The first asymmetric esterification of free carboxylic acids with racemic alcohols using benzoic anhydrides and tetramisole derivatives: an application to the kinetic resolution of secondary benzylic alcohols

A variety of optically active carboxylic esters are produced by the kinetic resolution of racemic secondary benzylic alcohols using free carboxylic acids with benzoic anhydride and tetramisole derivatives. 4-Methoxybenzoic anhydride (PMBA) is the best reagent to use in producing the corresponding esters in high ee when the reaction is catalyzed by (+)-benzotetramisole (BTM); by contrast, when non-substituted benzoic anhydride is used as a coupling reagent, the resulting optically active alcohols are obtained with high selectivities. This protocol directly produces chiral carboxylic esters from free carboxylic acids and racemic secondary alcohols by utilizing the trans-acylation process to generate mixed anhydrides from acid components and benzoic anhydride derivatives under the influence of chiral catalysts.     

Representation of molecular configurations by CAST coding method

A configurational CAST (CAnonical representation of STereochemistry) coding method, which represents relative and absolute configuration, is described. The configurational CAST codes are constructed by canonical rotation of the dihedral angles of the input structure before the CAST codes are assigned. Using the configurational CAST, configurational differences can be distinguished independently of conformational differences. Representation of enantiomers is also achieved by a mirror image conversion method. The CAST representation shows the distinctive characteristics of several diastereomers and conformers that were examined. The method clearly represents the differences in configurations. Applications to organic molecules having complex stereochemistry are also demonstrated.     

Xenophilic complexes bearing a Tp(R) Ligand, [Tp(R)M--M'Ln] [Tp(R) = Tp(iPr2), Tp(#) (Tp(Me2,4-Br)); M=Ni, Co, Fe, Mn; M'Ln = Co(CO)4, Co(CO)3(PPh3), RuCp(CO)2]: the two metal centers are held together not by covalent interaction but by electrostatic attraction

A series of dinuclear complexes, [Tp(R)M--M'L(n)] [Tp(iPr(2) )M--Co(CO)(4) (1; M=Ni, Co, Fe, Mn); Tp(#)M--Co(CO)(4) (1'; M=Ni, Co); Tp(#)Ni--RuCp(CO)(2) (3')] (Tp(iPr(2) )=hydrotris(3,5-diisopropylpyrazolyl)borato; Tp(#) (Tp(Me(2),4-Br))=hydrotris(3,5-dimethyl-4-bromopyrazolyl)borato), has been prepared by treatment of the cationic complexes [Tp(iPr(2) )M(NCMe)(3)]PF(6) or the halo complexes [Tp(#)M--X] with the appropriate metalates. Spectroscopic and crystallographic characterization of 1-3' reveals that the tetrahedral, high-spin Tp(R)M fragment and the coordinatively saturated carbonyl-metal fragment (M'L(n)) are connected only by a metal-metal interaction and, thus, the dinuclear complexes belong to a unique class of xenophilic complexes. The metal-metal interaction in the xenophilic complexes is polarized, as revealed by their nu(CO) vibrations and structural features, which fall between those of reference complexes: covalently bonded species [R--M'L(n)] and ionic species [M'L(n)](-). Unrestricted DFT calculations for the model complexes [Tp(H(2) )Ni--Co(CO)(4)], [Tp(H(2) )Ni--Co(CO)(3)(PH(3))], and [Tp(H(2) )Ni--RuCp(CO)(2)] prove that the two metal centers are held together not by covalent interactions, but by electrostatic attractions. In other words, the obtained xenophilic complexes can be regarded as carbonylmetalates, in which the cationic counterpart interacts with the metal center rather than the oxygen atom of the carbonyl ligand. The xenophilic complexes show divergent reactivity dependent on the properties of donor molecules. Hard (N and O donors) and soft donors (P and C donors) attack the Tp(R)M part and the ML(n) moiety, respectively. The selectivity has been interpreted in terms of the hard-soft theory, and the reactions of the high-spin species 1-3' with singlet donor molecules should involve a spin-crossover process.     

Phenomenological analysis of elongational flow birefringence in semidilute solutions of hydroxypropylcellulose

The relaxation time of a polymer chain in an elongational flow field was investigated for hydroxypropylcellulose (HPC) semidilute solution systems by two methods: phenomenological analysis of elongational flow-induced birefringence, and dynamic light scattering (DLS) and rheological measurements. To understand the relaxation time of an entangled semiflexible polymer solution in an elongational flow field, scaling analysis of the elongational flow-induced birefringence curve was performed. The results of both temperature and concentration scaling analyses showed that birefringence curves at different temperatures and at several HPC concentrations were described well by a universal birefringence–strain rate curve. This scaling behavior was compared with the "fuzzy cylinder" model. The critical strain rate corresponded to the correlation time of the slow relaxation mode determined by DLS measurement and the relaxation spectrum obtained by dynamic viscoelasticity measurement. The elongational flow-induced birefringence observed in an HPC semidilute solution was concluded to be attributed to the orientation of the HPC segment in the entangled molecular system, because the dominant relaxation mode is found to be the concentration fluctuation of an entangled molecular cluster in a quiescent state.     

Gold nanoparticle arrays directly grown on nanostructured indium tin oxide electrodes: Characterization and electroanalytical application

This work describes an improved seed-mediated growth approach for the direct attachment and growth of mono-dispersed gold nanoparticles on nanostructured indium tin oxide (ITO) surfaces. It was demonstrated that, when the seeding procedure of our previously reported seed-mediated growth process on an ITO surface was modified, the density of gold nanospheres directly grown on the surface could be highly improved, while the emergence of nanorods was restrained. By field emission scanning electron microscopy (FE-SEM) and cyclic voltammetry, the growth of gold nanoparticles with increasing growth time on the defect sites of nanostructured ITO surface was monitored. Using a [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ redox probe, the increasingly facile heterogeneous electron transfer kinetics resulting from the deposition and growth of gold nanoparticle arrays was observed. The as-prepared gold nanoparticle arrays exhibited high catalytic activity toward the electrooxidation of nitric oxide, which could provide electroanalytical application for nitric oxide sensing.     

Crystal Structure and Property of Perovskite-Type Oxides Containing Ion Vacancy

Studies on the role of oxygen vacancy in structural change of nonstoichiometric perovskites and a property of oxygen-deficient perovskite-related K₂NiF₄ compounds are reviewed.The structural changes on which the authors focused are cation ordering and lattice distortion. The relationship between the distortion and oxygen vacancy was investigated by comparing the structures of Sr₂(Sr_1-xM_x)TaO_6-d (M = Ca²⁺ and Nd³⁺) solid solutions. It was found that distortion of a perovskite-type lattice decreased with an increasing amount of oxygen vacancies. In order to investigate the relationship between the cation ordering on octahedral sites and oxygen vacancy, structures of stoichiometric Sr_2-xLa_xCo_1-yTa_1+yO₆ and oxygen-deficient Sr_2-xLa_xMg_1-yTa_1+yO_6-d solid solutions were compared. The authors' work reveals that the cation ordering affects the amount of oxygen vacancies in addition to cation charge and size.     

Analysis by partial reflection spectrometry of protonated tetraphenylporphyrin adsorbed at a liquid-liquid interface

Visible reflection spectra of diprotonated meso-tetraphenylporphyrin adsorbates spontaneously formed at a dodecane-aqueous sulfuric acid interface have been measured using a home-made device comprising a prism-cell and variable-angle optics. The tilt angle of the pyrrole ring plane was estimated to be 47 degrees from the interface normal by use of an experimentally evaluated molecular density (1.20x10(-10) mol cm(-2)) of the diprotonated molecule in a monolayer form at the liquid-liquid interface. Positive and negative bands have been observed in the p-polarized partial internal reflection (p-PIR) spectra, whose band locations correspond to those in p-polarized external reflection (p-ER) spectra. Nevertheless, the bands in the p-PIR exhibited reversed sign to those of p-ER spectra. These suggest that the surface selection rule of the p-PIR spectrometry has a reversal rule of p-ER and p-PIR can also be used for the analysis of molecular orientation.     

Unusual enlargment of magnetic interactions in the lowest excited states of nitroxide radical chromium(III) complexes as revealed by magnetic circular dichroism and luminescence

Magnetic circular dichroism and NIR luminescence of nitroxide radical complexes, [Cr(III)(beta-diketonato)(2)(NIT2py or IM2py)]PF(6), demonstrate that the energy gaps between the singlet ((1)L(D)) and triplet ((3)L(D)) spin coupled levels in the lowest excited (2)E(g),(2)T(1g) states are much larger than those in the ground state. This is the first observation of magnetic interactions in the excited states of radical complexes, which could be elucidated in terms of the exchange mechanism.     

Molecular structure of 1,1-dichloroethylene as studied by gas electron diffraction and microwave data. Estimation of equilibrium structure by an extended anharmonic model analysis

The r_z structure of 1,1-dichloroethylene has been determined by a joint analysis of the electron diffraction intensity and the rotational constants as follows: $\text{r}{}_{\mathrm{<mtext>z</mtext>}}\text{(}\text{CH}\text{) = 1.088 ± 0.011, r}{}_{\mathrm{<mtext>z</mtext>}}\text{(}\text{CC}\text{) = 1.329 ± 0.003, r}{}_{\mathrm{<mtext>z</mtext>}}\text{(}\text{CCl}\text{) = 1.725 ± 0.002}\text{A}\text{?}\text{, ∠}{}_{\mathrm{<mtext>z</mtext>}}\text{HCH}\text{= 121.4 ± 0.7}\text{and}\text{∠}{}_{\mathrm{<mtext>z</mtext>}}\text{ClCCl}\text{= 114.1 ± 0.2°}$. The uncertainties represent estimated limits of error. The observed structural parameters are compared with those for related compounds and the systematic trends in the bond lengths and bond angles are discussed. The effective constants representing anharmonicity have been obtained from an analysis of the isotopic differences in the r_z structure. By using the r_z parameters and the effective constants, the equilibrium structure has been estimated as follows: $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{CH}\text{) = 1.079 ± 0.012, r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{CC}\text{) = 1.324 ± 0.005, r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{CCl}\text{) = 1.721 ± 0.003}\text{A}\text{?}\text{, ∠}{}_{\mathrm{<mtext>e</mtext>}}\text{HCH}\text{= 120.5 ± 0.8}\text{and}\text{∠}{}_{\mathrm{<mtext>e</mtext>}}\text{ClCCl}\text{= 114.0 ± 0.3°}$.