Lanthanide(III) Complexes of Bis‐semicarbazone and Bis‐imine‐Substituted Phenanthroline Ligands: Solid‐State Structures, Photophysical Properties, and Anion Sensing

Abstract

Phenanthroline-based hexadentate ligands L(1) and L(2) bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as La(III), Eu(III), Tb(III), Lu(III), and Y(III) metal ions, were synthesized, and the crystal structures of [ML(1)Cl(3)] (M=La(III), Eu(III), Tb(III), Lu(III), or Y(III)) complexes were determined. Solvent or water molecules act as coligands for the rare-earth metals in addition to halide anions. The big Ln(III) ion exhibits a coordination number (CN) of 10, whereas the corresponding Eu(III), Tb(III), Lu(III), and Y(III) centers with smaller ionic radii show CN=9. Complexes of L(2), namely [ML(2)Cl(3)] (M=Eu(III), Tb(III), Lu(III), or Y(III)) ions could also be prepared. Only the complex of Eu(III) showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine-5'-triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine-5'-diphosphate (ADP) and adenosine-5'-monophosphate (AMP) was found. (31)P NMR spectroscopic studies revealed the formation of a [EuL(2)(ATP)] coordination species.

Sensing of Phosphates by Using Luminescent EuIII and TbIII Complexes: Application to the Microalgal Cell Chlorella vulgaris

“…Conductivity measurements were performed in solution. The molar conductance was measured as 79.8, 90.6 S mol cm −2 with respect to complex 1 and 2 in aqueous solution matches to our earlier studies reported14 for similar complexes. This indicates the full dissociation of the lanthanide(III) salt in aqueous medium.…”

“…Those biophosphates show quenching with different specificities. The complex [EuL 1 Cl 3 ] has been reported recently for its superior specificity towards ATP compared with the other nucleoside phosphates 14. However, although complexes 1 and 2 act as efficient quenchers for the three nucleoside phosphates, their specificity for ATP, ADP, and AMP is very low.…”

“…With this understanding, we recently initiated a program to explore a series of LnL 1 complexes. Selective binding of ATP with EuL 1 has been reported 14. Following this, the present study utilizes the europium(III) or terbium(III) complexes [EuCl 3 L 2 ] ( 1 ) and [TbCl 3 L 2 ] ( 2 ) as fluorescent probes for the determination of ATP, AMP, and ADP (Figure 1).…”

Luminescent and Chiroptical Properties of 1 : 1 Eu (III) : Tetracycline Species Probed by Circularly Polarized Luminescence

“…The coordination of various carbonyl and amide‐containing ligands or solvent molecules provides a microenvironment to the Ln(III) metal ion, in which the luminescence is sensitive to the structural conformation of its surrounding environment . This characteristic has been exploited in various biological studies for the (a) development of a lanthanide‐complex molecular beacon used as an allosteric effector to allow for the split‐probing of specific genes, (b) use of lanthanide‐binding peptides with DNA intercalating units for the detection of double‐stranded DNA, (c) sensing of phosphate or other anions to assess the body's energy source, ATP, to understand how it causes ischemia, Parkinson's disease, and hyphoglycaemia, (d) conformational changes in calcium and iron binding proteins to assess their binding to the active site, coordination sphere of the metal, and distinct classes of binding sites, or (e) chiral discrimination of bioactive molecules to recognize their interactions with Ln(III) complexes …”

Anion–π interactions in active centers of superoxide dismutases

“…In addition, Moore and co-workers examined high-resolution structures of proteins and nucleic acids for the presence of " 6 "-type anion-π contacts, where the anion is placed directly above the centre of the six-membered ring [12]. Anion-π interactions are currently helpfully exploited in fields such as anion sensing [19][20][21], supramolecular assembly [7,22,23], and anion transport through membranes [24,25], even in biological systems [18].…”