Lanthanide III complexes of Aroylhydrazones DNA binding and fluorescence studies

Abstract

Schiff bases and their derivatives, particularly aroylhydrazones,have emerged as versatile ligands in coordination chemistry due totheir ease of synthesis, structural flexibility, and strong metal-bindingcapabilities. Their multidentate nature and ability to exhibit keto–enoltautomerism enable diverse coordination geometries and significantfunctional applications.This thesis focuses on the synthesis,characterization, fluorescence, and DNA-binding studies of threearoylhydrazones:salicylaldehydebenzoylhydrazone(H2salbh),salicylaldehydenicotinoylhydrazone(H2salnh),indole-3-andcarbaldehyde benzoylhydrazone (Hindbh) and their Ce(III), Dy(III),and Gd(III) complexes, with and without L-histidine as the coligand.The aroylhydrazones were successfully synthesized viacondensation reactions and characterized by elemental analysis, ESI-MS, FT-IR, UV–vis, NMR, and single-crystal X-ray diffraction. Thearoylhydrazones H2salbh and H2salnh act as tridentate (ONO) donors,while Hindbh behaves as a bidentate (NO) donor, forming stable, non-electrolytic complexes. The Ce(III), Dy(III), and Gd(III) complexesexhibited characteristic spectral features confirming metal–ligandinteractions, with histidine coordination further stabilizing thecomplexes and modulating their photophysical properties.The luminescence studies revealed significant enhancementupon metal coordination. The Ce(III) complexes displayed efficientd→f transitions with potential applications as blue-emitting materialsin optoelectronic devices.The Dy(III) complexes showed strongfluorescence due to the suppression of photoinduced electron transfer(PET) and activation of chelation-enhanced fluorescence (CHEF)mechanisms, indicating promise for bioimaging and luminescentprobes. The Gd(III) complexes exhibited increased emission intensityand structural rigidity, suggesting their utility in sensing andmultifunctional imaging platforms.DNA-binding studies, investigated by UV–vis absorptionspectroscopy, indicated that both aroylhydrazones and metalcomplexes interact with DNA primarily through external groovebinding. Metal coordination enhanced binding affinity, particularly inHindbh and its complexes (Kb ~105 M-1), due to increased planarityand π-conjugation.These findings highlight the crucial role of ligand design andmetal ion selection in tuning photophysical and biological properties.Overall,thisworkdemonstratesthataroylhydrazone-basedlanthanide(III) complexes possess significant potential for applicationsinluminescentsensing,bioimaging,andtherapeuticdesign,establishing a foundation for future exploration of multifunctionallanthanide-based materials in bioinorganic and photonic chemistry.