How Water Freezes Lower on a Negatively Charged Surface

I first heard this on National Public Radio and then I searched for it. In short, David Ehre, Etay Lavert, Meir Lahav, and Igor Lubomirsky report in Science, (Water Freezes Differently on Positively and Negatively Charged Surfaces of Pyroelectric Materials) water freezes at a lower temperature (-18°C) on the negatively charged side of a lithium tantalate plate with a strontium titanate film than on the positive side (-7°C, and -12°C uncharged).

Is this unique or is this a manifestation of something in our standard introductory organic chemistry textbooks? I thought it was the latter. Let me explain how.

For the purpose of thinking about this problem, let us assume the metal surface is simply a flat charged surface, without contour. If the surface has a negative charge, then the water should be attracted like a flagpole. One hydrogen should be anchored to the surface of the metal at right angles and the other hydrogen could spin about that axis with the flag hydrogen at 105°. It should not be surprising that this configuration should not be as good of a surface as one with greater rigidity.

If we compare with the positively charged surface, then both pairs of non-bonded electrons should be anchored to the surface and locking the hydrogens in a fixed position. This should limit the degrees of freedom and enable crystal growth.

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Breaking Stuff for Science

Most chemists will agree, a chemical spill on the floor is one of the most annoying things to have to deal with in a lab. With LBL policy, you have to adhere to the SWIMS protocol: Stop work, Warn others, Isolate the area, Monitor yourself, Stay in the area. Not to mention using the correct spill kit, dealing with all the paperwork of the spill and the opening of the spill kit, explaining to the safety people what happened and why (hopefully) it wasn’t your fault, etc.

Aside from making sure your people are competent and well trained, not much is often done to prevent spills. Engineering controls such as secondary containment, fume hoods, capped reagent bottles, etc. work well when people remember and plan to use them. All too often, we see good chemists forgo extra safety steps for speed or just plain old laziness. Sometimes, people get badly hurt not because they were bad chemists or bad scientists, but because they really needed to catch the 6:40 train that day.

What we need are more safety devices that prevent the accident caused by a failure of the preventative safety measures from being very dangerous. For example, take these safety-coated reagent bottles from VWR. They have some plastic coating (PVC I think) outside of the glass to prevent spills even if the glass shatters. Sure some solvents would eat through the coating, but it would still buy you time to contain the spill, or evacuate the room if necessary.

Recently, with LBL’s current safety kick, our lab ordered 40 of these babies to replace our older reagent bottles. Interestingly though, the coating is really hard to see. In fact, when we first examined the bottles there was a dispute between some lab members as to whether we received the correct shipment or not.

Here is how the bottle looked, next to a typical graduate student size scale:

Being scientists however, Mitch and I knew that we couldn’t just take VWR’s word that we now had safety-coated reagent bottles.  We needed to test whether it really had the safety-coating, whether the coating would actually stay intact after an impact strong enough to break the glass inside, and whether the coating would feel weird if we poked with our finger.







So, using my safety training, I put the reagent bottle into a plastic bag, and put the plastic bag inside a phototray. Note the secondary and tertiary containment.






I went and found a big wrench, donned my safety goggles, lab coat, nitrile gloves and put the soon to be destroyed bottle durability testing apparatus into a fume hood with the sash half open.  I then proceeded to smash it to pieces. It was a good day of science.

Here is the result after a good beating. The safety-coating is quite clearly visible now, along with the area where the hole would be, if the coating wasn’t still covering it. The interior glass shattered as expected, but the safety-coating simply flexed a bit and recovered. Also, no sharp pieces of glass pierced the coating, so the contents of the bottle would have been contained. It took a significant amount of effort with some sharp tweezers to illustrate the intact film of the coating. We also confirmed our hypothesis that poking the film with our finger would feel weird. The bottle met our expectations in all tested categories. It also looked really cool and took a great picture.

So in our effort to make the lab safer, we tested and confirmed the usefulness of these safety-coated reagent bottles in an easily repeatable scientific experiment. Tests would have been done in triplicate, however funding was abruptly cut off when we attempted to share our findings with others in the lab.  We recommend the safety-coated bottles for use throughout the chemistry lab. All waste was disposed of in coordinance with EH&S protocol.

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32-electron chemistry

We all remember learning about octets and valence electrons in school. We may also remember the first time we saw an 18-electron transition metal complex. This week Dognon et al. discuss the possibility of 32-electron organometallic complexes.^[JACS] In order to reach 32-electrons, f-orbital participation is essential. Below is a picture of a hypothetical organometallic complex with 28 carbons in a cage around an actinide element.

Although these systems are not new, as the Smalley group made U@C₂₈ in the gas-phase in ‘92,^[Science] Dognon et al. examine a series of these systems for different actinides. The major conclusion is that the plutonium system is theoretically predicted to have the largest bonding energy for its Pu⁴⁺@C₂₈ complex. Since fullerenes and the intercalation of metals often only need heat to be synthesized, I wouldn’t be surprised if these complexes have already been made but missed as impurities and byproducts.

Link to paper: A Predicted Organometallic Series Following a 32-Electron Principle: An@C28 (An = Th, Pa+, U2+, Pu4+)

Update 1: Jyllian Kemsley also covered it at C&EN — Stable Caged Actinides Proposed(subscription)

Mitch

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Halogen Bonding

Some of you may be familiar with the term “halogen bonding”. In analogy to hydrogen bonding, this weak interaction occurs between an electron donor, such as nitrogen, and a halogen (Cl, Br, I). The halogen acts as an electrophile.

This is possible because the halogen has a region of positive partial charge at its tip, the so-called sigma-hole, as shown by calculations (doi:10.1007/s00894-006-0130-2). The group of Resnati and Metrangolo in Milan have used this interaction to construct a variety of polymeric chains and networks for crystal engineering. As they discuss in their current Science paper (doi:10.1126/science.1162215), it also plays an important role for drug design, which I am particularly interested in. Many drugs on the market are halogenated aromatics. The exact role of the halogen for binding is not always known, since often it was introduced in order to tune the hydrophobicity of the compound. I suspect that in many instances, halogen bonding to a backbone carbonyl oxygen could be of importance.

Clearly, more work is required to further investigate halogen bonding in a biological context. If people want to incorporate this kind of interaction into rational drug design or crystal engineering, good quantitative models will be needed.

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Scientific Misconduct

This nature article discusses the results of a survey about scientific misconduct, while an editorial makes some comments.

Quote: “The 2,212 researchers we surveyed observed 201 instances of likely misconduct over a threeyear period. That’s 3 incidents per 100 researchers per year. A conservative extrapolation from our findings to all DHHS-funded researchers predicts that more than 2,300 observations of potential misconduct are made every year.” Almost 9% of the respondents had witnessed some sort of misconduct, and 37% of those incidents went unreported.

The authors conclude that, besides protecting the whistleblowers better, it is necessary “to create a zero-tolerance culture”. The editor, however, holds the opinion that one also needs to take a look at “the environment that has allowed misconduct to flourish”. In his opinion, there should be the possibility of finding a solution without ruining the career of a scientist, especially in mild cases.

I tend to follow the editor’s reasoning. In my opinion, the zero-tolerance culture already exists to a certain extent, because a scientist convicted of, e.g. faking data, can forget about his career. But the result of such a policy is clear: no-one wants to blow the whistle on a colleague, because they don’t want to end somebody else’s career and because they will make themselves very unpopular. The real problem is the way misconduct is treated at the moment: we want to identify the guilty scientist, and punish him/her.

While this makes sense for the worst cases of fraud, in milder cases one should try and ask the question *why* the misdeed was done. Take, for example, the way hospitals treat mistakes nowadays: they try to find out how it could happen, and how it can be avoided in the future. This is very sensible, because it treats the problem in a proactive way: instead of reacting to the incident by punishing somebody, future incidents are reduced by tackling the things that cause them in the first place.

If there is a lot of pressure to produce as much data as possible in a research group, it is tempting to cut a corner once in a while. Can this not partly be considered the prof’s fault? In a similar way, one should address the working atmosphere in the group in question. The problem with the academic system is that there is no informal institution to turn to, besides your boss, if you are to witness a case of scientific misconduct. So we fall back to the old issue: the only person you can contact in case of problems has all the power over you.

At the University of Toronto, a “Graduate Student Oath”, similar to the Hippocratic Oath, has been tried as a means to strengthen scientific ethics (Science). Although this is an interesting idea, I doubt it will change the behaviour of people very much.

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