Experimental and Computational Investigations of Selective Fluorogenic Recognition of Tryptophan Using a New Mixed Macrocyclic Ligand Complex

ABSTRACT A fluorescence (FL) molecular probe based on a naphthalene macrocycle, anchored to two porphyrin subunits ( Zn2p ), selective for L‐tryptophan (L‐Trp) has been synthesized. Single‐crystal X‐ray diffraction, FT‐IR, 1 H, 13 C NMR, and microelemental analyses were applied to characterize Zn2p . The FL spectroscopy represented Zn2p as a sensitive (LOD = 5 × 10 −7 M) and highly selective sensor toward L‐Trp in DMF among other selected amino acids. The L‐Trp recognition mechanism was studied by 1 H NMR, representing a downfield shift for the proton signals of the OCH 2 CH 2 O moiety on Zn2p in the presence of L‐Trp in CDCl 3 solution. Applying the supramolecular chemical analysis method, the K 11 value was calculated as 2.7496 (± 2.1963) × 10 4 M −1 , covering the least computed error. Computational studies were carried out by employing density functional theory (DFT calculations, which were performed in the gas phase using the B3LYP‐D3/def2‐TZVP basis set in the ORCA 4.1.0 quantum chemistry program, supporting the 1 H NMR result on the involvement of the ethereal oxygen in the supramolecular interaction with L‐Trp.