Evaluation of chiral bidentate ligand–metal complexes in asymmetric 1,3-dipolar cycloaddition reaction of nitrones with 3-alkenoyl-2-oxazolidinones

For evaluation of a chiral C₂-symmetric bis(oxazoline) ligand, its Lewis acid complexes-catalyzed asymmetric 1,3-dipolar cycloaddition reactions of nitrones with electron-deficient dipolarophiles, 3-(2-alkenoyl)-1,3-oxazolidin-2-ones, have been investigated and it was found that the cycloadditions using a Cu(II)-bis(oxazoline) complex under optimized reaction conditions induced extremely high enantioselectivity.     

Rotational isomerism as a dynamical molecular process

A critical review is presented on the studies of the internal rotation potential function which is indispensable in understanding rotational isomerism from a dynamical point of view. Molecules so far investigated are classified into a few groups to clarify what factors govern the potential function. As an application of these results, the molecular structures of some bicyclic compounds are discussed, where the internal rotation is shown to play an important role. The recent microwave studies on two molecules of fundamental importance in the internal rotation problem, namely ethane and dimethylacetylene, are briefly mentioned.     

Structure of aszonalenin,a new metabolite of aspergillus zonatus

Aszonalenin ($\text{1}$) has been isolated from $\text{Aspergillus zonatus}$ together with LL-S490β ($\text{2}$) and the structure of $\text{1}$ has been established by spectroscopic evidences and chemical transformation.     

New alkaline earth aluminum hydride with one-dimensional zigzag chains of [AlH6]: synthesis and crystal structure of BaAlH5

The title hydride and its deuteride were successfully synthesized. The crystal structure of the deuteride was determined by time-of-flight neutron powder diffraction. BaAlD(5) crystallizes with a new orthorhombic structure in space group Pna2(1) (No. 33), cell parameters a = 9.194(1) A, b = 7.0403(9) A, and c = 5.1061(6) A, Z = 4. BaAlH(5) is the first example that contains one-dimensional zigzag chains of [AlH(6)] along the crystallographic c axis.     

Fine structure and transition probabilities of the 2p 5 nl bound excited states of Ne atom

We present a semi-empirical calculational procedure for thep ⁵ nl bound excited states of rare gas atoms based on the use of an LS-dependent orbital for an excitednl electron outside a frozen Hartree-Fockp ⁵ core. The spin-orbit interaction is accounted for approximately using a localized Hartree potential. The contribution from the long-range core polarization is estimated by using a parametrized potential. A model potential is also introduced to represent partially the short-range multi-electron interactions for thep ⁵ np levels. The energy levels are calculated by diagonalizing the Hamiltonian matrix following anLS →jl transformation. The calculated fine structure of the Nep ⁵ ns,p ⁵ np,p ⁵ nd, andp ⁵ nf ¦ (jl)KJ〉 levels are in close agreement with the observed level splittings. The transition probabilities are also in agreement with earlier theoretical and experimental results.     

Controlled kinetics of non-enzymatic chemiluminescence reactions for simple imaging of DNA and protein

A robust and sensitive non-enzymatic chemiluminescence (CL) imaging method is presented. In the method a fast-emitting CL reaction is tuned to furnish a slower-emitting reaction suitable for simple CL imaging. Typically, non-enzymatic CL reactions between luminol or fluorescein and oxygen species generated by KCN as catalyst, were rather fast and unsuitable for CL imaging; the speed of the reactions could, however, be reduced substantially by changing KCN for CH(3)CN or benzonitrile. Light emission from the tuned CL reaction was intense and long-lived, and even with a simple arrangement high sensitivity could be achieved. The maximum CL peak was reached after approximately 1.5 min in the presence of 25% acetonitrile, and as little as 16 fmol commercial isoluminol-labeled streptavidin was detected and visualized on either microplate or membrane. The approach was further illustrated by imaging of DNA on a membrane and of antibody on a microplate by use of biotin-streptavidin chemistry. Overall, this simple, economical, and sensitive CL imaging system is expected to be very useful in biochemical analysis, and greatly complements currently used enzyme-based CL imaging methods, especially in routine applications.     

Theoretical study of benzonitrile clusters in the gas phase and their adsorption onto a Au(111) surface

We made theoretical calculations for a benzonitrile molecule and its clusters in the gas phase and as adsorbed on the Au(111) surface, to explain the observation by scanning tunneling microscope, that is, the trimer formation of cyanophenyl porphyrins adsorbed onto the Au(111) surface. With regard to the gas-phase species, ab initio calculations showed that (1) the benzonitrile dimer has a single stable structure that is planar and antiparallel; (2) the trimer has two isoenergetic stable structures, that is, a planar and cyclic structure and an antiparallel and nonplanar one; (3) the clusters are more stable, at low temperatures, than the monomer. For the adsorbed species, we made quantum mechanical/molecular mechanical calculations in which the interaction between the adsorbates and the surface is evaluated in a molecular-mechanical way by using analytical potential functions and an image charge model. Because the stable structures were found to be similar to those in the gas phase, the cluster formation of adsorbed cyanophenyl porphyrins was attributed to the interaction between cyanophenyl groups, which is barely affected by adsorbate-surface interaction. It was also found that the adsorbed cyclic benzonitrile trimer is more stable than the monomer and the dimer because the relative stability is dependent on enthalpy alone. We therefore concluded that the preferential formation of trimers by the adsorbed cyanophenyl porphyrins is due to the negligible contribution of entropy to the relative stability of the adsorbed species and that the adsorption hardly changes the situation found in the gas phase.     

Determination of methylated arginines by column-switching high-performance liquid chromatography-fluorescence detection

A column-switching high-performance liquid chromatography (HPLC)-fluorescence detection method for the determination of three methylated arginines, N(G)-monomethyl-L-arginine (L-NMMA), N(G),N(G)-dimethyl-L-arginine (asymmetric dimethyl-L-arginine, ADMA), and N(G),N(G)'-dimethyl-L-arginine (symmetric dimethyl-L-arginine, SDMA), which are endogenous nitric oxide synthase inhibitors, was developed. After fluorescence derivatization of plasma samples with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F), the samples were injected into the HPLC system. The NBD-derivatized methylated arginines were trapped on a cation exchange column with filter to remove proteins, separated within 42 min on a reversed-phase column, and detected at an emission wavelength of 530 nm with excitation at 470 nm. The detection limits were 10 fmol for L-NMMA and 20 fmol for ADMA and SDMA with a signal-to-noise ratio of 3. A good linearity for calibration curves for each methylated arginine was observed within the range of 50-5000 fmol using homoarginine as an internal standard. The proposed method was applied to the quantitative determination of L-NMMA, ADMA and SDMA in rat plasma. The concentrations of L-NMMA, ADMA and SDMA in rat plasma were 0.16 +/- 0.01, 0.73 +/- 0.02 and 0.41 +/- 0.05 micromol l(-1), respectively (n= 5).     

On-line preconcentration using dual mini-columns for the speciation of chromium(III) and chromium(VI) and its application to water samples as studied by inductively coupled plasma-atomic emission spectrometry

On-line preconcentration system for the selective, sensitive and simultaneous determination of chromium species was investigated. Dual mini-columns containing chelating resin were utilized for the speciation and preconcentration of Cr(III) and Cr(VI) in water samples. In this system, Cr(III) was collected on first column packed with iminodiacetate resin. Cr(VI) in the effluent from the first column was reduced to Cr(III), which was collected on the second column packed with iminodiacetate resin. Hydroxyammonium chloride was examined as a potential reducing agent for Cr(VI) to Cr(III).The effects of pH, sample flow rate, column length, and interfering ions on the recoveries of Cr(III) were carefully studied. Five millilitres of a sample solution was introduced into the system. The collected species were then sequentially washed by 1 M ammonium acetate, eluted by 2 M nitric acid and measured by ICP-AES. The detection limit for Cr(III) and Cr(VI) was 0.08 and 0.15 μg l⁻¹, respectively. The total analysis time was about 9.4 min.The developed method was successfully applied to the speciation of chromium in river, tap water and wastewater samples with satisfied results.     

Electron-phonon interactions in charged cubic fluorocarbon cluster, (CF)8

Electron-phonon interactions in the charged cubic fluorocarbon, (CF)8 are studied, and compared with those in charged (CH)8 and (CD)8. The A1g mode of 1470 cm(-1) much more strongly couples to the a1g lowest unoccupied molecular orbitals (LUMO) than the A1g mode of 554 cm(-1) in (CF)8. The T2g mode of 1030 cm(-1), the Eg mode of 980 cm(-1), and the A1g mode of 1470 cm(-1) strongly couple to the t2u highest occupied molecular orbitals (HOMO) in (CF)8. The total electron-phonon coupling constants for the monoanion (l(-1)) and monocation (l(+1)) of (CF)8 are estimated to be 0.932 and 0.585 eV, respectively. The logarithmically averaged phonon frequencies for the monoanion (omega(ln,-1)) and monocation (omega(ln,+1)) of (CF)8 are estimated to be 1365 and 998 cm(-1), respectively. The l(-1) and omega(ln,-1) values increase much more significantly by H-F substitution than by H-D substitution in cubane. The larger displacements of carbon atoms in the high frequency vibronic active mode in (CF)8 than those in (CD)8 due to larger atomic mass of fluorine than that of deuterium, and the unchanged electron distributions in the LUMO somewhat localized on carbon atoms as a consequence of H-F and H-D substitution in cubane, are the main reason why the l(-1) and omega(ln,-1) values increase much more significantly by H-F substitution than by H-D substitution. The l(+1) and omega(ln,+1) values less significantly change than the l(-1) and omega(ln,-1) values by H-F substitution as well as by H-D substitution in cubane. This is because the t2u HOMO in (CF)8 and the t2g HOMO in (CH)8 are somewhat localized on fluorine atoms, and thus, the high frequency vibronic active modes in which the displacements of carbon atoms are large cannot necessarily very strongly couple to the HOMO somewhat localized on fluorine atoms in (CF)8.