Valence controls crucial properties of molecules and materials, including their bonding, crystal structure, and electronic and magnetic properties.

Four decades ago, a class of materials called “mixed valence” compounds was discovered. Many of these compounds contain elements near the bottom of the periodic table, so-called “rare-earth” elements, whose valence was discovered to vary with changes in temperature in some cases. Materials comprising these elements can display unusual properties, such as exotic superconductivity and unusual magnetism.

Integral membrane proteins, or IMPs, are a major class of proteins that play crucial roles in many cellular processes, including the catalysis of disulfide bonds, which are essential for the function and stability of many proteins such as antibodies, which have significant therapeutic potential.

But IMPs are intrinsically hydrophobic and thus have low solubility in watery environments. Their natural environment is within the lipid bilayer membrane of a cell, which makes it difficult to study their structure and function.