New morphology, symmetry, orientation and perfection of lysozyme crystals grown in a magnetic field when paramagnetic salts (NiCl₂, CoCl₂ and MnCl₂) are used as crystallizing agents

Chlorides with different paramagnetic cations such as Ni²⁺, Co²⁺ and Mn²⁺ were used as crystallizing agents instead of NaCl to crystallize hen egg-white lysozyme. NiCl₂ was found to give two types of crystals with different morphologies: one (roof-like) is a new type of orthorhombic P2₁2₁2₁ crystal with lattice constants a = 79.0 Å, b = 80.8 Å, and c = 37.5 Å; the second is an ordinary tetragonal crystal of its characteristic shape with a = b = 80 Å and c = 38 Å. The appearance of the roof-like shape became dominant in the presence of a magnetic field. In the case of using CoCl₂ and MnCl₂, ordinary tetragonal crystals were formed. A striking fact was that the a-axis of the crystals oriented along the magnetic field when CoCl₂ was used, as opposed to the usual c-axis orientation. Large and optically perfect lysozyme crystals can be obtained in a magnetic field when NiCl₂ or MnCl₂ is used as a crystallizing agent. These profound effects of the paramagnetic cations may be caused by the coordination of Ni²⁺ and Co²⁺ ions to a lysozyme molecule, which was found by X-ray crystallography.