Mononuclear Mg(ii) and Ca(ii) metallocarboxylates of N-phthaloyl-γ-aminobutyric acid: synthesis, characterization, ds-DNA binding, preliminary anticancer evaluation against MDA-MB-231 cells, and computational studies.

This study reports the synthesis of neurotransmitter-inspired, biolabile mononuclear Mg(ii)/(NY1) and Ca(ii)/(NY2) metallocarboxylates of N-phthaloyl-γ-aminobutyric acid ligand (NPGABA), motivated by the growing relevance of metallocarboxylates in addressing essential metal-ion deficiencies. Extensive spectral (i.e. IR, UV-vis, 1H-NMR, 13C-NMR, AAS, and ICP-AES) and analytical (SEM, micro-analysis and thermal gravimetric analysis) techniques were used to characterize and confirm the formation of the ligand and its metal carboxylate complexes. The complexes were confirmed to have the formulas [Mg(NPGABA)2(H2O)2]4 (NY1) and [Mg(NPGABA)2(H2O)4] (NY2), where NPGABA is the abbreviation of the ligand in its deprotonated form. The DNA-binding interactions of the NPGABA ligand (NY0) and its alkaline earth metal carboxylate complexes with magnesium (Mg/NY1) and calcium (Ca/NY2) were investigated through a combination of biophysical, computational, and biological assays. UV-visible absorption studies revealed a significant hyperchromic effect without a bathochromic/hypsochromic shift, indicative of a non-intercalative external binding mode (i.e., minor groove binding or electrostatic interaction with the anionic sugar phosphate backbone of DNA). Binding constants (K b) were calculated by UV-vis spectroscopy at a temperature of 310.15 K and pH of 7.4 as 2.18 × 105 M-1 (NY0), 4.05 × 105 M-1 (NY1), and 4.21 × 105 M-1 (NY2), with Gibbs free energies (ΔG°) of -31.68, -33.28, and -33.38 kJ mol-1, respectively, confirming spontaneous interactions. Similarly, fluorescence emission spectroscopic studies demonstrated eminent quenching without any shift, providing complementary evidence for the presence of external non-intercalative interactions. Accordingly, the binding constants (K b) calculated by this technique under the same physiological conditions were 1.2 × 104 M-1 (NY0), 4.41 × 104 M-1 (NY1), and 8.61 × 104 M-1 (NY2), with binding site numbers of 0.86 (NY0), 0.95 (NY1), and 1.01 (NY2) and Gibbs free energies (ΔG°) of -24.23, -27.56, and -29.27 kJ mol-1, respectively, confirming the spontaneity of the interaction process. Molecular docking simulations against the canonical B-DNA (PDB: 1BNA) and the aromatase cytochrome P450 enzyme (PDB: 3EQM) also supported the occurrence of non-intercalative external binding interactions, with NY2 demonstrating the most favorable binding pose and energy. This non-intercalative external binding interaction was further endorsed by minute perturbation in the DNA solution viscosity and analogical consistency with classical groove binders like netropsin and distamycin A (K b ≈ 105-107 M-1). The observed DNA binding affinity trend (NY2 > NY1 > NY0) has a direct correlation with the cytotoxic potency of the investigated compounds against triple negative breast cancer cells (MDA-MB-231). This consolidated investigation proved NY2 as a non-intercalative DNA-binding small molecule with preliminary anticancer activity, offering a strategic route for developing sustainable metallocarboxylate-based therapeutics.