Salen, reduced salen and N-alkylated salen type compounds: Spectral characterization, theoretical investigation and biological studies

Salen [2,2′-{propane-1,3-diylbis[nitrilo(E)methylylidene]}bis(6-methoxyphenol)], reduced salen [(2,2′-[propane-1,3-diylbis(iminomethylene))]bis(6-methoxyphenol)] and N-alkylated salen [diethyl-2,2′-(propane-1,3-diylbis((2-hydroxy-3-methoxybenzyl) azanediyl))diacetate] compounds have been synthesized and characterized by IR, 1H NMR, 13C NMR and UV–vis. spectroscopy. Molecular geometry of the title compounds in the ground state has been optimized by density functional method (B3LYP) with 6-31G basis set. Vibrational frequencies of the compounds were computed and compared with the experimental values. Tautomeric stability study of salen inferred that the enolimine form is more stable than its ketoenamine form in gas phase. The spectral behavior of salen in polar and nonpolar solvents was examined demonstrate the positive solvatochromism. The synthesized compounds have been studied with respect to their binding to calf thymus DNA showed that there were interactions between the compounds and DNA through a groove binding mode. Furthermore, the DNA cleavage activity of the compounds has been investigated by gel electrophoresis. The antioxidant properties of compounds were evaluated by DPPH method. The N-alkylated compound has a higher DPPH free radical scavenging activity. The antimicrobial activity was investigated on various gram positive and gram negative bacteria.

Graphical abstractSalen type compounds were synthesized and characterized. Molecular geometry of the compounds was optimized by density functional method (B3LYP) with 6-31G basis set. The DNA binding value of the compounds was determined. The antioxidant activity of the compounds was studied using DPPH.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Salen type compounds were synthesized and characterized. ► Frontier molecular orbitals and vibrational frequencies were computed by DFT/B3LYP. ► pH and solvent effects on UV–vis spectra of the compounds were studied. ► DNA binding constants were determined. ► Antioxidant activities were evaluated.