Acid–base chemistry of amino acids — Molecules bearing both a positive and a negative charge on different functional groups at the same time are called what?

Introduction / Context:
At physiological pH, amino acids commonly exist as internal salts in which the amino group is protonated (positive) and the carboxyl group is deprotonated (negative). This dipolar state is essential for solubility, isoelectric behavior, and electrophoretic mobility.

Given Data / Assumptions:

• We are naming molecules with simultaneous positive and negative charges.
• Standard biochemical terminology is expected.
• Examples include free amino acids in aqueous solution near neutral pH.

Concept / Approach:
The term “zwitterion” (from German “Zwitter,” meaning hybrid) precisely describes molecules with both charges. Amino acids, betaines, and certain phospholipids often exist in zwitterionic forms, especially around their isoelectric point where the net charge is zero but internal charges are present.

Step-by-Step Solution:

Verification / Alternative check:
Electrophoresis and titration curves demonstrate amino acids behaving as dipolar ions near their pI, reinforcing the zwitterion concept.

Why Other Options Are Wrong:

• Ambions / amphions: nonstandard or obsolete terms; not accepted modern nomenclature.
• Ion conversion: not a molecular class; refers to a process, not a species.

Common Pitfalls:
Assuming “no net charge” means “uncharged.” Zwitterions have charges that cancel overall but strongly affect solvation and reactivity.

Final Answer:
zwitterions