A Star is Born

Watch out Beowulf, David Leigh of the University of Manchester has made much finer chainmail (yes, that reference was solely from the cover of the book; I saw it as a kid and now chainmail is forever associated with Beowulf in my mind). A couple of hundred years after we stopped using chainmail (it was good at stopping swords; not so much bullets) we’ve finally started producing it again.

The molecule is made of two interconnected rings, with a whopping 114 atoms each. At each bend (there are six of them) is an iron atom surrounded by organic ligands (bipyridine derivatives, if you want to get fancy). In the middle sits a PF6 ion that apparently refuses to leave.


The star.

The star-tling molecule. Yuck, yuck.

Chemists have been trying to make this molecule, nicknamed the “Star of David catenane” because in chemistry even your nickname has to be scientifically meaningful, for half a decade. Leigh, in a press release from Manchester University, gave full credit to his graduate student, Alex Stephens, before giving the typical why-did-you-do-this answer: “It was a great day when Alex finally got it in the lab. In nature, biology already uses molecular chainmail to make the tough, light shells of certain viruses and now we are on the path towards being able to reproduce its remarkable properties.”

In my Google search for “molecular chainmail” (because I had never heard the term before), I came across a book called “Beauty in Chemistry: Artistry in the Creation of New Molecules” and because that title was too intriguing they added the subtitle of “(Topics in Current Chemistry)”. The book is from 2012 so maybe we’ll see some more interesting molecules coming out soon. This kind of work goes to show that one can find beauty even in the smallest things.

Hemp: Not Just for Granola-Eating Hippies

Hemp is back, man, and more energizing than ever. David Mitlin, then at the University of Alberta and now at Clarkson University, has developed a method for making supercapacitors out of hemp that is not only much cheaper than graphene (the cream of the crop as far as organic conductors go), but also outperformed standard devices by nearly 200%.

In a press release from the American Chemical Society, Mitlin gives the best quote possible on his research: “We’ve pretty much figured out the secret sauce of it. The trick is to really understand the structure of a starter material and to tune how it’s processed to give you what would rightfully be called amazing properties.” Right on.


The American Society of Mechanical Engineers is down with hemp.

To make the supercapacitors, his group heated hemp waste at 180 °C (~350 °F) for a day to get a nice char going, then blasted it at 800 °C (~1470 °F) with a little potassium hydroxide. That final burn turned the char into carbon nanosheets (as so nicely depicted in the above picture from the American Society of Mechanical Engineers). The hemp precursor left a lasting impression on the nanosheets, giving them the unique molecular structure that Mitlin claims is key to his device performance. The sheets were riddled with holes 2–5 nanometers in diameter, making nice paths for charges to move in and out.

Yury Gogotsi, materials scientist at Drexel University, in a comment to Chemical & Engineering News, says that scaling up the process may be difficult (read: costly), what with the high temperatures and day-long heating process.

But that’s just, like, his opinion, man.

Big Ball Scars

Buckyballs are weird. They’re little soccer balls that collect electrons—one of the few materials used as electron acceptors in solar cells. They’re the largest object to show particle–wave duality, and that’s quite a feat for sixty carbon atoms. If an alkali-metal is shoved in the center, the whole thing acts metallic and, in some cases, superconducting. They even have a toy named after them. And we can’t forget that the 1996 Nobel Prize in Chemistry went to the discoverers of fullerene. Needless to say (of course, I’m about to say it anyways), these large spherical molecules are a hot topic.

Some researchers are moving away from the “small” fullerenes, C60 and C70, to larger versions. But as the size grows so do the problems. A recent report in ACS Nano by David Wales of the University of Cambridge details the defects that arise in larger configurations (sorry for the paywall link). This work is entirely theoretical, as causing defects in a specific arrangement is as difficult (or maybe more so) than forming defect-free molecules. The molecule can get a “scar” when the pentagon–hexagon–pentagon structure is dislocated to a pentagon–heptagon–pentagon structure.


C860 and C1160 fullerenes with red scars.

Defects are unavoidable in large spheres and the configuration of them constitutes a Thomson problem, the location of repulsive points on a sphere, which is one of eighteen unsolved mathematical problems on the list of Smale’s problems for the 21st century. While the Thomson model was previously used to describe the configuration of electrons in an electron shell (and has since been abandoned since it’s failure to do so), the problem is now being applied to fullerenes.


Defects in different sized fullerenes.


The paper also looked at funnels, or outward curving structures, and showed that defects can occur there, too. Interestingly, the fourth to last structure below (which is akin to a carbon nanotube) shows no defects (at least in their picture, they didn’t discuss the lack of defects in the text).


Defects in curved surfaces.

So what does this mean? What can defects do? Well, they can disrupt aromaticity and conjugation which would change the electronic structure of the molecule, diminishing conductivity and widening the band gap so that they’d be unsuitable for solar cells or other electronic applications. (That was a mouthful… fingerful?) But it’s not all bad. A paper from last year in the Journal of Physical Chemistry C (paywall again) states that defects in a graphene surface can lead to reactive sites. In other words, chemistry can happen. I don’t think it’s too far fetched to say there would be a similar situation with fullerenes. After all, they’re just balled-up graphene.

John Rogers In The 24th and a Half Century

In the lab of University of Illinois Urbana-Champaign Professor John Rogers, electronics fall apart or, more accurately, dissolve in water. Transient electronics, as they’re called, are designed to be temporary. They have the potential to be implanted in the body, monitor vital signs or fight infection, and slowly dissolve into harmless components. If scaled up to manufacturing levels, these devices have the potential to revolutionize electronics. And his group has been working hard by publishing a lot of papers on the subject.

So I was surprised when I saw a recent report by the Rogers group in Nature Communications on a wholly different class of electronics. (Though maybe I shouldn’t be surprised since Rogers got his Ph.D. under none other than George Whitesides who may be the most diverse chemist of today.) In this new report, he’s using fractal patterns to integrate metal wires into a stretchable substrate. At first I thought, “How the hell is he going to make an infinite recursion wire.” Then I found out that space-filling curves are fractals (thanks Wikipedia). You can think of the patterns like a winning game of Snake, lines packed as close as possible without overlapping. An excited group of mathematicians figured out mathematical functions for different varieties of packing and left us with the below patterns. (Traditionally, the mathematical functions have hard edges, but Rogers has replaced the edges with arcs to improve the mechanics—hard turns create stress points which break easily.)


Different fractal patterns used in the devices.

So wires of different patterns are embedded in a polymer substrate. So what? Well, it turns out interesting mechanical properties arise with the different patterns. These things can stretch. The “stretchability” is well above the 20% necessary to mimic skin. So that’s what they did. Using the Peano layout, they spelled out the word ILLINOIS and mounted it on someone’s actual skin. Then, using a “skin-replica” they took optical and scanning electron microscopy images to prove that the wires conform to the valleys and hills of normal human skin.


The word ILLINOIS was embedded on actual, living skin. Boxes e and f are optical and scanning electron microscopy images on a skin-replica.

“Amazing,” I thought. Wearable electronics may soon be reality. And if this was my work, I would probably stop there, too excited not to publish. But it’s not and a good thing, too. They went on to make actual functioning devices able to heat, sense temperature, and take electrocardiograms (ECGs). They made tiny heart monitors.


And not only that. The devices are compatible with MRIs. Because there are no closed loops in these devices, there aren’t any circulating magnetic currents that may cause signal loss. They’re completely invisible in an MRI scan.

It’s not often that math-inspired work crops up in chemistry (for a hard science, chemists are surprisingly squeamish about math), but when it does it’s always beautiful. It seems that John Rogers has made it his personal mission to advance us to the next level of technology… and into the twenty-fourth and a half century!

“Never give up. Never surrender.”

One of my favorite research projects to follow is Whitesides’ soft robot. Part of his platoon (since he has enough graduate students to call it such) has been developing a mobile robot made purely of polymers. No metal necessary. The body of the robot is divided into air sacs that are pumped full or evacuated to create movement. They’re supposed to resemble starfish, but they look more like army commandos crawling under enemy gates.

By filling the sacs in the right order, the soft robot can slip under a raised barrier.

By filling the sacs in the right order, the soft robot can slip under a barrier, such as your bedroom door at night.

Soft robots are cheap, easy to fabricate, lightweight, and have the advantage of picking up delicate objects, like an egg, without crushing it.


In a new paper in Advanced Functional Materials, the group shows that the robots can resist blunt impacts “better than hard robotic structures (and also most animals of comparable weight and size).” Though I hope they didn’t have a control for that parenthetical joke. The group wanted to quantify exactly how much damage these robots can take. So, in a comically sad fashion they hit their robot with a hammer. If you have access to the paper, check out the Supporting Information for some videos that will make you feel a little bit bad for laughing. Of course, the “hammer test” was in addition to more traditional scientific methods for measuring stress and strain.

You can knock him down, but he'll get right back up.

You can knock him down, but he’ll get right back up.

Since whacking the poor guy with a hammer wasn’t enough, they ran him over with a car. And when that wouldn’t stop him, they ran him over again but this time with a pile glass underneath. Yet, he continued to grip. They proved that these little guys are highly resistant to mechanical stress. Of course, if the glass had managed to poke a hole in one of the sacs the robot would cease to inflate, in effect maiming it, but the polymer they use, an Ecoflex silicone, is fairly puncture resistant.

He's a survivor.

He’s a survivor.

These flexible robots really delight me. They’re not creepy enough to give me chills (Boston Dynamics, I’m looking at you)  and they’re not human enough to make me think of bad sci-fi movies. Well, maybe my science fiction thoughts aren’t totally gone, because, after reading the paper and opening this text editor, I started to type:  I’m glad these guys aren’t sentient… yet.

Preceptor? Like in Harry Potter?

The University of Delaware is taking a hint from medical fields like nursing and pharmacy to join together two difficult topics: chemistry and biology. The goal is to help students learn complicated chemistry in relation to basic biology ideas, which C&EN reported in this week’s issue.

Basically, the program is taking graduate level scientists who have their Ph.D. or masters and having them act as a learning guide. These preceptors play a role between TA and professor. They’re in the labs and classes getting their hands dirty, but aren’t involved in grading or assessment. They’re mentors which give no judgement. Michael Weir, one of the preceptors, equates his role to that of a “friendly uncle” who will answer questions and solve problems without students being afraid of punishment. Students are divided into smaller groups (though still 48 large) and assigned to a specific preceptor. The students have more access to the preceptor as opposed to a professor overseeing a class of 200.

I really hope the idea catches on. Not only will the undergraduates have access to more personalized help (which I think is absolutely important for first and second year undergraduates) but the preceptors will have experience teaching at the university level. One thing I think larger schools suffer from is the larger class sizes, which is absolutely necessary unless you want a huge staff of professors whose priority is to teach rather than do research (which would cost more money and drive up tuition prices even more). Though I’m not sure that the preceptors need to be staff members as they are at University of Delaware. I think upper level graduate students who want to go into academia could nicely fill this role. It would give them a one-up on their resume, too.