Phenolic structures

General formula for a nitrile rubber-phenolic structural adhesive... 

BRUNE M, ROSSANDER L and HALLBERG L (1989) Irou absorption and phenolic compoimd Importance of different phenolic structures , Eur J Clin Nutr, 43, 547-58. 

Another point of importance about the film structure is the degree to which it can be permeated by various ions and molecules. It is of course essential that supporting electrolyte ions be able to penetrate the film, else the electrical double layer at the electrode/polymer interface could not be charged to potentials that drive electron transfers between the polymer and the electrode. The electroneutrality requirements of porphyrin sites as their electrical charges are changed by oxidation or reduction also could not be satisfied without electrolyte permeation. With the possible exception of the phenolic structure in Fig. 1, this level of permeability seems to be met by the ECP porphyrins. 

Reported redox potentials of laccases are lower than those of non-phenolic compounds, and therefore these enzymes cannot oxidize such substances [7]. However, it has been shown that in the presence of small molecules capable to act as electron transfer mediators, laccases are also able to oxidize non-phenolic structures [68, 69]. As part of their metabolism, WRF can produce several metabolites that play this role of laccase mediators. They include compounds such as /V-hvdi oxvacetan i I ide (NHA), /V-(4-cyanophenyl)acetohydroxamic acid (NCPA), 3-hydroxyanthranilate, syringaldehyde, 2,2 -azino-bis(3-ethylben-zothiazoline-6-sulfonic acid) (ABTS), 2,6-dimethoxyphenol (DMP), violuric acid, 1-hydroxybenzotriazole (HBT), 2,2,6,6-tetramethylpipperidin-iV-oxide radical and acetovanillone, and by expanding the range of compounds that can be oxidized, their presence enhances the degradation of pollutants [3]. 

Brune M, Rossander L and Hallberg L. 1989. Iron absorption and phenolic compounds importance of different phenolic structures. Eur J Clin Nutr 43(8) 547-557. 

The remaining shlklmates in Table III also are relatively simple, well known compounds. The phenolic structures of vanillin (125) and gallic acid (127) and the prephenolic structures of the common quinic acid (128) and chlorogenic acid (129) make them candidates for physiological activity. Gallic acid is the monomer for tannins, biological polymers found in the cotton plant (15, 37). 

Levels and detection frequency of TBBPA are generally lower than those of PBDEs and HBCDs in human samples. Consistent with its phenolic structure that can be rapidly conjugated in human hver and subsequently excreted in bile [36], TBBPA has a short human half-life that has been reported to be as low as 2 days in human plasma [28, 37]. In addition, HBCD and PBDEs are additive BERs, while TBBPA is a reactive BFR, meaning that TBBPA is chemically bound to the polymer structure and, thus, the leaching or release of TBBPA into the environment is limited [38]. Therefore, levels of TBBPA are often lower and detection of this... 

Importance of different phenolic structures. Eur. J. Clin. Nutr. 43,547-557. 

Polyphenols constitute one of the most and widely distributed groups of substances in the plant kingdom, with more than 8000 phenolic structures currently known. They can be divided into at least 10 different classes based upon their chemical structure, ranging from simple molecules, such as phenolic acids, to highly polymerized compounds, such as tannins. 

Little comment can be made about the hydrogen-bonded OH groups that absorb close to 3300 cm."1. It is unlikely, however, within the rank range of resinites covered here that much variation in the intensity of this absorption would be recorded. The broad region of absorption between 1100 and 1300 cm."1 common to vitrinite and sporinite spectra is also found in the resinite spectra. The peak at 1270 cm. 1 almost certainly corresponds to the 1250 cm."1 band assigned by other workers to hydrogen-bonded phenolic structures. Fol-... 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cyclized rubber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenolic structure renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxylic acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubility is controlled by chemical and polarity differences rather than molecular size. 

The change from the phenolic structure of epinephrine to the phenyl structure of ephedrine results in a marked difference in action. Unlike epinephrine, ephedrine is effective orally, has a prolonged action, exhibits tachyphylaxis, and is a potent corticomedullary stimulant. The oral effectiveness and prolonged action of ephedrine are apparently due to the presence of the methyl group on the a carbon atom, a configuration that renders the molecule refractory to deamination by the amine oxidase of the liver. 

Implications to Photoyellowing. On the basis of the Raman spectral results, survival of coniferyl alcohol structures (this includes both phenolics and those etherified at the para-position) in bleached and sulfite pulps would seem to be a major reason why pulps yellow in daylight. Such groups are expected to participate in the primary photochemical events that lead to yellowing. Thus, in pulps, coniferyl alcohol structures would act as leucochromophores. Photoyellowing of coniferyl alcohol structures has been evaluated [34], and it has been reported that the free phenolic structure contributes much more to yellowing than does the para-etherified unit. 

Recently, 2-hydroxypropyl cellulose (HPC) was demonstrated to be a very suitable matrix for UV/Vis absorption study of photoyellowing of milled-wood lignin in the solid state [10] where clean kinetics of discolouration were established after different chemical treatments of the lignin in solution. This indicates the importance in the discolouration process of phenolic structures without carbonyl groups and conjugated double bonds. The present communication describes a similar photochemical study on quinones and hydroquinones incorporated in HPC films under comparative concentrations ( 6.5xl0"5 mol/g HPC). For comparison, we also use UV/Vis reflectance spectroscopy to examine the behaviour of these compounds adsorbed on filter paper after light-exposure. 

The mechanism is strongly dependent on several factors, including phenol structure and concentration, solvent composition and electrode potential. 

R + R. OH - RH + R. o flow a combination of primary and secondary antioxidants functions in a SCHEME2.8 Stabilizing polyolefin matrix.82 Some metal-chelate scavengers may also be based on activity of chain-breaking, a tertiary phenolic structure, thereby introducing two antioxidant properprimary antioxidants. ties into the same molecule. 

Epoxy novolac resins are polyglycidyl ethers of a novolac resin. They are prepared by reacting epichlorohydrin with a novolac resin (see Chap. 2). The most common epoxy novolacs are based on medium-MW molecules with phenol and o-cresol novolacs. They generally have significantly different properties from DGEB A epoxies because of the presence of the phenolic structure. 

Because the phenol structure involves a benzene ring, the terms ortho (1,2-disubstituted), meta (1,3-disubstituted), and para (1,4-disubstituted) are often used in the common names. The following examples illustrate the systematic names and the common names of some simple phenols. 

Fig. 7-12. Reactions of phenolic /8-aryl ether and a-ether structures (1) during neutral sulfite pulping (Gierer, 1970). R = H, alkyl, or aryl group. The quinone methide intermediate (2) is sulfonated to structure (3). The negative charge of the a-sulfonic acid group facilitates the nucleophilic attack of the sulfite ion, resulting in /8-aryl ether bond cleavage and sulfonation. Structure (4) reacts further with elimination of the sulfonic acid group from a-position to form intermediate (5) which finally after abstraction of proton from /8-position is stabilized to a styrene-/8-sulfonic acid structure (6). Note that only the free phenolic structures are cleaved, whereas the nonphenolic units remain essentially unaffected.

Etherified Phenolic Structures Containing fi-Aryl Ether Bonds In ether-ified p-phenolic structures the/3-aryl ether linkage is cleaved by hydroxide... 

Free Phenolic Structures Containing /3-Ary I Ether Bonds The first step of the reaction involves the formation of a quinone methide from the phenolate anion by the elimination of a hydroxide, alkoxide, or phenoxide ion from the a-carbon (Fig. 7-25). The subsequent course of reactions depends on whether hydrosulfide ions are present or not. In the latter case (soda pulping), the dominant reaction is the elimination of the hydroxymethyl group from the quinone methide with formation of formaldehyde and a styryl aryl ether structure without cleavage of the /8-ether bond (Fig. 7-26). When hydrosulfide ions are present (strong nucleophiles) they react with the... 

Fig. 8-5. Reaction of oxygen with free phenolic structures leading to the resonance-stabilized phenoxy radicals.

Although the free phenolic structures are oxidized faster, chlorine dioxide also destroys nonphenolic phenyl propane units and double bonds present in the pulp chromophores. After cleavage of the benzene ring various di-carboxylic acids are formed, such as oxalic, muconic, maleic, and fumaric acids in addition to products substituted with chlorine (Fig. 8-10). As a result of depolymerization and formation of carboxyl groups the modified lignin is dissolved during the chlorine dioxide treatment and in the sodium hydroxide extraction stage that usually follows. 

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