Amorphous aggregates with a very wide size distribution play a central role in crystal nucleation.

There is mounting evidence that crystal nucleation from supersaturated solution involves the formation and reorganization of prenucleation clusters, contradicting classical nucleation theory. One of the key unresolved issues pertains to the origin, composition, and structure of these clusters. Here, a range of amino acids and peptides is investigated using light scattering, mass spectrometry, and terahertz Raman spectroscopy, showing that the presence of amorphous aggregates is a general phenomenon in supersaturated solutions.