New 2,4-dimethoxyphenyl-based of dithiophosphonic acid derivatives: Synthesis, structural investigations, DFT calculations and assessment of antioxidant and antimicrobial potentials

This study presents a contribution to the existing literature on the synthesis and characterization of new derivatives of perthiophosphonic acid anhydride, namely, 2,4-bis[2,4-dimethoxyphenyl]-1,3-dithia-2,4-diphosphetane 2,4-disulphide. New dithiophosphonic acids, (2,4-methoxyphenyl-(RO)PS2H, R= 2-propyl-, I and R=3methyl-1-butyl-, II), which were synthesized from the reaction of the starting material with 2-propyl alcohol and 3-methyl-1-butyl alcohol, were converted into their corresponding dithiophosphonate salts of the phosphonic acid esters (Ia and IIa). Compounds Ia and IIa react with NiCl2.6H2O to form new nickel(II)dithiophosphonato complexes (Ib and IIb, respectively). The structures of Ia, IIa, Ib and IIb were elucidated by spectroscopic methods. The structures of the complexes with square-plane geometry were also elucidated by single crystal Xray diffraction analysis (SCXRD) and supported by theoretical calculations. Moreover, some DFT studies in the gas phase including the geometrical structures, frontier molecular orbitals, chemical parameters and molecular electrostatic potential (MEP) surfaces were computed for Ib and IIb. The antibacterial activities of Ia and IIa were investigated on gram-positive and gram-negative bacteria, as well as the yeast strain Candida albicans. Of the compounds tested, IIa exhibited a relatively stronger antibacterial activity especially on Listeria monocytogenes, a foodborne pathogen. Weak antimicrobial activities were observed for Ia and IIa on other tested microorganisms, Staphylococcus aureus, Escherichia coli and Candida albicans. Antioxidant studies on Ia and IIa indicated a significantly high free radical scavenging potential.