI) contaminated groundwater remediation by molasses

The remediation of Cr(VI)-contaminated groundwater with molasses has many advantages compared with traditional in-situ chemical methods, including high cost-effectiveness and negligible secondary contamination. Hence, the reaction conditions and mechanisms of molasses were investigated in this study. The results showed that Cr(VI) was chemically reduced by molasses at acidic pH (3.0), wherein the dominant active components were the hydroxyl and carbonyl groups of molasses. At neutral pH (7.0), molasses mainly acted as an electron donor for direct or indirect reduction of Cr(VI) by microorganisms. The main functional microorganisms were Bacillus and Clostridium Sensu Stricto. Compared with chemical reduction, bio-reduction could completely reduce higher concentrations of Cr(VI) when molasses was added at a concentration of 3 g/L. Ascorbic acid was added to promote the removal rate of bioremediation. Owing to the antioxidant properties of ascorbic acid, the reaction rate increased by 9.3% and 37.5% when 0.05 g/L of ascorbic acid was added to the 50 and 100 mg/L Cr(VI) bioremediation systems, respectively. Due to the decrease in pH during bioremediation, NaHCO₃ was added to buffer the pH changes and promote Cr(III) precipitation. Compared with the addition of NaHCO₃ and molasses simultaneously, separate additions were more effective for precipitation. Furthermore, X-ray absorption near-edge structure analysis revealed that after chemical reduction and biological reduction, Cr was attached to the solid medium in the form of Cr(III).

UV responsive quercetin derived and functionalized CuO/ZnO nanocomposite in ameliorating photocatalytic degradation of rhodamine B dye and enhanced biocidal activity against selected pathogenic strains

Quercetin was investigated for its role as a reducing agent in biosynthesizing CuO/ZnO nanocomposite, its subsequent surface functionalization and influence in Rhodamine B dye degradation and biocidal activity. The as synthesized quercetin functionalized CuO/ZnO nanocomposite (CuO/ZnO@Q) was analyzed using X-ray diffraction (XRD), Fourier transform infra red spectroscopy (FTIR), Transmission electron microscopy (TEM), Energy dispersive spectroscopy (EDS) and Ultraviolet-visible spectroscopy (UV-Vis). XRD showed the formation of crystalline CuO, ZnO phases and FTIR analysis revealed the incorporation of quercetin functional groups in the synthesized nanocomposite. TEM image displayed the formation of quercetin deposited spherical CuO/ZnO nanostructure with the EDAX results confirming the presence of organic carbon composition from quercetin. The UV absorption spectra ascertained the presence and role of quercetin in the enhanced absorption of radiation in the UV range. CuO/ZnO@Q showed improved photocatalysis with complete Rhodamine B dye degradation after 75 min of UV irradiation, as against pure CuO/ZnO, which exhibited incomplete dye degradation even after 90 min of irradiation. Moreover, quercetin surface functionalization effectively ameliorated its antimicrobial activity against E. coli, S. aureus, Shigella, B. subtilis, A. niger and C. albicans, proving its potential in significantly enhancing biocidal activity along with photocatalytic dye degradation in a natural and eco-friendly route.

Efficient Removal of Cr (VI) with Biochar and Optimized Parameters by Response Surface Methodology

A highly efficient reduction process of Cr (VI) with biochar was conducted in this paper. The results showed that nearly 100% Cr (VI) was reduced at selected reaction conditions: Dosage of biochar at m (C)/m(Cr) = 3.0, reaction temperature of 90 °C, reaction time of60 min, and concentration of H2SO4 of 20 g/L. The reduction kinetics analysis demonstrated that the reduction of Cr (VI) fitted well with the pseudo-first-order model and the apparent activation energy was calculated to be 40.24 kJ/mol. Response surface methodology confirmed that all of the experimental parameters had a positive effect on the reduction of Cr (VI). The influence of each parameter on the reduction process followed the order: Dosage of biochar>concentration of H2SO4>reaction temperature >reaction time. This paper provides a versatile strategy for the treatment of wastewater containing Cr (VI) and shows a bright tomorrow for wastewater treatment.

Chemical-Assisted Microbially Mediated Chromium (Cr) (VI) Reduction Under the Influence of Various Electron Donors, Redox Mediators, and Other Additives: An Outlook on Enhanced Cr(VI) Removal

Chromium (Cr) (VI) is a well-known toxin to all types of biological organisms. Over the past few decades, many investigators have employed numerous bioprocesses to neutralize the toxic effects of Cr(VI). One of the main process for its treatment is bioreduction into Cr(III). Key to this process is the ability of microbial enzymes, which facilitate the transfer of electrons into the high valence state of the metal that acts as an electron acceptor. Many underlying previous efforts have stressed on the use of different external organic and inorganic substances as electron donors to promote Cr(VI) reduction process by different microorganisms. The use of various redox mediators enabled electron transport facility for extracellular Cr(VI) reduction and accelerated the reaction. Also, many chemicals have employed diverse roles to improve the Cr(VI) reduction process in different microorganisms. The application of aforementioned materials at the contaminated systems has offered a variety of influence on Cr(VI) bioremediation by altering microbial community structures and functions and redox environment. The collective insights suggest that the knowledge of appropriate implementation of suitable nutrients can strongly inspire the Cr(VI) reduction rate and efficiency. However, a comprehensive information on such substances and their roles and biochemical pathways in different microorganisms remains elusive. In this regard, our review sheds light on the contributions of various chemicals as electron donors, redox mediators, cofactors, etc., on microbial Cr(VI) reduction for enhanced treatment practices.

Reduction behavior of chromium(VI) with oxalic acid in aqueous solution

The direct Cr(VI) reduction process by oxalic acid was conducted. The existence of Cr(VI) in the reaction medium was measured by software Visual MINTEQ and the concentration of Cr(VI) was measured by ICP-OES. The results showed that the Cr(VI) was efficiently reduced by oxalic acid at high reaction temperature and high dosage of oxalic acid. The reduced product, Cr(III), was easily generated stable complex compounds (Cr(HC2O4)3) with oxalate, which displayed a negative effect on the reduction process. The high reaction temperature and high acidic medium could destroy the stable structure of a complex compound to release oxalate, and facilitate the reduction of Cr(VI). Generally, the results showed in this paper provided a versatile strategy for Cr(VI) reduction and exhibited a bright application future for real wastewater treatment.

An overview of palladium supported on carbon-based materials: Synthesis, characterization, and its catalytic activity for reduction of hexavalent chromium

Palladium plays a pivotal role in most of the industrial heterogeneous catalysts, because of its unique properties such as well-defined structure, great intrinsic carrier, outstanding electronic, mechanical and thermal stability. The combination of palladium and various porous carbons (PCs) can widen the use of heterogeneous catalysts. This review highlights the advantages and limitations of carbon supported palladium-based heterogeneous catalyst in reduction of toxic hexavalent chromium (Cr^(VI)). In addition, we address recent progress on synthesis routes for mono and bimetallic palladium nanoparticles supported by various carbon composites including graphene-based materials, carbon nanotubes, mesoporous carbons, and activated carbons. The related reaction mechanisms for the Cr^(VI) reduction are also suggested. Finally, the challenge and perspective are proposed.

Novel quercetin and apigenin-acetamide derivatives: design, synthesis, characterization, biological evaluation and molecular docking studies

Flavonoids exhibit essential but limited biological properties which can be enhanced through chemical modifications. In this study, we designed, synthesized, and characterized two novel flavonoid derivatives, quercetin penta-acetamide (1S3) and apigenin tri-acetamide (2S3). These compounds were confirmed using (1H, 13C) NMR, UV-Vis, and FT-IR characterizations. Their interaction with fish sperm DNA (FS-DNA) at physiological pH was investigated by UV-Vis and fluorescence spectrophotometry. The binding constant (K b) for the UV-Vis experiment was found to be 1.43 ± 0.3 × 104 M-1 for 1S3 and 2.08 ± 0.2 × 104 M-1 for 2S3. The binding constants (K SV) for the fluorescence quenching experiment were 1.83 × 104 M-1 and 1.96 × 104 M-1 for 1S3 and 2S3, respectively. Based on molecular modeling and docking studies, the binding affinities were found to be -7.9 and -9.1 kcal mol-1, for 1S3 and 2S3, respectively. The compound-DNA docked model correlated with our experimental results, and they are groove binders. Furthermore, mutagenicity potential was examined. 1S3 and its metabolites showed no mutagenic activity for both TA98 and TA100 strains. 2S3 did not show any mutagenic activity for the strain TA 98, while its metabolites were only active at high doses. Both 2S3 and its metabolites showed mutagenic activity in the TA100 strain.

Efficient Photoreduction of Hexavalent Chromium Using the Reduced Graphene Oxide-Sm2MoO6-TiO2 Catalyst under Visible Light Illumination

In past years, the presence of toxic heavy metal ions in water and soil has caused major health problems. The ternary type semiconductor material, reduced graphene oxide (rGO)-Sm₂MoO₆-TiO₂, has been investigated as a photocatalyst for the reduction of soluble chromium(VI) into (III) for the first time. The as-synthesized rGO-Sm₂MoO₆-TiO₂ catalyst was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, X-ray photoelectron spectroscopy, FT-Raman, Fourier transform infrared, and optical spectroscopy. The maximum Cr(VI) reduction of 96% was achieved within 70 min under visible light illumination. The powder XRD analysis confirmed the formation of anatase TiO₂. Field-emission SEM images depicted well-dispersed rGO sheets, and TiO₂ and Sm₂MoO₆ particles are randomly distributed onto rGO. The reduction of Cr(VI) by rGO-Sm₂MoO₆-TiO₂ was considerably greater than the reduction by Sm₂MoO₆, TiO₂, Sm₂MoO₆-rGO, TiO₂-rGO, and Sm₂MoO₆-TiO₂. Sm₂MoO₆ acts as an effective cocatalyst to TiO₂ to enhance the separation of photo-generated electron-holes. Even after six consecutive cycles, the photoreduction of Cr(VI) was more than 85%, which reveals that the excellent reusability performance of the catalyst for practical applications. The photogenerated electron plays an important role in the reduction of Cr(VI) into nontoxic Cr(III), and the synergistic effect of rGO greatly improved the separation of h⁺ and e^- pairs.

Enhanced removal of Cr(VI) in the Fe(III)/natural polyphenols system: role of the in situ generated Fe(II)

This study developed a cost-effective and eco-friendly method by coupling plant extracts (take green tea for example) and Fe(III) to reduce Cr(VI) and precipitate Cr(III). At acidic pH, 1.43 mM Fe(III) combined with 1.33 g/L green tea extracts could reduce 93% of Cr(VI) in 180 min, which was much larger than ˜50% by green tea extracts alone. Moreover, 52% of Cr(III) could automatically precipitate out as mixed Fe(III)-Cr(III) (oxy)-hydroxide solids. In the viewpoint of mechanism, polyphenols in green tea extracts were the reactive constituents and transformed Fe(III) to Fe(II), by which step the aqueous Fe(II) level was maintained to continuously reduce Cr(VI) to Cr(III), and thus accelerating Cr(VI) reduction. The generated Fe(III) partially participated in the reaction with polyphenols again and some Fe(III) formed precipitates with Cr(III). Overall, the electron transfers in the polyphenol-Fe-Cr cyclic reactions made Fe(III) used for multiple times, thus accelerated Cr(VI) reduction. The applicability of the combined process was further verified by removing 100% and 70% of Cr(VI) from electroplating wastewater and contaminated soil, respectively. As polyphenols can be derived from plant wastes and Fe(III) is naturally abundant, this study provides a promising method for in situ remediation of Cr(VI)-contaminated sites.

Antimicrobial Activity of a New Class of Phosphorylated and Modified Flavonoids

The surge of resistant food pathogens is a major threat worldwide. Previous research conducted on phytochemicals has shown their antibacterial activity against pathogenic bacteria. The design of antimicrobial agents to curb pathogenic disease remains a challenge demanding critical attention. Flavonoids such as apigenin and quercetin were evaluated against Gram-positive and Gram-negative bacteria. The results indicated that the antibacterial activity of each flavonoid occurred at a different minimum inhibitory concentration. However, the antimicrobial activity results of the modified flavonoids were also reported, and it was observed that the Gram-positive bacteria were more susceptible in comparison to the Gram-negative bacteria. The cell wall structure of the Gram-positive and Gram-negative bacteria could be the main reason for the bacteria susceptibility. Modified flavonoids could be used as a suitable alternative antimicrobial agent for the treatment of infectious diseases. Our results indicated 100% inhibition of Listeria monocytogenes, Pseudomonas aeruginosa, and Aeromonas hydrophila with modified flavonoids.

Electrochemical Removal of Chromium (VI) from Wastewater

The removal of hexavalent chromium has attracted much attention as it is a hazardous contaminant. Electrochemical reduction technology was applied to remove chromium (VI) from wastewater. The mechanisms and parameters that affect the reduction process were investigated. The results showed that the reduction efficiency was significantly affected by the concentration of H2SO4, current density, and reaction temperature. The reduction efficiency was up to 86.45% at an H2SO4 concentration of 100 g/L, reaction temperature of 70 °C, current density at 50 A/m2, reaction time at 180 min, and stirring rate of 500 rpm. The reduction process of chromium (VI) followed a pseudo-first-order equation, and the reduction rate constant could be expressed as Kobs = k [H2SO4]1·[j]4·exp−4170/RT.

Adsorption and Reduction of Cr(VI) Together with Cr(III) Sequestration by Polyaniline Confined in Pores of Polystyrene Beads

The simultaneous reduction and sequestration of Cr(VI) from wastewater is desirable as a cost-effective and environmentally friendly approach. In this study, we execute a one-step facile synthesis strategy on polyaniline (PANI) composites based on aniline adsorption and polymerization on pores of millimeter-scale polystyrene balls (PANI@PS). The well-defined PANI@PS increased the removal capacity of Cr(VI) by 5.4 times, going from 43.6 (bulky PANI) to 233.7 mg g^-1 near neutral pH (6.0) instead of the pH 1-3 documented in other reports, which was higher than that of many reported adsorbents due to its porous structure, numerous interaction sites, and confinement effects in the polymer. Most importantly, PANI@PS could efficiently sequester positive Cr(III) after reducing Cr(VI) to Cr(III) due to its negative surface created by confinement effects confined to the nanopores of PS. Conversely, positively charged bulky PANI repelled electrostatically positive Cr(III); thus, additional precipitation or adsorption treatments were needed in practical applications. Moreover, a coating of PANI can protect PS, as a substrate and a composite, from irreversible damage due to the strong oxidation capacity of Cr(VI), which is another major concern in adsorbing strong oxidants using polymers. A novel strategy to regenerate the exhausted PANI@PS was efficiently executed based on the electrochemical redox reversibility of PANI. Finally, the comprehensive adsorption/reduction/sequestration of Cr on PANI@PS was elucidated in detail.

Plant extract as environmental-friendly green catalyst for the reduction of hexavalent chromium in tannery effluent

The aqueous extract of various plants like Coriandrum sativum (AECS), Alternanthera tenella colla (AEAT), Spermacoce hispida (AESH) and Mollugo verticillata (AEMV) was studied for its hexavalent chromium (Cr^VI) reduction property. Even though antioxidant activity was present, AEAT, AESH and AEMV did not reduce Cr^VI. AECS showed rapid and dose-dependent Cr^VI reduction. The efficient reduction of 50 mg/L of Cr^VI using AECS was attained in the presence of 250 µg/mL of starting plant material, incubating the reaction mixture at pH 2, 30°C and agitation at 190 rpm. Under such conditions, about 40 mg/L of Cr^VI was reduced at 3 h of incubation. FT-IR analysis revealed the involvement of phenols, alcohols, alpha-hydroxy acid and flavonoids present in the AECS for the Cr^VI reduction. These results indicate that not all the plant extracts with rich antioxidants are capable of reducing Cr^VI. Using the conditions standardized in the present study, AECS reduced about 80% of Cr^VI present in the tannery effluent. These results signify the application of AECS as an eco-friendly method in the wastewater treatment.

Flavonoid-derived anisotropic silver nanoparticles inhibit growth and change the expression of virulence genes in Escherichia coli SM10

We hereby present a novel greener and ecofriendly synthesis of anisotropic silver nanoparticles (AgNPs) using water soluble quercetin diphosphate (QDP). QDP was employed as a reducing, capping and stabilizing agent at room temperature without any extraneous reagents. The purpose of this study was to determine the effects of modified quercetin pentaphosphate silver nanoparticles (QPP-AgNPs) and quercetin diphosphate derived silver nanoparticles (QDP-AgNPs) on microbial growth and expressions of virulence-related genes in Escherichia coli SM10. The gene expression analysis was carried out for 12 genes which are related to virulence and stress in E. coli SM10, namely: RpoD, RpoS, ibpB, clpB, uspA, fliC, fimH, fimF, kdpE, artJ, hyaA, and gyrA. Results showed that QDP-AgNPs reduced the swarming motility by 98% which correlated with the reduction in the expression of FliC flagellar gene. A simultaneous increase in the expression of the fimbrial genes FimH and FimF that are related to motility was recorded. In contrast, treatment of the microbes with QPP-AgNPs resulted in 90% of the swarming motility at different patterns compared to QDP-AgNPs treatment for the gene expressions of motility elements. The study revealed that QDP-AgNPs up-regulated the stress related RpoD and ibpB expressions, while QPP-AgNPs up-regulated the stress related RpoS and uspA gene expressions. However, both QDP-AgNPs and QPP-AgNPs up-regulated kpdE, artJ and gry at different levels. QDP-AgNPs were also tested for their antibacterial and antifungal activities, which showed μmolar cidal activity. The growth kinetics of both Gram (−) and Gram (+) bacteria were strongly altered by QDP-AgNPs activity. Energy dispersive absorption spectroscopy (EDS) studies revealed that silver ions and/or the nanoparticles themselves transferred into bacterial cells. To the best of our knowledge, this is the first report of studying the genetic and kinetic response of bacteria to modified quercetin phosphate mediated silver nanoparticles and we hereby report that the molecules used to synthesize AgNPs bring about a strong effect on AgNPs manipulatory activity on the tested 12-genes.

We hereby present a novel greener and ecofriendly synthesis of anisotropic silver nanoparticles (AgNPs) using water soluble quercetin diphosphate (QDP). QDP was employed as a reducing, capping and stabilizing agent at room temperature without any extraneous reagents.

Synthesis and antibacterial characterization of sustainable nanosilver using naturally-derived macromolecules

Greener nanosynthesis utilizes fewer amounts of materials, water, and energy; while reducing or replacing the need for organic solvents. A novel approach is presented using naturally-derived flavonoids including Quercetin pentaphosphate (QPP), Quercetin sulfonic acid (QSA) and Apigenin Triphosphate (ATRP). These water soluble, phosphorylated flavonoids were utilized both as reducing agent and stabilizer. The synthesis was achieved at room temperature using water as a solvent and it requires no capping agents. The efficiency of the resulting silver nanoparticle synthesis was compared with naturally-occurring flavonoid such as Quercetin (QCR). Results show that QCR reduced Ag(+) faster followed by QPP, QSA and ATRP respectively. This is the first evidence of direct utilization of QCR for synthesis of silver nanoparticles (AgNPs) in water. The percentage conversion of Ag(+) to Ag(0) was determined to be 96% after 35min. The synthesized nanoparticles were characterized using Transmission electron microscopy (TEM), Energy dispersive absorption spectroscopy (EDS), UV-vis spectroscopy, High resolution TEM (HR-TEM) with selected area electron diffraction (SAED). The particle sizes ranged from 2 to 80nm with an average size of 22nm and in the case of ATRP, the nanoparticle shapes varied from spherical to hexagonal with dispersed particle size ranging from 2 to 30nm. Crystallinity was confirmed by XRD and the SAED of (111), (200), and the fringes observed in HRTEM images. Results were in agreement with the UV resonance peaks of 369-440nm. The particles also exhibit excellent antibacterial activity against Staphylococcus epidermidis, Escherichia coli and Citrobacter freundii in water.

Reactivity, characterization of reaction products and immobilization of lead in water and sediments using quercetin pentaphosphate

Lead is currently ranked the number one heavy metal pollutant with a maximum contaminant level (MCL) of 0.015 mg L(-1). The use of organic solvent-free methods to immobilize lead from the environment is attracting the attention of scientists and environmental engineers. This study reports the application of water soluble quercetin pentaphosphate (QPP), a derivative of quercetin, for the detection and immobilization of Pb(2+) from water and soil samples. The techniques employed include UV-visible, fluorescence, atomic absorption; inductively coupled plasma optical emission and Fourier transform infrared (FTIR) techniques. Results indicated the formation of a QPP-Pb complex that inhibits the fluorescence intensity of the parent molecule. The fluorimetric limit of detection was found to be 3.46 × 10(-4) M. The QPP-Pb complex exhibited a corresponding stoichiometry with the predominant complex PX2. A Scatchard plot of y = -4 × 10(6)x + 2916.3 was observed with a negative slope giving an equilibrium constant of 4 × 10(6) M(-1) and 5.4 × 10(5) M(-1) in acidic and alkaline conditions respectively. Results show 90.4% and 91.5% lead(ii) immobilization from BRS and BU soil samples respectively. On the other hand, 91% lead immobilization efficiency from a water sample was achieved at room temperature and is in compliance with the MCL level of 15 ppm at ∼3.82% error margin. This approach does not require the use of organic solvents or the disposal of large amounts of sludge. Once complexed with lead, QPP may not release phosphate to cause any secondary pollution.

Greener synthesis and characterization, antimicrobial and cytotoxicity studies of gold nanoparticles of novel shapes and sizes

We hereby present a novel approach for the synthesis of gold nanoparticles (AuNPs) using water soluble, naturally-derived flavonoids.

Reduction of hexavalent chromium using epigallocatechin gallate in aqueous solutions: kinetics and mechanism

Green tea polyphenol EGCG was utilized as nontoxic reductant for hexavalent chromium reduction in aqueous solution.

Dipyrrin complex assisted in situ synthesis of ultra-small gold nanoparticles decorated on a partially reduced graphene oxide nanocomposite for efficient catalytic reduction of Cr(vi) to Cr(iii)

Applicability of a novel heteroleptic dipyrrin complex exhibiting dual functionality (reducing and capping agent) in rapid synthesis of small sized AuNPs has been described.

Mechanistic insight into chromium(VI) reduction by oxalic acid in the presence of manganese(II)

Over the past few decades, reduction of hexavalent chromium (Cr(VI)) has been studied in many physicochemical contexts. In this research, we reveal the mechanism underlying the favorable effect of Mn(II) observed during Cr(VI) reduction by oxalic acid using liquid chromatography with spectrophotometric diode array detector (HPLC-DAD), nitrogen microwave plasma atomic emission spectrometry (HPLC-MP-AES), and high resolution mass spectrometry (ESI-QTOFMS). Both reaction mixtures contained potassium dichromate (0.67 mM Cr(VI)) and oxalic acid (13.3mM), pH 3, one reaction mixture contained manganese sulfate (0.33 mM Mn(II)). In the absence of Mn(II) only trace amounts of reaction intermediates were generated, most likely in the following pathways: (1) Cr(VI)→ Cr(IV) and (2) Cr(VI)+Cr(IV)→ 2Cr(V). In the presence of Mn(II), the active reducing species appeared to be Mn(II) bis-oxalato complex (J); the proposed reaction mechanism involves a one-electron transfer from J to any chromium compound containing CrO bond, which is reduced to CrOH, and the generation of Mn(III) bis-oxalato complex (K). Conversion of K to J was observed, confirming the catalytic role of Mn(II). Since no additional acidification was required, the results obtained in this study may be helpful in designing a new, environmentally friendly strategy for the remediation of environments contaminated with Cr(VI).

Microfluidic Flow through Polyaniline Supported by Lamellar-Structured Graphene for Mass-Transfer-Enhanced Electrocatalytic Reduction of Hexavalent Chromium

Owing to its high efficiency and environmental compatibility, electroreduction holds great promise for the detoxification of aqueous Cr(VI). However, the typical electroreduction system often shows poor mass transfer, which results in slow reduction kinetics and hence higher energy consumption. Here, we demonstrate a flow-through electrode of polyaniline supported on lamellar-structured graphene (LGS-PANI) for electrocatalytic reduction of Cr(VI). The reaction kinetics of the LGS-PANI flow-through electrodes are 6.4 times (at acidic condition) and 17.3 times (at neutral condition) faster than traditional immersed parallel-plate electrodes. Computational fluid dynamics simulation suggests that the flow-through mode greatly enhances the mass transfer and that the nanoscale convection induced by the PANI nanodots increases the nanoscale mass transport in the interfacial region of the electrode/solution. In situ Raman spectroscopy shows that the PANI-Cr(VI) redox reactions are dominated by the leucoemeraldine/emeraldine transition at 1.5 V cell voltage, which also remarkably contributes to the fast reaction kinetics. Using single-pass flow-through mode, the LGS-PANI electrode reaches an average reduction efficiency of 99.8% with residual Cr(VI) concentration of 22.3 ppb (initial [Cr(VI)] = 10 ppm, flux = 20 L h(-1) m(-2)). A long-term stability test shows that the LGS-PANI maintains stable performance over 40 days of operation and achieves >98% reduction efficiency, with average current efficiency of as high as 99.1% (initial [Cr(VI)] = 10 ppm, flux = 50 L h(-1) m(-2)).

A new substrate for alkaline phosphatase based on quercetin pentaphosphate

We describe the characterization and application of quercetin pentaphosphate (QPP), a new fluorimetric substrate for the detection of alkaline phosphatase (ALP) activity. QPP exhibits major absorbance peaks at 260/410 nm and a strong fluorescence at λex/λem = 425/510 nm at alkaline pH. The product of enzymatic reaction between QPP and ALP has a strong absorbance peak at 324 nm with no fluorescence at the investigated wavelengths. The product generated from the enzymatic reaction was found to be proportional to ALP activity, and the ALP activity was monitored by the absorbance difference at 310 nm and 410 nm. The change in absorbance was found to be proportional to the ALP concentration with a linear detection range and a limit of detection of 0.01-16 U L(-1) and 0.766 U L(-1), respectively. The enzyme activity was also monitored by evaluating the change in fluorescence emission at 530 nm with a linear range of 0.01-8 U L(-1) and a detection limit of 0.062 U L(-1). Further, the validity of the new substrate for ALP in conjugated form was tested using Bacillus globigii spores as the model sample. A detection limit of 5998 spores per mL was obtained using QPP as the substrate. Unlike the parent compound, QPP substrate exhibits stability in solution for over three and half months and was stable under storage for over 12 months. The results obtained demonstrate the effectiveness of QPP for ALP and compare well with other fluorescent substrates, such as Fluorescein, Alexa Fluor and Cy5.

Novel reduction of Cr(VI) from wastewater using a naturally derived microcapsule loaded with rutin-Cr(III) complex

The harmfulness of carcinogenic hexavalent chromium (Cr(VI)) is dramatically decreased when Cr(VI) is reduced to trivalent chromium (Cr(III)). Rutin, a natural flavonoid, exhibits excellent antioxidant activity by coordinating metal ions. In this study, a complex containing rutin and Cr(III) (rutin-Cr(III)) was synthesized and characterized. The rutin-Cr(III) complex was much easier to reduce than rutin. The reduction of the rutin-Cr(III) complex was highly pH-dependent, with 90% of the Cr(VI) being reduced to Cr(III) in 2h under optimal conditions. A biodegradable, sustained-release system encapsulating the rutin-Cr(III) complex in a alginate-chitosan microcapsule (rutin-Cr(III) ACMS) was also evaluated, and the reduction of Cr(VI) was assessed. This study also demonstrated that low-pH solutions increased the reduction rate of Cr(VI). The environmentally friendly microcapsules can reduce Cr(VI) for prolonged periods of time and can easily biodegrade after releasing the rutin-Cr(III) complex. Given the excellent performance of rutin-Cr(III) ACMS, the microcapsule system represents an effective system for the remediation of Cr(VI) pollution.

Properties and applications of flavonoid metal complexes

Flavonoid metal complexes have a wide spectrum of activities as well as potential and actual applications.

Characteristics and kinetics of hexavalent chromium reduction by gallic acid in aqueous solutions

Gallic acid (GA) is a naturally occurring plant polyphenol compound. Experiments were conducted to study the kinetics and effects of pH, temperature, irradiation, and initial hexavalent chromium (Cr(VI)) concentration on Cr(VI) reduction by GA. Results indicated that Cr(VI) could be reduced to chromium oxide (Cr(III)) with GA in a wide range of pH values from 2.0 to 8.5. The reaction followed a pseudo-first-order kinetic model with respect to Cr(VI) and GA in acid conditions (pH 2.0-5.0). However, the reaction did not follow the pseudo-first-order kinetic model at pH 6.5 and 8.5. Removal efficiencies and reaction rate constants of Cr(VI) significantly increased with decreasing pH value and increasing temperature. The effect of irradiation on Cr(VI) reduction increased with increasing pH, and irradiation improved the removal efficiency of Cr(VI) by 11.29% at pH 6.5. At pH 2.0, nearly all molar ratios of GA required for the reduction of Cr(VI) were 1:2 (±0.1) under different initial Cr(VI) concentrations; however, the molar ratios of GA required for the reduction of Cr(VI) were 1:1.29, 1:1.43, and 1:1.69, respectively, when the initial Cr(VI) concentrations were 10, 25, and 50 mg/L at pH 5.5.

Punica granatum L. protects mice against hexavalent chromium-induced genotoxicity

This study investigated the chemoprotective effects of Punica granatum L. (Punicaceae) fruits alcoholic extract (PGE) on mice exposed to hexavalent chromium [Cr(VI)]. Animals were pretreated with PGE (25, 50 or 75 mg/kg/day) for 10 days and subsequently exposed to a sub-lethal dose of Cr(VI) (30 mg/kg). The frequency of micronucleated polychromatic erythrocytes in the bone marrow was investigated and the Cr(VI) levels were measured in the kidneys, liver and plasm. For the survival analysis, mice were previously treated with PGE for 10 days and exposed to a single lethal dose of Cr(VI) (50 mg/kg). Exposure to a sub-lethal dose of Cr(VI) induced a significant increase in the frequency of micronucleated cells. However, the prophylactic treatment with PGE led to a reduction of 44.5% (25 mg/kg), 86.3% (50 mg/kg) and 64.2% (75 mg/kg) in the incidence of micronuclei. In addition, the 50 mg/kg dose of PGE produced a higher chemoprotective effect, since the survival rate was 90%, when compared to that of the non-treated group. In these animals, reduced amounts of chromium were detected in the biological materials, in comparison with the other groups. Taken together, the results demonstrated that PGE exerts a protective effect against Cr(VI)-induced genotoxicity.