Spectral change of curcumin in DMSO-NaOH solution after exposure to air

Abstract

Abstract Curcumin (CurH3) forms a blue derivative (CurH2−) when it combines with superoxide radicals. The blue colouring is caused by the proton loss of curcumin to the superoxide radicals. In DMSO, in the presence of excess NaOH and dissolved oxygen, superoxide radicals are produced by consuming the hydroxyl ion which causes the deprotonation of curcumin (Cur3−) and gives the corresponding orange colour. The production of superoxide radicals increased as it was more exposed to air (maybe oxygen). As a result, the pH drops, and the orange derivative is protonated by one H+ ion, producing the corresponding blue colour derivative (CurH2−). The conversion of the orange derivate to the blue derivative may suggest the presence of oxygen in the surrounding atmosphere, allowing the feasibility of a novel oxygen sensor. The physicochemical characteristics and stability of this blue-coloured curcumin derivative are investigated. The distinct colour shifts of curcumin upon the addition of different volumes of NaOH were also investigated. The UV-Vis and FTIR analyses were used to study the stability of the blue curcumin derivative.