Synthesis of polymer microspheres functionalized with chiral ligand by precipitation polymerization and their application to asymmetric transfer hydrogenation

Monodisperse, crosslinked poly(divinylbenzene) and poly(methacrylic acid‐co‐ethylene glycol dimethacrylate) microspheres with (1R,2R)‐N¹‐toluenesulfonyl‐1,2‐diphenylethylene‐1,2‐diamine ((R,R)‐TsDPEN) moiety were successfully prepared by precipitation polymerization. Introduction site of the (R,R)‐TsDPEN moiety into the polymer microspheres could be controlled by changing the order of addition of the corresponding monomers. The functionalized polymer microspheres were applied to asymmetric transfer hydrogenation of ketone and imine. Polymer microsphere‐supported chiral catalysts showed good reactivity and enantioselectivity in the catalytic asymmetric transfer hydrogenations. Chiral secondary alcohol was quantitatively obtained with 94% ee in the asymmetric transfer hydrogenation of acetophenone in water. We also found that introduction site of the chiral catalyst and hydrophobicity of the microspheres, as well as degree of the crosslinking, affected the yield and enantioselectivity of chiral product in this reaction. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3340–3349, 2010     

Broad-spectrum radical cyclizations boosted by polarity matching. Carbonylative access to alpha-stannylmethylene lactams from azaenynes and CO

Free-radical mediated stannylcarbonylation of azaenynes provides a general [n + 1]-type annulation approach leading to alpha-stannylmethylene lactams. The cyclization is unusual in its breadth, covering 4-exo, 5-exo, 6-exo, 7-exo, and 8-exo modes.     

Optimized separation and determination of methyl sulfone metabolites of polychlorinated biphenyls (PCBs) and p,p'-DDE in biota samples

An optimised method is described for the determination of 27 methyl sulfone polychlorobiphenyls (PCBs) and DDE in biota samples. Initially, the samples were extracted by hot Soxhlet and the methyl sulfones were separated by liquid/liquid extraction with concentrated sulfuric acid and back-extracted with hexane. The parameters of the back-extraction were studied and it was found that for a quantitative extraction of the methyl sulfones from the concentrated acid layer, a 50% dilution with cold water should be done. The hexane layer containing the methyl sulfones was further cleaned-up on basic silica (33% KOH) and Florisil. After concentration, the extract was analysed by gas chromatography-mass spectrometry (GC-MS) with electron capture negative ionisation (ECNI) in selected ion monitoring mode (SIM). It was shown that, for methyl sulfones, the ion formation was dependent on the chlorine substitution, position of the MeSO2-group and the ion source temperature. If the ion source temperature was higher than 200 degrees C, [M-CH3]- was the predominant ion for most methyl sulfones. Therefore, for increased sensitivity, quantitation of most congeners was done using [M-CH3]- ions instead of the molecular ion as used in previously reported methods. The method was validated for the determination of 26 tri- to hepta- 3- and 4-substituted MeSO2-PCBs and 3-MeSO2-DDE in animal and human tissues. Good sensitivity and selectivity of the method were obtained. Limits of detection (LODs) ranged from 0.06 to 0.10 ng g(-1) lipid weight. Average recoveries of individual congeners from vegetable oil spiked with individual standards (3.33 ng g(-1)) ranged from 73 to 112% with a mean value of 89%. The coefficients of variation ranged from 5.2 to 12.2%, which is within the acceptable range for environmental analyses.     

Poly(diacetylene)-nanofibers can be fabricated through photo-irradiation using natural polysaccharide schizophyllan as a one-dimensional mold

Schizophyllan interacts with various 1,4-diphenylbutadiyne derivatives to induce their chirally-twisted packing. A series of referential experiments using other polysaccharides (amylose, pullulan, dextran, etc.) and a carbohydrate-appended detergent (dodecyl-beta-d-glucopyranoside) indicates that these 1,4-diphenylbutadiyne derivatives are accommodated within a tubular cavity constructed by a helical superstructure of schizophyllan. In these 1,4-diphenylbutadiyne derivatives, 1,4-bis(p-propionamidophenyl)butadiyne can be easily polymerized through UV-irradiation, in which schizophyllan acts as a one-dimensional mold to produce the corresponding poly(diacetylene)s with fibrous morphologies. Detailed investigations on this unique approach to prepare the nanofibers revealed that it includes two individual processes, that is, 1) UV-mediated polymerization of encapsulated 1,4-bis(p-propionamidophenyl)butadiyne to produce immature nanofibers and 2) their reorganization through hydrophobic interfiber interactions into ordered nanofibers. The other 1,4-diphenylbutadiyne derivatives could not be polymerized through UV-irradiation, indicating that the p-propionamido-functionalities play substantial roles for a suitable packing of the monomer for the polymerization. The other 1,4-diphenylbutadiyne derivatives, however, can be also polymerized through gamma-ray irradiation in the presence of schizophyllan to give the corresponding poly(diacetylene)-nanofibers, emphasizing the wide applicability of the schizophyllan-based strategy for polymerization of various 1,4-diphenylbutadiyne derivatives.     

Retention behaviour of binaphthyl compounds in enantiomeric separation by microcolumn liquid chromatography with micellar bile-salt mobile phases

Summary Optical isomers of substituted binaphthyl, compounds such as 2,2-dihydroxy-1,1-dinaphthyl and 1,1-binaphthyl-2,2-diyl hydrogenphosphate are, separated by HPLC using micellar bile-salt mobile phases. Operating conditions which affect the optical resolution of these enantiomers are examined. The largest separation factor achieved for these enantiomers is 2.74. The elution order of the latter enantiomers changes with mobile phase composition.     

Synthesis of oligonucleotides containing Fapy.dG (N(6)-(2-deoxy-alpha,beta-D-erythropentofuranosyl)-2,6-diamino-4-hydroxy-5-formamidopyrimidine) using a 5'-dimethoxytrityl dinucleotide phosphoramidite

Fapy.dG (N(6)()-(2-deoxy-alpha,beta-d-erythropentofuranosyl)-2,6-diamino-4-hydroxy-5-formamidopyrimidine) is a modified purine lesion produced by a variety of DNA-damaging agents, which shows interesting biochemical properties. The previous method for synthesizing oligonucleotides containing Fapy.dG utilized a reverse dinucleotide phosphoramidite, which also required the synthesis of the appropriate reverse phosphoramidites. An improved method for synthesizing oligonucleotides containing Fapy.dG, which does not require reverse phosphoramidites, is described. Fapy.dG containing dinucleotide phosphoramidites containing 5'-thymidine (11a) or 5'-deoxycytidine (15) are prepared and employed in oligonucleotide synthesis. Oligonucleotide purity is assayed using the DNA repair enzyme formamidopyrimidine DNA glycosylase and by ESI-MS.     

Electrostatic Interactions That Determine the Rate of Pseudorotation Processes in Oxyphosphorane Intermediates: Implications with Respect to the Roles of Metal Ions in the Enzymatic Cleavage of RNA

The enzymatic cleavage of RNA takes place via a cyclic pentacoordinate oxyphosphorane intermediate/transition state. We carried out ab initio investigations on the neutral cyclic oxyphosphorane, which exists as a stable intermediate. As a consequence of the conformational preferences of the pentacoordinate trigonal bipyramidal intermediates, the rotation of the P-OH bonds is strongly coupled with the reaction coordinate for the pseudorotation process. In addition, the neutral PF(4)OH species has a higher barrier to pseudorotation than the corresponding anionic species PF(4)O(-). These findings are related to the positive charge of the hydrogen atoms on the equatorial oxygens in the trigonal bipyramidal structures: the hydrogen atoms preferably adopt eclipsed positions relative to the axial ligands. Fixing the cationic species in these regions causes an increase in the barrier heights for pseudorotation processes and, thus, prevents isomerization by pseudorotation. Consequently, metal coordination in the double-metal ion mechanism for enzymatic cleavage of RNA should serve to exclusively stabilize the trigonal bipyramidal intermediate/transition state for the in-line attack and departure process.     

Speciation of mercury compounds in waste water by microcolumn liquid chromatography using a preconcentration column with cold-vapour atomic absorption spectrometric detection

A microcolumn liquid chromatographic method with cold-vapour atomic absorption spectrometric detection was developed for the speciation of mercury compounds in waste water. The sample solution containing mercury at the 4-ng level was injected onto a preconcentration column (27 mn × 0.51 mm i.d.) packed with Develosil-ODS (30 μm) and eluted with cysteine-acetic acid through a separation column (125 mm × 0.5 mm i.d.) packed with STR-ODS-H (5 μm). After oxidation, tin(II) chloride in sodium hydroxide solution was used to reduce mercury compounds to mercury. The generated mercury vapour was swept from a gas-liquid separator by argon into the detector cell and monitored at 253.7 nm. Mercury(II) chloride, methylmercury chloride and ethylmercury chloride, were well resolved and the determination was completed in less than 16 min. The method was successfully applied to the speciation of mercury compounds in waste water.     

Determination of trace iron in indium phosphide wafer by on-line matrix separation and inductively coupled plasma mass spectrometry

A method for the determination of iron in indium phosphide (InP) wafer is proposed. In the present experiment, an on-line matrix separation system using an ion exchange column was combined with inductively coupled plasma mass spectrometry (ICP-MS) for the determination of ng g⁻¹ level of iron. In the on-line matrix separation, indium and iron in the sample solution was passed through a strongly-basic anion exchange resin column with the 9 M HCl carrier solution, where indium was eluted from the column and iron was adsorbed on it. Then, iron was eluted with the carrier solution of 0.3 M HCl containing 1 ng ml⁻¹ cobalt, and it was directly introduced into the ICP-MS nebulizer. In ICP-MS measurement, cobalt in the carrier solution was used as an internal standard to correct the change in sensitivity due to matrix effect, and the peak area integration was performed to quantify iron and cobalt in the integration time range of 20-60 s from the start of the cobalt solution flow. The detection limit (3σ) for iron was 3 ng g⁻¹, and the recoveries for iron in the 0.8, 2.4, and 8.0% indium solutions were almost 100%. The method was applied to the determination of iron in commercially available iron-doped InP wafers. The obtained results for InP wafer samples with the high iron concentration were in good agreement with those obtained by graphite furnace atomic absorption spectrometry (GFAAS).