Z

Zwitterion

Quick Reference
Also Known AsInner salt, dipolar ion, amphoteric ion, amino acid neutral form

What is Zwitterion?

A zwitterion (also called an inner salt or dipolar ion) is a molecule that has both a positive and a negative electrical charge simultaneously, but is electrically neutral overall. Amino acids in their neutral form (at pH near their isoelectric point) exist as zwitterions — the carboxyl group loses a proton (−COO⁻) and the amino group gains a proton (−NH₃⁺). The term comes from the German "Zwitter" meaning hybrid or hermaphrodite.

Properties & Characteristics

Simultaneously carries + and − charges. Net charge = 0. Amino acid zwitterion at isoelectric point (pI): +H₃N-CHR-COO⁻. pI = (pKa₁ + pKa₂)/2. Below pI: cation (+H₃N-CHR-COOH). Above pI: anion (H₂N-CHR-COO⁻). High dipole moment. Good solubility in water (charge solvation). Insoluble in organic solvents.

Uses & Applications

Amino acid chemistry and protein structure. Isoelectric focusing (protein separation). Buffer solutions near pI. Understanding protein solubility and precipitation. Biological membrane zwitterionic lipids (phosphatidylcholine). Pharmaceutical formulation. Amphoteric surfactants (betaines).

Safety Information

Amino acids as zwitterions are biologically essential and non-toxic. Zwitterionic surfactants (betaines): low irritation profile. Safety depends on specific zwitterion.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Zwitterion
Synonyms Inner salt, dipolar ion, amphoteric ion, amino acid neutral form

Frequently Asked Questions

A zwitterion (also called an inner salt or dipolar ion) is a molecule that has both a positive and a negative electrical charge simultaneously, but is electrically neutral overall. Amino acids in their neutral form (at pH near their isoelectric point) exist as zwitterions — the carboxyl group loses a proton (−COO⁻) and the amino group gains a proton (−NH₃⁺). The term comes from the German "Zwitter" meaning hybrid or hermaphrodite.

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