Acylation CONTENTS

Gellan gum with various acyl contents in the presence or absence of potassium. Food Hydrocolloids 22,1148-1159. 

The cellulose esters that result from the process described are chemical raw materials and are used by many branches of the chemical industry. They are generally characterized by acyl content in weight percent and viscosity in seconds, the viscosity being obtained by timing the fall of a steel ball through a solution of the cellulose ester in accordance with ASTM Method D 134 . Low-viscosity esters are generally used in solution processes high-viscosity esters are used in the production of plastics. 

There are various ways wherein esters can be synthesised. An effective method is to react an acid chloride with an alcohol in the presence of pyridine yield. Acid anhydrides also react with alcohols to esters, but are less reactive. Moreover, the reaction is wasteful because half of the acyl content on the acid anhydride is wasted as the leaving group (i.e. the carboxylate ion). If the acid anhydride is cheap and readily available, this method can be used, e.g., acetic anhydride is useful for the synthesis of a range of acetate esters ... 

Cine Films must withstand severe mechanical wear and must be of good dimensional stability for projection. Cellulose nitrate has qualities which are very desirable for this purpose, and remains the standard product for the professional moving picture industry. Amateur and educational Cine Films must be made of less inflammable material. Cellulose acetate has been used for this purpose but is limited in its moisture resistance, its strength and its tendency toward brittleness at low humidities. Improvements have been obtained by the employment of cellulose mixed esters possessing a moderate higher acyl content. Such products are widely used for narrow width Cine Films. 

Finally, for the quantitative estimation of the 0-acyl content of sialic-acid-containing samples (Hestrin assay), also a colorimetric assay is routinely used. The method is based on the reaction with hydroxylamine in alkaline medium yielding hydroxamates, which form with Fe(C104)3 red chromophores, the absorbance of which is measured at 520 run [262]. 

Noda, S., Eunami, T., Nakauma, M. et al (2008) Molecular structures of gellan gum imaged with atomic force microscopy in relation to the rheological behavior in aqueous systems. 1. Gellan gum with various acyl contents in the presence and absence of potassium. Food... 

FIGURE 1.12 structure of acylgjycerol esters. The aliphatic chains of acyl groups are noted R. The nature of these R chains should be given to write the structure of a particular acylglycerol. In di- and triacylglycerol, Rl, R2, and (when concerned) R3 can be either the same or distinct acyl chains. Thus, the terms MAG, DAG, and TAG are generic, and these molecules have a wide biochemical diversity based on their acyl content. 

FIGURE 1.16 Structure of phosphatidylethanolamine (PE) and phosphatidylserine (PS). At pH 7 PE (top) is zwitterionic but PS (bottom) bears two negative charges and one positive charge so that its mean electric charge is -1. For this reason it belongs to the class of anionic lipids. The acyl chains of PE are palmitic acid (Rl) and oleic add (R2). Note that the PS molecule represented here contains two saturated acyl chains (palmitic acid in Rl and stearic add in R2) instead of the usual saturated/unsaturated acyl content shown for PE. 

Quantitative estimation of the O-acyl content of sialic acid preparations can be made using the hydroxamic acid reaction as described by Ludowieg and Dorfman (1960), modified from the method of Hestrin (1949). Calibration with ethyl acetate or other ester standards provides a simple quantitative assay, measuring the chromophore at 520 nm. Volume reductions in the assay procedure allow quantitation of 0.05(i,mole of sialic acid acyl ester (Schauer 1978). Qualitative identification of different acylhydroxamates can be made on thin-layer chromatography (see section III.3.b)). 

Sucrose esters (Cis-Cig) acyl content 60-80% determination of sucrose and acyl constituents... 

Acylation. To achieve acylation of thiophenes, acid anhydrides with phosphoric acid, iodine, or other catalysts have been widely used. Acid chlorides with AlCl, SnCl, ZnCl2, and BF also give 2-thienylketones. AH reactions give between 0.5 and 2.0% of the 3-isomer. There has been much striving to find catalyst systems that minimize the 3-isomer content attempting to meet to customer specifications. The standard procedure for formylation is via the Vil smeier-H a ack reaction, using phosphoms o xycbl o ri de / /V, / V- dim e tb yl fo rm a m i de (POCl /DMF) or /V-m ethyl form an i1 i de. 

In Table 4, intrinsic viscosities and carboxyl contents of different fractions of modified PS obtained at different catalyst media are presented. As evidenced from these data, all PS samples used were acylated. As the viscosity of the fractions decreases, the carboxyl contents in the product increase. The highest degree of acylation for all fractions is observed when BF3-OEt2 is used as the catalyst. 

Figures DSC scans of (1) PS (M = 2.5.1(F) and its acylated derivatives with following contents of carboxyl group (2) 4.5, (3) 14.3, (4) 16.6, (5) 20.0 mol%, prepared by using FeCh, SnCLi, AICI3, and BF3-OEt2, respectively.

Lipases have also been used as initiators for the polymerization of lactones such as /3-bu tyro lac tone, <5-valerolactone, e-caprolactone, and macrolides.341,352-357 In this case, the key step is the reaction of lactone with die serine residue at the catalytically active site to form an acyl-enzyme hydroxy-terminated activated intermediate. This intermediate then reacts with the terminal hydroxyl group of a n-mer chain to produce an (n + i)-mer.325,355,358,359 Enzymatic lactone polymerization follows a conventional Michaelis-Menten enzymatic kinetics353 and presents a controlled character, without termination and chain transfer,355 although more or less controlled factors, such as water content of the enzyme, may affect polymerization rate and the nature of endgroups.360... 

The free acid devices were substantially free of acylation byproducts. Infared spectra shown in Fig. 26 supports the conclusion that as the injection-molding temperature increased, the phthalic anhydride content (1853, 1789, and 1777 cm l) decreased and the content of the corresponding half ester (1735 cm"l) increased. 

Tomoyuki, O. et al., Determination of acylated anthocyanin in human urine after ingesting a purple-fleshed sweet potato beverage with various contents of anthocyanin by LC-ESI-MS/MS, Biosci. Biotechnol Biochem., 70, 2540, 2006. 

The fate of injected liposomes is drastically altered by administration route, dose and size, lipid composition, surface modification, and encapsulated drugs. Liposomes encapsulating drugs are often administered iv, therefore, the stability of liposomes in plasma is important. When liposomes composed of PC with unsaturated fatty acyl chains are incubated in the presence of serum, an efflux of internal solute from the liposomes is observed. This increase in permeability is caused by the transfer of phospholipids to high density lipoprotein (HDL) in serum (55). To reduce the efflux of liposomal contents, cholesterol is added as a liposomal component... 

The explosive decomposition of the solid has been studied in detail [6], The effect of moisture upon ignitibility and explosive behaviour under confinement was studied. A moisture content of 3% allowed slow burning only, and at 5% ignition did not occur [7], Thermal instability was studied using a pressure vessel test, ignition delay time, TGA and DSC, and decomposition products were identified [8], The presence of acyl chlorides renders dibenzoyl peroxide impact-sensitive [9], There is a further report of a violent explosion during purification of the peroxide by Soxhlet extraction with hot chloroform [10], Residual traces of the peroxide in a polythene feed pipe exploded when it was cut with a handsaw [11]. The heat of decomposition has been determined as 1.39 kJ/g. The recently calculated value of 69° C for critical ignition temperature coincides with that previously recorded. 

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