Computer-assisted optimization of reversed-phase HPLC isocratic separation of neutral compounds

An appropriate optimization strategy should be used to find a desired resolution or selectivity with a minimum number of experiments in a limited time, which could assure the baseline separation of all target compounds. It was usually realized by means of a specialized computer program. In this paper, mapping optimization method and overlapping resolution mapping were compared for the optimization of a reversed-phase high-performance liquid chromatography (HPLC) isocratic separation of neutral compounds. The calculated resolutions and separation time of 7 to 10 experiments are fitted by different equations, which were used to build a contour plot with a minimum effective resolution and maximum retention time as a function of a mobile phase composition. The balance between resolution and analysis time could be easily realized by the overlapping of the final overlapping resolution mapping and analysis time mapping. The validity of the two methods was confirmed by some typical experiments. The models are simple, visual, and common without theoretical arithmetic.     

A novel and efficient route to diarylmethanes catalyzed by nickel(II) ion on nanoporous carbon

Much improved catalytic carbon-carbon bond-forming reactions between aryl chlorides and Grignard reagents has been achieved using nickel(II) ion on nanoporous carbon.     

Dicobalt octacarbonyl-catalyzed tandem

Novel 5-5-6 tricyclic compounds containing cyclopentenone have been constructed by the dicobalt octacarbonyl catalyzed tandem [2 + 2 + 1] and [2 + 2 + 2] cycloaddition reaction between a diyne and two phenylacethylene under CO pressure.     

Intermolecular coupling in nanometric domains of light-harvesting dendrimer films studied by photoluminescence near-field scanning optical microscopy (PL NSOM)

Near-field scanning optical microscopy (NSOM) has been used to investigate the photophysical characteristics of first- to fourth-generation (G1 to G4) light-harvesting dendrimer thin films containing coumarin-343 and coumarin-2 as the core and peripheral chromophores, respectively. Thin film photoluminescence (PL) spectra exhibit a significant red shift in the lower generations (G1, G2, and G3) as compared to their respective solution PL spectra, implying the formation of excimers. Spatially resolved PL NSOM images exhibit pronounced nanoscopic domains in G1, which become more homogeneous in higher generations due to site-isolation of the core chromophore. G4 exhibits complete site-isolation for these light-harvesting dendrimer films.     

Optimum conditions for preparing micron-sized PMMA beads in the dispersion polymerization using PVA

The optimum conditions for preparing micron-sized monodisperse polymethylmethacrylate (PMMA) beads by dispersion polymerization in a methanol/water mixture were proposed. PMMA forming microspheres having an average molecular weight of 55,300 g/mol, 2.6 μm weight-average diameter, with a 5.3% coefficient of variation and 91% conversion, were successfully obtained in the presence of 15 wt.% of polyvinylalcohol (PVA), 100/50 (g/g) of MeOH/water mixtures at 70°C; the reaction lasted for 8 h. Compared to dispersion polymerization using polyvinylpirrolydone, PVA proved to be an extremely stable steric stabilizer in the dispersion polymerization of methylmethacrylate.     

Reduced Overlap Population Analysis for Triosmium Clusters

The use of reduced overlap population (ROP) analysis from EHMO calculations as a means to gauge the presence of metal–metal bonds in triosmium clusters is examined. A number of triosmium clusters containing bridging ligands have been used as test cases, including the bis-ethoxy bridged cluster Os₃(μ-OEt)₂(CO)₁₀, 1b, and some of its group 15 derivatives Os₃(μ-OEt)₂(CO)₉(EPh₃), 2. These latter clusters are newly synthesized and have been characterized completely, including by single-crystal X-ray crystallographic studies. In honour of Professor Dieter Fenske on his 65th birthday.     

Semialactone, isofouquierone peroxide and fouquierone, three new dammarane triterpenes from Rhus javanica

Three new dammarane triterpenes and semialactic acid were isolated from the stem bark of Rhus javanica. The structures of these triterpenes, named semialactone, isofouquierone peroxide and fouquierone, were elucidated by 2D-NMR analysis (HMQC, 1H-1H COSY and HMBC), and the 13C-NMR data of semialatic acid is revised.     

IDENTIFICATION OF A LUMAZINE PROTEIN FROM PHOTOBACTERIUM LEIOGNATHI BY COHERENT ANTI-STOKES RAMAN SPECTROSCOPY

The vibrational fingerprint in the frequency region 1700-1100 cm^-1 has been obtained for a fluorescent protein purified from the bioluminescent bacterium Photobacterium leiognathi. using the technique of resonance coherent anti-Stokes Raman scattering. The frequencies of the 4 prominent modes are the same as for lumazine protein purified from Photobacterium phosphoreum , and for an authentic sample of 6,7-dimethyl-8-ribityllumazine. The fluorophore in the new protein, therefore, must have the same chemical structure. The absence of frequency shifts between the free and bound ligand, in contrast to observations of fiavoproteins, implies that the lumazine ring undergoes no changes in hydrogen bonding between the free and protein-bound ligand in its ground electronic state. However, changes in relative intensities of two modes are seen, arising from differences in interactions in the excited state, and this is also reflected by differences in fluorescence properties.     

The preparation,isomerization, and characterization of some phosphagerma- and arsagermacarboranes

Treatment of the disodium salts of 7,8- and 7,9-B₉H₉CHE^2? with germanium diiodide in refluxing benzene results in the formation of 1,2,3- and 1,2,7-GeB₉H₉CHE (E = P or As), icosahedral boranes containing three different heteroatoms in the cage. Heating 1,2,7-GeB₉H₉CHP at 512° for 8 hours in an evacuated sealed tube yields a mixture of three new isomers one of which has been isolated and characterized.     

Hydrogen–hydrogen bonding in biphenyl revisited

The evidence for the stabilizing nature of the H–H bonding in planar biphenyl is succinctly reviewed. The stabilizing nature of the H–H bonding is revealed through a comparison of the atomic energy of every atom in planar biphenyl with the same atom in the twisted equilibrium structure. It is shown that the barrier to rotation via the planar transition state is the net resultant of a stabilisation of the four ortho-hydrogen atoms (by 8 kcal/mol each), a stabilisation of the two para-carbon atoms (by 3 kcal/mol each) and by the dominant destabilisation of the two carbon atoms joining the two rings—the two junction carbon atoms—(by 22 kcal/mol each). The energetic stabilisation of the four ortho-hydrogen atoms is further shown to be in large proportion due to the formation of the hydrogen–hydrogen interatomic surface. Furthermore, neither the “bond order” between the two junction carbon atoms nor the total electron delocalisation between the two rings exhibit a significant change in going from the planar to the twisted equilibrium geometry. These findings are in contrast with the classical view of a balance between “steric non-bonded repulsion” and better electron delocalisation as a function of the twist dihedral angle. Similar conclusions have been recently reached by Pacios and Gómez through a study of the electrostatic potential at the position of the hydrogen nuclei. We dedicate this article to Professor TM Krygowski on the occasion of his 70th birthday wishing him a long and productive life.