Evaluating superparamagnetic Ni0.65Zn0.35Fe2-xInxO4 (0≤ x ≤0.24) for Rietveld, magnetometry-Mössbauer, antimicrobial and molecular docking insights

The studies of indium (In 3+ ) doped Ni-Zn spinel ferrite having chemical formula Ni 0.65 Zn 0.35 Fe 2-x In x O 4 (x = 0.00, 0.08, 0.16, and 0.24) prepared by sol-gel combustion technique in which nitrates were used as reducing agents and citric acid as a fuel. The structural, morphological, magnetic, Mössbauer, elastic and antimicrobial properties have been studied by using various techniques like X-ray diffraction (XRD), Fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), superconducting quantum interference device (SQUID) and Mössbauer spectrometer. Rietveld analysis of XRD patterns showed characteristic Bragg's peaks confirming formation of single phase cubic spinel structure with an average particle size of 17–25 nm. FTIR analysis revealed tetrahedral and octahedral configurational modes with cubic symmetry. FESEM supports the formation of spherical, dense and agglomerated nanoparticles. Moreover, TEM images revealed size of nanoparticles to 23 nm and SAED pattern confirmed the polycrystalline nanostructure. The saturation magnetization and magnetic moment at 300 K and 5 K are in the range of 37.72–59.95 emu/gm, 65.29–85.83 emu/gm and 1.70–2.62μ B , 2.76–3.71μ B respectively. The saturation magnetization increased up to x = 0.08 and after that it decreases, attributed to difference in magnetic moments of In 3+ and Fe 3+ ions and explained on the basis of exchange interaction. Field cooled and zero field cooled spectra resemble the M − H results. Mössbauer spectra support VSM results. The lowest pharmacological concentration test showed efficacy against Bacillus subtilis at 245 μg/ml, Escherichia coli at 203 μg/ml and Candida albicans at 315 μg/ml. Molecular docking showed that samples x = 0.08, 0.16, and 0.24 bind the Escherichia coli 30S tetracycline site more favorably than the positive control tetracycline (Δ G docking = −7.20; −7.37; −7.83 vs −6.16 kcal/mol). The sample x = 0.16 also bound the Candida albicans Cdr1 efflux pump more strongly than fluconazole (Δ G docking = −10.05 vs −6.54 kcal/mol). Docking data, thus, implicate ribosomal targeting and efflux suppression as plausible mechanisms of antibacterial effect.