Synthesis, spectroscopic characterization, molecular docking, quantum chemical studies, topological analysis (RDG, ELF, LOL), and evaluation of antibacterial and anticancer activities of Thiomorpholinium 4-Nitrobenzoate crystalline salt

• The new proton-transfer crystalline salt (4-NBA-TM) was synthesized from 4-nitro benzoic acid and thiomorpholine . • Experimental studies were conducted by using FT-IR, 1 H NMR, 13 C NMR, and SCXRD. • HSA confirmed the presence of strong and weak noncovalent interactions. • FMO , MEP , NBO , NPO, Molecular Docking, and Topological studies were performed. • 4-NBA-TM exhibited significant antibacterial activity and demonstrated potent antitumor efficacy against the A549 cell line. Thiomorpholinium-4-nitrobenzoate (4-NBA-TM) was effectively synthesized, and single crystals were produced at room temperature by the gradual evaporation approach. The compound was studied using single-crystal X-ray diffraction, Infrared, 1 HNMR , and 13 CNMR spectroscopy. The substance crystallizes within the triclinic space group P-1. The compound's molecular geometry was optimized using the Density Functional Theory (DFT/B3LYP) approach and a 6–31++ G (d,p) basis set in the ground state. The improved geometric parameters correspond well with the results of the X-ray crystallographic study. The energy and charge transport properties of the compound are analyzed in terms of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs). Additionally, the molecular electrostatic potential (MEP), frontier molecular orbitals (FMOs), thermodynamic characteristics, natural bond orbital (NBO) analysis, and Mulliken charge distribution were theoretically evaluated using the same DFT/B3LYP method in the gas phase. The nature of the hydrogen bonding interactions between 4-nitrobenzoic acid and thiomorpholine was examined using the Electron Localization Function (ELF), Localized Orbital Locator (LOL), and non-covalent reduced density gradient (NCI-RDG) analysis. Hirshfeld surface analysis and associated fingerprint plots were visualized to understand the noncovalent interactions and their impact on crystal packing. The antibacterial activities against Gram-positive Staphylococcus aureus and Gram-negative Klebsiella pneumoniae exhibited strong inhibitory capability. Additionally, 4-NBA-TM demonstrated superior activity against the human cervical cancer cell line (HeLa) in bioinformatics analysis as well as in vitro and in silico anticancer investigations. The synthesized compound has also shown significant and effective biological effects in inhibiting the human lung cancer cell line A549.