Nano-structured polyaniline in biocatalysis: Manifesting simultaneous competence of polyaniline nanofibers and nanotubes as immobilization matrices for laccase mediated synthesis of drug intermediates.

Customized nano-biocatalysts of laccase have been made using nano-structured polyaniline viz. nano-fibers and nano-tubes, as immobilization supports and a simultaneous comparison between them has been made. Laccases are poly-phenol oxidases having tremendous utility concerning wider areas of application especially in the field of organic and drug syntheses. Considering importance of laccases in drug syntheses, an effort has been made to immobilize laccase on the nano-structured polyaniline by adsorption. Immobilization was assessed using percentage enzyme loading as well as immobilization efficiency. Further immobilization process was strengthened using statistical optimization (Response Surface Methodology) for the parameters affecting immobilization viz. pH, Stirring rate, Enzyme Support ratio. In comparison to free enzyme, better thermal stability was depicted with almost 3- and 4-fold increase in half-life for immobilized laccase on nanofibers and nanotubes, respectively, at 80 °C. The storage stability of the nano-biocatalysts was revealed by the retention >50 % of higher enzyme activity in comparison to free form, when stored at 4 °C for up to 60 days. Moreover, slow and gradual decline in activity was observed when the immobilized laccase preparations were re-utilized for ten consecutive cycles of guaiacol oxidation. Greater than 60 % retention of enzyme activity after consistent catalytic cycles renders the utilization of immobilization preparations in industrial biocatalysis. Manifestation of efficient nano-biocatalysts has portrayed superior enzyme kinetics in rendering efficient biotransformations of ortho-phenylenediamine analogues to subsequent Phenazines which are known to possess therapeutic properties ranging from anti-microbial to anti-proliferative and so on.