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).

Herein, we report the rich morphological and conformational versatility of ab iologically active peptide (PEP-1), whichf ollows diverse self-assembly pathwayst o form up to six distinct nanostructures and up to four different secondary structures through subtle modulation in pH, concentration and temperature. PEP-1 forms twisted b-sheet secondary structures and nanofibers at pH 7.4, which transform into fractal-like structures with strong b-sheet conformations at pH 13.0 or short disorganized elliptical aggregates at pH 5.5. Upon dilution at pH 7.4, the nanofibers with twisted bsheet secondary structural elements convert into nanoparticles with random coil conformations.I nterestingly,t hese two selfassembled states at pH 7.4 and room temperature are kinetically controlled and undergo af urther transformation into thermodynamically stable states upon thermal annealing: whereas the twisted b-sheet structures and corresponding nanofibers transform into 2D sheets with well-defined b-sheet domains,the nanoparticles with random coil structures convert into short nanorods with a-helix conformations.N otably, PEP-1 also showed high biocompatibility,l ow hemolytic activity and marked antibacterial activity,rendering our system apromising candidate for multiple bio-applications.

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 article elucidates H-bonding-regulated directional supramolecular assembly of naphthalene diimide (NDI)-derived unsymmetric cationic bola-shaped π-amphiphiles and systematic investigations on the thermodynamics of their interaction with bacteria mimic lipid vesicles and antimicrobial activity with mechanistic insights. Four NDIamphiphiles (NDI-1, NDI-2, NDI-3, and NDI-2a) have been studied, all of which contain a central NDI chromophore, a nonionic wedge, an amine containing a head group, and a hydrazide group. In NDI-2 and NDI-2a, the hydrophilic wedge and the head group (pyridine) are the same but the location of the hydrazide group is different. On the basis of this difference, the pyridyl groups are displayed at the outer and inner walls of the vesicle, respectively. Isothermal titration calorimetry (ITC) studies revealed the spontaneous interaction of NDI-2 assembly with bacteria membrane mimic DPPE liposome (ΔG = −6.35 kcal/mol), whereas the NDI-2a assembly did not interact at all, confirming a strong influence of the H-bonding-regulated functional group display. On the other hand, the location of the hydrazide group remains the same in NDI-1, NDI-2, and NDI-3, but they differ in the head group structure. ITC binding studies confirmed spontaneous interaction of all three assemblies with DPPE liposome with negative ΔG values following the order NDI-1 > NDI-2 > NDI-3, indicating significant influence of the structure of the head group on the interaction with the model membrane. In fact, in all cases, the interaction was favorable both by enthalpy and entropy contribution, indicating dual involvement of the electrostatic interaction and hydrophobic effect. Notably, ΔS value for NDI-1 containing a tertiary amine head group was found to be significantly higher than that for NDI-3 containing a primary amine, which is attributed to the enhanced hydrophobic effect in the former case. Furthermore, ITC experiments revealed no interaction by any of these assemblies with the mammalian cell membrane mimic liposome, indicating their high selectivity toward bacterial membranes. Antimicrobial activity studies showed NDI-2 to be lethal selectively against Gram-positive bacteria, whereas NDI-2a did not show any activity. NDI-3 with a primary amine showed moderate activity but no selectivity over the erythrocytes. NDI-1 with the tertiary amine group was found to be the most outstanding candidate, exhibiting broad-spectrum antimicrobial activity with very low minimum inhibitory concentration values of 15.8 and 62 μg/mL for Staphylococcus aureus and Escherichia coli, respectively, and high selectivity over erythrocytes. These results fully corroborate with the physical insights obtained from the ITC studies on their interaction with the model liposome. Control molecules, lacking either the NDI chromophore or the hydrazide nonionic containing wedge, did not exhibit any notable antibacterial activity. Live-dead assay with fluorescence microscopy studies indicated that the antimicrobial activity of NDI-1 operates through the ...

This manuscript reports supramolecular copolymerization of amphiphilic donor (D) and acceptor (A) units and their antibacterial activity.