Glycine methyl ester based Schiff base bearing long alkoxy arm and its zinc(II) and copper(II) complexes: Synthesis, mesomorphism, photoluminescence, CT-DNA interaction and DFT study

Abstract

A new photoluminescent mesogenic glycine methyl ester based Schiff base ligand and its zinc(II) and copper(II) complexes have been synthesised. The compounds were characterized by elemental analyses, Fourier transform infrared spectroscopy (FT-IR), 1H, 13C nuclear magnetic resonance (NMR), ultraviolet–visible spectroscopy (UV–Vis), ESI-MS, MALDI-TOF, EDX and thermogravimetric analysis (TGA). The polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) study revealed that the ligand and zinc(II) complex possess SmecticA mesophase on heating but copper(II) complex is non-mesogenic. The optical absorption and fluorescence spectroscopy studies of zinc(II) complex indicate the existence of aggregation/ de-aggregation species in the presence of non-coordinating and coordinating solvents. The Density Functional Theory (DFT) study was carried out using LanL2DZ and 6–31 G (d, p) basis set with meta-hybrid Truhlar's functional M06–2X to obtain a stable, optimized structure, HOMO-LUMO energy gap and chemical hardness. As designed, the combination of both the –CN- and -COO- linkages plays significant role to influence the mesomorphic behaviour as well as biogenic properties of the compounds. The in vitro interactions of the compounds with CT-DNA has been investigated using UV–Vis and fluorescence spectroscopy. To the best of our knowledge, this is one of the few report on DNA binding studies of mesogenic amino acid Schiff base, which is having binding constant in the same range with the gold standard compound, ethidium bromide.