Synthesis of novel 1H-tetrazole derivatives of chitosan via metal-catalyzed 1,3-dipolar cycloaddition. Catalytic and antibacterial properties of [3-(1H-tetrazole-5-yl)ethyl]chitosan and its nanoparticles

New tetrazole derivatives of chitosan with low, moderate, and high degrees of substitution were obtained using a novel approach, i.e. metal-catalyzed 1,3-dipolar cycloaddition of azide ion to cyanoethyl chitosan in water – the most straightforward, selective and preparatively convenient route to tetrazole chitosan derivatives. Ionic gelation of these tetrazole derivatives with sodium tripolyphosphate resulted in nanoparticles with an apparent hydrodynamic diameter of 100–800 nm and ζ-potential of 22–57 mV. The tetrazole derivatives of chitosan and their nanoparticles were tested as catalysts of the aldol reaction between p-chlorobenzaldehyde and acetone. The tetrazole derivatives have been found to possess better catalytic properties than the corresponding nanoparticles. The obtained data indicate that the tetrazole-chitosan polymers exhibit high catalytic activity in aldol reaction, and these catalysts are among the best studied so far. Tetrazole derivatives and their nanoparticles were also tested as antibacterial agents. The in vitro antibacterial activity against S. aureus and E. coli of the tetrazole-chitosan-based nanoparticles is much more than the activity of the corresponding tetrazole-chitosan polymers, and their activity is comparable with that of antibiotics ampicillin and gentamicin. © 201

Natural polysaccharide-based smart (temperature sensing) and active (antibacterial, antioxidant and photoprotective) nanoparticles with potential application in biocompatible food coatings

Smart and active nanoparticles are of increasing interest in food films and coatings application. In the current study, we purpose novel nanoparticles NPs-4(1:5) and NPs-4(1:5.5), which possess simultaneously both smart (temperature sensitive) and active (antibacterial, light absorbing and antioxidant) properties. The obtained nanoparticles are based on PEG/MC core with anthocyanidin and sodium acetate, and chitosan/gallotannin-based shell. The nanoparticles have hydrodynamic diameter ca. 450 nm and are positively charged (ζ-potential is 21 mV for NPs-4(1:5) and +23 mV for NPs-4(1:5.5). NPs-4(1:5) and NPs-4(1:5.5) are thermochromic and turn from colorless to purple at ca. 20 °C 0 °C respectively. The nanoparticles possess antibacterial activity much more than the starting chitosan (MIC, μg/mL, E. coli: 1.35 (NPs-4(1:5)), 1.18 (NPs-4(1:5.5)) and 10.12 (chitosan); S. aureus: 1.14 (NPs-4(1:5)), 1.10 (NPs-4(1:5.5)) and 6.20 (chitosan)). The nanoparticles efficiently absorb ultraviolet light, have high antioxidant effect (0.051 trolox equivalents), are non-toxic and fully composed of substances approved for use in the food industry. © 2019 Elsevier B.V