Anthrapyridone-based amino acids as colorimetric probes for Cu²⁺ ion determination

Previously unknown derivatives of anthrapyridone and α-amino acids were synthesized, which can be used as analytical reagents for the selective and sensitive photometric determination of Cu²⁺ cations. The obtained derivatives form 1 : 1 complexes with Cu²⁺ at pH 7.4 and 1 : 2 complexes at pH 11.9 in H₂O/DMSO (9 : 1 v/v) medium, and a change in the solution color from yellow to red (Δλ 56-90 nm) is observed. The presence of metal ions (Ca²⁺, Na⁺, Ba²⁺, Mg²⁺, Mn²⁺, Cr³⁺, Hg²⁺, Zn²⁺, Al³⁺, Cd²⁺, La³⁺, Ag⁺, Ni²⁺, Co²⁺, Pb²⁺, Fe²⁺, Fe³⁺) does not interfere with the colorimetric determination of Cu²⁺ cations. At pH 7.4, good linearity between absorption and concentration of Cu²⁺ ions is maintained within the range of 0.4-60.0 μM, and the detection limit reaches 0.017 μM. Solutions of the obtained amino acids can be used for determining Cu²⁺ cations at the TLV level (20 μM) with the naked eye at pH 11.9.