Phenol normal value

These three groups have an essentially normal intrinsic pK and their titration curve yields essentially normal values for the interaction parameter w (Tanford et al., 1955a). The three phenolic groups which are not available for titration in the native protein are titrated at 25°C near pH 13, where the protein becomes denatured. At 6°C, where the rate of denaturation is slower, a pH of 14 can be reached with only partial titration of these groups. 

With another group of abnormal liquids the value of k was smaller than 2-12 and varied between fairly wide limits. This was explained by assuming that these liquids are associated, the value of M being greater than the normal value used in (3). Such liquids include water, alcohols, glycols, most ketones, propionitrile, phenol, nitroethane, organic acids, sulphuric acid, nitric acid, and (to a smaller extent) bromine. 

Chelation therapy in individuals exposed to gasoline indicates that inorganic lead is eliminated in the urine of patients exposed to leaded gasoline (Robinson 1978). Urinary phenol, which is commonly used to indicate benzene exposure, was measured in gasoline pump workers (Pandya et al. 1975). There was an elevated amount of phenol (40 mg/L) in these subjects compared to normal values (<... 

Most of the propagation-rate constants (/Cp) listed in 8.5.3 have been measured relative to the rate constant for self-reaction, i.e., cdculated from the rate constant ratio kp/(2k,). Very few absolute rate constants estimated from co-oxidation studies have been included. Similarly many of the rate constants for reaction of RO2 with phenols and aromatic amines (kj h) have been estimated from rate constant ratios, kp/kj h- Consequently values of kp and km), depend critically on the accuracy of the measurement of 2k. It should be noted that we have made no attempt to normalize values of kp and k) , to a best value for 2k,. All the rate constants are based on the authors own measurement of 2k, which may differ from the value obtained in another laboratory. The reader should bear this in mind when he is using rate constants for peroxyl radical-molecule reactions. 

Whilst the Vicat test usually gives the higher values the differences are quite modest with many polymers (e.g. those of types A, B and C). For example, in the case of the polycarbonate of bis-phenol A (Chapter 20) the heat distortion temperatures are 135-140°C and 140-146°C for the high and low stress levels respectively and the Vicat softening point is about 165°C. In the case of an acetal homopolymer the temperatures are 100, 170 and 185°C respectively. With nylon 66 the two ASTM heat distortion tests give values as different as 75 and 200°C. A low-density polyethylene may have a Vicat temperature of 90°C but a heat distortion temperature below normal ambient temperatures. 

Polyphenols are ubiquitous in all plant organs where they are found as monomers or in polymerised forms (Schofield et al, 2001). In addition to the beneficial effect of poljq)henols, they also bind minerals and precipitate proteins and carbohydrates, in effect reducing the nutritive value of foods. Polyphenols have been classified for nutritional purposes into extractable and non-extractable types (Bravo, 1998). Extractable polyphenols are low-and intermediate-weight phenolics while non-extractable polyphenols have high molecular weight and are insoluble in normal solvents. 

Permeability coefficients for phenol in isolated skin patches from nude mice have been determined (Behl et al. 1983). The permeability coefficient increased as the concentration of the applied aqueous phenol solution increased doubling the concentration from 20 to 40 g/L resulted in a 12-fold increase in mean permeability coefficient (0.007-0.085 cm/hour). The value obtained for the permeability coefficient when 60 g/L was applied to the skin patch (0.169 cm/hour) was similar to that obtained for skin patches in which the stratum comeum had been removed. It was concluded that phenol concentrations exceeding 20 g/L may destroy a diffusion barrier normally provided by the intact stratum comeum, permitting increased percutaneous absorption. 

The accumulation or oxidation of phenolic compounds principally in stored agricultural products normally gives rise to the physiological disorders that result in a major loss of commercial value of the products. Among the most common of these disorders in which phenol metabolism is involved is fruit browning and the russet spotting (RS) in harvested lettuce. 

Another important field of application concerns food and beverages, especially wine, juices, and tea (A2, A11, A17, B4, K12, V7, Yl). The antioxidant components of food include vitamin E (a-tocopherol), vitamin A (retinoids), vitamin C (ascorbic acid), and also fi-carotene (provitamin A), other carotenoids (of which more than 600 compounds have been identified), flavonoids, simple phenols, and glucobrasicins (H3). Unfortunately, the TAC value of a food is not informative on the bioavailability of its antioxidants. It has been estimated that polyphenols are normally present in blood plasma at concentrations of 0.2-2 //M (PI). However, it has been demonstrated that feeding rats a quercetin-augmented diet can increase their plasma levels of quercetin and its metabolites up to 10-100 //M (M27), and transient increases in the concentration of plant-derived phenolic compounds can take place after ingestion of food and beverages, which may affect blood plasma TAC (see later). 

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