Monday, November 26, 2007
HMQC Responses in HMBC Data
Despite the built in low pass J filters written into the HMBC pulse sequences, the much larger one-bond 1H - 13C coupling responses are not fully suppressed. These one-bond HMQC responses show up as a pair of responses in the acquisition domain separated by the one-bond 1H - 13C coupling. The responses are doubled since 13C decoupling is not typically used in HMBC sequences. An example of these artifacts is shown below.
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6 comments:
How to avoid such artefacts?
Anonymous,
To the best of my knowledge, there is no way to fully suppress these on-bond correlations aside from using various "low pass filters" written into the pulse programs.
Glenn
Why is decoupling not employed for HMBC? The resulting crosspeaks are 'split' into quadrants, and S/N is insufferable. In HSQC, decoupling is employed, and the crosspeaks are nice and round. Can I turn the decoupler on for HMBC to get harvest more S/N per scan?
Anonymous,
You can certainly decouple 13C if you wish but then the HMQC artifacts will also collapse and it may be difficult to distinguish HMBC from HMQC responses.
Glenn
Anonymous,
On this topic, here are two articles that you may find informative:
Concepts in Magnetic Resonance A, 2012, 40, 101-127 (A comprehensive discussion of HMBC pulse sequences, part 1: The classical HMBC)
Concepts in Magnetic Resonance A, 2012, 40, 146-169 (A comprehensive discussion of HMBC pulse sequences. part 2: Some useful variants)
Craig.
Hello!
In my selective HMBC, I see artefacts positioned symmetrically along F1 direction, not along F2 direction. They are less intense but have the same appearance as the 13C-1H correlations. I found that these are most probably "proton–proton couplings
in the X-spin f1 dimension, a consequence of the evolution of 1H–X multiple-quantum coherence during t1." This is a quote from "High-Resolution NMR Techniques in Organic Chemistry" Claridge T.
I did not see much information about it. Just wanted to mention this because this is another type of artefacts in HMBC.
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