The influence of transverse differential swelling stresses on the kinetics of sorption of penetrants by polymer membranes

The influence of transverse differential swelling stresses on the kinetics of sorption of a penetrant in a polymer membrane exhibiting linear viscoelasticity is described by a model developed from the much simpler one of Crank. Sorption and transverse swelling kinetic curves are computed numerically. The character of absorption and desorption curves is examined systematically mainly as a function of (i) the magnitude of the stresses set up and of the stress-dependence of the diffusion coefficient, (ii) the relative rates of stress relaxation and of diffusion, and (iii) the degree of plasticization or “softening” of the polymer by the penetrant. It is shown that important general features of experimental sorption kinetic curves can be reproduced satisfactorily under well defined conditions. Attention is also given to transverse swelling kinetic curves. Their correlation with the corresponding sorption curves is examined briefly but systematically and discussed with reference to experimental data.     

A detailed study of the viscoelastic nature of vapor sorption and transport in a cellulosic polymer. II. Sorption and longitudinal swelling kinetic correlations

Longitudinal swelling kinetics of cellulose acetate films sorbing acetone vapor at 30°C were studied under various conditions and correlated with the corresponding sorption kinetic measurements reported in Part I. The results were analyzed in the light of (1) previous theoretical studies of simple viscoelastic polymer-penetrant model systems and (2) mechanical stress-strain data on the cellulose acetate-acetone system, which are also reported here. The conclusions drawn from this analysis confirm and/or amplify (particularly as regards the effect of longitudinal differential swelling stresses) our previous interpretations based on sorption kinetic analysis, concerning the physical nature and causes of various features of the non-Fickian kinetic behavior of cellulosic polymer-micromolecular penetrant systems. History-dependent long-term aging effects were also observed and investigated. © 1995 John Wiley & Sons, Inc.     

The cycloaddition of diethyl chlorophosphite with norbornadiene: Synthesis and crystal structure of the cycloadduct.

In the presence of Lewis acids, diethyl phosphorochloridite reacts with norbornadiene to afford the tetracyclic phosphinate ester 3 . The reaction is believed to involve formation of phosphenium ions stabilized only by alkoxy substituents. The cycloadduct of the reaction was characterized by its spectral data, by single crystal diffraction analysis of the parent acid, and ³¹P and ²⁷Al nmr experiments.     

Heteroannulation of naphthoquinones. Studies on the reaction of 2-bromo-2,3-dihydronaphthoquinone derivatives with 1,2-binucleophiles.

Heterocyclic derivatives of naphthoquinones were synthesized via their 2-bromo-2,3-dehydro-intermediates. This new route may lead to the formation of benzo[a]phenothiazin-5-ones, benzo[f]quinoxalin-6-ones as well as their 1,4 (or 7,10) dihydroxy-derivatives in high yields. The possible mechanisms involved in the formation of these compounds are discussed.     

Atomarianones A and B: two cytotoxic meroditerpenes from the brown alga Taonia atomaria

Two novel cyclized meroditerpenoids atomarianones A, and B (1 and 2), were isolated from the organic extract of the brown alga Taonia atomaria collected at Serifos island in the Central Aegean Sea. This is only the second report on metabolites having a functionalized indane moiety instead of a benzofurano- or a benzopyrano-ring connecting their aromatic and diterpenoid parts. Atomarianone A contains an unprecedented cis B-C ring fusion while atomarianone B is the epimer of A at C-7. Both metabolites were found to exhibit significant cytotoxic activity against two lung cancer cell lines.     

Kappa-casein based electrochemical and surface plasmon resonance biosensors for the assessment of the clotting activity of rennet

We report for the first time the development of kappa-casein (κ-CN)-based electrochemical and surface plasmon resonance (SPR) biosensors for the assessment of the clotting activity of rennet. Electrochemical biosensors were developed over gold electrodes modified with a self-assembled monolayer of dithiobis-N-succinimidyl propionate, while SPR measurements were performed on regenerated carboxymethylated dextran gold surfaces. In both types of biosensor, κ-CN molecules were immobilized onto modified gold surfaces through covalent bonding. In electrochemical biosensors, interactions between the immobilized κ-CN molecules and chymosin (the active component of rennet) were studied by performing cyclic voltammetry, differential pulsed voltammetry, and electrochemical impedance spectroscopy (EIS) measurements, using hexacyanoferrate(II)/(III) couple as a redox probe. κ-CN is cleaved by rennet at the Phe105–Met106 bond, producing a soluble glycomacropeptide, which is released to the electrolyte, and the positively charged insoluble para-κ-casein molecule, which remains attached to the surface of the electrode. This induced reduction of the net negative charge of the sensing surface, along with the partial degradation of the sensing layer, results in an increase of the flux of the redox probe, which exists in the solution, and consequently, to signal variations, which are associated with the increased electrocatalysis of the hexacyanoferrate(II)/(III) couple on the gold surface. SPR experiments were performed in the absence of the redox probe and the observed SPR angle alterations were solely attributed to the cleavage of the immobilized κ-CN molecules. Various experimental variables were investigated and under the selected conditions the proposed biosensors were successfully tried to real samples. The ratios of the clotting power units in various commercial solid or liquid samples, as they are calculated by the EIS-based data, were almost identical to those obtained with a reference method. In addition, EIS measurements showed an excellent reproducibility, lower than 5%.     

Reactions of Podophyllotoxin with DDQ

Introduction 2, 3-Dichloro-5, 6-dicyanobenzoquinone (DDQ) can react with lignans of the mono- arylidene-butyrolactone1, aryltetralin2, dibenzylbutane3 and aryltetralin-butyrolactone4,5 series. We have studied the reactions of this reagent with podophyllotoxin 1, which is a well-known natural product on account of its long history of use in folk medicine and the biological activity of its many derivatives6. In particular, derivatives of 4-demethyl epipodophyllotoxin are used in cancer chemo…     

Brasilane-type sesquiterpenoids from Laurencia obtusa

[structure: see text] Three novel halogenated rearranged sesquiterpenes (1-3) have been isolated along with brasilenol (4) and epibrasilenol (5) from the organic extract of the red alga Laurencia obtusa, collected at Symi island in the Aegean Sea, Greece. The new metabolites possess the unusual skeleton of brasilane and contain the unprecedented 1,6-epoxy moiety. The structures of the new natural products, as well as their relative stereochemistry, were established by means of spectral data analyses, including two-dimensional NMR experiments along with molecular calculations.     

Lupane triterpenoids from Acacia mellifera with cytotoxic activity

Three new pentacyclic triterpenoids: (20R)-3-oxolupan-30-al (1), (20S)-3-oxolupan-30-al (2) and (20R)-28-hydroxylupen-30-al-3-one (3), along with (20S)-3beta-hydroxylupan-30-al (4), the latter previously described as a constituent of an epimeric mixture, were isolated from Acacia mellifera. In addition, the known metabolites 30-hydroxylup-20-(29)-en-3-one (5), 30-hydroxylup-20-(29)-en-3beta-ol (6), atranorin, methyl 2,4-dihydroxy-3,6 dimethyl benzoate, sitosterol-3beta-O-glucoside and linoleic acid were found in the analyzed plant species for the first time. The structures of the new metabolites were elucidated by extensive spectroscopic analyses and their relative stereochemistry was determined by NOESY experiments. The new metabolite 3 exhibited significant cytotoxic activity against the NSCLC-N6 cell line, derived from a human non-small-cell bronchopulmonary carcinoma.