Structure Elucidation of Chromogen Resulting from Jaffe's Reaction

Jaffe's reaction is a reaction of creatinine with alkaline picric acid resulting in red chromogen. This color is being used widely for the estimation of creatinine in biological fluids without knowing the exact structure of the chromogen. The red species is isolated and its UV/Visible, H-1- and C-13- NMR studies are carried out. It is found that the red species is not a pure compound but a mixture of stereoisomers. Moreover, the red species in water reflects the same UV/Visible spectra as given by the reaction of creatinine with alkaline picrate in aqueous media. The red species is a 2:3 molar Meisenheimer sigma-complex of creatinine-picric acid (6).