A spectrum of molecular size

Small molecules are generally low-molecular-weight organic compounds. Peptides are chains of amino acids, while proteins are typically larger, more structurally complex amino-acid polymers. The boundaries can overlap, but the categories are useful for experimental planning.

Structure affects handling

Peptides and proteins may be sensitive to heat, moisture, oxidation, adsorption or agitation. Small molecules can present different solubility and stability challenges. Appropriate storage and analytical methods therefore depend on the specific material rather than the category name alone.

Choose methods that fit the molecule

Chromatography, mass spectrometry, spectroscopy and biological assays contribute different information. Researchers should select methods based on molecular properties and the question being investigated.