Preparation and characterization of modified 3-aminopropylsilyl silica phases with 1,8-naphthalic anhydrides in HPLC

Modified 3-aminopropylsilyl silica stationary phases with 1,8-naphthalic anhydrides [3-(1,8-naphthalimido)propyl (NAIP), 3-(4-amino-1,8-naphthalimido)propyl (4A-NAIP), 3-(3-nitro-1,8-naphthalimido)propyl (3N-NAIP), and 3-(4-nitro-1,8-naphthalimido)propyl modified silyl silica gel (4N-NAIP)] are prepared in a single reaction. Chromatographic properties of these phases are characterized using various solutes including monosubstituted benzenes, alkyl benzenes, and polycyclic aromatic hydrocarbons (PAHs) in high-performance liquid chromatography. Even though the retention in these NAIPs is mainly based on the reversed-phase mode, 3N- and 4N-NAIP show a remarkable recognition toward aromatic hydrocarbons, which is attributed to their strong pi-pi interaction. Furthermore, the recognition ability is according to the molecular planarity and non-linearity of PAHs. Subsequently, 3N- and 4N-NAIP has a distinct selectivity from octadecyl silica and, therefore, will be a valuable alternative for a separation or a solid-phase extraction of aromatic compounds.     

Peroxotungstate immobilized on ionic liquid-modified silica as a heterogeneous epoxidation catalyst with hydrogen peroxide

Peroxotungstate immobilized on ionic liquid-modified SiO2 is capable of heterogeneously epoxidizing a wide range of olefins with the maintenance of the catalytic activity of homogeneous analogue. The epoxidation was immediately stopped by the removal of the catalyst, and no tungsten species could be found in the filtrate after the removal of the catalyst. These results can rule out any contribution to the observed catalysis from the tungsten species that leached into the reaction solution, and the observed catalysis is truly heterogeneous in nature. Furthermore, the catalyst was reusable without the loss of the catalytic performance.     

Reactivity and catalytic activity of cationic lonomers for the nucleophilic substitution reactions

Polystyrene-based crosslinked cationic ionomers containing ammonium or phosphonium chlorides (AxRCI and PxBuCI) were reacted with decyl methanesulfonate. The kinetic data were correlated with the swelling behavior of the ionomers and the solution viscosity of the corresponding linear ionomers. The reactivity of the ionomers was independent of the particle size of the ionomer beads, indicating no diffusion control of the reaction. The solvent and the ion content of the ionomers greatly affect the reactivity. In nonpolar solvents with a low acceptor number, A_N, such as toluene, the aggregation of ionic groups with an increasing ion content reduces the reactivity. A solvent with a high value of A_N, such as chloroform, led a very low reactivity independent of the ion content. Aprotic polar solvent, such as acetonitrila, promoted the dissociation of the ionic groups and furnished a relatively high reactivity independent of the ion content. Several catalytic substitution reactions were carried out under liquid-solid-solid triphase conditions. The kinetic results were accounted for in terms of slow nucleophile transport and fast chemical reaction within the ionomer particles. © 1994 John Wiley & Sons, Inc.     

Separation of N2-ethyl-2'-deoxyguanosine-5'-monophosphate and four native deoxyribonucleoside monophosphates using capillary zone electrophoresis with polyethylene glycol as buffer additive

We investigated the separation of five deoxyribonucleoside monophosphates: 2'-deoxyguanosine-5'-monophosphate (dGMP), 2'-deoxyadenosine-5'-monophosphate (dAMP), 2'-deoxycytosine-5'-monophosphate (dCMP), 2'-deoxythymidine-5'-monophosphate (dTMP) and a dGMP adduct possessing N2-ethyl-guanine, which has been noted in relation to mutagenesis of alcohol, using capillary zone electrophoresis (CZE). The concentration of polyethylene glycol (PEG) as a modifier and the pH of the running solutions can efficiently control the observed separation. Interaction of PEG with analytes was quantitatively evaluated. PEG worked effectively as a hydrophobic selector in these separations. The values of pKa of the acidic-NH-groups in the base moieties of dGMP, dTMP, and the dGMP adduct are close to that of boric acid used as buffer of the running solutions. The control of their charge was facilitated, enabling improved separations. A more sufficient and fast separation was achieved by both optimization of pH of the running solutions and PEG concentration compared with that obtained by pH control alone. On-line concentration using a stacking method followed by the PEG-assisted CZE was briefly studied.     

Synthesis and applications of [1-(15)N]-labeled 4,6-dimethyl-4H-[1,2,5]oxadiazolo[3,4-d]pyrimidine-5,7-dione 1-oxide as a useful tool for mechanistic investigations

[1-(15)N]-Labeled 4,6-dimethyl-4H-[1,2,5]oxadiazolo[3,4-d]pyrimidine-5,7-dione 1-oxide (1-(15)N1) was easily prepared by nitration of commercially available 6-amino-1,3-dimethyl-1H-pyrimidine-2,4-dione using 15N-enriched nitric acid followed by an intramolecular oxidative cyclization with iodosylbenzene diacetate under mild conditions. On the basis of the experimental results using 1-(15)N1, the formation of 8-phenyltheophylline (3), the 1,3-dimethylalloxazines (4: n = 0, 1), and 1,3,7,9-tetramethyl-1H,9H-pyrimido[5,4-g]pteridine-2,4,6,8-tetraone++ + (5) in the thermal reaction of the N-oxide 1 with benzylamine, aniline, or piperidine, and the generation of NO or NO-related species in the reaction with N-acetylcysteamine were reasonably explained by considering the initial attack of the employed nucleophiles on the 3a-position of 1.     

Radiation-induced polymerization at high dose rate. II. α-Methylstyrene in bulk

Bulk polymerization of α-methylstyrene was carried out in a wide dose rate range, 7.6–256 rad/sec by γ rays and 8.5 × 10³–2.1 × 10⁵ rad/sec by electron beams. At high dose rate by electron beams, cationic polymerization took place along with formation of oligomeric product of DP _n = ～4. At low dose rate by γ rays, radical polymerization was found to occur in water-saturated monomer. The cationic polymerization at high dose rate proceeds with essentially the same mechanism as was already known in γ-ray polymerization of dry monomers. Relatively low reaction rate of the cationic polymerization compared with that of styrene is explained with the fact that the propagation of α-methylstyrene is much more easily inhibited by a slight amount of water.     

Solution viscosity behavior of polystyrene-based cationic ionomers. Effects of ion content and solvent

Dilute-solution viscosities of polystyrene-based cationic ionomers containing ammonio or phosphonio groups were measured in several solvents. In polar solvents with dielectric constant (ε_r) beyond 10, the ionomers showed a typical polyelectrolyte behavior, indicating that a large part of ionic groups were dissociated into ions. In nonpolar solvents with low ε_r, the reduced viscosity of the ionomers linearly decreased with a decreasing ionomer concentration. At low polymer concentrations, every ionomer gave a reduced viscosity lower than that of the corresponding chloromethylated polystyrene. With an increasing ion content, the intrinsic viscosity progressively decreased if the nonpolar solvents had a low acceptor number (A_N), such as toluene or tetrahydrofran (THF). In the halogenated solvents with high A_N value, such as chloroform, however, the intrinsic viscosity was hardly dependent on the ion content. This indicates that the intramolecular aggregation among the ionic groups is inhibited in the halogenated solvents due to a strong anion solvation. An addition of a protic solvent to a nonpolar solvent eliminates the aggregation between ionic groups and leads to polyelectrolyte behavior. © 1994 John Wiley & Sons, Inc.     

An effective method to use ionic liquids as reaction media for asymmetric reduction by Geotrichum candidum

An effective method was developed to use an enzyme in ionic liquids; the asymmetric reduction of ketones by Geotrichum candidum in ionic liquids proceeded smoothly with excellent enantioselectivity when the cell was immobilized on water-absorbing polymer containing water, while the reaction without the polymer did not proceed.     

Total synthesis of (-)-stevastelin B

The total synthesis and an unambiguous structure confirmation of stevastelin B 1, a novel 15-membered cyclic depsipeptide, are described; the fatty acid moiety in 1, prepared stereoselectively from L-quebrachitol was converted into the amino carboxylic acid, whose macrolactamization by Shioiri's procedure effectively constructed the cyclic structure of 1.