Amine Henderson-Hasselbalch equation

What about amine bases In what form do they exist at the physiological pH inside cells—as the amine (A- = RNH2), or as the ammonium ion (HA = RNH3+) Let s take a 0.0010 Vf solution of methylamine at pH = 7.3, for example. According to Table 24.1, the pKa of methvlammonium ion is 10.64, so from the Henderson-Hasselbalch equation, we have... 

The Henderson-Hasselbalch equation described in Section 19.4 can be applied to bases such as amines, as well as carboxylic acids. The ratio [CH3NH3+]/[CH3NH2] is given by... 

Biological amines and the Henderson-Hasselbalch equation (Section 24.5). 

The Henderson-Hasselbalch equation can be very useful in the laboratory when compounds need to be separated from each other. Water and diethyl ether are not miscible liquids and, therefore, will form two layers when combined. The ether layer will lie above the more dense water layer. Charged compounds are more soluble in water, whereas neutral compounds are more soluble in diethyl ether. Two compounds, such as a carboxylic acid (RCOOH) with a pA g of 5.0 and a protonated amine (RNH3 ) with a pA a of 10.0, dissolved in a mixture of water and diethyl ether, can be separated by adjusting the pH of the water layer. For example, if the pH of the water layer is 2, the carboxylic acid and the amine will both be in their acidic forms because the pH of the water is less than the pAg s of both compounds. The acidic form of a carboxylic acid is neutral, whereas the acidic form of an amine is charged. Therefore, the carboxylic acid will be more soluble in the ether layer, whereas the protonated amine will be more soluble in the water layer. 

In Chapter 21, we used the Henderson-Hasselbalch equation to show that a carboxyhc acid moiety (COOH) exists primarily as a carboxylate ion at physiological pH. A similar argument can be used to show that an amine moiety also exists primarily as a charged ammonium ion at physiolc ical pH ... 

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