Synthesis and characterization of a new hydrogel were carried out using a chemically modified starch (starch‐M) consisting of coupling CC bounds coming from glycidil methacrylate (GMA) onto the polysaccharide structure. 13C NMR, 1H NMR, and FT‐IR spectroscopies were used to confirm the incorporation of such groups onto the starch‐M. The hydrogel was prepared by a crosslinking polymerization of starch‐M using sodium persulfate as an initiating agent. The starch‐M hydrogel shows morphology clearly different from that of the raw starch film due to the presence of voids on its surface. The swelling process of the starch‐M hydrogel was not significantly affected by changes on the temperature or on pH of the surrounding liquid, indicating the such behavior can be then understood by a diffusional process, resulting from its physical–chemical interactions with the solvent. The values of the diffusional exponent n were on the order of 0.45–0.49 for the range of pHs investigated, demonstrating that the water transport mechanism of starch‐M hydrogel is more dependent on Fickian diffusion, that is, controlled by water diffusion. Such starch‐M hydrogel is a promising candidate to be used in transporting and in preserving acid‐responsive drugs, such as corticoids, for the treatment of colon‐specific diseases, for example, Crohn's disease. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2567–2574, 2008

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A pectin-based hydrogel was used as a remover of Cu 2þ and Pb 2þ ions from water and wastewater and in the release of phosphate, potassium, and urea. The swelling studies in either aqueous or saline solutions were analyzed at different pressures, and the prediction of profile of water and solute transports was further analyzed on basis of transport process by diffusion in swellable polymer networks. The hydrogel composed of 0.10 g mL À1 final polymer concentration showed an excellent absorption capacity for removal of Cu 2þ and Pb 2þ from the solution: 120 mg Cu 2þ and 130 mg Pb 2þ per g hydrogel, both at pH 5.5. The hydrogel help to conserve water in a pressure range in which a variety of horticultural plants can absorb it. The release process of urea, phosphate, and potassium from the hydrogels is controlled by non-Fickian mechanism with a tendency to macromolecular relaxation. This type of hydrogel is an interesting system for applications in which the efficient use of water is required and release of fertilizers for agriculture.

This contribution describes the absorption percentage of Pb 2þ and Cu 2þ from water by a superabsorbent hydrogel matrix (SH) made from an anionic polysaccharide copolymerized with acrylic acid (AAc) and acrylamide (AAm). Metal-absorption tests, upon sequential pH variation, indicated that the SH has pH-sensitivity for the absorption of both metals from solution, attributed to the functional ionic groups (À ÀCOOH) present in the AAc and arabic gum (AG) segments. At the pH 5.0, the SH exhibited good absorption capacity: 73.10% for Pb 2þ , 81.99% for Cu 2þ in water and 63.64% for Pb 2þ , and 76.67% for Cu 2þ in saline water with 0.1 mol kg À1 ionic strength. A replicated 2 2 full factorial design with a central point was built to evaluate the maximum absorption capacity of the metals into the SH. It was found that both the interaction and main effects of the pH and the initial concentration of metal solution on absorption percentage of the metals were statistically significant. Surface response plots indicated that the absorption capacity of both metals into the SH may be appreciably improved by using the solutions with lower initial concentration of metal and with higher pH values. Metal-absorption results demonstrated that the SH is a convenient material for absorption of Pb 2þ and Cu 2þ from pure aqueous and saline aqueous environments.

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Given the importance of protease's worldwide market, the determination of optimum conditions and the development of a standard protocol are critical during selection of a reliable method to determine its bioactivity. This paper uses quality control theory to validate a modified version of a method proposed by Charney and Tomarelli in 1947. The results obtained showed that using azocasein substrate bromelain had its optimum at 45°C and pH 9 (Glycine-NaOH 100 mM). We also quantified the limit of detection (LoD) and limit of quantification (LoQ) in the above-mentioned optimum (0.072 and 0.494 mg·mL−1 of azocasein, resp.) and a calibration curve that correlates optical density with the amount of substrate digested. In all analysed samples, we observed a significant decrease in response after storage (around 17%), which suggests its use must be immediately after preparation. Thus, the protocol presented in this paper offers a significant improvement, given that subjective definitions are commonly used in the literature and this simple mathematical approach makes it clear and concise.

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