Quenching of Tryptophan Fluorescence in the Presence of 2,4-DNP, 2,6-DNP, 2,4-DNA and DNOC and Their Mechanism of Toxicity

Although they are widely used as insecticides, acaricides and fungicides in the agriculture or as raw materials in the dye industry, dinitrophenols (DNPs) are extremely noxious, death cases having been registered. These compounds produce cataracts, lower leucocyte levels, disturb the general metabolism and can cause cancer. It is also assumed that DNPs hinder the proton translocation through the mitochondrial inner membrane and therefore inhibit oxidative phosphorylation. Their fluorescence quenching properties can help understand and explain their toxicity. Fluorescence quenching of tryptophan was tested using different dinitrophenols such as 2,4-dinitrophenol (2,4-DNP), 4,6-dinitro-orthocresol (DNOC), 2-[(2,4-dinitrophenyl)amino]acetic acid (GlyDNP), 2-(1-methyl-heptyl)-4.6-dinitrophenyl crotonate (Karathan), 2-amino-5-[(1-((carboxymethyl)amino)-3-((2,4-dinitrophenyl)thio)-1-oxopropan-2-yl)amino]-5-oxopentanoic acid (SDN GSH), 2,4-dinitroanisole (2,4-DNA) and 2,4-dinitrobenzoic acid (2,4-DNB). 2,4-DNP and DNOC showed the highest tryptophan fluorescence quenching constant values, these being also the most toxic compounds. The electronic chemical potential value of the most stable complex of 2,4-DNP-with tryptophan is higher than the values of the electronic chemical potentials of complexes corresponding to the derivatives.