Spectroscopic and pH-metric studies on the complexation of a novel tripodal amine-phenol ligand towards Al(III), Ga(III) and In(III)

The aqueous coordination chemistry of a newly synthesized tripodal amine-phenol ligand, cis,cis-1,3,5-tris{(2-hydroxybenzyl)aminomethyl}cyclohexane (THAC) towards H+, Al3+, Ga3+ and In3+ ions have been investigated in aqueous medium of 0.1 M KCl ionic strength and 25 ± 1 °C by potentiometric and spectrophotometric methods. Three protonation constants assigned to phenolic hydroxyl groups were determined and were used as input data to evaluate the formation constants of the metal complexes. The ligand formed various monomeric metal complex species MLH3, MLH2, MLH, ML and MLH-1 with Ga(III) and In(III); MLH3, ML and MLH−1 with Al(III). The calculated stability constants followed the order Ga(III) > In(III) > Al(III), and their pM values at physiological condition were found to be higher than the corresponding transferrin complexes.

Graphical abstractA new tripodal amine-phenol ligand, cis,cis-1,3,5-tris{(2-hydroxybenzyl)aminomethyl}cyclohexane (THAC) has been synthesized and characterized by elemental analyses, UV–VIS, IR and NMR spectral data. The complexation behaviour of the ligand with H+, Al3+, Ga3+ and In3+ was studied by potentiometric and spectrophotometric methods.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A novel tripodal amine-phenol ligand has been synthesized and characterized. ► Complexation towards H+, Al3+, Ga3+ and In3+ ions have been investigated in water by potentiometric and spectrophotometric methods. ► The ligand showed the potential to encapsulate Al3+, Ga3+ and In3+ to form a tris(aminophenolate) type metal complexes. The stability order Ga(III) > In(III) > Al(III) correlates well with their calculated pM values at pH 7.4, pGa (21.90) > pIn (20.95) > pAl (17.98). ► The pM values for the metal complexes were higher than their corresponding transferrin complexes, which is important for different biological applications.