An azonia derivative of hexahelicene

In 8a‐azonia­[6]­helicene hexa­fluoro­phos­phate or 8a‐azoniaphenanthro[3,4‐c]phen­an­threne hexa­fluoro­phos­phate, C₂₅H₁₆N⁺·PF₆⁻, replacement of an outer bridgehead carbon of hexahelicene by a quaternary Nsp² atom results in a geometrical change in the helical structure. The racemic heterohelicene forms homochiral columnar stacks through intermolecular π–π donor–acceptor interactions in the crystalline state.     

Mechanism of silver(I)-catalyzed Mukaiyama aldol reaction: active species in solution in AgPF6-(S)-BINAP versus AgOAc-(S)-BINAP systems

Silver(I)-diphosphine complex is an effective catalyst for Mukaiyama Aldol reaction in polar solvents. AgPF₆-(S)-BINAP cationic chiral complex indicated a good activity and could afford fairly high enantioselectivity in the reaction of aromatic aldehydes and silyl enol ethers. On the other hand, AgOAc-(S)-BINAP system afforded the aldol product of the absolute configuration opposite to that by AgPF₆-(S)-BINAP and very high catalytic activity was shown. The structure and equilibrium state of Ag(I)-BINAP complexes in solution were examined to understand the reaction mechanism. In AgPF₆ system [Ag((S)-BINAP)₂]PF₆ (1a), [Ag((S)-BINAP)]PF₆ (1b), [Ag₂((S)-BINAP)](PF₆)₂ (1c) and AgPF₆ are present in solution. The active species of the aldol reaction in DMF is [Ag((S)-BINAP)]PF₆ (1b), which exists as a minor species in solution. For this cationic Ag(I) catalyst, cyclic transition state containing substrate and silyl enol ether is assumed. In AgOAc-(S)-BINAP system, active species is also monomeric AgOAc((S)-BINAP) (2b) species which exists as a major component in solution and strong interaction was observed with a silyl enol ether. The reaction by AgOAc-(S)-BINAP catalyst is concluded to proceed as follows: nucleophile forms a complex with AgOAc-(S)-BINAP species and is activated. This complex attacks aldehydes to afford aldol adduct via acyclic transition state.     

Formation and structural observation of cesium encapsulated single-walled carbon nanotubes

Cesium encapsulation inside single-walled carbon nanotubes (SWNTs) is for the first time realized by ion irradiation of SWNTs immersed in a magnetized alkali-metal plasma, the configuration of which is confirmed to comprise three varieties by field emission type transmission electron microscopy (FE-TEM) and scanning TEM (STEM) observation.     

Synthesis and reactions of methylbenzo[c]quinolizinium salts

Six isomers of the methylbenzo[c]quinolizinium salt 3 including four new monomethyl derivatives were synthesized by thermal-intramolecular quaternization of the cis-methyl-substituted 2-[2-(2-chlorophenyl)-vinyl]pyridines 4 or by the irradiation of trans- 4 with selected wavelengths (290 < λ < 340 nm and λ > 400 nm) in acetonitrile. Among the regioisomeric monomethyl derivatives 3 , the 1-, 3-, and 6-methyl derivatives 3b, 3d , and 3g reacted with p-methoxybenzaldehyde in the presence of bis(l-piperidino)-(p-methoxyphenyl)-methane 7 to yield trans-(p-methoxystyryl)benzo[c]quinolizinium salts 6 . The reactivity of 3 and methylbenzo[a]quinolizinium salts 1 was discussed on the basis of their π-electron energy.     

Hopping electron model with geometrical frustration: kinetic Monte Carlo simulations

The hopping electron model on the Kagome lattice was investigated by kinetic Monte Carlo simulations, and the non-equilibrium nature of the system was studied. We have numerically confirmed that aging phenomena are present in the autocorrelation function \hbox{$C \, \left({t,t_{W} } \right)$}C?t,tW)( of the electron system on the Kagome lattice, which is a geometrically frustrated lattice without any disorder. The waiting-time distributions \hbox{$p\left(\tau \right)$}pτ)( of hopping electrons of the system on Kagome lattice has been also studied. It is confirmed that the profile of \hbox{$p\, \left(\tau \right)$}p?τ)( obtained at lower temperatures obeys the power-law behavior, which is a characteristic feature of continuous time random walk of electrons. These features were also compared with the characteristics of the Coulomb glass model, used as a model of disordered thin films and doped semiconductors. This work represents an advance in the understanding of the dynamics of geometrically frustrated systems and will serve as a basis for further studies of these physical systems.     

Enzymatic synthesis of cellulose in space: gravity is a crucial factor for building cellulose II gel structure

Cellulose - We previously reported in vitro synthesis of highly ordered crystalline cellulose II by reverse reaction of cellodextrin phosphorylase from the cellulolytic bacterium Clostridium...