Amphoteric compounds, amino acids

Amino acids show basic properties because of the amino group (— NH2) and acidic properties because of the carboxyl group (— COOH), so they are amphoteric compounds. Amino acids act as a base when they react with an acid and act as an acid when they react with a base, in both cases a salt is formed. 

Amphoteric. Compounds having the capability of acting as an acid or a base. Amino acids are amphoteric—their molecules contain both an acid group (-COOH) and a basic group (-NH2). 

Amphoteric compounds such as amino acids can be resolved as acid or amine forms after deriving corresponding esters or N-acyl compounds. Racemic alcohols and amines are also resolved by use of optically active isocyanates, where the alcohols and amines are derived the corresponding diastereomeric urethanes or ureas. 

Amphoteric compounds that contain both basic (e.g., -NH2) and acidic (e.g., -COOH) groups, such as amino acids. 

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 ... 

Amino acids are amphoteric compounds i.e., they contain both acidic and basic groups. Because of this, they arc capable of bearing a net electrical charge, which depends on the nature of the solution. 

The amino acids you encountered in Chapter 2 are amphoteric. Unlike water, however, these compounds have separate acidic and basic groups built into the same molecule. 

Ampholyte — A substance that can react both as an acid and as abase is called an ampholyte, or amphoteric compound. Usually this property refers to the - Bronsted acid-base theory. An example is HCOj which can act as a proton acceptor and as a proton donator. An ampholyte can be a zwitterion, as in case of amino acids in the range between pH = pJCai and pH = pfCa2, they exist as [+(H3N)HRC-COO-]. 

The organic compounds called amino acids are unusual. They have an acid group at one end of the molecule (COOH) and a base group (NH2) at the other. We call a molecule that has both acid and base properties amphoteric . 

Theoretically, the precipitation of a protein, which is built up of amino-acids and functions as a typical amphoteric electrolyte, should best be accomplished at the isoelectric point, that is, at the hydrogen ion concentration at which the acidic and basic functions of the protein are equal and at a minimum. According to Soerensen, the iso-electric point of egg albumin is at pH 4.8,10 and while precipitation would undoubtedly be most complete at this point, it is not necessarily the most favorable for crystallization, as the egg albumin crystals are not isoelectric protein, but a compound of this with the sulfate ion, and perhaps the ammonium ion as well.11... 

Imidazoles are amphoteric compounds with a basic, pyridine-type nitrogen (they are about 106 times more basic than oxazoles and 104 times more basic than thiazoles173), and (where the NH is unsubstituted) a weakly acidic, pyrrole-type amino nitrogen in the ring. In consequence, imidazoles readily form salts with acids and often form salts (or complexes) with metals. The sparingly soluble silver salts formed by imidazoles have been used by Giesemann et al.174 as intermediates in the synthesis of 1-triphenylmethylimidazoles. Normally, however, the salts formed with acids are more important in isolation and purification procedures. 

Amino acids constitute a particularly important class of bifiinctional compounds the two functional groups in an amino acid are, respectively, basic and acidic, the compounds are amphoteric, and in fact exist as zwit-terions or inner salts. For example, glycine, the simplest amino acid, exists mosdy in the zwitterion form shown first, rather than as aminoacetic acid... 

We call compounds, like amino acids, that can act as acids or bases depending on their environment amphoteric compounds. The body uses this dual property in the stomach, as the protein stomach juices and lining can react to mop up any adverse effects of overeating or drinking (within reason). If the system is overloaded you might have to help a bit by taking a Rennie or stomach powder to help restore the correct acidity to the stomach. 

Several drugs and amino acids, peptides and proteins are amphoteric, displaying both basic and acidic characteristics. Frequently encountered dmgs in this category are the sulfonamides and the tetracyclines. If, for simplicity, one were to use a generalised stmcture for an amphoteric compound... 

Amino acids are amphoteric compounds that is, they may exist in anionic, cationic, and zwitterionic form, depending on the pH ... 

Explain why amino acids are generally amphoteric compounds. 

The Ionization of Amino Acids, The Zwitterion or Dipole Ion. As is well known amino adds are of importance in that they are the structural units from which proteins are formed, and into which food proteins break down during digestion. The simplest compound of the series is glycine, NHaCH2COOH, which like all other amino adds contains an amino and a carboxyl group. The type formula for the series may thus be represented by NH2RCOOH. Amino acids are able to combine with both adds and bases, i.e., they are amphoteric. 

Amino acids. A compound that contains at least one amino group and at least one carboxyl group. (25.3) Amorphous solid. A solid that lacks a regular three-dimensional arrangement of atoms or molecules. (11.7) Amphoteric oxide. An oxide that exhibits both acidic and basic properties. (8.6)... 

The zwitterion contains carboxlate and ammonium ionic centers but has a net charge of zero. a-Amino acids exist exclusively as zwitterions in the solid state. Even when drawn as the uncharged molecule, we must understand that the actual structure is that of the dipolar ion. Amino acids are referred to as amphoteric compounds because both acidic and basic groups are contained in the same molecule. 

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