We, for the first time, report a green, solid-state method for synthesizing maleated chitosan, wherein maleation is brought about by stirring chitosan flakes in molten maleic anhydride. In a similar manner, other derivatives like succinated chitosan could also be prepared. Maleated chitosan, given its polyanionic nature in solution form, could be further used to cross-link chitosan polycation through electrostatic complexation. The resulting "all-chitosan" gel, having very low cytotoxicity and a conducive surface for cell attachment, could be used as scaffolds for tissue engineering. In this context it is to be noted that presently, maleation of chitosan has been invariably carried out in solution phase, using harsh, environmentally aggressive solvents such as DMSO, DMF, acetamide and the like.
A facile, rapid, and sustainable
synthesis of amorphous, photoluminescent,
carbon nanodots in high yields (∼51%), by cogrinding of maleic
anhydride and imidazole, is reported for the first time. The heat
liberated during the exothermic oligomerization of maleic anhydride,
initiated by imidazole in the solid state, was identified to be the
cause of carbonization of the reaction mixture. These carbon nanodots
showed very low cytotoxicity toward mesenchymal stem
cells, even at very high concentrations (1 mg/mL). Having the highest
adsorption capacity for ammonia among unmodified carbons reported
to date (∼19.3 mg/g), these carbon nanodots could be used for
the removal of ammonia from the gas phase. In addition, these carbon
nanodots could be used as an ionotropic cross-linker for chitosan,
to prepare stable gels, suitable for a wide variety of applications.
In contrast to the present solid-state methodologies which involve
the use of hazardous chemicals or high temperatures, this solvent-free
method of preparing carbon nanodots is sustainable, facile, safe,
and inexpensive.
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