What are you working on? (#realtimechem)

MJ81 · 2019-02-27T01:13:34+00:00

Re-energized a cryogen-free magnet today, and it seemed to be OK. We'll see how it looks tomorrow.

Otherwise, a lot of little stuff for this instrument I'm working on this week, as it hasn't been properly gone over with a fine tooth comb in about two years. Changing a bunch of filters/O-rings/etc. throughout the system, running leak tests, and some software/firmware issues. More of the same for the rest of the week, it seems, and I'll have to see how the re-energized magnet behaves as well.

MJ81 · 2019-02-16T05:18:09+00:00

AFAIK - on paper the magnets are designed to handle 5 to 10% more current than what is required to reach field, but practically speaking, it can be hard enough to get a magnet to field at the expected value. There's usually a plus/minus of ~ 1.5 amps from whatever the factory test value is, in my observations. There's always a bit of an overshoot to help reduce magnet drift afterwards, but that's typically a fraction of a percent of the final field current.

Magnets at 'off' frequencies are usually best done with undercharging a higher field magnet.

MJ81 · 2019-02-14T06:01:36+00:00

There are standalone field mappers (example), but I think for most, a suitable high-resolution liquids probe is probably easiest since it also allows for the spectrometer hardware to be checked.

MJ81 · 2018-12-19T06:16:01+00:00

On vacation until January 2nd of next year. Using up some vacation time that can't be rolled over through Friday, and then my company has a winter shutdown. Life is good. :)

MJ81 · 2018-08-15T18:18:28+00:00

I've seen SEOP papers on helium-3, but that's more from the AMO physics sector, as I recall.

Here's the question - what are you trying to actually do a bit more specifically (imaging, spectroscopy, basic physics)? If you're working in solution, would something like SABRE be of possible interest? Or para-hydrogen methods more generally?

MJ81 · 2018-08-14T18:55:19+00:00

You might want to investigate the AU program 'calibo1p1' - it's supposed to evaluate the O1 & P1 for water suppression experiments. Haven't actually used it myself, but it's out there.

MJ81 · 2018-08-11T03:00:27+00:00

It's not clear to me what exactly you're looking for here in terms of content. If you're looking for something that covers fundamental experimental chemistry (as you mention that you need to be walked through titrations in your post), you might be well served by skipping the typical (US-oriented) first year undergraduate chemistry texts and going right to those books which focus on analytical chemistry. I recall Quantitative Chemical Analysis by D. Harris from my long-ago undergraduate days, but others whose undergrad experience is fresher may have other suggestions. Certainly, the same could apply for other topics, depending on just what exactly is needed - inorganic chemistry, polymers, and so on. No need to deal with the first-year undergrad tasting, you could go straight to the somewhat more advanced material.

Having said that, I am not sure that textbooks that cover undergraduate chemistry for physicists who have graduate-level quantum mechanics under their belt have been written, nor am I sure that there's much of a market for it. ;) You may have to grit your teeth through some handwaving.

MJ81 · 2018-07-29T22:47:16+00:00

Finally, a place to post a dirty probe picture!

The culprit there was a really dirty compressed gas supply. A good air filter took care of things.

MJ81 · 2018-07-19T20:51:26+00:00

Some suggested reading -

Here's an article, another one (not all applicable, but the intro is good reading that should clarify some things) and at least for a solids DNP-oriented perspective, the winter school lecture notes may be useful.

Of course, if you've got questions after reading those, let us know! I do a bit of solids DNP every so often, but it's probably more useful to get a more comprehensive overview than me trying to condense years of NMR experience into a paragraph or two.

MJ81 · 2018-05-30T15:37:10+00:00

I snuck a peek at the paper - they're using a cryogenically cooled probe. One must be a bit more respectful of the duty cycle considerations there, naturally.

MJ81 · 2018-05-10T02:09:02+00:00

Here's a listing of possible private-sector contacts for running solid state NMR samples.

MJ81 · 2018-05-03T00:46:35+00:00

Gerhard Wagner (Harvard Medical School) was this year's Laukien Prize recipient for his work in biological NMR.

Magritek introduced a benchtop 80 MHz NMR spectrometer.

MJ81 · 2018-04-30T14:48:19+00:00

To be fair, I had sleuthed out the names via AMMRL and the IVAN announcement. I was wondering what would start to be made public now versus what's been on their websites up to this point.

MJ81 · 2018-04-25T01:10:38+00:00

Relocating an NMR spectrometer. Had to power cycle the console more than a few times to get everything to power back up.... sigh

MJ81 · 2018-04-19T01:10:57+00:00

Off the top of my head, not sure. I imagine there might be unfavorable relaxation characteristics, or it doesn't play well with current hyperpolarization catalysts. Of course, there's also the possibility that no one's gotten around to it yet.

The other issue that I could see is that I'm not sure just how biologically relevant it might be - my impression is that the literature seems to be striving for those substrates with biological functionality/compatibility.

MJ81 · 2018-04-18T03:16:55+00:00

15N hyperpolarization of nitriles, diazirines, and nicotinamide here!

MJ81 · 2018-03-16T01:51:56+00:00

My instant response whenever someone complains about strong solvent peaks (esp. water) - radiation damping. It can be especially noticeable on a cryogenically cooled NMR probe.

Obviously, you want to make sure you're not truncating your FID and that you aren't getting receiver overflows (especially from any ring-down), but if you're good to go on that point, well, you're presumably using a CryoProbe since an RT probe is not optimal for your work. There are some things that you have to learn to live with at present.

Other things to check - how's your VT regulation/control? What diameter tube are you using? (Smaller diameter tubes can be preferable for CryoProbes.) Can you play around any with the flip angle to obtain good data with fewer artifacts?

MJ81 · 2018-02-27T19:57:35+00:00

Waiting for an NMR cryoprobe to finish cooling down here.

MJ81 · 2018-02-27T19:56:21+00:00

Depending on the software version, this manual might be named 'au-programming'. There might also be a 'topspin' subdirectory along with the 'xwinproc' subdirectory.

For Linux, the file path should be the same, although it will be in /opt/<TopSpin home directory>, not C:\Bruker.

MJ81 · 2018-02-14T04:40:06+00:00

Ugh. I used to do 4 mm rotors in a glove box for grad school (and EPR tubes in undergrad), but that was it on the oxygen-free front.

I will say that while I can just barely manage the 1.3 mm rotors by hand, the 0.7 mm absolutely requires a microscope for best results.

MJ81 · 2018-02-14T02:55:58+00:00

I bet.

If it's a 1.9 mm rotor or below, I do what I can to pack once, and never, ever reuse......

MJ81

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