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• A new Schiff base ligand N1, N5-bis[2-hydroxyphenyl]−2-methyl-1,5-diaminopentane is synthesized and characterized. • In-Silico studies of compounds to support the in-vitro results. • The increase in the spacer group in Schiff base compounds increases the biological activities. A novel ONNO donor tetradentate Schiff base ligand N,N' -bis[2- hydroxyphenyl]-2-methyl-1,5-diaminopentane (1) is synthesized and characterized by using 1H, 13C NMR spectroscopy and mass spectrometry. Biological studies on newly synthesized ligand are carried out and results are compared with the biological activities of known Schiff base ligands: N,N' -bis[{2- hydroxyphenyl }]-1,4-diaminobutane (2) and N,N' -bis[{2- hydroxyphenyl }]-1,3-diaminopropane (3). This comparative study highlights the effect of increasing methylene linkage on the biological activity of these ligands. The anti-microbial activities of all three ligands have been screened against two distinct gram-positive and gram-negative bacteria. In-vitro results of this comparative analysis are also supported by comprehensive molecular docking studies with DNA gyrase subunit B protein of gram-positive bacterium S. aureus and FabH–CoA complex of gram-negative bacterium E. coli. Experimental studies reveal that the spacer group plays a vital role in controlling the biological activities of the ligand. These findings are in good agreement with the theoretical findings. The study demonstrates that the biological activity of ligands is enhanced with increments in the number of spacers. Thus, the newly synthesized ligand (1) with the most extended spacer among the three showed the highest biological activity compared to other two ligands, similar to the popular drug Ciprofloxacin. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • We report a simple, cost-effective, eco-sustainable synthesis of fluorescent carbon quantum dots derived from precursor Cissus quadrangularis. • The as-synthesized nitrogen doped-CQDs demonstrated a homogeneous size distribution (4–9 nm), green fluorescent nature, great photo-stability, excellent water solubility, and a quantum yield of around 5 %. • A biodegradable wheat-starch-based bioplastic was employed to fabricate an N-doped CQDs@bioplastic composite to demonstrate its potential applications in quantum dot-based optical displays and down-conversion light emitting diodes. • The influence of different CQD concentrations and pH sensitivity were investigated further utilizing fabricated optical displays and LEDs. Carbon quantum dots (CQDs)-based composites as luminous down-conversion materials are becoming more popular due to several advantages such as steady fluorescence, ease of functionalization, tailoring of emission in the visible range, and so on. We report an inexpensive and environmentally sustainable synthesis of fluorescent nitrogen doped-CQDs produced from Cissus quadrangularis , a low-cost plant precursor with therapeutic value. The morphological, structural, and physicochemical features of the material were carefully investigated. Under UV stimulation (365 nm), almost spherical shaped N-CQDs with an average diameter of 5.1 nm were discovered to generate yellow-green fluorescence, have excellent photostability, and strong water solubility, with a quantum yield of up to 5 %. Furthermore, as a solid-phase dispersion matrix for CQDs, ecologically friendly and biodegradable bioplastic is appealing. The down-conversion of solid-state fluorescence of LEDs and UVC tubes was demonstrated by creating a nanocomposite by inserting N-CQDs into the solid matrix of a wheat starch-based bioplastic. Furthermore, employing constructed quantum dot-based optical displays, down-converted LEDs, and UVC tubes, the impacts of varied CQD concentrations and pH sensitivity were examined. [ABSTRACT FROM AUTHOR]