L histidine

N‐chlorotaurine (NCT) (molecular weight 181·57 g mol⁻¹, lot 2018‐11‐06) was prepared as crystalline sodium salt (Cl‐HN‐CH₂‐CH₂‐SO₃⁻ Na⁺) from taurine and chloramine T in our laboratory at pharmaceutical grade, as reported (Gottardi and Nagl 2010 (link)), stored at minus 20°C, and freshly dissolved in sterile phosphate buffer (0·1 mol l⁻¹) to a concentration of 1% for each experiment. The chemical structure is shown in Fig. 1. Identity and purity were verified by spectrophotometric analysis (peak at 251·5 nm), infrared spectrometry (band at 3260 cm⁻¹), and mass spectrometry, and the content of active chlorine by iodometric titration (maximum chlorine content 19·52%) (Gottardi and Nagl 2002 ). The sodium salt can be stored at 20°C for about 2 weeks, at 2–4°C for 1 year, at −20°C or lower for at least 2 years, so that cooling is necessary for long‐term storage. Solutions can be stored up to 1 year at 2–4°C and 2 weeks at room temperature protected from UV light. Phosphate buffer (0·1 mol l⁻¹), and tryptic soy broth were from Merck (Darmstadt, Germany), l‐histidine from Serva (Heidelberg, Germany), and dl‐methionine from Sigma‐Aldrich (Steinheim, Germany).