Peptide-based hydrogels are highly promising for various biomedical applications owing to their precise selfassembly, biocompatibility, and sensitivity toward biologically relevant external stimuli. Herein, we report pH-responsive selfassembly and gelation of a highly biocompatible amphiphilic peptide PEP-1. This is an octa-peptide and double mutant of a naturally occurring β-strand peptide fragment of the protein Galectin-1, available in bovine spleen. PEP-1 was synthesized by using the Rink amide resin as the solid support in a homemade apparatus. At pH 7.4, it exhibits spontaneous gelation with very high yield stress of 88.0 Pa and gel-to-sol temperature of 84 °C at C = 2.0 wt %. Microscopy studies revealed entangled fibrillar morphology whereas circular dichroism, Fourier tranform IR, and Thioflavin T assay indicated formation of β-sheet rich secondary structure. The assembled state was found to be stable in neutral pH whereas either decrease or increase in the pH resulted in disassembly owing to the presence of the pH responsive Asp and Lys residues. The gel network showed ability to entrap water-soluble guest molecules such as Calcein which could be selectively released at acidic pH whereas under neutral condition the release was negligible. MTT assay revealed remarkable biocompatibility of the PEP-1 gel as almost 100% cells were alive after 48 h incubation in the presence of PEP-1 (2.0 mg/mL).

This article reports the antimicrobial activity of two segmented amphiphilic polyurethanes, PU-1 and PU-2, containing a primary or secondary amine group, respectively. In acidic water, intrachain H-bonding among the urethanes followed by hierarchical assembly resulted in the formation of capsules (D h = 120 ± 20 and 100 ± 17 nm for PU-1 and PU-2, respectively) with a highly positive surface charge. They showed selective interactions with bacterial cell mimicking liposomes over mammalian cell mimicking liposomes with favorable enthalpy and entropy contributions, which was attributed to the electrostatic interaction and hydrophobic effect. Antimicrobial studies with Escherichia coli revealed very low minimum inhibitory concentration (MIC) values of 7.8 and 15.6 μg/mL for PU-1 and PU-2, respectively, indicating their ability to efficiently kill Gram-negative bacteria. Killing of Gram-positive Staphylococcus aureus was noticed only at C = 500 μg/mL, indicating unprecedented selectivity for E. coli, which was further confirmed by scanning electron microscopy (SEM) studies. Hemolysis assay revealed HC50 values of 453 and 847 μg/mL for PU-1 and PU-2, respectively, which were >50 times higher than their respective MIC values, thus making them attractive antimicrobial materials. Ortho-nitrophenyl-β-galactoside (ONPG) assay and live–dead fluorescence assay confirmed that for both the polymers, a membrane disruption pathway was operative for wrapping of the bacterial membrane, similar to what was proposed for antimicrobial peptides. SEM images of polymer-treated E. coli bacteria helped in visualization of the pore formation and the disrupted membrane structure.

This manuscript reports solvent tunable functional nano-assemblies of an unsymmetrical bola-shaped π-amphiphile (NDI-PY) which consists of a hydrophobic naphthalene-diimide (NDI) chromophore connected to a non-ionic hydrophilic wedge and a pyridine group at its two opposite arms. Importantly, it contains a hydrazide group located at the hydrophobic domain between the NDI-chromophore and the hydrophilic-wedge to drive the supramolecular assembly by directional H-bonding. NDI-PY exhibits spontaneous assembly in water as well as in a highly non-polar solvent like tetra-chloroethylene (TCE) by the synergistic effect of H-bonding and π-stacking interaction. Spectroscopy studies reveal almost identical self-assembly features in water and TCE with critical aggregation concentrations in the range of 0.3 mM, which matches the values obtained from the isothermal calorimetry (ITC) dilution experiment. Differential scanning calorimetry (DSC) experiments reveal a single endothermic peak at 31 °C (ΔH = -12.3 kJ mol) and 40 °C (ΔH = -5.35 kJ mol) for water and TCE, respectively, indicating marginally higher thermal stability in TCE, which is consistent with the FT-IR data, suggesting stronger H-bonding in TCE. Although the molecular assembly features appear to be similar, NDI-PY produces distinctly different mesoscopic structures in water and TCE. In water, it forms vesicles (D = 150-180 nm) with the pyridine groups displayed at the outer surface, while in TCE it generates a transparent gel (CGC = 8.0 mM) with a nanotubular (width ∼50 nm, wall thickness ∼10 nm) morphology. Powder X-ray diffraction studies show clearly different packing structures; in water a single sharp peak at the low angle (d = 19.3 Å, a little shorter than the extended length of the molecule) suggests the formation of a monolayer membrane, while in TCE several sharp peaks appear with the d values maintaining a ratio of 1 : 1/√3 : 1/2 : 1/√7 : 1/3 : 1/√12, indicating the formation of a 2D hexagonal lattice. Photoconductivity measurements reveal moderate electronic conduction in both cases. However, it shows a remarkable enhancement of the life time of the charge-carriers for the nanotubular structure compared to the vesicular morphology. On the other hand, the vesicles in water display antimicrobial activity against Gram-positive S. aureus with a highly promising MIC value of 29.4 μg mL. In contrast, it does not lyse human red blood cells even at as high a concentration as 2.5 mg mL (HC > 2.5 mg mL), implying high selectivity of the NDI-PY vesicles towards bacterial cells over mammalian cells. Display of the pyridine groups at the outer surface of the membrane enables molecular recognition by complementary H-bonding with a carboxylic acid group and thereby facilitates uptake of the attached pyrene chromophores in the NDI-membrane by charge-transfer interaction between the NDI acceptor and the pyrene donor. In fact a Job's plot experiment reveals maximum uptake at a 1 : 1 ratio of the NDI-PY and the pyrene guest, indicating all the pyridine groups are accessi...

Background: Microbes are rich sources of enzymes and esterases are one of the most important classes of enzymes because of their potential for application in the field of food, agriculture, pharmaceuticals and bioremediation. Due to limitations in their cultivation, only a small fraction of the complex microbial communities can be cultured from natural habitats. Thus to explore the catalytic potential of uncultured organisms, the metagenomic approach has turned out to be an effective alternative method for direct mining of enzymes of interest. Based on activity-based screening method, an esterase-positive clone was obtained from metagenomic libraries. Results: Functional screening of a soil metagenomic fosmid library, followed by transposon mutagenesis led to the identification of a 1179 bp esterase gene, estM2, that encodes a 392 amino acids long protein (EstM2) with a translated molecular weight of 43.12 kDa. Overproduction, purification and biochemical characterization of the recombinant protein demonstrated carboxylesterase activity towards short-chain fatty acyl esters with optimal activity for p-nitrophenyl butyrate at pH 8.0 and 37 °C. Amino acid sequence analysis and subsequent phylogenetic analysis suggested that EstM2 belongs to the family VIII esterases that bear modest similarities to class C β-lactamases. EstM2 possessed the conserved S-x-x-K motif of class C β-lactamases but did not exhibit β-lactamase activity. Guided by molecular docking analysis, EstM2 was shown to hydrolyze a wide range of di-and monoesters of alkyl-, aryl-and benzyl-substituted phthalates. Thus, EstM2 displays an atypical hydrolytic potential of biotechnological significance within family VIII esterases. Conclusions: This study has led to the discovery of a new member of family VIII esterases. To the best of our knowledge, this is the first phthalate hydrolase (EstM2), isolated from a soil metagenomic library that belongs to a family possessing β-lactamase like catalytic triad. Based on its catalytic potential towards hydrolysis of both phthalate diesters and phthalate monoesters, this enzyme may find use to counter the growing pollution caused by phthalatebased plasticizers in diverse geological environment and in other aspects of biotechnological applications.

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