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High selectivity of fluorescent (triazole)coumarin peptides to metal cations – fluorimetric and NMR approach

The basis for the biological functioning of many proteins is the creation of metal complexes [1], in which metals have structural and functional roles [2]. Our recently published paper shows some interesting nanomolar affinity of FKA(triazole) and KA(triazole) coumarin peptoids towards Cu2+ cations in water [3]. This prompted us to continue with further complexation studies using other metal cations. We performed fluorimetric titrations of FKA(triazole) and KA(triazole) analogues (Fig. 1. LEFT) with different metal cations: Cu+, Ag+, Zn2+, Co2+, Cd2+and Hg+, experiments yielding micromolar binding constants in aqueous solution. The addition of Cu2+, Cu+ and Ag+ resulted in pronounced quenching of the emission of KA(triazole) peptoid, compared to other studied metal cations. Using 2D NMR techniques (COSY, HSQC and HMBC), 1H and 13C chemical shifts of KA(triazole) ligand were successfully assigned [3]. In novel NMR spectroscopic study of KA(triazole) ligand complexation with Cu2+ in pure D2O showed evident differences in chemical shifts and shape of some proton signals between KA(triazole) ligand and Cu2+, also supported by the analogous results in the 13C NMR data (significant shift of the triazole carbon C-5’ signal). Detailed analysis of NMR data confirmed KA(triazole)/Cu2+ complex formation and allowed the determination structure of just one dominant type of complex between Cu2+ and KA(triazole) ligand (Fig. 1 RIGHT).

metalloproteins ; KA(triazole)-coumarin ; CuAAC click reaction, copper sensing, sensing of transitional metal cations ; fluorescence quenching ; NMR

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