Zwitterion Structure and Formation in Amino Acids
Zwitterion is essential in chemistry and helps students understand various practical and theoretical applications related to this topic.
What is Zwitterion in Chemistry?
A zwitterion refers to a molecule that contains both a positive and a negative charge on different atoms but is overall electrically neutral.
This concept appears in chapters related to Amino Acids, Acid-Base Reactions, and Isoelectric Point, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula of a zwitterion varies depending on the molecule. For example, the zwitterion form of glycine is NH3+–CH2–COO−.
It consists of a carboxylate group (–COO−) and an ammonium group (–NH3+) attached to the same molecule, classifying it under amphoteric and dipolar compounds.
Preparation and Synthesis Methods
Zwitterions form naturally in aqueous solutions, especially in the case of amino acids. When an amino acid is placed in water, the amino group can accept a proton, and the carboxylic group can donate a proton, resulting in the zwitterionic form.
No special industrial process is required to synthesize zwitterions—they form automatically at the right pH.
Physical Properties of Zwitterion
Zwitterion compounds are usually crystalline solids with high melting points. They are highly soluble in water but insoluble in non-polar solvents. The presence of both positive and negative charges allows strong interactions with water molecules.
Zwitterions do not conduct electricity in the solid state but can in solution, thanks to their ionic character.
Chemical Properties and Reactions
Zwitterions show interesting acid-base behavior. They can act as buffers and help maintain pH stability. In amino acids, the zwitterion can lose H+ to become an anion under basic conditions or gain H+ to become a cation under acidic conditions. At a specific pH—the isoelectric point—they exist mainly as zwitterions.
Frequent Related Errors
- Confusing zwitterions with fully neutral (uncharged) molecules.
- Forgetting that both charges exist on the same molecule—unlike a simple salt.
- Mixing up zwitterion with amphoteric substances, which only means a compound can react as an acid or base, not that it has both charges at once.
- Not mentioning that zwitterions are involved in protein structures and biological processes.
Uses of Zwitterion in Real Life
Zwitterions are used in many fields. Amino acids, the building blocks of proteins, exist as zwitterions in our bodies at physiological pH. Zwitterionic surfactants and polymers are used to make anti-fouling coatings, drug delivery systems, and medical implants.
Their unique charge properties make them important in buffer solutions and in the separation of proteins using techniques like electrophoresis.
Relation with Other Chemistry Concepts
Zwitterion is closely related to topics such as Amino Acids and Acid-Base Reactions, helping students build a conceptual bridge between various chapters. Understanding zwitterions also supports learning about chemical equilibrium and isoelectric point.
Step-by-Step Reaction Example
1. Place glycine (NH2–CH2–COOH) in water.2. The amino group (NH2) accepts a proton (H+) and becomes NH3+.
3. The carboxyl group (COOH) loses a proton and becomes COO−.
4. Final structure: NH3+–CH2–COO−. This is the zwitterion form of glycine.
Lab or Experimental Tips
Remember zwitterion by the rule of “internal salt”: within one molecule, a proton transfer creates both a positive and a negative charge. Vedantu educators often use this analogy in live classes for easy recall.
Try This Yourself
- Draw the zwitterion structure of alanine at pH 7.
- Explain why all amino acids (except glycine) are chiral zwitterions.
- List two industrial uses of zwitterionic polymers.
Final Wrap-Up
We explored zwitterion—its structure, formation, real-life uses, and how it connects to your chemistry fundamentals. For more expert guidance and exam strategies, check lesson notes and live sessions at Vedantu.
FAQs on Zwitterion: Meaning, Structure, and Examples
1. What is a zwitterion in Chemistry?
A zwitterion is a neutral molecule that contains both a positive and a negative charge simultaneously on different atoms. For example:
- In amino acids, the amino group is protonated (+NH3+) and the carboxyl group is deprotonated (–COO–).
- Zwitterions are also called dipolar ions or inner salts.
2. Is a zwitterion positive or negative?
Zwitterions are overall electrically neutral because their positive and negative charges are balanced.
- They have equal but opposite charges at different sites.
- The molecule carries both, but their sum is zero.
3. What are some examples of zwitterions?
Common examples of zwitterions include:
- Amino acids (such as glycine, alanine) at physiological pH
- Sarcosine
- Bicine
- Zwitterionic surfactants and buffers
4. How does a zwitterion form from an amino acid?
Amino acids form zwitterions by internal proton transfer:
- The carboxylic acid group donates a proton (H+) to the amino group.
- This creates a negatively charged carboxylate (–COO–) and a positively charged ammonium group (+NH3+).
- This structure exists at pH near the isoelectric point.
5. What is the difference between a zwitterion and an amphoteric compound?
Zwitterion:
- Has both positive and negative charges within the same molecule at the same time.
- Example: Glycine in water at neutral pH.
- Can act as both an acid and a base (may or may not have both charges at once).
- Example: Water (H2O).
6. What is the significance of the isoelectric point for zwitterions?
The isoelectric point (pI) is the pH at which a molecule like an amino acid exists mainly as a zwitterion.
- At pI, the molecule has no net charge.
- It is least soluble in water and does not migrate in an electric field.
7. Are all amino acids zwitterionic in nature?
Most amino acids exist as zwitterions at physiological pH (around 7), except when in very acidic or basic environments.
- All standard α-amino acids can form zwitterions in aqueous solution.
8. Why are zwitterions soluble in water but not in non-polar solvents?
Zwitterions dissolve well in water due to their ionic nature:
- The positive and negative charges interact strongly with polar water molecules (hydrogen bonding & ion-dipole interactions).
- They are poorly soluble in non-polar solvents where such interactions are absent.
9. Can zwitterions act as buffers in biological systems?
Yes, zwitterions can help buffer solutions by accepting or donating protons.
- Amino acids and proteins act as buffers near their isoelectric points.
- This maintains a stable pH in biological fluids.
10. How do zwitterions affect protein structure and function?
Zwitterionic regions in amino acids facilitate protein folding and stability:
- They enable charged interactions (salt bridges) within and between protein chains.
- This impacts solubility, enzyme activity, and biological function.
11. Do zwitterions exist in crystals, liquids, or gases?
Zwitterions are most stable and observable in solid (crystalline) and aqueous (solution) states.
- In solids, many amino acids crystallize as zwitterions.
- In solution, zwitterion formation is favored at suitable pH.
- In the gas phase, zwitterionic forms are rare and unstable.
12. What is the structure of a glycine zwitterion?
Glycine zwitterion has the following structure:
NH3+—CH2—COO–
- Nitrogen bears a positive charge; carboxyl oxygen bears a negative charge.
- This structure is common for amino acids in water.
