Tightening of knots in proteins

We perform theoretical studies of stretching of 20 proteins with knots within a coarse-grained model. The knot's ends are found to jump to well defined sequential locations that are associated with sharp turns, whereas in homopolymers they diffuse around and eventually slide off. The waiting times of the jumps are increasingly stochastic as the temperature is raised. Knots typically do not return to their native locations when a protein is released after stretching.     

Temperature variation of bubble domains in Dy0.3Tm0.7FeO3 mixed orthoferrite

Bubble domain structure in Dy_0.3Tm_0.7FeO₃ mixed orthoferrite was studied between room temperature and 480 K using the Faraday effect. Temperature dependence of the magnetization and domain wall energy density has been determined. Starting from the molecular field theory and one-ion theory of magnetocrystalline anisotropy, expressions describing a temperature dependence of the domain wall energy density in orthoferrites have been derived. In the expression for magnetocrystalline energy, uniaxial as well as cubic anisotropy have been accounted for.     

Proteins in a shear flow

The conformational dynamics of a single protein molecule in a shear flow is investigated using Brownian dynamics simulations. A structure-based coarse grained model of a protein is used. We consider two proteins, ubiquitin and integrin, and find that at moderate shear rates they unfold through a sequence of metastable states-a pattern which is distinct from a smooth unraveling found in homopolymers. Full unfolding occurs only at very large shear rates. Furthermore, the hydrodynamic interactions between the amino acids are shown to hinder the shear flow unfolding. The characteristics of the unfolding process depend on whether a protein is anchored or not, and if it is, on the choice of an anchoring point.     

Electrochemical growth and properties of LaMn1−xCoxO3 (0 < x ≤ 1) single crystals

Single crystals of LaMn_1−xCo_xO₃ (0 < x < 1) with distorted perovskite structure have been obtained by the electrodeposition technique at anode from flux melt using Cs₂MoO₄‐MoO₃ binary system as solvent. An investigation of magnetic and electrical properties of the obtained crystals as well as its comparison with those for ceramic samples of the same composition were carried out. A much weaker interplay between magnetic and electrical properties and a smaller ∼8% magnetoresistance were found in the ternary oxide crystals slightly doped by Co on the verge of transition to ferromagnetic state in comparison to the data have been reported for LaMnO_3+δ single crystals. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nitrite reduction by copper through ligand-mediated proton and electron transfer

Nitrite reduction by a copper complex featuring a proton-responsive tripodal ligand is demonstrated. Gaseous nitric oxide was confirmed as the sole NO_X by-product in quantitative yield. DFT calculations predict that nitrite reduction occurs via a proton and electron transfer process mediated by the ligand. The reported mechanism parallels nitrite reduction by copper nitrite reductase.     

High-pressure synthesis and magnetic properties of Bi<Subscript>0.5</Subscript>D<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> (<Emphasis Type="Italic">D</Emphasis> = Pb,Ba) solid solutions

Perovskites Bi_0.5D_0.5MnO₃(D = Pb, Ba) were prepared under high pressure (4 GPa) at 1200–1300°C. According to the X-ray diffraction data, crystalline Bi_0.5Pb_0.5MnO₃ has a tetragonal unit cell with the parameters a = 3.940 Å and c = 3.800 Å, whereas Bi_0.5Ba_0.5MnO₃ crystals are cubic with a = 3.940 Å. It is concluded from magnetic studies that lead-containing manganite is an antiferromagnet with T_N = 120 K, whereas Bi_0.5Ba_0.5MnO₃ is a spin glass with spin-freezing temperature T _f = 38 K. Both compounds are decomposed upon heating in air at temperatures above 500°C. With the use of synthesis in air, Bi_0.5Ca_{0.5 ? x}D _x MnO₃ solid solutions with x as high as 0.25 were obtained.     

Mathematical study of a tissue-implant connection in a ventral hernia repair in a context of the system's parameters

Ventral hernia repair is nowadays a well recognized matter in surgery and advanced techniques of operating are developed. However, mechanical properties of the system after an operation are not known so recurrences of the illness happen. The paper describes a simple mathematical model of a human fascia-synthetic implant system. The synthetic mesh is modeled by a cable structure and its elastic supports simulate the human fascia. The junction force in the fascia-implant system is sought. A relation of the force change to variations of some parameters of the system is also studied by applying a sensitivity analysis. The authors conclude that a crucial role for the junction force and a patient's comfort plays the implant's elasticity modulus and initial tension of the mesh is the least important factor. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Protein folding in a force clamp

Kinetics of folding of a protein held in a force clamp are compared to an unconstrained folding. The comparison is made within a simple topology-based dynamical model of ubiquitin. We demonstrate that the experimentally observed variations in the end-to-end distance reflect microscopic events during folding. However, the folding scenarios in and out of the force clamp are distinct.     

Crystal and magnetic structures of the Bi1 ? xSrxFeO3 ? δ and Bi1 ? xAxFe1 ? xMnxO3 (A = Sr, Ca) solid solutions

Bi_{1 − x} Sr _x FeO_{3 − x/2} (I), Bi_{1 − x} Sr _x Fe_{1 − x} MnxO₃ (II), and Bi_{1 − x} Ca _x Fe_{1 − x} Mn _x O₃ (III) solid solutions have been obtained. Their magnetization has been measured by X-ray and neutron diffraction and M?ssbauer spectroscopy. According to the M?ssbauer spectroscopy data, iron ions are in the trivalent state in system I. Near the concentration x ≈ 0.2, rhombohedral distortions (sp. gr. R3c) are transformed into tetragonal (P4/mmm). The symmetry of system II changes at x > 0.2 (R3c → R3c), whereas orthorhombic distortions (R3c → Pbnm) arise in system III at x > 0.2. The magnetic structure is antiferromagnetic (of G type). The samples of systems II and III exhibit weak ferromagnetism at x > 0.2 due to the Dzyaloshinski-Moriya interaction.