Sandwich-ELISE NMR: Reducing the sample volume of NMR samples

We present Sandwich-ELISE, a concatenated version of our previously proposed Experimental LIquid SEaling (ELISE) protocol, in which an aqueous sample is effectively sealed by the addition of a small layer of mineral oil, or, alternatively, a chloroform sample was sealed by a water layer. With Sandwich-ELISE, a triple layered geometry composed of deuterated chloroform/aqueous buffer/mineral oil can be used to limit the sample to the active coil volume, effectively replacing the popular Shigemi tubes. Importantly, this procedure is readily applicable to smaller diameter tubes, for which no Shigemi tubes are available. We further present spectra of a 1 μl protein sample sandwiched between the chloroform and Nujol phases in a 1 mm tube, demonstrating thereby that the volume of the aqueous phase of interest can be reduced even further.