Rhizopus oryzae-Mediated Green Synthesis of Magnesium Oxide Nanoparticles (MgO-NPs): A Promising Tool for Antimicrobial, Mosquitocidal Action, and Tanning Effluent Treatment

The metabolites of the fungal strain Rhizopus oryaze were used as a biocatalyst for the green-synthesis of magnesium oxide nanoparticles (MgO-NPs). The production methodology was optimized to attain the maximum productivity as follows: 4 mM of precursor, at pH 8, incubation temperature of 35 °C, and reaction time of 36 h between metabolites and precursor. The as-formed MgO-NPs were characterized by UV-Vis spectroscopy, TEM, SEM-EDX, XRD, DLS, FT-IR, and XPS analyses. These analytical techniques proved to gain crystalline, homogenous, and well-dispersed spherical MgO-NPs with an average size of 20.38 ± 9.9 nm. The potentiality of MgO-NPs was dose- and time-dependent. The biogenic MgO-NPs was found to be a promising antimicrobial agent against the pathogens including Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans with inhibition zones of 10.6 ± 0.4, 11.5 ± 0.5, 13.7 ± 0.5, 14.3 ± 0.7, and 14.7 ± 0.6 mm, respectively, at 200 μg mL-1. Moreover, MgO-NPs manifested larvicidal and adult repellence activity against Culex pipiens at very low concentrations. The highest decolorization percentages of tanning effluents were 95.6 ± 1.6% at 100 µg/ 100 mL after 180 min. At this condition, the physicochemical parameters of tannery effluents, including TSS, TDS, BOD, COD, and conductivity were reduced with percentages of 97.9%, 98.2%, 87.8%, 95.9%, and 97.3%, respectively. Moreover, the chromium ion was adsorbed with percentages of 98.2% at optimum experimental conditions.

Microwave-Assisted Rapid Synthesis of Reduced Graphene Oxide-Based Gum Tragacanth Hydrogel Nanocomposite for Heavy Metal Ions Adsorption

Reduced graphene oxide (RGO) was synthesized in this research via Tour's method for the use of filler in the hydrogel matrix. The copolymerization of N,N-dimethylacrylamide (DMA) onto the gum tragacanth (GT) was carried out to develop gum tragacanth-cl-N,N-dimethylacrylamide (GT-cl-poly(DMA)) hydrogel using N,N'-methylenebisacrylamide (NMBA) and potassium persulfate (KPS) as cross-linker and initiator correspondingly. The various GT-cl-poly(DMA) hydrogel synthesis parameters were optimized to achieve maximum swelling of GT-cl-poly(DMA) hydrogel. The optimized GT-cl-poly(DMA) hydrogel was then filled with RGO to form reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide (GT-cl-poly(DMA)/RGO) hydrogel composite. The synthesized samples were used for competent adsorption of Hg²⁺ and Cr⁶⁺ ions. Fourier transform infrared, X-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy were used to characterize the gum tragacanth-cl-N,N-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide hydrogel composite. The experiments of adsorption-desorption cycles for Hg²⁺ and Cr⁶⁺ ions were carried out to perform the reusability of gum tragacanth-cl-N,N-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide hydrogel composite. From these two samples, reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide exhibited high adsorption ability. The Hg²⁺ and Cr⁶⁺ ions adsorption by gum tragacanth-cl-N,N-dimethylacrylamide and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide were best suited for pseudo-second-order kinetics and Langmuir isotherm. The reported maximum Hg²⁺ and Cr⁶⁺ ions adsorption capacities were 666.6 mg g^-1 and 473.9 mg g^-1 respectively.

Effect of a dentifrice containing different particle sizes of hydroxyapatite on dentin tubule occlusion and aqueous Cr (VI) sorption

Background

Dentin hypersensitivity is a common negative oral condition that can be treated with dentifrice containing hydroxyapatite (HA). The study evaluated the effect of nano-HA dentifrice on plugging the dentinal tubules for an anti-sensitivity reaction compared to a dentifrice containing common-sized particles. Also, the adsorption capacity of different particle sizes of HA mixed in a dentifrice and which is the optimal particle size was considered.

Methods

Fourty premolar dentine discs and fourty molar dentine discs were randomly divided into 4 groups: distilled water group, ordinary dentifrice group and 80, 300 nm HA dentifrice group. Each dentin disc was brushed with a dentifrice twice daily at 7600 rpm under 100 g force for 2 mins for 7 consecutive days and divided into two parts, half of the dentin disc was detected by the scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), the other half was brushed with distilled water and observed by SEM. One milliliter dentifrice solution (80 nm HA dentifrice, 300 nm HA dentifrice, ordinary dentifrice) was added to 50 ml potassium dichromate solution for 1, 14, and 28 d. The residual Chromium (Cr⁶⁺) concentration in the supernatant was measured by the diphenylcarbon phthalocyanine hydrazine method. The elemental constitution in the precipitate was detected by EDS. The Kruskal-Wallis test was used to analyze surface mineralization and different plugging rates of dentinal tubules. The absorption capacity of dentifrices were also evaluated by the Kruskal-Wallis test.

Results

The plugging rate in the HA dentifrice group was higher than that in the ordinary dentifrice group, and the 80 nm HA dentifrice group showed the best result. The atomic percentages of Ca and P of 80 nm dentifrice group on the surface of dentinal tubules were the highest. The 80 nm HA dentifrice group showed the best adsorption and stable effect of Cr⁶⁺, followed by the 300 nm HA dentifrice group. The 300 nm HA dentifrice and the ordinary dentifrice showed desorption phenomenon.

Conclusions

The dentifrice containing HA, especially the 80 nm HA dentifrice, exerts good dentinal tubule occlusion and surface mineralization effect. This dentifrice was also a good adsorbent of Cr⁶⁺.

Preparation and Characterization of Novel Polyvinylidene Fluoride/2-Aminobenzothiazole Modified Ultrafiltration Membrane for the Removal of Cr(VI) in Wastewater

Hexavalent chromium is one of the main heavy metal pollutants. As the environmental legislation becomes increasingly strict, seeking new technology to treat wastewater containing hexavalent chromium is becoming more and more important. In this research, a novel modified ultrafiltration membrane that could be applied to adsorb and purify water containing hexavalent chromium, was prepared by polyvinylidene fluoride (PVDF) blending with 2-aminobenzothiazole via phase inversion. The membrane performance was characterized by evaluation of the instrument of membrane performance, infrared spectroscopy (FTIR), scanning electron microscope (SEM), and water contact angle measurements. The results showed that the pure water flux of the PVDF/2-aminobenzothiazole modified ultrafiltration membrane was 231.27 L/m²·h, the contact angle was 76.1°, and the adsorption capacity of chromium ion was 157.75 µg/cm². The PVDF/2-aminobenzothiazole modified ultrafiltration membrane presented better adsorption abilities for chromium ion than that of the traditional PVDF membrane.

Regulatory role of B-cell maturation antigen on the toxic effect of chromium ions on human SaOS-2 osteoblasts

Metal prostheses of artificial joints undergo wear, producing numerous metal particles and ions, such as Cr³⁺ . Cr³⁺ is considered a key factor leading to aseptic loosening. Many studies focus on the effect of Cr³⁺ on osteoblasts; however, little is known about the effect of Cr³⁺ on the B-cell maturation antigen (BCMA) in the osteoblasts. In this study, we first demonstrated the BCMA expressed in human SaOS-2 osteoblasts through reverse transcriptase-PCR, Western blot, and immunocytochemical analyses. Cr³⁺ decreased alkaline phosphatase (ALP), osteocalcin (OC), cell mineralization, and collagen type I mRNA and protein expression. Moreover, Cr³⁺ has an inhibitive effect on the expression of the BCMA in human SaOS-2 osteoblasts. However, after we upregulated the expression of the BCMA, ALP, OC, cell mineralization, and collagen type I mRNA and protein expression were increased. Overall, this study demonstrates that the BCMA is involved in human SaOS-2 osteoblast osteogenetic metabolism and plays a regulatory role on the toxic effect of chromium ions on human SaOS-2 osteoblasts.

Chromium reduces the in vitro activity and fidelity of DNA replication mediated by the human cell DNA synthesome

Hexavalent chromium Cr(VI) is known to be a carcinogenic metal ion, with a complicated mechanism of action. It can be found within our environment in soil and water contaminated by manufacturing processes. Cr(VI) ion is readily taken up by cells, and is recognized to be both genotoxic and cytotoxic; following its reduction to the stable trivalent form of the ion, chromium(Cr(III)), within cells. This form of the ion is known to impede the activity of cellular DNA polymerase and polymerase-mediated DNA replication. Here, we report the effects of chromium on the activity and fidelity of the DNA replication process mediated by the human cell DNA synthesome. The DNA synthesome is a functional multiprotein complex that is fully competent to carry-out each phase of the DNA replication process. The IC(50) of Cr(III) toward the activity of DNA synthesome-associated DNA polymerases alpha, delta and epsilon is 15, 45 and 125 muM, respectively. Cr(III) inhibits synthesome-mediated DNA synthesis (IC(50)=88 muM), and significantly reduces the fidelity of synthesome-mediated DNA replication. The mutation frequency induced by the different concentrations of Cr(III) ion used in our assays ranges from 2-13 fold higher than that which occurs spontaneously, and the types of mutations include single nucleotide substitutions, insertions, and deletions. Single nucleotide substitutions are the predominant type of mutation, and they occur primarily at GC base-pairs. Cr(III) ion produces a lower number of transition and a higher number of transversion mutations than occur spontaneously. Unlike Cr(III), Cr(VI) ion has little effect on the in vitro DNA synthetic activity and fidelity of the DNA synthesome, but does significantly inhibit DNA synthesis in intact cells. Cell growth and proliferation is also arrested by increasing concentrations of Cr(VI) ion. Our studies provide evidence indicating that the chromium ion induced decrease in the fidelity and activity of synthesome mediated DNA replication correlates with the genotoxic and cytotoxic effects of this metal ion; and promotes cell killing via inhibition of the DNA polymerase activity mediating the DNA replication and repair processes utilized by human cells.