Hi David,
The information in this link may help you.
http://nmr.chem.ucsb.edu/protocols/fast1pulse.html
Best,
Weidong
From: Walter Massefski [mailto:massefskiww_at_gmail.com]
Sent: Friday, March 06, 2015 4:35 AM
To: David Richardson
Cc: ammrl_at_ammrl.org
Subject: Re: ammrl: steady-state gradients and the need for a long d1
Hi David,
The crusher gradients won't do much to the longitudinal (z-axis) magnetization, so you're not at thermal equilibrium with respect to T1, only with respect to T2. However, the point of the INADEQUATE is typically to see the connectivities, not to quantify them, so your d1 only needs to be long enough that the sensitivity for the longest-relaxing carbons (the quaternary carbons, typically) is good enough. I've had luck using a 3 second delay for small-quantity samples with quaternary carbons at 500 MHz. Of course, you might direct them to some of the indirect near-equivalents (H2BC, ADEQUATE) if they don't have adjacent quaternary centers...
Good luck,
Walt
On Mar 5, 2015, at 9:58 AM, David Richardson wrote:
Hi all,
I need some advice. I have a professor regularly doing INADEQUATE experiments on natural products. We use a shegemi tube and have been getting pretty good data, but obviously the concentrations are low and the experiments long. He is a solid-state spectrocopist so 6-7 day experiments are not a big deal to him, but on my shared liquids instruments it has become an issue. We are having a dispute about using a lengthy d1 and making the experiment much longer than I think is necessary. We did a C13 T1 measurement on the most recent compound and found the longest T1 to be about 12 seconds, so he wants to run with a d1 of nearly 30 seconds. I think this is utterly insane, especially for an INADEQUATE. I tried to explain about the steady-state gradient pulses (see the attached picture - hopefully screenshots make it through the filters) that precede every scan in most of the modern advanced pulse sequences and that they exclude the need for a long d1 even when some of the spins have a long T1. He didn't buy my explanation and still has his students run 6-7 day experiments; I am about to restrict his access to our 500 and make him use the 300 exclusively. I understand the steady-state gradient pulses (apparently called crusher gradients, as I learned in my reading yesterday) kill any remaining transverse magnetization, but I am unable to explain how. Does it actually return the system to the equivalent of thermal equilibrium? Even if not, I imagine any signal loss would be more than compensated for by running 10+ scans with a short d1 in the same amount of time he runs 1 scan with a long d1. Can anyone please help clarify this for me so I can better explain to him it is unnecessary. Also, if I am completely wrong and a long d1 is still needed please tell me that too. I can understand if it were, perhaps, a DOSY or some other quantitative experiment, but not on your general 2D experiments.
Thanks in advance,
David
David Richardson, Ph.D.
NMR Instrumentation Specialist
Chemistry Department
University of Central Florida
david.richardson_at_ucf.edu<mailto:david.richardson_at_ucf.edu>
407-823-2961
http://chemistry.cos.ucf.edu/nmr/
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Received on Fri Mar 06 2015 - 09:19:11 MST