Investigating metal-binding properties and characteristics in bis-2-(2-hydroxyphenyl)-thiazole-carboxamide chelators, indicating their potential applications.
In this study, we investigate three members of the HPTC family─the monomeric ligand L1 and the bipodal ligands L2E and L2A, HPTC = 2-(2-hydroxyphenyl)-thiazole-4-carboxamide─to elucidate their acido-basic behavior, photophysical characteristics, and metal-binding properties. Protonation studies revealed that phenolate and carboxylate sites significantly influence fluorescence responses, including tautomeric equilibria and ESIPT processes. L1 forms mono- and bis-chelates with Fe(III) and Ni(II), while L2E and L2A yielded stable monochelates with Fe(III) and other divalent metal ions. Hydrolysis of ester functionalities in L2A markedly enhances Cu(II) complex stability relative to L2E. Electrochemical measurements on L1 demonstrate strong Fe(III)/Fe(II) selectivity, and kinetic data support a dissociative ligand exchange mechanism limited by metal desolvation. Overall, the presence of carboxamide and carboxylate groups plays a pivotal role in tuning metal affinity and reactivity.
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Hmadeh et al. (2026) studied this question.
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