Caffeic Acid/Eu(III) Complexes: Solution Equilibrium Studies, Structure Characterization and Biological Activity.

Żaneta Arciszewska,Adam Cudowski,Concetta De Stefano,Demetrio Milea,Anna Pietryczuk,Włodzimierz Lewandowski,Beata Godlewska-Żyłkiewicz,Ewelina Gołębiewska,Monika Naumowicz,Renata Świsłocka,Monika Kalinowska,Grzegorz Świderski,Mateusz Worobiczuk,Sofia Gama

doi:10.3390/ijms23020888

Abstract

Caffeic acid (CFA) is one of the various natural antioxidants and chemoprotective agents occurring in the human diet. In addition, its metal complexes play fundamental roles in biological systems. Nevertheless, research on the properties of CFA with lanthanide metals is very scarce, and little to no chemical or biological information is known about these particular systems. Most of their properties, including their biological activity and environmental impact, strictly depend on their structure, stability, and solution behaviour. In this work, a multi-analytical-technique approach was used to study these relationships for the Eu(III)/CFA complex. The synthesized metal complex was studied by FT-IR, FT-Raman, elemental, and thermal (TGA) analysis. In order to examine the chemical speciation of the Eu(III)/CFA system in an aqueous solution, several independent potentiometric and spectrophotometric UV-Vis titrations were performed at different M:L (metal:ligand) and pH ratios. The general molecular formula of the synthesized metal complex in the solid state was [Eu(CFA)3(H2O)3]∙2H2O (M:L ratio 1:3), while in aqueous solution the 1:1 species were observed at the optimum pH of 6 ≤ pH ≤ 10, ([Eu(CFA)] and [Eu(CFA)(OH)]−). These results were confirmed by 1H-NMR experiments and electrospray-ionization mass spectrometry (ESI-MS). To evaluate the interaction of Eu(III)/CFA and CFA alone with cell membranes, electrophoretic mobility assays were used. Various antioxidant tests have shown that Eu(III)/CFA exhibits lower antioxidant activity than the free CFA ligand. In addition, the antimicrobial properties of Eu(III)/CFA and CFA against Escherichia coli, Bacillus subtilis and Candida albicans were investigated by evaluation of the minimum inhibitory concentration (MIC). Eu(III)/CFA shows higher antibacterial activity against bacteria compared to CFA, which can be explained by the highly probable increased lipophilicity of the Eu(III) complex.

Highlights

Natural carboxylic acids occur widely in nature
The europium sequestering ability of caffeic acid, an important natural derivative of abundant hydroxycinnamic acids, has been investigated in aqueous solutions and in solid state, in order to obtain some insights on the coordination mode of Caffeic acid (CFA) towards Eu(III)
Eu(III) complexation by CFA affects the biological properties of the ligand, including antioxidant and antimicrobial activity

Summary

Introduction

Natural carboxylic acids occur widely in nature. Among them, polyphenols are carboxylic acidsagents occurresponsible widely in nature.Among them, polyphenols are considered to Natural be the most important for many biological functions.considered to be the most important agents many biologicalPlant phenolics include simple phenols, phenolic acids,responsible flavonoids, for coumarins, stilbenes,functions.Plantand phenolics include simple phenols, acids, flavonoids, coumarins, hydrolysable condensed tannins, lignans, and phenolic lignins. Polyphenols are considered to Natural be the most important for many biological functions. Plant phenolics include simple phenols, phenolic acids,responsible flavonoids, for coumarins, stilbenes,functions. Plantand phenolics include simple phenols, acids, flavonoids, coumarins, hydrolysable condensed tannins, lignans, and phenolic lignins They can be found in the edible stilbenes, hydrolysable and condensed tannins, lignans, They occurrence, can be found in the parts of many plants such as fruits, seeds, leaves, stems,and andlignins. Their edible parts ofstructure, many plants such as fruits, seeds, roots Their occurrence, distribution in plants, biochemical activity andleaves, otherstems, uniqueand properties have distribution in plants, structure, biochemical activity and other unique properties been extensively studied in the field of bioinorganic, food and pharmaceutical chemistry,have been extensively in the field of bioinorganic, activities, food and pharmaceutical chemistry, due to due to their variousstudied biological and pharmacological including antioxidant, theirand various biological and pharmacological activities, including antioxidant, antimicrobial antimicrobial anticancer activities [1]

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