Acetyl groups, determination value

Acetyl values were determined by base hydrolysis of the acetyl groups of a weighed sample, followed by back-titration to determine the number of milliequivalents of acetic acid. 

The inherent viscosity values have been compared with end group determinations of the acetate end groups of completely acetylated poly-n-butyralde-hyde. For this purpose, the intensity of the carbonyl band of the acetate end groups (5.72 p) was determined by infrared and was related to an internal standard giving what we call the end group ratio (15.72 4.75 ) The end... 

Fig. 10 presents the values of distances between the cofactors in the reaction centers of Rb. sphaeroides and Rp. viridis obtained in a structural determination at 2.65 A resolution as reported by Ermler, Fritzsch, Buchanan and Michel Some of these results will now be described. The pyrrole rings I of and Db are 3.2 A apart, but the ring centers are 1 A apart and thus the tetrapyrrole rings are inclined to each other by -15°. The Mg atoms of and Db are each ligated to L-His 173 and M-His200, respectively, as marked by upward arrows in Fig. 3 (A). The acetyl group on ring I of Da forms a hydrogen bond with...

As a result of the reaction the hydrogen in the hydroxyl group in alcohol is replaced by the acetyl group. If a diatomic alcohol is used two acetyl groups are introduced. The reaction is of great analytical value as by means of its use the number of hydroxyl groups present in a substance of unknown structure can be determined. 

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]. 

Degree of acetylation or substitution (DS) is specified by two terms acetyl value (%) and combined acetic acid (%). The ratio of these terms is determined by the moleeular weight ratio of acetyl group to acetic acid, (CH3CO)/(CH3COOH), or 43/60. 

The loss of carbon atoms, which is correlated with the removal of acetyl groups, explains the film thickness of 17 A, as determined with XPS after deprotection of the molecules at the surface. The higher value found for the film that was deprotected prior to adsorption can be understood in terms of a higher density of saccharide molecules on the surface after adsorption from solution. Steric reasons are probably responsible for the higher space requirement per molecide in its protected form (AHS) compared to a deacetylated molecule (DHS) due to the bulky protective acetoxy groups. 

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