Influence of chirality and sequence in lysine-rich lipopeptide biosurfactants and micellar model colloid systems.

Lipopeptides can self-assemble into diverse nanostructures which can be programmed to incorporate peptide sequences to achieve a remarkable range of bioactivities. Here, the influence of peptide sequence and chirality on micelle structure and interactions is investigated in a series of lipopeptides bearing two lysine or D-lysine residues and tyrosine or tryptophan residues, attached to a hexadecyl lipid chain. All molecules self-assemble into micelles above a critical micelle concentration (CMC). Small-angle x-ray scattering (SAXS) is used to probe micelle shape and structure from the form factor and to probe inter-micellar interactions via analysis of structure factor. The CMC is obtained consistently from surface tension and electrical conductivity measurements. We introduce a method to obtain the zeta potential from the SAXS structure factor which is in good agreement with directly measured values. Atomistic molecular dynamics simulations provide insights into molecular packing and conformation within the lipopeptide micelles which constitute model self-assembling colloidal systems and biomaterials.

Cyclodextrin-Induced Suppression of the Crystallization of Low-Molar-Mass Poly(ethylene glycol).

We examine the effect of alpha-cyclodextrin (αCD) on the crystallization of poly(ethylene glycol) (PEG) [poly(ethylene oxide), PEO] in low-molar-mass polymers, with M w = 1000, 3000, or 6000 g mol-1. Differential scanning calorimetry (DSC) and simultaneous synchrotron small-/wide-angle X-ray scattering (SAXS/WAXS) show that crystallization of PEG is suppressed by αCD, provided that the cyclodextrin content is sufficient. The PEG crystal structure is replaced by a hexagonal mesophase of αCD-threaded polymer chains. The αCD threading reduces the conformational flexibility of PEG and, hence, suppresses crystallization. These findings point to the use of cyclodextrin additives as a powerful means to tune the crystallization of PEG (PEO), which, in turn, will impact bulk properties including biodegradability.

Minimal Peptide Sequences That Undergo Liquid-Liquid Phase Separation via Self-Coacervation or Complex Coacervation with ATP.

The simple (self-)coacervation of the minimal tryptophan/arginine peptide sequences W2R2 and W3R3 was observed in salt-free aqueous solution. The phase diagrams were mapped using turbidimetry and optical microscopy, and the coacervate droplets were imaged using confocal microscopy complemented by cryo-TEM to image smaller droplets. The droplet size distribution and stability were probed using dynamic light scattering, and the droplet surface potential was obtained from zeta potential measurements. SAXS was used to elucidate the structure within the coacervate droplets, and circular dichroism spectroscopy was used to probe the conformation of the peptides, a characteristic signature for cation-π interactions being present under conditions of coacervation. These observations were rationalized using a simple model for the Rayleigh stability of charged coacervate droplets, along with atomistic molecular dynamics simulations which provide insight into stabilizing π-π stacking interactions of tryptophan as well as arginine-tryptophan cation-π interactions (which modulate the charge of the tryptophan π-electron system). Remarkably, the dipeptide WR did not show simple coacervation under the conditions examined, but complex coacervation was observed in mixtures with ATP (adenosine triphosphate). The electrostatically stabilized coacervation in this case provides a minimal model for peptide/nucleotide membraneless organelle formation. These are among the simplest model peptide systems observed to date able to undergo either simple or complex coacervation and are of future interest as protocell systems.

Chirality and pH Influence the Self-Assembly of Antimicrobial Lipopeptides with Diverse Nanostructures.

Chirality plays a crucial role in the self-assembly of biomolecules in nature. Peptides show chirality-dependent conformation and self-assembly. Lipidation of peptides occurs in vivo and has recently been exploited in designed conjugates to drive self-assembly and enhance bioactivity. Here, a library of pH-responsive homochiral and heterochiral lipidated tripeptides has been designed. The designed lipopeptides comprise homochiral C16-YKK or C16-WKK (where all the amino acids are l-isomers), and two heterochiral conjugates C16-Ykk and C16-Wkk (where the two lysines are d-isomers). The self-assembly of all the synthesized lipopeptides in aqueous solution was examined using a combination of spectroscopic methods along with cryogenic-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS). Interestingly, it was observed that at acidic pH all the lipopeptides self-assemble into micelles, whereas at basic pH the homochiral lipopeptides self-assemble into nanofibers, whereas the heterochiral lipopeptides self-assemble into nanotapes and nanotubes. A pH switch was demonstrated using a thioflavin T fluorescence probe of ß-sheet structure present in the extended structures at pH 8. We demonstrate that both chirality and pH in lipopeptides influence the self-assembly behavior of the model tripeptides, which also show promising bioactivity. Good cytocompatibility is observed in hemolytic assays and antimicrobial activity against both Gram-negative and Gram-positive bacteria is shown through the determination of minimum inhibition concentration (MIC) and minimum bactericidal concentration (MBC) values and live/dead bacteria staining assay.

pH-Induced conversion of bolaamphiphilic vesicles to reduction-responsive nanogels for enhanced Nile Red and Rose Bengal delivery.

This study details the preparation and investigation of molecular nanogels formed by the self-assembly of bolaamphiphilic dipeptide derivatives containing a reduction-sensitive disulfide unit. The described bolaamphiphiles, featuring amino acid terminal groups, generate cationic vesicles at pH 4, which evolve into gel-like nanoparticles at pH 7. The critical aggregation concentration has been determined, and the nanogels' size and morphology have been characterized through Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). Circular Dichroism (CD) spectroscopy reveals substantial molecular reconfigurations accompanying the pH shift. These nanogels enhance the in vitro cellular uptake of the lipophilic dye Nile Red and the ionic photosensitizer Rose Bengal into Human colon adenocarcinoma (HT-29) cells, eliminating the need for organic co-solvents in the former case. Fluorescence measurements with Nile Red as a probe indicate the reduction-sensitive disassembly of the nanogels. In photodynamic therapy (PDT) applications, Rose Bengal-loaded nanogels demonstrate notable improvements, with flow cytometry analysis evidencing increased apoptotic activity in the study with HT-29 cells.

Cyclodextrin-Induced Suppression of PEG Crystallization from the Melt in a PEG-Peptide Conjugate.

The influence of alpha-cyclodextrin (αCD) on PEG crystallization is examined for a peptide-PEG conjugate, YYKLVFF-PEG3k comprising an amyloid peptide YYKLVFF linked to PEG with molar mass 3 kg mol-1. Remarkably, differential scanning calorimetry (DSC) and simultaneous synchrotron small-angle/wide-angle X-ray scattering (SAXS/WAXS) show that crystallization of PEG is suppressed by αCD, provided that the cyclodextrin content is sufficient. A hexagonal mesophase is formed instead. The αCD threading reduces the conformational flexibility of PEG, and hence suppresses crystallization. These results show that addition of cyclodextrins can be used to tune the crystallization of peptide-polymer conjugates and potentially other polymer/biomolecular hybrids.

Comparison of the self-assembly and cytocompatibility of conjugates of Fmoc (9-fluorenylmethoxycarbonyl) with hydrophobic, aromatic, or charged amino acids.

The self-assembly in aqueous solution of three Fmoc-amino acids with hydrophobic (aliphatic or aromatic, alanine or phenylalanine) or hydrophilic cationic residues (arginine) is compared. The critical aggregation concentrations were obtained using intrinsic fluorescence or fluorescence probe measurements, and conformation was probed using circular dichroism spectroscopy. Self-assembled nanostructures were imaged using cryo-transmission electron microscopy and small-angle X-ray scattering (SAXS). Fmoc-Ala is found to form remarkable structures comprising extended fibril-like objects nucleating from spherical cores. In contrast, Fmoc-Arg self-assembles into plate-like crystals. Fmoc-Phe forms extended structures, in a mixture of straight and twisted fibrils coexisting with nanotapes. Spontaneous flow alignment of solutions of Fmoc-Phe assemblies is observed by SAXS. The cytocompatibility of the three Fmoc-amino acids was also compared via MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] mitochondrial activity assays. All three Fmoc-amino acids are cytocompatible with L929 fibroblasts at low concentration, and Fmoc-Arg shows cell viability up to comparatively high concentration (0.63 mM).

Self-Assembly and Antimicrobial Activity of Lipopeptides Containing Lysine-Rich Tripeptides.

The conformation and self-assembly of two pairs of model lipidated tripeptides in aqueous solution are probed using a combination of spectroscopic methods along with cryogenic-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS). The palmitoylated lipopeptides comprise C16-YKK or C16-WKK (with two l-lysine residues) or their respective derivatives containing d-lysine (k), i.e., C16-Ykk and C16-Wkk. All four molecules self-assemble into spherical micelles which show structure factor effects in SAXS profiles due to intermicellar packing in aqueous solution. Consistent with micellar structures, the tripeptides in the coronas have a largely unordered conformation, as probed using spectroscopic methods. The molecules are found to have good cytocompatibility with fibroblasts at sufficiently low concentrations, although some loss of cell viability is noted at the highest concentrations examined (above the critical aggregation concentration of the lipopeptides, determined from fluorescence dye probe measurements). Preliminary tests also showed antimicrobial activity against both Gram-negative and Gram-positive bacteria.

Self-Assembly and Cytocompatibility of Amino Acid Conjugates Containing a Novel Water-Soluble Aromatic Protecting Group.

There has been considerable interest in peptides in which the Fmoc (9-fluorenylmethoxycarbonyl) protecting group is retained at the N-terminus, since this bulky aromatic group can drive self-assembly, and Fmoc-peptides are biocompatible and have applications in cell culture biomaterials. Recently, analogues of new amino acids with 2,7-disulfo-9-fluorenylmethoxycarbonyl (Smoc) protecting groups have been developed for water-based peptide synthesis. Here, we report on the self-assembly and biocompatibility of Smoc-Ala, Smoc-Phe and Smoc-Arg as examples of Smoc conjugates to aliphatic, aromatic, and charged amino acids, respectively. Self-assembly occurs at concentrations above the critical aggregation concentration (CAC). Cryo-TEM imaging and SAXS reveal the presence of nanosheet, nanoribbon or nanotube structures, and spectroscopic methods (ThT fluorescence circular dichroism and FTIR) show the presence of ß-sheet secondary structure, although Smoc-Ala solutions contain significant unaggregated monomer content. Smoc shows self-fluorescence, which was used to determine CAC values of the Smoc-amino acids from fluorescence assays. Smoc fluorescence was also exploited in confocal microscopy imaging with fibroblast cells, which revealed its uptake into the cytoplasm. The biocompatibility of these Smoc-amino acids was found to be excellent with zero cytotoxicity (in fact increased metabolism) to fibroblasts at low concentration.

Effect of molar ratio and concentration on the rheological properties of two-component supramolecular hydrogels: tuning of the morphological and drug releasing behaviour.

Self-assembled supramolecular hydrogels offer great potential as biomaterials and drug delivery systems. Specifically, peptide-based multicomponent hydrogels are promising materials due to their advantage that their mechanical and physical properties can be tuned to enhance their functionalities and broaden their applications. Herein, we report two-component assembly and formation of hydrogels containing inexpensive complementary anionic, BUVV-OH (A), and cationic, KFFC12 (B), peptide amphiphiles. Individually, neither of these components formed a hydrogel, while mixtures with compositions 1 : 1, 1 : 2, and 2 : 1 (molar ratio) as A : B show hydrogel formation (Milli-Q water, at pH = 6.79). These hydrogels displayed a good shear-thinning behaviour with different mechanical stabilities and nano-fibrous network structures. The 1 : 1 hydrogel shows good cell viability for human embryonic kidney (HEK-293) cells and CHO cells indicating its non-cytotoxicity. The biocompatible, thixotropic 1 : 1 hydrogel with a nanofiber network structure shows the highest mechanical strength with a storage modulus of 3.4 × 103 Pa. The hydrogel is able to encapsulate drugs including antibiotics amoxicillin and rifampicin, and anticancer drug doxorubicin, and it exhibits sustainable release of 76%, 70%, and 81% respectively in vitro after 3 days. The other two mixtures (composition 1 : 2 and 2 : 1) are unable to form a hydrogel when they are loaded with these drugs. Interestingly, it is noticed that with an increase in concentration, the mechanical strength of a 1 : 1 hydrogel is significantly enhanced, showing potential that may act as a scaffold for tissue engineering. The two-component gel offers tunable mechanical properties, thixotropy, injectability, and biocompatibility and has great potential as a scaffold for sustained drug release and tissue engineering.

Tuning the Solution Self-Assembly of a Peptide-PEG (Polyethylene Glycol) Conjugate with α-Cyclodextrin.

Cyclodextrins are saccharide ring molecules which act as host cavities that can encapsulate small guest molecules or thread polymer chains. We investigate the influence of alpha-cyclodextrin (αCD) on the aqueous solution self-assembly of a peptide-polymer conjugate YYKLVFF-PEG3K previously studied by our group [Castelletto et al., Polym. Chem., 2010, 1, 453-459]. This conjugate comprises a designed amyloid-forming peptide YYKLVFF that contains the KLVFF sequence from Amyloid ß peptide, Aß16-20, along with two aromatic tyrosine residues to enhance hydrophobicity, as well as polyethylene glycol PEG with molar mass 3 kg mol-1 . The conjugate self-assembles into ß-sheet fibrils in aqueous solution. Here we show that complexation with αCD instead generates free-floating nanosheets in aqueous solution (with a ß-sheet structure). The nanosheets comprise a bilayer with a hydrophobic peptide core and highly swollen PEG outer layers. The transition from fibrils to nanosheets is driven by an increase in the number of αCD molecules threaded on the PEG chains, as determined by 1 H NMR spectroscopy. These findings point to the use of cyclodextrin additives as a powerful means to tune the solution self-assembly in peptide-polymer conjugates and potentially other polymer/biomolecular hybrids.

Small-angle scattering techniques for peptide and peptide hybrid nanostructures and peptide-based biomaterials.

The use of small-angle scattering (SAS) in the study of the self-assembly of peptides and peptide conjugates (lipopeptides, polymer-peptide conjugates and others) is reviewed, highlighting selected research that illustrates different methods and analysis techniques. Both small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) are considered along with examples that exploit their unique capabilities. For SAXS, this includes the ability to perform rapid measurements enabling high throughput or fast kinetic studies and measurements under dilute conditions. For SANS, contrast variation using H2O/D2O mixtures enables the study of peptides interacting with lipids and TR-SANS (time-resolved SANS) studies of exchange kinetics and/or peptide-induced structural changes. Examples are provided of studies measuring form factors of different self-assembled structures (micelles, fibrils, nanotapes, nanotubes etc) as well as structure factors from ordered phases (lyotropic mesophases), peptide gels and hybrid materials such as membranes formed by mixing peptides with polysaccharides or peptide/liposome mixtures. SAXS/WAXS (WAXS: wide-angle x-ray scattering) on peptides and peptide hybrids is also discussed, and the review concludes with a perspective on potential future directions for research in the field.

DNA-templated self-assembly of bradykinin into bioactive nanofibrils.

Bradykinin (BK) is a peptide hormone that plays a crucial role in blood pressure control, regulates inflammation in the human body, and has recently been implicated in the pathophysiology of COVID-19. In this study, we report a strategy for fabricating highly ordered 1D nanostructures of BK using DNA fragments as a template for self-assembly. We have combined synchrotron small-angle X-ray scattering and high-resolution microscopy to provide insights into the nanoscale structure of BK-DNA complexes, unveiling the formation of ordered nanofibrils. Fluorescence assays hint that BK is more efficient at displacing minor-groove binders in comparison with base-intercalant dyes, thus, suggesting that interaction with DNA strands is mediated by electrostatic attraction between cationic groups at BK and the high negative electron density of minor-grooves. Our data also revealed an intriguing finding that BK-DNA complexes can induce a limited uptake of nucleotides by HEK-293t cells, which is a feature that has not been previously reported for BK. Moreover, we observed that the complexes retained the native bioactivity of BK, including the ability to modulate Ca2+ response into endothelial HUVEC cells. Overall, the findings presented here demonstrate a promising strategy for the fabrication of fibrillar structures of BK using DNA as a template, which keep bioactivity features of the native peptide and may have implications in the development of nanotherapeutics for hypertension and related disorders.

Effect of Glycosylation on Self-Assembly of Lipid A Lipopolysaccharides in Aqueous Solutions.

Lipopolysaccharides (LPSs) based on lipid A produced by bacteria are of interest due to their bioactivity in stimulating immune responses, as are simpler synthetic components or analogues. Here, the self-assembly in water of two monodisperse lipid A derivatives based on simplified bacterial LPS structures is examined and compared to that of a native Escherichia coli LPS using small-angle X-ray scattering and cryogenic transmission electron microscopy. The critical aggregation concentration is obtained from fluorescence probe experiments, and conformation is probed using circular dichroism spectroscopy. The E. coli LPS is found to form wormlike micelles, whereas the synthetic analogues bearing six lipid chains and with four or two saccharide head groups (Kdo2-lipid A and monophosphoryl lipid A) self-assemble into nanosheets or vesicles, respectively. These observations are rationalized by considering the surfactant packing parameter.

Histidine-Containing Amphiphilic Peptide-Based Non-Cytotoxic Hydrogelator with Antibacterial Activity and Sustainable Drug Release.

A histidine-based amphiphilic peptide (P) has been found to form an injectable transparent hydrogel in phosphate buffer solution over a pH range from 7.0 to 8.5 with an inherent antibacterial property. It also formed a hydrogel in water at pH = 6.7. The peptide self-assembles into a nanofibrillar network structure which is characterized by high-resolution transmission electron microscopy, field-emission scanning electron microscopy, atomic force microscopy, small-angle X-ray scattering, Fourier-transform infrared spectroscopy, and wide-angle powder X-ray diffraction. The hydrogel exhibits efficient antibacterial activity against both Gram-positive bacteria Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli). The minimum inhibitory concentration of the hydrogel ranges from 20 to 100 µg/mL. The hydrogel is capable of encapsulation of the drugs naproxen (a non-steroidal anti-inflammatory drug), amoxicillin (an antibiotic), and doxorubicin, (an anticancer drug), but, selectively and sustainably, the gel releases naproxen, 84% being released in 84 h and amoxicillin was released more or less in same manner with that of the naproxen. The hydrogel is biocompatible with HEK 293T cells as well as NIH (mouse fibroblast cell line) cells and thus has potential as a potent antibacterial and drug releasing agent. Another remarkable feature of this hydrogel is its magnification property like a convex lens.

Cell Adhesion Motif-Functionalized Lipopeptides: Nanostructure and Selective Myoblast Cytocompatibility.

The conformation and self-assembly of four lipopeptides, peptide amphiphiles comprising peptides conjugated to lipid chains, in aqueous solution have been examined. The peptide sequence in all four lipopeptides contains the integrin cell adhesion RGDS motif, and the cytocompatibility of the lipopeptides is also analyzed. Lipopeptides have either tetradecyl (C14, myristyl) or hexadecyl (C16, palmitoyl) lipid chains and peptide sequence WGGRGDS or GGGRGDS, that is, with either a tryptophan-containing WGG or triglycine GGG tripeptide spacer between the bioactive peptide motif and the alkyl chain. All four lipopeptides self-assemble above a critical aggregation concentration (CAC), determined through several comparative methods using circular dichroism (CD) and fluorescence. Spectroscopic methods [CD and Fourier transform infrared (FTIR) spectroscopy] show the presence of ß-sheet structures, consistent with the extended nanotape, helical ribbon, and nanotube structures observed by cryogenic transmission electron microscopy (cryo-TEM). The high-quality cryo-TEM images clearly show the coexistence of helically twisted ribbon and nanotube structures for C14-WGGRGDS, which highlight the mechanism of nanotube formation by the closure of the ribbons. Small-angle X-ray scattering shows that the nanotapes comprise highly interdigitated peptide bilayers, which are also present in the walls of the nanotubes. Hydrogel formation was observed at sufficiently high concentrations or could be induced by a heat/cool protocol at lower concentrations. Birefringence due to nematic phase formation was observed for several of the lipopeptides, along with spontaneous flow alignment of the lyotropic liquid crystal structure in capillaries. Cell viability assays were performed using both L929 fibroblasts and C2C12 myoblasts to examine the potential uses of the lipopeptides in tissue engineering, with a specific focus on application to cultured (lab-grown) meat, based on myoblast cytocompatibility. Indeed, significantly higher cytocompatibility of myoblasts was observed for all four lipopeptides compared to that for fibroblasts, in particular at a lipopeptide concentration below the CAC. Cytocompatibility could also be improved using hydrogels as cell supports for fibroblasts or myoblasts. Our work highlights that precision control of peptide sequences using bulky aromatic residues within "linker sequences" along with alkyl chain selection can be used to tune the self-assembled nanostructure. In addition, the RGDS-based lipopeptides show promise as materials for tissue engineering, especially those of muscle precursor cells.

Nanostructure Formation and Cell Spheroid Morphogenesis of a Peptide Supramolecular Hydrogel.

Peptide-based hydrogels have attracted much attention due to their extraordinary applications in biomedicine and offer an excellent mimic for the 3D microenvironment of the extracellular matrix. These hydrated matrices comprise fibrous networks held together by a delicate balance of intermolecular forces. Here, we investigate the hydrogelation behavior of a designed decapeptide containing a tetraleucine self-assembling backbone and fibronectin-related tripeptides near both ends of the strand. We have observed that this synthetic peptide can produce hydrogel matrices entrapping >99% wt/vol % water. Ultrastructural analyses combining atomic force microscopy, small-angle neutron scattering, and X-ray diffraction revealed that amyloid-like fibrils form cross-linked networks endowed with remarkable thermal stability, the structure of which is not disrupted up to temperatures >80 °C. We also examined the interaction of peptide hydrogels with either NIH3T3 mouse fibroblasts or HeLa cells and discovered that the matrices sustain cell viability and induce morphogenesis into grape-like cell spheroids. The results presented here show that this decapeptide is a remarkable building block to prepare highly stable scaffolds simultaneously endowed with high water retention capacity and the ability to instruct cell growth into tumor-like spheroids even in noncarcinoma lineages.

Self-Assembly of Angiotensin-Converting Enzyme Inhibitors Captopril and Lisinopril and Their Crystal Structures.

The peptide angiotensin-converting enzyme inhibitors captopril and lisinopril are unexpectedly shown to exhibit critical aggregation concentration (CAC) behavior through measurements of surface tension, electrical conductivity, and dye probe fluorescence. These three measurements provide similar values for the CAC, and there is also evidence from circular dichroism spectroscopy for a possible conformational change in the peptides at the same concentration. Cryogenic transmission electron microscopy indicates the formation of micelle-like aggregates above the CAC, which can thus be considered a critical micelle concentration, and the formation of aggregates with a hydrodynamic radius of ∼6-7 nm is also evidenced by dynamic light scattering. We also used synchrotron radiation X-ray diffraction to determine the single-crystal structure of captopril and lisinopril. Our results improve the accuracy of previous data reported in the literature, obtained using conventional X-ray sources. We also studied the structure of aqueous solutions containing captopril or lisinopril at high concentrations. The aggregation may be driven by intermolecular interactions between the proline moiety of captopril molecules or between the phenylalanine moiety of lisinopril molecules.

Alpha helical surfactant-like peptides self-assemble into pH-dependent nanostructures.

A designed surfactant-like peptide is shown, using a combination of cryogenic-transmission electron microscopy and small-angle X-ray scattering, to have remarkable pH-dependent self-assembly properties. Peptide Arg3-Leu12 (R3L12) forms a network of peptide nanotubes at pH 9 and below. These are associated with α-helical conformation in a "cross-α" nanotube structure, in which peptide dimers lie perpendicular to the nanotube axis, with arginine coated inner and outer nanotube walls. In contrast, this peptide forms decorated vesicular aggregates at higher pH values, close to the pKa of the arginine residues. These structures are associated with a loss of α-helical order as detected through X-ray scattering, circular dichroism and FTIR spectroscopy, the latter technique also revealing a loss of ordering of leucine side chains. This suggests a proposed model for the decorated or patchy vesicular structures that comprises disordered peptide as the matrix of the membrane, with small domains of ordered peptide dimers forming the minority domains. We ascribe this to a lipid-raft like phase separation process, due to conformational disordering of the leucine hydrophobic chains. The observation of the self-assembly of a simple surfactant-like peptide into these types of nanostructure is remarkable, and peptide R3L12 shows unique pH-dependent morphological and conformational behaviour, with the potential for a range of future applications.

Peptide-Based Gel in Environmental Remediation: Removal of Toxic Organic Dyes and Hazardous Pb2+ and Cd2+ Ions from Wastewater and Oil Spill Recovery.

A dipeptide-based synthetic amphiphile bearing a myristyl chain has been found to form hydrogels in the pH range 6.9-8.5 and organogels in various organic solvents including petroleum ether, diesel, kerosene, and petrol. These organogels and hydrogels have been thoroughly studied and characterized by different techniques including high-resolution transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and rheology. It has been found that the xerogel obtained from the peptide gelator can trap various toxic organic dyes from wastewater efficiently. Moreover, the hydrogel has been used to remove toxic heavy metal ions Pb2+ and Cd2+ from wastewater. Dye adsorption kinetics has been studied, and it has been fitted by using the Freundlich isotherm equation. Interestingly, the gelator amphiphilic peptide gels fuel oil, kerosene, diesel, and petrol in a biphasic mixture of salt water and oil within a few seconds. This indicates that these gels not only may find application in oil spill recovery but also can be used to remove toxic organic dyes and hazardous toxic metal ions from wastewater. Moreover, the gelator can be recycled several times without significant loss of activity, suggesting the sustainability of this new gelator. This holds future promise for environmental remediation by using peptide-based gelators.