<title>Effect of a strong magnetic field on protein crystal growth</title>

Abstract

Recently, a superconducting magnet has been used to obtain better quality protein crystals. It is possible to reduce effective gravity and damp natural convection by applying a vertical magnetic field gradient to cause an upward magnetization (Kelvin) force. When protein crystals (snake muscle fructose-1,6-bisphosphatase) were formed in 0.7-0.8 g, their resolutions of X-ray diffraction were improved by 30% compared with those formed outside the magnet. On the other hand, in a uniform field of 10 T which did not cause an upward force, the improvement of the quality of orthorhombic lysozyme crystals was found. In this paper, besides through the upward magnetization force, we studied how a strong magnetic field damps natural convection and influences the crystal quality. First, we discussed the damping of natural convection by Lorentz force, and concluded it almost negligible because Hartman number is about 3.5 for the typical protein crystal formation experiments. Second, we studied the magnetic effect on the viscosity of protein solutions and found that the viscosity increases under 10 T when the solution contains suspended small crystals. Numerical simulations showed that the viscosity increase causes the damping of natural convection during protein crystal growth. Furthermore, the effect of magnetic orientation of suspended crystals on the crystal quality was also discussed. These types of magnetic effect will occur both in gradient and uniform magnetic fields. If we use these kinds of magnetic effects efficiently, it will be possible to improve the crystal quality.