The structural characterization and biological activity of sulfamethoxazolyl-azo-p-cresol, its copper(ii) complex and their theoretical studies

Abstract

(E)-4-((2-Hydroxy-5-methylphenyl)diazenyl)-N-(5-methylisoxazole-3-yl)benzene sulfonamide (SMX-NN-C₆H₃(p-Me)-OH, 1) and its Cu(II) complex, [Cu(SMX-NN-C₆H₃(p-Me)-O)₂]_n (2), have been characterized by spectroscopic data and single crystal X-ray diffraction studies. The supramolecular 1D chain of 1 is constituted by inter- and intra-molecular hydrogen bonds and also by π⋯π interactions of aromatic rings. Complex 2 has a tetragonally distorted octahedral structure in which ligand 1 serves as an N,O chelator and forms a planar Cu(N,O)₂ motif; two axial positions are occupied by the oxazolyl-N of neighbouring units and a 3D structure is formed. The biological activities of these compounds have been evaluated against Gram positive (B. subtilis; IC₅₀: 105 μg ml⁻¹ (1) and 105 μg ml⁻¹ (2)) and Gram negative bacteria (E. coli; IC₅₀: 66.36 μg ml⁻¹ (1) and 62.2 μg ml⁻¹ (2)) and the complexes exhibit better efficiency. Interactions of DNA with 1 and 2 have been examined and the binding constants are K_b(1), 5.920 × 10⁴ M⁻¹ and K_b(2), 4.445 × 10⁴ M⁻¹. The in silico test is used to predict the most favoured binding mode of 1 and 2 with the active site residues of DHPS (dihydropteroate synthetase) of E. coli and of DNA. The Cu(II) complex (2) binds more efficiently (CDOCKER energy, 2, −61.35 a.u.) in the DHPS cavity than ligand 1 (CDOCKER energy, 1, −43.90 a.u.). The electronic structures and spectral properties of 1 and 2 have been investigated by DFT and TD-DFT computation of optimized geometries of the compounds.