4. Acquisition

Time requirement: 2.5 h Sample: Recrystallize 300 mg normal glycine and 30 mg 2-¹³C,¹⁵N-glycine from wa- For the experiment a triple-resonance solid-state probe-head tuned to ¹H, ¹³C and ¹⁵N is required and must be equipped with the corresponding r-f. filters in all three channels. Powder the sample finely and fill a solid-state rotor. Spin the sample at 5.5 kHz at the magic angle and carefully control the spinning during the whole experiment. It is for the evaluation essential that the spinning speed is stable and exactly known. The pulse duration on the third channel must be determined before the experiment, and it is best to use a 1D REDOR experiment to determine the most effective 180° ¹⁵N pulse. The experiment is run as a pseudo.2D sequence, where instead of t, the loop parameter nis increased from | to 3, 5, 7... You have to set:

td2: 3992 data points in F (¹³C) tdl: 128 data points for the REDOR decay sw2: 331 ppm o1: on resonance of the 2-¹³C signal of glycine [48 ppm] o2: middle of ¹H NMR spectrum [4 ppm] 03: on resonance of ¹⁵N signal of glycine [37 ppm] p1: 90° ¹H decoupler pulse [2.4 μs, 3 dB] p2: shaped ¹H decoupler pulse, ramp starting at 100% and ending at 50% [3 ms, 6 dB] p3: ¹³C spin-lock transmitter pulse [3 ms, –3 dB] p4: ¹³C 180° transmitter pulse [7.2 μs, -3 dB] p5, p6: 180° ¹⁵N decoupler pulse [8 μs, -2 dB] MAS spinning speed 5500 Hz dl: 4s d2: 1/[4-MAS] = 45.45 μs d3: 1/[4-MAS] – p5/2 = 41.45 μs decoupler attenuation for high-power tppm15 decoupling [3 dB] rg: receiver gain for correct ADC input Repeat the experiment under exactly the same conditions, but with the attenuation for the “¹⁵N decoupler pulses set to 120 dB. This repetition was done here in an interleaved mode; thus for any REDOR loop one FID with and one without ¹⁵N pulses were re- corded directly after each other.