核磁共振

　　几种常用核磁共振NMR实验的基本参数:

　　General information

　　SENSITIVITY

　　Higher field gives better S/N, so 600>500 > >400>300 MHz

　　Probes optimized for a particular nucleus give the best S/N for that nucleus. The TXI-500 is an indirect detection probe and is thus most sensitive to proton. The most commonly used probes are QNP-500 and QNP-400. The QNP(Quattro Nuclear Probe) has 4 channels for running 1H, 13C, 19F and 31P. Other probes are also available.

　　RESOLUTION and DISPERSION

　　Higher field spreads out the signal better, makes coupling patterns simpler, separates different signals better. Again, 600>500 > 400>300 MHz.

　　Linewidths in Hz are similar whatever the field, so the linewidths in ppm are smaller at the higher field strengths, unless a frequency-dependent line broadening mechanism interferes.

　　Proton-detected experiments

　　Availability

　　H1 experiments are available on all instruments.

　　1D Proton experiment

　　Default Parameters

　　~2 second acquisition time

　　~1.5 second relaxation delay

　　Spectral width -2ppm to 18ppm

　　16 scans

　　Total time: 1 minute

　　Variations on the 1D experiment include

　　1D NOE or selective NOE (difference or gradient)

　　1D COSY or Selective COSY (gradient)

　　T1 determination

　　Recommended Concentration

　　> 0.1mM

　　COSY - Proton-proton correlation experiment

　　Gives information about pairs of protons that are J-coupled. This usually indicates that the protons are on adjacent carbons, e.g., 3-bonds away (though protons further apart may in some cases be J-coupled).

　　Default Parameters

　　1.5 second relaxation delay

　　512 complex points in t2 and 192 increments in t1

　　4 scans per increment (no PFG) / 1 scan per increment (PFG)

　　Total time: 20 minutes (no PFG) / 5 minutes (PFG)

　　Recommended Concentration

　　> 10mM

　　Variations on COSY

　　DQF-COSY

　　phase-sensitive experiment

　　diagonal peaks are narrower

　　less-sensitive

　　TOCSY - total correlation spectroscopy

　　gives correlations for all protons within a spin system

　　NOESY - Proton-proton through-space interactions via NOE

　　Gives information about pairs of protons that are close in space (<5 A apart)

　　Default Parameters

　　1.5 second relaxation delay

　　1024 complex points in t2 and 256 increments in t1

　　2-8 scans per increment

　　Total time: 1 - 5 hours.

　　Recommended Concentration

　　> 10mM

　　ROESY - rotating frame NOE

　　Compounds of molecular weight ~1000-2000

　　Exchange peaks are opposite sign from NOE peaks

　　HMQC - Heteronuclear Multiple Quantum Correlation experiment

　　Gives information about strong proton-carbon J-couplings. A strong proton-carbon J-coupling indicates that the proton is directly bonded to the carbon. This experiment gives information that is identical to HETCOR, but because it is proton-detected, it is more sensitive than the standard HETCOR especially on indirect-detection probes.

　　Default Parameters

　　1.5 second relaxation delay

　　512 complex points in t2 and 192 increments in t1

　　4 scans per increment (no Pulsed Field Gradient) / 1 scan per increment (PFG)

　　Total time: 20 minutes (no PFG) / 5 minutes (PFG)

　　Recommended Concentration

　　> 50mM

　　HMBC - Heteronuclear Multiple Bond Correlation experiment

　　Gives information about weak proton-carbon J-couplings. A weak proton-carbon J-coupling indicates that the proton is two, three, or four bonds away from the carbon. This experiment gives information about which protons are near to (but not directly bonded to) different carbons. This experiment (in conjunction with the HMQC) can give an enormous amount of information about molecular structure, since the long range proton-carbon correlations can include quaternary carbons, in addition to protonated carbons.

　　Default Parameters

　　1.5 second relaxation delay

　　512 complex points in t2 and 192 increments in t1

　　4 scans per increment (no PFG) / 4 scan per increment (PFG)

　　Total time: 20 minutes (no PFG) / 20 minutes (PFG) (NOTE: PFG HMBC experiments usually have less t1 noise than non-PFG HMBC experiments.)

　　Recommended Concentration

　　> 50mM

　　Carbon-detected experiments

　　General

　　Availability

　　Probes optimized for X-nuclei give better S/N. The direct detection probes are either QNP or Broadband Observe.

　　Sensitivity is approximately 5700 times less than for proton, so adequate S/N for a reasonable length experiment (10 minutes, 256 scans) requires a concentration of > 100mM.

　　1D Carbon experiment

　　Default Parameters

　　0.8 second acquisition time with proton decoupling

　　2.0 second relaxation delay (with NOE enhancement)

　　Spectral width -10ppm to 225ppm

　　1024-256 scans

　　1 hour

　　Recommended Concentration

　　> 100mM

　　Special Considerations

　　Increase d1 for carbons with long T1's (quaternary, carbonyls)

　　DEPT experiment

　　Gives information about the number of protons bonded to each carbon.

　　Default Parameters

　　0.8 second acquisition time with proton decoupling

　　2.0 second relaxation delay (with NOE enhancement)

　　Spectral width -10ppm to 225ppm

　　96 scans per spectrum (2 spectra total)

　　Total time: 10 minute

　　Recommended Concentration

　　> 100mM

　　HETCOR - Proton-carbon correlation experiment

　　Gives information about strong proton-carbon J-couplings. A strong proton-carbon J-coupling indicates that the proton is directly bonded to the carbon. This experiment gives information that is identical to HMQC, but because it is carbon-detected, it is less sensitive than the HMQC experiment.

　　Default Parameters

　　2.0 second relaxation delay

　　512 complex points in t2 and 128 increments in t1

　　4 scans per increment

　　Total time: 30 minutes (make a not that time required for HETCOR is approximately 6 times the time required for HMQC)

　　Recommended Concentration

　　> 100mM

　　Phosphorus-detected experiments

　　General

　　Availability

　　The 500 Bruker Avance, 400 Bruker Avance can run 31P without changing any cable.

　　Sensitivity is approximately 15 times less than for proton, so adequate S/N for a reasonable length experiment (10 minutes, 256 scans) requires a concentration of > 0.1mM.

　　1D Phosphorus experiment

　　Default Parameters

　　0.8 second acquisition time with proton decoupling

　　3.0 second relaxation delay (d1; with NOE enhancement)

　　Spectral width -100ppm to 250ppm

　　32 scans

　　Total time: 2 minute

　　Recommended Concentration

　　> 0.1mM

　　Fluorine-detected experiments

　　General

　　Availability

　　The 400 Bruker Avance with QNP probe is best suited for direct observe 19F experiments.

　　Sensitivity is approximately the same as for proton, so adequate S/N can be obtained with concentration > 0.1mM.

　　1D Fluorine experiment

　　Default Parameters

　　0.8 second acquisition time

　　3.0 second relaxation delay

　　Spectral width 150ppm to -200ppm

　　32 scans

　　Total time: 2 minute

　　Recommended Concentration

　　> 0.1mM

　　3. 1D Fluorine observe 1H decouple

　　Setup is exactly like direct observe 19F, only F2 is 1H and uses Waltz 16 decoupling.

　　Higher field spreads out the signal better, makes coupling patterns simpler, https://1686990.com/view/zsh/index.html?lottype=sgAirshipseparates different signals better. Again, 600>500 > 400>300 MHz.

　　Linewidths in Hz are similar whatever the field, so the linewidths in ppm are smaller at the higher field strengths, unless a frequency-dependent line broadening mechanism interferes.

　　Proton-detected experiments

　　Availability

　　H1 experiments are available on all instruments.

　　1D Proton experiment

　　Default Parameters

　　~2 second acquisition time

　　~1.5 second relaxation delay

　　Spectral width -2ppm to 18ppm

　　16 scans

　　Total time: 1 minutehttps://1686990.com/view/jisusaiche/pk10kai.html

　　Variations on the 1D experiment include

　　1D NOE or selective NOE (difference or gradient)

　　1D COSY or Selective COSY (gradient)

　　T1 determinationhttps://1686990.com/view/uklotto8/klsf_index.html

　　Recommended Concentration

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