Exploring the complex map of insulin polymorphism: a novel crystalline form in the presence of m‐cresol

In this study, the first crystal structure of a novel crystal form of human insulin bound to meta‐cresol in an acidic environment is reported. The combination of single‐crystal and powder X‐ray diffraction crystallography led to the detection of a previously unknown monoclinic phase (P21). The structure was identified from the powder patterns and was solved using single‐crystal diffraction data at 2.2 Å resolution. The unit‐cell parameters at pH 6.1 are a = 47.66, b = 70.36, c = 84.75 Å, β = 105.21°. The structure consists of two insulin hexamers per asymmetric unit. The potential use of this insulin form in microcrystalline drugs is discussed. A novel monoclinic phase of human insulin co‐crystallized with m‐cresol was structurally characterized by means of powder and single‐crystal X‐ray diffraction.