Ion-specific nanoscale compaction of cysteine-modified poly(acrylic acid) brushes revealed by 3D scanning force microscopy with frequency modulation detection

Stimuli-responsive polyelectrolyte brushes adapt their physico-chemical properties according to pH and ion concentrations of the solution in contact. We synthesized a poly(acrylic acid) bearing cysteine residues at side chains and a lipid head group at the terminal, and incorporated them into a phospholipid monolayer deposited on a hydrophobic silane monolayer. The ion-specific, nanoscale response of polyelectrolyte brushes was detected by using three-dimensional scanning force microscopy (3D-SFM) combined with frequency modulation detection. The obtained topographic and mechanical landscapes indicated that the brushes were uniformly stretched, undergoing a gradual transition from the brush to the bulk electrolyte in the absence of divalent cations. When 1 mM calcium ions were added, the brushes were uniformly compacted, exhibiting a sharper brush-to-bulk transition. Remarkably, the addition of 1 mM cadmium ions made the brush surface significantly rough and the mechanical landscape highly heterogeneous. Currently, cadmium-specific nanoscale compaction of the brushes is attributed to the coordination of thiol and carboxyl side chains with cadmium ions, as suggested for naturally occurring, heavy metal binding proteins

Crystallization Behavior of Amorphous Fe-Tb-M (M=Si or Al) Alloys and High Magnetostriction of their Crystallized Phases

The addition of 2.5 at% Si or Al to Fe_2Tb causes the formation of an amorphous single phase and the glass formation range extends up to 15 at% Si or Al which is the maximum additional amount in the present study. The amorphous (Fe_2Tb)_M_ (M=Si or Al) alloys crystallize through two stages consisting of Am→Fe_2Tb+Am→Fe_2Tb+unknown compound. The Fe_2Tb phase in coexistent with the amorphous phase has a very fine spherical morphology with a particle size of 5 to 20 nm. The additional Si or Al element is enriched into the unknown compounds. The coexistent state of the nanocrystalline Fe_2Tb and amorphous phases extends over the temperature region of about 300 K because of the high thermal stability of the remaining amorphous phase. The high thermal stability of the amorphous phase and the formation of the nanoscale Fe_2Tb grains are presumably due to the necessity of the redistribution of Si or Al into the remaining amorphous phase. The best magnetostrictive properties of high σ_, low H_c, high λ_s and high λ/H were obtained in the coexistent nanocrystalline Fe_2Tb and amorphous phases and the phase transition into Fe_2Tb and unknown compounds caused the depression of the magnetostrictive properties

Water modulates the lamellar structure and interlayer correlation of poly(perfluorooctyl acrylate) films: a specular and off-specular neutron scattering study

Comb-like polymers with pendant-like perfluorocarbon side chains self-assemble into smectic lamellae and have been extensively used as water-repellent, hydrophobic coating materials characterized by large water contact angles (θ > 120°). As poly(perfluorooctyl acrylate) films are “apparently hydrophobic” (θ > 120°), the interaction of such materials and water molecules has been largely overlooked. To unravel the molecular-level interactions between water and apparently hydrophobic polymers, specular and off-specular neutron scattering experiments were conducted at defined osmotic pressure ΠH2O. The poly{2-[(perfluorooctylethyl)carbamate]ethyl} acrylate (PFAUr-C₈), which had a carbamate linker, transitioned to another lamellar phase at 89 °C. At T = 25 °C; the lamellar periodicity of PFAUr-C₈ slightly increased with decreasing osmotic pressure, while the vertical correlation length increased. However, the poly[(perfluorooctyl)ethyl] acrylate (PFA-C₈) that did not contain a carbamate linker directly transitioned to a disordered phase at 84 °C. The lamellar periodicity of PFA-C₈ was largely independent of the osmotic pressure, suggesting that PFA-C₈ was poorly hydrated. Remarkably, the vertical correlation length decreased with decreasing osmotic pressure. Because hydration facilitated by the linker modulated the smectic lamellae of the poly(perfluoroalkyl acrylate), water molecules could be used to optimize the self-assembly of apparently hydrophobic liquid crystalline polymers

Templated polypyrrole electro-polymerization: Self-assembled bundles of bilayer membranes of amphiphiles and their actuation behavior

Abstract The electrochemical properties of conducting polymers are highly dependent on the microstructure. We report a method to produce specific microstructures of polypyrrole through electro-polymerization in the presence of the amphiphile N-{11-(2-hydroxyethyldimethylammonium)undecanoyl}-N,N -dioctyl-l-glutamate, bromide, which forms supramolecular hydrogels with pyrrole in aqueous solution. These hydrogels were used as templates during polypyrrole electro-polymerization to give microstructures composed of the bundles of bilayer membranes. The highly porous nature of these films resulted in electrochemical properties superior to polypyrrole deposited under the same condition without use of an amphiphilic template. Analysis of the scan rate dependence on cyclic voltammogram reveals that the porous templated films facilitate fast diffusion of dopant ions. The actuation properties were also investigated in aqueous solutions containing sodium p-toluene sulfonate electrolyte. The strains displayed by the template polypyrrole films were twice those synthesized without the use of a template

Discreteness of cell–surface contacts affects spatio-temporal dynamics, adhesion, and proliferation of mouse embryonic stem cells

The self-renewal and lineage-specific differentiation of stem cells are regulated by interactions with their microenvironments, called stem cell niche. Stem cells receive both biochemical and biophysical cues from their niche, which leads to the activation of signaling pathways, resulting in the modulation of gene expressions to guide their fate. Most of previous studies are focused on the effect of substrate stiffness using hydrogels with different Young’s moduli, and information is lacking on the effect of the discreteness of cell–substrate contacts on stem cells. Using mouse pluripotent, embryonic stem cells (mESCs) as the model system for early development, we quantitatively investigated the migration, dynamic deformation, and adhesion of mESCs on sparse and dense gelatin nanofibers deposited on glass surfaces, with a continuous layer of gelatin coated on glass substrates as the control. After confirming the maintenance of pluripotency on all the surfaces throughout the experiments, the centroid trajectories were monitored using timelapse imaging. The mean square displacement analysis indicated that both the diffusion coefficient and exponent were largest on sparse nanofibers, while the diffusion coefficient of mESCs on dense nanofibers was comparable to that on the control. Moreover, power spectral analysis of the shape deformation in the Fourier mode indicated that mESCs predominantly underwent elliptic deformation (mode 2), with the largest energy dissipation on sparse nanofibers. These data suggest that mESCs can deform and move on sparse nanofibers owing to the discrete cell–surface contact points. Intriguingly, using a self-developed technique based on laser-induced shock waves, a distinctly larger critical pressure was required to detach cells from nanofibers than from continuous gelatin. This finding suggests that the continuous but weak cell-substrate contacts suppress the deformation-driven mESC migration. As one of the key biological functions of stem cells, the proliferation rate of mESCs on these surfaces was determined. Although the observed difference was not statistically significant, the highest proliferation rate was observed on nanofibers, suggesting that the discreteness of cell–surface contacts can be used to regulate not only spatio-temporal dynamics but also the biological function of pluripotent stem cells

Solubility of artificial proteins with random sequences

AbstractA library of artificial random proteins of 141 amino acid residues of which 95 are random and which includes the 20 kinds of amino acids was prepared. Out of the 25 identified random proteins, 5 were soluble in the cell lysate, indicating that about 20% of the random proteins expressed in Escherichia coli are expected to be soluble. The soluble random proteins RP3–42 and RP3–45 and insoluble RP3–70 were purified. The solubility of the purified form is the same as that in the cell lysate

The antioxidant N-acetyl cysteine suppresses lidocaine-induced intracellular reactive oxygen species production and cell death in neuronal SH-SY5Y cells

Analysis of cell apoptosis by FACS. Levels of cell apoptosis were measured using an Annexin V-FITC Apoptosis Detection Kit (BioVision, Milpitas, CA, USA), according to the manufacturer’s instructions. For these analyses, SH-SY5Y cells were seeded into 6-well plates (3 × 105 cells/well) and incubated overnight. The following day, cells were treated with the indicated concentrations of the appropriate drug(s) for varying lengths of time and harvested by centrifugation at 1200 rpm for 3 min. The culture supernatants were discharged, and the resulting pellets were resuspended in a mixture comprised of 500 μl binding buffer, 5 μl Annexing V-FITC, and 5 μl propidium iodide (PI; 50 μg/ml) for 5 min at room temperature in the dark and analyzed using a FACSCalibur flow cytometer (BD Biosciences, San Jose, CA, USA). (PDF 2009 kb