4. Acquisition

Time requirement: 11h Sample: 2 mmol sucrose in 90% H,0/10% D₂O + 0.5 mmol DSS (2,2-dimethyl-2- silapentan-5-sulfonate, sodium salt) including a trace of NaNO; against bacteria growth.

The probe-head must be tuned to the water sample. Record a normal ¹H NMR spectrum and redetermine the 90° pulse. Record a 1D spectrum with water presaturation and optimize the transmitter power for presaturation (Exp. 6.18). Change to the 2D mode of the spectrometer software and load the pulse program for phase-sensitive double-quantum COSY with presaturation. You have to set:

td2: 2 k data points in F, td1: 256 data points in F;

sw2: 10 ppm swl: 10 ppm o1: on resonance of water signal p1: 2 s at transmitter attenuation corresponding to 7B, ~ 25 Hz, 90° pulse = 10 ms, typically 65 dB, see Experiments 2.9 and 6.18 p2, p3, p4: 90° ¹H transmitter pulse dl: 30 ms initial value for ¢1 evolution: 3 μs increment for ¢1 evolution: 1/[2-sw1]

5. Processing

Apply zero-filling in F, to 1 k real data points to obtain a symmetrical matrix of 1024x1024 real points. Use a Gaussian window in both dimensions. Apply real Fourier transformation corresponding to the TPPI mode of data acquisition in F.

6. Result

The figure shows an expansion of the DQF-COSY spectrum obtained on an AMX-500 spectrometer. Note that the water signal of the 1D spectrum, which was obtained by applying presaturation, is much larger than the residual water signal in the 2D spectrum. At the contour level chosen, the cross-peak of the anomeric proton at 54 = 5.41 can be seen only in the upper left part of the matrix.