Carboxylate anion, basicity Carboxyl group

In base the tetrahedral intermediate is formed m a manner analogous to that pro posed for ester saponification Steps 1 and 2 m Figure 20 8 show the formation of the tetrahedral intermediate m the basic hydrolysis of amides In step 3 the basic ammo group of the tetrahedral intermediate abstracts a proton from water and m step 4 the derived ammonium ion dissociates Conversion of the carboxylic acid to its corresponding carboxylate anion m step 5 completes the process and renders the overall reaction irreversible... 

ACID DYES Commercial acid dyes contain one or more sulfonate groups, thereby providing solubility in aqueous media. These dyes are apphed in the presence of organic or mineral acids (pH 2—6). Such acids protonate any available cationic sites on the fiber, thereby making possible bonding between the fiber and the anionic dye molecule. Wool, an animal fiber, is an amphoteric coUoid, possessing both basic and acidic properties because of the amino and carboxylic groups of the protein stmcture. In order to dye such a system, coulombic interactions between the dye molecule and the fiber must take place ie, H2N" -wool-COO + H2N" -wool-COOH. The term acid dye is appHed to those that are capable of such interactions. Acid dyes... 

Solvent dyes [1] cannot be classified according to a specific chemical type of dyes. Solvent dyes can be found among the azo, disperse, anthraquinone, metal-complex, cationic, and phthalocyanine dyes. The only common characteristic is a chemical structure devoid of sulfonic and carboxylic groups, except for cationic dyes as salts with an organic base as anion. Solvent dyes are basically insoluble in water, but soluble in the different types of solvents. Organic dye salts represent an important type of solvent dyes. Solvent dyes also function as dyes for certain polymers, such as polyacrylonitrile, polystyrene, polymethacrylates, and polyester, in which they are soluble. Polyester dyes are principally disperse dyes (see Section 3.2). 

First the carboxylic acid 10 reacts with the amino group of the amino acid L-serine methyl ester 44. This reaction is carried out with DCC 45 and DMAP 46 as activators of the carboxyl group.20,21 With the basic DMAP 46 as the catalyst, a proton transfer between the carboxylic acid 10 and the diimide 45 yields the carboxylate anion 47 which undergoes nucleophilic addition to the protonated diimide 48. This activated ester 49 is readily attacked by the amino group of L-serine methyl ester 44 as a nucleophile. 

The dipolar ion has both an acidic group, the ammonium cation, and a basic group, the carboxylate anion, so it can act as either an acid or a base. Such compounds are termed amphoteric. The species that is present in aqueous solution depends on the pH. In the pH range near neutral the amino acid is present in the form of the dipolar ion. In acidic solution the carboxylate group becomes protonated and the amino acid is present as a cation, whereas in basic solution the ammonium group gives up a proton and the molecule exists as an anion ... 

The hydrogen bond formation has also an influence on the acidities of, for example, the above-mentioned hydroxybenzoic acids since the proton attraction of the carboxyl group is partially saturated by it and the basicity of the anion is therefore smaller. 

Carboxylates as the phenylacetate anion also eject electrons in methanol [75] giving benzyl anion after recombination between solvated electron and benzyl radical [76]. In phenyl substituted carboxylate anions (from benzoate to phenylbutyrate) in water the quantum yield of photoejected electron was found between 0.002 and 0.03 these values increase with increasing excitation energy and with the number of CH2 separating the phenyl and carboxylate group [77], In the case of phenylalanine and tryptophan in water, the mechanism seems to differ according to the conditions biphotonic and from a triplet state in neutral solution or monophotonic in basic medium [78, 79, 80]. In certain cases, the quantum yield for electron ejection is found to increase with pH [79], The anion of bromouracil also gives hydrated electron [81]. 

Acetylcholinesterase is only cholinesterase in insects. It is mainly located in the neuropile (area of synapses between nerve fibers) of the CNS in insects (Toutant, 1989). AChE contains two active sites, the esteratic site and the anionic site. The esteratic site possesses the hydroxyl group of serine and a basic nucleophilic imidazole group of histidine. The anionic site has a free carboxyl group (aspartic acid and/or glutamic acid). The interaction of ACh with AChE can be divided into three steps, as shown in Figure 7.13. The first... 

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