The synthesis, crystal structure and enhanced biological activities of a new calcium(II) complex of alizarin.

A new calcium(II) complex of alizarin (Az-Ca), which is a natural bioactive anthraquinone, was synthesized and characterized by FTIR, ESI-MS and single-crystal X-ray diffraction, which formulated as [Ca(μ2-O-Az)(H2O)2]n (Az-Ca). It crystallizes in the monoclinic crystal system with space group P21/n, featuring a seven-coordinated distorted pentagonal bipyramidal geometry, forming into a one-dimensional (1D) zigzag chain crystal structure. Az-Ca displays selective antibacterial activity against Aeromonas hydrophila (A. hydrophila) with MIC and MBC values of 0.3125 and 0.625 mg/mL, respectively, which is two-fold better than free alizarin. It also shows enhanced antioxidant activities, with IC50 values of 4.86 μM for DPPH, 4.60 μM for ABTS•+, and 1.88 μM for superoxide anion (O2-). Az-Ca also effectively reduces intracellular reactive oxygen species (ROS) in HL-7702 cells. Az-Ca suppresses H2O2-induced oxidative stress and CuSO4-induced neutrophil aggregation in zebrafish models, indicating a concentration-dependent inhibition of neutrophil aggregation. Az-Ca is the first reported calcium complex of alizarin, which shows promising biological applications, and has potential as aquatic antimicrobial agents.