Extremophiles produce
macromolecules which inhibit ice recrystallization,
but there is increasing interest in discovering and developing small
molecules that can modulate ice growth. Realizing their potential
requires an understanding of how these molecules function at the atomistic
level. Here, we report the discovery that the amino acid
l
-α-alanine demonstrates ice recrystallization inhibition (IRI)
activity, functioning at 100 mM (∼10 mg/mL). We combined experimental
assays with molecular simulations to investigate this IRI agent, drawing
comparison to β-alanine, an isomer of
l
-α-alanine
which displays no IRI activity. We found that the difference in the
IRI activity of these molecules does not originate from their ice
binding affinity, but from their capacity to (not) become overgrown,
dictated by the degree of structural (in)compatibility within the
growing ice lattice. These findings shed new light on the microscopic
mechanisms of small molecule cryoprotectants, particularly in terms
of their molecular structure and overgrowth by ice.