Synthesis and characterization of hairy aminated nanocrystalline cellulose

The synthesis and characterization of aminated nanocrystalline cellulose (ANCC), a new member of the hairy nanocellulose family, is reported. Hairy nanocelluloses consist of a crystalline rod-like body with amorphous cellulose chains ("hairs") at both ends, on which various functional groups can be accommodated. In ANCC these groups are reactive primary amine groups, which are useful for bioconjugation- and Schiff base-centered modifications. We hypothesize that a two-step oxidation-reductive amination of cellulose fibers followed by hydrothermal treatment will result in the formation of rod-like hairy ANCC.

ANCC was prepared by converting the aldehyde groups in cellulose, introduced by a periodate oxidation, to primary amines using ammonia and sodium borohydride, followed by a hot water treatment, during which diamine modified cellulose fibers were converted to ANCC. ANCC was characterized by AFM, TEM, DLS, ELS, FTIR, NMR, XPS and conductometric titration. Antibacterial activity of ANCC was assessed by the viable cell counting method.

ANCC, with an amine content of 5.5 mmol g^-1 is a bare nanocolloid (i.e. non-coated, without adsorbed polyelectrolytes or surfactants) which, as far as we know, has a positive charge density larger than any other bare cationic nanocolloid. It was observed that ANCC particles have a needle-like morphology with a width of ~ 5 nm and a length ~ 120 nm. DLS results proof that ANCC is hairy. Spectroscopic analysis confirmed the introduction of surface primary amine groups. ANCC showed promising bactericidal activities, against Gram-negative species due to their thinner and penetrable cell wall.