Biological carboxylic acid, dissociation

In acidic solution at low pH, a carboxylic acid is completely undissociated and exists entirely as RCO2H- In basic solution at high pH, a carboxylic acid is completely dissociated and exists entirely as RC02 - Inside living cells, however, the pH is neither acidic nor basic but is instead buffered to nearly neutral pH—in humans, to pH = 7.3, a value often referred to as physiological pH. In what form, then, do carboxylic acids exist inside cells The question is an important one for understanding the acid catalysts so often found in biological reactions. 

In addition to intramolecular effects, intermolecular interactions have been shown to modify the observed partition coefficient. These include association of polar molecules in apolar systems, or dissociation of acids (e.g., carboxylic acids or pro-tonated forms of amines, which are the conjugated acids of the amines). The analysis of these effects has been presented in an explicit form (136, 149, 150). A distinction has to be made however, between the types of intermolecular interactions. Association of neutral polar molecules in apolar solvents may influence the observed partition coefficient, but there is little doubt that the monomer is the compound that influences the biological activity through its interaction with the biological system. 

One of the major applications of pM buffers is in maintaining concentrations of necessary metal ions in biological nutrient media at essentially constant levels. As free metal ions are removed from the system, perhaps by hydrolysis or by incorporation into metalloenzymes, they are replenished by the reversible dissociation from a reservoir of metal complex. Among the first complexing agents used in this way were citrate and tartrate ions, but more recently aminopoly-carboxylic acids such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and nitrilotriacetic acid (NTA) have become the chelating agents... 

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