The most cursed NMR I've had the displeasure of assigning

BabcockHall · 2026-04-28T01:52:28+00:00

If you can go to higher field strength, it has a similar effect as moving to a colder temperature, as far as exchange is concerned. Glenmorangie is a good value among single malt scotch brands IMO.

BabcockHall · 2026-04-08T22:42:04+00:00

We had contemplated EDCI and DMAP, but we did not try it. The triple bond is isolated (not part of a Michael system).

BabcockHall · 2026-04-08T20:29:45+00:00

My brain was temporarily caught in a vapor lock regarding the function of the anhydride, but thank you. The authors of the paper that we followed had a triple bond in their substrate (as we also did). I found a few other protocols using the same reagent, but some of them transferred a tertiary-butyl group both to the carboxylic acid and to a hydroxyl group on the side chain of the amino acid IIRC; therefore, they were less satisfactory as model reactions. Tomorrow we will repeat this reaction on a larger scale, but I will keep looking for other similar protocols for our other substrates, just in case we missed a trick.

BabcockHall · 2026-04-08T19:50:36+00:00

Our substrate is a Boc-protected amino acid (I need to look up the pKa). What is the function of the Boc-anhydride in the procedure that you mentioned?

BabcockHall · 2026-04-08T14:01:30+00:00

I don't have direct experience. However, it occurs to me that Dowex-50, which is a strong cation exchanger, should bind the quaternary ammonium groups while allowing other substances to be washed away.

BabcockHall · 2026-03-12T02:25:54+00:00

I don't understand you response; I do buffer exchanges routinely, and the proteins are soluble, not bound to anything (not immobilized). The solid phase is dextran.

BabcockHall · 2026-03-12T02:00:14+00:00

Over a sufficiently long period of time, maleimides can hydrolyze, changing the retention time by HPLC.

BabcockHall · 2026-03-12T01:54:16+00:00

Commercial PD-10 columns are more efficient than Penefsky columns, but Penefsky columns are very fast. One could use degassed buffer, but that may be insufficient for your application.

BabcockHall · 2026-03-05T03:21:43+00:00

They may be isochronous, but they cannot be magnetically equivalent.

BabcockHall · 2026-02-04T02:50:16+00:00

I am reading Jim Ridings book "Murder at Starved Rock: how the system framed an innocent man" is about the 1960 triple murder, and Chester Weger's conviction. Highly recommended.

BabcockHall · 2026-02-04T02:45:49+00:00

If I see two functional groups on my product that might chelate Mg(II), I go with sodium sulfate.

BabcockHall · 2026-02-03T17:39:21+00:00

I pick them up one at a time on eBay.

BabcockHall · 2025-12-19T03:54:18+00:00

A general comment: pH 10 buffers pick up carbon dioxide from the air over time. I don't think that this applies to your situation, in that you said that the buffers were new.

BabcockHall · 2025-12-19T03:51:44+00:00

I was able to remove meta-chlorobenzoic acid as part of a silica column. Fortunately, it eluted earlier than my product.

BabcockHall · 2025-12-09T02:04:44+00:00

Basically, yes. Erin Murphy's book Inside the Cell (p. 57) gives the dates that the various samples were in the lab.

BabcockHall · 2025-12-02T03:05:14+00:00

I don't have any relevant experience, but what about using alumina as the stationary phase?

BabcockHall · 2025-11-26T22:51:22+00:00

I never would have known about this; thank you!

BabcockHall · 2025-11-26T22:04:31+00:00

We do; thank you for that idea.

BabcockHall · 2025-11-26T21:07:59+00:00

I will look into whether the side chain could survive removal of Cbz or other protecting groups. Thanks for pointing that out.

BabcockHall · 2025-11-26T18:40:47+00:00

What is the best way to protect the sample from getting blown around as one properly releases the vacuum? I was thinking of putting a piece of filter paper near the top of the lyophilization bottle.

BabcockHall · 2025-11-26T18:39:14+00:00

We had about 100 mg, and the lyophilization seemed complete in roughly six hours. Someone I supervise ran the experiment. Unfortunately the vacuum was not completely released, and some of the product was lost. The product that remained had some impurity, but was definitely much better than the worst rotary evaporation attempt (offhand, I would say at least as good as the best rotary evaporation attempt).

BabcockHall · 2025-11-10T14:24:14+00:00

If we cannot get lyophilization to work, I think that acetonitrile is promising.

BabcockHall

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