A new trinuclear oxo-centered chromium(III) complex with formula Cr3O(CH3CO2)6(L)(H2O)2 (L = 5-hydroxyflavone, known as primuletin) was synthetized and characterized by ESI mass spectrometry, ...thermogravimetry, and 1H-NMR, UV-Vis, and FTIR spectroscopies. In agreement with the experimental results, DFT calculations indicated that the flavonoid ligand is coordinated to one of the three Cr(III) centers in an O,O-bidentate mode through the 5-hydroxy/4-keto groups. In a comparative study involving the uncoordinated primuletin and its corresponding complex, systematic reactions with the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) showed that antiradical activity increases upon complexation.
A model octapeptide peptide consisting of an alternating sequence of arginine (Arg) and phenylalanine (Phe) residues, namely, Arg-Phe4, was prepared, and its self-assembly in solution studied. The ...simple alternating Arg-Phe4 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.
The trinuclear chromium(III) complex Cr
3
O(CH
3
CO
2
)
6
(L)(H
2
O)
2
(where L is the monoanion of the flavonoid naringenin) was synthesized and characterized. Density functional theory (DFT) ...calculations and quantum theory of atoms in molecules (QTAIM) analysis show that the flavonoid binds to Cr
III
as an O,O-bidentate ligand via the 5-hydroxy and 4-oxo groups. Reactions with 2,2-diphenyl-1-picrylhydrazyl (DPPH) indicate that the antiradical activity of this flavonoid-metal complex is enhanced in comparison with uncoordinated naringenin.
Hybrid-peptide hydrogel arrangements are a promising alternative to obtaining biocompatible structures at the nanoscopic scale. In this work, a new class of hybrid hydrogels was obtained through the ...sol-gel process based on the reaction between an amyloid-like octapeptide sequence RF4 (where R = arginine and F = phenylalanine) covalently bonded with glycine-linked alkoxysilanes, and hybrid silylated polyethylene glycol (PEG). 1H nuclear magnetic resonance (NMR), liquid chromatography-mass spectrometry (LC-MS), and Fourier transform infrared spectroscopy (FTIR) analyses were used, resulting in synthesized precursor/intermediate molecules. The structure of hybrid hydrogel fibers was studied by atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS), where the existence of two regions in the Guinier plot was observed, one being predominantly formed by polymer while the other one by peptide chains. The rheological measurements showed that viscoelastic parameters depend on both the amount of silane peptide in the hydrogel matrix and increased temperature. Also, the FTIR spectra indicated the coexistence of antiparallel and parallel β-sheet structure patterns into amyloid fibril hydrogels, which can be modulated by peptide-silane coupling in each formulation. The analyzed hydrogels showed thixotropic and shear-thinning rheology at physiological pH, leaving open the opportunity to topical drug delivery system applications in the future.
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