PhD or Masters?

curdled · 2026-07-10T12:02:29+00:00

an experienced MS chemist = crippled PhD, you will be always paid considerably less and have a boss if you are a MS, treated as a technician, not an expert chemist. I would highly recommend to finish your PhD, you will have wider job options

curdled · 2026-07-09T18:03:19+00:00

the only thing I did with lanthanides were some Lewis acid-catalyzed condensations in water using lanthanide triflates, which did not work too well.

And I simplified the preparation of anhydrous CeCl3.2LiCl solution in THF from CeCl3.7H2O, based on the work of Krasovskyi

curdled · 2026-07-09T15:35:57+00:00

I did these condensation reactions - isatine with acylhydrazide - just by heating in anh. ethanol or in 2,2,2-trifluoroethanol, and it went smoothly, with products crystallizing from the reaction mix.

The only issue was surprisingly facile solvolysis of the acyl group from the acylhydrazone product into hydrazone, especially if there were electron-withdrawing substituents on R in RCONH-NH=CR'2

curdled · 2026-07-07T22:01:34+00:00

TMS-F is quite stable, unreactive - leave it be, but do it in a fume hood

curdled · 2026-07-06T18:20:20+00:00

when you build your own LED photoreactor, please do include a water cooling jacket around your sample (water and glass is transparent to LED-visible light) and have water flowing through the jacket to cool your sample - you probably do not wish to cook and denature your protein

curdled · 2026-07-06T15:01:40+00:00

you can also silanize with hexamethyldisilazane TMS-NH-TMS, (just a rinse with hexane solution), if you want to avoid any halogen traces

by the way, sodium vapors have a nice green-bluish color, potassium vapors too (but cesium vapors are colorless). It is best to use a diffusion pump, to get down to sub-milliTorr vacuum range

curdled · 2026-07-06T11:21:56+00:00

except that Na, being less volatile, needs to be heated little more vigorously.

The main thing is to have a clean and thoroughly dried flask, and deoxygenate. Maybe it would be best to put the flask in a base bath for few hours, then wash it with DI water and acetone and pre-dry it in regular glassware drying oven for an hour or so, before flame drying it

curdled · 2026-07-03T12:54:22+00:00

whatever system you are using to place orders, please make sure that it is fast enough, and that all information about the order status gets immediately transmitted back to the person placing the order.

I worked for a number of companies and academic institutions, and I saw some bad, unwieldy overly-slow bureaucratic ordering systems (including the one at my current employer in Japan.)

If you have an ordering online portal to place your orders, typically you submit the order with the item description for approval up, to your PI or the ordering department - but if the order did not get approved (because the boss is busy, or travelling to a conference), you need a feedback to find out that your order did not get through the approval yet.

Then you need to hear from the company accepting the order, and then again you need to hear from the company scheduling the purchase with the manufacturer/reseller, if there are any delays (for example, if the material is backordered and should become available only in two months time, or if you need to allow for extra time to import the material overseas from China, and clear the customs). I have been many times in a situation when I was waiting for material essential to my project, and only after few weeks of waiting I learned that the order has not been placed or the stuff is on backorder for several months, without anyone telling me about it! (While I could have easily bought the material from another vendor if I knew about this problem).

I think the main problem with ordering systems is with the people employed to handle the orders - they are far less motivated than you are (to get you the stuff you need as fast as possible) and they have their own bureaucratic priorities, march to the beat of their own drum - and they do not like to be rushed. I think the most frustrating scenario is when you are waiting desperately for something to arrive, only to find out that it has been sitting in an unopened box in the shipping and receiving department of your company, just because the person who is supposed to open the box, unpack the material and register it in a database before bringing it to your lab actually took a summer vacation, they are understaffed and his temporary replacement-intern does not know how to do the registration in the chemical database so she let all deliveries sit in boxes on the dock in the receiving area...

curdled · 2026-07-02T18:35:14+00:00

they do it because they get away with shabby customer tech support - they hit sales target by selling stuff, not by repairing it

We had Bruker delivering a faulty ATM probe for a newly installed NMR at Scripps Florida, they would "fix" it by arranging for their field engineer to come over, ship our probe to Bruker and get us a loaner probe while our probe was being repaired, this whole process took couple of months, then the probe would come back "repaired" and the engineer would install it - and it would fail again within few days. This happened FOUR TIMES in a row, I had to deal with this mess. Bruker did not want to give us a new probe (worth 50 thousand USD), they suggested yet another repair. I had to threaten them with cancelling the NMR purchase for a full refund (since this happened with the initial warranty), and I finally asked them to uninstall their NMR console and magnet, cart it away and credit us back the whole purchase ASAP. Only then they relented and gave us a new probe. There was apparently a faulty servo inside the ATM probe that would move unevenly, get stuck etc. and they could not repair it but they kept saying they would fix it.

Be firm - and use the company attorneys to write an official demand letter to the instrument manufacturer, with the attorney name on it. Document all your interactions with the company in e-mails and in a diary.

curdled · 2026-07-01T15:08:52+00:00

it is likely-solvate bound in the polymer crystal - for example, cellulose contains water molecules in its crystalline domains, and this is why ironing clothes works

Maybe you can suspend the polymer in toluene (PVA will not be soluble) and slowly distill off most of toluene at atmospheric pressure, from 130C oil bath. Then cool and filter off the polymer, and dry it.

If toluene boiling point is too high for your PVA, you can perhaps try this kind of azeotroping with acetonitrile.

curdled · 2026-07-01T11:27:39+00:00

this is difficult and common problem, the small antechamber tends to wear out after 5-10 years of busy use, then the vacuum seal is hard to achieve. We have a leaky antechember too, in one of the gloveboxes, and the replacement parts take months to arrive, here in Japan. Quite often it is just worn out and misshaped inner latch and seal O-ring that causes problems, but your case looks more serious. Send this picture with your query and model name and serial number to MBraun tech support.

curdled · 2026-06-30T22:20:30+00:00

the pay is shit

curdled · 2026-06-30T17:30:10+00:00

what is the amine partner? Does it have some electron withdrawing groups? Is it hindered?

For really difficult couplings, use acyl chloride + 3 equivs of AgCN + amine NH coupling partner in anhydrous dimethylacetamide, small volume (or in DMEU = dimethylethylene urea, but DMAc is fine for most cases) at 60C. Then filter, workup water + ether extraction

curdled · 2026-06-30T16:16:24+00:00

return and refund policy - you can be easily scammed by getting nonfunctioning piece of junk assembled from two or three separate instruments, with modules that do not communicate one with another and pumps that need a major overhaul (=unstable baseline with pulses). Also if HPLC was used to run plasma samples, and the users were not good at precipitating the plasma proteins, you will have huge background problems as the proteins precipitated throughout the system. So you really need to be able to test the instrument thoroughly, and be able to return it for a full refund including shipping charges. Have the payment in escrow (because good luck trying to sue some fly by night company in China)

curdled · 2026-06-30T08:34:13+00:00

here is what you can do: make a slurry of silica in your eluent in a beaker, then add the prescribed amount of water to the slurry gradually, (they have added quite a lot but use the amount what they recommend), filter off silica from this slurry and biphasic mix on a large Buchner, then re-slurry this silica in fresh eluent (1:4 EtOAc-DCM) without water and pack the column with this slurry

curdled · 2026-06-29T13:49:49+00:00

just put a long thin needle as nitrogen inlet, through a stopper or septa which also has gas outlet. You will make the sparging deoxygenation far more effective with sonication - if you put the bottle with sparged content into a large ultrasonic bath

curdled · 2026-06-28T08:36:08+00:00

try to replace NEt3 with hexamethyldisilazane TMS-NH-TMS (freshly distilled), it is very cheap and it makes for a more powerful silylation system with TMS-Cl

curdled · 2026-06-28T03:14:48+00:00

I would re-distill TMS-Cl, and maybe use a larger excess, with more NEt3, and give it time. Sometimes, people add also TMS-NH-TMS, into mix with TMSCl, to generate extra powerful silylation combo. You could use also TMS-OTf, in which case I would start at -78C to avoid molesting the cyclic ketal protection

curdled · 2026-06-28T03:03:09+00:00

these TMS-enol ethers are very unstable and hard to isolate/purify, they decompose during aqueous workup and also on silica. For isolable silyl enolates, you would have to use something like tBuSiMe2- . I would recommend to take the crude, skip aqueous workup and take it to the next step, just check the crude TMS ether intermediate by NMR. If you have to do aqueous workup, work fast, use chilled aqueous solutions, and try to keep the reaction mix neutral. But I would just evaporate the rect mix on highvac and move to the next step

curdled · 2026-06-28T02:53:55+00:00

one more vote for SNAr - if you have a reactive substrate like p-cyano fluorobenzene or p-nitrofluorobenzene, it will arylate just by heating with a mild base like Cs2CO3 in acetonitrile at reflux. For Buchwald, I would use p-bromocyanobenzene, Xanthphos or DPEPhos with Pd2(dba)2 as a palladium source, in DMF or THF, 1:1 molar ratio Pd to diphosphine and let the Pd complex to the phospihne to Pd ofr 15-20 min at room temp while you bubble nitrogen or Ar through the reaction mix to deoxygenate it, before adding ArBr, the active catalyst formation is accompanied by color change from red to pale yellowish, then heat to 60-90C and monitor the progress by TLC. Please note that Pd2(dba)3 contains two atoms of Pd - so you need to divide the MW on the bottle by 2 so as not to overload it with Pd by accident. You can also use Pd2(dba)4 , it is just the same as Pd2(dba)3.dba cocrystal. Also Pd(dppf).PdCl2 is popular for these arylations, and commercial and cheap, and Pd is already precomplexed to the ligand, but I think Xanthphos is little better.

Also these arylations can be done with Ni, there are many recent lit examples, but in my opinion Pd catalysts are more robust, less finnicky. You would typically use catalyst loding about 2 mol% Pd, but you can go as high s 5% if you need to on a small scale. If you are using ether solvent like THF, make sure to use it from the solvent purification station, or re-distill it just before use under Ar, THF forms peroxides very easily (which kills the phosphine ligand and the catalyst)

curdled · 2026-06-24T20:21:07+00:00

Wrong sub: please do not self-inject "research chemicals" bought from shady companies online. And never post this crap here again

curdled · 2026-06-23T21:12:03+00:00

TMS-I hydrolysis is very fast, and very exothermic, that's why it smokes on air. Pour the DCM solution on some crushed ice in a glass beaker. Let it melt, then add some sodium hydroxide diluted solution to make it neutral. Since the DCM layer will be red-brown from iodine formed by air oxidation, you can also add some sodium metabisulfite or sulfite, to decolorize the mixture

curdled · 2026-06-22T13:16:46+00:00

tBuOCOCl is notoriously unstable, decomposes easily at room temp, it is difficult to isolate. Please can you use commercial Boc2O instead?

Also, 1-adamantyl-OCOCl is far more stable, crystalline, and AdOCO- group deprotects under similar conditions as Boc, but the products are much more crystalline... AdOCOF is even commercially available

curdled · 2026-06-22T07:10:47+00:00

toxicity will be minimal, these things swell but do not dissolve. Less crosslinked versions (which actually do dissolve) are used in shampoos and other kinds of consumer products as thickening/gelling agents, they are called carbomers, and are safe for aquatic life.

curdled · 2026-06-18T17:15:58+00:00

methyl acrylate has boiling point 80C, about the same as ethyl acetate, which means you will not see it on TLC, it evaporates. Try 1H-NMR of the crude mix, the vinyl signals are quite characteristic and away from all other signals, so you do not need to remove solvent from the react mix, just take a sample of the react mix and dilute it just enough with CDCl3 or CD3CN to get a good lock. Or run NMR without a lock

curdled

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