A CuII-Salicylidene Glycinato Complex for the Selective Fluorometric Detection of Homocysteine over 20 Proteinogenic Amino Acids

Homocysteine (Hcy) is a sulfur-containing α-amino acid that differs by one methylene (CH₂) subunit from homologous cysteine (Cys). Elevated levels of Hcy are diagnostic markers of cardiovascular disease and other medical conditions. We present a new Cu^II-salicylidene glycinato complex 1 for the selective fluorometric detection of Hcy in water. In the presence of this analyte, the non-fluorescent copper-complex demetallates and disassembles into its building blocks. This process liberates a 3-chloro-5-sulfosalicylaldehyde signaling unit and is accompanied by a 51-fold turn-on fluorescence at 485 nm (λ_ex=350 nm). Out of twenty proteinogenic amino acids, only histidine (12-fold turn-on fluorescence) and Cys (8-fold turn-on fluorescence) trigger some disassembly of probe 1 . In comparison with important pioneering work on the detection of biothiols, this study strikingly demonstrates that structural modifications of chelate core structures steer substrate selectivity of metal-based probes. Importantly, probe 1 has proven suitable for the detection of Hcy in artificial urine.