Aggregation of the Dipeptide Leu-Gly in Alcohol-Water Binary Solvents Elucidated from the Solvation Structure for Each Moiety

Alcohol-Induced Denaturation of Hen Egg White Lysozyme Studied by Infrared, Circular Dichroism, and Small-Angle Neutron Scattering

In aqueous binary solvents with fluorinated alcohols, 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), and aliphatic alcohols, ethanol (EtOH) and 2-propanol (2-PrOH), the denaturation of hen egg white lysozyme (HEWL) with increasing alcohol mole fraction xA has been investigated in a wide view from the molecular vibration to the secondary and ternary structures. Circular dichroism (CD) measurement showed that the secondary structure of α-helix content of HEWL increases on adding a small amount of the fluorinated alcohol to the aqueous solution, while the β-sheet content decreases. On the contrary, the secondary structure does not significantly change by the addition of the aliphatic alcohols. Correspondingly, the infrared (IR) spectroscopic measurements revealed that the amide I band red-shifts on the addition of the fluorinated alcohol. However, the band remains unchanged in the aliphatic alcohol systems with increasing alcohol content. To observe the ternary structure of HEWL, small-angle neutron scattering (SANS) experiments with H/D substitution technique have been applied to the HEWL solutions. The SANS experiments were successful in revealing the details of how the geometry of the HEWL changes as a function of xA. The SANS profiles indicated the spherical structure of HEWL in all of the alcohol systems in the xA range examined. The mean radius of HEWL in the two fluorinated alcohol systems increases from ∼16 to ∼18 Å during the change in the secondary structure against the increase in the fluorinated alcohol content. On contrast, the radius does not significantly change in both aliphatic alcohol systems below xA = 0.3 but expands to ∼19 Å as the alcohol content is close to the limitation of the HEWL solubility. According to the present results, together with our knowledge of the alcohol cluster formation and the interaction of the trifluoromethyl (CF3) groups with the hydrophobic moieties of biomolecules, the effects of alcohols on the denaturation of the protein have been discussed on a molecular scale.

YAFAF-Based Hydrogel: Characterization, Mechanism, and Factors Influencing Micro-organization

The YAFAF-based hydrogel was a three-dimensional network cross-linked by grooved fiber bundles. The fiber bundles were formed by entanglement of fibrils with a diameter of 2 nm, and the surface of the fibrils also presented grooves. Spectroscopic analysis revealed that the main secondary structures were β-sheets and β-turns, which led to the grooved feature of fibrils. In comparison of the nuclear magnetic resonance spectra of peptide solutions at 313 and 277 K, the nuclear Overhauser effects can be clearly observed, indicating that hydrogen-bondings and π-π stacking interactions play important roles in self-assembly. The micro-organization of the self-assemblies was affected by the ratio of solvents (x_A) remarkably. Unexpectedly, x_A of 0.05 produced hollow spherical aggregates. The result of these investigations on the mechanism and organization of the YAFAF-based hydrogel can contribute to the development of strategies using hydrogels in the food industry.

Antioxidative, cytotoxic, and antibacterial properties of self-assembled glycine-histidine-based dipeptides with or without silver nanoparticles in bio-inspired film

Recent years have seen much attention being given to self-assembly of dipeptide-based structures, especially to self-regulation of dipeptide structures with different amino acid sequences. In this study we investigated the effects of varying solvent environments on the self-assembly of glycine-histidine (Gly-His) dipeptide structures. First we determined the morphological properties of Gly-His films formed in different solvent environments with scanning electron microscopy and then structural properties with Fourier-transform infrared (FTIR) spectroscopy. In addition, we studied the effects of Gly-His films on silver nanoparticle (AgNP) formation and the antioxidant and cytotoxic properties of AgNPs obtained in this way. We also, assessed antibacterial activities of Gly-His films against Gram-negative Escherichia coli and Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. Silver nanoparticle-decorated Gly-His films were not significantly cytotoxic at concentrations below 2 mg/mL but had antibacterial activity. We therefore believe that AgNP-decorated Gly-His films at concentrations below 2 mg/mL can be used safely against bacteria.