Designing a β-nitrostyrene derived chitosan Schiff base with potent antimicrobial and antioxidant activities and drug delivery applications

A novel reaction between chitosan and β-nitrostyrene was carried out to obtain Schiff base based chitosan derivative β-NS-CS via aza-Michael addition followed by elimination reaction (retro-aza-Henry type process). FT-IR, P-XRD, ¹H NMR and FE-SEM analyses supported the result. With the FT-IR stretches at 1617 cm⁻¹, the successful formation of imine bond (>CN-) was verified. In case of P-XRD, we procured two additional peaks at 2θ = 21.3° and 2θ = 23.3° (other than that in chitosan) which indicated better crystalline behaviour of β-NS-CS in comparison to chitosan. ¹H NMR signals in the aromatic region verified the thriving inclusion of trans-β-nitrostyrene derived moeity into chitosan backbone. The planar sheet-like and asymmetrical morphology of the β-NS-CS conjugate was exhibited by FE-SEM images. The derivative was further analysed by DLS (average particle size of β-NS-CS = 70 nm) and zeta potential (+41.9 mV) studies. In terms of biological applications, β-NS-CS showed implicit antimicrobial property when studied against gram negative bacteria (Escherichia coli), gram positive bacteria (Bacillus subtillis) and fungus (Aspergillus niger). It also showed good antioxidant activity against DPPH and ABTS antioxidant assessment i.e, 22.5 % and 80.5 % radical scavenging potential respectively. It also proved to be an efficient candidate as a drug carrier having drug encapsulation efficiency of 80 % with quercetin as a model drug. The drug release kinetics was found to be 81 % at pH = 5.0 and 7 % at pH = 7.4 after 96 h. Hence, β-NS-CS is expected to find potential applications in biological and medicinal field in future.