The result is a shift in the temperature of maximum density to lower temperatures. At high enough pressures the density maximum is shifted to below 0 °C (at just over MPa). Above MPa it cannot be observed above the melting point (now at K), except in supercooled water [ 1860 ], and it cannot be observed at all above about 200 MPa where it encounters the homogeneous nucleation limit. The stronger and more linear hydrogen bonding in D 2 O gives rise to a 25% smaller shift in the temperature of maximum density (from °C at MPa) with respect to increasing pressure [ 726 ].
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Solvent suppression is needed when the solvent contains non-deuterated proton atoms, because the solvent signal could be over 1000 times stronger comparing to other signals of interest. It is a common technique for protein NMR since protein samples usually dissolve in 90%H2O/10%D2O solution instead of 100% D2O in order to investigate exchangble protons such as amide groups. In this case water suppression is absolutely necessary. On the other hand, the introduction of cold probes brings 3-4 times sensitivity gain over room temperature probes. Although it is great for some precious dilute samples, solvent suppression becomes more difficult with cold probes.