The reaction between phosphatidylethanolamines and HOCl investigated by TLC: Fading of the dye primuline is induced by dichloramines

Phosphatidylethanolamines (PEs) and phosphatidylglycerols (PGs) are abundant lipid constituents of the membranes of Escherichia coli. The reaction between these lipids and hypochlorous acid (HOCl), an important constituent of disinfectants, was investigated by combined thin-layer chromatography (TLC), mass spectrometry (MS), UV and fluorescence spectroscopy. Primuline is a common dye in lipid research that binds non-covalently to lipids and allows, thus, the direct evaluation of TLC plates by MS. However, primuline staining of the products between PE and HOCl is accompanied by fading of the dye. This only holds if acidic but not alkaline conditions are applied. Using a combination of TLC, UV and fluorescence spectroscopy, it will be shown that dichloramines of PE are responsible for the observed primuline fading. Since dichloramines are slowly converted under alkaline conditions into the nitriles that lack the characteristic UV properties of dichloramines, fading is not observed under alkaline conditions.