Investigation of a novel mixed-mode stationary phase for capillary electrochromatography. Part III: Separation of nucleosides and nucleic acid bases on sulfonated naphthalimido-modified silyl silica gel

Capillary electrochromatography (CEC) with a novel stationary phase, 3-(4-sulfo-1,8-naphthalimido)propyl-modified silyl silica gel (SNAIP), proved useful for the separation of nucleosides and nucleic acid bases. The application scope of SNAIP, which is a relatively polar reversed-phase (RP)-type stationary phase, was successfully expanded to include the CEC separation of polar compounds although the combination of non-polar RP phase with highly aqueous mobile phase is often inadequate. Due to the permanently charged sulfonic acid groups and the naphthalimidopropyl moiety, the retention of charged and relatively polar nucleosides as well as bases on the SNAIP stationary phase was effected by electrostatic and hydrophobic interactions. This yielded a unique selectivity on SNAIP toward nucleosides and bases. The characteristic EOF on SNAIP, which was stronger at higher aqueous content in the mobile phase, proved suitable for the separation of polar compounds in reversed-phase mode with highly aqueous mobile phase. In addition, when a double stepwise gradient was employed to accelerate the latest peak (adenine), the elution time was shortened to less than half its original duration.     

Modulated hydrogen beam study of adsorption-induced desorption of deuterium from Si(100)-3x1:D surfaces

We have studied the kinetic mechanism of the adsorption-induced-desorption (AID) reaction, H+D/Si(100) --> D2. Using a modulated atomic hydrogen beam, two different types of AID reaction are revealed: one is the fast AID reaction occurring only at the beam on-cycles and the other the slow AID reaction occurring even at the beam off-cycles. Both the fast and slow AID reactions show the different dependence on surface temperature Ts, suggesting that their kinetic mechanisms are different. The fast AID reaction overwhelms the slow one in the desorption yield for 300 K < or = Ts < or = 650 K. It proceeds along a first-order kinetics with respect to the incident H flux. Based on the experimental results, both two AID reactions are suggested to occur only on the 3x1 dihydride phase accumulated during surface exposure to H atoms. Possible mechanisms for the AID reactions are discussed.     

Efficient optical resolution of secondary alkyl alcohols by chiral supramolecular hosts

A novel tunable multi-chiral supramolecular host system was developed from non-chiral dicarboxylic acid and (1R, 2R)-diphenylethylenediamine via chirality transfer, which enabled highly efficient optical resolution of secondary alkyl alcohols by simple crystallization of host compounds from alcohol solution.     

A selective lon-exchange separation and spectrophotometric determination of traces of copper in silicate rocks

Summary A combined cation-exchange separation-spectrophotometric procedure has been worked out for the accurate determination of traces of copper in silicate rocks. Silicates are opened up with sulfuric and hydrofluoric acids. The residue is taken up into a 0.5 M hydrochloric acid −0.05 M oxalic acid −1% hydrogen peroxide solution and loaded on a strongly acidic cation-exchange resin column. Polyvalent ions including ferric ions do not adsorb on the column, while copper (II) retains together with divalent metal ions as well as aluminum (III). Copper (II) can selectively be eluted by a small volume of 0.05 M thiosulfate solution. This fraction is sufficiently pure to allow a direct spectrophotometric determination of copper with Na-DDTC without the addition of tartrate and EDTA as masking agents. Quantitative results are quoted for the determination of copper in international standard rocks of the Geological Survey of Japan (GSJ) and the U.S. Geological Survey (USGS).     

Effect of ligand in ethylene/styrene copolymerization by [Me2Si(C5Me4)(NR)]TiCl2 (R = tert-Bu, cyclohexyl) and (1,3-Me2C5H3)TiCl2(O-2,6-Pr2C6H3)-MAO catalyst system

Copolymerization of ethylene with styrene using linked cyclopentadienyl-amide titanium(IV) complexes, [Me₂Si(C₅Me₄)(R)]TiCl₂ [R=tert-Bu (1), cyclohexyl (2)], and non-bridged (1,3-Me₂C₅H₃)TiCl₂(O-2,6-ⁱPr₂C₆H₃) (3)-MAO catalysts have been explored. Although the catalytic activity by 2 was lower than 1, 2 showed more efficient styrene incorporation than 1 under the same conditions. Moreover, the resultant copolymer prepared by 2 possessed completely different microstructure from those by 1, indicating that the nature of amide ligand affects both styrene incorporation and monomer sequence.     

A facile and novel synthesis of 5-phenylimidazo[4,5-c][1,8]naphthyridin-4(5H)-ones

A convenient and regioselective synthesis of a new heterocycle, 5-phenyl-1H or 3H-imidazo[4,5-c][1,8]-naphthyridin-4(5H)-one 1-a or 1-b , is described. Methyl 2-anilinonicotinate 15 was transformed into the valuable intermediate, N-phenyl-3-azaisatoic anhydride 4 using trichloromethyl chloroformate (TCF). Treatment of 4 with the anion of ethyl nitroacetate gave 4-hydroxy-3-nitro-1-phenyl-1,8-naphthyridin-4(5H)-one 3 . Compound 3 was chlorinated, aminated, reduced, and cyclized to afford 5-phenylimidazo[4,5-c][1,8]naphthyridin-4(5H)-one 1 . Regioselective substitution at the 1 or 3-position in the imidazole moiety of 1 was achieved by minor changes of the above scheme.     

Precipitation behavior of 1,1,Di-(p-hydroxyphenyl)-cyclohexane clathrate crystals from acetone solutions containingd-limonene

The precipitation behavior of 1,1-di(p-hydroxyphenyl)cyclohexane (DHC) from acetone solutions containing d-Limonene (1-methyl-4(I-methylethenyl)cyclohexene) was studied. From the pure acetone solution or the solutions containing a small amount of d-Limonene crystals (B) precipitated, which clathrate only acetone with a guest/host (G/H) molar ratio of 1.0. However, when thed-Limonene concentration is increased to more than ca. 2 mol/L, crystals (A) precipitated which had a different habit from the B crystals. In the A crystalsd-Limonene is clathrated together with a large amount of acetone and the G/H value ofd-Limonene increases with the concentration in the solution up to the maximum value of 0.2. As the diffraction patterns of the A and B crystals are similar, it is assumed that a part of the acetone molecules in the B crystals are replaced byd-Limonene molecules. The acetone in the A crystals escapes rapidly, but thed-Limonene remains for a long time. This may indicate that the large molecule ofd-Limonene cannot diffuse rapidly within the host lattice owing to three-dimensional hindrance. It was clear that the solubility of the A crystals is higher than that of the B crystals and the transformation from the'metastable A to the stable B crystals proceeds during the crystallization of A crystals.     

Dynamic ion-exchange chromatography with post-column reaction detection for the determination of the rare earth elements in monazites

Summary Separation and determination of lanthanum, cerium, praseodymium, neodymium and samarium in monazites have been achieved by dynamic ion-exchange chromatography. The ore samples are decomposed by sulfuric acid and the rare earths are separated in a group as oxalates. The rare earth elements are then separated from each other on a column of bonded phase silica by gradient elution with 0.05 to 0.5 M lactic acid (pH 3.5) in the presence of 0.01 M sodium 1-octanesulfonate. Post-column reaction with Arsenazo III is used for detection and quantification of the individual rare earth elements. Results are quoted for lanthanum, cerium, praseodymium, neodymium and samarium in monazites. Detection limit is 1 μg ml⁻¹ with a S/N ratio of 3. The separation is complete within 27 min valley to valley resolution. Precision of better than 1% can usually be obtained.     

Palladium-catalyzed allylic alkenylation of allylic alcohols with n-butyl acrylate

Various allylic alcohols reacted with n-butyl acrylate in the presence of p-toluenesulfonic anhydride and palladium catalysts to yield the corresponding n-butyl 2,5-dienoates with high regioselectivity.     

Solvent effects in 5-deazaflavin oxidation as a model for NAD+ dependent enzymes

The oxidation rate of 3,5-di-t-butylsalicyl alcohol by 3-methyl-10-ethyl-5-deazaisoalloxazine was found to be very sensitive to solvent effect, the rate constant in 99 vol% DMF being greater by a factor of 37 than that in 50:50 (v/v) DMF-water mixed solvent. The result suggests the importance of the aprotic nature of the reaction environment during the oxidation of alcohols by NAD⁺.