Synthesis of optically active leukotriene (SRS-A) intermediates

In an approach to SRS-A and analogues thereof, the key (5$\text{S}$, 6$\text{S}$)-epoxy alcohol $\text{9}$ and its 6-epimer $\text{18}$ were prepared starting from $\text{D}$-araboascorbic acid and $\text{L}$-diethyl tartrate, respectively.     

Discrimination of guests encapsulation in large hexameric molecular capsules in solution: pyrogallol[4]arene versus resorcin[4]arene capsules

NMR experiments demonstrate that, although 2b and 3b form hexameric capsules in chloroform solutions and despite the very similar building units of these hexamers, 3b encapsulates only the noncharged trialkylamines while 2b can encapsulate both the noncharged trialkylamines and the respective ammonium salts obtained by the addition of DCl. In fact, it was found that protonation that forms in situ the ammonium salt ejects the guest from the hexameric capsule of 3b. This is a general observation as it was found for guests containing alkyl chains of four, five, six, and eight carbons.     

Towards advanced circuit board materials: adhesion of copper foil to ultra‐high molecular weight polyethylene composite

Polyethylene based composites are attractive materials for advanced circuit board applications because of their unique combination of properties: low dielectric constant and loss factor, light weight, high flexural modulus and low thermal expansion coefficient controlled in all spatial directions. This investigation describes a process to consolidate chopped fibers of ultra‐high molecular weight polyethylene concurrently with its bonding to a copper foil. Bonding is affected by a thin sheet of low‐density polyethylene, incorporating a crosslinking agent with a concentration gradient across the sheets thickness. In this single step process, the composite material is formed and bonded to the metal foil, achieving good adhesion without the use of extraneous glue. Copyright © 2002 John Wiley & Sons, Ltd.     

ALTERNATIVE MEASURES OF PHOTOSYSTEM II ELECTRON TRANSFER INHIBITION IN ANTHRAQUINONE-TREATED CHLOROPLASTS

We have previously used chlorophyll fluorescence measurements at Fmax conditions (i.e. with Photosystem II electron acceptor QA reduced) to monitor the action of 9,10-anthraquinones on photosynthetic electron transport in plant chloroplasts. The present investigation employs two additional techniques to characterize the extent of electron transport inhibition induced by the addition of substituted anthraquinones to the suspending medium of spinach chloroplasts. Results are presented for spectrophotometric assays of the rate of electron transfer to an exogenous electron acceptor, 2,6-dichloroindophenol (DCIP) and for electrochemical determinations of the rate of oxygen evolution in anthraquinone-treated chloroplasts. In general, amino-substituted anthraquinones are ineffective inhibitors, maintaining electron transfer rates to DCIP at levels ranging from 50 to 90% of normal rates and yielding rates of O2 evolution averaging at 70% of the rate in untreated chloroplasts. In contrast, hydroxy-substituted anthraquinones efficiently block Photosystem II electron transport, resulting in low rates of DCIP photoreduction ranging from 0 to 20% of normal values and reducing O2 evolution rates to an average of 30% of the rate observed for untreated chloroplasts. Relative rates of DCIP photoreduction for anthraquinone-treated chloroplasts show a strong linear correlation with the reported relative Fmax chlorophyll fluorescence intensities. Relative O2 evolution rates are observed to correlate with the Stern-Volmer fluorescence quenching parameter Ksv. We suggest that slight differences in the extent of inhibitory activity of an anthraquinone as measured by the three techniques are consistent with certain known Photosystem II heterogeneities. The similarities in relative rankings of inhibitory effects for the 9, 10-anthraquinones, however, demonstrate that the three techniques employed (measurements of Fmax chlorophyll fluorescence, DCIP photoreduction rates, and O2 evolution rates) are alternative assays of anthraquinone-induced Photosystem II electron transport inhibition.     

EVIDENCE AGAINST THE PRODUCTION OF SUPEROXIDE BY PHOTOIRRADIATION OF HEMATOPORPHYRIN DERIVATIVE

Abstract Experiments were performed to ascertain whether superoxide anion (O₂⁻) was produced by the photodynamic activation of hematoporphyrin derivative (HPD). Three different systems were utilized to detect formation of O₂⁻, oxidation of epinephrine to adrenochrome, reduction of cytochrome c and reduction of nitro blue tetrazolium (NBT). The effects on these detectors under identical conditions for HPD + h ν were compared to those obtained with two O₂⁻ generating systems, riboflavin + by and xanthine-xanthine oxidase, and to a singlet oxygen generating system, photoradiation of methylene blue. The results indicated that HPD + hv differed from the two O₂⁻ generating systems in failing to reduce cytochrome c or NET, and that HPD + h ν was similar to the behavior of methylene blue + h ν . In addition, HPD + h ν but not the O₂⁻ generating systems could inhibit mitochondrial cytochrome c oxidase activity. We conclude that the photodynamic activation of HPD does not produce O₂⁻ as a major oxygen radical and that the effects of HPD + h ν on mitochondrial cytochrome c oxidase are not caused by O₂⁻.     

Synthesis of some dibenzodiazepinone derivatives as potent and m2-selective antimuscarinic compounds

Two series of 5-[[4-[4-(dialkylamino)butyl]-l-cyclohexyl]acetyl], and 5-[(dialkylamino)acyl]-10,11-dihydro-5H- dibenzo[b,e][1,4]diazepin-11-ones were synthesized as potential m2-selective ligands 1,2. Their affinity and selectivity for the muscarinic cholinergic receptor m-AChR subtypes were determined. Replacing a nitrogen with CH in the piperidine ring of 5-[[4-[4-(dialkylamino)butyl]-l-piperidinyl]acetyl]-10,11-dihydro-5H-dibenzo-[b,e][1,4]diazepin-11-ones 3 significantly altered the affinity and selectivity to the muscarinic receptor subtypes.     

Correlation hole and physical properties: A model calculation

The correlation hole of Coulson and Nielson and its extension to momentum space by Banyard and Reed is studied by using an exactly solvable model. For this model all relevant quantities pertaining to the correlation hole have been calculated exactly. We use this model to study the relationship between the fit to the correlation hole for an approximate wave function and the closeness of the approximate energies to the exact ones. We show that, although in general the better the fit the closer are the approximate physical quantities to the exact ones, there are exceptions where that is not the case. Also, we present a convenient method for the calculation of the two particle distribution in momentum space and generalize the concept of the correlation hole by defining it in the pseudophase space of position and momentum.     

Synthesis, structure, and spectroscopy of phenylacetylenylene rods incorporating meso-substituted dipyrrin ligands

The synthesis, structure, and spectroscopic characterization of a series of phenylacetylenylene rodlike molecules containing dipyrromethene (dipyrrin) ligands are described. The combination of the phenylacetylenylene groups with the porphyrinogenic dipyrrin moieties results in a rich absorption spectroscopy for these compounds, although the fluorescence of the phenylacetylenylene moiety is quenched by presence of the dipyrrin chelator. The Cu(2+) and Fe(3+) complexes of these ligands have been prepared and three of these compounds have been structurally characterized by using single-crystal X-ray diffraction. Unlike other octahedral metal-dipyrrin complexes described to date, one of the iron complexes demonstrates ideal threefold symmetry in the solid-state. The elongated structure and high symmetry of these complexes suggests the use of these meso-substituted phenylacetylenylene ligands as an interesting class of extended, branched molecules for the construction of supramolecular architectures.     

Effects of alkali metal halide salts on the hydrogen bond network of liquid water

Measurements of the oxygen K-edge X-ray absorption spectrum (XAS) of aqueous sodium halide solutions demonstrate that ions significantly perturb the electronic structure of adjacent water molecules. The addition of halide salts to water engenders an increase in the preedge intensity and a decrease in the postedge intensity of the XAS, analogous to those observed when increasing the temperature of pure water. The main-edge feature exhibits unique behavior and becomes more intense when salt is added. Density functional theory calculations of the XAS indicate that the observed red shift of the water transitions as a function of salt concentration arises from a strong, direct perturbation of the unoccupied molecular orbitals on water by anions, and does not require significant distortion of the hydrogen bond network beyond the first solvation shell. This contrasts the temperature-dependent spectral variations, which result primarily from intensity changes of specific transitions due to geometric rearrangement of the hydrogen bond network.     

The use of transition-state theory to extrapolate rate coefficients for reactions of H atoms with alkanes

The thermochemical kinetics formulation of conventional transition state theory has been applied to metathesis reactions of H atoms with a series of alkanes in order to provide a sound framework for the intercomparison of experimental data, and also to extrapolate rate coefficients to temperature regimes that may lie beyond the range of experiments. The calculations require a value for the rate coefficient at some temperature, necessitating a discussion of the extant experimental data and their reliability. The procedures are described, the results of the calculations are presented, and their agreement with experimental data (for methane, ethane, propane, butane, pentane, isobutane, cyclopropane, cyclohexane, neopentane, neooctane, and 2,2,3-trimethylbutane) is discussed. A general expression for reactions of H with large (more than 4 carbons) alkanes is proposed: where n_p, n_s, and n_t are the numbers of primary, secondary, and tertiary H atoms available for abstraction.