Fast mixing device inside a nuclear magnetic resonance magnet: A tool for observing early steps in protein folding

We describe a device designed to perform a fast mixing of two solutions ins ide the magnet of a nuclear magnetic resonance (NMR) spectrometer. The appa ratus is totally nonmagnetic; it operates via a system of pneumatic valves, which drives a syringe to inject the first solution into the NMR tube that already contains the other solution. An important point is that before and after the injection, the solution in the NMR tube is free of any perturbin g injecting device. The injection is controlled by the spectrometer softwar e in the NMR pulse sequence. Simple experiments have been performed to asse ss the viability of the device, and evaluate the dead time after injection, as well as the loss of homogeneity and the mixing capabilities. The device described can mix up to 200 mu l of solution with the solution already pre sent in the NMR tube in less than 50 ms, with a negligible loss of homogene ity during injection. The device was specifically designed for protein fold ing studies but can find a general purpose for chemical reactions involving small amounts of compounds. (C) 2000 American Institute of Physics. [S0034 -6748(00)05305-3].