Carboxyl charged

As already indicated, plastocyanin can also be modified by reacting remote site carboxylate residues with ethylenediamine [157]. This results in the replacement of a negative carboxylate charge by a positive amine (16). 

A polyanion s sediment layer is more diffuse than that of a neutral polysaccharide, because of interparticle carboxyl-charge repulsion. Easy repeptization of uronan-containing sediment in juices and wines presents difficulty during filtration and decantation. 

Anionic carboxylate charges [-COO ] were neutralized by the unchelated silver ions. This resulted decrease in repulsion among anionic carboxylate groups. 

Figure 9.31 Electrophoretic mobility of S. faecalis as a function of cetyltrimethylam-monium bromide concentration at two pH values and the constant ionic strength of 0.01 m. O, pH 7.0 , pH 3.4. From Schott and Young [80]. Cetyltrimethylammonium bromide uptake by the cell wall resulted in reduced electrophoretic mobility as the negative carboxylate charges were neutralized by the positive charges of the surface-active cation. This is chemisorption via the ion-exchange reactions ...

The emulsion copolymerization of styrene and methacrylic acid in the presence of a new polymerizable macromonomer based on PEG as stabilizer is proposed by Hincel and Serpen [55] to obtain larger and more surface-carboxyl-charged monodisperse particles relative to those obtained by the same emulsifier-free emulsion copolymerization. 

A selection of important anionic surfactants is displayed in table C2.3.1. Carboxylic acid salts or tire soaps are tire best known anionic surfactants. These materials were originally derived from animal fats by saponification. The ionized carboxyl group provides tire anionic charge. Examples witlr hydrocarbon chains of fewer tlran ten carbon atoms are too soluble and tliose witlr chains longer tlran 20 carbon atoms are too insoluble to be useful in aqueous applications. They may be prepared witlr cations otlrer tlran sodium. 

Carboxylate ion (RC—O ) An ester IS formed when the negatively charged oxygen of a carboxylate re places the halogen of an alkyl halide... 

Neutral Lewis bases such as water alcohols and carboxylic acids are much weaker nucleophiles than their conjugate bases When comparing species that have the same nucleophilic atom a negatively charged nucleophile is more reactive than a neutral one... 

Notice too that the carbonyl oxygen of the carboxylic acid is protonated m the first step and not the hydroxyl oxygen The species formed by protonation of the car bonyl oxygen is more stable because it is stabilized by electron delocalization The pos itive charge is shared equally by both oxygens... 

Carboxylic acids are weak acids and m the absence of electron attracting substituents have s of approximately 5 Carboxylic acids are much stronger acids than alcohols because of the electron withdrawing power of the carbonyl group (inductive effect) and its ability to delocalize negative charge m the carboxylate anion (resonance effect)... 

The negatively charged oxygen substituent is a powerful electron donor to the carbonyl group Resonance m carboxylate anions is more effective than resonance m carboxylic acids acyl chlorides anhydrides thioesters esters and amides... 

While the previous receptors are typically used in organic solvents, except for the cyclodextrins, there are special cases of cyclophane receptors supphed with peripheral charges (ammonium units) (107—12) or ionizable groups (carboxylate functions) (113,114) (Fig. 17) to allow substrate recognition, as in nature, in an aqueous medium, profiting from the solvophobic effects of water (115). 

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