Average Degree Of Acetylation Research Articles

ATIVIDADE ANTIMICROBIANA DE QUITOSANAS E SEUS DERIVADOS: INFLUÊNCIA DAS CARACTERÍSTICAS ESTRUTURAIS

ANTIMICROBIAL ACTIVITY OF CHITOSAN AND ITS DERIVATIVES: INFLUENCE OF ITS STRUCTURAL CHARACTERISTICS. In recent years, there has been an increasing interest in the development of antimicrobial materials for different applications, especially in the biomedical field. In this context, chitosan is one of the most employed materials due to its highly attractive properties, such as biocompatibility, biodegradability, non-toxicity, and antimicrobial activity against gram-negative and gram-positive bacteria and fungi. In this review, we discuss the different methods used to obtain chitosan and point out how they affect the structural and chemical properties of this material, followed by a detailed discussion on how these properties influence its antimicrobial activities. Additionally, we summarize the most accepted antimicrobial mechanisms of action for chitosans. Specifically, we aim to provide a comprehensive overview on the last findings and progress reported in the literature on the factors that influence the antimicrobial activity of chitosan, e.g., polymeric average molecular weight (MV ), average degree of acetylation (DA), water-soluble derivatization and sample degree of purity. The data available in the literature indicate that in addition to the structural properties, the effectiveness of such antimicrobial activity of chitosan is also dependent on the target microorganisms. This review will help researchers to better understand the mechanism of action of chitosan against microorganisms based on its structural characteristics.

Enzymatic production of all fourteen partially acetylated chitosan tetramers using different chitin deacetylases acting in forward or reverse mode

Some of the most abundant biomolecules on earth are the polysaccharides chitin and chitosan of which especially the oligomeric fractions have been extensively studied regarding their biological activities. However, most of these studies have not been able to assess the activity of a single, defined, partially acetylated chitosan oligosaccharide (paCOS). Instead, they have typically analyzed chemically produced, rather poorly characterized mixtures, at best with a single, defined degree of polymerization (DP) and a known average degree of acetylation (DA), as no pure and well-defined paCOS are currently available. We here present data on the enzymatic production of all 14 possible partially acetylated chitosan tetramers, out of which four were purified (>95%) regarding DP, DA, and pattern of acetylation (PA). We used bacterial, fungal, and viral chitin deacetylases (CDAs), either to partially deacetylate the chitin tetramer; or to partially re-N-acetylate the glucosamine tetramer. Both reactions proceeded with surprisingly strong and enzyme-specific regio-specificity. These pure and fully defined chitosans will allow to investigate the particular influence of DP, DA, and PA on the biological activities of chitosans, improving our basic understanding of their modes of action, e.g. their molecular perception by patter recognition receptors, but also increasing their usefulness in industrial applications.

Determination of the distributions of degrees of acetylation of chitosan

Chitosan is often characterized by its average degree of acetylation. To increase chitosan’s use in various industries, a more thorough characterization is necessary as the acetylation of chitosan affects properties such as dissolution and mechanical properties of chitosan films. Despite the poor solubility of chitosan, free solution capillary electrophoresis (CE) allows a robust separation of chitosan by the degree of acetylation. The distribution of degrees of acetylation of various chitosan samples was characterized through their distributions of electrophoretic mobilities. These distributions can be obtained easily and with high precision. The heterogeneity of the chitosan chains in terms of acetylation was characterized through the dispersity of the electrophoretic mobility distributions obtained. The relationship between the number-average degree of acetylation obtained by solid-state NMR spectroscopy and the weight-average electrophoretic mobilities was established. The distribution of degrees of acetylation was determined using capillary electrophoresis in the critical conditions (CE-CC).

Towards a less biased dissolution of chitosan

The dissolution of polysaccharides is notoriously challenging, especially when one needs a “true” solution. Factors influencing chitosan's solubility include composition, also known as degree of acetylation (DA). The dissolution of chitosan was investigated by visual observation, size-exclusion chromatography (SEC), pressure mobilization (PM), free-solution capillary electrophoresis (CE) and real-time solution-state NMR spectroscopy. Aqueous HCl dissolves around 15% more chitosan than the commonly used aqueous acetic acid (AcOH), however aggregates were detected in SEC suggesting incomplete dissolution. Significant deacetylation of chitosan over the period needed for dissolution at high temperature was observed by NMR spectroscopy in DCl by about 20% of the initial DA value. Accurate DA determination by NMR spectroscopy may thus be possible only in the solid state (with a precision within 1% on the DA % scale above a DA of 10%). Overall a compromise between maximum solubilization and minimum degradation is required in attempting to obtain a “true” solution of chitosan. The completeness of the dissolution may be more influenced by the average DA than by molar mass.

Ultrasound-assisted conversion of alpha-chitin into chitosan

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<32%; 100,000g/mol⩽Mv⩽200,000g/mol) are produced at very high yield (>95%) by applying non-isothermal ultrasound-assisted N-deacetylation process to alpha-chitin suspension (44mg/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.

EFFECTS OF CHITOSAN CHARACTERISTICS ON ITS THERMAL STABILITY

Chitosan samples exhibiting different characteristics, namely average degree of acetylation (7.5% 280 0 C) corresponded to the samples whose crystallinity indexes were inserted in a quite narrow interval (45%<CI<50%). Expresses normalized values of T onset , Mv and DA.

Ultrasound‐assisted deacetylation of beta‐chitin: influence of processing parameters

AbstractUltrasound‐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 (Mw ≈ 106 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. Copyright © 2011 Society of Chemical Industry

Transient rheological behavior of lyotropic (acetyl)(ethyl)cellulose/m-cresol solutions

The chiroptical properties and transient rheological behavior of (acetyl)(ethyl)cellulose (AEC) m-cresol liquid crystalline solutions have been investigated. Chiroptical properties were manipulated through (i) increasing degree of acetylation of ethyl cellulose (EC), and (ii) blending AEC with EC. At the same average degree of acetylation (DA), the chiroptical properties of pure AEC were different from those of the EC/AEC mixtures. However, at the same DA, the AEC and mixed AEC/EC solutions showed similar steady state flow and oscillatory behaviors, but the transient behaviors were different. At high flow rates the mixed AEC/EC solutions exhibited double recoil after cessation of steady-state flow, whereas the AEC solutions showed double recoil only in the high DA AEC solutions. All solutions, pure and mixed, had the same stress relaxation behavior. Both pitch and handedness affected the transient behavior. After cessation of high shear rate flow, the rate of modulus evolution decreased with increasing pitch, and was faster in right-handed mesophases than in left-handed ones at a similar pitch.

Viscosity Behavior of Chitosan and N,N,N‐Trimethylchitosan Chloride Salts in Acid‐Free Aqueous Solution

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 Smidsrød 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.

Caracterização de quitosanas comerciais de diferentes origens

A quitosana é um polissacarídeo linear obtido da desacetilação da quitina. As propriedades físico-químicas da quitosana são função do grau médio de acetilacão &lt;img border=0 id="_x0000_i1026" src="../../../../img/revistas/po/v13n4/19880x1.gif" align=absmiddle&gt;e da massa molar média (&lt;img border=0 id="_x0000_i1027" src="../../../../img/revistas/po/v13n4/19880x2.gif" align=absmiddle&gt;). Várias aplicações da quitosana foram propostas na literatura, principalmente no tratamento de águas, produção de cosméticos, drogas e medicamentos, aditivos alimentícios, membranas semipermeáveis e no desenvolvimento de biomateriais. Neste trabalho, três diferentes tipos de quitosanas comerciais foram caracterizados por ressonância magnética nuclear de hidrogênio (RMN ¹H), espectroscopia de absorção na região do infravermelho (IV), titulação condutimétrica e análise térmica (TG e DSC) com o objetivo de comparar as características de quitosanas provenientes de diferentes fornecedores. A massa molar média das amostras foi determinada a partir de medidas de viscosidade intrínseca. Os resultados obtidos por estas técnicas mostraram diferenças quanto ao grau médio de acetilação (ou desacetilação), em função da procedência do material. Os resultados obtidos da análise térmica permitiram acompanhar os processos de desidratação, decomposição e a temperatura de transição vítrea (Tg).

The degree of acetylation of chitosans and its effect on the chain conformation in aqueous solution

The average degree of acetylation (DA) of chitosans from several sources as well as the distribution of the DA across the molecular weight distribution was measured by titration with poly(styrene sulphonate) as counter polyanion and toluidine blue as metachromatic indicator. The method was shown to be useful within a broad range of DAs. There was no compositional heterogeneity for more than 90% of the population in any sample. Parallel macromolecular characterisation by static light scattering and viscometry standing alone or connected with gel permeation chromatography (GPC) revealed no measurable effect of the DA on the chain conformation where the DA varied between a few percent and ∼60%. Relationships between intrinsic viscosity and radius of gyration with molecular mass were established. The data when considered with previous work suggest no evident differences between chitosans from different sources and no significant effect of the ionic strength between ∼0.1 and 0.3 M on the conformation.

Physico-chemical characterization of chitosans varying in degree of acetylation

Three commercial chitosans varying in average degree of acetylation (DA) were characterized in terms of average molar masses M n , M w , the second virial coefficient B and radius of gyration R gz , and intrinsic viscosities by membrane osmometry, static light scattering, and capillary viscometry in acetate buffer of pH 4.5. To obtain satisfactory light scattering data, the method used for clarification was of great importance. Combined ultracentrifugation and membrane filtration was found to be the method of choice. Using the model for wormlike chains with excluded volume and a logarithmic molar mass distribution, the persistence length L p was determined as L p = 6 nm . No concentration-dependent association was observed for the low concentrations studied. Samples were also fractionated on Sepharose CL-2B for subsequent light scattering and viscosity measurements to establish relationships between M wand [η] and R g , respectively. These relationships were found to be independent of the DA for the bulk of molecularly dispersed chitosan. Model calculations aimed at checking the consistency of data led, as to be expected, to an increasing excluded volume effect with increasing molar mass and steadily increasing polydispersities of the fractions with increasing elution volume. The levelling off of the [η]- M w and R g-M g relations for fractions of increasingly high molar mass was assigned to chemical heterogeneity of samples in terms of DA distributions.

Purification, characterization, and immunological cross-reactivity of alginates produced by mucoid Pseudomonas aeruginosa from patients with cystic fibrosis.

Alginates from nine mucoid Pseudomonas aeruginosa isolates from patients with cystic fibrosis were purified by repeated ethanol precipitation, nuclease digestion, anion-exchange chromatography, dialysis, and lyophilization. Uronic acid constituted 72% of the dry weight when mannuronolactone was used as the internal standard in the carbazole-borate assay for uronic acids. The average degree of acetylation was 16%, and the ratio of mannuronic acid to gluluronic acid was 4.7. No homopolymeric blocks of guluronic acid were found when analyzed by nuclear magnetic resonance spectroscopy. Contaminating proteins were denatured by heating, and during purification the content of protein relative to alginate fell from 566 to 0.9%. The content of lipopolysaccharide was 0.012%. No immunological or biological activity was attributable to the protein or lipopolysaccharide content as estimated by immunoblotting, enzyme-linked immunosorbent assay (ELISA), and a neutrophil chemotaxis assay. Rabbits were hyperimmunized with P. aeruginosa alginates and alginate from the seaweed Laminaria hyperborea, and an ELISA that detected alginate-specific antibodies was developed. Antibodies to P. aeruginosa alginate were detected by ELISA in 1:4,000 dilutions of serum from patients with cystic fibrosis with chronic P. aeruginosa lung infection. The serological cross-reactions between serum from the nine patients with cystic fibrosis and the corresponding P. aeruginosa alginates were investigated and showed considerable heterogeneity. This finding indicates that P. aeruginosa alginate from more than one P. aeruginosa strain should be used in serological tests. There was no serological cross-reactivity between P. aeruginosa and Laminaria hyperborea alginate in either rabbits or patients with cystic fibrosis.