11+ Important Anion Example You Need To Know

In this article, we discuss different anion examples and their biological importance.

Anions are those species in which an atom or group of atoms contain a negative charge by accepting one or more than one electron. Mainly formed by non-metal atoms. In electrolysis, an anion attracted the anode part of a cell.

A list of important anion examples is given below.

  1. Hydride
  2. Fluoride
  3. Chloride
  4. Bromide
  5. Iodide
  6. Hydroxide
  7. Sulfate
  8. Bicarbonate
  9. Phosphate
  10. Superoxide
  11. Nitrate and Nitrite

Hydride (H)

Hydride is one of the simple anion examples, it is an anion of Hydrogen. The oxidation number of Hydrogen is here -1. By the reduction of Hydrogen containing molecules, it can be formed.

There are different types of hydride present, covalent hydride, and ionic hydride are the most common in them. Also, a binary hydride is available.

In bioinorganic chemistry, there is an important role of hydride ions in the nitrogen fixation process.

In a chemical reaction, Hydride acts as a strong base and nucleophile. Hydride ion is used to form methanol from aldehyde.

anion example
Using of Hydride as reducing agent

Fluoride (F)

Fluoride Is the most electronegative anion.  Elemental Fluorine (F2) when released two electrons then Fluoride is formed. The oxidation number of Fluorine is -1 here.

Fluoride has greater importance in our human body. It strengthens the teeth and protects our teeth from different kinds of dental diseases. Fluoride can replace hydroxide in hydroxyapatite [Ca10(PO4)6(OH)2], which is an important component of the tooth enamel and bone mineral to form fluorapatite [Ca10(PO4)6(F)2] which is higher resistance against acid for the teeth. It is an important anion examples.

Chloride (Cl)

Chloride is the simple anion of chlorine. Due to the reduction of Chlorine, we get chloride ions.

Chloride ion has greater importance to form hydrochloric acid in the human stomach which is maintaining the acidic environment in the enzyme.

Chloride ions in blood plasma enter the RBC in order to maintain the electrical balance as well as acid-base balance RBC. The process is called the chloride shift.

A heme protein Myeloperoxidase is converted chloride ion converted to hypochlorous acid at a plasma concentration of halide. It is a major phagocyte that is killing bacteria is an important role. It is an important anion examples.

Bromide (Br)

By reducing of bromide element, we get a bromide ion. The oxidation number Br is also here -1. It is an anion example.

Bromide ion has no such essential contribution in bioinorganic chemistry, but in the past for treating seizures bromides as a form of potassium bromide were used as sedative agents or anticonvulsive agents. It is an important anion examples.

In Eosinophil granulocyte is a peroxidase enzyme where bromide is more acceptable over chloride.

Iodide (I)

Iodide is one of the largest anions. It acts as a mild reducing agent. By reduction of Iodine, we can form iodide.

Iodine is an essential mineral of the human body but in bioinorganic chemistry, the contribution of Iodide is more than free Iodine.

Iodide is accumulated in the thyroid gland and its main role is its constituents of thyroxine and triiodothyronine. These thyroid hormones are formed by the condensation of tyrosine amino acids and stored in thyroglobulin.

Thyroid hormones play an important role in gene transcription to regulate the basal rate of the human body. The T4 hormones can increase the basal rate by 50-100%. Without iodide, thyroid hormone cannot be produced and the thyroid gland will swell and produce goiter. Which leads to infertility, miscarriages, and breast and ovarian cancer.


Hydroxide ion is an oxo anion example. The removal of H+ ion from water molecule leads to the formation of hydroxide ion.

Hydroxide ion has more affinity to bind with a proton. In a living system, proton transfer occurs via the binding with hydroxide ions. Hydroxide ions bind with a proton to transport it through a lipid monolayer, it can also diffuse the proton along with bacterial membrane fragments.

Besides this hydroxide ion has a greater role in enzyme catalysis. It is an important anion examples.

Sulfate (SO42-)

Sulfate is the oxoanion of sulfur. The charge of the anion is 2 so it is a dianion. The oxidation number of S, in sulfate is +6. So, it is an oxidized form of S.

Sulfate has an important role in the growth of cells and the development of many organisms in the human body. Sulfate can detoxify many endogenous and exogenous compounds by the process called sulfation.

Sulfate has greater and essential role in fertilization and maintenance of pregnancy. A nonheme protein called zona pellucida glycoproteins during sulphonation contributes to the ZP acquiring the capacity of sperm. Even sulfate can improve the tyrosine-sulphonated proteins in sperm to lead to reduced infertility. It is an important anion examples.

Bicarbonate (HCO3-)

Bicarbonate is monoanionic of carbonate, it is formed from carbonic acid (H2CO3). The oxidation number of C is here +4. It is an oxoanion of C.

In respiration, CO2 is first converted to H2CO3 in presence of carbonic anhydrase. Then carbonic acid loses its proton to deoxyhemoglobin and is converted to HCO3. This bicarbonate diffuses into the blood plasma and is transported to the lungs. By the convention of carbonate from carbonic acid, this way carbonate maintains the pH of the blood at around 7.4. It is an important anion examples.

In photosystem II, carbonate is bound to the non-heme iron site between the primary and secondary quinone electron acceptor. The electron will be accepted at the bicarbonate bound site and thus CO2 is converted to oxygen and carbonate has an important role in electron transfer and protonation in that particular reaction.


Phosphate is an oxoanion of P. Four oxygen are attached via a double bond with P, so the negative charge over P only. The oxidation number of P is +5 here.

Phosphate has a greater role in forming a bridge between DNA and RNA. Phosphate ions play a crucial role in cell replication. ATP (Adenosine triphosphate) is the main source of energy for all living beings, this ATP can transfer the terminal phosphate group to glucose under the influence of hexokinase enzyme to produce ADP (adenosine diphosphate). This transformation is required for all living animals for muscle movement. It is an important anion examples.

image 164
Phosphate in ATP and ATP
image 165
ATP Transfer Presence of Hexokinase Enzyme to produce ADP

For all vertebrates, the bone skeleton is, made of a fibrous protein named collagen which is a crystal of calcium phosphate(hydroxyapatite, Ca5(PO4)3OH).

Superoxide (O2)

Superoxide is an anion of dioxide. There is a peroxy linkage between two oxygen atoms in superoxide. It can behave as both oxidant as well as reductant. It is paramagnetic in nature.

In oxyhemoglobin, oxygen bind to the Fe(III) as superoxide form as end -on-bent fashion. Oxygen cannot bind there due to neutral species, so superoxide is a greater role in oxygen circulation via blood. Superoxide is linked with Fe an end-on-bent fashion o that it can form an H bond with the -NH group of distal His-residue.

Superoxide also plays a role in ORR (oxygen reduction reaction) involving 4 electrons transfer convert oxygen to a water molecule. Again, it takes part in super oxidase dismutase to produce less harmful hydrogen peroxide. It is an important anion examples.

Nitrate (NO3) and Nitrite(NO2)

Nitrite and nitrite both are oxoanion of Nitrogen. The oxidation number of N in nitrate and nitrite are +5 and +4 respectively.

Nitrite and nitrate both have an important role in nitration fixation for many plants. They can form nitric oxide, which has a greater role in cell signaling and the blood flow regulation process.

In the nitrogen, cycle nitrate converted the nitrite and complete the circle. The nitrate reductase is a Mo-containing enzyme that is a greater role in nitration fixation. These are an important anion examples in biological role.