Formation of excited formaldehyde in model reactions simulating real biological systems

Abstract

By studying the oxidation of CH 2O by H 2O 2 in the presence of l-lysine under real biological circumstances (pH 7.4, T 298 K) we have found excited CH 2O molecules and singlet oxygen. Analysis of the chemiluminescence spectral distribution allows singlet oxygen lines and a band at 23 000 cm −1 characterizing the 3 A 2→ 1 A 1 transition of formaldehyde to be identified. According to ab initio SCF calculations, in our model reaction excited triplet formaldehyde could be liberated besides the ground state formaldehyde. The lowest 3 A 2 CH 2O state has an extremely long lifetime (about 0.025 s) because of the strongly forbidden triplet→singlet transition. We recognise the biological importance of this excited formaldehyde: because of its biradical character the molecule shows extreme reactivity, and may attack even the smallest reactive regions of biomolecules causing toxicity and carcinogenesis.