Water content irradiation

Alternatively, esterification of carboxylic acid can be carried out in aqueous media by reacting carboxylic acid salts with alkyl halides through nucleophilic substitutions (Eq. 9.10).20 The reaction rate of alkyl halides with alkali metal salts of carboxylic acids to give esters increases with the increasing concentration of catalyst, halide, and solvent polarity and is reduced by water. Various thymyl ethers and esters can be synthesized by the reactions of thymol with alkyl halides and acid chlorides, respectively, in aqueous medium under microwave irradiation (Eq. 9.11).21 Such an esterification reaction of poly(methacrylic acid) can be performed readily with alkyl halides using DBU in aqueous solutions, although the rate of the reaction decreases with increasing water content.22... 

Unique radiolytical products (URP) in irradiated food are usually formed by the secondary reactions of water radicals, eh, H, and OH, and to a lesser extent by the direct action of radiation, especially for foods with considerable water content. Due... 

What had happened to this sample to yield such unexpected results The purity of the starting monomer, other than its water content, was probably no better or worse than that used in previous studies. The final degassing of the monomer had been conventional. Only one difference had been introduced in the preparative scheme—the monomer had been dried over baked silica gel, and the glassware of the vacuum apparatus had been flame-dried under vacuum. In other words, the irradiated styrene had been exhaustively dried. 

The water content of fresh fruits and vegetables varies from approximately 80 to 95%, so radicals induced in the pulp by irradiation are not stable. However, the seeds, shells or skins can trap free radicals and so could be used to monitor radiation exposure. 

Most of the other products found in irradiated meat volatiles except those containing sulfur or aromatic rings may also be accounted for by mechanisms associated with alkyl free radical formation in the fat. Oxygenated compounds are far less abundant than hydrocarbons, but appreciable amounts of a homologous series of n-aliphatic alcohols up to hexanol are found. Of these, only ethanol is detected in the unirradiated controls. Since the water content of meat averages nearly 60%, the formation of alcohols may be thought to occur by reaction of the alkyl free radical with water. Such a mechanism is supported by the fact that only traces of alcohols are found in irradiated dry butterfat and were undetected in irradiated triglycerides or methyl esters of fatty acids. 

Because water is a polar substance that can be heated by microwave irradiation, it can often improve analyte recovery. In a study of focused MAE of PAHs from soil and sediments [6], sample moisture level showed significant influence on extraction efficiency, and 30% water in the sample provided the highest recovery. Similarly, the maximum recovery of phenyl-urea herbicides was obtained with 10% water in soils [75], In the extraction of triazines from soil, water content in the range 10 to 15% yielded the highest recovery [7],... 

FIG. 21.—Quantities (Q) [mg/mL] of water-soluble dextrins as a function of water content (W) in potato starch (o, irradiation under oxygen , irradiation under nitrogen) (from Ref. 101). 

Maize starch may be separated after irradiation into several fractions, based on solubility in alcohol and aqueous alcohol. The size of the fractions and their composition depends on the radiation dose, as shown in Table X which also shows the distribution of organic products of destruction (aldehydes and carboxylic acids) in particular fractions.118 The relations presented in this Table are S-shaped. Under irradiation with increasing doses, the destruction of starch obviously increases. The nature of the increase of acidity in com starch has also been studied by Athanassiades and Berger.119 Thollier and Guilbot120 have conducted similar studies on potato starch, and Raffi et al99 have extended their studies to more varieties of starch. The results expressed as free and total acidities, as well as the quantity of formic acid at equilibrium water content, are given in Table XI. These data vary rather nonlinearly with increase of the irradiation dose and water content. 

Tsuchiya, T., Horii, I., and Nakayama, Y. Interrelationship between the change in the water content of the stratum corneum and the amount of natural moisturising factor of the stratum corneum after UVB irradiation. J. Soc. Cosmet. Chem. Jpn. 22 10-14 (1988). 

A number of observations (Scheme 29) suggest that alkali metal ions present in zeolites play an important role in the asymmetric induction process, (a) The de was dependent on the nature of the alkali metal ion (e.g., % de in the case of 42 in LiY, NaY, KY, RbY, and CsY are 80, 28, 14, 5, and 5, respectively), (b) The de varied with the water content of NaY used (42 dry 80%, wet 8%). (c) The de upon irradiation of 42 adsorbed on silica gel, a surface that does not contain cations, was only 8%. (d) Diastereomeric excess in the case of 42 decreased from 80% to 10% when the Si/Al ratio of NaY zeolite was changed from 2.4 to 40. The less the aluminum on the framework of the zeolite, the less the number of alkali metal ions. The number of cations per unit cell decreases from 55 to 5... 

The technique for forced destruction by a-particle irradiation has been developed also for foams under strictly defined conditions (pressure, water content, etc.) in order to establish a correlation with the rupture of single black foam films (see Section 7.2). 

In a Soviet study23,24 the mobility of cellulose macromolecular fragments was investigated by means of the paramagnetic label technique. Cellulose macroradicals serving as paramagnetic centres were obtained by irradiation of cellulose at —120° to —140 °C. The mobility of their fragments was found to increase sharply with the water content in the sample to reach a maximum at 10% water. It is this increase which appears to be responsible for the rapid decomposition of macroradicals in moist cellulose. 

The enhancement of catalytic activity proved to be connected with the residual water content of the sample. Samples thoroughly outgassed at 500° to 550° were highly active before irradiation and were not... 

Figure 5.49 shows the transport numbers of various anions (sulfate, fluoride, bromide and nitrate) relative to chloride ions for a membrane having an azobenzene moiety (M-2 membrane) before and after UV irradiation when 1 1 mixed salt solutions (concentration of sodium ions 0.150 N) were electrodialyzed. The transport numbers of all anions increase upon UV irradiation due to the increase in water content, which is based on the increase in dipole moment of the azobenzene moiety of the membrane by UV irradiation, and the increase in pore size of the membrane due to isomerization from the trans to the cis form.135 In particular the permeation of halide ions, (fluoride and bromide) increases remarkably. Fluoride ions permeate more selectively through the membrane than chloride ions.135 The increase in permeation of multi-atomic anions (sulfate and nitrate) is not large, which might be because they suffer steric hindrance. After amination of the M-2 membrane with trimethylamine (M-3 membrane), the permeation of sulfate and fluoride ions decreases and that of bromide and nitrate ions increases compared with the M-l membrane without UV irradiation. This is due to introduction of a bulky, hydrophobic group, the azobenzene moiety, into the membrane. However, the transport numbers of the measured anions (sulfate,... 

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