Recebido em 8/3/06; aceito em 14/6/06; publicado na web em 10/1/07 EXTRACTION, STRUCTURES AND PROPERTIES OF α-AND β-CHITIN. The fact that α-and β-chitin adopt different arrays in the solid state is explored to emphasize their different properties and distinct spectral characteristics and X ray diffraction patterns. The methods for their extraction from the biomass in view of the preservation of their native structures and aiming to fulfill the claims of purity and uniformity for potential applications are discussed. The different arrays adopted by α-and β-chitin also result in distinct reactivities toward the deacetylation reaction. Thus, the deacetylation of β-chitin is more efficient owing to the better accessibility to amide groups due to the lower crystallinity of this polymorph.Keywords: polymorphs; chitin; chitosan. INTRODUÇÃOA quitina foi isolada por Braconnot em 1881, trinta anos antes do isolamento da celulose, mas a falta de conhecimento básico sobre suas propriedades, incluindo a reatividade química, limitou severamente suas aplicações industriais até o início dos anos 1970 1 . A partir de então, o interesse progressivo na química de quitina resultou no desenvolvimento de muitos estudos que visaram aumentar o conhecimento sobre as relações estruturas/propriedades deste polímero e seus derivados. Atualmente, os usos industriais e em larga escala de quitina ainda são muito menos importantes que os de celulose, mas alguns importantes segmentos do mercado já são ocupados por derivados de quitina. A quitosana, por ex., é um polímero muito versátil com aplicações nas indústrias cosmética 2 e alimentícia 3 e que a mais de 25 anos é empregado como agente de floculação no tratamento de efluentes aquosos 4 . Sua capacidade de interagir com variada gama de substâncias, tais como proteínas, lipídeos, pesticidas, corantes, íons metálicos e radioisótopos, qualifica a quitosana para aplicações voltadas tanto para detecção e análise dessas substâncias como para sua concentração ou recuperação 1,5 . Além disso, a quitosana exibe atividade antimicrobiana e devido a sua atoxicidade, biocompatibilidade e biodegradabilidade também tem grande potencial para aplicações na agricultura, em medicina, odontologia e formulações farmacêuticas 1,[5][6][7][8][9][10] . As possibilidades de aplicações são ainda enriquecidas pelo fato que a quitosana pode ser preparada em diferentes formas, tais como soluções de viscosidade controlada, géis, filmes e membranas, microesferas e nanopartículas.Nos últimos 40 anos foram realizados muitos estudos que demonstraram haver uma estreita relação de dependência entre as características estruturais e morfológicas de quitina, quitosana e seus derivados, suas propriedades e aplicações potenciais. De fato, o interesse comercial nas aplicações de quitosana e derivados aumentou vertiginosamente nas últimas três décadas, o que pode ser constatado pelo depósito de patentes no Japão, Europa, China, Coréia e, principalmente, nos EUA. Assim, conforme o "United States Patent and Trademark Office", foram regi...

The early diagnosis of diseases related to phosphate metabolism is very important for preventing, in most cases, severe kidney failure and cardiovascular events that have an increased risk of death. In this work, we present biofunctionalized quantum dots (b-QDs) prepared with chitosan and its chemically modified derivatives to detect and capture phosphate in water media. Chitosan (CHI), N,N,N-trimethylchitosan (TMC) and carboxymethylchitosan (CMC) were used as ligands for producing colloidal CdS nanocrystals in aqueous systems. UV-Visible spectroscopy (UV-Vis), photoluminescence spectroscopy (PL), fluorescence microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), zeta potential analysis (ZP), and transmission electron microscopy (TEM) were used to characterize the colloidal QDs.Additionally, in vitro assays based on the b-QDs were designed and used to evaluate phosphate ion adsorption. The results clearly indicated that chitosan and chitosan derivatives were effective in nucleating and stabilizing CdS QDs in aqueous colloidal suspensions with an average nanocrystal size ranging from 2.2 to 3.6 nm. The photoluminescent behavior of the CdS bioconjugates was highly dependent on the chemical functionality introduced in the chitosan-derivative polymer. Moreover, the presence of different chemical groups in chitosan significantly affected the capacity of the bioconjugates to bind phosphates. Finally, a "pseudo in vivo" assay was designed using an artificial biomembrane based on phospholipid bilayers to preliminarily assess the possibility of using the bioconjugates to biolabel cell membranes. Therefore, a new class of fluorescent biosorbent nanohybrids was developed using chemically functionalized chitosan conjugated to quantum dots for potential applications in biochemical analysis and nanomedicine.

N,N,N‐trimethylchitosan (TMC) was prepared by reacting purified chitosan with iodomethane, in the presence of sodium hydroxide, water and sodium iodide, at room temperature. The reaction medium was N‐methyl‐2‐pyrrolidone. Different samples of TMC were obtained by adding to the reaction medium a fixed volume (5.5 mL) of aqueous NaOH solutions at different concentrations (15, 20, 30 and 40 wt.‐%) and carrying out the reactions for 9 or 24 h. The features observed in the 1H and 13C NMR spectra of these chitosan derivatives, in respect of the chemical shift, number and relative intensity of the signals, depended strongly on the excess of NaOH and H3CI added to the reaction medium, but when the lowest excess was employed, the characteristics of the derivative were not affected by the reaction time to the same extent. The average degree of quaternization of these N‐methylated derivatives of chitosan ranged from 10.5% to 44.8%, according to the reaction conditions. Increasing the excess of NaOH, in reactions carried out for 9 h, resulted in TMC samples with progressively higher content of trimethylated sites however, the reaction yields were correspondingly lower and O‐alkylation was favored in these cases.1H NMR spectrum of sample [AX]24h dissolved in D2O (Cp = 10 g/L).magnified image1H NMR spectrum of sample [AX]24h dissolved in D2O (Cp = 10 g/L).

Novel carbohydrate-based hybrids combining chitosan and chemically modified chitosan with CdS inorganic nanoparticles were designed and prepared via aqueous route at room temperature. N,N,N-trimethylchitosan (TM-chitosan) was synthesized aiming at substantially improving the water solubility of chitosan for producing stable colloidal systems. UV-vis spectroscopy, photoluminescence spectroscopy, Nuclear magnetic resonance spectroscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the synthesis and the relative stability of biopolymer-capped CdS nanocrystals. The results have clearly indicated that chitosan and chitosan-derivative (TM-chitosan) were remarkably effective on nucleating and stabilizing CdS nanoparticles in aqueous suspensions. In addition, the CdS nanocrystals were produced in the so-called "quantum-size confinement regime", with the calculated average size below 3.5 nm and fluorescent activity in the visible range of the spectra. Therefore, a new single-step process was developed for the bioconjugation of quantum dots with water soluble chemically functionalized carbohydrates at room temperature for potential biomedical applications.