Acid-catalyzed cyclization of vinylsilanes bearing an amino group. Stereoselective synthesis of pyrrolidines

[reaction: see text] In the presence of an acid catalyst, vinylsilanes 1 bearing an amino group protected by an electron-withdrawing group were smoothly cyclized to 2-(silylmethyl)pyrrolidines 2. This cyclization was utilized for the stereoselective synthesis of 2,n-disubstituted pyrrolidines (n = 3-5). The cyclized products could be converted to the corresponding alcohols by oxidative cleavage of the carbon-silicon bond with TBAF and H2O2.     

Polymerization of phenylacetylene by WCl6·Ph4Sn: Synthesis of high polymer achieved by selection of solvents

Phenylacetylene was polymerized by WCl₆·Ph₄Sn (1:1) in 1,4-dioxane to provide in high yield a polymer whose molecular weight reached 1 × 10⁵. The polymerization also proceeded in other oxygen-containing solvents (ethers, esters, and ketones) but the polymer molecular weights were lower than 1 × 10⁴. Certain hydrocarbon solvents such as cyclohexene, tetralin, and indan also afforded high-molecular-weight polyphenylacetylene [M _n = (5–8) × 10⁴], as compared with those (M _n ≤ 1.5 × 10⁴) obtained in conventional aromatic hydrocarbons like benzene. A high polymer (M _n = 1.6 × 10⁵) was also formed from β-naphthylacetylene in 1,4-dioxane. It was inferred that the active hydrogens of these solvents prevent the formed polymer from being decomposed by a radical mechanism and/or modify the nature of active species.     

Stability of two-dimensional crystalline aggregates of a protein studied by molecular dynamics

Two-dimensional protein (ferritin) aggregates with a square lattice symmetry, which were formed within a thin liquid layer on a mercury surface, were studied by molecular dynamics (MD) simulation. For the simulation, the ferritin molecule was modeled by an assembly of 49 spheres, and the intermolecular interactions were given by simple formulae. During the simulation, molecules were confined within a layer, which corresponds to the thin liquid layer. An annealing MD simulation was done starting from a random molecular configuration within the layer, and aggregates with the square lattice symmetry were also obtained. To study the stability of aggregates, dissociation processes of the aggregates were analyzed using MD simulations at room temperature. Interactions between the nearest-neighbor molecules were regarded as bonds. Mean bond energies and correlation coefficients between the bond energies were calculated from the MD trajectories. A decay profile according to the dissociation was obtained, yielding a dissociation rate constant. Buried bonds were stronger than peripheral bonds. The larger the aggregate size, the stronger the bond for each of the buried and peripheral bonds. A simple theoretical account, which is applicable to a general bonded network, was introduced to analyze the dynamics of the aggregates. © 1994 by John Wiley & Sons, Inc.     

Novel Ti-O-Ti bonding species constructed in a metal-oxide cluster

The preparation and structural characterization of a novel Ti-O-Ti bonding complex constructed in the mono-lacunary alpha-Keggin polyoxometalate (POM), are described. The water-soluble, crystalline complex with a formula of K5H2[[{Ti(OH)(ox)}2(micro-O)](alpha-PW11O39)] x 13H2O 1 was prepared in 30.2% (0.60 g scale) yield in a 1 : 3 molar-ratio reaction of the tri-lacunary species of alpha-Keggin POM, Na9[A-PW9O34] x 19H2O, with the titanium(IV) source, K2TiO(ox)2 x 2H2O (H2ox = oxalic acid), in HCl-acidic solution (pH 0.08), and characterized by complete elemental analysis, thermogravimetric and differential thermal analyses (TG/DTA), FTIR, solution (31P, 183W, 1H and 13C) NMR spectroscopy and X-ray crystallography. The complex was also obtained in 47.6% (0.81 g scale) yield in a 1 : 2 molar-ratio reaction of the mono-lacunary Keggin POM, K7[PW11O39] x 10H2O, with the anionic titanium(IV) complex under acidic conditions. The molecular structure of [[{Ti(OH)(ox)}2(micro-O)](alpha-PW11O39)]7- 1a, was successfully determined. This POM in the solid state is composed of one host (mono-lacunary site) and two guests (two octahedral Ti groups), in contrast to most titanium (IV)-substituted POMs consisting of one host and one guest. On the other hand, the 31P NMR measurements revealed that in aqueous solution this POM was present under a dissociation equilibrium which depends upon both temperature and pH.     

Synthesis of Unsymmetrical Tetrathiafulvalene Derivatives via Me(3)Al-Promoted Reactions of Organotin Compounds with Esters

Efficient synthetic methods for the construction of a wide variety of unsymmetrical tetrathiafulvalenes (TTFs) via the Me(3)Al-promoted reactions of organotin thiolates or selenolates with esters are described. Reaction of tin thiolates (3a-c and 10) and selenolates (3d, 5, and 7) with esters (11a,b) in the presence of Me(3)Al as a Lewis acid gave dihydrotetrathiafulvalene derivatives (12, 14, 15, and 17-20) and 1,3-dithiane derivatives (13 and 16). In addition, the synthesis of diselenadithiafulvalene derivatives (25-28) could be accomplished by Me(3)Al-mediated reaction of tin thiolate (2a) or selenolates (3d and 5) with esters (22a, 22d, and 24). Furthermore, the application of the Me(3)Al-promoted reaction of tin thiolate (34) with esters (11a-b, 22a-d, and 35a-b) for the synthesis of unsymmetrical TTFs-fused donors enabled us to obtain various TTFs-fused systems (29-33) in short steps.     

Non-equilibrium molecular dynamics simulation study on permeation phenomena of LJ particles in slit-shaped membranes with periodic belt-like heterogeneous surfaces

In order to make clear the relationship between the pore structure and the diffusivity, we have carried out permeation simulations of pure gases through simple model membranes by using the external-field non-equilibrium molecular dynamics method. As the membrane, we model slit-shaped pores with periodic belt-like heterogeneous pore surfaces which are caused by the upheaval of surface atoms. Applying simulation results for membranes with several upheaval interval distances to Maxwell–Stefan (MS) theory, we calculate the effects of the molecular loading of permeating molecules in the pores on MS diffusivity (D_MS). In addition, the permeation potential barrier is estimated as the difference between the maximum and minimum permeation potential energies. The effect of the molecular loading on the permeation potential barrier and the D_MS are in inverse proportion. It is noted that, when the width of the adsorption area in the permeation direction is not common multiples of the molecular diameter, the permeation potential barrier decreases with the increase in the molecular loading. This is because the positive force against the permeation direction is caused to the permeating molecules by interactions with permeating molecules in the adsorpton area between adjacent upheavals. Therefore, we could suggest that the key factor for controlling diffusion property is the structural relationship between the adsorption area and the permeating molecules.     

Concurrent induction of two chiral centers from symmetrical 3, 4-disubstituted and 3,3,4-trisubstituted 4-pentenals using Rh-catalyzed asymmetric cyclizations

Asymmetric cyclization of symmetrical 3,4-disubstituted and 3,3, 4-trisubstituted 4-pentenals was studied using Rh-complexes with chiral ligands. The cyclization of symmetrical 4-pentenals 4a,b by a neutral Rh[(R)-BINAP]Cl afforded cis-3,4-disubstituted (4R)-cyclopentanones 9a,b of >95% ee in 25-31% yields; on the other hand, the cyclization of 4a-c by a cationic Rh[(R)-BINAP]ClO(4) afforded trans-3,4-disubstituted (4S)-cyclopentanones 10a-c of >95% ee in 70-81% yields. All stereoisomers could be stereoselectively made by the selection of a neutral or cationic Rh-complex, and (R)- or (S)-BINAP ligand. The Rh-catalyzed cyclization could be applied to the construction of cyclopentanones 17 and 18 bearing a chiral quaternary carbon. The cyclization by the cationic Rh[(R)-BINAP]ClO(4) afforded the optically active trans-3,3, 4-trisubstituted cyclopentanones 18a-c of 92-95% ee in 75-83% yields. The catalytic cycle was also studied by using deuterium aldehyde, and the tentative mechanisms of the enantio- and diastereoselection were proposed.     

Sterilization of health care products by 5 MeV bremsstrahlung (X ray)

Radiation sensitivities of . pumilus and spores were examined to bremsstrahlung of 5 MeV EB and Cobalt -60 γ rays in order to confirm the effects of radiation and dose rate. Biological indicators (SPORTROL, NAmSA, USA) were irradiated with the X ray in the dose rate range of 4.7–47kGy/h. D-value of spores was 1.4–1.5 kGy, and that of was 1.1–1.3 kGy. The D-values of and have very small dose rate dependences to X ray, and the D-values are similar to those of γ ray. Dose distribution by X-ray and γ irradiation was measured for cartons containing 32 unit dialyzers. The D_max./D_min. of the X-ray irradiation (1.2) was smaller than that of γ ray (1.3).