I haven't looked at HMQC for low-gamma nuclei since the compounds we've looked
at had a small J (always < 10 Hz). So the shorter HMBC sequence
not involving refocusing seemed best.
On 8/31/2023 3:30 PM, Vander Velde, David wrote:
> No, but the unadorned HMBC will reward you with some signal even if
> your initial estimates for pulse width and J turn out to be quite bad.
> I think it's very helpful in that regard that the number of pulses in
> the sequence is so small. The level of optimization is a matter of
> personal preference.
> ------------------------------------------------------------------------
> *From:* main_at_ammrl.groups.io <main_at_ammrl.groups.io> on behalf of
> Walter Massefski <massefskiww_at_gmail.com>
> *Sent:* Thursday, August 31, 2023 12:47 PM
> *To:* main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> *Subject:* Re: [AMMRL] Y89 measurement
> Clemens usually recommends HMQC (either 1H or 31P) for low-gamma work=
> - have either of you done the comparison with HMBC for various systems?
> Best,
> Walt
>
>
>
>> On Aug 31, 2023, at 1:06 PM, CHARLES G FRY via groups.io
>> <fry=chem.wisc.edu_at_groups.io> wrote:
>>
>> I was about to respond similar to Dave's email stating that getting
>> to low gamma nuclei via 1H (and perhaps 31P) HMBC has been the most
>> successful route we've used. The combination of polarization
>> enhancement and T1 savings is very powerful and makes many of our
>> studies viable that otherwise would not have been. 103Rh and 183W
>> are just a couple of other nuclei we've had 1H-X successes with, in
>> addition to 89Y.
>>
>>
>> On 8/31/2023 11:49 AM, Vander Velde, David wrote:
>>> 1H-89Y HMBC is pretty straightforward and 89Y sits just above 109Ag
>>> which is the nominal low frequency limit of many Bruker broadband
>>> probes. Setting it up from scratch, you can guess the length of a
>>> 89Y pulse by extrapolating from anything which is calibrated nearby
>>> assuming the pulse voltage is constant and then the pulse just
>>> scales with the gyromagnetic ratio. The simplest version of an HMBC
>>> is pretty forgiving (starting from the 1H-15N parameters with no 1
>>> bond couplings suppressed, no filters on the size of the J). That
>>> pulse estimate is enough to get started. You can refine the
>>> parameters by running arrays of just the first block of the HMBC. If
>>> you don't know where they X signal is (a problem especially for
>>> something like 195Pt), you can find it quickly with an array of X
>>> nucleus carrier frequencies. With the X signal frequency known, the
>>> low gamma pulse width can be calibrated with an array. Likewise, if
>>> the 1H-X J coupling is not resolved in the 1H, you can find the
>>> value that gives the most signal.
>>>
>>> Our experience here is limited to a few 89Y organometallics and the
>>> 89Y shifts calculated by absolute referencing were bigger than we
>>> expected, but that was the outcome. We never saw any 89Y signals by
>>> direct observation, very long T1's and low concentration likely
>>> weren't helping.
>>>
>>> The same approach has worked for some really low gamma nuclei. We
>>> have a newer type Bruker iProbe that is rated to reach 109Ag, and
>>> that is the lowest frequency it will reach. However we have a
>>> previous generation Bruker probe that will go to lower frequencies.
>>> It will tune but not quite match the 12.5 MHz frequency for 103Rh,
>>> close enough for HMBC. I got an HMBC signal from Rh(acac)3 even
>>> though there is no resolved Rh multiple bond coupling in the 1H
>>> spectrum. To get this going, we got some valuable help from Brian
>>> Andrew at Bruker with putting firmware entries for these wacky
>>> nuclei into that probe.
>>>
>>> ------------------------------------------------------------------------
>>> *From:* main_at_ammrl.groups.io <mailto:main_at_ammrl.groups.io>
>>> <main_at_ammrl.groups.io> <mailto:main_at_ammrl.groups.io> on behalf of
>>> Craig Grimmer <craig.grimmer_at_gmail.com> <mailto:craig.grimmer_at_gmail.com>
>>> *Sent:* Thursday, August 31, 2023 5:29 AM
>>> *To:* main_at_ammrl.groups.io <mailto:main_at_ammrl.groups.io>
>>> <main_at_ammrl.groups.io> <mailto:main_at_ammrl.groups.io>
>>> *Subject:* Re: [AMMRL] Y89 measurement
>>> Good afternoon Stephen
>>>
>>> For 89Y (transmitter frequency 24.5013454) on a 5 mm broadband probe
>>> on a "500" magnet, I use a 3 M solution of Y(NO3)3.6H2O and I get a
>>> reasonable signal from 4 scans (transients) with d1 = 720 seconds
>>> with pw = 18 us at 150 W. I've not measured the T1 of this sample
>>> but 720 seconds seemed a reasonable figure based on the information
>>> in Brevard & Granger's book that reads "/T1 typical value (s): >
>>> 50/"). If you're struggling to find a signal from a multi-molar
>>> solution, set a wide sweep width to start with, ~1000 ppm.
>>>
>>> Kind regards,
>>> Craig.
>>>
>>>
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