Alkaline pH conditions

Direct Blue 218 had reported sales of 623 t valued at 4.4 million ia 1987. It is produced from Direct Blue 15 (76) by metallizing and elimination of methyl groups from the methoxide to form the copper complex. Direct Blue 15 (76) is prepared by coupling o-dianisidine [119-90-4] to two moles of H-acid (4-amiQO-5-hydroxy-2,7-naphthalenedisulfonic acid) under alkaline pH conditions. Other important direct blues iaclude Direct Blue 80 (74), (9-dianisidine coupled to two moles of R-acid (3-hydroxy-2,7-naphthalenedisulfonic acid [148-75-4]) followed by metallizing to form a bis copper complex, and Direct Blue 22 (77), an asymmetrical disazo dye, prepared by coupling o-dianisidine to Chicago acid [82-47-3] and 2-naphthol. Direct Blue 75 (78) is an example of a trisazo dye represented as metanilic acid — 1,6-Q.eve s acid — 1,6-Q.eve s acid — (alb) Ai-phenyl J-acid. 

Urea is sufficiently important as an additive to PF resins for OSB to warrant some discussion. It has had a large favorable economie impact on the OSB industry. When used, it is generally added after the polymerization is complete. Thus, it is not part of the polymer and does not have any direet effect on polymer resistance to hydrolysis, as might be expected if it was part of the polymer backbone. Under alkaline pH conditions, urea-formaldehyde adducts do not polymerize at a rate that is significant compared to the PF polymerization therefore, the urea does not participate signifieantly in the euring proeess of the PF, despite the faet that it is present during the cure. Since urea is not present in the cured PF polymer per se, it does not detract from the durability of the polymer. Despite this, it is possible to see redueed OSB durability as a result of formulated urea if its use has led to actual PF polymer application rates that are too low. 

Azoles are not very soluble at acidic pH levels (less than 0.5 % solubility) but are increasingly so under alkaline pH conditions. These products usually are supplied as the sodium salt. For example, TTA is available as a 50% sodium salt solution under the trade name Cobratec TT-100/T-50-S from PMC Specialties, Inc. It is also available as a powder and 80% strength product under the names Beldene 511 and 512 from BioLabs/Great Lakes Chemical Corp. (The brand originally was held by Ciba-Geigy, then FMC, and now BioLabs/GLC.)... 

Reactions are improved in alkaline pH conditions (and at higher temperatures), Consequently, HQ is usually blended with volatile amines, including methoxypropylamme, diethylaminoethanol (DEAE), or (mono)ethanolamme, to ensure that the correct alkaline pH condition is maintained. 

Chemical composition of packings. Today, a wider variety of different support materials is available from which to choose. Silica is still widely used, though preparative grades often possess a relatively wide particle size distribution as compared to polymer-based supports. One serious limitation of silica-based supports is the low stability of silicas to alkaline pH conditions, which limits use of caustic solutions in sanitization and depyrogenation. Polymer-based supports, which include poly(styrene-divi-nyl benzene)- or methacrylate-based materials, are widely available and have gained increased acceptance and use. Nonfunctionalized poly(styrene-divinyl... 

The ion-exchange process is applicable for removing a broad range of ionic species from water containing all metallic elements, inorganic anion such as halides, sulfates, nitrates, cyanides, organic acids such as carboxylics, sulfonics, some phenols at sufficiently alkaline pH conditions, and organic amines at sufficiently acidic conditions. 

Most references to the use of EDC describe the optimal reaction medium to be at a pH from 4.7 to 6.0. However, the carbodiimide reaction occurs effectively up to at least pH 7.5 without significant loss of yield. Conjugations done under mildly alkaline pH conditions (e.g., pH 8.5) also can be done to limit the polymerization of proteins, while still facilitating the coupling of a carboxylate-containing molecule at a low substitution level per protein. See Chapter 19,... 

Thus, glycoproteins such as HRP, GO, or most antibody molecules can be activated for conjugation by brief treatment with periodate. Crosslinking with an amine-containing protein takes place under alkaline pH conditions through the formation of Schiff base intermediates. These relatively labile intermediates can be stabilized by reduction to a secondary amine linkage with sodium cyanoborohydride (Figure 20.8). 

Figure 3.7 Removal of noncovalent-bound probes under alkaline pH conditions. (From Call, D.R. et al.. Biotechniques, 30, 368-379, 2001. With permission.)...

All samples contained the metabolite 4-epi-tetracycline, and this was even more pronounced in the liquid manure. Under strong acidic conditions (pH < 2), tetracycline is metabolized to anhydro-tetracyclines, which are bioactive, whereas alkaline pH conditions (pH > 7.5) can favor the formation of isotetracyclines, which show almost no in vitro activity. Tetracycline can also undergo extensive photodecomposition, forming a variety of products (Oka et al., 1989 Peterson et al., 1993). 

Because most drugs exist in a reduced form, there may be an increased instability when the solution is consistently introduced into an atmosphere of 20% oxygen. The pH of the solution may effect the oxidation of phenolic and sulfhydryl group containing drugs because it is principally the ionized form of these drugs that participate in the oxidation (11). For example, epinephrine is only slowly oxidized at pH < 4 but rapidly degrades under alkaline pH conditions. 

Beta-elimination reactions have been observed in a number of proteins. This reaction occurs primarily at alkaline pH conditions. Abstraction of the hydrogen atom from the alpha-carbon of a cysteine, serine, threonine, phenylalanine, or lysine residue leads to racemization or loss of part of the side chain and the formation of dehydroalanine (26). 

Arsenic and selenium demonstrate many similarities in their behavior in the environment. Both are redox sensitive and occur in several oxidation states under different environmental conditions. Both partition preferentially into sulfide minerals and metal oxides and are concentrated naturally in areas of mineralization and geothermal activity. Both elements occur as oxyanions in solution and, depending on redox status, are potentially mobile in the near-neutral to alkaline pH conditions that typify many natural waters. However, there are also some major differences. Selenium is immobile under reducing conditions while the mobility of arsenic is less predictable and depends on a range of other factors. Selenium also appears to partition more strongly with organic matter than arsenic. 

Our preliminary experiments showed that a mixed solution of PNIPA and PAAc was transparent under alkaline pH conditions but became turbid under acidic conditions, where most of the PAAc-bound COO- groups are proton-ated. Moreover, the acidic mixture turned from opaque to transparent by the addition of 4 M urea and upon cooling, while such a change did not take place in the absence of urea. These results suggest the complexation of PNIPA with PAAc via hydrogen bonding between —COOH and —CONH—groups for example,... 

Isomerization and hydrolysis of chlorphenesin carbamate under strongly alkaline pH condition256 and epimerization and hydrolysis of carumonam (Fig. 15)257 and moxalac-tam160161 all appear to conform to this model. Hydrolysis of chlorothiazide, under alkaline pH conditions,258 is explained by this model when k3 is set to zero (Fig. 16). 

Under neutral-to-alkaline pH conditions, the degradation of ampicillin (Fig. 17),260 amoxicillin,261 262 cefaclor,263 and cefatrizine263 can be reasonably described by this model. 

Nonenzymatic phosphorylation with STMP appears to be able to solve many of the problems associated with POCl3. For example, STMP is an FDA-approved food additive [71], does not cause protein cross-linking, and its hydrolysis in water produces only harmless Pi. However, phosphorylation with STMP occurs at alkaline pH, which could lead to undesirable reactions and products as described earlier. STMP shows potential for food protein modification, but further research is needed to determine the exact incorporation of covalently bound Pi, to avoid alkaline pH conditions, and to move its specificity toward O-esterification rather than a mixture of O- and N-esterifica-tions. 

Incorrect Disulfide Formation. This reaction occurs in neutral and alkaline pH conditions. Under such conditions, deamidation also occurs. The thiols (formed by beta elimination) can promote the disufide bond formation [8]. In an acidic environment, sulfenium ion promotes the incorrect disulfide bonds [9]. Proteins with scrambled disulfide bridges have been shown to yield native structure by incubating the protein with small amounts of mercaptoethanol or Cys. 

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