Reaction of singlet oxygen with trans-4-propenylanisole. Formation Of

We report the effects of added acid in the reaction of singlet oxygen with trans-4-propenylanisole (1). We provide evidence that solvent acidity modifies the behavior of the transient intermediates. Relative to reactions in aprotic solvent, enhanced dioxetane concentrations are observed in MeOH and in nonprotic solvents with acid. We suggest a new mechanism that invokes a proton transfer from MeOH and benzoic acid to perepoxide (2) and zwitterion (3) intermediates.     

Theoretical and experimental studies of the electrochemistry of <Emphasis Type="Italic">p</Emphasis>-aminophenol on a golden electrode

The geometric parameters, vibrational frequencies, and thermochemical values of p-quinonimine (p-AQ) and p-aminophenol (p-AP) were computed ab initio (IIF) and by the density functional theory (DFT) method with the 6-31G(d, p) basis set. Cyclic voltammetry with a golden electrode of p-AP solutions in phosphate buffers at pH 7.30 showed that the standard electrode potential of half reaction for p-QI and p-AP was 0.728 V. The standard electrode potentials of half reactions for p-QI and p-AP were calculated using the free energies and solvation energies of p-QI, p-AP, p-benzoquinone (p-BQ), and hydroquinone (p-HQ). The results showed that the standard electrode potential of half reaction for p-QI and p-AP was 0.743 V at the B3LYP/6-31G(d, p) level and 0.755 V at the HF/6-31G(d, p) level. The standard electrode potentials computed at the B3LYP/6-31G(d, p) and HF/6-31G(d, p) levels were close to their experimental values. The article is published in the original.     

Embedded polymerization driven asymmetric PEM for direct methanol fuel cells

This work reports the fabrication of proton exchange membranes (PEM) with stronger resistance to methanol penetration than Nafion^®117. A three-component acrylic polymer blend (TCPB) consisting of a copolymer of 4-vinylphenol-methyl methacrylate, poly(butyl methacrylate) (PBMA) and a copolymer of methyl methacrylate-ethyl acrylate is used as the methanol barrier. In order to implant a proton source phase within the membrane as homogeneously as possible, the hydrophilic monomers, 2-acrylamido-2-methyl propanesulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) dimethylacrylate (PEGDMA), are polymerized only after they have been embedded in the TCPB matrix. The embedded polymerization has resulted in an asymmetric membrane structure, in which the hydrophilic network is sandwiched by two layers of matrixes with high percentages of TCPB. As expected, this asymmetric membrane structure exhibits lower methanol uptake than Nafion^®117; and a proton conductivity in the range of 10⁻³–10⁻⁴ S/cm, which is dependent on the concentration of the sulfonic acid content. It is suggested that the two external layers in this asymmetric membrane provide primarily methanol-blocking and supporting proton-conducting properties; while the middle layer supplies protons and conserves water. This unique sandwiched PEM structure from embedded polymerization is confirmed by microstructure characterizations and by physical property measurements.     

In Vitro Determination of Dobesilate in Medicine and Human Urine with Chemiluminescence Detection

A unique flow injection chemiluminescence (CL) method for the determination of calcium dobesilate in pharmaceutical preparations and human urine is presented in this paper. The analytical reagents involved in the CL reaction, luminol and ferricyanide, were both immobilized on an anion-exchange column in an FI system. The CL signal produced by the reaction of luminol with ferricyanide (the reagents had been eluted from the column through sodium phosphate injection) decreased in the presence of dobesilate. The decreased CL intensity was linear to the dobesilate concentration in the range 0.2100.0ngmL^–1. At a flow rate of 2.0mLmin^–1, one analytical cycle can be completed in 1.5min, including sampling and washing, resulting in a throughput of 40 cycles per hour. The proposed method was applied successfully to the determination of dobesilate in pharmaceutical preparations and human urine without any pre-treatment. It was found that, after oral administration, the dobesilate concentration reached its maximum after three hours, and the dobesilate metabolism ratio in 24 hours was 57.1% in the bodies of volunteers.Received September 14, 2002; accepted March 11, 2003 Published online July 16, 2003     

Syntheses of 1beta-methylcarbapenems bearing 5-methyl-4-hydroxypyrrolidinone

A new series of 1beta-methylcarbapenems 1a-d bearing 5-methyl-4-mercaptopyrrolidinone rings has been prepared and evaluated for in vitro antibacterial activity and pharmacokinetic parameters. Most compounds showed excellent antibacterial activity and high stability to dehydropeptidase-1. We have synthesized optically active 5-methyl-4-hydroxypyrrolidinones from enantiomerically pure aziridine esters.     

A new method for the generation of isobenzofurans: A simple entry to substituted naphthalenes

5,6-Dimethoxy isobenzofuran is generated $\text{in situ}$ from the dimethylacetal of 6-hydroxymethyl veratraldehyde and intercepted by a variety of dienophiles to produce the expected oxygen-bridged adducts in good yield. Many of the latter are easily aromatised to naphthalenes.     

Single step synthesis of propionitrile over K/MgO from acetonitrile methylation with methanol

A series of potassium-doped MgO catalysts loaded with KOH up to 15 mol% was prepared and evaluated for a single step synthesis of propionitrile from acetonitrile methylation with methanol. As the amount of potassium dope increased, both the acetonitrile conversion and the selectivity toward propionitrile increased. Based on the activity data coupled with CO₂-TPD and NH₃-IR ones, it was concluded that potassium doping to MgO resulted in the enhancement of both basicity and bifunctionality — methylation and hydrogenation.     

Theoretical and experimental investigation of the effect of proton transfer on the (27)al MAS NMR line shapes of zeolite-adsorbate complexes: an independent measure of solid Acid strength

Assessing the degree of proton transfer from a Br?nsted acid site to one or more adsorbed bases is central to arguments regarding the strength of zeolites and other solid acids. In this regard certain solid-state NMR measurements have been fruitful; for example, some (13)C, (15)N, or (31)P resonances of adsorbed bases are sensitive to protonation, and the (1)H chemical shift of the Br?nsted site itself reflects hydrogen bonding. We modeled theoretically the structures of adsorption complexes of several bases on zeolite HZSM-5, calculated the quadrupole coupling constants (Q(cc)) and asymmetry parameters (eta) for aluminum in these complexes and then in turn simulated the central transitions of their (27)Al MAS NMR spectra. The theoretical line width decreased monotonically with the degree of proton transfer, reflecting structural relaxation around aluminum as the proton was transferred to a base. We verified this experimentally for a series of adsorbed bases by way of single-pulse MAS and triple quantum MQMAS (27)Al NMR. The combined theoretical and experimental approach described here provides a strategy by which (27)Al data can be applied to resolve disputed interpretations of proton transfer based on other evidence.     

Moisture absorption and absorption kinetics in polyelectrolyte films: influence of film thickness

Specular X-ray reflectivity (XR) and quartz crystal microbalance (QCM) measurements were used to determine the absorption of water into thin poly(4-ammonium styrenesulfonic acid) films from saturated vapor at 25 degrees C. The effect of film thickness on the absorption kinetics and overall absorption was investigated in the range of thickness from (3 to 200) nm. The equilibrium swelling of all the films irrespective of film thickness was (0.57+/-0.03) volume fraction. Although the equilibrium absorption is independent ofthickness, the absorption rate substantially decreases for film thickness < 100 nm. For the thinnest film (3 nm), there is a 5 orders of magnitude decrease in the diffusion coefficient for water.     

Synthesis of Hexa-O-Methyl-8-(8“-Naringeninyl)Apigenin

The title compound was prepared from 8-iodo-5,7,4′-trimethoxyflavone and 8-iodo-5,7,4′-trimethoxyflavanone using modified condition for the Ullmann condensation.