Category: Bunsen Byrner

It was great news today to hear the 2016 Nobel Prize in Chemistry was awarded to some pioneers in the field of supramolecular chemistry: Jean-Pierre Sauvage, J Fraser Stoddart and Bernard Feringa. During my PhD studies, I read the work of Sauvage and Stoddart a lot for inspiration; they are constantly producinSauvage's article in Tetrahedron Letters 1983g beautiful and elegant structures from discrete molecular units interacting in controlled ways. While most of my PhD ended up focussing on lanthanide-directed self assembly and luminescent compounds, I was always chasing the goal of interlocked structures and remember being fascinated by Sauvage’s early results describing the first metal-directed catenanes (Tetrahedron Letters 1983), mechanically interlocked rings with no chemical bonds between the two molecular components. This article laid the groundwork for the tiny molecular machines for which the trio were given the prestigious award today. Stoddart’s contributions to controlling rotaxane movement and Feringa’s publication of the first ‘molecular motor’ were remarkable breakthroughs, but the elegance of interlocked systems has fascinated me since I first saw them and I was delighted to finally publish some of my own work on catenanes in Angewandte Chemie this year, contributing in a small way to the ever-expanding supramolecular field.

To end this post, I’ll add a quote from my PhD supervisor Prof Thorri Gunnlaugsson (Trinity College Dublin) talking today about Sir JF Stoddart, a man he greatly admires and who received an honorary doctorate from Trinity a few years ago:

Speaking about the significance of the work that led to him sharing the 2016 Nobel Prize, Professor of Chemistry at Trinity, Thorri Gunnlaugsson, said: This is truly a fantastic day for chemists and specially for those of us who are involved in the development of supramolecular and nano-chemistry. The development of molecules that are functional and can carry out actions such as programmed operations, and can mimic macroscopic function on the nanoscale, such as that of machines, has been at the heart of this area of chemistry.”

“Today’s announcement of the Nobel Prize in Chemistry being awarded to Professors Stoddart, Sauvage and Feringa, for their development of molecular machines, acknowledges the major scientific achievement made to date in this important field.”

 

 

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Monosaccharide azides – challenges

I am not a carbohydrate chemist by training. I remember as an undergrad being very intimidated by the chair conformations, Fischer projections and the seemingly endless chiral centres, so I filed that knowledge away as “unlikely to use” and focussed on supramolecular chemistry. In recent times however, I couldn’t help but be drawn back to looking at these natural sources of chirality, particularly as a next direction to turn after my investigations to amino-acid derived triazolyl(pyridine) ligands. Sugars seemed a way to get chirality and solubility all in one go with the potential for biological interactions as a bonus.

oac-n3 sugar scheme

So, I began researching how to make various monosaccharide azides of the above form in a selective way, so that I could very the stereochemical properties at will when making families of compounds. It required a lot of searching to find everything I need, so I will present it here for anyone else who might be interested in making (in particular) tetra-acetylated glucose, galactose and mannose with an azide in the anomeric position, either α or β.

For glucose and galactose, buried in the German-language pages of a paper by Paulsen et al. from 1974 is a Lewis acid catalysed reaction, which selectively gives the β-azide derivative directly from reacting the penta-acetylated sugar (with mixed anomeric configuration) with tin(IV) chloride and trimethylsilyl-azide. This reaction has some nasty components and leaves you with a lot of tin-contaminated water to dispose of. I was delighted, therefore to find that the reaction can also be carried out rather straightforwardly from the commercially-available α-bromo tetra-acetylated compounds (for glucose and galactose) by simply heating overnight with sodium azide in a water-acetone mixture, a methodology that comes from that oft-overlooked source: Journal of Chemical Education (Norris and co-workers, 2012).

With mannose, things are a little trickier! It differs from glucose and galactose, by having the C-2 hydroxyl group in the axial position, and since this is adjacent to the reactive anomeric position, this will influence the outcome. Using tin(IV) chloride, as above, for instance, will yield the α-azide. This is a result of the reaction, as above, favour a 1,2-trans geometry. For the purposes of my research, however, I was really interested in using the β-azide to make a compound which differed from the glucose derivative in only one position. After a lot of hunting, I stumbled upon a two-step reaction in an article by Prof Paul Murphy from NUI Galway (Chem. Eur. J. 2013), which had originated with an early study from University of California. This approach generated an α-glycosyl-iodide in situ and reaction with tetrabutylammonium azide gave the desired β-azide product in good yields. Importantly, this gives β-azides in all cases and allowed me access to the building blocks I need to pursue my current project.

“Captured and put in chains” – new article in Angewandte Chemie

“Captured and put in chains” – new article in Angewandte Chemie

I recently finished working in Trinity College Dublin after five and a half productive years. My final project was completed in the weeks before I left and submitted to the prestigious journal Angewandte Chemie on the 1st April, the day I started in my new position at Universität Bern.

This article has just come out, and I’m rather proud of it, and happy that it is a fitting ending to my time in Dublin. My original goal in Thorri Gunnlaugsson’s research groupwas to form interlocked molecules, such as “catenanes”, but this challenging goal kept moving further down the queue as we discovered new and interesting ways to exploit the “btp” motif (which has been the topic of all my research to date). But finally, and somewhat unexpectedly, we achieved this goal.

Creating these new structures built upon interesting behaviour we reported in our Chemistry – A European Journal article early this year – where we saw that btp molecules could interact with each other, forming pairs through weak hydrogen bonding. We wondered if this could be used to pre-organise molecules together in such a way that they could be ‘clipped’ together into interlocked rings (by “RCM”, as outlined in the Scheme above). This approach has occasionally been reported before for amides,but not for molecules like the ones we describe.

A representation of the formation of catenanes from btp ligands

In fact, this reaction was more successful than expected – and in the first case I tried, we were surprised to find the majority product (50% yield) was the interlocked “catenane”, with independent non-interlocked rings also observed. We were able to fully identify and characterise these molecules using X-ray crystallographic analysis, giving the clear pictures below (thanks to Dr Salvador Blasco).

These were nice structures, but I wanted them to do something more than look pretty! Discussions with my friend Anna Aletti opened up the idea that the cavity in the middle of the structures might be a perfect fit for some negatively charged ion guest, such as chloride, nitrate or sulfate – none of these ions did very much, but phosphate (the tetrahedral H2PO4- ion), on the other hand, caused changes in the “catenane” host, indicating specific interactions between these two molecules. This was exciting. It makes these the first catenanes in the literature to have such interactions with tetrahedral anions.

The catenane acts as a selective host for phosphate, as can be seen from changes in the NMR spectrum

Detailed analysis of the formation of these interesting compounds, as well as their adducts with phosphate was important to strengthening these results and making sure we understood what we were seeing. Working closely with Dr Gary Hessman, Technical Officer at TCD, allowed further insight into the systems and their composition.

If any of this sounds interesting, then you should read the article (http://dx.doi.org/10.1002/anie.201603213) or at least look at the pictures! One fun advantage of publishing in Angewandte Chemie is that they translate your abstract into German (which I am currently learning), which means I now know the useful everyday term “Triazolylwasserstoffbrüken“, which – of course – means “triazolyl hydrogen-bonding interactions”. I now use that in the pubs of Bern almost daily!

TG Group travel to Southampton for Supramolecular Symposium

It was nice to catch up with some old colleagues in Southampton and chat molecular logic with my “academic grandfather” AP de Silva, as well as why he enjoyed being educated by Buddhist monks and Catholic nuns at the same time in Sri Lanka!

Gunnlaugsson Group, Trinity College Dublin

Anna Aletti, Samuel Bradberry and Dr. Oxana Kotova of the TG group attended Southampton Supramolecular Chemistry Symposium on the 24th of June 2016.

delegates Southamption Supramolecular Symposium 2016 Delegates

All of them presented posters and, in addition, Samuel gave an excellent talk on “Lanthanide Luminescent Logic – functional organic scaffolds and soft polymers gels as logic gate mimics”.

DSC_0048 Sam giving his talk

DSC_0036 Sam and A P at the poster session

DSC_0043 Oxana with her poster

DSC_0035 Anna presenting her poster

2016-06-24 18.02.36 A P de Silva, Oxana, Anna, Joe and Sam at the drinks reception

Our former group member Dr. Joseph Byrne who is currently a postdoctoral researcher in the University of Bern attended the conference as well and presented a poster on his recent work published in Angew. Chem. Int. Ed. on self-templated btp [2]Catenane.

The meeting included speakers and posters from UK Universities and beyond, including an outstanding lecture from the…

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Collaborations in Hong Kong

Collaborations in Hong Kong

I had the pleasure of spending some time this month in Hong Kong University in the laboratory of Professor Vivian Wing-Wah Yam, a high-profile inorganic chemist. We had previously had conversations about some overlap in our research interests and, thanks to the generous support of Science Foundation Ireland’s “International Strategic Collaboration Programme for China“, I was able to visit HKU and begin collaborative work, investigating luminescent inorganic compounds. I am also very grateful for the support of my supervisor Professor Thorri Gunnlaugsson in encouraging this endeavour and Professor Yam and her group for their hospitality: I ate the best authentic Cantonese food for lunch all through my stay!

Dr Sammual Yu-Lut Leung was exceptionally generous with his time during
my visit, arranging an office for me and teaching me some new techniques in the laboratory. The work we carried out during my visit will form the foundations for an exciting project.

I was invited to give a research seminar to members of the Chemistry Department in HKU on Friday 11th December 2015 and was delighted to have the opportunity to share my work with researchers so far geographically from home and discuss it in detail afterwards.

I gave a seminar on my research to researchers in HKU while visiting

Hong Kong is a beautiful city, a real melting pot of cultures, cuisine and indeed science. I immensely enjoyed my time there and believe this trip was the start of something fruitful.

 

Chiroptical probing of self-assembly with ligands formed in one-pot ‘click’ reaction from chiral amines (Chem. Eur. J.)

Chiroptical probing of self-assembly with ligands formed in one-pot 'click' reaction from chiral amines (Chem. Eur. J.)

After a lot of work, we finally got these results off my bench and into the literature. In our new article in “Chemistry – A European Journal” (Wiley), we present a convenient one-pot approach to synthesising chiral bis(triazolyl)pyridine ligands from enantiopure amines with the stereochemistry retained. This approach is broadly applicable.

Molecular structures of ligands 1a and 1b derived from X-ray crystallography
Molecular structures of ligands 1a and 1b derived from X-ray crystallography showing noteworthy dimer formation between the bis(triazolyl)pyridine cores

The beautiful mirror-image crystal structures were obtained by Dr Miguel Martínez-Calvo (now in Santiago) and show interesting supramolecular hydrogen bonding interactions between the ligands which we will exploit in the future.

Dr Bob Peacock in Glasgow performed circularly polarised luminescence spectroscopic measurements on the coloured lanthanide(III) complexes of these ligands, illustrating their optically active nature.

CD titrations for both enantiomers of 1 (a,b) and recalculated spectra arising from fitting of the titration of 1b with Eu(III) in acetonitrile

In this article, we were able to show interesting behaviour which has only really been studied so far by researchers in Prof Thorri Gunnlaugsson’s lab (with two other examples published recently in projects led by Dr Oxana Kotova and Sam Bradberry, respectively). This behaviour was the notable changes in the circular dichroism (CD) spectra of these chiral molecules upon addition of lanthanide(III) ions. These spectral changes could be fit to determine binding constants of this self-assembly. These clear chiroptical spectra are in contrast to a dissapointing aspect of results we published earlier this year in Inorganic Chemistry (with remote amino acid substituents giving rise to weak CPL and CD) and shows that placing the chiral centre nearer to the metal ion binding location enhanced the effect on the chiroptical properties of such systems.

URL: http://onlinelibrary.wiley.com/doi/10.1002/chem.201504257/full

“Luminescent Logic in Soft Materials” presentation wins prize at Discover Research Dublin open night

I was very proud of our outreach activities as part of Discover Research Dublin. We interested the public and appeared on the news. A good evening’s work!

Gunnlaugsson Group, Trinity College Dublin

Recent research from the TG Group on the use of lanthanide luminescent soft materials as molecular logic gate mimics was presented to the public as part of the Discover Dublin ResearchNight in the Trinity Biomedical Sciences Institute on 25th September 2015. The work was described in an RTÉ News bulletin the day before and many people attended the laboratory where Sam Bradberry, Joe Byrne and Anna Aletti showed them how research chemists can create functional materials from commercially available building blocks, step by step. Illustrations by artist Sophie Longwill helped communicate the complex ideas to an audience of all ages. The presentation won a prize as a result of feedback from visitors.

The research was recently published in an article in Chemical Communications. It describes the use of lanthanide luminescent bundles based on the “Trinity Sliotar” and the btp motif as components in methacrylate-based soft materials and their…

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Irish Universities Chemistry Colloquium

I really enjoyed going back to my alma mater to share some research, but also to lead delegates on a unique kind of walking tour. Not every chemistry conference comes with complimentary ghost stories!

Gunnlaugsson Group, Trinity College Dublin

imageThe majority of the research group attended the Irish Universities Chemistry Research Colloquium in Maynooth University on 25-26 June, many presenting posters over the two days. Sam Bradberry gave a talk presenting his work on polymeric soft materials, including hydrogels and luminescent logic gate mimic systems. This prompted some discussion from the audience.

imageIn the evening, Joe Byrne – a Maynooth alumnus – led the delegates on a walking tour of the historical campus, telling ghost stories he collected from staff during his undergraduate studies there. This alternative conference entertainment was enjoyed by those who attended.

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