The devil makes the pots but not the lids.

il diavolo fa le pentole ma non i coperchi

The title of this post is the literal translation of a proverb. The proverb means that Devil’s pot of wickedness sooner or later will boil – and, as there’s no lid, someone will see its content and reveal the truth. That’s the old innocent idea that, finally, justice will prevail over evil… well, I like it so much I use it as title. Rather than devils, this post is actually about pots and lids – of molecular size, of course.

As that’s not a Masterchef contest at the nanoscale, let’s get rid of the pot for the moment, and call it ‘container’. In the nanoworld there are many such containers, which can be filled with molecules. In this way, you can produce new materials with applications in various areas of technology: from solar energy to sustainability and human health.

Our containers are named zeolites – porous materials which are commonly used as adsorbents and catalysts in various commercial, industrial, and even medical applications as well as in our everyday life.  Also, if you fill zeolites with dye molecules, you’ll get materials able to capture and transfer solar energy very efficiently. You would do it much easier if you first know how their pores look like.

In particular, how do their entrances appear to an incoming molecule? This question is our “step one”,  because this information is really hard to get from experiments.

step01

Fortunately, modeling comes to the rescue…. and that’s one of the reasons why I love so much doing #compchem (computational chemistry)!!

step02

Step 2 revealed that the channel openings expose hydroxyl groups, and look somewhat like this:

zeoliteLChannel
Entrance of zeolite L channel, showing the terminal -OH groups and the channel accessibility.

Those terminal hydroxils can be condensed with other molecules, carrying specific groups, hence new properties and functionalities. Among them, the possibility of “closing” the pores. Why is it so important?

Zeolites are resistant to heat and pressure, and act as a protective shield around the dye. But every “pot” needs a “lid”:  plugging the zeolite pore entrances, so that the dyes, once included, cannot escape into the environment, would further enhance their stability.  This has already been done experimentally,  by attaching at the channel entrances peculiar molecules nicknamed “stopcocks”. They consist of two “parts”:

  • the “tail”, which can penetrate zeolite pores;
  • the “head”, which is too big to enter the pore and remains outside, thus blocking (at least partially) the channel opening.

Two typical stopcocks, one with a small tail, and the other with a long, bulkier tail, are shown below.

stopcoc

Such “molecular stoppers” do indeed a great job in preventing molecules to escape from zeolites.  However, there were no clear ideas about how these stoppers were attached to the pore entrance, and how much space they occupied.  This knowledge would help finding better “lids” for our zeolite “pots”. How do we get it? Of course by modeling, as sketched in step 3 and 4.

step03

Here’s what we learned:

  • stopper molecules prefer to bind aluminum sites at the channel entrance;
  • the tail group always penetrates inside the pore, while the head stays outside;
  • the extent of blocking depends on the stopcock.
    In particular:

     – small-tailed stopcocks are like partially opened “lids” : no full closure                – bulky-tailed stopcoks behave like “corks”: full closure

So the zeolite pore may be fully sealed by one bulky stopper, like a molecular cork on a Prosecco nano-bottle. On the contrary,  one “lid” (small stopper) leaves our “pot” partially opened. Fortunately, there’s enough room to attach a second small stopper to the opening, that can now fully be closed.

And this brings us to step 5…

step05

… which could well be the end of this story, first told some time ago. Thank you for reading it!

Anyway, there’s an epilogue, which is perhaps the nicest part (“dulcis in fundo“).  Using such information, obtained from modeling, experimental colleagues recently trapped indigo (that’s, your denim’s blue) in zeolite L, and blocked the channel entrances with two small stopcocks. In this way, they made a new pigment, exceptionally resistant, with an amazingly beautiful blue color.  For me #compchemist, that blue was simply….. the color of happiness.

zeolite_channel_openings

 

For more information…

 

Understanding an efficient light harvesting material

When we fill porous materials with dye molecules of the right size, we obtain useful compounds for solar energy technology. These compounds can transfer solar energy efficiently because pores and channels fit to the dyes “like a glove”. In this way, molecules are forced to stay in line, and energy can easily pass from a molecule to the next one in the line. If we knew in detail the structure of the dye arrays, we’d have better chances to improve these compounds.

Unfortunately, the precise positioning of the molecules inside the pores is very hard to determine.  Recently, we solved this problem for a class of particularly efficient dyes filling the channels of zeolite L.  Key to success was diversity within the team, which favored the combination of multiple techniques involving both experiments and calculations.

The useful properties of these materials arise from the arrangement of dye molecules inside the porous host, which depends on the interactions among molecules and with the porous host. After this work, now it seems we understand a little better these complex materials. Indeed, our dyes are linear, symmetric and fit to the zeolite channels. Yet they adopt a slightly asymmetric positioning to maximize the interactions with the zeolite cations, which stabilize the compound.

Senzanome
Perylene-bisimide dye (cyan) in zeolite L (gray). The purple spheres represent the zeolite potassium cations

This work also suggests some possible ideas to improve these compounds by modifying either the porous container (the “host”) or the dye molecule (the “guest”). In my view, this is also a good example of how computational modeling may help to rationalize experimental results in apparent contrast with each other, yielding a consistent picture of a useful and intriguing material.

perylene

Gigli et al. (2018)  “Structure and Host–Guest Interactions of Perylene–Diimide Dyes in Zeolite L Nanochannels”  J. Phys. Chem. C 122, 6, 3401-3418

RSC Twitter conference 2018

The Twitter Poster Conference is an annual event organized by the Royal Society of Chemistry, which consists of sharing chemical research using tweets. You may take part either by tweeting an image of your poster or by commenting on other poster (doing both is better, in my view). As in a traditional conference, you see great research, are asked interesting questions, meet old friends, and come in contact with new colleagues or potential collaborators. Only, at the twitter conference this happens 24 hours non-stop  on global scale; so, it’s a good idea to get there prepared!

I enjoyed so much my 2017 participation that I couldn’t miss the 2018 edition.  Of course, it was awesome, and I am grateful to the organizers, the sessions’ chairs, and all participants, particularly those with whom I interacted.  Indeed, I have learnt new stuff, seen exciting science, been inspired, without moving from my office and paying any conference fees. Really cannot ask for more. Many thanks to all of you!

Tweeting posters is not trivial. For optimal readability,  you should keep into account, for example,  that mobile phones have small screens, and that Twitter images are resized and cropped down – so, it would be better to prepare the poster in landscape format. These and other useful tips can be found in this excellent post. I came across it when the event was over, but it would surely be useful in the future.

Below you can find my poster, illustrating the fruitful collaboration between calculations and diffraction experiments at high-pressure conditions.

Besides water and ethanol in ferrierite (discussed in this post), the poster shows our new work on a host-guest compound of zeolite L and fluorenone dye under high pressure. These host-guest materials have excellent optical properties, useful for many applications, from solar cells to sensing in medical technology. Knowing their structure and working principles could help improve their performances – that’s why we try so hard to understand dye-zeolite composites at molecular level.

Basically fluorenone inside the channels of zeolite L forms a molecular ladder, which is very stable at room conditions because the carbonyl groups of the dye interact very strongly with the potassium cations of the zeolite.

Is this peculiar structure also stable under GPa pressures?

According to experiments and simulations, the answer is apparently yes!  Our composite  maintains its structure, and the interactions between the dye and the zeolite cations become stronger. The exceptional resilience of this material to compression highlights its outstanding mechanical properties. These are important to extend the application of dye-zeolite composites beyond room-pressure conditions.

More about this research can be found in this recently published paper (“Unravelling the High-Pressure Behaviour of Dye-Zeolite L Hybrid Materials”) – which is open access. The high-resolution poster and the green open access version of the ferrierite paper can be downloaded at figshare.

 

twitter2018_3_b

RSC Twitter poster session 2017

On March 20th, i took part to the RSC Twitter Poster Conference 2017, an online event organized by The Royal Society of Chemistry to favour new contacts and exchanges among researchers in chemical sciences. The event was a big success.

To those of you that might wonder what a twitter poster session is, here’s an excerpt from The Analytical Scientist:

How do Twitter poster sessions work?
Participants tweet an image of their poster with the title and hashtags #RSCPoster and the area (e.g. #RSCAnal) at any point throughout a 24-hour period. This means that people anywhere in the world can join in.  

It’s a fully global event open to every chemist on twitter. No conference fees: by following the hashtag #RSCPoster, anyone could attend and submit their poster.

What a nice surprise when nice images of posters started appearing in the feed on that Monday morning. Awesome idea – i thought,  tweeting my contribution a few seconds later.

To be honest, the poster was not prepared for the occasion – I simply recycled a poster presented at a traditional conference, and I shared it just to see what would happen.  It was great. Not only people were tweeting their images, they were also commenting on the posters, just like in a standard conference but within 140 characters.  The participants were discussing technical aspects of the results or methodology, asking more general questions on the featured research, and all of this worked wonderfully.   It was exciting: every few seconds, a new contribution was added to the feed, containing interesting and well presented science.

As in normal conferences, this wasn’t just a chance to present your own project, but also a fantastic opportunity to look at what the researchers out there were doing, and to learn a lot from it. New ideas were inspired by work in apparently unrelated research areas. Beside science, it was also a very useful experience in communicating research to a heterogeneous audience using few, carefully selected words.  Yet another demonstration of how twitter can be useful to scientists!

I regret that i wasn’t able to look at all the posters during the session – they were definitely too many.  Fortunately, even if the conference is over, the posters are still hanging on the virtual wall at the RSC Tumblir site, so that in the case you missed the event, you might still catch up with the interesting science. I’d strongly recommend to give a look at them: they’re awesome!

Some lucky participants got the coolest thing you could ever imagine: a cartoon abstact of their poster – like this one:

C7X5Qa8XkAAa3FQ

So I’m very grateful to @MCeeP (ErrantScience.com) for making my day with this, and for the incredible tour-de-force of drawing the cartoons! I much enjoyed to see all of them: not only they were funny, but also further engaged the participants, stimulating curiosity and new conversations. These brilliant poster abstracts really made the conference unique.

This is crazy but …what if cartoon abstracts were introduced in traditional conferences as well?  To get a feeling, just check out the complete gallery of these cool cartoons of posters at ErrantScience.

EAy-hfno

Finally, many thanks to the RSC, the organizers, and the participants for such a great experience. A superb way to promote chemical research. I’m glad to have been some little part of it, and looking forward for the next year event.

Just for the records, here’s my humble contribution to #RSCposter.  For those interested, what featured in the poster is briefly explained here (left side) and blogged here (right side).

High pressure and small spaces create order from disorder

Our work on ethanol and water in ferrierite, published here and blogged in my previous post,  has been recently covered by MRS Bulletin in an excellent news article – “High pressure and small spaces create order from disorder”  by science writer Tim Palucka. Some time ago, I had a very pleasant communication with Tim about the main ideas and results of the paper. That interview also helped me a lot to understand how science communication is done professionally. The piece by Tim really does a great job in explaining the scientific background, the main findings and the perspectives of our research – and, of course, all of us are so happy about it!

MRS Bulletin contains other interesting news articles, which are very useful to get a first impression about what’s going on in the many diverse areas of materials science –  we’re very proud to be featured there! Big thanks, therefore, to MRS Bulletin and Dr. Palucka for the awesome coverage, and to Prof. Gion Calzaferri for commenting on our work as an external expert. A pdf version of the news article is freely available at MRS Bulletin (Volume 42, Issue 3, pp. 176-177, DOI: https://doi.org/10.1557/mrs.2017.38 ), while the illustration showing the arrangement of water and ethanol in the zeolite is just here below:
mrs_42_3_175-179-March17.indd

Many thanks also to my institution, @Uni_ Insubria, for issuing a piece on our research and sharing it on the social media. The Uni_Insubria release – including also an English translation, can be found at this Facebook link  (Italian version also at: Chemistry & Earth Science Department of Uni Modena-Reggio Emilia – that we thank as well).

Under pressure, from chaos to order.

What happens to a liquid mixture when it is driven by pressure into an initially empty container? What if the container has an ordered pattern of molecular-sized pores? To answer this question, we prepared a sort of good vodka drink – three parts water, and one ethanol – and we injected it into the pores of an hydrophobic container – the zeolite ferrierite. As hydrophobic materials  don’t like water and don’t care about drinks, we had to be very drastic:  we used a diamond anvil cell. In this apparatus, the sample – the empty container and the mixture, in our case –  is compressed between the tips of two opposing diamonds and experiences huge pressures – about 10.000 times the normal atmospheric pressure.  At these conditions,  matter is subjected to unimaginable forces, comparable to internal atomic forces: this means that strange, unexpected phenomena could show up. Now, let’s combine the power of high-pressures  with the ordering effect of the pore matrix and see what happens to our mixture.

Just to start with, the water-ethanol mixture – the pressure-transmitting medium – enters the pores of the matrix.  But how do the molecules occupy the pores? You don’t need to be a chemist to know how it is difficult to separate alcohol from water. This is a critical issue also for sustainable processes – such as the production of biofuels.

Thanks to high pressure and to the porous matrix – and with the help of computational modeling – here we obtained the separation of ethanol from water, and the formation of a beautiful pattern of clusters.  The clusters – rows of ethanol dimers, and square water tetramers – occupy different regions of the host matrix and alternate like tiles forming a nice molecular mosaic – a “two-dimensional architecture” – inside the porous host.  What’s really exciting about it is that the ordered pattern, created by high pressure, also remained stable by bringing the material back to atmospheric pressure.  This means that using high pressures and porous hosts, we can create new materials, which are stable at normal conditions, and could potentially be exploited in applications.

The metamorphosis of the initial water-ethanol solution into a beautiful two-dimensional pattern remains somewhat mysterious. More in general, how organization arises from chaos is still one big question in science.  However, our molecular dynamics simulations show that water molecules, already inside the pores, can spontaneously self-organize in square tetramers:

The final result, is the formation of the stable two-dimensional architecture of water and ethanol clusters. As the movie shows, the molecules move, but the clusters do not break apart. – even upon returning to room pressure.

Perspectives

Disclosing the way in which molecules and nanoparticles assemble at high pressure conditions, under the guidance of a suitable matrix would be a great and intriguing challenge for future studies. Another one would be the actual production of technologically relevant materials through the combined use of pressures and suitable porous matrices.  These goals could be achieved only through a close collaboration between experiment and theory – a synergy which has been at the very origin of the present work.

In a wider perspective, understanding the behavior of matter at high pressures is  of central relevance in science, as explained in this excellent introductory feature article.  Pressure effects are ubiquitous, in chemistry, physics, earth and planetary sciences, as well as in many industrial processes and technological applications.  High-pressure conditions are also hypothesized to explain the origin of complex chemistry and life. The study of this exotic regime, so different from our everyday-life, may reveal plenty of phenomena which would be hard to imagine based on our experience.

Reference: Irreversible Conversion of a Water–Ethanol Solution into an Organized Two-Dimensional Network of Alternating Supramolecular Units in a Hydrophobic Zeolite under Pressure, by Rossella Arletti, Ettore Fois, Lara Gigli,  Giovanna Vezzalini, Simona Quartieri, and myself. Angewandte Chemie 2017 – DOI:  http://dx.doi.org/10.1002/anie.201610949
http://dx.doi.org/10.1002/ange.201610949

Special thanks to Andrea Stangoni (@andrea_stangoni), author of the cover artwork.  His image summarizes the ideas of our work much more beautifully than my blog post!

ange201700219-toc-0001anie201700219-toc-0001-m

And, of course, big thanks to Angewandte too! 🙂

Here are the official versions of the cover:

http://dx.doi.org/10.1002/anie.201700219
http://dx.doi.org/10.1002/ange.201700219

Hope you enjoyed the movies, both (equilibration and final) available at figshare.

Update:  the green open access (accepted article) version of this paper is now freely downloadable from the figshare repository.

How large molecules cross narrow pore entrances

How can a snake swallow a mouse bigger than its mouth?

Weird as it seems, questions like this emerge very often at the molecular scale. For example, we can fill porous materials with molecules larger than the diameter of the pores: in this way, we may obtain devices for energy and health applications. What makes this useful process possible? Flexibility is the key: both the porous host (the “snake”) and the molecule (the “mouse”) must deform for the process to occur. But here, contrary to the mouse-snake case, cooperation between the two partners is needed.

We captured the passage of a bulky molecule through the very narrow opening of one of these pores. We did this by computer simulations, because it is very hard to get such information experimentally. To get an idea of what we found, you don’t even need to read the paper – and i’m not kidding. Just look at the movie below!

What we’ve seen first, is that the pore is slightly larger at its entrance. This surely helps the molecule to go in.

Second: contrary to the mouse, which would escape the snake as fast as it could, the molecule is indeed “magically” drawn to the pore entrance – by electrostatic forces.

“So what?” – you may say.

Keep in mind that the molecule is still larger than the pore opening. No kind of “fatal attraction” could do the trick, in a world of rigid bodies.

We’ve found that the molecule can pass through the opening and slip inside the pore only because it’s flexible, and its motion is “in tune” with the vibrations of the porous matrix. All this factors cope to make the entrance process more favorable than the exit process – that’s why the molecule gets finally swallowed by the pore, and remains trapped inside the material.

For me, it was very nice to see how bulky molecules manage to pass through narrow openings and travel inside a porous material. But finding out the reason why they stay inside was, probably, even more exciting:  because it explains how materials of this kind can form and remain stable. Which is exactly one of the things you may need, in the quest of  easier and smarter ways to produce better materials.

newchannel
Acknowledgments
 As we have to give credit where credit is due, i must confess that i borrowed the mouse-and-snake idea used in this post. But you’ll never know from whom. Me neither: (s)he was an anonymous referee of the paper. I am very grateful to this person: i can hardly imagine a nicest way to sketch our work.
Update: 
Many thanks, of course, also to ChemComm for the cover!
cc_cover