Quantum Chemical Studies of Potential Associates in Europium (III) Alginate Solutions


Metal-alginate complexes (especially, lanthanide gels) are particularly interesting for medical and biological analysis due to their luminescent properties upon UV light excitation. Unfortunately, synthesis and further physical and chemical studies of such complexes is inhibited by their high cost. However, this problem can be solved by using quantum chemical methods to predict potential properties of lanthanide alginates based on the results of their geometry optimization and electronic structure calculation. This study presents the results of quantum chemical analysis of possible structures and UV-vis spectra of europium (III) alginates and comparison of these spectra with existing experimental data. Geometry optimization was performed by PM7/SPARKLE method (software – MOPAC 2012) combined with COSMO solvation model. UV-vis spectra were calculated using ZINDO/S method (Orca software). We have studied 6 possible structures with various metal-to-ligand ratios (1:1, 1:2 and 1:3) and different ligand composition (using both monoprotonated (HAlg- ) and deprotonated alginate ions (Alg2-). The greater amount of ligands participating in coordination lead to significant decrease in complex stability (due to increased number of Ln-O bonds and decrease of their energy) and increase of electron acceptor properties. Comparison between calculated and experimental UV-vis spectra of studied complexes showed that Eu alginate solution contains several types of complex ions, most likely – Eu(Halg)(Alg) and [Eu(Alg)3 ] 3- . This shows that chosen computation method allows to predict UV-vis absorption spectra of lanthanide complexes with polymeric acids which can be used for medical and biological analysis. 


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