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Aspartic Acid

There are two functional groups present in one molecule of amino acid which is of opposite nature. One is amino group show basic nature and another is acidic carboxyl group. Therefore, amino acid molecule exists as a dipolar ion also called as zwitterion in which amino group converts in ammonium ion (NH4+) and carboxyl group changes to carboxylate ion (-COO-). The overall molecule is neutral in nature due to the presence of opposite charges. 

During the electrolysis of amino acid solution, the movement of ion depends upon the pH of medium. In acidic medium, amino group converts to ammonium ion and molecule converts to cation which mover towards cathode. On the other hand, in basic medium carboxyl group convert in carboxylate ion and show the movement towards anode.

The presence of any other functional group in side chain decides the polarity and charge of amino acid molecule. The presence of non-polar side chain makes the molecule non-polar and polar group like carboxyl and amino makes the molecule polar. For example, the presence of an additional carboxyl group in the side chain of aspartic acid is responsible for the polarity of molecule.


Whatis Aspartic Acid?

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Aspartic acid is a natural dibasic amino acid with two carboxyl group (one on alpha carbon atom and another in side chain) and also called as aminosuccinic acid. It is a nonessential amino acid generally found in proteins and acts as an excitatory neurotransmitter in the central nervous system.
Aspartic acid is also useful in culture media, detergents, dietary supplements, germicides and fungicides. Aspartic acid is abbreviated as Asp or D. The main food sources for aspartic acid are sugar cane and beet molasses. Some other food sources of aspartic acid are as follow.

Animal sources
Vegetable sources
Other sources
Luncheon meat Sprout seeds
Salts of aspartic acid like magnesium aspartate
Sausage meat Oat flakes
Sweeter aspartame like canderel
Wild game

Pure aspartic acid is a colourless crystalline substance which melts at 543K temperature and boiled at 597 K. The molecular formula of aspartic acid is C4H7NO4 and molecular mass is 133.1 g $mol^-1$. Just like other amino acids, aspartic acid is also soluble in water around 4.5 g/L.

Aspartic Acid

Like other amino acids, aspartic acid also exists in two configurations; D and L. Out of that L-aspartic are more common and involve in several biochemical processes. Both configurations are differing from each other in the orientation of amino group with respect to carboxyl group in molecule. The biological roles of D-aspartic acid" is much less compare to L-aspartic acid. The enzymatic synthesis of aspartic acid produced both D and L configurations and form racemic mixture or DL-aspartic acid as final product.
DL-Aspartic Acid

Aspartic acid can be easily converted in oxaloacetate by transamination reaction which acts as one of the intermediates of the Krebs cycle. This reaction is reversible in nature and used for the biosynthesis of aspartic acid.

Krebs Cycle

  1. The aspartic acid plays a very vital role in the Krebs cycle or the citric acid cycle, in which it involve in the formation of other biochemical and amino acids like asparagine, methionine, isoleucine and arginine, threonine, lysine , are synthesized.
  2. This acidic amino acid also involve in the treatment of chronic fatigue. Aspartic acid initiates the movement of the co-enzyme NADH or nicotinamide adenine dinucleotide molecules from the main cell body to its mitochondria and then use it to produce adenosine triphosphate (ATP) which acts as fuel powers for all cellular activity.
  3. Aspartic acid is also helpful in the transportation of minerals which are essential for healthy RNA and DNA to the cells. It also strengthens the overall immune system by helping in increasing the production of antibodies and immunoglobulins which are basically the immune system proteins.
  4. Aspartic acid helps in keeping the concentrations of NADH high in brain cells and also increase the mind sharpness leading to further production of neurotransmitters as well as chemicals needed for normal mental functioning.
  5. It also involves in some of the biochemical reactions for the removal of excess toxins like ammonia from the cells, found to be very damaging to the brain, nervous system and liver.
  6. In the conditions of body stress, like other non-essential amino acids, the extra dose of aspartic acid will be helpful which generally provided by protein supplements often marketed as energy boosters.

Aspartic Acid Structure

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Aspartic acid is an acidic polar α-amino acid with one additional methylene group bonded with one carboxyl group. Hence aspartic acid is dicarboxylic amino acids. Because of the presence of second carboxyl group makes the molecule very hydrophilic. The pKa of the second carboxyl group is about 3.85 and the overall molecule is negatively charged at neutral pH. 
Due to the presence of negatively charged carboxyl group, it is found almost at the surface of proteins. The charged group can form ionic bond with various metal ions as well as dipole interaction with water which is important concept of solubility of amino acid in water. The isoelectric point of aspartic acid is 2.77 because of two carboxyl groups in molecule.
  • The pKa value of carboxyl group bonded on alpha carbon is 1.88, for -COOH group at side chain is 3.65 and for amino group are 9.60.
  • The iso-electric point is equal to half of the sum of pKa1 and pKa3.
  • The neutral form of aspartic acid is dominant between pH 1.88 and 3.65, thus the isoelectric point is halfway between these two values, i.e. 1/2 (pKa1 + pKa3), so isoelectric point will be 2.77.

Aspartic Acid

Amino acids with some additional functional group like aspartic acid shows three inflection points in their titration curves. There are total four possible charged species, three of which are chargeable while one has no overall charge. 

 Titration Curves

Hybridizationof Aspartic Acid

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Hybridization of Aspartic Acid

The IUPAC name of aspartic acid is 2-Aminobutanedioic acid with the molecular formula HOOCCH (NH2)CH2COOH. There are total four carbon atoms in molecule. Out of which two are carbonyl carbon atoms of carboxyl group. The carbon atoms of both carboxyl groups (C1 and C4) are sp2 hybridized with trigonal planer geometry with 120$A^{\circ}$ bond angle. C2 and C3 are sp3 hybridized and arranged in tetrahedral geometry with 109.28$A^{\circ}$ bond angle. 

Both carbonyl carbon atoms of carboxyl group are sp2 hybridized with 120$A^{\circ}$ bond angle. The nitrogen atom of amino group is sp3 hybridized in which two hybridized orbital bonded with s-orbital of hydrogen atoms and one sp3 hybridized orbital overlap with sp3 hybrid orbital of C2 atom of parent chain.

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