Zwitterion - Definition, Example, Structure, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:57 PM IST

Zwitterion is basically derived from the German word Zwitter, which means hermaphrodite or roughly we can say hybrid ion. A zwitterion consists of two main functional groups. Zwitterion generally contains both the charges, in other words we can say that zwitterion is electrically neutral. The net formal charge ion zwitterion is zero. In case of dipolar compounds zwitterion are not designated as dipolar compounds but these are inner salts. This can be distinguished with the help of plus and minus sign on amine oxide, which signifies the formal charge.

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What is zwitterion or Zwitterion Definition:
Zwitterion Example:
Zwitterion structure of alanine:
Zwitterion structure of glycine:

Zwitterion

What is zwitterion or Zwitterion Definition:

Zwitterion can be defined as the molecule which contains both negatively charged ions as well as positively charged ions. Amino acids can exist in dipolar forming the solid state and are termed as Zwitterion. For a compound to be zwitterion it is important to understand the concept of pH. As it is important to specify the cation and anion as anion can be formed when a sufficient amount of alkaline solution is available whereas cation can be formed when sufficient amount of acid is available. The polymers of zwitterion are also available in the form of positive and negative functional groups which are present at the end of the chain. The nature of zwitterion is amphoteric in nature. Electrical neutrality of the zwitterion does not migrate during electrolysis (neither anode or cathode).

Zwitterion

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Zwitterion Example:

The best example of zwitterion is alpha amino acids. Due to the formation of zwitterion alpha amino acids show the crystalline properties. While dissolving alpha amino acids in aqueous solution it gives zwitterion. For example, when we dissolve R-CH- NH₃-COOH in aqueous medium then oxygen atom present in the functional group pulls electron from the hydrogen. Here hydrogen gets positive charge and oxygen becomes negative, Now the hydrogen ion gets bonded with the nitrogen atom. Therefore, nitrogen gains the positive charge thereby forming the NH₃.

The other examples of zwitterion are as follows: trimethylglycine, psilocybin, cocamidopropyl. The amino acids which is optically inactive are termed as glycine.

examples of zwitterion

Betaine is also one such example of zwitterion which is a chemically neutral compound. Betaine is a special type of zwitterion as it does not have any hydrogen atom in it. It contains positively charged ammonium or phosphonium groups and negatively charged carboxylate groups.

example of zwitterion

Sulfamic acid exists as a neutral as well as zwitterion form.

Zwitterionic forms:

The compounds of zwitterion are formed like ampholytes which contain both acids and bases in their molecules.

In zwitterion the charged atoms are held together by bond i.e. covalent bond.

Zwitterion form of amino acids:

As we discussed earlier, the best examples of zwitterion are amino acids. As amino acids contain amino group and carboxyl functional group i.e. individually amino acids are not zwitterion it can behave only in aqueous solution by attaining the proton on hydrogen atom and loses to become carboxyl group with negative charge. Such a reaction is called an isomerisation reaction. At neutral pH range of water.

The equilibrium exists between parent amino acid and its zwitterion. Amine is present in the amino acid group which is the stronger basic group while carboxylic is an acidic group. Zwitterion of an amino exists with pH range equal to isoelectric point. Based on the properties of amino acids each has its own pH value. Above and below the isoelectric point the molecule shows the pH values and has net charge which directly depends on the pH of the molecule and pH of the solution.

Zwitterion form of amino acids

Isoelectric point:

Isoelectric points can be defined according to specific pH range. The net electric charge is found to have zero value at characteristic pH value. Such a point is defined as an isoelectric point.

Isoelectric point of amino acids:

The solubility of the molecule is affected by its isoelectric point value at a certain pH range.

Checking the pH as according to isoelectric point:

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When pH is less than isoelectric point.

The presence of hydrogen ions in the solution is found to be more when the value of pH is less than isoelectric point. This causes protonation as the excess hydrogen ions attract the carboxylate ion. Leaving only positive charge on amine, as carbohydrate ions are protonated making the compound neutral. In the overall scenario amino acids have charge +1. Below showing you the structure of protonated amino acid.

When the value of pH is higher than isoelectric point.

The presence of hydroxyl ion in the solution is found to be more when the value of pH is more than isoelectric point. This causes excess hydroxyl ions to attract the amine group which results in removal of hydrogen ions. Leaving only negative charge on the carboxylate group, amine has neutral charge on it. In the overall scenario amino acids have charge -1.

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Zwitterion structure of alanine:

The alanine is a form of amino acid which means it contains one carboxylic group and one amino group. While defining the alpha amino acid the alanine is the example of such alpha amino acid group. The alanine is consisting of two carbon atoms where the same carbon atom has both amine and carboxylic group with molecular formulaC₃H₇NO₂. The structure of alanine can be depicted as follows:

Zwitterion structure of alanine

In the above structure we can see that protons from the carboxylic group will shift to the amine group. This happens as the carboxylic acid has a tendency to accept protons and amine to release the proton. The zwitterion is formed can be depicted as below

zwitterion

At pH 4 glycine exists as:

The simplest form of amino acid is glycine which can be represented by the symbol G or Gly. It is a form of amino acid which has a hydrogen atom in its side chain. Glycine is the only amino acid that can exist as achiral proteinogenic amino acid and can be fitted in both the environment as hydrophilic and hydrophobic. This happens because of one hydrogen atom.

At pH 4 glycine is found as in acidic form.

Zwitterion structure of glycine:

The zwitterion structure can be represented at this pH range.
When reacts with hydrogen ion such reaction can proceed further:

Zwitterion structure of glycine

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NCERT Chemistry Notes :

Frequently Asked Questions (FAQs)

1. Define isoelectric pH?

Isoelectric point pH can be defined as a particular pH range molecule carrying no net charge on it. The net charge is affected by the pH and its surrounding.

2. What is the zwitterion of amino acids?

Zwitterion is composed of positively and negatively charged electrons and are neutral in nature. By adding the hydroxide ions the pH increases which ultimately exclude the hydrogen ions from the amine group.

3. Write down the example of zwitterion?

The best example of zwitterion is amino acids. Amino acids consist of two functional groups: amine group and carboxyl group.

4. Define isoelectric point of amino acids?

The isoelectric point definition is given by those points where the pH of anion are equal to pH of cation. At this point amino acids do not migrate, when a field is applied on it.

5. What do you mean by dipolar ion?

Dipolar ions are those that have both charges positive and negative and are amphoteric in nature.

6. Define zwitterion?

Zwitterion can be defined as the molecule which is made up of two functional groups. The opposite charges present on the group will cancel out each other making the compound neutral.

7. What is a zwitterion?

A zwitterion is a molecule that contains both positive and negative electrical charges at different locations within the same molecule. In chemistry, it's a neutral molecule with a positive and negative ionic group. This structure is common in amino acids at certain pH levels.

8. How does a zwitterion form in amino acids?

In amino acids, a zwitterion forms when the carboxyl group (-COOH) loses a proton to become negatively charged (-COO-), while the amino group (-NH2) gains a proton to become positively charged (-NH3+). This occurs at a specific pH called the isoelectric point.

9. What is the isoelectric point of a zwitterion?

The isoelectric point is the pH at which a molecule exists as a zwitterion with a net charge of zero. At this pH, the positive and negative charges within the molecule are balanced, resulting in an overall neutral charge.

10. How does the zwitterion structure contribute to the amphoteric nature of amino acids?

The zwitterion structure allows amino acids to act as both acids and bases (amphoteric). The carboxyl group can donate a proton (act as an acid), while the amino group can accept a proton (act as a base), depending on the pH of the solution.

11. What is the difference between a zwitterion and a dipolar ion?

There is no difference. "Zwitterion" and "dipolar ion" are synonymous terms. Both refer to a molecule with spatially separated positive and negative charges that result in a net neutral charge overall.

12. Can non-amino acid molecules form zwitterions?

Yes, zwitterions are not limited to amino acids. Other organic compounds with both acidic and basic functional groups can form zwitterions under appropriate conditions. Examples include certain surfactants and some drug molecules.

13. Can zwitterions form intermolecular hydrogen bonds?

Yes, zwitterions can form intermolecular hydrogen bonds. The positively charged groups (like -NH3+) can act as hydrogen bond donors, while negatively charged groups (like -COO-) can act as hydrogen bond acceptors. This contributes to their unique properties in solid state and solution.

14. How does the zwitterion structure influence the reactivity of amino acids?

The zwitterion structure affects amino acid reactivity by influencing the nucleophilicity and electrophilicity of different parts of the molecule. The charged groups can participate in ionic reactions, while the overall neutral charge allows for certain non-ionic reactions to occur as well.

15. What is the relationship between zwitterions and buffer solutions?

Zwitterions, particularly amino acids, can act as effective buffers. Their ability to exist in different charged states allows them to resist changes in pH by accepting or donating protons. This property makes them important components of biological buffer systems.

16. How do zwitterions affect the surface tension of water?

Zwitterions can lower the surface tension of water. Their charged groups interact with water molecules at the surface, disrupting the cohesive forces between water molecules and reducing surface tension. This property makes some zwitterionic compounds useful as surfactants.

17. How does the zwitterion structure affect the melting point of amino acids?

Zwitterions typically have higher melting points compared to similar non-ionic molecules. This is due to the strong electrostatic interactions between the positive and negative charges of different zwitterion molecules, requiring more energy to break these interactions and melt the substance.

18. How does the zwitterion structure influence the pKa values of amino acids?

The zwitterion structure affects the pKa values of amino acids by influencing the ease with which protons are donated or accepted. The presence of nearby charged groups can stabilize or destabilize the protonated or deprotonated forms, shifting the pKa values compared to similar non-zwitterionic molecules.

19. What role do zwitterions play in protein crystallization?

Zwitterions are crucial in protein crystallization. Their charged groups can form intermolecular interactions that help stabilize the crystal lattice. Understanding the zwitterionic properties of amino acids is important for optimizing crystallization conditions in protein structure studies.

20. How do zwitterions interact with water molecules?

Zwitterions interact strongly with water molecules through hydrogen bonding and ion-dipole interactions. The positively charged groups can interact with the oxygen of water, while the negatively charged groups can interact with the hydrogen of water, leading to a hydration shell around the zwitterion.

21. What is the significance of zwitterions in biological systems?

Zwitterions are vital in biological systems. They contribute to the buffering capacity of biological fluids, influence protein structure and function, and play a role in membrane transport processes. Their unique properties also affect the behavior of biomolecules in different cellular environments.

22. Are all amino acids zwitterions at physiological pH?

Most amino acids exist as zwitterions at physiological pH (around 7.4). However, some amino acids with ionizable side chains may have different charge states depending on their specific pKa values and the solution pH.

23. Can zwitterions exist in solution?

Yes, zwitterions can exist in solution. In fact, many amino acids exist predominantly as zwitterions in aqueous solutions at physiological pH. The presence of both positive and negative charges affects their solubility and behavior in solution.

24. How does the structure of a zwitterion affect its solubility?

The presence of both positive and negative charges in a zwitterion makes it highly soluble in polar solvents like water. The charges interact with water molecules, forming hydrogen bonds and ion-dipole interactions, which enhance solubility.

25. How does pH affect the zwitterion structure of an amino acid?

pH greatly influences the zwitterion structure. At low pH, the amino group is protonated (-NH3+) and the carboxyl group is neutral (-COOH). At high pH, the amino group is neutral (-NH2) and the carboxyl group is deprotonated (-COO-). At the isoelectric point, the zwitterion form dominates.

26. How do zwitterions contribute to protein structure?

Zwitterionic amino acids play a crucial role in protein structure. Their charged groups can form ionic bonds with other amino acids, contributing to the tertiary and quaternary structure of proteins. They also influence protein solubility and interactions with water.

27. Can the zwitterion structure be detected using spectroscopic methods?

Yes, spectroscopic methods can detect zwitterion structures. Infrared spectroscopy can show characteristic peaks for the charged groups. Nuclear Magnetic Resonance (NMR) spectroscopy can reveal the chemical environment of atoms in a zwitterion. Mass spectrometry can also provide information about the overall charge state.

28. What is the role of zwitterions in enzymatic catalysis?

Zwitterions play crucial roles in enzymatic catalysis. The charged groups of zwitterionic amino acids in enzyme active sites can participate in acid-base catalysis, stabilize transition states, and contribute to substrate binding through electrostatic interactions.

29. What is the significance of zwitterions in prebiotic chemistry theories?

Zwitterions, particularly amino acids, are significant in prebiotic chemistry theories. Their ability to self-assemble, their stability in aqueous environments, and their potential to form peptides make them key players in hypotheses about the origin of life and the formation of early biological molecules.

30. Can zwitterions be used in green chemistry applications?

Yes, zwitterions have potential applications in green chemistry. Their unique properties, such as high solubility in water without adding to the ionic strength of the solution, make them interesting candidates for environmentally friendly solvents, catalysts, and reaction media in various chemical processes.

31. Can zwitterions conduct electricity?

While zwitterions have charged groups, they do not conduct electricity in their solid form because the positive and negative charges are balanced within each molecule. In solution, however, they can contribute to conductivity if they dissociate or interact with other ions.

32. How does the presence of zwitterions affect the osmotic pressure of a solution?

Zwitterions contribute to the osmotic pressure of a solution, but less than if the positive and negative charges were on separate molecules. This is because the zwitterion acts as a single particle in solution, despite having both positive and negative charges.

33. What is the importance of zwitterions in drug design?

Zwitterions are important in drug design because they can enhance a drug's solubility in water while potentially improving its ability to cross biological membranes. The balance of charges can also affect a drug's binding to target molecules and its overall pharmacokinetic properties.

34. How do zwitterions contribute to the buffering capacity of blood?

Zwitterionic amino acids, particularly histidine residues in proteins, contribute significantly to the buffering capacity of blood. Their ability to accept or donate protons helps maintain the blood's pH within a narrow range, which is crucial for proper physiological function.

35. Can zwitterions participate in acid-base reactions?

Yes, zwitterions can participate in acid-base reactions. They can act as both proton donors (acids) and proton acceptors (bases) depending on the pH of the solution and the specific pKa values of their ionizable groups.

36. How does the zwitterion structure affect the optical properties of amino acids?

The zwitterion structure can influence the optical properties of amino acids. The charged groups can affect the electronic transitions within the molecule, potentially altering its absorption and emission spectra. Additionally, the asymmetry introduced by the zwitterion structure contributes to the optical activity of chiral amino acids.

37. What is the role of zwitterions in membrane biology?

Zwitterions play important roles in membrane biology. Some phospholipids have zwitterionic head groups that contribute to membrane structure and function. Zwitterionic amino acids in membrane proteins can interact with both the aqueous environment and the lipid bilayer, influencing protein folding and membrane interactions.

38. How do zwitterions affect the freezing point of solutions?

Zwitterions, like other solutes, lower the freezing point of water. However, because a zwitterion acts as a single particle in solution (despite having both positive and negative charges), its effect on freezing point depression is less than that of two separate ions.

39. Can zwitterions form coordination complexes with metal ions?

Yes, zwitterions can form coordination complexes with metal ions. The negatively charged groups (like carboxylate) can coordinate with metal ions, while the overall neutral charge of the zwitterion can affect the stability and properties of the resulting complex.

40. How does the zwitterion structure influence the chromatographic behavior of amino acids?

The zwitterion structure significantly affects the chromatographic behavior of amino acids. The presence of both positive and negative charges influences their interactions with stationary phases in various types of chromatography, affecting retention times and separation. This property is utilized in techniques like ion-exchange chromatography for amino acid analysis.

41. What is the significance of zwitterions in protein folding?

Zwitterions play a crucial role in protein folding. The charged groups of zwitterionic amino acids can form salt bridges and hydrogen bonds that stabilize protein secondary and tertiary structures. Their interactions with water also influence the hydrophobic collapse during protein folding.

42. How do zwitterions contribute to the colligative properties of solutions?

Zwitterions contribute to colligative properties (like boiling point elevation and freezing point depression) as single particles, despite having two charged groups. This means their effect on colligative properties is less than that of fully dissociated ions but more than uncharged molecules of similar size.

43. Can zwitterions form micelles?

Some zwitterionic compounds, particularly those with a hydrophobic tail and a zwitterionic head group, can form micelles in aqueous solutions. These zwitterionic micelles have unique properties and applications in areas like drug delivery and surface chemistry.

44. How does the presence of zwitterions affect the viscosity of solutions?

Zwitterions can increase the viscosity of aqueous solutions. Their charged groups interact with water molecules, creating a hydration shell that increases the effective size of the solute particles. This leads to greater resistance to flow and thus higher viscosity compared to solutions of non-ionic molecules of similar size.

45. What is the importance of zwitterions in protein-protein interactions?

Zwitterions are crucial in protein-protein interactions. The charged groups of zwitterionic amino acids on protein surfaces can form electrostatic interactions and hydrogen bonds with other proteins. These interactions are often key in protein complex formation, enzyme-substrate binding, and other biological recognition processes.

46. How do zwitterions affect the stability of proteins in solution?

Zwitterions contribute to protein stability in solution through several mechanisms. They can form stabilizing interactions within the protein structure, interact with water to maintain protein hydration, and contribute to the overall charge balance that prevents protein aggregation.

47. Can zwitterions participate in redox reactions?

While the zwitterionic structure itself doesn't typically participate in redox reactions, some amino acids with additional functional groups (like cysteine with its thiol group) can undergo redox reactions. The zwitterionic portion may influence the redox potential by affecting the local chemical environment.

48. How does the zwitterion structure influence the pI (isoelectric point) of proteins?

The zwitterionic properties of amino acids directly influence a protein's isoelectric point (pI). The pI is determined by the balance of positive and negative charges on the protein, which depends on the pKa values of the constituent amino acids' side chains and terminal groups.

49. What role do zwitterions play in ion exchange processes?

Zwitterions can participate in ion exchange processes due to their charged groups. Depending on the pH, they can exchange either positive or negative ions with the surrounding solution or an ion exchange resin. This property is utilized in various separation and purification techniques.

50. How do zwitterions affect the Hofmeister series?

Zwitterions can influence the Hofmeister series, which ranks ions based on their ability to salt out or salt in proteins. The unique charge distribution of zwitterions can affect their position in this series and their impact on protein solubility and stability in solution.

51. Can zwitterions form inclusion complexes?

While not as common as with other types of molecules, some zwitterions can form inclusion complexes. The charged groups can interact with complementary charges on host molecules like cyclodextrins, creating stable complexes with unique properties.

52. How does the zwitterion structure affect the dipole moment of amino acids?

The zwitterion structure significantly increases the dipole moment of amino acids compared to their uncharged form. The separation of positive and negative charges creates a strong dipole, which influences their interactions with water, other molecules, and electric fields.

53. How do zwitterions influence the Donnan equilibrium in biological systems?

Zwitterions contribute to the Donnan equilibrium, which describes the uneven distribution of charged particles across a semipermeable membrane. Their ability to exist in different charge states depending on pH affects the distribution of other ions and the membrane potential in biological systems.

54. Can zwitterions form liquid crystals?

Yes, some zwitterionic compounds can form liquid crystals. The presence of both hydrophilic (charged) and hydrophobic regions in these molecules can lead to self-assembly into ordered structures with liquid crystalline properties.

55. How does the zwitterion structure affect the rate of amino acid racemization?

The zwitterion structure can influence amino acid racemization rates. The charged groups can stabilize or destabilize the transition state of the racemization reaction, affecting the energy barrier. This is particularly relevant in archaeological and geological dating techniques using amino acid racemization.

56. How do zwitterions contribute to the taste of foods?

Zwitterionic amino acids contribute significantly to the taste of foods. For example, glutamate in its zwitterionic form is responsible for the umami taste. The zwitterionic structure affects how these molecules interact with taste receptors, influencing flavor perception.