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Wound repair is a complex process that calls for strategies to allow a rapid and effective regeneration of injured skin, which has stimulated the research of advanced wound dressings. Herein, highly porous membranes of N,O-carboxymethylchitosan (CMCh), and poly (vinyl alcohol) (PVA) were successfully prepared via a green and facile freeze-drying method of blend solutions containing CMCh/PVA at weight ratio 25/75. Membranes composed only by CMCh were also prepared and genipin was used for crosslinking. Different contents of TiO2 nanoparticles were incorporated to both type of membranes, which were characterized in terms of morphology, porosity (Φ), swelling capacity (S.C.), mechanical properties, susceptibility to lysozyme degradation and in vitro cytotoxicity toward human fibroblast (HDFn) and keratinocytes (HaCaT) cells. Larger apparent pores were observed in the surface of the genipin-crosslinked CMCh membrane, which resulted in higher porosity (Φ ≈ 76%) and swelling capacity (S.C. ≈ 1720%) as compared to CMCh/PVA membrane (Φ ≈ 68%; S.C. ≈ 1660%). The porosity of both types of membranes decreased upon the addition of TiO2 nanoparticles while swelling capacity increased. Due to their high porosity and swelling capacity, adequate mechanical properties, controlled degradability, and cytocompatibility, such carboxymethylchitosan-based membranes are potentially useful as wound dressings.

Since chitosan presents the ability to interact with a wide range of molecules, it has been one of the most popular natural polymers for the construction of layer-by-layer thin films. In this study, depth-profiling X-ray photoelectron spectroscopy (XPS) was employed to track the diffusion of sulfonated polystyrene (SPS) in carboxymethyl cellulose/chitosan (CMC/Chi) multilayers. Our findings suggest that the CMC/Chi film does not constitute an electrostatic barrier sufficient to block diffusion of SPS, and that diffusion can be controlled by adjusting the diffusion time and the molecular weight of the polymers that compose the CMC/Chi system. In addition to monitoring the diffusion, it was also possible to observe a process of preferential interaction between Chi and SPS. Thus, the nitrogen N 1s peak, due to functional groups found exclusively in chitosan chains, was the key factor to identifying the molecular interactions involving chitosan and the different polyanions. Accordingly, the presence of a strong polyanion such as SPS shifts the N 1s peak to a higher level of binding energy. Such results highlight that understanding the fundamentals of polymer interactions is a major step to fine-tuning the internal architecture of LbL structures for specific applications (e.g., drug release).

Langmuir monolayers are used to simulate the biological membrane environment, acting as a mimetic system of the outer or the inner membrane leaflet. Herein, we analyze the interaction of membrane models with a partially N-acetylated chitosan (Ch35%) possessing a quasi-ideal random pattern of acetylation, full water solubility up to pH ≈ 8.5 and unusually high weight average molecular weight. Lipid monolayers containing dipalmitoyl phosphatidyl choline (DPPC), dipalmitoyl phosphatidyl ethalonamine (DPPE), dipalmitoyl phosphatidyl glycerol (DPPG) or E. coli total lipid extract were spread onto subphases buffered at pH 4.5 or 7.4. The incorporation of Ch35% chitosan caused monolayer expansion and a general trend of decreasing monolayer rigidity with Ch35% concentration. Due to its relatively high content of N-acetylglucosamine (GlcNAc) units, Ch35% interactions with negatively charged monolayers and with E. coli extract were weaker than those involving zwitterionic monolayers or lipid rafts. While the smaller interaction with negatively charged lipids was unexpected, this finding can be attributed to the degree of acetylation (35%) which imparts a small number of charged groups for Ch35% to interact. Chitosan properties are therefore determinant for interactions with model cell membranes, which explains the variability in chitosan bactericide activity in the literature. This is the first study on the effects from chitosans on realistic models of bacterial membranes under physiological pH.

Immobilization of cells on surfaces can be strongly affected by several properties of a substrate, including surface properties, topography and charge density. Controlling the cell adhesion mechanism is a real challenge in biotechnological processes. Here, we assessed the influence of the average degree of deacetylation of chitosan ( DD ¯ ) and the polyelectrolyte solution pH on the physicochemical properties of multilayered hyaluronan/chitosan films and their ability to bind tumor cells. These functional coatings explore CD44-hyaluronate interactions to improve the capture of tumor cells (PC3 line). Film characterization was carried out using XPS, UV–Vis and scanning probe techniques such as Capacitance, KPFM and AFM-IR measurements. The increase in the solution pH from 3.0 to 5.0 was the major factor to control both the film structure and the cell capture, enhancing the number of cells adhered in a range of 1.5 to 3.5-fold. These results also suggest that limited HA availability induces cell-film adhesion, whereas more irregular and rougher surfaces inhibit this process. These findings indicate that surface chemistry and morphology are critical factors for the development of new biomaterials designed to capture cells selectively.

Made available in DSpace on 2021-06-26T06:17:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Auxilio Financeiro a Projeto Educacional ou de Pesquisa Two samples of N-(2-hydroxy)-propyl-3-trimethylammonium, O-palmitoyl chitosan (DPCat) with different av-erage degrees of quaternization named as DPCat35 (DQ = 35%) and DPCat80 (DQ = 80%), were successfully syn-thesized by reacting glycidyltrimethylammonium chloride (GTMAC) with O-palmitoyl chitosan (DPCh) derivative (DS = 12%). Such amphiphilic derivatives of chitosan were fully water-soluble at 1.0 < pH < 12.0 and showed significant electrostatic stability enhancement of a self-assembly micellar nanostructure (100 & ndash;320 nm) due to its positively-charged out-layer. In vitro mucoadhesive and cytotoxicity essays toward healthy fibroblast cells (Balb/C 3T3 clone A31 cell), human prostate cancer (DU145) and liver cancer (HepG2/ C3A) cell lines revealed that the biological properties of DPCat derivatives were strongly dependent on DQ. Ad-ditionally, DPCat35 had better interactions with the biological tissue and with mucin glycoproteins at pH 7.4 as well as exhibited potential to be used on the development of drug delivery systems for prostate and liver cancer treatment. (c) 2021 Elsevier B.V. All rights reserved. Sao Paulo State Univ, Inst Chem, Av Prof Francisco Degni 55,237, BR-14800900 Araraquara, SP, Brazil Univ Sao Paulo, Sao Carlos Inst Chem, Av Trabalhador Sao Carlense 400,780, BR-13566590 Sao Carlos, SP, Brazil Brazilian Corp Agr Res, Embrapa Instrumentat, Rua XV Novembro 1452, BR-13560970 Sao Carlos, SP, Brazil Sao Paulo State Univ, Sch Pharmaceut Sci, Rod Araraquara Jau Km 01 S-N, BR-14800903 Araraquara, SP, Brazil Sao Paulo State Univ, Inst Chem, Av Prof Francisco Degni 55,237, BR-14800900 Araraquara, SP, Brazil Sao Paulo State Univ, Sch Pharmaceut Sci, Rod Araraquara Jau Km 01 S-N, BR-14800903 Araraquara, SP, Brazil FAPESP: FAPESP 2016/20970-2 FAPESP: 2017/20973-4 FAPESP: 2019/13656-8 CNPq: CNPq 141353/2016-3 CNPq: 150964/2017-0 CNPq: 309568/2019-6 CAPES: 001 Auxilio Financeiro a Projeto Educacional ou de Pesquisa: AUXPE 139/2015

We report on layer-by-layer (LbL) films of chitosans (CHI) and hyaluronic acid (HA) whose properties could be controlled by employing chitosans with different degrees of deacetylation ( DD ¯ ≈ 85%; 65%; 40%) and high average molecular weight (ca. 106 g/mol). In spite of their high molecular weight, these chitosans are soluble within a wide pH range, including physiological pH. HA/CHI LbL films produced from polymer solutions at pH 4.5 were thinner, smoother, more hydrophilic than those prepared at pH 7.2. This is attributed to the more extended conformation adopted by chitosan due to its very high charge density at low pH, favoring a compact chain packing during the film formation and resulting in lower film thickness and roughness. The smoother HA/CHI LbL films obtained at pH 4.5 were effective against Escherichia coli, while the thicker, rougher LbL films fabricated at pH 7.2 could be used in the controlled released of Rose Bengal dye. In summary, the tuning of only two parameters, i.e. solution pH and DD ¯ of chitosans, provides access to a library of HA/CHI LbL films for tailored, diversified applications.

In this paper, chitosan was used as protective agent for dual temperature-/pH-sensitive poly(N-vinylcaprolactam-co-itaconic acid-co-ethylene- glycol dimethacrylate)- based hydrogel nanoparticles (poly(NVCL-co-IA-co-EGDMA)) aiming avoid their undesirable colloidal destabilization at different conditions of body human tissues. Thus, poly(NVCL-co-IA-co-EGDMA) was embedded into chitosan and a new solid dispersion was prepared via spray-drying and ketoprofen was used as carrier. Two different sizes of hydrogel nanoparticles (120.6 nm and 185.9 nm) were evaluated and they exhibited a drug encapsulation efficiency of the 39.6% and 57.8%, respectively. The smaller nanoparticles showed to be faster for releasing of ketoprofen at pH 7.4 and 37 °C due to their larger surface area and higher swelling ability. Chitosan played a role of a secondary barrier for the ketoprofen diffusion, extending its release compared to hydrogel nanoparticles alone. Among two concentrations (40 wt% and 70 wt%) of hydrogel nanoparticles related to chitosan, the first one induced higher percentages of ketoprofen release: 74.2% against 64.6%. In addition, the interactions between chitosan matrix and poly(NVCL-co-IA-co-EGDMA) did not change the multi-responsive behavior of hydrogels, suggesting the chitosan was efficient for keeping integrity of nanoparticles hydrogels. Chitosan/poly(NVCL-co-IA-co-EGDMA) hybrid microparticles seems to be a promising new carrier for release of hydrophobic drugs, such as ketoprofen.

The chitin insoluble characteristics in aqueous media creates a barrier for biological applications. While the chitosan, the most used derivative from chitin, have been widely used for several applications, due to high solubility in slightly acidic aqueous solution. Reported herein is a new approach, consisting of ultrasound irradiation of beta-chitin, which can produce stable suspensions in water (pH= 7.0). With the aim of obtained the most stable beta-chitin suspensions, we played with beta-chitin concentration (0.4 g/L and 1.6 g/L), sonication time (ranged in the interval from 5 min. to 30 min.) and the irradiation amplitude (from 30 % to 50%). When beta-chitin is processed by ultrasound, in aqueous media, we observed the decrease of crystallinity (DRX) and the appearance of micro and nanofibers (MEV). Testing the stability of beta-chitin suspensions, was demonstrate that these suspensions can be stable since 5 min. until several days. Coupling the efficient process to produce stable suspensions in water with biodegradable and biocompatible characteristics of beta-chitin holds great considerable promise for advanced in biological applications.

Blend solutions of poly(e-caprolactone) (PCL) and N-(2-hydroxy)-propyl-3-trimethylammonium chitosan chloride (QCh) were successfully electrospun. The weight ratio PCL/QCh ranged in the interval 95/5–70/30 while two QCh samples were used, namely QCh1 ( D Q ¯ = 47.3%; D P v ¯ = 2218) and QCh2 ( D Q ¯ = 71.1%; D P v ¯ = 1427). According to the characteristics of QCh derivative and to the QCh content on the resulting PCL/QCh nonwoven, the nanofibers displayed different average diameter (175 nm–415 nm), and the nonwovens exhibited variable porosity (57.0%–81.6%), swelling capacity (175%–425%) and water vapor transmission rate (1600 g m−2 24 h–2500 g m−2 24 h). The surface hydrophilicity of nonwovens increases with increasing QCh content, favoring fibroblast (HDFn) adhesion and spreading. Tensile tests revealed that the nonwovens present a good balance between elasticity and strength under both dry and hydrated state. Results indicate that the PCL/QCh electrospun nonwovens are new nanofibers-based biomaterials potentially useful as wound dressings.

Langmuir monolayers have been used as cell membrane models, where lipid composition is normally varied to mimic distinct types of membranes. For eukaryotic membranes, for instance, rather than using only zwitterionic phospholipids there is now a trend to employ mixtures to simulate the lipid rafts known to be relevant for various cellular processes. In this study, we demonstrate that effects from chitosans on Langmuir monolayers are considerably higher if lipid raft compositions (ternary mixtures of dipalmitoyl phosphatidyl choline (DPPC), sphingomyelin (SM) and cholesterol) are used. Significantly, measurable effects on the surface pressure isotherms start at 10-6 mg mL-1 for chitosans in lipid rafts, to be compared with 10-2 mg mL-1 for neat dipalmitoyl phosphatidylcholine (DPPC). This applies to both a commercial chitosan and chitosans soluble at physiological pH. Incorporation of these chitosans in the raft monolayers was confirmed in polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) experiments, where both the tail groups and headgroups were found to interact with chitosan. Since the effects on membrane models may be observed at such small concentrations for chitosans and probably other molecules, some studies may have to be revisited where neat phospholipids should be replaced by lipid raft compositions.

Made available in DSpace on 2020-12-12T01:47:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-01-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Core-sheath nanofibers were successfully prepared via coaxial electrospinning by using chitosan with well-defined structural characteristics as the shell layer and poly (vinyl alcohol) (PVA) containing tetracycline hydrochloride (TH) as the core layer. The effects of the average degree of deacetylation (DD‾) of chitosan and the post-electrospinning genipin crosslinking on physicochemical and biological properties of resulting nonwovens were evaluated. Defect-free and geometrically uniform nanofibers with diameters predominantly in the range of 100–300 nm were prepared, and transmission electron microscopy (TEM) revealed the core-sheath structures and its preservation after crosslinking. The mechanical properties, as well as the stability of nonwovens in aqueous medium, were greatly improved by genipin-crosslinking, which enabled a sustained release of TH over 14 days. Results also revealed that the release profile of TH in the presence of lysozyme was affected by the composition of the shell layer, as the TH release rate increases with decreasing of DD‾. Further in vitro antimicrobial activity demonstrated that the cross-linked nonwovens containing TH showed strong activity against bacterial strains associated with periodontal disease. Additionally, the nonwovens did not demonstrate cytotoxic toward fibroblast (HDFn) cells, hence showing their potential for applications as a novel drug delivery platform for periodontitis treatment. Nanotechnology National Laboratory for Agriculture (LNNA), Embrapa Instrumentação, 13560-970 São Carlos PPG-Biotec Center for Exact Sciences and Technology Federal University of São Carlos (UFSCar) Sao Carlos Institute of Physics/University of São Paulo, PO Box 369, 13560-970 São Carlos Department of Clinical Analysis School of Pharmaceutical Sciences São Paulo State University (UNESP) Sao Carlos Institute of Chemistry/University of São Paulo, Av. Trabalhador sao-carlense, 400, 13566-590 São Carlos Department of Clinical Analysis School of Pharmaceutical Sciences São Paulo State University (UNESP) FAPESP: 2013/07276-1 FAPESP: 2017/12174-4 FAPESP: 2017/20973-4 FAPESP: 2018/09088-1 FAPESP: 2018/23015-7

We propose a novel approach relied on high-resolution solid-state 13C NMR spectroscopy to quantify the crystallinity index of chitosans (Ch) prepared with variable average degrees of acetylation ( D A ¯ ) from 5% to 60 % and average weight molecular weight ( M ¯ w ) ranged in 0.15 × 106 g mol−1–1.2 × 106 g mol−1. The Dipolar Chemical Shift Correlation (DIPSHIFT) curve of the C(6)OH segment revealed increased mobility dynamic, which induced different distribution from trans-to-gauche conformations in relation to C(4). Indeed, 1H-13C Heteronuclear Correlation (2D HETCOR) showed that distinguished C4 chemical shifts correlates with the same aliphatic protons. The short-range ordering can be assigned to C4/C6 signals on 13C CPMAS and, for our case, the deconvolution procedure between disordered and ordered phases revealed increasing crystallinity with D A ¯ , as confirmed by SVD multivariate analysis. This work extended the knowledge regarding the use of 13C CPMAS technique to predict the crystallinity of chitosans without the use of amorphous standards.

A hybrid hydrogel combining collagen and chitosan (Ch) and human amniotic membranes (AM) were produced. To produce hybrid hydrogels, a fixed concentration of chitosan (2%) was used, adding AM as a ...

Miniaturized and inexpensive sensing platforms remains an important goal for the field-deployable monitoring of toxic gases. In this work, we report a disposable ethanol sensor based on nanochitin-composite containing chitin nanowhiskers/zinc oxide nanoparticles/polyaniline (ChitNW-ZnO/PANI) produced via solution casting method. The as-prepared material was fully characterized by transmission electron microscopy, atomic force microscopy, contact angle measurements, mechanical tests, thermogravimetric analysis and X-ray diffraction, confirming its successful preparation and revealing its morphology, microstructure and composition. Such nanocomposite showed enhanced ethanol sensing performance at room temperature, in which quantitative analysis was obtained in the range 20–100 ppm with a detection limit of 17 ppm (S/N = 3). We further validated that common potential interfering agents were not misidentified with ethanol. The development of such a unique nanochitin-based composite as a disposable sensor is a great step ahead in flexible and wearable electronics having potential applications in different fields such as biomedical and biotechnological engineering, security and internet of things (IoT).

N-acetyl-D-glucosamine (GlcNAc) is an important amino-monosaccharide with great potential for biotechnological applications. It has traditionally been produced by the chemical hydrolysis of chitin, despite certain industrial and environmental drawbacks, including acidic wastes, low yields and high costs. Therefore, enzymatic production has gained attention as a promising environmentally-friendly alternative to the chemical processes. In this study we demonstrate the GlcNAc bioproduction from colloidal α-chitin using an enzyme cocktail containing endochitinases and exochitinases (chitobiosidases and N-acetyl-glucosaminidases). The enzyme cocktail was extracted after fermentation in a bioreactor by Aeromonas caviae CHZ306, a chitinolytic marine bacterium with great potential for chitinase production. Hydrolysis parameters were studied in terms of temperature, pH, enzyme and substrate concentration, and reaction time, achieving over 90% GlcNAc yield within 6 h. The use of colloidal α-chitin as substrate showed a substantial improvement of GlcNAc yields, when compared with β-chitin and α-chitin polymorphs. Such result is directly related to a significant decrease in crystallinity and viscosity from natural α-chitin, providing the chitinase with greater accessibility to the depolymerized chains. This study provides valuable information on the GlcNAc bioproduction from chitin using an enzymatic approach, addressing the key points for its production, including the enzyme cocktail composition and the substrate structures.

An amphiphilic derivative of chitosan containing quaternary ammonium and myristoyl groups, herein named as ammonium myristoyl chitosan (DMCat), was synthesized by reacting glycidyltrimethylammonium chloride (GTMAC) and myristoyl chitosan (DMCh). The success of the modification was confirmed using Fourier-transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (NMR) spectroscopy. The average degrees of alkylation and quaternization ( D Q &macr, ) were determined by using 1H NMR and conductometric titration. The zeta potential of the micelles was higher than 28 mV while its average size and encapsulation efficiency ranged from 280 nm to 375 nm and 68% to 100%, respectively. The in vitro cytotoxicity of the unloaded and curcumin (CUR)-loaded micelles was tested against Caco-2 and HT29-MTX intestinal epithelial cell lines. The results showed no cytotoxic effect from loaded and unloaded micelles as compared to free CUR. In the permeability test, it was observed that both types of micelles, i.e., DMCh and DMCat, improved CUR permeability. Additionally, higher permeability was verified for both systems in Caco-2/HT29-MTX:Raji B because of the mucoadhesive character of chitosan and its ability to open tight junctions. The results indicated that DMCat micelles, due to the physico-chemical, improved characteristics may be a promising carrier to encapsulate CUR aiming cancer therapy.

Methoxypoly(ethyleneglycol)-graft-chitosan (PEG-g-Ch) was prepared by grafting polyethyleneglycol into chitosans (Ch) exhibiting different average degree of deacetylation (60% DD ¯ DS ¯ ≈ 40%) and such derivatives exhibited full water solubility at 1.0 DD ¯ ≈ 76%; [η] ≈ 1201 mL g−1) showed a distinct rheological behavior as it formed a physically cross-linked hydrogel that exhibited a thermo-induced sol-gel transition at ≈38 °C.

International audience; The interactions between a polyelectrolyte and an oppositely charged surfactant allows obtaining complexes with specific properties. Such complexes between a quaternized chitosan, obtained from the reaction between chitosan and quaternary ammonium epoxides, and sodium 1-decanesulfonate were studied. Physico-chemical characteristics were obtained from conductimetric experiments as well as surface tension studies. A strong associative electrostatic interaction between the polysaccharide and the surfactant was shown from conductimetric experiments and a degree of association equal to 0.74 was determined. The complex presents better interfacial properties than surfactant and polysaccharide alone. The critical aggregation concentration is much smaller than the critical micellar concentration of the surfactant alone in solution. Moreover the viscoelastic moduli of the interfacial layer was increased in presence of the complex by comparing with surfactant alone. All these considerations allow using the surfactant-polysaccharide complex as a better emulsion stabilizer than either surfactant or polysaccharide alone.

This paper discusses the production of chitosan by applying high intensity ultrasound irradiation to alpha-chitin suspended in 40% aqueous sodium hydroxide. The average degree of acetylation (DA) of chitosan was determined by 1H NMR spectroscopy and titrimetry while its viscosity average molecular weight (Mv) was calculated from the intrinsic viscosity as determined by capillary viscometry. The results show that fully acid-soluble chitosans (DA 95%) by applying non-isothermal ultrasound-assisted N-deacetylation process to alpha-chitin suspension (44 mg/mL). It is also shown that such a process is more efficient than thermochemical N-deacetylation, even being carried out at a lower temperature due to the effects of high intensity ultrasound irradiation.

The effects of reaction time, concentration of aqueous sodium hydroxide and molar ratio iodomethane/chitosan on the yield of the reaction of chitosan with iodomethane in N-methyl-2-pyrrolidone (NMP) at 25.0 ± 0.1 °C, as well as on the characteristics of the resulting N,N,N-trimethylchitosan (TMCh), were evaluated by using full-factorial 23 design analysis and response surface methodology. This study also aimed to determine the reaction conditions allowing the production of water-soluble TMCh presenting a high average degree of quaternization and intrinsic viscosity at high reaction yield. 1H NMR spectroscopy was employed for structural characterization, including the determination of average degrees of acetylation (DA‾) and quaternization (DQ‾), while capillary viscometry was used to determine intrinsic viscosity [η]. The results show that when the extensive N-methylation is carried out for 24 h in NMP/15% NaOH (w/v) employing a lower excess of iodomethane (CH3I/Ch = 9), water-soluble highly substituted (DQ‾ = 46.0%) TMCh ([η] = 213.0 mL g−1) can be produced in high yield (81.8%). The highly significant mathematical models resulting from this study describe the dependence of the experimental responses on the reaction conditions and allow the characteristics and properties of the resulting TMCh to be defined by properly choosing the reaction conditions. © 2015 Society of Chemical Industry

This chapter proposes Chitosan, a natural polymer with excellent properties, as the ideal candidate for the hydrophilic part of polymeric micelles or nanoparticles (NPs). The generation of NPs includes natural or synthetic biocompatible and biodegradable polymers. The chapter focuses on NPs obtained from amphiphilic chitosan derivatives. It also focuses on chemical modifications of chitosan, highlighting those that allow the preparation of amphiphilic derivatives that are intended to encapsulate therapeutic agents for biomedical and biopharmaceutical applications. The chapter revises the literature on the regioselective synthesis of chitosan derivatives, focusing on the addition of hydrophobic groups to the chitosan chain through alkylation and acylation reactions, aiming to tailor the polymer solubility. As a viable and cost-effective strategy, amphiphilic derivatives with self-assembly properties has been widely used to prepare chitosan nanocarriers that have been investigated as vehicles for the drug delivery, such as proteins and peptides, anti-inflammatory drugs, and anticancer drugs.

Streams situated in areas of sugarcane cultivation receive high concentrations of metal ions from the adjacent areas, causing accumulation of metals in the aquatic sediment. Several adsorbents have been used to remove metal from water. Activated carbons clays and biopolymers are among the common adsorbents utilized. Chitosan beads, an alternative biopolymer that exhibits a high affinity for metal ions, are easy to prepare under laboratory conditions, have low overall cost and can be indicated for the removal of metals from aquatic sediments. This work studied, for the first time, the possible use of Chitosan beads in the adsorption of metals from sediments of streams located in areas adjacent to sugarcane cultivation. The sediments were collected from four streams historically impacted by sugarcane; one of them is located in a preserved area, used as the control site. The sediments were evaluated for adsorption of Cr, Cu, Zn, Mn and Mg. The results showed that the maximum adsorption of metals in chitosan beads (containing only 5.5% of chitosan) were obtained in Sao Joao Stream, such as: 0.65 mg kg−1 for Cr6+, 2.85 mg kg−1 for Cu2+, 2.5 mg kg−1 for Mg2+ and 0.85 mg kg−1 for Zn2+. For manganese, the maximum adsorption was 0.84 mg kg−1, obtained for the Agua Sumida Stream. The adsorption had high affinity for Cu, Zn and Cr and low affinity for Mg and Mn. Chitosan presented potential and viability for use in the remediation of the impacts of metals on aquatic sediment systems, with high adsorption and capacity to be applied “in loco”.

Made available in DSpace on 2018-12-11T17:35:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-01-08 European Regional Development Fund Fundação para a Ciência e a Tecnologia Ministério da Ciência, Tecnologia e Ensino Superior This work addresses the establishment and characterization of gellan gum:pectin (GG:P) biodegradable mucoadhesive beads intended for the colon-targeted delivery of resveratrol (RES). The impact of the polymer carrier system on the cytotoxicity and permeability of RES was evaluated. Beads of circular shape (circularity index of 0.81) with an average diameter of 914 μm, Span index of 0.29, and RES entrapment efficiency of 76% were developed. In vitro drug release demonstrated that beads were able to reduce release rates in gastric media and control release for up to 48 h at an intestinal pH of 6.8. Weibull's model correlated better with release data and b parameter (0.79) indicated that the release process was driven by a combination of Fickian diffusion and Case II transport, indicating that both diffusion and swelling/polymer chains relaxation are processes that contribute equally to control drug release rates. Beads and isolated polymers were observed to be safe for Caco-2 and HT29-MTX intestinal cell lines. RES encapsulation into the beads allowed for an expressive reduction of drug permeation in an in vitro triple intestinal model. This feature, associated with low RES release rates in acidic media, can favor targeted drug delivery from the beads in the colon, a promising behavior to improve the local activity of RES. Faculdade de Ciências Farmacêuticas Universidade Estadual Paulista (UNESP), Araraquara, Rodovia Araraquara-Jaú, Km 1 Instituto de Química de São Carlos Universidade de São Paulo (USP), Avenida Trabalhador São-Carlense, 400 I3S-Instituto de Investigação e Inovação em Saúde Universidade do Porto, Rua Alfredo Allen, 208 INEB-Instituto de Engenharia Biomédica Universidade do Porto, Rua Alfredo Allen, 208 CESPU-Instituto de Investigacao e Formacao Avancada em Ciencias e Tecnologias da Saude, Rua Central de Gandra 1317 School of Pharmacy Queen's University Belfast Medical Biology Centre, 97 Lisburn Road Faculdade de Ciências Farmacêuticas Universidade Estadual Paulista (UNESP), Araraquara, Rodovia Araraquara-Jaú, Km 1 Fundação para a Ciência e a Tecnologia: NORTE-01-0145-FEDER-000012 Fundação para a Ciência e a Tecnologia: SFRH/BD/118721/2016

Chitosan-based thin films were assembled using the layer-by-layer technique, and the axial composition was accessed using X-ray photoelectron spectroscopy with depth profiling. Chitosan (CHI) samples possessing different degrees of acetylation ([Formula: see text]) and molecular weight ([Formula: see text]) produced via the ultrasound-assisted deacetylation reaction were used in this study along with two different polyanions, namely, sodium polystyrenesulfonate (PSS) and carboxymethylcellulose (CMC). When chitosan, a positively charged polymer in aqueous acid medium, was combined with a strong polyanion (PSS), the total positive charge of chitosan, directly related to its [Formula: see text], was the key factor affecting the film formation. However, for CMC/CHI films, the pH of the medium and [Formula: see text] of chitosan strongly affected the film structure and composition. Consequently, the structure and the axial composition of chitosan-based films can be finely adjusted by choosing the polyanion and defining the chitosan to be used according to its DA and [Formula: see text] for the desired application, as demonstrated by the antibacterial tests.

Made available in DSpace on 2018-12-11T17:09:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-04-01 The aim of the present study was to investigate the potential application of 3,6-O,O’- dimyristoyl chitosan DMCh, an amphiphilic derivative of chitosan, for improving the oral bioavailability of paclitaxel (PTX), a water insoluble anticancer drug. The O-acylation of chitosan with myristoyl chloride was carried out by employing high (≈13.3) or low (2.0) molar excess of chitosan to result in samples DMCh07 and DMCh12, respectively. The successful O-acylation of chitosan was confirmed by FTIR and 1H NMR spectroscopy, the latter allowing also the determination of average degree of substitution (DS). The critical aggregation concentration (CAC) of samples DMCh07 (DS ≈ 6.8%) and DMCh12 (DS ≈ 12.0%) were 8.9 × 10−3 mg/mL and 13.2 × 103 mg/mL, respectively. It was observed by TEM that the DMCh micelles showed spherical shape while DLS measurements allowed the determination of their average size (287 nm–490 nm) and zeta potential (+32 mV to +44 mV). Such DMCh micelles were able to encapsulate paclitaxel with high drug encapsulation efficiency (EE), as confirmed by HPLC analyses. Studies on the cytotoxicity of DMCh07 micelles toward Caco-2 and HT29-MTX cells showed that, regardless the PTX loaded, DMCh07 micelles slightly decreased cellular viability at low micelles concentration (≤1 μg/mL) while at high concentration (>10 μg/mL) PTX-loaded DMCh07 micelles were less toxic toward Caco-2 cells when compared to free PTX. The PTX permeation across Caco-2 monoculture and Caco-2/HT29-MTX co-culture model confirmed the potential of DMCh micelles in improving the intestinal absorption of PTX. These results suggest that DMCh micelles may be a promising carrier to encapsulate PTX aiming cancer therapy. Institute of Chemistry of São Carlos University of São Paulo, Avenida Trabalhador São-Carlense Institute for Research and Innovation in Health (i3S) and Institute of Biomedical Engineering (INEB) University of Porto, Rua Alfredo Allen, 208 Graduate Program in Pharmaceutical Sciences Department of Drugs and Pharmaceuticals School of Pharmaceutical Sciences São Paulo State University - UNESP, Rodovia Araraquara-Jaú, Km 1 CESPU Instituto de Investigação e Formação Avançada em Ciências e Tecnologias da Saúde Instituto Universitário de Ciências da Saúde Graduate Program in Pharmaceutical Sciences Department of Drugs and Pharmaceuticals School of Pharmaceutical Sciences São Paulo State University - UNESP, Rodovia Araraquara-Jaú, Km 1

One of the major challenges in establishing the mechanisms responsible for the chitosan action in biomedical applications lies in the determination of the molecular-level interactions with the cell membrane. In this study, we probed hydrophobic interactions and H-bonding in experiments with O,O'-diacetylchitosan (DACT) and O,O'-dipropionylchitosan (DPPCT) incorporated into monolayers of distinct phospholipids, the zwitterionic dipalmitoyl phosphatidyl choline (DPPC), and the negatively charged dipalmitoyl phosphatidyl glycerol (DPPG) and dimyristoyl phosphatidic acid (DMPA). The importance of hydrophobic interactions was confirmed with the larger effects observed for DACT and DPPCT than for parent chitosan (Chi), particularly for the more hydrophobic DPPCT. Such larger effects were noted in surface pressure isotherms and elasticity of the monolayers. Since H-bonding is hampered for the chitosan derivatives, which have part of their hydroxyl groups shielded by O-acylation, these effects indicate that H-bonding does not play an important role in the chitosan-membrane interactions. Using polarization-modulated infrared reflection absorption (PM-IRRAS) spectroscopy, we found that the chitosan derivatives were incorporated into the hydrophobic chain of the phospholipids, even at high surface pressures comparable to those in a real cell membrane. Taken together, these results indicate that the chitosan derivatives containing hydrophobic moieties would probably be more efficient than parent chitosan as antimicrobial agents, where interaction with the cell membrane is crucial.

The influence from the chitosan molecular weight on its interaction with cell membrane models has been studied. A low molecular weight chitosan (LMWChi) adsorbed from the subphase expanded the surface pressure-area and surface potential-area isotherms of dimyristoyl phosphatidic acid (DMPA) monolayers and decreased the compressional modulus. The expansion in the monolayers and the decrease in the compressional modulus were larger for LMWChi than for a high molecular weight chitosan (Chi). The polymeric nature is still essential for the interaction though, which was demonstrated by measuring negligible changes in the mechanical properties of the DMPA monolayer when the subphase contained glucosamine and acetyl-glucosamine. The results were rationalized in a model through which chitosan interacted with the membrane via electrostatic and hydrophobic interactions, with the smaller chains of LMWChi having less steric hindrance to be accommodated in the membrane. In summary, the activity based on membrane interactions depends on the distribution of molar mass, with lower molecular weight chitosan more likely to have stronger effects.

Made available in DSpace on 2018-12-11T17:29:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-01-02 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In this paper, we show that chitosan may induce conformation changes in silk fibroin (SF) in layer-by-layer (LbL) films, which were used as matrix for immobilization of the enzyme phytase to detect phytic acid. Three chitosan (CH) samples possessing distinct molecular weights were used to build CH/SF LbL films, and a larger change in conformation from random coils to β-sheets for SF was observed for high molecular weight chitosan (CHH). The CHH/SF LbL films deposited onto interdigitated gold electrodes were coated with a layer of phytase, with which phytic acid could be detected down to 10−9 M using impedance spectroscopy as the principle of detection and treating the data with a multidimensional projection technique. This high sensitivity may be ascribed to the suitability of the CHH/SF matrix, thus indicating that the molecular-level interactions between chitosan and SF may be exploited in other biosensors and biodevices. São Carlos Institute of Physics University of São Paulo (USP), CP 369 Institute of Science and Technology at the Federal University of São Paulo (UNIFESP), 330 Talim Street São Carlos Institute of Chemistry University of São Paulo (USP), CP 780 Institute of Chemistry São Paulo State University (UNESP), CP 355 Institute of Chemistry São Paulo State University (UNESP), CP 355

The aim of this study was to evaluate the influence of cellulose and/or lignin on the properties of mats prepared from dissolution (for 48 h or 72 h, solvent: trifluoroacetic acid) of recycled poly (ethylene terephthalate) (PET). Briefly, the presence of cellulose led to a tendency of higher average fiber diameter and average pore area as well as lower average porosity compared to the neat mat (PETref, 242 ± 59 nm, 9.6 ± 1.1 104 nm2 and 19.0 ± 1.1%, respectively). The Tg values for electrospun PET combined with cellulose and/or lignin were higher than that of PETref (92.5 ± 0.1 °C), and the tensile strength increased with the cellulose and/or lignin loading. In addition, the presence of lignin (72 h of dissolution) led to a mat with an elongation at break of 149 ± 9% compared to 14 ± 2% for PETref. The results indicated that the properties of mats based on PET can be tuned by adding cellulose and/or lignin to solutions posteriorly electrospun as well as by varying the dissolution time.

Made available in DSpace on 2018-12-11T17:14:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-12-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Fuel Cell Technologies Office Federación Española de Enfermedades Raras The aim of this work was to investigate the potential of a new 3,6-O,O’-dimyristoyl derivative amphiphilic chitosan (DMCh), in improving the solubility of camptothecin (CPT), a hydrophobic anticancer drug, and its potential oral delivery. FTIR, 1H NMR and solid-state 13C NMR spectroscopy were used to characterize DMCh and to determine its average degree of substitution (DS¯ = 6.8%). DMCh/CPT micelles size ranged from (281–357 nm), zeta potential (+32–50 mV) of encapsulation efficiency of 42–100%. The in vitro cell viability showed that DMCh/CPT micelles were able to reduce the toxicity of CPT. The in vitro permeability of CPT through Caco-2 and Caco-2/HT29-MTX intestinal models was increased up to ten fold when formulated into DMCh micelles, underlining the mucoadhesive properties of the nanocarrier. DMCh/CPT micelles are able to enhance CPT solubility and bioavailability while reduce its cytotoxicity, showing the great potential for intestinal delivery of hydrophobic drugs. São Carlos Institute of Chemistry University of Sao Paulo Avenida Trabalhador São-Carlense Institute for Research and Innovation in Health (i3S) and Institute of Biomedical Engineering (INEB) University of Porto, Rua Alfredo Allen, 208 Graduate Program in Pharmaceutical Sciences Department of Drugs and Pharmaceuticals School of Pharmaceutical Sciences São Paulo State University—UNESP, Rodovia Araraquara–Jaú, Km 1 Embrapa Instrumentação, Rua XV de Novembro 1452 IIFACTS—Institute for Research and Advanced Training in Health Sciences and Technologies, Rua Central de Gandra 1317 Graduate Program in Pharmaceutical Sciences Department of Drugs and Pharmaceuticals School of Pharmaceutical Sciences São Paulo State University—UNESP, Rodovia Araraquara–Jaú, Km 1

International audience; High intensity ultrasound irradiation was used to convert beta-chitin (BCHt) into chitosan (CHs). Typically, beta-chitin was suspended in 40% (w/w) aqueous sodium hydroxide at a ratio 1/10 (g mL(-1)) and then submitted to ultrasound-assisted deacetylation (USAD) during 50 min at 60 degrees C and a fixed irradiation surface intensity (52.6 W cm(-2)). Hydrogen nuclear magnetic resonance spectroscopy and capillary viscometry were used to determine the average degree of acetylation ((DA) over bar) and viscosity average degree of polymerization ((DPv) over bar), respectively, of the parent beta-chitin ((DA) over bar = 80.7%; (DPv) over bar = 6865) and USAD chitosans. A first USAD reaction resulted in chitosan CHs1 ((DA) over bar = 36.7%; (DPv) over bar = 5838). Chitosans CHs2 ((DA) over bar = 15.0%; (DPv) over bar = 5128) and CHs3 ((DA) over bar = 4.3%; (DPv) over bar = 4889) resulted after repeating the USAD procedure to CHs1 consecutively once and twice, respectively. Size-exclusion chromatography analyzes allowed the determination of the weight average molecular weight ((M-w) over bar) and dispersity (D) of CHs1 ((M-w) over bar = 1,260,000 g mol(-1); D =1.4), CHs2 ((M-w) over bar = 1,137,000 g mol(-1); D =1.4) and CHs3 ((M-w) over bar = 912,000 g mol(-1); D = 1.3). Such results revealed that, thanks to the action of high intensity ultrasound irradiation, the USAD process allowed the preparation of unusually high molecular weight, randomly deacetylated chitosan, an important breakthrough to the development of new high grade chitosan-based materials displaying superior mechanical properties.

International audience; The formation of chitosan hydrogels without any external cross-linking agent was successfully achieved by inducing the gelation of a viscous chitosan solution with aqueous NaOH or gaseous NH3. The hydrogels produced from high molecular weight (M-w approximate to 640 000 g mol(-1)) and extensively deacetylated chitosan (DA approximate to 2.8%) at polymer concentrations above similar to 2.0% exhibited improved mechanical properties due to the increase of the chain entanglements and intermolecular junctions. The results also show that the physicochemical and mechanical properties of chitosan hydrogels can be controlled by varying their polymer concentration and by controlling the gelation conditions, that is, by using different gelation routes. The biological evaluation of such hydrogels for regeneration of infarcted myocardium revealed that chitosan hydrogels prepared from 1.5% polymer solutions were perfectly incorporated onto the epicardial surface of the heart and presented partial degradation accompanied by mononuclear cell infiltration.

Ultrasound-assisted deacetylation (USAD) produces chitosan by treating beta-chitin suspended in 40% aqueous sodium hydroxide with high-intensity ultrasound irradiation. Chitosans resulting from the application of non-isothermal and isothermal USAD processes were characterized using NMR spectroscopy, X-ray diffraction, scanning electron microscopy, viscosity measurements and size-exclusion chromatography. The characteristics of the USAD-produced chitosan strongly depend on the processing temperature and ultrasound parameters, namely the irradiation amplitude and duration, with viscosity-average molecular weight in the range 100 000―750 000 g mol ―1 and average degree of acetylation in the range 6.0―25.0%. Moreover, appropriate adjustment of the USAD parameters allows the production of chitosan with high molecular weight (M w ≈ 10 6 g mol ―1 ) and low degree of acetylation (ca 7.0%) after a single-step short-time processing (30 min) carried out at low to moderate temperature (50―80 °C). The occurrence of cavitation, a phenomenon whose intensity depends on the irradiation amplitude and duration as well as on the processing temperature, is responsible for reducing the average size of the polysaccharide particles, favoring the accessibility of sodium hydroxide to the reactive sites and supporting a more efficient deacetylation of beta-chitin as compared to the thermochemical process.

The development and application of a functionalized carbon nanotubes paste electrode (CNPE) modified with crosslinked chitosan for determination of Cu(II) in industrial wastewater, natural water and human urine samples by linear scan anodic stripping voltammetry (LSASV) are described. Different electrodes were constructed using chitosan and chitosan crosslinked with glutaraldehyde (CTS-GA) and epichlorohydrin (CTS-ECH). The best voltammetric response for Cu(II) was obtained with a paste composition of 65% (m/m) of functionalized carbon nanotubes, 15% (m/m) of CTS-ECH, and 20% (m/m) of mineral oil using a solution of 0.05 mol L−1 KNO3 with pH adjusted to 2.25 with HNO3, an accumulation potential of −0.3 V vs. Ag/AgCl (3.0 mol L−1 KCl) for 300 s and a scan rate of 100 mV s−1. Under these optimal experimental conditions, the voltammetric response was linearly dependent on the Cu(II) concentration in the range from 7.90 × 10−8 to 1.60 × 10−5 mol L−1 with a detection limit of 1.00 × 10−8 mol L−1. The samples analyses were evaluated using the proposed sensor and a good recovery of Cu(II) was obtained with results in the range from 98.0% to 104%. The analysis of industrial wastewater, natural water and human urine samples obtained using the proposed CNPE modified with CTS-ECH electrode and those obtained using a comparative method are in agreement at the 95% confidence level.

Background: Several methods have been utilized to prevent pericardial and retrosternal adhesions, but none of them evaluated the mesothelial regenerative hypothesis. There are evidences that the mesothelial trauma reduces pericardial fibrinolytic capability and induces an adhesion process. Keratinocyte growth factor (KGF) has proven to improve mesothelial cells proliferation. This study investigated the influence of keratinocyte growth factor in reducing post-surgical adhesions. Methods: Twelve pigs were operated and an adhesion protocol was employed. Following a stratified randomization, the animals received a topical application of KGF or saline. At 8 weeks, intrapericardial adhesions were evaluated and a severity score was established. The time spent to dissect the adhesions and the amount of sharp dissection used, were recorded. Histological sections were stained with sirius red and morphometric analyses were assessed with a computer-assisted image analysis system. Results: The severity score was lower in the KGF group than in the control group (11.5 vs 17, p = 0.005). The dissection time was lower in the KGF group (9.2 1.4 min vs 33.9 9.2 min, p = 0.004) and presented a significant correlation with the severity score (r = 0.83, p = 0.001). A significantly less sharp dissection was also required in the KGF group. Also, adhesion area and adhesion collagen were significantly lower in the KGF group than in the control group.Conclusion:The stimulation of pericardial cells with KGF reduced the intensityof postoperative adhesions and facilitated the re-operation. This study suggests that the mesothelial regeneration is the new horizon in anti-adhesion therapies. # 2008 European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved.

Four samples of N , O -carboxymethylchitosan ( 0.5 DS ¯ 1.5 ) were prepared by reacting chitosan ( DA ¯ = 24 % ) with monochloroacetic acid in the presence of excess sodium hydroxide. The carboxymethylchitosan samples were soluble in a wider range of pH as compared to the parent chitosan and the X-ray diffraction showed that they adopt a less ordered arrangement. The carboxymethylation of chitosan decreased the thermal stability of the polymer as evaluated by thermogravimetry but no clear dependence of the activation energy on the average degree of substitution of carboxymethylchitosan was identified. However, the values of activation energy of carboxymethylchitosan issued from the isothermal study depended on the degree of conversion, suggesting the occurrence of a complex set of simultaneous reactions.

Highly porous genipin cross-linked membranes of carboxymethylchitosan exhibiting different crosslinking degree (3%

The interaction between chitosans and Langmuir monolayers mimicking cell membranes has been explained with an empirical scheme based on electrostatic and hydrophobic forces, but so far this has been tested only for dimyristoyl phosphatidic acid (DMPA). In this paper, we show that the mode of action in such a scheme is also valid for dipalmitoyl phosphatidyl choline (DPPC) and dipalmitoyl phosphatidyl glycerol (DPPG), whose monolayers were expanded and their compressibility modulus decreased by interacting with chitosans. In general, the effects were stronger for the negatively charged DPPG in comparison to DPPC, and for the low molecular weight chitosan (LMWChi) which was better able to penetrate into the hydrophobic chains than the high molecular weight chitosan (Chi). Penetration into the hydrophobic chains was confirmed with polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) and sum frequency generation (SFG) spectroscopy. A slight reduction in conformational order of the lipid chains induced by the chitosans was quantitatively estimated by measuring the ratio between the intensities of the methyl (r(+)) and methylene (d(+)) peaks in the SFG spectra for DPPG. The ratio decreased from 35.6 for the closely packed DPPG monolayer to 7.0 and 6.6 for monolayers containing Chi and LMWChi, respectively. Since in both cases there was a significant phospholipid monolayer expansion, the incorporation of chitosans led to chitosan-rich and lipid-rich condensed domains, which mantained conformational order for their hydrophobic tails. The stronger effects from LMWChi are ascribed to an easier access to the hydrophobic tails, as corroborated by measuring aggregation in solution with dynamic light scattering, where the hydrodynamic radius for LMWChi was close to half of that for Chi. Taken together, the results presented here confirm that the same mode of action applies to different phospholipids that are important constituents of mammalian (DPPC) and bacterial (DPPG) cell membranes.

The thermal degradation of chitosan, degree of acetylation 12%, was studied by using TG in nitrogen atmosphere in isothermal and dynamic conditions. Temperatures ranging from 240 °C to 280 °C were studied in isothermal conditions while heating rates in the interval 2.5–15.0 °C/min were employed when using dynamic conditions. The data issued from the dynamic experiments were treated by the methods proposed by Ozawa–Flynn–Wall and Kissinger, resulting in apparent activation energy of 149.6 kJ/mol and 138.5 kJ/mol, respectively. The approach proposed by MacCallum was used to treat the data issued from the isothermal experiments, resulting in E a = 153 kJ/mol in good agreement with the results issued from the dynamic experiments. The use of the isoconvertional method due to Vyazovkin also showed a good agreement with the value of the activation energy issued by applying the method of Ozawa–Flynn–Wall. It was also observed that regardless of using isothermal or dynamic experimental conditions, the kinetic model best suited to describe the thermal degradation of chitosan is the catalytic Sestak–Berggren model.

The fact that alpha- and beta-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 alpha- and beta-chitin also result in distinct reactivities toward the deacetylation reaction. Thus, the deacetylation of beta-chitin is more efficient owing to the better accessibility to amide groups due to the lower crystallinity of this polymorph.

A quaternized derivative of chitosan, namely N-(2-hydroxy)-propyl-3-trimethylammonium chitosan chloride (QCh), was synthesized by reacting glycidyltrimethylammonium chloride (GTMAC) and chitosan (Ch) in acid medium under microwave irradiation. Full-factorial 2(3) central composite design and response surface methodology (RSM) were applied to evaluate the effects of molar ratio GTMAC/Ch, reaction time and temperature on the reaction yield, average degree of quaternization (DQ) and intrinsic viscosity ([η]) of QCh. The molar ratio GTMAC/Ch was the most important factor affecting the response variables and RSM results showed that highly substituted QCh (DQ = 71.1%) was produced at high yield (164%) when the reaction was carried out for 30min. at 85°C by using molar ratio GTMAC/Ch 6/1. Results showed that microwave-assisted synthesis is much faster (≤30min.) as compared to conventional reaction procedures (>4h) carried out in similar conditions except for the use of microwave irradiation.

The viscosity behavior of the chloride salts of chitosan ( ) an N,N,N‐trimethylchitosan ( ) was studied at 25°C. The dependence of the intrinsic viscosity ([η]) on the ionic strength (μ) was investigated by using acid‐free aqueous solutions of NaCl (0.06 M≤[NaCl]≤0.3 M). The linear dependence of the intrinsic viscosity on the reciprocal of the square‐root of the ionic strength (μ−1/2) and the decrease of the salt tolerance parameter (S) with decreasing molecular weight were observed in both cases. The method proposed by Smidsrod was employed to estimate the chain stiffness of the polyelectrolytes resulting in B≅0.11 for both polymers. Taking into consideration that the average degree of acetylation of N,N,N‐trimethylchitosan is lower than that of chitosan and that most of the hydroxyl groups of the former polymer is also methylated, it is suggested that the content of acetamido groups is not the most important factor for the stiffness of chitosan.

Films of chitosan and N,N,N-trimethylchitosan were cast from aqueous solutions. Chitosan was dissolved in 1% acetic acid while deionized water was the solvent for N,N,N-trimethylchitosan chloride. The resulting films presented different mechanical behaviors as evaluated by DMTA. The film of chitosan exhibited an elastic-type behavior while that of N,N,N-trimethylchitosan was typically viscous. No glass transition temperatures were observed; however, a discrete thermal transition was detected at 25 °C in the case of the N,N,N-trimethylchitosan.

The thermal degradation of chitosan and N,N,N-trimethylchitosan, degrees of quaternization 5%, 21% and 33%, was studied by using TG in nitrogen atmosphere. The methylation of chitosan decreased its thermal stability, the decrease being more important the greater the degree of quaternization attained. The absolute values of the activation energy of chitosan and N,N,N-trimethylchitosan calculated from different methods, Broido's and MacCallum's methods, do not agree but they do show the same general trend. The activation energy for the less methylated derivative is higher than that of chitosan but it decreases as the degree of quaternization increases, independently of the method used for its determination. The use of the MacCallum's method reveals that the activation energy increases with increasing degree of conversion for chitosan but no clear trend is observed for the N,N,N-trimethylchitosans. The occurrence of a more complex set of reactions is suggested for the N,N,N-trimethylchitosan samples, including acid-catalyzed processes.

The formation of micelles of hexadecyltrimethylammonium chloride (CTAC) and sodium dodecylsulfate (SDS) in aqueous solutions containing charged polysaccharides was studied by steady-state and time-resolved fluorescence measurements using pyrene as a photophysical probe. Micropolarity studies using the I1/I3 ratio of the vibronic emission bands of pyrene and the behaviour of the IE/IM ratio between the excimer and monomer emissions show the formation of hydrophobic domains. The interactions between the polyelectrolytes and surfactants of opposite charge lead to the formation of induced pre-micelles at surfactant concentrations lower than the critical micellar concentration (cmc) of the surfactants. At similar concentrations, the IE/IM ratio shows a peak. This aggregation process is assumed to be due to electrostatic attractions. At higher surfactant concentrations, near the critical micellar concentration, micelles with the same properties as those found in pure aqueous solution are formed. On the other hand, systems containing polyelectrolytes and surfactants of the same charge do not show this behaviour at low concentrations. The presence of long alkyl chains bound to the polyelectrolytes also induces the formation of free micelles at concentrations somewhat below the aqueous cmc.

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 1 H and 13 C 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 H 3 CI 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.

Samples of chitin were submitted to heterogeneous deacetylation in aqueous sodium hydroxide (40%) during 6 hours at 115 - 2°C. These reactions were carried out with crude chitin and also with samples previously submitted to ultrasound treatment in aqueous suspension for different periods of time. The previous sonication of chitin strongly enhanced its reactivity toward the deacetylation reaction but only slightly favored the depolymerization process. Adding sodium borohydride to the reaction medium reduced the occurrence of depolymerization when untreated chitin was employed but it had no such effect if sonicated chitin was reacted.

Commercial chitosan was purified, dissolved in 1.5% acetic acid and then submitted to deacetylation in aqueous sodium hydroxide solution at 110°C during 3 h. Different conditions were employed to minimize the simultaneous occurrence of depolymerization, including the bubbling of nitrogen through the reaction medium and/or the addition of sodium borohydride or anthraquinone. Severe depolymerization occurred except when some measure was taken to minimize it. However more acetylated products resulted in these conditions. Adding anthraquinone and/or bubbling nitrogen through the reaction medium resulted in less degraded chitosans but the addition of sodium borohydride was not so effective. The more deacetylated and less degraded products were obtained when purified chitosan acetate was submitted to deacetylation in the presence of anthraquinone and simultaneous bubbling of nitrogen.

The pre-sonication provoked noticeable changes in the chitin morphology but its overall crystallinity was unaffected. The sonication of chitin seemed to improve its homogeneity and to increase the particles surface, enhancing the accessibility of reagents. Pre-sonicated chitin was more efficiently deacetylated (up to 95%) than commercial chitin (up to 88%) probably due to the mechanical action of ultra-sound since the previous stirring of solid chitin while suspended in hot or cold water for 1 hour also enhanced the deacetylation efficiency.