In Vitro Degradation of Poly(lactic-co2-glycolic) Acid Random Copolymers

We have investigated the in vitro degradation of poly(lactic-co-glycolic) acid copolymer with a lactic to glycolic ratio of 65/35. The degradation studies were performed on solvent-cast films of controlled thickness and shape. The samples were then incubated at 37 °C in phosphate buffered saline solution. The degradation was followed using potentiometry, light microscopy, gravimetry, gel permeation chromatography and differential scanning calorimetry. Water was found to diffuse inside the film as soon as the sample was placed in the degradation media. Wrinkles formed on the upper layer while degradation took place via chain scission in the bulk of the film. After 10 days, this led to the creation of a vesicle where liquid low molecular weight oligomers were trapped inside a thin film of high molecular weight polymer. This thin film acted as a membrane allowing only low molecular weight compounds to diffuse out of the film.     

Direct in vitro and in vivo monitoring of destruxins metabolism in insects using internal surface reversed-phase high-performance liquid chromatography. I. Behaviour of E destruxin in locusts

High-performance liquid chromatography with internal surface reversed-phase packing provides an analytical tool for studying the in vitro and in vivo metabolism of A and E destruxins in the haemolymph and various organs of male adults of Locusta migratoria. A slight amount of injected E destruxin is shown to be hydrated into E-diol destruxin in the haemolymph. The rest of the toxin is recovered unchanged in the fat-body, pericardial tissues and Malpighian tubules, and some further E-diol destruxin formation occurs in these organs. Because E-diol destruxin is only weakly toxic, this appears to be a detoxication process.     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

Ueber Ptomatine

Ohne Zusammenfassung     

Zeros of the Whittaker function associated to Coulomb waves

The zeros in the complex z plane of the Whittaker function W_c/z,µ(z),closely related to spherical waves in the quantum-mechanicalCoulomb problem, are investigated for varying real values ofthe parameters c and µ     

Some remarks on solvability and various indices for implicit differential equations

It has been shown [17,18,21] that the notion of index for DAEs (Differential Algebraic Equations), or more generally implicit differential equations, could be interpreted in the framework of the formal theory of PDEs. Such an approach has at least two decisive advantages: on the one hand, its definition is not restricted to a “state-space” formulation (order one systems), so that it may be computed on “natural” model equations coming from physics (which can be, for example, second or fourth order in mechanics, second order in electricity, etc.) and there is no need to destroy this natural way through a first order rewriting. On the other hand, this formal framework allows for a straightforward generalization of the index to the case of PDEs (either “ordinary” or “algebraic”). In the present work, we analyze several notions of index that appeared in the literature and give a simple interpretation of each of them in the same general framework and exhibit the links they have with each other, from the formal point of view. Namely, we shall revisit the notions of differential, perturbation, local, global indices and try to give some clarification on the solvability of DAEs, with examples on time-varying implicit linear DAEs. No algorithmic results will be given here (see [34,35] for computational issues) but it has to be said that the complexity of computing the index, whatever approach is taken, is that of differential elimination, which makes it a difficult problem. We show that in fact one essential concept for our approach is that of formal integrability for usual DAEs and that of involution for PDEs. We concentrate here on the first, for the sake of simplicity. Last, because of the huge amount of work on DAEs in the past two decades, we shall mainly mention the most recent results. This revised version was published online in June 2006 with corrections to the Cover Date.     

Degradation mechanism of poly(lactic-co-glycolic) acid block copolymer cast films in phosphate buffer solution

We have investigated the degradation of poly(lactic-co-glycolic) acid copolymer with a lactic to glycolic ratio of 50:50. Solvent-cast films were incubated at 37 °C in phosphate buffered saline solution and their degradation was followed using potentiometry, light microscopy, gravimetry, size exclusion chromatography, differential scanning calorimetry and infrared spectroscopy. The degradation process was found to have two main steps. The first step was observed from 0 to 7 days of degradation. During the first few days a soft layer formed at the surface of the film. As degradation time increased this soft surface layer was found to swell and wrinkle. The polymer molecular weight in the bulk was found to decrease as soon as the film was placed in the medium while the polymer present in the surface layer was found to degrade at a much slower rate. The second step of degradation was found to occur after 8 days. At this stage of the degradation process the molecular weight of the polymer in the bulk of the films was so low that the materials became liquid resulting in the detachment of the film from the glass slide. At this stage the mass loss and amount of acid released in the media were found to increase significantly.