PPT Slide

1D-1H-NMR spectrum of a protein in water (95% H2O / 5%D2O)

The shown spectrum has roughly a signal to noise ratio of 250 : 1. Although we can do better (with modern spectrometers 3000:1 and more) , the intense water signal will dominate the spectrum, and signal of interest will not be visible, i.e. covered by the tails/flanks of water or by the noise.

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The first problem encountered in biological NMR spectroscopy concerns the native solvent: WATER.

The most informative nucleus is 1H (proton), however, water contains protons! In particular, solvent protons have a significantly higher concentration than the solutes. For a typical protein/DNA -sample that means: the protons of interest /the protein sample, are about 0.5 to 2 mM in concentration, water however, is 55M = 110 M in 1H. This water signal dominates the entire spectrum (10000 fold excess!); sample peaks are not or only barely visible.