Chemistry

Spectroscopy: Laser vaporization improves surface-enhanced Raman spectroscopy for cultural heritage research
Spectroscopy: Laser vaporization improves surface-enhanced Raman spectroscopy for cultural heritage research
about 8 hours ago
Training: Resource hosts comprehensive video library
Training: Resource hosts comprehensive video library
about 8 hours ago
Senate: Breakthrough bipartisan proposal would update Toxic Substances Control Act
Senate: Breakthrough bipartisan proposal would update Toxic Substances Control Act
about 8 hours ago
I just had the fastest and cleanest pump oil change of my career, thanks to an invention of my colleague. We use large Welsh DuoSeal belt-driven pumps installed in metal cabinets under the hoods and these beasts are reliable – but ...
I just had the fastest and cleanest pump oil change of my career, thanks to an invention of my colleague. We use large Welsh DuoSeal belt-driven pumps installed in metal cabinets under the hoods and these beasts are reliable – but so heavy: They take over 3 liters of oil to fill and the whole thing weights about 50 kilos. The oil drain valve is inconveniently located right near the bottom so the pump cannot be easily drained inside the cabinet. The normal oil change procedure requires disconnecting the vacuum hose and dragging the pump out. I would prop the pump on an empty solvent barrel, put oil collection bucket beneath the drain valve and keep draining, tilting, flushing, draining, filling, cursing. Lifting the pump requires two pairs of hands, the oil drips everywhere, and given the large and awkward shape of the (very heavy) re-filled pump that has to be then coaxed back in and over the cabinet lip, the vacuum hose reattached and vacuum leaks fixed, it is a pretty unpopular job – one that gets postponed for as long as possible, resulting in pumps sloshing in very tired crud that has the look and smell of burnt molasses. But not any longer! Motivated by his hurt back and desperation, my colleague recently got a brilliant idea to take a large (4L) Erlenmeyer filtration flask closed with a stopper with a tube, attach cheap vinyl transparent tubing (like you would use for water in reflux condensers) and connect it to the oil drain valve at the bottom of the pump. If the spent oil is still warm (from a pump that has been run, so it is less viscous), it can by sucked out through the drain valve into the Erlenmeyer under house vacuum in just few minutes. After a flushing oil fill, 2 min pump run and another suction-assisted drain and final re-fill, the entire oil changing operation can be completed in less than 15 minutes. No mess, no need to take the pump out, no need to disconnect the vacuum hose from the pump. Our biologists of course claimed a credit for the pump oil change idea, having used this sort of setup for sucking off liquor from cells in multi-well plates. But I think the true origin of this pump oil change breakthrough is slightly more disturbing. You see, my colleague who came up with this idea is leaving for medical school in few weeks. In preparation he has taken the anatomy labs already. As I was sucking out nearly a gallon of alarmingly dark rotten sludge from my pump using his gadget, he calmly observed that the really good, top-of-the-line embalming machines can aspirate blood while at the same time injecting the formaldehyde solution back into the empty veins: One just needs to correctly insert the inlet and outlet tubes into the patient, turn on the flush routine and wait until the aspirate finally starts coming out clear…
about 8 hours ago
Tweet of the week: “In discrepancy is discovery” – Lesson learnt from scientific research. — Curious Wavefunction (@curiouswavefn) May 20, 2013 To the network: Artful Science: Was antiquity really so tacky? Cleantech Chemistry: Ne...
Tweet of the week: “In discrepancy is discovery” – Lesson learnt from scientific research. — Curious Wavefunction (@curiouswavefn) May 20, 2013 To the network: Artful Science: Was antiquity really so tacky? Cleantech Chemistry: Never Mind All That: Solar on the upswing Newscripts: In Print: Toys Will Be Toys and Amusing News Aliquots The Safety Zone: Dow launches Lab Safety Academy website The Watch Glass: Teflon: Newcomer to heat exchange and What's That Stuff? Chicken Eggs and Texas City: Portrait of a Chemical Town and C&EN Talks With Mae Jemison and Chemist tried in Chicago riot case Related Posts:This Week on CENtral Science: Harlem Shake, Natural gas, andThis Week on CENtral Science: Whale Fossils, Oscar Noms, UC…This Week on CENtral Science: Mona Lisas, Spider Sex,…This Week on CENtral Science: #scioDC , World's…This Week On CENtral Science: Richard's Lionheart,…
about 8 hours ago
A CYNIC might dismiss the "quantified self" movement, whose adherents use an array of gizmos to record all aspects of their physical existence, as gimmicky navel-gazing by geeky workout nuts, eager to gamify ever bigger chunks of life. T...
A CYNIC might dismiss the "quantified self" movement, whose adherents use an array of gizmos to record all aspects of their physical existence, as gimmicky navel-gazing by geeky workout nuts, eager to gamify ever bigger chunks of life. That, as Babbage has recently come to realise, is unfair. Better information about your actual exertions makes for more informed decisions. This is as true of exercise as it is of personal spending, say. Little wonder that, as monitoring devices become smaller, cheaper and better integrated with smartphones, more people are embracing their quantified selves. For your correspondent, the conversion began a year and a half ago, when he moved his office from rented space into his basement, purchased an adjustable standing desk and, shortly afterwards, a flat treadmill designed to work at low speeds underneath the desk while displaying miles walked. He has become, in other words, a walking worker of the sort described by Susan Orlean in a recent New Yorker story. (Standing turned out easy—and a nice change; learning to type and focus on two computer screens while trundling proved a bigger challenge.)To keep himself motivated, Babbage recently purchased a self-tracker made by Fitbit, a Californian company. Fitbit's devices (similarly to the Nike Fuelband, the Jawbone UP and others) use an accelerometer to track steps. Fancier models include an altimeter to capture ascending stairs and inclines. Smartphone apps pair with these devices, naturally. (Software developers have also created software that relies on the built-in GPS and other sensors in mobiles, with varying accuracy.) Most of the standalone trackers are designed as wristbands, others (like Babbage's Fitbit One) are smaller than a pack of gum and can be slipped into a clip or strapped around a wrist inside a pouch.As the data streams from the sensors to smartphones or computers and on to the device-makers' central servers, the associated apps offer feedback and encouragement based on targets set or reached. The Fitbit app, for example, tells you that a few more steps will take you past the daily target, or give you a pat on the back for exceeding a goal or setting a new all-time high. Small targets, reminders, stretch goals and awards all help nudge you towards personal betterment.The systems increasingly welcome data from other hardware and software. Wi-Fi scales, popular a few years ago, can be linked up to some systems. (Babbage added his to a new Fitbit account.) Smartphone apps like Runkeeper, which use GPS to plot routes and measure distance and altitude changes, can be integrated, too. For a more detailed picture, you can enter food consumed and describe other activities that the devices are unable to capture.Many of the gizmos link directly to an online social network, inviting you to compete with friends. Babbage's long-shinned chum regularly racks up over 125,000 steps in a week. (Your correspondent managed briefly to pass him with about 95,000 after the rival had spent a day away from his own treadmill and another day in transit to Australia; the advantage did not last long.)Goaded, envious or proud—perhaps all three—Babbage has walked about 40 miles each of the past two weeks, a fourfold improvement on pre-tracking times by his reckoning. He has also shed a few pounds and, by slipping the Fitbit inside its wrist strap overnight, has learned how well, or poorly, he sleeps. The system responds to fidgeting and can thus tell deep slumber from light, or from waking. Your correspondent sleeps deeply, it turns out. But the data make one thing clear: he ought to hit the sack a bit earlier.
about 8 hours ago
Beth Halford and I sat down to have a quick chat about the life of postdocs, based on her really interesting article in this week's C&EN. It was really fun and the edited recording is below:Timepoints:0:00 - 2:00: What's been the backgro...
Beth Halford and I sat down to have a quick chat about the life of postdocs, based on her really interesting article in this week's C&EN. It was really fun and the edited recording is below:Timepoints:0:00 - 2:00: What's been the background of postdocs?4:30: The happiness of postdocs6:30: The postdocs that Beth knew7:00: Crowdfunding a postdoc (CJ grossly underestimates the cost of a FTE)8:55: PIs and their postdocs9:50: Should we pay postdocs more? Beth on Paula Stephan11:00: $16/hour12:00: Why do a postdoc?13:30: The finances of postdocs15:11: Jessica Breen's cogent comments on delaying life milestones?17:15: Are postdocs really broader?19:45: The postdoc arms race22:17: The longest postdoc you've heard of23:55: When will the arms race be over?27:55: What should postdocs do about getting a job?Thanks to Beth for a great conversation!
about 13 hours ago
There's a new paper out today in Nature on a very unusual way to determine the chirality of organic molecules. It uses an exotic effect of microwave spectroscopy, and I will immediately confess that the physics is (as of this morning, an...
There's a new paper out today in Nature on a very unusual way to determine the chirality of organic molecules. It uses an exotic effect of microwave spectroscopy, and I will immediately confess that the physics is (as of this morning, anyway) outside my range. This is going to be one of those posts that comes across as gibberish to the non-chemists in the audience. Chirality seems to be a concept that confuses people pretty rapidly, even though the examples of right and left shoes or gloves (or right and left-handed screw threads) are familiar from everyday objects, and exactly the same principles apply to molecules. But the further you dig into the concept, the trickier it gets, and when you start dragging the physics of it in, you start shedding your audience quickly. Get a dozen chemists together and ask them how, exactly, chiral compounds rotate plane-polarized light and see how that goes. (I wouldn't distinguish myself by the clarity of my explanation, either). But this paper is something else again. Here, see how you do: Here we extend this class of approaches by carrying out nonlinear resonant phase-sensitive microwave spectroscopy of gas phase samples in the presence of an adiabatically switched non-resonant orthogonal electric field; we use this technique to map the enantiomer-dependent sign of an electric dipole Rabi frequency onto the phase of emitted microwave radiation. The best I can do with this is that the two enantiomers have the same dipole moment, but that the electric field interacts with them in a manner that gives different signs. This shows up in the phase of the emitted microwaves, and (as long as the sample is cooled down, to cut back on the possible rotational states), it seems to give a very clear signal. This is a completely different way to determine chirality from the existing polarized-light ones, or the use of anomalous dispersion in X-ray data (although that one can be tricky). Here's a rundown on this new paper from Chemistry World. My guess is that this is going to be one of those techniques that will be used rarely, but when it comes up it'll be because nothing else will work at all. I also wonder if, possibly, the effect might be noticed on molecules in interstellar space under the right conditions, giving us a read on chirality from a distance?
about 14 hours ago
There's a new paper out today in Nature on a very unusual way to determine the chirality of organic molecules. It uses an exotic effect of microwave spectroscopy, and I will immediately confess that the physics is (as of this morning, an...
There's a new paper out today in Nature on a very unusual way to determine the chirality of organic molecules. It uses an exotic effect of microwave spectroscopy, and I will immediately confess that the physics is (as of this morning, anyway) outside my range. This is going to be one of those posts that comes across as gibberish to the non-chemists in the audience. Chirality seems to be a concept that confuses people pretty rapidly, even though the examples of right and left shoes or gloves (or right and left-handed screw threads) are familiar from everyday objects, and exactly the same principles apply to molecules. But the further you dig into the concept, the trickier it gets, and when you start dragging the physics of it in, you start shedding your audience quickly. Get a dozen chemists together and ask them how, exactly, chiral compounds rotate plane-polarized light and see how that goes. (I wouldn't distinguish myself by the clarity of my explanation, either). But this paper is something else again. Here, see how you do: Here we extend this class of approaches by carrying out nonlinear resonant phase-sensitive microwave spectroscopy of gas phase samples in the presence of an adiabatically switched non-resonant orthogonal electric field; we use this technique to map the enantiomer-dependent sign of an electric dipole Rabi frequency onto the phase of emitted microwave radiation. The best I can do with this is that the two enantiomers have the same dipole moment, but that the electric field interacts with them in a manner that gives different signs. This shows up in the phase of the emitted microwaves, and (as long as the sample is cooled down, to cut back on the possible rotational states), it seems to give a very clear signal. This is a completely different way to determine chirality from the existing polarized-light ones, or the use of anomalous dispersion in X-ray data (although that one can be tricky). Here's a rundown on this new paper from Chemistry World. My guess is that this is going to be one of those techniques that will be used rarely, but when it comes up it'll be because nothing else will work at all. I also wonder if, possibly, the effect might be noticed on molecules in interstellar space under the right conditions, giving us a read on chirality from a distance?
about 14 hours ago
In the previous three posts on alkynes we've introduced some new reactions that are specific to alkynes (versus alkenes): deprotonation (and subsequent substitution), partial reduction to alkenes, and the formation of aldehydes and keton...
In the previous three posts on alkynes we've introduced some new reactions that are specific to alkynes (versus alkenes): deprotonation (and subsequent substitution), partial reduction to alkenes, and the formation of aldehydes and ketones through net “hydration”. With all the focus on the ways in which alkyne chemistry can differ from alkene chemistry, it's helpful to be reminded of all the ways in which they are similar. In this post we'll go back to a key reaction mechanism pattern we observed with alkenes: the so-called, “carbocation pathway” – and explore how many of the reactions of alkenes we're familiar with can also be used with alkynes. The three major examples in this category are the reaction of hydrohalic acids (H-Cl, H-Br, and H-I) with alkynes. If you recall, when added to alkenes these reagents were attacked by the ? bond of the alkene to give a carbocation (on the most substituted carbon, giving “Markovnikov” regioselectivity) followed by attack of halide ion on the carbocation. Since alkynes merely differ from alkenes in the addition of a second ? bond, we would expect that these reactions would also work for alkynes as well – and they do! If we treat an alkyne with a single equivalent of H–Cl [note - we'll just use H-Cl in all of these examples, but HBr and HI work in exactly the same way] we end up forming an alkenyl chloride. Note that the chlorine atom ends up attached to the most substituted carbon of the alkene ["Markovnikov" regioselectivity]. Note that the product here still has a ? bond. You might be wondering if it's possible to for this ? bond to react with a second equivalent of H-Cl. The answer is yes. [Note - it is possible to just "stop" the reaction at this stage if we use just one equivalent, because the product (alkenyl chloride) is less reactive towards HCl than the starting alkyne]. Indeed, if we add a second equivalent of H-Cl, it adds to either side of the C-C ? bond, giving us the product where two chlorine atoms are on the same carbon. By the way, we call this a “geminal” dichloride (think Latin – “gemini” = twins). We can also get this product if we simply add two equivalents of H-Cl to the starting alkyne. So how might this reaction work? In a very similar fashion to how H-Cl adds to alkenes. The first step is protonation of the alkyne with H-Cl in such a manner as to give the most stable carbocation intermediate. Since carbocations are stabilized to a greater extent by electron releasing alkyl substituents than by hydrogen, the new carbocation will form at the end of the alkyne bearing the carbon substituent. In the next step, the carbocation is attacked by the chloride ion to give the alkenyl chloride. What about the second equivalent of H-Cl ? Given the fact that the geminal dichloride is the product here, the most reasonable mechanism for its formation is merely a repeat of the steps from the first reaction (as shown). However it's worth pointing out one interesting feature. Note that the carbocation in this case bears a chloride ion. Since carbocations are electron poor, and chlorine is quite an electronegative element, it's interesting to point out that the electron releasing ability of the alkyl group [and the ability of chlorine to donate a lone pair to the carbocation] “win out” here over the electron-withdrawing character of chloride ion. As mentioned above, the reactions of alkynes with HBr and HI (as well as HF, just in case you're curious) follow the exact same pathway. It's probably worth tying back this post to the post on alkenes and the carbocation pathway, noting the similarities and differences between the chemistry of alkenes and alkynes. Hopefully this table will prove useful: As with alkenes, reactions that follow this pathway proceed through a carbocation intermediate and provide the “Markovnikov” products as major. The key difference in this pathway is that hydration of alkenes gives alcohols, whereas hydration of alkynes gives carbonyl de
about 15 hours ago