LAUSR

Leucocytes generate hypohalous acids (HOCl and HOBr) to defend the host against pathogens. In cells, hypohalous acids react with amine‐containing molecules, such as amino acids and polyamines, producing chloramines and bromamines, reservoirs of oxidizing power that can potentially damage host tissues at sites of inflammation. Hypohalous acids also react with H2O2 to produce stoichiometric amounts of singlet molecular oxygen ( 1O2 ), but its generation in leucocytes is still under debate. Additionally, it is unclear whether haloamines generate 1O2 following a reaction with H2O2. Herein, we provide evidence of the generation of 1O2 in the reactions between amino acid‐derived (taurine, N‐α‐acetyl‐Lysine and glycine) and polyamine‐derived (spermine and spermidine) haloamines and H2O2 in an aqueous solution. The unequivocal formation of 1O2 was detected by monitoring its characteristic monomol light emission at 1270 nm in the near‐infrared region. For amino acid‐derived haloamines, the presence of 1O2 was further confirmed by chemical trapping with anthracene‐9,10‐divinylsulfonate and HPLC‐MS/MS detection. Altogether, photoemission and chemical trapping studies demonstrated that chloramines were less effective at producing 1O2 than bromamines of amino acids and polyamines. Thus, 1O2 formation via bromamines and H2O2 may be a potential source of 1O2 in nonilluminated biological systems.