Selective reactivity of biochemically relevant quinones towards chitosans

Biologically significant quinones, such as menadione (vitamin K), plumbagin, ubiquinone (CoQ10) and CoQ3 were examined along with 1,2-naphthoquinone and 1,4-naphthoquinone for their capacity to react with five chitosans in freeze-dried or film form. The chitosans tested were: chitosan acetate salt, re-acetylated chitosan, amorphous chitosan, 5-methylpyrrolidinone chitosan and N-carboxymethyl chitosan. It was surprisingly found that CoQ10 and CoQ3 do not react with the chitosans, whilst menadione and even more 1,4-naphthoquinone are reactive and yield deeply coloured modified chitosans. The reactivities of plumbagin and 1,2-naphthoquinone are modest or nil, depending on the chitosan tested. The maximum capacity of chitosans for 1,4-naphthoquinone corresponded to an amine/quinone molar ratio close to 2, indicative of saturation over a 12 h contact period: the relevant infrared spectra did not show the typical bands of 1,4-naphthoquinone. Uv–vis measurements on methanol solutions indicated that chitosan acetate salt and re-acetylated chitosan were most reactive with menadione. Menadione-treated chitosans gave infrared spectra containing typical quinone bands, and the films had altered surface properties, their contact angles with saline being much higher than for controls. The absence of reactivity between ubiquinone and N-carboxymethyl chitosan, both widely accepted functional cosmetic ingredients, could constitute the basis for the formulation of toot-pastes and gingival gels, possessing enhanced reparative properties due to the synergistic actions of intact ubiquinone and N-carboxymethyl chitosan.