Immobilization of colloidal crystals, formed by polymer-grafted silica in organic solvent, in physical gels

Immobilization of colloidal crystals by gelation of polymer-grafted silica suspension in acetonitrile with alkyl amides derived from amino acids was investigated. Addition of N-benzyloxycarbonyl-l-isoleucylaminooctadecane (Z-Ile-C18) and 1,12-bis(N-benzyloxycarbonyl-l-valylamino)dodecane [Bis(Z-Val)-C12] to poly(maleic anhydride-co-styrene)-grafted silica suspension in acetonitrile resulted in formation of physical gels preserved colloidal crystal structure. From the reflection spectra, intersphere distance and size of crystallite in the gel formed with Bis(Z-Val)-C12 were confirmed to be mostly same as those of colloidal crystals in suspension.     

Substituent effects of methoxy,methyl, and vinyl groups on glow discharge polymerization

Glow discharge polymerizations in systems of trimethoxymethylsilane, trimethoxyvinylsilane, tetramethylsilane, and trimethylvinylsilane were compared by elemental analysis, infrared (IR) spectroscopy, and ESCA to reveal effects of methoxyl, methyl, and vinyl substituents. The substituent effects appeared in the chemical composition of the polymers formed especially at low W/FM values. Methoxy groups depressed the C/Si and H/Si ratios of the polymers rather than the methyl groups, whereas vinyl groups increased the C/Si and H/Si ratios. On IR spectra the polymers formed from silanes that contained methoxy groups showed fewer absorptions due to Si? H groups and strong absorptions due to Si? OH groups. The polymers from those that contained no methoxy groups showed absorptions of Si? H groups and no absorptions of Si? OH groups. These differences in the environment of Si atoms of polymeric chains also appeared in the Si_2p core level spectra, thus indicating the different fragmentation patterns of the starting materials in glow discharge.     

Synthesis of [1]rotaxane via covalent bond formation and its unique fluorescent response by energy transfer in the presence of lithium ion

Although there have been a lot of reports on the synthesis and properties of [n]rotaxanes (mainly n = 2), only a few reports on the synthesis of [1]rotaxane has been published by V?gtle's group and others (see ref 5). Generally speaking, [1]rotaxane might be expected to exhibit properties different from other rotaxanes, because the rotor and the axle in the [1]rotaxane is bound covalently and closely. We report on a novel method to make [1]rotaxanes via covalent bond formation from a macrocyclic compound. That is, we first prepared a bicyclic compound from macrocycle and then proceeded to [1]rotaxane by aminolysis. This is the first synthetic example of preparation of [1]rotaxane via covalent bond formation, not utilizing weak interactions such as hydrogen bonding, charge transfer, via metal complexation, etc. This method might provide a powerful and new tool for construction of [1]rotaxane as a new supramolecular system. In addition, we investigated energy transfer from rotor to axle using [1]rotaxane that we prepared. Energy transfer occurred perfectly from the naphthalene ring of the rotor to the anthracene ring of the axle. We found also that only lithium ion among alkali ions can drastically enhance the fluorescence intensity. This finding could be applicable to ion-sensing systems, switching devices, and so on.     

Magnetic molecular conductors based on BETS molecules and divalent magnetic anions [BETS = bis(ethylenedithio)tetraselenafulvalene

Several conducting salts based on BETS [where BETS = bis(ethylenedithio)tetraselenafulvalene] molecules and divalent magnetic anions such as the (CoCl(4))(2-), (CoBr(4))(2-), and (MnBr(4))(2-) were prepared. Electrocrystallization by using the (CoCl(4))(2-) anion gave two kinds of crystals. Block-shaped crystals were cleared to be (BETS)(2)CoCl(4), which is an insulator with the high-spin state of cobalt 3d spin. On the other hand, the X-ray crystal structure analysis of a plate-shaped crystal of the (CoCl(4))(2-) salt revealed the system to be kappa-(BETS)(4)CoCl(4)(EtOH), which is metallic down to 0.7 K. The electronic band structure calculation gave a typical two-dimensional cylindrical Fermi surface. However, there is only very weak antiferromagnetic interaction between the S = 3/2 cobalt 3d spins because of its anion-solvent-intermingled layer structure. On the other hand, the electrocrystallization by using the (MnBr(4))(2-) anion yielded the plate-shaped black crystals of the (MnBr(4))(2-) salt. Crystal structure analysis of the (MnBr(4))(2-) salt showed that the salt is theta;-(BETS)(4)MnBr(4)(EtOH)(2) with alternating donor and anion-solvent mixed layers. The stacking direction in one donor layer is perpendicular to those of the neighboring layers. The electrical and magnetic properties of the theta;-(BETS)(4)MnBr(4)(EtOH)(2) salt showed the metallic behavior down to approximately 30 K and the paramagnetism of the high-spin manganese 3d spins. Band structure calculation of this salt gave an elliptical cylindrical Fermi surface. Because the Fermi surfaces of the adjacent donor layers are rotated to each other by 90 degrees, the theta-(BETS)(4)MnBr(4)(EtOH)(2) salt becomes a two-dimensionally isotropic metal.     

Study of the ligand substitution reactions of cis,cis-[(bpy)(2)(L)RuORu(L')(bpy)(2)](n+) (L,L' = H(2)O,OH(-), NH(3)) using electrospray ionization mass spectrometry and (1)H NMR

We have successfully applied electrospray ionization mass spectrometry (ESI-MS) and (1)H NMR analyses to study ligand substitution reactions of mu-oxo ruthenium bipyridine dimers cis,cis-[(bpy)(2)(L)RuORu(L')(bpy)(2)](n+) (bpy = 2,2'-bipyridine; L and L' = NH(3), H(2)O, and HO(-)) with solvent molecules, that is, acetonitrile, methanol, and acetone. The results clearly show that the ammine ligand is very stable and was not substituted by any solvents, while the aqua ligand was rapidly substituted by all the solvents. In acetonitrile and acetone solutions, the substitution reaction of the aqua ligand(s) competed with a deprotonation reaction from the ligand. The hydroxyl ligand was not substituted by acetonitrile or acetone, but it exchanged slowly with CH(3)O(-) in methanol. The substitution reaction of the aqua ligands in [(bpy)(2)(H(2)O)Ru(III)ORu(III)(H(2)O)(bpy)(2)](4+) was more rapid than that of the hydroxyl ligand in [(bpy)(2)(H(2)O)Ru(III)ORu(IV)(OH)(bpy)(2)](4+). In methanol, slow reduction of Ru(III) to Ru(II) was observed in all the mu-oxo dimers, and the Ru-O-Ru bridge was then cleaved to give mononuclear Ru(II) complexes.     

Vapor phase transport and stoichiometry control of cadmium sulfo-selenide

Cadmium sulfo-selenide Cd_1+y(S_xSe_1?x) single crystals were grown by the sublimation method under controlled partial pressures of sulfur and selenium. The partial pressure control was achieved by amounts of sulfur and selenium introduced in a closed growth tube. To control the deviation from stoichiometry y for the specified compositions x, the sum of chalcogen partial pressures Pps(=p_S2+P_Se2) was regulated, holding the partial pressure ratio () constant. The comp osition x of single crystals, grown with appreciable growth rate, was found to be the same one as the source specimen but the electrical conductivity changed extremely from 1 to 10^-12 (ω cm)^-1 with increasing Pps. Hall effect and thermally stimulated current (TSC) were also measured on the high and low conductivity specimens respectively and found to depend upon the controlled Pps. From these experimental results, it was confirmed that the deviation from stoichiometry y was effectively controlled. The transport rate was also precisely measured as a function of controlled Pps.     

Awareness, Belief, and Communication Reaching Consensus

This article studies graph-theoretical conditions under which communication will lead to consensus among players about their decisions in circumstances where there are more than two players and they interact in pair without public announcement. It is shown that consensus on their decisions can be guaranteed if the communication graph contains no cycle. Where none of the requirements for player's knowledge is imposed as in the standard model of knowledge with partitional information structure.     

Carpetlike dense‐layer formation in a polyelectrolyte brush at the air/water interface

A carpetlike dense‐layer formation between a hydrophobic layer and a polyelectrolyte brush layer has been found in the monolayers of an ionic amphiphilic diblock copolymer, poly(1,1‐diethylsilacyclobutane)_m‐block‐poly(methacrylic acid)_n, on a water surface by an X‐ray reflectivity technique. By detailed analysis, we have found that the hydrophilic layer under the water is not a simple layer but is divided into two layers, that is, a carpetlike dense methacrylic acid (MAA) layer near the hydrophobic layer and a polyelectrolyte brush layer. We have also confirmed that a well‐established polyelectrolyte brush is formed only for the m:n = 43:81 polymer monolayer: For m:n = 40:10 and m:n = 45:60 polymer monolayers, only a dense MAA layer is formed. This dense‐layer formation should be the origin of the interesting hydrophobic‐layer thickness variation previously reported; The hydrophobic‐layer thickness takes a minimum as a function of the hydrophilic chain length at any surface pressure studied. An overview of the data for three samples with different chain lengths (m:n = 40:10, 45:60, or 43:81) has shown that the thickness of this dense layer is 10–20 Å and is independent of the surface pressure and polymerization degree of poly(methacrylic acid) (PMAA) in the range studied. This dense‐layer formation is explained by the reasonable speculation that contact with PMAA is thermodynamically more stable than direct contact with water for the diethylsilacyclobutane (Et₂SB) layer on water. In this sense, the dense layer acts like a carpet for the hydrophobic Et₂SB layer, and a 10–20‐Å thickness could be a critical value for the carpet. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1921–1928, 2003     

Observation of B0-->pLambda(pi)(-)

We report the first observation of the charmless hyperonic B decay, B0-->pLambda(pi)(-), using a 78 fb(-1) data sample recorded on the Upsilon(4S) resonance with the Belle detector at KEKB. The measured branching fraction is B(B0-->pLambda(pi)(-))=(3.97(+1.00)(-0.80)+/-0.56)x10(-6). Searches for B0-->pLambda(K)- and pSigma(0)pi(-) yield no significant signals and we set 90% confidence-level upper limits of B(B0-->pLambda(K)-)<8.2x10(-7) and B(B0-->pSigma(0)pi(-))<3.8x10(-6).