Decarboxylation Reaction

Gain or loss of a single carbon by an organic molecule in the form of $$C{O}_2$$ is the most important carbon-carbon bond forming and breaking in biological chemistry. You must have come across an equation like this in one of your biology classes.

$$6C{O}_2+6H_{2}O+energy\to C_6{H}_{12}{O}_6+6O_2$$

It refers to the photosynthetic process, in which plants use sunshine to synthesize glucose from individual carbon dioxide molecules. The carboxylation reaction is the main step in which carbon dioxide gets fixed (condensed with an organic molecule).

You should also be familiar with the chemical equation in reverse:

$$C_6{H}_{12}{O}_6+6O_2\to 6C{O}_2+6H_{2}O+energy$$

The oxidative breakdown of glucose to create water, carbon dioxide, and energy is described by the above chemical reaction in respiration. During the transformation of glucose, every carbon atom is transformed into $$C{O}_2$$ molecules. The Decarboxylation Reaction is the main step in which a carbon atom separates from a bigger chemical compound. The citric acid cycle and the pentose phosphate route are the key decarboxylation stages in the conversion of glucose to carbon dioxide.

In a carboxylic acid, the decarboxylation mechanism exchanges the carboxyl group with hydrogen. A set of enzymes known as decarboxylases or carboxy-lyases aid the procedure. Soda-lime is a regent that aids in the reaction. It's made out of a combination of caustic soda and quick lime. Three steps are involved in the reaction's mechanism. 

The first involves removing the $$H^{+}$$ ion from the carboxylic acid and replacing it with Na. This procedure resulted in the release of sodium salt of carboxylic acid and a water molecule.

A negative charge from oxygen is transported between the carbon-oxygen bonds in the second stage. As a result, the alkyl group(-R) and carbon bond split. In this stage, $$C{O}_2$$ is released. The $$H_{2}O$$ created in the previous phase is used in the third step. It splits to release a proton ion, which reacts with an alkyl group to form an alkane.

The removal of carbon dioxide from organic acids, known as decarboxylation, is a crucial event in biology. Decarboxylase enzymes play an important role in glucose metabolism and amino acid conversion in both aerobic and anaerobic environments. Our understanding of the processes that enable these critical decarboxylase events has continued to grow and inspire during the last decade. The organic cofactors biotin, flavin, NAD, pyridoxal 5'-phosphate, pyruvoyl, and thiamin pyrophosphate are discussed as catalytic centers in this article. Metal-dependent decarboxylase processes are also given a lot of studies.

Amino acids produced through fermentation or recovered from protein waste hydrolysates are a great renewable resource for bio-based chemical synthesis. We provide a chemocatalytic, metal-free technique for the decarboxylation of amino acids, allowing direct access to primary amines, to recycle both carbon and nitrogen. The amino acid is briefly locked into a Schiff base in the presence of a carbonyl molecule, allowing for easier $$C{O}_2$$ removal. Isophorone was recognized as a potent organocatalyst under mild conditions after examining several types of aldehydes and ketones on their activity at modest catalyst loadings (5 mol percent). Many amino acids with a neutral side chain were transformed into 2-propanol at 150 °C in 28–99 percent yield after optimization. The amine is sensitive to N-formylation when the reaction is carried out in DMF. 

Amino acids produced through fermentation or recovered from protein waste hydrolysates are a great renewable resource for bio-based chemical synthesis. We provide a chemocatalytic, metal-free technique for the decarboxylation of amino acids, allowing direct access to primary amines, to recycle both carbon and nitrogen. The amino acid is briefly locked into a Schiff base in the presence of a carbonyl molecule, allowing for easier $$C{O}_2$$ removal. Isophorone was recognized as a potent organocatalyst under mild conditions after examining several types of aldehydes and ketones on their activity at modest catalyst loadings (5 mol percent). Many amino acids with a neutral side chain were transformed into 2-propanol at 150 °C in 28–99 percent yield after optimization. The amine is sensitive to N-formylation when the reaction is carried out in DMF.

Histidine and Glutamate are both amino acids decarboxylated to form alkaline amine compounds on the body.   

• Decarboxylation of Histidine: Histidine gets decarboxylated in presence of the enzyme histidine decarboxylase, catalyzed by a coenzyme $$B_6-P{O}_4$$. The reaction produces Histamine and $$C{O}_2$$. The decarboxylation process takes place in the Basophils, gut, gastric mucosa cell, and histaminergic neurons of the CNS.  Excessive release of Histamine occurs at the site of a wound, in injured tissues.

• Decarboxylation of Glutamate: Glutamate decarboxylation is catalyzed by glutamate decarboxylase enzyme with the help of coenzyme $$B_6-P{O}_4$$. The reaction forms the product γ-aminobutyric acid (GABA) along with the liberation of $$C{O}_2$$. The reaction takes place in the gray matter of CNS. GABA acts as an inhibitory transmitter when released from axon terminals of neurons. 

The following are the uses of the Decarboxylation test.

• The test is efficient in differentiating members of the Enterobacteriaceae with similar physiological activities.

• The decarboxylase test for lysine decarboxylase helps differentiate the bacteria Salmonella (+) and Shigella (-).

• Arginine decarboxylase test results in the identification of Enterococcus species based on their Arginine metabolizing activity. 

There are some limitations to the test. They are:

• The test is time-consuming. Results cannot be interpreted before 18-24 hours of incubation. Microorganisms that do not ferment glucose sometimes show weak decarboxylase activity.

• The test fails to measure the intracellular amount of the enzyme. The enzyme presence is only detected by the change in pH.