Extra‐weak chemiluminescence of drugs. VIII. Extra‐weak chemiluminescence arising from the amino‐carbonyl reaction

Extra-weak chemiluminescence (CL) from amino-carbonyl reactions of L-lysine with various sugars and aldehydes in aqueous solution was examined. Amongst the aldehydes and sugars tested, glycoaldehyde and D-arabinose produced the highest CL intensity. The CL of the amino-carbonyl reaction reached a maximum after about 60 minutes. The CL was pH dependent, and a linear relation between CL intensity and hydrogen-ion concentration was demonstrated. Low oxygen levels inhibited CL and no CL was produced in nitrogen purged solutions. Addition of cupric or ferrous ion, decreased the CL. The involvement of free radical intermediates was demonstrated by ESR. Our findings suggest that the CL of the amino-carbonyl reaction arises from free radicals derived from melanoidines or their intermediates. CL should prove useful for evaluating the stability of crude drugs extracted from natural resources that contain various amino acid derivatives protein and sugar components.