Sensitivity in reduced diameter tubes

Sensitivity is the bane of NMR. Spectroscopists are always looking for ways of increasing it, particularly when sample is limited. One suggested method to increase sensitivity is to reduce the volume while keeping the amount of material constant, thereby increasing the concentration. This can be done by using a smaller diameter NMR tube, e.g a 3 mm or 1.7 mm tube. I have been skeptical of this method for a long time and finally decided to test how well it works.

Binding: Saturation Transfer Difference

One of the strengths of NMR is the variety of methods that have been developed to understand different aspects of molecular interactions. The previous post discussed the waterLOGSY experiment, which identifies small molecules that bind to larger molecules. The saturation transfer difference experiment is another method that identifies molecules that bind another, but it relies on a different mechanism than the waterLOGSY experiment and so is often useful in different situations.

Binding: the waterLOGSY experiment

NMR is one of the best methods for studying molecular interactions. To identify small molecules that bind to macromolecules many different experiments can be used, one of which is the waterLOGSY experiment. This is a 1D, ¹H-detected experiment that can be run in five minutes and is best suited for weakly interacting complexes (mM K_Ds), a binding regime that is difficult to probe by other techniques. To demonstrate how it works I will show spectra of a mixture of L-tryptophan and D-sucrose in the presence and absence of bovine serum albumin.