NMR service

Characterization of the molecular structure or sample constitution is an important aspect of chemical research and can be supremely accomplished by NMR. Routine service or direct access for DKFZ researchers - and others by prior consultation - is available for the examination of a wide range of samples, though typical analyses are mostly concerned with small organic molecules by way of standard experiments (routine 1D and 2D experiments) for a selection of nuclei (1H, 13C, 19F, 15N, etc.). Information on the NMR service and the submission of samples is available here. Users of the service do need to read and agree to the General Terms and Conditions for the execution of research and development orders in the DKFZ as well as the General Terms and Conditions for the execution of research and development orders in the GPFC and the rules for users when running their own samples.

Submitting a sample

To make use of the NMR service, researchers need only fill a requisition form (non-DKFZ researchers should consult with Dr. Karel Klika first) and deliver both the completed form and the sample to room H2.02.029a as well as reading and agreeing to the General Terms and Conditions for the execution of research and development orders in the DKFZ and also the General Terms and Conditions for the execution of research and development orders in the GPFC and the rules for users when running their own samples. Completed forms can be left in the tray on the right upon immediately entering from the corridor whilst samples can be left on the bench next to the tray for forms or left in the refridgerator beneath the bench marked "NMR-Proben".

Samples can be submitted either neat (i.e. as solids or liquids) or already made up in an NMR tube (preferred), but not as solutions unless that solution is to go in the NMR (exceptions for unusual cases should be consulted beforehand). All necessary and important information to safely handle the sample, acquire the spectra expediently, and to produce the required results has to be provided on the form - the dangers of handling the compound, possible instability of the compound, expected solubility of the compound, what spectra are required, how to process the results, etc. Researchers are required to supply their own user codes for each sample though the NMR staff will also define for each sample an NMR sample code for cataloging purposes.

How much sample should be provided?

Depends. What do you want...to see low-level impurities?, which nucleus? what spectra? (and what is the mol. wt. and purity? and how does the sample behave with respect to dynamics, T1, T2, etc. ?) For just acquisition of a simple 1H spectrum, a few mgs is usually sufficient (assuming a mol. wt. of a few hundred to several hundred Da); for a decent 13C spectrum in a reasonable time, 10-15 mgs is usually sufficient. If sample amount is limited, long-run acquisitions are not problematic (presently at least) but researchers should be considerate of others and limited resources and provide sufficient sample when it is available to expedite spectral acquisition. For 2D spectra, a few mgs is sufficient also for COSY or TOCSY whilst several mgs or more are preferred for heteronuclear or NOE correlations to maintain reasonable acquisition times. Sample amounts for other nuclei and experiments are best determined by consultation prior to sample submission.

When making up the sample, does one need to be careful about exact weight?

Not really.

What about the height of the solution in the NMR tube?

4-5 cm of solution is fine, more is just a waste of expensive deuterated solvent and doesn‘t help with acquisition (only that part of the solution which is in the coil region - ca. 2 cm in length - contributes to the actual signal), less volume of solution makes for problematic shimming but it can be advantageous to make up shorter samples when sample amount is extremely limited (in which case, 2.5 cm is the absolute minimum), but gains in sensitivity can easily be offset by deterioration in signal width and time spent getting shim instead of acquisition.

What about quality of the NMR tube?

If you want a good quality 1H (or 19F) spectrum, then yes, a good quality NMR tube should be used (e.g. Wilmad 507 or equivalent or better). If you want to just see if the compound is what it is, or if a reaction has occurred, or the purity, then tube quality is not important (maybe you‘ll get a poor spectrum in terms of linewidth, but if you see what you need to see, then job done). For all other nuclei and experiments, the demand for tube quality is generally very modest to completely unimportant, but since generally in most cases all experiments are done on the one sample, it is the quality demand for the 1H spectrum that determines the minimum quality of tube to be used.

Does one need to filter the solution?

Same answer as tube quality. HPLC filters (e.g. the 0.45 µ filters) do an excellent job but are generally unnecessary (overkill one might say); centrifugation can also provide a "particulate-free" sample; and finally, filtering through a plug of rolled up fiber-free tissue ("Kim wipes" or the such like) jammed into a Pasteur pipette directly into the NMR tube is a wonderfully low-tech and simple process that normally suffices to get a "particulate-free" sample for the purpose of attaining good shim (i.e. nice linewidth in the 1H NMR spectrum, downwards of 0.3 Hz or even less and Lorentzian in shape).

And does TMS/TSP need to be added?

It is preferred since it gives more reliable chemical shift referencing than the solvent signals (much more reliable in some cases) and can also be used as a shim reference (i.e. to adjudge the quality of the resultant shim). But researchers can suit themselves, if TMS or TSP is not included then the chemical shifts for referencing (i.e. of the solvent signals) should be indicated on the requisition form when processing is required.

What nuclei can be observed?

All that are normally NMR-accessible: 1H, 13C, 15N, 19F, 31P, 17O, 29Si, 195Pt, 2H, 6/7Li, ...

What spectra are available?

All that are considered standard + more: 1D experiments such as direct observation of 1H, 13C, other nuclei ↑, DEPT, selective COSY, TOCSY, NOESY, ROESY,... ; 2D experiments such as COSY, TOCSY, NOESY, ROESY, HSQC, HSQC-TOCSY, HMBC,... ; other experiments such as variable temperature, 3D and multidimensional, diffusion, microimaging, relaxation time measurements, etc. are of course available. Best for researchers to simply enquire about any particular experiment or nucleus.

What do you get back?

A hardcopy (printout) or electronic files (preferred) on memory stick/emailed/placed on a central server as preferentially indicated on the requisition form. Requested processing (integration, peak list, etc.) will be produced as stated on the requisition form. N.b. Post-acquisition requests for both processing and experiments readily accepted (a new form is not required if subsequent experiment requests are made within one week of the original submission). All spectral data will be stored for an indefinite period and can be accessed by providing the NMR sample code (given in the spectrum title and filename).

What level of analysis/interpretation is available?

As required:

  • basic interpretation (e.g. yes, it is the known compound; yes, it is pure)
  • full interpretation (e.g. yes, it is the structure depicted)
  • full spectral assignment and analysis using standard array of pulse sequences and spectral analysis tools {e.g. Perch spin simulation software for extraction of 1H chemical shifts (δH) and scalar coupling constants (JH,H) or prediction of NMR parameters using Gaussian software.

Finally, can researchers have the opportunity to run samples themselves?

Yes. Consult with Dr. Karel Klika. Users interested in running their own spectra need to read and agree to the three items listed in the Miscellaneous section on the frontpage and print out and sign the final page of the listed rules.

At present no booking system is in place and NMR time is booked in consultation with Dr. Karel Klika. A listing of common commands and macros for our instruments is available here. Users can also be present whilst the spectra are acquired if they like, this too should be arranged with either Dr. Karel Klika or Gabi Schwebel as appropriate.

 

last update:
27/02/2019
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