A model octapeptide peptide consisting of an alternating sequence of arginine (Arg) and phenylalanine (Phe) residues, namely, [Arg-Phe]4, was prepared, and its self-assembly in solution studied. The simple alternating [Arg-Phe]4 peptide sequence allows for unique insights into the aggregation process and the structure of the self-assembled motifs. Fluorescence and UV-vis assays were used to determine critical aggregation concentrations, corresponding to the formation of oligomeric species and β-sheet rich structures organized into both spheroidal aggregates and highly ordered fibrils. Electron and atomic force microscopy images show globular aggregates and long unbranched fibers with diameters ranging from ∼4 nm up to ∼40 nm. Infrared and circular dichroism spectroscopy show the formation of β-sheet structures. X-ray diffraction on oriented stalks show that the peptide fibers have an internal lamellar structure, with an orthorhombic unit cell with parameters a ∼ 27.6 Å, b ∼ 9.7 Å, and c ∼ 9.6 Å. In situ small-angle X-ray scattering (SAXS) shows the presence of low molecular weight oligomers in equilibrium with mature fibers which are likely made up from 5 or 6 intertwined protofilaments. Finally, weak gel solutions are probed under gentle shear, suggesting the ability of these arginine-rich fibers to form networks.

We report for the first time on the self-assembly of nanostructures composed exclusively of alternating positively charged and hydrophobic amino acids. A novel arginine/phenylalanine octapeptide, RF8, was synthesized. Because the low hydrophobicity of this sequence makes its spontaneous ordering through solution-based methods difficult, a recently proposed solid-vapor approach was used to obtain nanometric architectures on ITO/PET substrates. The formation of the nanostructures was investigated under different preparation conditions, specifically, under different gas-phase solvents (aniline, water, and dichloromethane), different peptide concentrations in the precursor solution, and different incubation times. The stability of the assemblies was experimentally studied by electron microscopy and thermogravimetric analysis coupled with mass spectrometry. The secondary structure was assessed by infrared and Raman spectroscopy, and the arrays were found to assume an antiparallel β-sheet conformation. FEG-SEM images clearly reveal the appearance of fibrillar structures that form extensive homogeneously distributed networks. A close relationship between the morphology and preparation parameters was found, and a concentration-triggered mechanism was suggested. Molecular dynamics simulations were performed to address the thermal stability and nature of intermolecular interactions of the putative assembly structure. Results obtained when water is considered as solvent shows that a stable lamellar structure is formed containing a thin layer of water in between the RF8 peptides that is stabilized by H-bonding.

The conjugation between micro/nanotubes of l,l-diphenylalanine and polycaprolactone has led to ductile composite fibers suitable for designing polymer membranes potentially usable as degradable skin patches in drug delivery.

Carbohydrates can be used during SiONPs freeze-drying process to obtain redispersable solids that maintain original sizes without residual aggregation.

We report here the fabrication of a biomimetic sensor for direct oxygen reduction; the sensor consists of multicopper oxidases derived from cyclic-tetrameric copper(II) species containing the ligand (4-imidazolyl)ethylene-2-amino-1-ethylpyridine (apyhist) that are self-assembled with L-diphenylalanine micro/nanostructures (FF-MNTs). The [Cu 4 (apyhist) 4 ] 4+ /FF-MNT complex was immobilized onto the surface of a glassy carbon (GC) electrode by poly ion complex formation with a Nafion film. This hybrid membrane allows regular proton transport to a Cu-based molecular oxygen reduction reaction catalyst, and the imidazole group in the imine ligand (apyhist) acts as a local buffer in the vicinity of the O 2 reducing center, thus aiding the catalyst in retaining its selectivity for 4e − / 4H + oxygen reduction reaction. This nanocomposite provided improved sensing characteristics in the electrode interface with respect to the electroactive surface area, the diffusion coefficient, and the electron transfer kinetics. In addition, the hybrid film [Cu 4 (apyhist) 4 ] 4+ /FF-MNT-coated GC electrode was successfully used as an enzymeless electrochemical sensor for the detection of dissolved oxygen in aqueous media at two concentration intervals, viz., 0.2−3.0 mg L −1 and greater than 3.0 mg L −1 , with sensitivities of 25.0 and 80.2 μA L mg −1 cm −2 , respectively, and a detection limit of 0.1 mg L −1 . Evaluated in terms of relative standard deviation, the repeatability of the proposed sensor was less than 9.0% for ten measurements of a solution of 6.5 mg L −1 oxygen. Experimental efforts were conducted to use this proposed platform for O 2 determination with real samples. Results from theoretical investigations using density functional theory support the hypothesis that the [Cu 4 (apyhist) 4 ] 4+ complex can act as the sole source of protons and electrons in the O 2 reduction reaction.

A novel enzymatic platform for the sensing of H2O2 and glucose that uses L,L-diphenylalanine micro/nanostructures (FF-MNSs) as an enzyme support is shown. This platform is obtained by the self-assembly of poly(allylamine hydrochloride) (PAH), FF-MNSs, and microperoxidase-11 (MP11) anchored onto the peptide matrix, in two different crystal structures of FF-MNSs: hexagonal (P61) and orthorhombic (P22121). The electroactive area of the electrodes increases in the presence of FF-MNSs. We also demonstrate via theoretical calculations that the valence band energy of the orthorhombic structure allows it to be doped, similarly to p-type semiconductors, where PAH acts as a doping agent for the orthorhombic peptide structure, decreasing the band-gap by around 1 eV, which results in a smaller charge transfer resistance. These results are consistent with electrochemical impedance spectroscopy measurements, which further elucidate the role of the band structure of the orthorhombic FF-MNSs in the conductivity and electron transfer rates of the hybrid material. An effective communication between the electrode and the active site of a glucose oxidase enzyme through MP11-protein complexes occurs, paving the way for FF-MNSs in the orthorhombic phase for the future development of bioelectronics sensing devices.

An alternative label-free electrochemical immunosensor for the rapid detection of Leishmania braziliensis was developed by immobilizing a peptide-based probe of the promastigote surface antigen (PSA-38S) onto electrospun polyamide-6 (PA6)/chitosan nanofibers. An increase in chitosan content in the spinning solution leads to a decrease in the diameter of the formed fibers, whereas the differential scanning calorimetry (DSC) and X-ray diffraction (XRD) data showed a decrease in crystallinity upon increasing the chitosan content in the formulation. In addition, the incorporation of chitosan into the PA6 nanofibers tends to decrease the resistance to the charge-transfer process at the electrode surface. A 40 wt % chitosan content was used for immobilization of the peptide antigen, which was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The detection was performed by measuring the relative change in impedance before and after the anti-Leishmania braziliensis reaction by EIS. Under the optimized conditions, the relative change in impedance was proportional to the logarithmic value of PSA concentrations in the range of 2.5 to 10 pg•mL −1 (r 2 = 0.9946) with a detection limit of 0.2 pg•mL −1 , which was slightly lower than that of the enzyme-linked immunosorbent assay. Additionally, the sensor was tested against two nonspecific antibodies (T. cruzi and β-actin), whereas multivariate analysis using unsupervised pattern recognition through principal component analysis was successfully applied to identification of the pattern relative to each antibody. Finally, the optimized electrochemical immunoassay can be a favorable approach for Leishmania detection tests, as it is able to differentiate negative and positive visceral leishmaniasis human serum samples.

2D piezoelectric materials such as transition metal dichalcogenides are attracting significant attention because they offer various benefits over bulk piezoelectrics. In this work, the fabrication of layered biomolecular crystals of diphenylalanine (FF) obtained via a co‐assembly of l,l‐ and d,d‐ enantiomers of FF monomers is reported. Their crystal structure, thermal and chemical stabilities, and piezoelectric properties are investigated. Single crystal X‐ray diffraction results show that FF enantiomers are arranged in the form of bilayers consisting of monomers with alternating chirality packed into a tape‐like monoclinic structure belonging to a polar space group P21. Each bilayer (≈1.5 nm thick) demonstrates strong out‐of‐plane piezoelectricity (d33 ≈ 20 pm V−1) that is almost an order of magnitude higher than in the archetypical piezoelectric material quartz. The grown crystals demonstrate better thermal and chemical stabilities than self‐assembled hexagonal FF nanotubes studied in the past. Piezoelectric bilayers, being held via weak aromatic interaction in the bulk crystals, can be exfoliated by mechanical or chemical methods, thus resulting in a 2D piezoelectric material, which can find various applications in biocompatible and ecologically friendly electromechanical microdevices, such as sensors, actuators, and energy harvesting elements used in implantable and wearable electronics.