Mechanical Unfolding of Spectrin Repeats Induces Water-Molecule Ordering

Hemolytic Response of Iron Oxide Magnetic Nanoparticles at the Interface and in Bulk: Extraction of Blood Cells by Magnetic Nanoparticles

Surface-active and water-soluble magnetic nanoparticles (NPs) were synthesized in the presence of a series of amphiphilic molecules of different functional groups to determine the hemolytic response and their ability to extract blood cells across the interface and aqueous bulk while maintaining minimum hemolysis. Amphiphilic molecules such as Gemini surfactants of strong hydrophobicity and low hydrophilic-lipophilic balance produced surface-active magnetic NPs, which were highly cytotoxic even when placed at the blood suspension (aqueous)-air interface. A similar behavior was shown by water-soluble magnetic NPs produced using monomeric ionic and nonionic surfactants and different amino acids. The NPs produced using mild biological surfactants and mono- and oligosaccharides of the same functional group proved to be excellent blood cell extractors with minimum hemolysis. α/β-cyclodextrin and dextrose-stabilized magnetic NPs induced negligible hemolysis and extracted more than 50% of blood cells. The results showed that nontoxic magnetic NPs are excellent blood cell extractors from the blood suspension when tagged with amphiphilic molecules possessing good biocompatibility with cell membranes without inducing hemolysis. The work highlights the biological applicability of nontoxic magnetic NPs at biointerfaces and in blood suspensions.

Energetics and structure of alanine-rich α-helices via adaptive steered molecular dynamics

The energetics and hydrogen bonding profiles of the helix-to-coil transition were found to be an additive property and to increase linearly with chain length, respectively, in alanine-rich α-helical peptides. A model system of polyalanine repeats was used to establish this hypothesis for the energetic trends and hydrogen bonding profiles. Numerical measurements of a synthesized polypeptide Ac-Y(AEAAKA)kF-NH2 and a natural α-helical peptide a2N (1-17) provide evidence of the hypothesis's generality. Adaptive steered molecular dynamics was employed to investigate the mechanical unfolding of all of these alanine-rich polypeptides. We found that the helix-to-coil transition is primarily dependent on the breaking of the intramolecular backbone hydrogen bonds and independent of specific side-chain interactions and chain length. The mechanical unfolding of the α-helical peptides results in a turnover mechanism in which a 310-helical structure forms during the unfolding, remaining at a near constant population and thereby maintaining additivity in the free energy. The intermediate partially unfolded structures exhibited polyproline II helical structure as previously seen by others. In summary, we found that the average force required to pull alanine-rich α-helical peptides in between the endpoints-namely the native structure and free coil-is nearly independent of the length or the specific primary structure.