Alexandre T. Paulino

Synthesis and water absorption transport mechanism of a pH-sensitive polymer network structured on vinyl-functionalized pectin.

Polysaccharide-structured copolymer hydrogel having excellent pH-sensitivity was developed from N,N-dimethylacrylamide (DMAc) and vinyl-functionalized Pectin (Pec). The Pec was vinyl-functionalized by way of chemical reaction with glycidyl metacrylate (GMA) in water under acidic and thermal stimuli. 13C NMR, 1H NMR, and FT-IR spectra revealed that the vinyl groups coming from the GMA were attached onto backbone of the polysaccharide. The hydrogels were obtained by polymerization of the Pec-vinyl with the DMAc. 13C-CP/MAS NMR and FTIR spectra confirmed that the gelling process occurred by way of the vinyl groups attached on Pec-vinyl backbone. The values of apparent swelling rate constant (k) decreased appreciably for pH greater than 6, demonstrating the swelling process of the hydrogel becomes slower at more alkaline conditions. There was an increase of diffusional exponent (n) with increasing pH of the surrounding liquid. This means the water absorption profile becomes more dependent on the polymer relaxation in basified swelling media. In this condition, a longer water absorption half-time (t1/2) was verified, suggesting the polymer relaxation mechanism of the hydrogel would have a considerable effect on the t1/2.

Synthesis of Hollow-Structured Nano- and Microspheres from Pectin in a Nanodroplet Emulsion

Hollow-structured nano- and microspheres with diameters ranging from 24 microm to 160 nm were successfully produced from chemically modified pectin (Ma-Pec) through a two-step synthesis. In a first step, the Pec was modified with glycidyl methacrylate (GMA) in a heterogeneous phase system, indeed consisting of water-soluble Pec and water-insoluble GMA, via an interfacial reaction at the interface of the GMA-water phase system after 12 h under continuous stirring of 1000 rpm at 60 degrees C. In a second step, the spheres were prepared in a water-in-benzyl alcohol nanodroplet emulsion at 12000 rpm under a bubbling stream of nitrogen in the presence of sodium persulfate, as initiator, and TEMED, as catalytic agent. FT-IR spectra revealed that the vinyl groups (CC) coming from the GMA were attached onto backbone of the polysaccharide. 13C-CP/MAS NMR spectra demonstrated that the spheres were formed via carbon-carbon pi-bonds on Ma-Pec in the water phase, for the duration of the dispersion stage. The dark center (an empty core) and edge of the hollow spheres could be easily identified by SEM micrographs. This type of polymer structure represents a class of unique material with particular importance in terms of state-of the-art applications in both nano- and microencapsulation of drugs, for example, protection shields of biologically active agents.

Toxic effects of dietary of Al3+ ions in tilapias (Oreochromis niloticus) and protective effect of Zn2+ ion

The lethal effects of aluminum ion (Al3+) in tilapia (Oreochromis niloticus) raised in concrete tanks were investigated. Tilapias were fed daily with commercial feed enriched with known concentrations of Al3+ and analyzed by differential pulse anodic stripping voltammetry (DPASV). The concentrations of Al3+ in feces, water, muscle tissue, viscera, and heads were determined every 3 months for a period of 365 days. The Tilapia head was the most affected tissue by Al3+. In general, Al3+ bioaccumulation reached the lethal dose (LD50) after 335 days of experiment as follows: 34.9 mg kg−1 (muscle tissue), 88.2 mg kg−1 (viscera), and 126.9 mg kg−1 (head without gills). After determining Cu2+, Zn2+, and Ca2+ by absorption spectrometry, a decrease in the Ca2+ concentration was noted in the head during the experimental period. These observations were associated with the occurrence of a decalcification in the bone tissue in the presence of Al3+. In contrast, it was found that Zn2+ ions may act as a protective agent against Al3+-induced contamination.

Recentes Avanços no Design de Hidrogéis de Chitina e Derivados de Chitina e seu Impacto sobre Meio Ambiente e Agricultura: Uma Revisão

Our purpose is to show and discuss the most relevant data on the synthesis approach and the characterization of hydrogels based on chitin and chitin-derivatives, such as chitosan, as well as their applications in several materials technologies. The current and future relevance of materials based on chitin, chitosan and derivatives have been verified by the impressive number of scientific and technological publications (both papers and patents) that appears day-by-day. This review is divided into four Sections. Section 1 reports some basic concepts of hydrogels. Section 2 deals with properties of chitin, and gelation chemistries. Applications in environment and agriculture are described in Section 3. Future trends and perspectives are considered in Section 4.

Adsorption and controlled release of potassium, phosphate and ammonia from modified Arabic gum-based hydrogel

In this work, a modified Arabic gum-based hydrogel copolymerized with acrylamide was synthesized and characterized for application in adsorption and controlled release of potassium, phosphate and ammonia. From FT-IR results, it would be reasonable to assume that the hydrogel was effectively synthesized. The degree of swelling at pure water with pH 6.0 was 21.0g water per g dried hydrogel whereas the degrees of swelling at buffer solutions with pH 4.5 and 7.0 were 7.2 and 9.2g water per g dried hydrogel, respectively. The water diffusion mechanism was governed by Fickian transport with tendency to occur macromolecular relaxation. The adsorption capacities of potassium, phosphate and ammonia were higher by increasing the initial concentrations due to availability of active sites in the hydrogel network, nutrient size and ionic charge. Potassium, phosphate and ammonia concentrations released from the modified Arabic gum-based hydrogel increased by increasing the release time from 0 to 1440min. Release profiles indicated that this hydrogel could be applied for the enrichment and hydration of deserted soil, avoiding losses of nutrients by leaching and percolation, with an advantage of being constituted by an eco-friendly polysaccharide.

Morfologia de hidrogéis-ipn termo-sensíveis e ph-responsivos para aplicação como biomaterial na cultura de células

In the present investigation, hydrogels with pH-responsive and temperature-sensitive properties were obtained by formation of alginate-Ca network inside the PNIPAAm network resulting in an interpenetrated network system (IPN). From scanning electron microscopy (SEM) images and water uptake (WU) tests one observed that IPN hydrogels exhibited a drastic shrinking when heated above 30-35 oC. The shrinking resulted in decreased average pore size, thus affect the hydrogel morphology significantly. In the pH range studied, IPN hydrogels showed significant pH dependence, which was attributed to the charged alginate groups. The results indicated that the pH-responsiveness and temperature-dependence of alginate and PNIPAAm, respectively, were preserved in IPN hydrogels. In addition, such hydrogels become less deformable when subjected to compressive stress. These hydrogels presented porous morphology that may be tuned by controlling the temperature, and this makes them attractive for applications as biomaterial in cell growth.

Effects of daily nickel intake on the bio-accumulation, body weight and length in tilapia (Oreochromis niloticus)

Nickel pollution is a serious environmental problem, and its effects may provoke alterations in the ecosystem and in organism of animals and humans. Dermatitis, eczema, and asthma are some illnesses caused by Ni2+ poisoning. In this work, fish fed either Ni2+-enriched pellets or commercial pellets were studied. The amount of Ni2+ in fish were measurements by adsorptive stripping voltammetry (AdSV) with dimethylglyoxime as a complexing agent. The analysis of Ni2+ in fish by AdSV established that its accumulation occurs principally in viscera (670.86 ± 5.82 µg g−1), in the head (697.12 ± 2.77 µg g−1) and in the muscle (405.82 ± 3.26 µg g−1), both after 12 months of experiments. Ni2+ adsorbs preferentially in organs such as the stomach, the intestine, and the kidneys and acts in the central nervous system as well. Tilapia growth and mass were significantly affected by Ni2+ poisoning. From statistical analysis, observed that the results for lengths, weights and metal concentration were different for each sampling at significance level of p < 0.05. The Ni2+ concentration in tilapia was enough to cause the death of tilapias; however, it did not occur because the presence of Zn2+ might act as protective agent of heavy metals.

Protective action of zinc against lead poisoning in tilapia Oreochromis niloticus

The accumulation of lead (Pb) in tilapias Oreochromis niloticus, acclimatized in cement tanks, and fed once a day with pellets of commercial food with lead nitrate, was investigated by square wave anodic stripping voltammetry (SWV). The head (including head bones, proteins, and brain) was the main target of lead uptake by tilapias, with a small amount in muscle tissue. A high concentration of Pb was found in feces which indicated low absorption by the organism when fed with high Pb concentration. The protective effects of zinc (Zn) against the Pb poisoning, the accumulation of Pb in the heads of the fishes of 107.8 ± 3.1 mg kg−1 and in the viscera of 57.1 ± 2.9 mg kg−1 with consequent decrease of calcium (Ca) concentration, were observed. In spite of the experimental time of 16 months and higher Pb concentration in the dietary food of 320 mg kg−1, no death of tilapias was observed due to the protective action of Zn.

Hydrolysis of lactose using β- d -galactosidase immobilized in a modified Arabic gum-based hydrogel for the production of lactose-free/low-lactose milk

β-d-galactosidase was immobilized in a modified Arabic gum-based hydrogel for the hydrolysis of standard lactose and lactose contained in UHT milk with the aim of producing lactose-free/low-lactose milk. The hydrogel was synthesized by cross-linking the modified Arabic gum with acrylamide, using potassium persulfate as initiator. Fourier-transform infrared spectroscopy and scanning electron microscopy confirmed the formation of the hydrogel and its three-dimensional porous network. Swelling degrees in distilled water, drinking water, phosphate buffer solution at pH7.0 and acetate buffer solution at pH4.0 were 12.56 and 17.72, 10.65 and 12.58, 8.58 and 10.71, and 6.49 and 8.16g water per g dried hydrogel at room temperature and 37.0±1.0°C, respectively. The immobilization capacities of β-d-galactosidase in acetate and phosphate buffer solutions at room temperature were 242.52±0.13 and 118.42±0.23mg enzyme per g dried hydrogel, respectively, after 1440min of contact. Higher enzymatic activities were found after immobilization in phosphate buffer solution due to the isoelectric point of β-d-galactosidase. Hydrolysis of standard lactose and lactose contained in UHT milk was more efficient using immobilized β-d-galactosidase than free β-d-galactosidase. Immobilized β-d-galactosidase was applied for three cycles of hydrolysis of lactose without significantly losing enzymatic activity.

Polysaccharide-based hydrogels for the immobilization and controlled release of bovine serum albumin

Arabic gum-based and chitosan-based hydrogels were synthesized through chemical crosslinking for the immobilization and controlled release of bovine serum albumin (BSA) and characterized by Fourier-transform infrared spectrometry, scanning electron microscopy and swelling assays. The degrees of swelling of the Arabic gum-based hydrogel were 13.22 and 22.95 g water per g dried hydrogel at pH 4.5 and 7.0, respectively, whereas the degrees of swelling of the chitosan-based hydrogel were 15.32 and 36.10 g water per g dried hydrogel, respectively. The water absorption mechanism in both hydrogels was non-Fickian, which involves diffusion through pores and macromolecular relaxation of the hydrophilic three-dimensional polymer network. BSA immobilization capacities of the Arabic gum-based and chitosan-based hydrogels after 240 min at pH 4.5 were 71.0 and 175.6 mg protein per g dried hydrogel, respectively. BSA immobilization capacities after 240 min at pH 7.0 were 62.5 and 154.2 mg protein per g dried hydrogel, respectively. The controlled release of BSA from the Arabic gum-based hydrogel was slightly more efficient than that of the chitosan-based hydrogel due to its more porous structure and weaker physiochemical interactions between the polymer network and protein molecule. Both hydrogels could be employed as carriers of proteins and as capsules for food supplements.