Global analysis of dynamic changes in lipid raft proteins during T-cell activation

Lipid rafts are considered as specialized microdomains within the plasma membrane with unique lipid compositions different from surrounding membranes. Following T-cell receptor (TCR) stimulation, lipid rafts assemble in T-cell/antigen-presenting cell (APC) contact site known as the immunological synapse, inner leaflets of which serve as activation or docking sites for downstream signaling components. To understand the signaling events occurring in lipid rafts, we globally analyzed dynamic changes in lipid raft proteins during TCR/CD28 costimulation using 2-D fluorescence difference gel electrophoresis. We detected multiple spots whose intensities were enhanced after costimulation, and identified proteins in these spots by PMF. Identified proteins include Src family tyrosine kinases, tyrosine phosphatase, phosphatidylinositol 3-kinase (PI3-kinase), actin-binding proteins, and regulators for small GTPases. Of particular interest, a number of pleckstrin homology (PH) domain-containing proteins were identified. Biochemical and histochemical analyses confirmed the translocation of these proteins from cytosol to lipid rafts. We also demonstrated that these proteins assembled at the T-cell/APC interface. These results indicate the efficacy of our system to systematically analyze dynamics of lipid raft proteins during extracellular stimulation.     

From insulator to electride: a theoretical model of nanoporous oxide 12CaO.7Al2O3

Recently, a novel inorganic electride stable at room temperatures has been obtained by reducing a complex nanoporous oxide 12CaO.7Al2O3 (C12A7) in a Ca atmosphere (Matsuishi, S.; Toda, Y.; Miyakawa, M.; Hayashi, K.; Kamiya, T.; Hirano, M.; Tanaka, I.; Hosono, H. Science 2003, 301, 626). In this system, up to 2.3 x 1021/cm3 electrons can be accommodated in a three-dimensional network of cages formed by a positively charged oxide framework. We demonstrate theoretically that at all concentrations, ne, the electrons are neither associated with specific atoms nor fully delocalized. At low ne, the electrons are isolated from each other and resemble the color centers in insulating materials. They are well localized in some of the lattice cages and yield strong inhomogeneous lattice distortions that provide polaron-type cage-to-cage electron hopping. As ne increases, the electrons form a denser electron gas and become more evenly spread over all available lattice cages. At sufficiently high ne, the system becomes metallic but still retains partially localized character of the conducting electrons. We describe the nature of the electronic states at the Fermi level and predict the changes in the optical and magnetic properties of this system as a function of ne.     

Metal patterning on silicon surface by site-selective electroless deposition through colloidal crystal templating

Site-selective Cu deposition on a Si substrate was achieved by a combination of colloidal crystal templating, hydrophobic treatment, and electroless plating. Uniformly sized nano/microstructures were produced on the substrate using a monolayer coating of colloidal spheres instead of a conventional resist. The Cu patterns obtained were of two different types: networklike honeycomb and isolated-island patterns with a minimum period of 200 nm. Each ordered pattern with the desired intervals was composed of clusters of Cu nanoparticles with a size range of 50-100 nm. By the present method, it is possible to control the periodicity of metal arrays by changing the diameter of the colloidal spheres used as an initial mask and to adjust the shape of the metal patterns by changing the mask structure for electroless plating.     

Simultaneous long‐chain branching and random scission: I. Monte Carlo simulation

In free‐radical olefin polymerizations, the polymer transfer reactions could lead to chain scission as well as forming long‐chain branches. For the random scission of branched polymers, it is virtually impossible to apply usual differential population balance equations because the number of possible scission points is dependent on the complex molecular architecture. On the other hand, the present problem can be solved on the basis of the probability theory by considering the history of each primary polymer molecule in a straightforward manner. The random sampling technique is used to solve this problem and a Monte Carlo simulation method is proposed. In this simulation method, one can observe the structure of each polymer molecule formed in this complex reaction system, and virtually any structural information can be obtained. In the illustrative calculations, the full molecular weight distribution development, the gel point determination, and examples of two‐ and three‐dimensional polymer structure are shown. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 391–403, 2001     

Markovian approach to nonlinear polymer formation: Free-radical polymerization with chain transfer to polymer

A Markovian model is proposed for nonrandom branching reactions, by using free-radical polymerization that involves chain transfer to polymer as an example. Free-radical polymerizations are kinetically controlled; therefore, each primary polymer molecule experiences different history of branched structure formation. By assuming that the primary chains with the identical birth time conform to the same chain connection probabilities, the nonlinear structural development can be viewed as a system in which the primary chains formed at different birth times are combined into nonlinear polymers in accordance with the first-order Markov chain statistics. An explicit formula for the weight-average chain length is derived in a matrix form. The onset of gelation is simply stated as a point at which the largest eigenvalue of the transition matrix X reaches unity, i.e., det(X − I) = 0. This criterion for the onset of gelation can be considered as an extension of the Flory/Stockmayer theory to a nonequilibrium reaction system. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 357–371, 1998     

Markovian approach to nonlinear polymer formation: Free-radical crosslinking copolymerization

A Markovian model is used to extend the Flory/Stockmayer gelation theory to nonequilibrium reaction systems, by taking free-radical crosslinking copolymerization of vinyl and divinyl monomer as an example. Free-radical polymerizations are kinetically controlled; therefore, each primary polymer molecule experiences a different history of crosslinked structure formation. By assuming that the primary chains with identical birth time conform to the same chain connection probabilities, the nonlinear structural development can be viewed as a system in which the primary chains formed at different birth times are combined into nonlinear polymers in accordance with the first-order Markov chain statistics. According to the present Markovian model, the weight-average chain length, P̄_w is given by a matrix formula, P̄_w = W _p( E — Q )⁻¹ l where W _p is the row vector that concerns the weight contribution of a primary chain, E is a unit matrix, Q is the transition matrix representing the chain connection statistics, and I is a column vector whose elements are all unity. For an equilibrium system, W _p = P̄_wp (weight-average chain length of the primary chains), E = 1, Q = ρP̄_wp (ρ is the crosslinking density), and I = 1; therefore, the present formula reduces to the Flory/Stockmayer equation, P̄_w = P̄_wp/(1 − ρP̄_wp). The criterion for the onset of gelation is simply stated as a point at which the largest eigenvalue of the transition matrix Q reaches unity, i.e., det( E − Q ) = 0. The present Markovian approach elucidates important characteristics of the kinetically controlled network formation, and provides greater insight into nonequilibrium gelling systems.     

Large magnetocaloric effect in van der Waals crystal CrBr3

We study the magnetocaloric effect (MCE) in van der Waals (vdW) crystal CrBr₃. Bulk CrBr₃ exhibits a second-order paramagnetic-ferromagnetic phase transition with T_C = 33 K. The maximum magnetic entropy change −ΔS_M near T_C is about 7.2 J·kg⁻¹·K⁻¹ with the maximum adiabatic temperature change ΔT^max_ad = 2.37 K and the relative cooling power RCP= 191.5 J·kg⁻¹ at μ₀H = 5 T, all of which are remarkably larger than those in CrI₃. These results suggest that the vdW crystal CrBr₃ is a promising candidate for the low-dimensional magnetic refrigeration in low temperature region.     

Two classes of superconductors discovered in our material research: Iron-based high temperature superconductor and electride superconductor

We discovered two new classes of superconductors in the course of material exploration for electronic-active oxides. One is 12CaO · 7Al₂O₃ crystal in which electrons accomodate in the crystallographic sub-nanometer-sized cavities. This material exhibiting metal–superconductor transition at 0.2 K is the first electride superconductor. The other is iron oxypnicitides with a layered structure. This superconductor is rather different from high T_c cuprates in several respects. The high T_c is emerged by doping carriers to the metallic parent phases which undergo crystallographic transition (tetra to ortho) and Pauli para to antiferromagnetic transition at ～150 K. The T_c is robust to impurity doping to the Fe sites or is induced by partial substitution of the Fe²⁺ sites with Co²⁺ or Ni²⁺. This article gives a brief summary of these discoveries and recent advances.     

Oxygen ion conduction in 12CaO·7Al2O3: O2− conduction mechanism and possibility of O− fast conduction

12CaO·7Al₂O₃ (C12A7) with a unique nano-porous structure and free O^2? ions entrapped in sub-nanometer-sized cages is a fast oxygen-ion-conducting material. These free O^2– may be replaced by various oxygen-related species, OH^?, O^2? and O^?, by tuning the atmosphere during the heat treatment. We examined the conduction mechanism for stoichiometric C12A7 (C12A7:O^2?), in which O^2? ions exist as counter anions in sub-nanometer-sized cages, by Raman measurement of C12A7:O^2? annealed in a dry ¹⁸O₂ atmosphere. It was revealed that the primary ion conducting species is an O^2? ion which diffuses via exchange with O^2? in the cage wall. An experimental result on the sample containing O^? ions implied that O^? is more mobile than O^2? in C12A7. Ab initio calculations on the diffusion paths of O^2? and O^? ions in C12A7 supported the above experimental results.