Chitin Deacetylase from Bacillus aryabhattai TCI-16: Heterologous Expression, Characterization, and Deacetylation Performance

Chitin deacetylase (CDA) removes the acetyl group from the chitin molecule to generate chitosan in a uniform, high-quality deacetylation pattern. Herein, BaCDA was a novel CDA discovered from our previously isolated Bacillus aryabhattai strain TCI-16, which was excavated from mangrove soil. The gene BaCDA was cloned and overexpressed in Escherichia coli BL21 (DE3) to facilitate its subsequent purification. The purified recombinant protein BaCDA was obtained at a concentration of about 1.2 mg/mL after Ni2+ affinity chromatography. The molecular weight of BaCDA was around 28 kDa according to the sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) analysis. In addition, BaCDA exhibited a significant deacetylation effect on colloidal chitin, and the deacetylation degree was measured from the initial 25.69 to 69.23% by Fourier transform infrared (FT-IR) spectroscopy. Scanning electron microscopy (SEM) observation showed that the surface of colloidal chitin after enzymatic digestion was rough, the crystal fibers disappeared, and the chitin structure was loose and porous with grooves. The results of electrospray ionization mass spectrometry (ESI-MS) showed that BaCDA had full-deacetylation activity against (GlcNAc)4. Molecular docking revealed that BaCDA had an open active pocket capable of binding to the GlcNAc unit. This study not only provides a novel enzymatic resource for the green and efficient application of chitin but also helps to deepen the understanding of the catalytic mechanism of CDA

Synergetic Transformations of Multiple Pollutants Driven by Cr(VI)–Sulfite Reactions

Reduction of Cr­(VI) is often deemed necessary to detoxify chromium contaminants; however, few investigations utilized this reaction for the purpose of treating other industrial wastewaters. Here a widely used Cr­(VI)–sulfite reaction system was upgraded to simultaneously transform multiple pollutants, namely, the reduction of Cr­(VI) and oxidation of sulfite and other organic/inorganic pollutants in an acidic solution. As­(III) was selected as a probe pollutant to examine the oxidation capacity of a Cr­(VI)–sulfite system. Both ^•OH and SO₄^•– were considered as the primary oxidants for As­(III) oxidation, based on the results of electron spin resonance, fluorescence spectroscopy, and specific radicals quenching. As­(III)-scavenging, oxidative radicals greatly accelerated Cr­(VI) reduction and simultaneously consumed less sulfite. In comparison with a Cr­(VI)–H₂O₂ system with 50 μM Cr­(VI), Cr­(VI), the sulfite system had excellent performance for both As­(III) oxidation and Cr­(VI) reduction at pH 3.5. Moreover, in this escalated process, less sulfite was required to reduce Cr­(VI) than the traditional Cr­(VI) reduction by sulfite process. This effectively improves the environmental compatibility of this Cr­(VI) detoxification process, alleviating the potential for SO₂ release and sulfate ion production in water. Generally, this study provides an excellent example of a “waste control by waste” strategy for the detoxification of multiple industrial pollutants

Monodispersed Hollow SO₃H‑Functionalized Carbon/Silica as Efficient Solid Acid Catalyst for Esterification of Oleic Acid

SO₃H-functionalized monodispersed hollow carbon/silica spheres (HS/C-SO₃H) with primary mesopores were prepared with polystyrene as a template and <i>p</i>-toluenesulfonic acid (TsOH) as a carbon precursor and −SO₃H source simultaneously. The physical and chemical properties of HS/C-SO₃H were characterized by N₂ adsorption, TEM, SEM, XPS, XRD, Raman spectrum, NH₃-TPD, element analysis and acid–base titration techniques. As a solid acid catalyst, HS/C-SO₃H shows excellent performance in the esterification of oleic acid with methanol, which is a crucial reaction in biodiesel production. The well-defined hollow architecture and enhanced active sites accessibility of HS/C-SO₃H guarantee the highest catalytic performance compared with the catalysts prepared by activation of TsOH deposited on the ordered mesoporous silicas SBA-15 and MCM-41. At the optimized conditions, high conversion (96.9%) was achieved and no distinct activity drop was observed after 5 recycles. This synthesis strategy will provide a highly effective solid acid catalyst for green chemical processes