Tramadol Release from a Delivery System Based on Alginate‐Chitosan Microcapsules

Alginate‐chitosan microcapsules to control the release of Tramadol‐HCl were prepared using two different methods. In the two‐stage procedure (Variant I) alginate was first pumped into a CaCl₂/NaCl solution and then transferred into a chitosan solution. In the one‐stage procedure (Variant II) alginate was directly pumped into a chitosan/CaCl₂ solution, and different behavior could be noted in each case. The microcapsules were spherical in both variants and they swelled to a greater extent in a basic medium as compared to an acid one. The drug release profile of Tramadol from microcapsules in simulated gastric fluid and simulated intestinal fluid was also studied. The maximum release of Tramadol at 24 h was 64% and 86% for Variant I and II, respectively, in simulated intestinal fluid. Release was adjusted using the power law of the semi‐empirical Peppas equation in order to gain information about the release mechanism. In both cases the values of the exponent were found to be between 0.53 and 0.84 for swellable microcapsules in simulated gastric and intestinal fluids, respectively, indicating anomalous drug transport for both variants. The good results obtained with alginate‐chitosan microcapsules are comparable to those of the best products so far described in the scientific bibliography and in addition, chitosan is useful in pharmacy.

Surface morphology of Tramadol‐loaded microcapsule.     

Isolation techniques for long‐term bistability of the bistable twisted nematic mode

Low power, storage liquid crystal displays are of interest in the foreseeable future in portable applications. The use of a bistable twisted namatic (BTN) mode in a true storage device requires long term bistability of its operating states since it is intrinsically a metastable device. Two novel isolation techniques are described and demonstrated to isolate and stabilize the operating states in a BTN device. Existing limitations are highlighted and further areas for research suggested.     

Design and synthesis of highly reactive photopolymerizable epoxy monomers

The synthesis of a series of novel cationically photopolymerizable epoxide monomers bearing benzyl, allyl, and propargyl acetal and ether groups that can stabilize free radicals was carried out. These monomers display enhanced reactivity in cationic photopolymerization in the presence of certain onium salt photoinitiators. Specifically, this article describes schemes for the synthesis of cycloaliphatic epoxy monomers bearing free‐radical stabilizing groups. During UV irradiation of an onium salt cationic photoinitiator, the aryl radicals that are generated abstract labile protons present in such monomers to generate the corresponding carbon‐centered radicals. Subsequently, these radicals can interact with the onium salt by a redox mechanism to induce the decomposition of these salts. The overall result is that additional cationic species are generated by this mechanism that increase the rate and extent of the cationic ring‐opening polymerization of the epoxide monomer. An investigation of the photopolymerizations of the monomers prepared during this work was carried out using Fourier transform real‐time infrared spectroscopy, and conclusions were drawn with respect to the relationship between their structures and reactivity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2385–2395, 2001     

Water‐Filtered Infrared Radiation Decreases the Generation of Photodermatoses Dependent on Ultraviolet and Visible Radiation

The potential role of infrared radiation in photodermatoses has received very little attention, even though the main sources of radiation used for photobiological studies (UVA, UVB and visible light) include infrared radiation. The objective of the work was to assess whether infrared radiation is involved in the development of skin lesions in patients with different types of photodermatoses. Twenty patients with different photodermatoses were exposed to UVA, UVB and visible radiation using a high‐pressure mercury UVA lamp, a fluorescent broadband UVB lamp, a tungsten bulb and a slide projector for visible radiation. Part of the radiation emitted by these lamps was water‐filtered to block infrared radiation above 1300 nm. All 20 patients developed lesions when exposed to different light sources used for phototest. When exposed to same sources without infrared radiation, 17 patients (85%) did not develop any lesions and the other three (15%) developed less severe lesions than in the area exposed to unfiltered light. Our results show that infrared radiation was necessary for the development of skin lesions in 85% of the patients with photodermatoses in our study. We believe that infrared radiation studies should be included in standard photobiology protocols.     

Discrimination of PHIP Signals Through their Evolution in Multipulse Sequences

The antiphase character of the PHIP associated signals after a hydrogenation reaction is particularly sensitive to line broadening introduced by magnetic field inhomogeneities and interferences by the presence of resonance lines steaming from a large amount of thermally polarized spins. These obstacles impose a limitation in the detection of reaction products as well as in the experimental setups. A simple way to overcome these impediments consists of acquiring the signal with a train of refocusing pulses instead of a single r.f. pulse. We present here a number of examples where this multipulse acquisition, denominated PhD-PHIP, displays its potentiality in improving the information related to hyperpolarized spins performed in a sample, where the former parahydrogen nuclei are part of a complex J-coupling network.     

Synchronization of non-identical extended chaotic systems

In this article a technique to achieve synchronization in spatially extended systems is introduced. The basic idea behind this method is to map a system of partial differential equations (PDEs) into a high-dimensional space where the representation of this PDE is an ordinary differential equation. By using semi-group theory, we are able to find conditions that ensure the synchronization of two systems of non-identical reaction–diffusion equations with a master–slave coupling.     

Acetylides from Alkyl Propiolates as Building Blocks for C3 Homologation

Three that matter : Metal acetylides from alkyl propiolates allow C₃ homologations with transference of their versatile reactivity profile to products that can then react without further elaboration. Metal‐free acetylides, which are generated by the action of a good nucleophile on the alkyl propiolate, react with suitable electrophiles through different domino reactions to generate skeletal diversity.

     

Convergent approaches for the synthesis of the antitumoral peptide, Kahalalide F. Study of orthogonal protecting groups

Kahalalide compounds are peptides that are isolated from a Hawaiian herbivorous marine species of mollusc, Elysia rufescens, and its diet, the green alga Bryopsis sp. Kahalalide F and its synthetic analogues are the most promising compounds of the Kahalalide family because they show antitumoral activity. Linear solid-phase syntheses of Kahalalide F have been reported. Here we describe several new improved synthetic routes based on convergent approaches with distinct orthogonal protection schemes for the preparation of Kahaladide analogues. These strategies allow a better control and characterization of the intermediates because more reactions are performed in solution.