The demand for compounds of therapeutic value is increasing mainly because of new applications of bioactive compounds in medicine, pharmaceutical, agricultural, and food industries. This has necessitated the search for cost-effective methods for producing bioactive compounds and therefore the intensification of the search for enzymatic approaches in organic synthesis. Laccase is one of the enzymes that have shown encouraging potential as biocatalysts in the synthesis of bioactive compounds. Laccases are multicopper oxidases with a diverse range of catalytic activities revolving around synthesis and degradative reactions. They have attracted much attention as potential industrial catalysts in organic synthesis mainly because they are essentially green catalysts with a diverse substrate range. Their reaction only requires molecular oxygen and releases water as the only by-product. Laccase catalysis involves the abstraction of a single electron from their substrates to produce reactive radicals. The free radicals subsequently undergo homo- and hetero-coupling to form dimeric, oligomeric, polymeric, or cross-coupling products which have practical implications in organic synthesis. Consequently, there is a growing body of research focused on the synthetic applications of laccases such as organic synthesis, hair and textile dyeing, polymer synthesis, and grafting processes. This paper reviews the major advances in laccase-mediated synthesis of bioactive compounds, the mechanisms of enzymatic coupling, structure-activity relationships of synthesized compounds, and the challenges that might guide future research directions.
Improving skills in STEM disciplines has been identified as essential in meeting South Africa’s economic growth targets. Despite this, learner uptake and completion rates within these subjects is currently well below international standards. We therefore examined key stages within the science education system to identify factors contributing to the low throughput in science education. We reviewed how national science policy changes have impacted the curriculum and teaching practices across different education establishments and socio-economic groups. We highlight that 80% of public schools have a lack of resources for practical learning, making it difficult for teachers to implement enquiry-based teaching methods. We explored strategies for effective engagement with science from the science communication literature and present recommendations to improve learner engagement with science in under-resourced school settings. Whilst education reform is needed at a national scale, we make a case for using science communication practices in science classes as a more immediate solution to generate greater interest and understanding, and encourage learners to pursue careers in science.
The rise in antioxidant demand for industrial applications has necessitated the need to investigate new methods for antioxidant production. Conventionally, antioxidants have been used in the food industry. However, newer applications in industries such as pharmaceuticals, cosmetics, medicine, nano-bioscience, as well as in chemical industries, have contributed to the increase in antioxidant demand. The market for antioxidants has been forecasted to increase by 6.42% compound annual growth rate (CAGR) between 2015 and 2022. Therefore, there is now a need to develop new processes for antioxidant synthesis to meet this rising demand. Biocatalysis has gained notable attention as a viable approach for antioxidant synthesis. Laccases are the preferred enzymes since their reaction mechanism involves the use of molecular oxygen to oxidise phenolic compounds to corresponding radicals, with water as the only by-product. Most laccase antioxidant synthesis research has employed fungal and plant laccases. However, bacterial laccases may be promising biocatalysts, considering the advances in molecular technology which make expression in bacterial hosts easier. This study focused on the biotransformation of natural phenolic compounds using small laccase (SLAC), a two-domain bacterial laccase native to Streptomyces coelicolor. Because of the low redox potential of the enzyme, a preliminary substrate screening process was conducted to identify phenolics oxidisable by the SLAC. Caffeic acid, 2,6-dimethoxyphenol, catechol, gallic acid, guaiacol, ferulic acid, and pyrogallol were identified as SLAC substrates and further coupling reaction studies were conducted using caffeic acid and gallic acid. Coupling reactions were carried out either in biphasic systems consisting of water-immiscible organic solvents and a buffer system or monophasic systems consisting of miscible organic solvents that form a homogenous phase with the buffer system. Coupling products were monitored using thin layer chromatography (TLC) and high performance liquid chromatography (HPLC), purified using preparative TLC and column chromatography, and characterised by liquid chromatography-mass spectrometry (LCMS) and nuclear magnetic resonance spectroscopy (NMR). Antioxidant capacity of the oxidation products were investigated by using the 2,2’-diphenyl-1- picrylhydrazyl (DPPH) and Trolox equivalence antioxidant capacity (TEAC) assays. Two oxidation products (one from caffeic acid and another from gallic acid) were successfully produced, purified and characterised. The oxidation product obtained from the SLAC-catalysed oxidation of caffeic acid was identified as a β-β dimer using LC-MS and NMR. When the reaction was carried out at a large-scale, a 32.8% yield of the dimer was achieved. Results showed that optimum yield of the dimer was achieved when the reaction was carried out for 6 h in a biphasic system consisting of 80% ethyl acetate and sodium acetate buffer pH 7.5. The dimer demonstrated superior antioxidant capacity, showing a 1.5- fold increase in DPPH radical scavenging capacity and a 1.8-fold improvement in TEAC. The dimer exhibited several positive physicochemical attributes, including improved solubility properties in aqueous media and remarkable stability in acidic pH (pH 2.2 and pH 5.5). One oxidation product from the SLAC-catalysed oxidation of gallic acid was successfully produced, purified and partially characterised. Optimum yield of gallic acid oxidation product was achieved when the reaction was conducted in a biphasic system consisting of 80% ethyl acetate and Tris-HCl buffer pH 8.0, using 0.5 U SLAC and a reaction time of 4 h. However, the oxidation product showed a lower antioxidant capacity than the substrate, as demonstrated by standard antioxidant assays (DPPH and TEAC). In conclusion, two antioxidant products were successfully produced, purified and characterised. Furthermore, selected physicochemical and antioxidant activities were determined. Overall, this study has highlighted the potential of the small laccase as a catalyst for the synthesis of antioxidants.
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