Sample Preparations, Observations and Quantifications by HR MAS NMR

We have addressed in our laboratory several aspects of the more rapid and robust identification of resin-bound entities. Firstly, related to the question of sensitivity and sample preparation, how much of a resin do we really need to obtain workable spectra in a given time lapse of 1 minute, and what is the optimal sample preparation procedure Whereas we and others in the early stages prepared the sample by swelling the resin in a separate recipient, and transferring part of the slurry into the rotor by a specially machined spatula, we later found out that swelling the resin beads directly into the rotor led in a faster and more economic way (less resin and deuterated solvent is needed) to more reprodu- 

75 ppm led to a loss of signal intensity only for the amide proton of the second-last amino acid (8.26 ppm). Water seems therefore sequestered near the free N terminus, while still communicating with the last two amino acids. We even observed an exchange crosspeak between water and the second-last amino acid amide proton in NOESY spectra. This is especially interesting since amide bond formation in peptide synthesis is done by activated esters and anhydrides, which are sensitive to moisture, and illustrates the gain of information by the analysis of polymer-bound structures by HR MAS NMR. 

---