Degree of deacetylation

The deacetylation process involves the removal of acetyl groups from chltln molecules. The DAC is defined as the average number of glucosamine units per 100 monomers expressed as a percentage. It determines the content of free amino groups [-NH2] in the chitosan and is one of the most important chemical characteristics that influence the physicochemical properties, biological properties, antibacterial activity, and applications of chitosan. In other words, DAC value determines the functionality, reactivity, polarity, and water solubility of the polymer. Chitin does not dissolve in dilute acetic acid. When chitin is deacetylated to a certain degree ( 60% deacetylation] where it becomes soluble in the acid, it is referred to as chitosan [18, 21]. 

The solubility of chitosan is very important for its utilization, such as for chemical modification and film or fiber formation. Although the polymer backbone consists of hydrophilic functional groups chitosan is normally insoluble in water and most common organic solvents (e.g., DMSO, DMF, NMP, organic alcohols, pyridine). The insolubility of chitosan in aqueous and organic solvents is a result of its crystalline structure, which is attributed to extensive 

The molecular weight of chitosan is another important property that determines its suitability for a particular application. It determines the viscosity of its solution and the strength of chitosan fiber and film. The molecular weight of chitin and chitosan depends on its source and deacetylation conditions [time, temperature, and concentration of NaOH], respectively [1, 4]. Molecular weight of chitosan determined by various methods such as viscometry [28], gel permeation chromatography [29] and light scattering spectrophotometry [30]. 

The viscosity of polymer solution, at the molecular level, is a direct measure of the hydrodynamic volume of the polymer molecules which in turn is governed by the molecular size or chain 

This method has the advantage of ease of operation with better control over depolymerization level besides reproducibility. It is envisaged from Fig. 19.10 that the IR spectra of chitosan and depolymerized chitosan are almost similar which indicates that the process of depolymerization caused no chemical change in the structure of the polymer except reduction in molecular weight, which is evident from the change in viscosity as presented in Table 19.1. Similar observations are reported by Hebeish et al. [35], and Mao et al. [49]. 

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Isolated chitins are highly ordered copolymers of 2-acetamido-2-deoxy-/3-D-glucose and 2-amino-2-deoxy-j6-D-glucose. The occurrence of the latter is explained by the fact that in vivo chitin is covalently finked to proteins via the nitrogen atom of approximately one repeating unit out of ten, therefore upon isolation a degree of deacetylation close to 0.10 is found. Chito-biose, 0-(2-amino-2-deoxy-j6-D-glucopyranosyl)-(l 4)-2-amino-2-deoxy-... 

Chitosan samples with degrees of deacetylation of 65,73,85, and 92% were almost completely adsorbed onto the surfaces of cellulosic fibers, especially onto the surfaces of fines in a variety of cellulosic systems used in industrial operations. Adsorption increased as the degree of deacetylation of chitosan increased. The aggregation of the fine cellulosic particles was maximum at a dosage of about 10 mg/kg. The interactions between chitosan and the cellulosic substrates were dominated by a bridging mechanism at about pH 7 [32]. 

Commercially chitosans can have molecular weights varying from 4 to 2000 kDa and vary in the degree of deacetylation from 66% to 95%. Because of the free amino groups chitosan behaves as a weak base, with a pKa of 6.2-7.0 and is insoluble in water or organic solvents. It is a polyamine and therefore dissolves in hydrochloric... 

The term chitosan describes a series of chitosan polymers with different molecular weight (MW), viscosity, and degree of deacetylation (DD) (40-98%). It is a linear polyamine with a number of amino groups that are readily available for chemical reaction and salt formation with acids. 

Because the biological properties of chitosan are dependent on its physico-chemical properties such as molecular weight (MW) and degree of deacetylation (DD), uniform physico-chemical properties are a prerequisite to specific industrial applications. As an alternative method, fermentation technology for chitosan preparation from fungal cell walls has received much attention as an eco-friendly pathway. Rane and... 

Trautwein, E. A., Jurgensen, U., and Erbersdobler, H. F. (1997). Cholesterol-lowering and gallstone-preventing action of chitosans with different degrees of deacetylation in hamsters fed cholesterol-rich diets. Nutr. Res. 17,1053-1065. 

Mun, S., Decker, E.A., McClements, D.J. (2006). Effect of molecular weight and degree of deacetylation of chitosan on the formation of oil-in-water emulsions stabilized by surfactant-chitosan membranes. Journal of Colloid and Interface Science, 296, 581-590. 

Wang, W., et al. 1991. Determination of the Mark-Houwink equation for chitosans with different degrees of deacetylation. Int J Biol Macromol 13 281. 

It has been shown by using NMR spectroscopy in conjunction with isotopelabelling studies that there is a significant degree of deacetylation followed by reacetylation (futile deacetylation) of paracetamol metabolites in vivo in the rat [58]. If this also occurs in humans, then it may help to explain the observed incidence of nephrotoxicity of paracetamol in that the process would result in levels of the potent nephrotoxin 4-aminophenol in vivo. Confirmation of the levels of futile deacetylation in individual metabolites of isotopically labelled paracetamol in man has been achieved by using directly coupled HPLC-NMR... 

Huang M, Fong C-W, Khor E et al (2005) Transfection efficiency of chitosan vectors effect of polymer molecular weight and degree of deacetylation. J Control Release 106(3) 391—406... 

A graft copolymer of chitosan (degree of deacetylation, DD = 88%) was prepared by grafting D,L-lactic acid (LA) onto the primary amino groups in... 

Chitosan is produced commercially by deacetylation of chitin. It is a linear polysaccharide composed of randomly distributed /i-( l-4)-linkcd D-glucosamine (deacetylated unit) and N -acetyl-D-glucosamine (acetylated unit). The degree of deacetylation in commercial chitosans is in the range 60-100% (Figure 5.19). 

Chitin is the naturally occurring, insoluble acetylamino derivative of cellulose yielding the polycation chitosan when deacetylated (with concentrated NaOH and heat). Chitosan is water-soluble in proportion to the degree of deacetylation. 

Figure 2.30A shows the X-ray powder diffraction (XRPD) patterns of chifin and chitosan with different degree of deacetylation (DD). Five crystalline index (CrI) reflections 020, 110, 120, 101, and 130 from the lower... 

TABLE 2.18 XRPD parameters for chitin/chitosan at different degrees of deacetylation (DD)... 

The degree of deacetylation (DD) of chitin/chitosan samples was successfully determined using NMR spectroscopy. Chitin/chitosan samples were dissolved in a mixture of 25% DCl in D2O and chitosan samples in a mixture of 0.25% DCl in D2O. The concentration of chitosan in the solution was about 0.5% (w/v). The NMR spectra were recorded using a Varian Mercury 400 MHz spectrometer (Fig. 2.35). Table 2.20 shows the chemical shifts of chitin/chitosan protons in D2O/DCI at 70 °C. The DD values were calculated using integrals of the peak of proton HI of... 

Wound healing - High degree of deacetylation (DD) chitosan preferred over chitin - Low molecular weight samples (oligomers)... 

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