几种常用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.
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