It turns out that this means that the relaxation rate of nuclear magnetization is affected by the orientation of bonds, e.g. NH or CH, relative to the various axes of rotation. If the bond points along an axis about which tumbling is rapid the relaxation is slower than if it points along a slow tumbling axis. Such relaxation rate data provide valuable extra restraints for structural calculations. Recently other groups have shown that this type of orientation may be better achieved using liquid crystalline solutions. A second orientational effect may also be used.
Some molecules adopt a preferred orientation in a magnetic field.
An NMR experiment may be used to monitor the orientation of the NH and CH bonds in a protein with respect to the magnetic field and provide further long range restraints. These effects are more pronounced at high magnetic field and will benefit from the new 800 MHz machine. We are collaborating with the DuPont Pharmaceutical Company and James Keeler of the Chemistry Department in Cambridge. Daniel Nietlispach and Katherine Stott are working on these projects in the Department of Biochemistry.