Structural studies of human insulin cocrystallized with phenol or resorcinol via powder diffraction

The effects of the ligands phenol and resorcinol on the crystallization of human insulin have been investigated as a function of pH. Powder diffraction data were used to characterize several distinct polymorphic forms. A previously unknown polymorph with monoclinic symmetry (P2₁) was identified for both types of ligand with similar characteristics [the unit-cell parameters for the insulin–resorcinol complex were a = 114.0228 (8), b = 335.43 (3), c = 49.211 (6) Å, β = 101.531 (8)°].