NCA

Experiment Details

Dimensions = 2

Isotope labeling required = ¹³C and ¹⁵N

Magnetization transfer = magnetization originates on ¹H and is transferred to ¹⁵N, via cross polarization and then is transferred to ¹³C nuclei through specific CP.

Chemical shift evolves on ¹⁵N and detected on ¹³C.

Image courtesy: www.protein-nmr.org.uk/

Pulse program: hNCa.dcp

Parameters:

F1, C and F2, H and F3, N

p1: C 90 at pl1

p2: C 180 at pl1

p3: H 90 at pl2

p16: NCa CP at pl5 (f3,N), sp50 (f1,C), pl33 (f2,H)

p25: HN CP at sp43 (f3,N) and sp42 (f2,H)

pl1: C pulse power

pl2: H pulse power

pl5: N NCa CP power

pl12: H dec power

pl33: H dec power during NCa CP

sp42: H HN CP power

sp43: N HN CP power

sp50: C NCa CP power

d0: incremented delay (t1)

d1: recycle delay; 1 to 5 times T1

d30: extra time for constant duty cycle

pcpd2: H dec pulse cpdprg2

cpdprg2: Decoupling file cw, tppm (at pl12)

spnam42: H ramp use e.g. ramp.10070 for variable amplitude CP

spnam43: N ramp use e.g. square.100 for square pulse CP

spnam50: CA ramp use e.g. tcn for amplitude modulated tangential pulse CP

cnst10: Frequency reset to Carrier (o1, usually ~100 ppm)

cnst22: Frequency offset for CA (~55 ppm)

cnst30: expected td1 for use in constant duty cycle (-DCDC)

cnst31: MAS rotation rate in Hz

inf1: 1/SW(N) = 2 * DW(N)

in0 : = inf1

in30: = inf1

l0 : loopcounter for F1

ZGOPTNS : -DCDC : for constant duty cycle or blank

FnMODE: TPPI, States or States-TPPI

ns: MIN. 4 (full:8)

Comment on key optimization:

parmode = 2D; p2 = 2*p1; p22 = 2*p21; o1p = '55'; cnst22 = '55'; o2p = '3'; o3p = '115'; ZGOPTNS = '-DCDC' for constant duty cycle

Example spectrum of GB1: Recorded with a 3.2 mm rotor with MAS @ 17587 Hz.

The spectrum gives ¹⁵N -¹³C correlation.

References:

1. M. Baldus, A.T. Petkova, J. Herzfeld and R.G. Griffin (1998) Mol. Phys. 95 1197-1207.

2. J. Lewandowski, G. De Pape, and R. G. Griffin; J Am Chem Soc. 129(4): 728-29.