X-ray Crystallographic Observation of Chiral Transformations within a Metal–Peptide Pore

Porous metal complexes enable single-crystal X-ray crystallographic observation of included guests or reaction intermediates through simple soaking with the guests/substrates. Previous studies on this technique have often encountered difficulties in the observation of chiral structures because the host frameworks had no chirality. We synthesized a new metal–peptide porous complex through a folding-and-assembly strategy and utilized the chiral pore for trapping chiral guests. Chiral alcohols and ketones were successfully included within the pore. Crystallographic analyses clearly revealed not only their chemical structures but also chiral transformation events within the pore such as fixed conformations or an unstable hemiacetal formation.     

A Hexagonal Planar Metal Complex

A six‐coordinate [ML₃Z₃]‐type transition‐metal complex with a hexagonal planar geometry has been isolated and characterized, extending the scope of six‐coordinate metal coordination compounds to those with a geometry beyond octahedral and trigonal prismatic.     

Chiral resolution of monosaccharides as 1-phenyl-3-methyl-5-pyrazolone derivatives by ligand-exchange CE using borate anion as a central ion of the chiral selector

Six reducing monosaccharides (mannose, galactose, fucose, glucose, xylose, and arabinose) were derivatized with 1-phenyl-3-methyl-5-pyrazolone (PMP) and chiral resolution of these racemic PMP-monosaccharides was studied by ligand-exchange CE using borate anion as a central ion of the chiral selector and (S)-3-amino-1,2-propanediol (SAP) as a chiral selector ligand. PMP-mannose, PMP-galactose and PMP-fucose were successfully enantioseparated. Lowering the capillary temperature increased the resolution of PMP-mannose system, but decreased that of PMP-galactose and PMP-fucose systems. Whereas the maximum resolution was obtained at pH 8.9 in the PMP-mannose system, resolution increased gradually with pH in the PMP-galactose and PMP-fucose systems. Expecting the formation of the ternary borate complexes with SAP and PMP-monosaccharide in the CE experiments, the optimized structures of the borate diastereomers were obtained by semiempirical molecular orbital calculations to discuss the structural difference of the diastereomers in connection with the enantioseparation behaviors.     

Layer-by-layer assembly of partially sulfonated isotactic polystyrene with poly(vinylamine)

The stereoregular synthetic polymer isotactic polystyrene bearing partially sulfonated groups (SiPS) was used as a layer-by-layer assembled thin film for the first time. When a low molecular weight compound was employed as the pair for the alternative layer-by-layer (LbL) assembly, the frequency shift was very small using quartz crystal microbalance (QCM) analysis, whereas poly(vinylamine) (PVAm) formed an effective pair for the construction of LbL films with SiPS. When it was neutralized, SiPS was not assembled, probably due to the loss of effective polymer-polymer interactions. The ionic strength conditions revealed a slight difference of the assembly behavior on the isotactic polymer as compared to the atactic one. The assembled LbL film showed the same peaks over the range from 1141 to 1227 cm(-1) and 700 cm(-1) in the FT-IR/ATR spectra as the bulk complex of SiPS/PVAm, and the thickness on one side was calculated at 76 nm by QCM analysis. The surface roughness of the film was also observed by AFM.     

Molecular weight between entanglements for linear d-glucans

Dynamic viscoelasticity measurements were carried out for concentrated solutions of linear d-glucans in BmimCl to examine the effect of the linkage between repeating units of glucose on the rheological properties. The values of molecular weight between entanglements (M _e) were determined for four d-glucans: curdlan, pullulan, cellulose, and amylose. From the concentration dependence of M _e, the value of M _e in the molten state (M _e,melt) for each d-glucan was estimated as a material constant. The order of M _e,melt became cellulose?<?pullulan?<?curdlan?<?amylose, indicating that the linkage is actually influential in M _e,melt for the linear d-glucans. The relationship between M _e,melt and the molecular structure of the d-glucans were discussed assuming that the values of M _e,melt for the d-glucans primarily reflect the chain stiffness such as the characteristic ratio C _∞ on the analogy of synthetic polymers. Although the trend was not so clear, it was shown that N _unit is a decreasing function of C _∞ .     

Onsager coefficients of a Brownian Carnot cycle

We study a Brownian Carnot cycle introduced by Schmiedl and Seifert [Europhys. Lett. 81, 20003 (2008)] from a viewpoint of the linear irreversible thermodynamics. By considering the entropy production rate of this cycle, we can determine thermodynamic forces and fluxes of the cycle and calculate the Onsager coefficients for general protocols, that is, arbitrary schedules to change the potential confining the Brownian particle. We show that these Onsager coefficients contain the information of the protocol shape and they satisfy the tight-coupling condition irrespective of whatever protocol shape we choose. These properties may give an explanation why the Curzon-Ahlborn efficiency often appears in the finite-time heat engines.     

Binding of metal ions by polyethylenimine and its derivatives

Measurements have been made of the binding of divalent metal ions, Cu²⁺, Ni²⁺, Co²⁺, and Zn²⁺ ions, by polyethylenimine (PEI) and its acetyl or alkyl derivatives by the equilibriumdialysis technique. These metal ions, in particular the Cu²⁺ ion, exhibited tremendously remarkable binding affinity toward PEI. The extent of complexation of the polymer with the metal ions was decreased markedly by acetylation or alkylation of the polymer. PEI with no primary amine showed an appreciable decrease in its affinity for the metal ion. These results indicate the participation of the primary amine of the polymer in the formation of the complex. A cooperative binding isotherm was observed in PEI–metal ion complex formation, suggesting swelling or conformational change of the polymer induced by this coordination process. Binding of the Cu²⁺ ion by PEI was found to be essentially independent of temperature over the range 5–35°C.