Permeability of N2, Ar,He, O2, and CO2 through as‐extruded amorphous and biaxially oriented polyester films: Dependence on chain mobility

For as‐extruded amorphous and biaxially orientated polyester films based on poly(ethylene terephthalate), poly(ethylene naphthalate), and copolymers containing poly(ethylene terephthalate) and poly(ethylene naphthalate) moieties, permeability, diffusion, and solubility coefficients are interpreted in terms of chain mobility. The influence of polymer morphology is determined by comparison of the data for as‐extruded amorphous sheets and materials produced with different biaxial draw ratios. The crystallinities of the samples were assessed using differential scanning calorimetry and density measurements. Changes in mobility at a molecular level were investigated using dielectric spectroscopy and dynamic mechanical thermal analysis. The study, in conjunction with our earlier work, leads to the conclusion that the key to understanding differences in gas transport is the difference in local chain motions rather than in free volume. This was illustrated by the permeability results for He, Ar, N₂, and O₂ in the range of polyesters. However, the permeability of CO₂ was found to require alternative explanations because of polymer–penetrant interactions. For biaxially oriented samples, the differences in diffusivity are not only due to differences in local chain motions, but also additional constraints resulting from the increased crystallinity and chain rigidity—which also act to hinder segmental mobility. The effectiveness of the reduction in permeability in the biaxially oriented films is consequently determined by the ability of the polymer chains to effectively align and form crystalline structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2916–2929, 2004     

Combined confocal and magnetic resonance microscopy

Confocal fluorescence optical microscopy and magnetic resonance microscopy are each used to study live cells in a minimally invasive way. Both techniques provide complementary information. Therefore, by examining cells simultaneously with both methodologies, more detailed information is obtained than is possible with each microscope individually. In this paper two configurations of a combined confocal and magnetic resonance microscope are described. The first configuration is capable of studying large single cells or three-dimensional cell agglomerates, whereas the second configuration is designed for the investigation of monolayers of mammalian cells. In both cases the sample compartment is part of a temperature regulated perfusion system. Images obtained with the combined system are shown forXenopus laevis oocytes, model JB6 tumor spheroids, and a single layer of Chinese hamster ovary cells. Finally, potential applications of the combined microscope are discussed.     

Level structure of 68 149 Er81 and high-spin isomerism in proton-richN=81, 82, 83 nuclei

The level structure of theN=81 nucleus¹⁴⁹Er has been studied by γ-ray spectroscopy following the reaction⁹²Mo+255 MeV⁶⁰Ni. Yrast levels in¹⁴⁹Er are established up to ~3.3 MeV, including 0.61 and 4.8 μs isomeric states. Most of the observed levels are interpreted as seniority-three states arising from the coupling of s_1/2, d_3/2 and h_11/2 neutron holes with πh ₁₁ ^2/n . Isomers identified in the reaction⁹⁶Ru+255 MeV⁵⁸Ni are tentatively assigned to¹⁵¹Yb. TheB (E2) values of high-spin isomers inZ=66?70,N=81?83 nuclei are surveyed.     

Copolymerization characteristics of S-vinyl-O-tert-butylthiocarbonate

Poly-S-vinyl-O-tert-butylthiocarbonate is an excellent precursor to poly(vinyl mercaptan) because the tert-butyloxycarbonyl blocking group can be removed by either acid hydrolysis or thermolysis under conditions which minimize the oxidation of the liberated mercaptan to disulfide. Dilatometric studies of the homopolymerization of S-vinyl-O-tert-butylthiocarbonate demonstrated that the polymerization rate was directly proportional to the concentration of free-radical initiator; no thermal initiation was observed. The molecular weight of the homopolymers and copolymers ranged from 30,000 to 50,000 (GPC). Copolymerization of S-vinyl-O-tert-butylthiocarbonate (M₂) with styrene, (r₁ = 3.0, r₂ = 0.2), methyl methacrylate (r₁ = 1.40, r₂ = 0.17) and vinyl acetate (r₁ = 0.04, r₂ = 11.0) indicated that a sulfur atom adjacent to the vinyl group increases the resonance stability (Q₂ = 0.5) and the electron density (e₂ = ?1.4) of the double bond and the corresponding radical. Water-soluble copolymers could be prépared by incorporating either N-vinylpyrrolidone (r₁ = 0.12, r₂ = 3.94) or N-isopropylacrylamide (r₁ = 1.17, r₂ = 0.3) with M₂. The water solubility of the copolymers decreased markedly when the tert-butyloxycarbonyl group was removed. Copolymers of M₂ with N-vinyl-O-tert-butylcarbamate (r₁ = 0.13, r₂ = 5.10) were utilized to prepare crosslinked poly(vinyl amine–vinyl mercaptan); the crosslinking resulted from urea linkages formed during thermolysis of the copolymer.     

Preparative isolation of (+)-beta-eudesmol fromAmyris balsamifera

Summary Optically pure (+)-beta-eudesmol is a possible starting material for the synthesis of several termite defense compounds. A two step procedure for the isolation of gram quantities of (+)-beta-eudesmol from commercially availableAmyris balsamifera oil (syn. West Indian sandalwood oil), containing 8% beta-eudesmol, was developed. Step one consisted of an efficient vacuum distillation of the total oil. Step two was a medium pressure LC separation with an AgNO₃ impregnated silica gel stationary phase. Several other separation procedures failed due to the presence of many closely related sesquiterpene alcohols (75% of the oil).     

Observations of the low Earth orbit radiation environment from Mir

Recent measurements of the high-energy charged particle environment with the Radiation Environment Monitor (REM) aboard the Russian Mir space station are presented. Ionizing dose rates in a silicon detector have been measured with two shieldings. The dose is mainly accumulated in two distinct areas, the South Atlantic Anomaly (SAA) and the region of closest approach to the magnetic poles. Whereas the radiation in the South Atlantic Anomaly varied little during 1995, large changes of the daily absorbed doses in the polar regions are observed. A comparison of REM doses with the NASA AP-8 and AE-8 radiation models revealed major differences. AP-8 tends to underestimate the average REM doses, whereas AE-8 overestimates REM doses, and rather describes the worst case.     

High-performance liquid chromatographic assay for mitoxantrone in plasma using electrochemical detection

A sensitive and specific high-performance liquid chromatographic (HPLC) assay was developed for the quantitation of mitoxantrone in plasma using electrochemical detection. Bisantrene was chosen as the internal standard. A reversed-phase, 10-microns muBondapak C18 analytical column (30 cm X 3.9 mm) with an isocratic mobile phase of 28% acetonitrile in 80 mM sodium formate buffer (pH 3.0) was used. The eluent was monitored by both electrochemical detection at an applied potential of +0.75 V vs. Ag/AgCl and visible absorbance at 660 nm. Only electrochemical detection was able to quantitate the internal standard and provided ten times higher sensitivity than visible absorbance for mitoxantrone with a detection limit as low as 0.1 ng/ml. Calibration curves in the range 0.1-1000 ng/ml showed good linearity (r = 0.998) and precision (coefficient of variation less than 10%). This HPLC method utilized a reproducible and inexpensive liquid-liquid extraction procedure. Using methylene chloride, the extraction efficacy of mitoxantrone from plasma was 85.3% with a coefficient of variation less than 2.1%. This new assay was then applied to measure mitoxantrone concentrations in plasma obtained from two leukemic patients receiving 12 mg/m2 mitoxantrone as a 1-h infusion.     

5-(N-Arylnortropan-3-yl)- and 5-(N-Arylpiperidin-4-yl)-2,4-diaminopyrimidines. Novel Inhibitors of Dihydrofolate Reductase

Based on a computer-assisted analysis of the three-dimensional structure of the binary complex of E.coli dihydrofolate reductase (DHFR) with methotrexate, 5-(N-arylnortropan-3-yl)- and 5-(N-arylpiperidin-4-yl)-2,4-diaminopyrimidines 2 and 4 were designed as inhibitors of DHFR. Syntheses of the designed compounds have been carried out. The most potent compound 2a inhibited E. coli DHFR with K_i = 0.49.10^?9M. The activities within the series of compounds synthesized could be rationalized by molecular-modelling experiments which served as the basis of this work. Several compounds within the presented series exhibit antimalarial activities in vitro and in vivo.