Hi David,
low S/N on 15N is not a bug, it's a feature (of mother nature). So fa I've
never managed to get a useful 1D 15N spectrum, not even a miserably noisy one ...
1. the INEPT will anyways have a lower S/N by ca. a factor of gamma (3/2)
ca. 30 compared to a 1H,15N-HSQC/HMBC, because you are detecting the very
low gamma nucelus instead of 1H.
So expect a 30*30 = ca. 1000-fold (!!!) longer total measuremement time for
comparable S/N. If you are using an X-detection probe wiht 15N on the inner coil,
S/N fot the INEPT will be higher by ca. a factor of 2, if it is an inverse /
1H-detection probe, a factor of 2 worse.
2. you mention the HMBC, but not an HSQC / HMQC, so I guess all your
nitrogens are non-protonated. The INEPT works nicely with 1H-15N pairs, where
you have a rather large 1J coupling (ca. 90 Hz => ca. 5.5 ms J transfer delay)
AND you know how big it is. For 2,3J couplings their size is much smaller (order of 1-10 Hz?),
so you would need a much longer delay - like the one you have used in your HMBC
(ca. 30-100 ms I'd guess) - TWICE! And your delay setting will be a wild guess anyway,
because you have no good estimate (2 Hz? 5 Hz?? 10 Hz???). T1 would be governed by
the proton T1 - if your 1H -> 15N INEPT transfer works / worked (like in the HMBC),
so I'd assume that's not the main problem.
I agree with the Spin-Doc that a high resolution (in F1) H,N-HMBC would have a
better chance, best to use an HMBC sequence that is phase sensitive in F1 (like
echo-antiecho / grad. selection HMBC, sorry, I'm not familiar with Varian pulse sequences)
and process it phase sensitive in F1, to get a decent resolution.
Good luck,
gg
>
>> Am 31.03.2025 um 22:04 schrieb Vander Velde, David via groups.io
>>
>> You should get their standard sequence if you just type inept on the command line in vnmrj.
>> ------------------------------------------------------------------------
>> *From:*main_at_ammrl.groups.io on behalf of Shawn Wagner via groups.io
>> *Sent:*Monday, March 31, 2025 12:08 PM
>> *To:*main_at_ammrl.groups.io
>> *Subject:*[AMMRL] INEPT
>> Does any have an INEPT sequence for Varian spectrometers? I haven't been able to find one posted anywhere. I am interested in
>> obtaining 1D 15N spectra, but so far have been unsuccessful with the low SNR and long T1 values. I am able to get a good 15N
>> HMBC but cannot get a good 1D spectra even with reducing the acquisition window to the resonance frequency of the 15N nuclei
>> in the molecule. My end goal is to try to measure 2J and 3J scalar couplings.
>>
>>
--
PD Dr. Gerd Gemmecker
Bayerisches NMR-Zentrum
NAT School, TU München
Lichtenbergstr. 4
D-85747 Garching
Germany
Raum/Room 2108 / BNMRZ, E.O.Fischer-Str. 2
Tel. +49 (89) 289-52604
Fax +49 (89) 289-52669
e-mail: Gerd.Gemmecker_at_tum.de
Internet: http://www.gemmecker.de
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Received on Wed Apr 02 2025 - 06:06:06 MST