The presence of lipopolysaccharide and emergence of drug resistance make the treatment of Gramnegative bacterial infections highly challenging. Herein, we present the synthesis and antibacterial activities of cholic acid−peptide conjugates (CAPs), demonstrating that valine− glycine dipeptide-derived CAP 3 is the most effective antimicrobial. Molecular dynamics simulations and structural analysis revealed that a precise intramolecular network of CAP 3 is maintained in the form of evolving edges, suggesting intramolecular connectivity. Further, we found high conformational rigidity in CAP 3 that confers maximum perturbations in bacterial membranes relative to other small molecules. Interestingly, CAP 3-coated catheters did not allow the formation of biofilms in mice, and treatment of wound infections with CAP 3 was able to clear the bacterial infection. Our results demonstrate that molecular conformation and internal connectivity are critical parameters to describe the antimicrobial nature of compounds, and the analysis presented here may serve as a general principle for the design of future antimicrobials.

TEMPO-oxidize nanocellulose (TONC) suspension has been obtained from total chlorine free (TCF) oil palm empty-fruit-bunches (OPEFB) pulp using 4-acetamido-TEMPO (2,2,6,6-tetramethyl piperidin-1-oxyl) mediated oxidation with sodium hypochlorite and sodium bromide in water at 25 °C and pH 10. TONC suspension with varied content from 0.5 to 6% (w/w) reinforced polyvinyl alcohol (PVA) polymer based nanocomposite films were prepared by the casting method. The structural interaction between the TONC and PVA was characterized by the Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that the 4% (w/w) TONC content reinforced nanocomposite exhibited the highest tensile strength and modulus with an increase of 122% and 291% respectively, compared to PVA while the elongation at break decreased about 42.7%. Thermal stability of PVA based nanocomposite films was improved after incorporation of TONC. Incorporation of TONC in PVA film increases its crystallinity due to strongly linking between the hydroxyl groups of materials however considerable decreases beyond 2 wt% loading are observed. TONC incorporation beyond 2 wt% also reduces the melting temperature peaks and enthalpy of nanocomposite films. FT-IR spectra, NMR and SEM indicate that there is interaction between the TONC and PVA.

As mechanisms underpinning the molecular interactions between membrane-targeting antimicrobials and Gram-negative bacterial membranes at atomistic scale remain elusive, we used Cholic Acid (CA)-derived amphiphiles with different hydrophobicity as model antimicrobials and assessed the effect of their conformational flexibility on antimicrobial activity. Relative to other hydrophobic counterparts, compound with hexyl chain (6) showed strongest binding with lipopolysaccharide (LPS) of Gram-negative bacterial membranes and acted as an effective antimicrobial. Biomolecular simulations, validated by complimentary approaches, revealed that specific intra-molecular hydrogen-bonding imparts conformationally rigid character to compound 6. This conformational stability of compound 6 allows minimum but specific interactions of the amphiphile with LPS that are a sum of exothermic processes like electrostatic interactions, membrane insertion and endothermic contributions from disaggregation of LPS. Therefore, our study reveals that membranetargeting mechanism with the help of conformationally selective molecules offers a roadmap for developing future therapeutics against bacterial infections.

The chalcone 3 was synthesized from 3-acetyl-4-hydroxy coumarin and 3-formylchromone by refluxing in ethanol in the presence of a catalytic amount of pyridine. 3 was converted to bipyrazoles 4a-b by treatment with hydrazine and phenylhydrazine. The compounds were screened for their antibacterial activity.