Spectral Characterization and Antimicrobial Activity of Chenodeoxycholic Acid Complexes with Zn(II), Mg(II), and Ca(II) Ions

Abstract

Chenodeoxycholic acid (CA) is a naturally occurring bile acid that is produced in the liver from cholesterol. Three CA complexes using Zn(II), Mg(II), and Ca(II) ions were synthesized to examine the chelation tendencies of CA towards these metal ions. The complexation reaction of CA with the metal ions under investigation was conducted with a 1:1 molar ratio (CA to metal) at 60–70 °C in neutralized media, which consisted of a binary solvent of MeOH and H2O (1:1). The resulting CA complexes were characterized using elemental data (metal, H, C, and Cl analysis) and spectral data (UV–visible, FT-IR, and 1H NMR). The results suggested that CA in anion form utilized oxygen atoms of the carboxylate group (-COO−) to capture Zn(II), Mg(II), and Ca(II) ions. This produced complexes with the general compositions of [Zn(CA)(H2O)Cl], [Mg2(CA)2(H2O)4Cl2], and [Ca2(CA)2(H2O)4Cl2]·2H2O, respectively. The Kirby–Bauer disc diffusion assay was then used to explore the bioactivity of the CA complexes toward three fungal species (Aspergillus niger, Candida albicans, and Penicillium sp.), three Gram-positive bacteria (Staphylococcus aureus, Streptococcus pneumoniae, and Bacillus subtilis), and two Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli). The Ca(II) and Mg(II) complexes exhibited marked inhibitory effects on the cell growth of the fungal species Aspergillus niger with potency equal to 127 and 116% of the activity of the positive control, respectively. The Zn(II) and Ca(II) complexes strongly inhibited the growth of Penicillium sp., while the Zn(II) and Mg(II) complexes showed strong growth inhibition towards the Gram-negative species Pseudomonas aeruginosa.