Figure 2. DQDRAWS and REDOR characterization of statherin structure on HAP. The left panel displays the results of the DQDRAWS experiment to measure the backbone angle phi at the pS-pS position. The filled diamonds are data on the hydrated sample, the open diamonds are for the same sample that was subsequently lyophilized, and the dotted line is a simulated data fit to 45% -helix and 55% ß-sheet. The data were taken at room temperature on a 500-MHz home-built spectrometer with a 4-kHz spinning speed, a 34-kHz ¹³C RF field, and 100-kHz proton decoupling. The REDOR experiment shown in the right panel was performed on a Chemagnetics Infinity 300 spectrometer at a spinning speed of 4 kHz, a 43-kHz ¹³C RF field, a 45-kHz ¹⁵N RF field, XY8 phase cycling on both channels, and 70-kHz decoupling. Measurements on the hydrated samples were done at -25°C to remove any motions on the timescale of the REDOR experiment (as verified by T₁ relaxation measurements). The solid lines represent fits to distances of 4.2 Å for the hydrated sample and 5.2 Å for the sample that was lyophilized after adsorption in buffered solution. The dotted lines are fits to 5.2 Å and 45% -helix, 55% ß-sheet.