Preparation and characterization of chitosans carrying aldehyde functions generated by nitrogen oxides

In this work, aldehyde-functionalized chitosan is produced by the reaction of chitosan with nitrogen oxides generated in situ from a HNO3/H3PO4–NaNO2 mixture. This method is more advantageous than the existing approaches, since the depolymerization is slower and the purification process is straightforward. The appearance of characteristic peaks in the Fourier transform infrared and carbon-13 nuclear magnetic resonance spectra (1733 cm−1 and 183.4 ppm, respectively) of the product confirms the presence of the aldehyde functionality in the modified chitosans. The 1H NMR spectra also revealed the presence of aldehyde groups. Furthermore, the gradual disappearance of the peaks due to aldehyde protons and a concomitant appearance of a new resonance at ∼8.05 ppm with increasing pH indicate the formation of Schiffʹs base between the aldehyde and the free amine groups. The aldehyde-functionalized chitosan prepared with 6 h of reaction time (chitosan-6h) forms a gel in situ without any added external crosslinker and it may potentially be useful as a vehicle for drug delivery.