Histidine-based hydrogels via singlet-oxygen photooxidation.

The formation of hydrogels by photosensitized oxidation and crosslinking of histidine-derived polymers is demonstrated for the first time. The photooxidation of pendant His mediated by singlet oxygen was used to promote covalent coupling by its dimerization. As a proof-of-concept, two systems were studied: (i) chondroitin sulfate (CS) functionalized with His, and (ii) an elastin-like peptide (ELP) containing His produced by recombinant techniques. Both materials were crosslinked by irradiation at 425 nm in the presence of Zn-porphyrin derivatives yielding His-based hydrogels. The molecular structure and physicochemical properties of ELP-His and other 5 ELPs with photooxidizable amino acids were studied in silica by computer simulation. A correlation between the protein conformation and its elastic properties is discussed. CS-His hydrogels demonstrate larger storage moduli than ELPs with other amino acids. The obtained results show the potential use of photooxidation to create a new type of His-based hydrogels.

Freeze-drying of silica nanoparticles: redispersibility toward nanomedicine applications.

AIM: To study freeze-drying of silica nanoparticles (SiO2NPs) in order to find suitable conditions to produce lyophilized powders with no aggregation after resuspension and storage. METHODS: SiO2NPs were synthesized using a Stöber-based procedure, and characterized by scanning electron microscopy, dynamic light scattering and nitrogen adsorption/desorption isotherms. SiO2NPs hydrodynamic diameters were compared prior and after freeze-drying in the presence/absence of carbohydrate protectants. RESULTS: Glucose was found to be the most suitable protectant against the detrimental effects of lyophilization. The minimum concentration of carbohydrate required to effectively protect SiO2NPs from aggregation during freeze-drying is influenced by the nanoparticle's size and texture. Negligible aggregation was observed during storage. CONCLUSION: Carbohydrates can be used during SiO2NPs freeze-drying process to obtain redispersable solids that maintain original sizes without residual aggregation.

Self-Assembly of a Designed Alternating Arginine/Phenylalanine Oligopeptide.

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 ß-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 ß-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.

Self-assembly of Arg-Phe nanostructures via the solid-vapor phase method.

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 ß-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.