Homogeneous synthesis of quaternized chitin in NaOH/urea aqueous solution as a potential gene vector

• A series of quaternized chitins (QCs) were homogenously synthesized via a simple and “green” process.
• The degree of substitution of QC (0.27–0.54) could be obtained by adjusting the reaction conditions.
• QCs had a good ability of condensing plasmid DNA into compact nanoparticles with the size of 100–200 nm and zeta potential of +18 to + 36 mV.
• The QCs exhibited low cytotoxicity and effective transfection activity.

Water-soluble quaternized chitins (QCs) were homogeneously synthesized by reacting chitin with (3-chloro-2-hydroxypropyl) trimethylammonium chloride (CHPTAC) in 8 wt% NaOH/4 wt% urea aqueous solutions. The chemical structure and solution properties of the quaternized chitins were characterized by 1H NMR, FT-IR, elemental analysis, dynamic light scattering (DLS) and zeta potential measurements. The results demonstrated that the water-soluble QCs, with a degree of substitution (DS) values of 0.27–0.54, could be obtained by varying the concentration of chitin, the molar ratio of CHPTAC to chitin unit, and the reaction time at room temperature (25 °C). Two QCs (DS = 0.36 and 0.54) were selected and studied as gene carriers. Agarose gel retardation assay revealed that both QCs could condense DNA efficiently when N/P ratio > 3. The results of particle size and zeta potential indicated that both QCs had a good ability of condensing plasmid DNA into compact nanoparticles with the size of 100–200 nm and zeta potential of +18 to + 36 mV. Compared to polyethylenimine (PEI, 25 kDa), the QCs exhibited outstanding low cytotoxicity. Transfection efficiencies of the QCs/DNA complexes were measured using pGL-3 encoding luciferase as the foreign DNA, and the QCs/DNA complexes showed effective transfection efficiencies in 293T cells. These results revealed that the QCs prepared in NaOH/urea aqueous solutions could be used as promising non-viral gene carriers owing to their excellent characteristics.