Lower Torsion Angle Research Articles

Microstructure and mechanical properties of (CrCoNi)97Al1.5Ti1.5 medium entropy alloy twisted by free-end-torsion at room and cryogenic temperatures

In this study, the swaged (CrCoNi)97Al1.5Ti1.5 medium entropy alloys (MEAs) were twisted by free-end-torsion at room and liquid nitrogen temperatures. Microstructure in different strained layers of the twisted sample was characterized by combined use of energy dispersive spectroscopy, electron channeling contrast imaging, and electron backscatter diffraction techniques. The microhardness and overall tensile properties of the twisted sample were analyzed. The results show that the MEAs exhibit higher torque and lower torsion angle during low-temperature torsion. The deformation mechanism during torsion is dominated by dislocation slip, and gradient dislocations and lamellar dislocation substructures gradually increasing from core to surface are formed in the twisted samples. The twin content gradually decreases in the surface layer, especially when twisted at room temperature or at liquid nitrogen temperature but with a small torsion angle. The reduction of twins is related to the addition of Al and Ti, the critical shear stress of twinning, and the unique strain state of torsional deformation. The twisted samples have gradient distributions of microhardness. Torsion can effectively improve the tensile strength of the MEAs at the expense of ductility.

Anti-degenerative effect of Apigenin, Luteolin and Quercetin on human keratinocyte and chondrocyte cultures: SAR evaluation.

Inflammation is a dynamic process that occur on vascularized tissue in response to different stimuli causing cell injury and tissue degeneration. Reactive oxygen and nitrogen species (ROS and RNS) and advanced glycation end products (AGEs) have a key mediatory role in the development and progression of degenerative tissue process. The bioflavonoids possess a broad-spectrum of pharmacological activities. Their capability is related to their chemical structure. In this study we evaluated and compare antioxidant, anti-glycative and anti-degenerative actions of two flavones apigenin and luteolin and a flavonol quercetin, in function of their hydroxyl groups arrangement. Moreover we assay, on NCTC 2544 and chondrocytes cultures, the flavonoids capacity to modulate NO and glycosamminoglycans levels, index of antidegenerative capacity. All tested flavonoids act as free radicals scavengers (ROO• and NO•) and advanced glycation end products inhibitors, in agreement with their BDE, IP and molecular planarity. Quercetin showed a high ORAC value (2.70±0.12 ORAC Units), according to a low BDE (74.54 Kcal/mol) and IP (174.44 Kcal/mol) values. Luteolin is the most active compound in the NO (48.19±0.18%) and AGEs (60.06±0.52%) inhibition, in function of a low torsion angle (16.3°) between the 3-OH moiety and C'6 carbon atom. All tested flavonoids posses a protective role on degenerative tissue events. They acts in different manner depending on the functional groups, the biological substrate and the concentration used. In any case, it can be considered a suitable product preventing a degenerative processes.

Relationship between Torsion and Anisotropic Exchange Coupling in a Tb(III)-Radical-Based Single-Molecule Magnet.

The incorporation of paramagnetic ligands within rare-earth ion clusters exhibiting large magnetic anisotropy has provided significant advancement in the design of single-molecule magnets (SMMs) with large blocking temperatures. However, the exchange interaction in such systems is complex and difficult to probe by conventional magnetometry techniques, and little is known about the structural relationships. Inelastic neutron scattering and terahertz electron paramagnetic resonance measurements are used complimentarily to investigate the large exchange interaction between a rare earth-radical pair in a Tb(III)-based SMM complex. The origin of the exchange interaction is investigated for two molecular species in the crystallographic unit cell that exhibit different bonding structures between Tb(III) and a 2pyNO radical. A correlation between the Tb-O-N-C torsion angles and the magnitudes of exchange couplings is found. Interestingly, a large nondegeneracy within the ground-state doublet is present for the larger torsion angle species. It is essential to consider the balance of two channels of exchange coupling, 2p-4f hybridization and 2p-5d charge transfer, to explain this characteristic behavior. The former channel gives the antiferromagnetic interaction, and the latter gives the ferromagnetic one. When an effective Ĵ = (1)/2 Ising-type Hamiltonian is applied, the exchange couplings are evaluated to be antiferromagnetic J(z) = 9.89 meV (79.8 cm(-1)) for the low torsion angle (3.8°) species and J(z) = 7.39 meV (59.6 cm(-1)) for the larger torsion angle (15.8°) species. It is also found that a small percentage of the transverse exchange component must be included for the larger torsion angle to account for the observed nondegenerate ground state. The symmetry of the exchange couplings is discussed by considering the characters of d and f orbitals.

Structural Analysis, Spectroscopic, and Magnetic Properties of the 1D Triple-Bridged Compounds [M(dca)2(bpa)] (M = Mn, Fe, Co, Zn; dca = dicyanamide; bpa = 1,2-bis(4-pyridyl)ethane) and the 3D [Ni(dca)(bpa)2]dca·6H2O

The family of compounds [Mn(dca)(2)(bpa)] (1), [Fe(dca)(2)(bpa)] (2), [Co(dca)(2)(bpa)] (3), [Zn(dca)(2)(bpa)] (4), and [Ni(dca)(bpa)(2)]dca·6H(2)O (5), with dca = dicyanamide and bpa = 1,2-bis(4-pyridyl)ethane, has been synthesized. These compounds have been characterized by single crystal (1, 2, 4, and 5) and powder X-ray diffraction (3), by Fourier transform infrared (FTIR), UV-vis, and electron paramagnetic resonance (EPR) spectroscopies, and by magnetic measurements. Compound 1 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.757(6), b = 9.692(3), and c = 13.073(4) Å, and β = 123.02(2)°; Compound 2 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.588(5), b = 9.661(3), c = 12.970(5) Å, and β = 123.16(3)°; Compound 4 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 16.519(2), b = 9.643(2), c = 12.943(2) Å, and β = 123.15(1)°; Compound 5 crystallizes in the monoclinic C2/c space group, Z = 4, with a = 18.504(4), b = 19.802(3), and c = 8.6570(18) Å, and β = 99.74(2)°. The compounds 1-4 are isostructural and show a one dimensional (1D) disposition, with the metal(II) ions bridged by double μ(1,5) dca ligands and unusually by a third bridge consisting of the bpa ligand, which adopts a very low torsion angle to accommodate in the structure. This kind of structure is unusual, even considering the voluminous bpa bridge. The compound 5 shows a 3D structure with layers of Ni-bpa joined by single dca bridges. Magnetic susceptibility measurements show antiferromagnetic couplings, increasing for 1-3. Compound 5 shows very slight antiferromagnetic interactions.

Probing thin-film morphology of conjugated polymers by Raman spectroscopy

We use Raman spectroscopy to investigate the thin-film morphology of conjugated polymers [poly(9,9-di-n-octylfluorene-alt-benzothiadiazole (F8BT)] in terms of the polymer chain conformation at interfaces with quartz, a crosslinked benzocyclobutene derivative, polyvinylphenol, and poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate). The polymer chains near the substrate interface adopt a more planar conformation (lower torsion angle between fluorene and benzothiadiazole units) than chains in the bulk of the film for all substrates studied. On annealing, polymer chains both near the interface and in the bulk of the film adopt more planar conformations than in their pristine states but to a different degree. The influence of F8BT molecular weight on polymer chain conformation near the substrate interface is also examined. These results are confirmed by additional absorption and photoluminescence measurements.

Characterization of lipid membrane dynamics by simulation: 3. Probing molecular transport across the phospholipid bilayer.

The goal of this study is to elucidate the role of the motions of the hydrocarbon chains of a phospholipid bilayer in penetrant diffusion. Penetrant size, as well as its position in the hydrocarbon core of the lipid bilayer, has also been explored regarding impact on the diffusion rate in a phospholipid bilayer. Molecular dynamics, MD, simulations were carried out on a model dimyristoyl phosphatidylcholine (DMPC) membrane bilayer with and without methanol and propanol as penetrants. The MD trajectories were analyzed in terms of estimating time and space properties. These simulations show that torsion angle kink shifts in the hydrocarbon chains of phospholipids are natural occurrences in a bilayer assembly. The diffusion coefficients of methanol and propanol in a DMPC lipid bilayer, as calculated from the MD simulations, agree with experimental measurements. Both methanol and propanol show different diffusion rates in different regions of the hydrocarbon chain matrix of the lipid bilayer. Solute size has more impact on diffusion rate in the bilayer regions with high torsion angle order parameters, as compared to the regions with low torsion angle order parameters. The simulated transport behavior suggests that a kink shift diffusion mechanism is more likely to occur in regions with high torsion angle order parameters, and a free volume transport mechanism is more likely operative in the region with low torsion angle order parameters, mainly the center core of the bilayer. A three zone diffusion model is proposed for transport of a penetrant across a bilayer.

Molecular dynamics simulation of solid biphenyl

Constrained molecular dynamics simulation of solid biphenyl is reported. The calculations were carried out for 432 molecules, i.e., 216 (6 × 12 × 3) unit cells and also for 108 molecules i.e. 54 (3 × 6 × 3) unit cells of the monoclinic crystal. The molecules were handled as rigid bodies except for the possibility of the torsional twist of the phenyl rings around their long molecular axes. Williams-type atom-atom pair-potentials were used to describe the intermolecular interactions. A simple double-well torsional potential governed the intramolecular motions. Starting from the experimentally determined room temperature arrangement, we studied the structure as a function of temperature. Our simulations indicate that the second order phase-transition at ∼ 40 K known from experiments, is associated with the ordering of the torsion angles in neighbouring molecules, but the resulting structure is qualitatively different from what was assumed from X-ray diffraction measurements. Rather than all the molecules having the same average torsion angle of ∼ 11°, as has hitherto been assumed, it has been found that the system can substantially reduce its free energy if some molecules have a low torsion angle (0–2°) and others a higher (∼ 22°) one. This splitting into two basically different conformations is rather insensitive to the simulation parameters but the proportions of molecules falling in the two regimes is sensitive to the scaling of the potentials. The structure accommodates these different torsion angles by tending to form an alternation of high and low torsion angle in successive sites along the b direction.