A Peptide Amphiphile Organogelator of Polar Organic Solvents

Gelation behavior of short protected peptides in organic medium

Peptide gelators have been widely explored in aqueous systems due to their prevalence in biological and medical applications. However, gelation behavior of peptides is less understood in organic medium, despite the extensive use of organic solvents in solid phase peptide synthesis, hybrid synthesis protocols, and the formation and application of organogels. Here, peptides with a short aqueous gelator sequence, lysine-tyrosine-phenylalanine or KYF, were investigated for the ability to form gels in dichloromethane (DCM) when their side groups are protected. Protected KYF-containing peptides formed gels in DCM at similar concentrations to deprotected KYF peptides in water. Structural characterization via Fourier transform infrared spectroscopy indicated the presence of antiparallel β-sheets in both the protected and the deprotected KYF gels. However, transmission electron microscopy and dynamic light scattering indicated the protected KYF gels in DCM consisted of short, anisotropic particles at the mesoscale, whereas the deprotected KYF gels in water showed entangled fibers. The protected KYF gels in DCM exhibited similar rheological properties to colloidal gels, namely an increasing resistance to flow at higher shear rates, a shear thinning profile, and a gel-to-fluid transition with increasing strain. Altogether, this study provides critical insights on the assembly behavior and structure of a tripeptide motif and its variants in organic medium, which can facilitate optimizing the processing conditions of similar peptides in organic solvents during synthesis or end-use applications.

Hypothesizing the Oleic Acid-Mediated Enhanced and Sustained Transdermal Codelivery of Pregabalin and Diclofenac Adhesive Nanogel: A Proof of Concept

Pregabalin (PG) and diclofenac diethylamine (DEE) are anti-inflammatory molecules that are effective in relieving inflammation and pain associated with musculoskeletal disorders, arthritis, and post-traumatic pain, among others. Intravenous and oral delivery of these two molecules has their limitations. However, the transdermal route is believed to be an alternate viable option for the delivery of therapeutic molecules with desired physicochemical properties. To this end, it is vital to understand the physicochemical properties of these drugs, dosage, and strategies to enhance permeation, thereby surmounting the associated constraints and concurrently attaining a sustained release of these therapeutic molecules when administered in combination. The present work hypothesizes the enhanced permeation and sustained release of pregabalin and diclofenac diethylamine across the skin, entrapped in the adhesive nano-organogel formulation, including permeation enhancers. The solubility studies of pregabalin and diclofenac diethylamine in combination were performed in different permeation enhancers. Oleic acid was optimized as the best permeation enhancer based on in vitro studies. Pluronic organogel containing pregabalin and diclofenac diethylamine with oleic acid was fabricated. Duro-Tak® (87-2196) was added to the organogel formulation as a pressure-sensitive adhesive to sustain the release profile of these two therapeutic molecules. The adhesive organogel was characterized for particle size, scanning electron microscopy, and contact angle measurement. The HPLC method developed for the quantification of the dual drug showed a retention time of 3.84 minutes and 9.69 minutes for pregabalin and diclofenac, respectively. The fabricated nanogel adhesive formulation showed the desired results with particle size and contact angle of 282 ± 57 nm and ≥120⁰, respectively. In vitro studies showed the percentage cumulative release of 24.90 ± 4.65% and 33.29 ± 4.81% for pregabalin and diclofenac, respectively. In order to accomplish transdermal permeation, the suggested hypothesis of fabricating PG and DEE nano-organogel in combination with permeation enhancers will be a viable drug delivery method. In comparison to a traditional gel formulation, oleic acid as a permeation enhancer increased the penetration of both PG and DEE from the organogel formulation. Notably, the studies showed that the use of pressure-sensitive adhesives enabled the sustained release of both PG and DEE.Therefore, the results anticipated the hypothesis that the transdermal delivery of adhesive PG and DEEbased nanogel across the human skin can be achieved to inhibit inflammation and pain.

Unnatural Amino Acid: 4-Aminopyrazolonyl Amino Acid Comprising Tri-Peptides Forms Organogel With Co-Solvent (EtOAc:Hexane)

Ampyrone is an amino-functionalized heterocyclic pyrazolone derivative that possesses therapeutic values such as analgesic, anti-inflammatory, and antipyretics. The chemical structure of ampyrone exhibits excellent hydrogen bonding sites and is considered as the potential scaffold of supramolecular self-assembly. Recently, this molecule has been derived into unnatural amino acids such as aminopyrazolone amino acid and its peptides. This report describes that one of its amino acids, O-alkylated ampyrone, containing hybrid (α/β) peptides forms organogel after sonication at 50–55°C with 0.7–0.9% (w/v) in ethyl acetate: hexane (1:3). The formation/morphology of such organogels is studied by nuclear magnetic resonance Fourier-transform infrared (FT-IR), circular dichroism (CD), scanning electron microscope (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (Powder-XRD), and thermogravimetric analysis (TGA). Energy-minimized conformation of APA-peptides reveals the possibility of intermolecular hydrogen bonding. Hence, APA-peptides are promising peptidomimetics for the organogel-peptides.

Self-assembly of pentapeptides in ethanol to develop organogels

Organogels have a wide variety of applications in the fields of chemistry, electricity, biomedicine and environmental engineering, which call for robust strategies for designing and developing novel organogelators. Here, we reported a pentapeptide, ECAYF, which was capable of forming a self-healing ethanol gel exhibiting viscoelastic and solid-like properties. The ethanol gel of ECAYF was stable for at least several months, suggesting strong non-covalent interactions between ethanol and the peptide in the gel. In the ethanol gel, self-assembled peptide fibrils were found to immobilize the ethanol molecules for gelation. Results also suggested that the EAF-5 peptide adopted H-bonding β-sheet secondary structures, which further assembled into fibrils. Meanwhile, the self-assembly of the ECAYF peptide in mixtures of differently fractioned ethanol and H₂O was observed, which clearly indicated that ethanol promoted the assembly of ECAYF in the solutions. These findings are helpful in understanding the roles of organic solvents as well as the complicated interactions between the solvent and gelator molecules in gelation.

Water-Alcohol Bigels from Fatty Acylated Dipeptides

Peptide-based gels are emerging as an interesting class of biocompatible soft materials. 9-Fluorenylmethoxycarbonyl-protected amino acids and short peptides have gained considerable attention as promising gelators. Peptide amphiphiles, wherein an alkyl chain is appended to a polar peptidic moiety, are another important class of peptide-based gelators. Here, we report the alcohol/water bigels formed by the rather simple fatty acylated dipeptides wherein the peptidic moiety is made up of hydrophobic amino acids, viz., Val, Ile, and Leu. Lauroyl, myristoyl, and palmitoyl were investigated as the N-terminal fatty acyl groups. None of the lauroylated peptides caused gelation of methanol/water and ethanol/water mixtures up to 2 wt % peptide concentration. Eight out of the 27 peptides resulted in distinct bigels. The gels are composed of fibrous aggregates as characterized by electron microscopy. Infrared spectroscopy suggests the β-sheet conformation of the peptidic region in the gels. Using the Ma-IV ethanol/water bigel as the representative gel, entrapment and steady release of the anticancer drug docetaxel are demonstrated. Such bigels from rather simple amphipathic peptides that are easily synthesized and purified through solvent extraction could be attractive gelator candidates with potential application in drug delivery.

Dimensional control of supramolecular assemblies of diacetylene-derived peptide gemini amphiphile: from spherical micelles to foamlike networks

Peptide amphiphiles capable of assembling into multidimensional nanostructures have attracted much attention over the past decade due to their potential applications in materials science. Herein, a novel diacetylene-derived peptide gemini amphiphile with a fluorenylmethyloxycarbonyl (Fmoc) group at the N-terminus is reported to hierarchically assemble into spherical micelles, one-dimensional nanorods, two-dimensional foamlike networks and lamellae. Solvent polarity shows a remarkable effect on the self-assembled structures by changing the balance of four weak noncovalent interactions (hydrogen-bonding, π-π stacking, hydrophobic interaction, and electrostatic repulsion). We also show the time-evolution not only from spherical micelles to helical nanofibers in aqueous solution, but also from branched wormlike micelles to foamlike networks in methanol solution. In this work, the presence of the Fmoc group plays a key role in the self-assembly process. This work provides an efficient strategy for precise morphological control, aiding the future development in materials science.