Early events in 2,4,6-trinitrotoluene (TNT) degradation by porphyrins: Binding of TNT to porphyrin by hydrophobic and hydrogen bonds

Abstract

The interaction of meso-tri(4-sulfonatophenyl)mono(4-carboxyphenyl) porphyrin (C 1TPP) with 2,4,6-trinitrotoluene (TNT) has been explored by UV–vis and fluorescence spectroscopy. The influence of temperature on the interaction has also been studied. C 1TPP binds to TNT at pH 7.0 at room temperature via 1.94 kcal/mole hydrogen bonds with absorbance loss at 412–413 nm and the appearance of a new peak at 422–424 nm. The hydrogen binding of TNT to C 1TPP was confirmed by the dissolution of the complex upon the addition of urea. Increasing the temperature results in the appearance of a new absorbance peak at 540 nm and absorbance loss at 515 nm with activation energy of 29.7 kcal/mole in the range of the hydrophobic bond energy. This suggests the hydrophobic bonding of TNT with the pyrrole nitrogens in the porphyrin. Increasing the concentration of the TNT in the solution quenches the fluorescence of the porphyrin following the Stern–Volmer equation. The association constants calculated from absorbance and fluorescence are expectedly similar.