A Comprehensive Study of the Ca2+ Ion Binding of Fluorescently Labelled BAPTA Analogues

• Published in: European journal of organic chemistry 2021-10, Vol.2021 (37), p.5248-5261
• Main Authors: Csomos, Attila, Kontra, Bence, Jancsó, Attila, Galbács, Gábor, Deme, Ruth, Kele, Zoltán, Rózsa, Balázs József, Kovács, Ervin, Mucsi, Zoltán
• Format: Article
• Language: English
• Subjects: Aromatic compounds; Atomic properties; Binding; Calcium; Calcium compounds; Calcium ions; Chains; Chelates; Density functional calculations; Dyes; Ethane; Fluorescence; Fluorescent probes; Molecular structure; Oxygen atoms; Titration
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202100948

Since its development, the ionophore BAPTA (1,2‐bis(2‐aminophenoxy)‐ethane‐N,N,N’,N’‐tetraacetic acid) has been used unchanged in calcium sensing applications. In this work we present a comprehensive experimental and theoretical study of novel alterations in the structure of BAPTA, with a focus on the systematic modification of the chain connecting the two aromatic rings of the molecule (denoted as “linker”). A bis‐(diethylamino)xantene fluorophore was also attached to the structures in a fixed position and the structure‐fluorescence response relationship of these molecules was investigated in addition. The effect of the linker's length, the number of oxygen atoms in this chain and even the removal of one of the rings was tested; these all proved to significantly alter the characteristics of the compounds. For example, it was found that the second aromatic ring of BAPTA is not essential for the turn‐on of the fluorescence. We also demonstrated that successful sensing can be realized even by replacing the chain with a single oxygen atom, which suggests the availability of a new calcium binding mode of the chelator. The reliable turn‐on characteristic, the steep Ca2+ fluorescence titration curve and the intense fluorescence emission combine to make this compound a prospective candidate as a calcium sensing molecular probe in diagnostic neurobiological applications. Novel and effective calcium ion binding molecular fluorescent probes have been developed by systematic structural modification of BAPTA ionophore. The comprehensive computational studies suggested the role of the coordination number in the chelator moiety.