{H1}P31 Experiment

P31 is a senstive nucleus to detect. At natural abundance (~100%), P31 has a relative sensitivity of 6.7% of that of H1 compared to 0.017% for C13. For P31-containing compounds, 1D P31 spectra can be collected with or without H1 decoupling. By comparing the two spectra, H1 coupled P31 peaks can be identified. H1 decoupling can be done either with a broadband decoupling scheme (to cover multiple H1 peaks) or with a weak power to decouple one or a group of H1 peaks at a time. For high-resolution P31 spectrum when the acquisition (and decoupling) time is long (>1 sec), selective H1 decoupling with weak power is preferred in order to minimize probe and sample heating.

P31's has a wide chemical shift range (roughly +/-200 ppm). For P31 chemical shift tables, refer to the following online pages:

• reference 1
• reference 2

P31 Referencing

1. For accurate P31 referencing, add TMS or DSS (in aqueous solution) to your deuterated solvent. Use 1H signal from TMS or DSS for 0.0ppm reference and P31 is indirectly referenced (relative to 85% H₃PO₄)) according to IUPAC standard .
2. For rough referencing with the lock signal, simply type setref.
3. For traditional referencing with a separate 85% H3PO4 sample: Make another sample with the same solvent (deuterated) and volume as your your actual sample with the compound. Lock and shim with this sample first. Then, turn the lock off (lock status shown as OFF) and load the H3PO4 sample. Collect a quick P31 spectrum and reference the signal to 0ppm. Next, load your compound sample, keep lock off and collect data.

Pulse sequence

Procedure (on NMR500 with SWP)

Step 1: Lock and shim

• Temperature should be regulated for best results (default on NMR500)
• Optional: Spin should be turned off for best stability, unless better linewidth with spinning is desired.
• Join exp1 (jexp1, or another exp #). Type init1h to load standard 1H parameters and shims
• Adjust solvent setting
• Lock and shim Z1, Z2. Adjust X1 and Y1 a bit if spin is turned off, and re-shim Z1 and Z2.
• Lock sample at ~ 70-80%.
• Check 1H channel tuning

Step 2: Optional: collect H1 spectrum without P31 decoupling

• Collect a standard 1H spectrum with nt=1 (or nt=4 for cleaner spectrum)
• Put the box cursor to enclose the signal region and to include ~10% flat baseline area at both ends. Type movesw.
• Collect another 1H spectrum with the new setting. Phase and reference the spectrum carefully.
• If you have TMS or DSS in the sample (recommended), reference the 1H peak to 0.0ppm. P31 spectrum will be indirectly referenced later.

Step 3: Load parameters and tune X-channel for P31

• Join exp2 (or another experiment #) with jexp2.
• Type setexp('P31_H1dec')
• Type su
• Tune probe X-channel for P31
• Insert tuning stick (labeled 13T) to bottom of probe for P31
• Use the broadband side of probe and output cables to tune channel 1 for P31
• Replace the default 1/4-wavelength cable (for C13) with one for P31 covering its frequency of 202.35Mhz.

Step 4: Set and submit experiment

• Readjust Z1 and Z2 after cabling change.
• The default setting is for two arrayed experiments, one without 1H decoupling and one with decoupling.
• If you only want to do the experiment with H1 decoupling, type dm='nny'.
• Type nt=1000 go (or other large nt). The two spectra are run in interleaved mode every 4 scans by default (il='y'). Stop the experiment when signal is good.
• The default center of P31 is ~10ppm, spectral width sw=60000 (~300ppm). Once P31 peaks are identified, the center and spectral window should be adjusted.
• To change the center and width of the P31 spectrum, use box cursor to enclose peak region and type movesw. Keep sw a minimal of 4000Hz.
• To reference the spectrum
• Type setref to use the lock signal (if locked to correct solvent) for rough referencing
• If 1H spectrum is available with TMS or DSS as reference from Step 2, type mref(1,2)

Step 5: Processing

• As in most experiments, click Process->Autoprocess to use vnmrJ's autoprocessing feature during or after experiment.
• For manual processing:
• After the 1st array element (reference) is done, type wft aph f full. Manually adjust phase and zoom/expand if necessary.
• Type dssa dscale to show arrayed spectra vertically. Type vs=vs*0.5 dssa dscale to shrink peaks by half.
• To display any one of the arrayed spectra, type ds(#) f full where # is the index number of the element (1,2, 3 .. etc.)

Step 6: Finishing up: tune probe X-channel to C13 and recable

• Insert the 100% cdcl3 "Idle" sample.
• Type tn='C13' su
• Tune probe X-channel (as channel 1) to C13
• Reconnect the two square filters back to the broadband preamp
• Connect the X-channel probe cable to the end of the filters
• Replace the 1/4-wavelength cable with the default cable for C13

Examples

Sample #1: 1% CH3I (99% C13-labeled) + 1% trimethyl phosphite in cdcl3 Data collected in Dec 2010

Bottom: H1-coupled P31 spectrum CH3I reacts with trimethyl phosphite to form (CH3)P(=O)(OCH3)2 with the P31 direct bonded CH3 partially 13C labeled. A P31 multiplet peak around 33ppm is broadened by J-coupling to C13 and H1. Top: H1-decoupled P31 spectrum H1 decoupling collapses the broad P31 multiplet into three sharp peaks: two outer peaks from P31 bonded to 13CH3 and the center one from P31 bonded to 12CH3.

Sample #2: 0.0485M Triphenyl phosphate in cdcl3 Data collected in Dec 2010 P31 couples to H1's in phenyl ring.

Bottom: H1-coupled P31 spectrum Top: H1-decouped P31 spectrum

H. Zhou updated Dec 2010