The C2 selective nucleophilic substitution reactions of 2,3-epoxy alcohols mediated by trialkyl borates: the first endo-mode epoxide-opening reaction through an intramolecular metal chelate

[reaction: see text] Highly efficient C2 selective substitution reactions of 2,3-epoxy alcohols with nucleophiles were developed by using NaN(3)-(CH(3)O)(3)B, NaSPh-(CH(3)O)(3)B, or NaCN-(C(2)H(5)O)(3)B system. The reaction proceeds through novel endo-mode epoxide opening of an intramolecular boron chelate, which was suggested from both experimental and quantum mechanic studies.     

Radical terpolymerization of sulfur dioxide,styrene, and methyl methacrylate

The radical terpolymerization of sulfur dioxide, styrene, and methyl methacrylate in o-dichlorobenzene with 2,2′-azobisisobutyronitrile was carried out in order to clarify the propagation mechanism of the radical copolymerization of sulfur dioxide and styrene, especially as a function of total concentration of sulfur dioxide and styrene. From the analysis of the trigonal composition diagrams it has been definitely shown that the radical copolymerization of sulfur dioxide and styrene proceeds by the propagation of two monomers, but the usual type of copolymerization mechanism, explicable in terms of the Lewis-Mayo equation, is not applicable to this copolymerization. The participation in the propagation of a monomer charge-transfer complex consisting of sulfur dioxide and styrene was also ruled out.     

Adsorption and order formation of colloidal nanoparticles on a substrate: a Brownian dynamics study

Adsorption process and order formation of electrostatically stabilized colloidal particles with a radius of 50 nm onto a planar surface with countercharge are examined. We perform Brownian dynamics simulations with a new three-dimensional cell model, in which the particle-particle and particle-substrate interactions are modeled based on the DLVO theory. The simulations yield the following results: (1) a larger bulk concentration would be required for larger kappaa to reach order formation to compensate for the decrease in the bulk potential; (2) the phase transition from a disordered to an ordered structure of the adsorbed particles on the substrate is considered to be of the Kirkwood-Alder type of transition through the examination of the two-dimensional pressure of the adsorbed particles; (3) the adsorbed particles are found to form a hexagonally ordered array, only if what we call "one-directional average force" acting on an adsorbed particle exceeds a critical value, which is independent of the ionic strength, or the interaction potentials. The critical value of the one-directional average force is interpreted as the force needed to keep an ordered structure by localizing adsorbed particles at fixed positions. In addition, the critical force is used to develop a new model to estimate the surface coverage at the order-disorder transition and it is demonstrated that the new model gives better estimation than other models previously reported.     

Radical polymerization behavior of N,N-disubstituted acrylamide: Absolute rate constants for polymerization and copolymerization of N-acryloylpiperidine

The absolute rate constants of propagation (k_p) and of termination (k_t) of N-acryloylpiperidine (NAPi) were determined by the rotating sector method in bulk; k_p = 273 and k_t = 1.79 × 10⁷ L/mol s at 30°C. It was noted that k_p for NAPi was 100 times smaller than that for N,N-dimethylacrylamide (DMAcAm). The absolute rate constants of cross-propagations for copolymerizations with common monomers were evaluated by combination of the k_p value and the monomer reactivity ratios. Quantitative comparison of the rate constants with those of DMAcAm and poly(DMAcAm) radical shows that NAPi is as reactive as DMAcAm and the smaller k_p value for NAPi is ascribable to much the lower reactivity of the poly(NAPi) radical. The large difference in reactivity of the polymer radicals is discussed in relation to the steric factor of the piperadino and the dimethylamino groups which seems to affect the capability of the carboxamide group to stabilize the polymer radical.     

Millisecond treatment of cells using microfluidic devices via two-step carrier-medium exchange

We present herein a simple but versatile microfluidic system for the treatment of cells with millisecond chemical stimulus, by rapidly exchanging the carrier-medium of cells twice in a microchannel. A technique we refer to as 'hydrodynamic filtration' has been employed for the exchange of medium, in which the virtual width of flow in the microchannel determines the size of filtered cells/particles. The treatment time of cells could be rigidly adjusted by controlling the inlet flow rates and by changing the volume of the stimulating area in the microchannel. In the experiment, two types of microdevices were designed and fabricated, and at first, the ability for carrier-medium exchange was confirmed. As an application of the presented system, we examined the influence of the treatment time of HeLa cells with Triton X-100, a non-ionic surfactant used to solubilize the cellular membrane, on cell viability, varying the average treatment time from 17 to 210 ms. Both quantitative and qualitative analyses were performed to estimate the damage on cell membrane, demonstrating that the cell viability dramatically decreased when the treatment time was longer than approximately 40 ms. The obtained results demonstrated the ability of the presented system to conduct the rapid stimulation of cells, which would be useful for the analysis of biochemical reactions at the cell surface.     

Electric dipole moments in pseudo-Dirac gauginos

The SUSY CP problem is one of serious problems in construction of realistic supersymmetric standard models. We consider the problem in a framework in which adjoint chiral multiplets are introduced and gauginos have Dirac mass terms induced by a U(1)$\mathrm{U}(1)$ gauge interaction in the hidden sector. This is realized in hidden sector models without singlet chiral multiplets, which are favored from a recent study of the Polonyi problem. We find that the dominant contributions to electron and neutron electric dipole moments (EDMs) in the model come from phases in the supersymmetric adjoint mass terms. When the supersymmetric adjoint masses are suppressed by a factor of ∼100 compared with the Dirac ones, the electron and neutron EDMs are suppressed below the experimental bound even if the SUSY particle masses are around 1 TeV. Thus, this model works as a framework to solve the SUSY CP problem.     

A 45-ns molecular dynamics simulation of hemoglobin in water by vectorizing and parallelizing COSMOS90 on the earth simulator: dynamics of tertiary and quaternary structures

Molecular dynamics (MD) simulations of human adult hemoglobin (HbA) were carried out for 45 ns in water with all degrees of freedom including bond stretching and without any artificial constraints. To perform such large-scale simulations, one of the authors (M.S.) accelerated his own software COSMOS90 on the Earth Simulator by vectorization and parallelization. The dynamical features of HbA were investigated by evaluating root-mean-square deviations from the initial X-ray structure (an oxy T-state hemoglobin with PDB code: 1GZX) and root-mean-square fluctuations around the average structure from the simulation trajectories. The four subunits (alpha(1), alpha(2), beta(1), and beta(2)) of HbA maintained structures close to their respective X-ray structures during the simulations even though no constraints were applied to HbA in the simulations. Dimers alpha(1)beta(1) and alpha(2)beta(2) also maintained structures close to their respective X-ray structures while they moved relative to each other like two stacks of dumbbells. The distance between the two dimers (alpha(1)beta(1) and alpha(2)beta(2)) increased by 2 A (7.4%) in the initial 15 ns and stably fluctuated at the distance with the standard deviation 0.2 A. The relative orientation of the two dimers fluctuated between the initial X-ray angle -100 degrees and about -105 degrees with intervals of a few tens of nanoseconds.     

Ascorbate analogs for use in medical imaging: synthesis and radical scavenging activity of 5-O-(4'-iodobenzyl)-L-ascorbic acid

As part of our program to develop potential imaging agents for ascorbate bioactivity in the brain, 5-O-(4'-iodobenzyl)-L-ascorbic acid was prepared through a seven-step sequence which involved C5-O-alkylation with p-iodobenzyl bromide in the presence of Ag2O and CaSO4 as the key step, starting from L-ascorbic acid. The scavenging activity of the p-iodobenzylated analog against 2,2-diphenyl-1-picrylhyrazyl (DPPH) radical was almost the same as that of L-ascorbic acid itself.