Archive for the ‘Supramolecular’ Category

Corporals can overrule Sergeants in self assembly

Creating chiral layers on a surface is attracting increased attention because of possible application in optical resolution and heterogeneous catalysis.  Chiral layers can be achieved by the self assembly of enantiopure molecules on a surface.

Alternatively, achiral molecules can be forced to form chiral surface assemblies by using a chiral building block or by adding a small amount of a chiral auxillary– the “Sergeant-and-Soldiers” effect first described by Mark Green (NYU-Poly) and co-workers in 1989.

In this HOT ChemComm article, Chem Soc Rev Associate Editor David Amabilino from ICMAB-CSIC, Barcelona, ChemComm Associate Editor Steven De Feyter from KU Leuven, and their co-workers have taken this principle a stage further and questioned if the intrinsic chirality of a building block (the “Sergeant”) can be overruled by using a chiral solvent (the “Corporal”).

They found that achiral porphyrin 1 could be forced to form chiral monolayers using (S)-and (R)-2-octanol as a solvent.  More impressively, they also found that the chirality of the assembly of chiral porphyrins (S)-2 and (R)-2 could be directed using these solvents.  The combination of (R)-2 and  (S)-2-octanol gave an enantiopure surface assembly, whereas using (R)-2-octanol resulted in a mixture of 2 different domains of opposite chirality.  Molecular dynamics simulations indicated that this could be due to hydrogen bonding between the solvent molecules and the amide groups of the porphyrins.  If more than one chiral centre was present (3 and 4), the chirality of the molecule was able to dominate the solvent effect.

This is a fascinating report of how a simple, weak interaction with solvent can overcome the inherent chirality of a stereogenic centre.  This work could lead to the preparation of bistable systems in which the chirality could be switched with a simple change of solvent.

Download this HOT ChemComm article today!

‘Sergeants-and-Corporals’ principle in chiral induction at an interface
Iris Destoop, Hong Xu, Cristina Oliveras-González, Elke Ghijsens, David B. Amabilino and Steven De Feyter
Chem. Commun., 2013, Advance Article
DOI: 10.1039/C3CC42584C

Cally Haynes is a guest web-writer for ChemComm.  She is currently a post doctoral researcher  at the University of Southampton, and her research interests include the supramolecular chemistry of anions.  When not in the laboratory, she likes travelling and watching football.

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Cram Lehn Pedersen Prize winner Tomoki Ogoshi: US lectures 2013

Our 2013 Cram Lehn Pedersen Prize winner, Professor Tomoki Ogoshi (Kanazawa University, Japan), is set to visit the US this year to deliver his award lectures.

Tomoki Ogoshi will first present his lecture, entitled “Pillararenes: Easy-to-make and versatile receptors for supramolecular chemistry,” at the 8th International Symposium on Macrocyclic and Supramolecular Chemistry (8-ISMSC) in Crystal City, Virginia, USA from 7-11 July 2013.

Later in the year, Tomoki Ogoshi will speak at the University of Texas at Austin (20 Sept) where he will be hosted by ChemComm Associate Editor Professor Jonathan Sessler.  He will then travel to San Diego, CA, to present his talk at the Scripps Research Institute (23 Sept), hosted by Professor Julius Rebek, Jr.

Register online for the 8-ISMSC between now and 1 July to catch Professor Ogoshi’s first award lecture this summer– reduced fees for students and post-docs are available!

2013 ISMSC-8

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ChemComm-RSC Prizes and Awards Symposium: Supramolecular Chemistry

We invite you to join us for the ChemComm-RSC Prizes and Awards Symposium which will be taking place on 24 May 2013 in Dublin, Ireland.

This free one-day event will comprise of stimulating lectures reflecting the academic and industrial breadth of supramolecular chemistry, delivered by RSC Prize and Award winners and leaders in the field.

Confirmed Speakers:

  • Jerry Atwood, University of Missouri-Columbia – Winner of the 2012 RSC Supramolecular Award
  • John Callan, University of Ulster
  • Chris Chang, University of California, Berkeley – Winner of the 2012 RSC Chemistry of Transition Metals Award
  • Sylvia Draper, Trinity College Dublin
  • Phil Gale, University of Southampton – ChemComm sponsored lecture
  • David Leigh, University of Manchester – ChemComm sponsored lecture
  • Donal O’Shea, University College Dublin
  • Susan Quinn, University College Dublin
  • Eoin Scanlon, Trinity College Dublin
  • Jonathan Steed, Durham University – ChemComm sponsored lecture

We hope you and your colleagues will be able to attend the ChemComm-RSC Prizes and Awards Symposium. For further information about this event and to register, please visit the dedicated webpage.

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Metal organic frameworks for moisture-triggered fragrance release

The controlled release of fragrance molecules is of great interest in the development of fragranced products such as deodorants, as the volatility of the fragrance molecules can reduce the action of the product over time.  In this HOT ChemComm article, Jing Li and her group at Rutgers University, New Jersey have joined forces with researchers from Colgate-Palmolive Company to investigate using metal organic frameworks (MOFs) to take up and release fragrances in response to external stimuli.

frangrance release by MOFs

MOFs are a class of porous materials that are receiving a significant amount of research interest.  In particular, their ability to take up and store small molecules makes them an exciting prospect for storing gases, such as hydrogen, for catalysis and for drug delivery.

In this study, researchers examined the ability of some zinc based MOFs containing hydrophobic channels to take up and release the fragrances ethyl butyrate and D-limonene.  They found that the release of these fragrances could be triggered by moisture.

Importantly, both the hydrophilic ethyl butyrate and the hydrophobic D-limonene could be stored and released in this way, whereas leading encapsulation technologies based on modified starch are generally only useful for storing hydrophobic fragrances.  MOFs could therefore well find commercial applications for storing a wide range of fragrances.

Read this ‘HOT’ ChemComm article today!

Encapsulated recyclable porous materials: an effective moisture-triggered fragrance release system
John Vaughn, Haohan Wu, Bisera Efremovska, David H. Olson, Jairajh Mattai, Claudio Oritz, Allen Puchalski, Jing Li and Long Pan
Chem. Commun., 2013, Advance Article
DOI: 10.1039/C3CC41236A

Cally Haynes is a guest web-writer for ChemComm.  She is currently a post doctoral researcher  at the University of Southampton, and her research interests include the supramolecular chemistry of anions.  When not in the laboratory, she likes travelling and watching football.

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Tomoki Ogoshi wins Cram Lehn Pedersen Prize 2013

Congratulations to Professor Tomoki Ogoshi (Kanazawa University, Japan), the winner of the 2013 Cram Lehn Pedersen Prize.

The annual prize, sponsored by ChemComm and named in honour of the winners of the 1987 Nobel Prize in Chemistry, recognises significant, original and independent work by emerging investigators in supramolecular chemistry.

This year the prize is awarded to Professor Ogoshi for his pioneering work in macrocyclic and supramolecular chemistry and, in particular, for his groundbreaking research on pillar[5]arenes, a new class of macrocyclic compounds.  “I’m really honoured to receive the 2013 Cram Lehn Pedersen Prize,” says Professor Ogoshi.  “Cram, Lehn and Pedersen were great pioneers in the synthesis of macrocyclic hosts, and thus receiving this prize is also a great honour for pillararene chemistry.  I hope this will someday place pillararenes alongside other well-known macrocyclic hosts.”

Professor Ogoshi will receive £2,000 and will present his award lecture at the 8th International Symposium on Macrocyclic and Supramolecular Chemistry (8-ISMSC) in Crystal City, Virginia, USA from 7-11 July 2013.  He will also speak at other events during the year– keep an eye on this blog for more details.

“With the introduction of a new class of macrocycles, the pillararenes, Professor Ogoshi has started another area of host-guest molecules,” says Professor Roger Harrison, Associate Professor at Brigham Young University and Secretary of the ISMSC International Scientific Committee.  He adds, “The over 90 publications on these molecules since they were introduced in 2008, show the fascination and possibilities these molecules afford.  Professor Ogoshi’s introduction of these new molecules, along with his insights, creativity, and persistence make him one of the most exciting and up-and-coming supramolecular chemists to follow.  I congratulate Prof. Ogoshi on receiving this award and look forward to seeing more of his discoveries.”

Pillar[5]arene structure

Pillararene structure

“Ogoshi has created a new class of easy-to-make macrocycles, pillar[5]arenes, with a novel cross section of properties,” says Professor Amar Flood (Indiana University), a member of the ISMSC International Committee and 2011 Cram Lehn Pedersen Prize winner.  “Ogoshi has highlighted the properties and features of pillararenes in a series of papers and we are now seeing many others in the field of supramolecular chemistry moving forwards with these compounds in their own research endeavors.”

Last year’s prize was awarded to Dr Jonathan Nitschke (University of Cambridge).

Early bird registration for 8-ISMSC closes on 15 April 2013, so do hurry and register online.  You can listen to Professor Ogoshi’s lecture, get to meet a mix of established and younger researchers in supramolecular and macrocyclic chemistry, and you may even submit an abstract to present a short talk or a poster to showcase your work.  ChemComm‘s own brilliant and dynamic Deputy Editor Jane Hordern will be at the symposium – let us know if you’ll be there, too.

Find out more about Professor Ogoshi’s innovative research by reading his recent articles in Chemical Science and in ChemComm:

Supramolecular polymers with alternating pillar[5]arene and pillar[6]arene units from a highly selective multiple host–guest complexation system and monofunctionalized pillar[6]arene
Tomoki Ogoshi, Hitoshi Kayama, Daiki Yamafuji, Takamichi Aoki and Tada-aki Yamagishi
Chem. Sci., 2012, 3, 3221-3226

Thermally responsive shuttling behavior of a pillar[6]arene-based [2]rotaxane
Tomoki Ogoshi, Daiki Yamafuji, Takamichi Aoki and Tada-aki Yamagishi
Chem. Commun., 2012, 48, 6842-6844

Ionic liquid pillar[5]arene: its ionic conductivity and solvent-free complexation with a guest
Tomoki Ogoshi, Naosuke Ueshima, Tada-aki Yamagishi, Yoshiyuki Toyota and Noriyoshi Matsumi
Chem. Commun., 2012, 48, 3536-3538

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Harnessing enzyme-substrate specificity for gel-based sensors

Gels that are held together by non-covalent interactions are a hot topic in supramolecular chemistry.  In this Communication, Itaru Hamachi’s research group from Kyoto University report a series of glycolipids that form  yellow hydrogels from orange suspensions when heated. The gelation and hence the colour change is reversible, and the authors hoped to use this response to create a sensor system.

Hamachi's gelator molecules

Once the gel has formed, adding a glycosidase enzyme which can selectively cleave the β-glucosidic bond leads to breakup of the gel and a colour change from yellow to orange. This response is only observed with an enzyme that is complimentary to the saccharide used as a “substrate unit” in the gelator. Hence, the authors have harnessed natural enzyme-substrate selectivity to yield a highly selective sensing system. The combination of a number of these gels into a sensor array chip yields a system that can simply and rapidly detect and distinguish a range of glycosidase enzymes. The ability to selectively sense these enzymes could have significant application for diagnosing disease and identifying bacterial contamination of drinking water.

Hamichi's sensor array

Read this ‘HOT’ ChemComm article today:

Supramolecular hydrogels based on bola-amphiphilic glycolipids showing color change in response to glycosidases

Rika Ochi, Kazuya Kurotani, Masato Ikeda, Shigeki Kiyonaka and Itaru Hamachi

Chem. Commun., 2013, 49, 2115-2117

DOI: 10.1039/C2CC37908B

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Cooperative Effects Enhance Biphasic Catalysis

Commodity chemicals are often produced using catalysts. Despite the many advantages of using catalysts (such as faster conversion, improved selectivity) a major difficulty is separating them from the product at the end of the reaction. Such is the significance of this problem, heterogeneous catalysts are often chosen ahead of their homogeneous brothers because they are simpler to remove at the end of the reaction, despite the homogeneous catalysts generally having better performance.

POM-phosphazene catalyst

Figure 1 Crystal packing diagram of a POM-phosphazene aggregate.

An alternative solution to the separation problem is to utilise a biphasic solvent system. Partitioning the catalyst and product into different phases provides inherent separation and removes the need for expensive procedures like distillations.  Ivan Kozhevnikov and Alexander Steiner at the University of Liverpool have collaborated to join their respective areas of expertise together and create catalytically active polyoxometalate (POM)-phosphazene aggregates (Figure 1) which can operate in a biphasic environment. Their communication reports rapid oxidation of test substrates by enhancing the transfer of the catalytically active POM across the two phases. Furthermore, the chemistry is “green” as it utilises relatively environmentally benign conditions.

The components of the aggregates are independently soluble in the different phases; therefore defining how this catalyst operates will be paramount to understanding and developing the system further. For example, reporting the performance of the POM or the phosphazene independently in the biphasic system would provide essential support to the claim that these aesthetically pleasing aggregates are responsible for the observed catalytic activity and remove some of the alternative potential sources.

Read the ‘HOT’ Chem Comm article today (Free to access until the 27th of December):

Novel polyoxometalate–phosphazene aggregates and their use as catalysts for biphasic oxidations with hydrogen peroxide

Michael Craven, Rana Yahya, Elena Kozhevnikova, Ramamoorthy Boomishankar, Craig M. Robertson, Alexander Steiner and Ivan Kozhevnikov
Chem. Commun., 2012, 48, Advance Article
DOI: 10.1039/c2cc36793a

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The Cram Lehn Pedersen Prize in Supramolecular Chemistry – Nominations Open

 2013 ISMSC-8 Crystal City, Virginia 7 July – 11 July, 2013 

The International Committee of the International Symposium on Macrocyclic and Supramolecular Chemistry is pleased to invite nominations for the Cram Lehn Pedersen Prize for young supramolecular chemists. 

The Cram Lehn Pedersen Prize, named in honour of the winners of the 1987 Nobel Prize in Chemistry, will recognise signicant original and independent work in supramolecular chemistry.

Those who are within 10 years of receiving their PhD on 31st December 2012 are eligible for the 2013 award. The winner will receive a prize of £2000 and free registration for the ISMSC meeting in Crystal City, Virginia. In addition to giving a lecture at ISMSC, a short lecture tour will be organised after the meeting in consultation with the Editor of Chemical Communications, the sponsor of the award. 
 
 
Nomination Details:

Please send your CV, list of publications (divided into publications from your PhD and post-doc and those form your independent work), and if desired, letter of support, or these materials for someone you wish to nominate to Prof. Roger Harrison (ISMSC Secretary) at rgharris@chem.byu.ed by 31st January 2013.

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Supramolecular splicing: Catalytic fusion of supramolecules

Non-covalent interactions dictate the assembly of many of nature’s most elegant structures. Similarly, supramolecular chemists have long been intrigued by the challenge of designing functional structures that spontaneously self-assemble from simpler fragments which mutually recognise each other.

A popular self-assembly approach is to produce coordination compounds from transition metal salts with rigid organic ligands. Directional bonding around transition metal centres allows the production of predictable and controllable shapes. Michael Schmittel’s group at the University of Siegen have been exploring a newer approach. They prepared two assemblies, a 2-component triangle T1 and a 3-component rectangle R1. The transition metal “corner” arrangements in T1 and R1 are disfavoured, so if the two assemblies are combined the components re-shuffle to form a more favourable assembly- the 5-component triangle T2. The transformation occurs at room temperature, and can be completed in just 1 hour in the presence of a catalyst, which accelerates the re-shuffling by labilising the metal-ligand bonds.

Supramolecular splicing: Catalytic fusion of supramolecules: re-shuffling of a 2-component triangle and a 3-component rectangle to give a more favoured supramolecular 5-component triangle

Unlike previous examples, the conditions needed for the transformation are very mild. The authors compare the process to gene shuffling, the combination of dissimilar genes to form new genetic material. The strategy could be considered a first step towards the evolution of supramolecular architectures, and a great route to more complex supramolecular assemblies with higher information content.

The full communication can be downloaded here (free to access for a limited period).

Cally Haynes

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High yielding catenane synthesis? Surely not!

Rapid thermally assisted donor–acceptor catenation

The X-ray crystal structures of two azide-functionalised catenanes

Entropy is not a friend of the macrocyclic chemist because creating large cyclic molecules by tying together several building blocks creates a high thermodynamic hurdle to cross. Nature has been forming these types of molecules for many millions of years and has provided inspiration for chemists to overcome these synthetic challenges. Perhaps purely for the academic interest, work began on investigating if it was possible to interlock two of these cyclic molecules together and form what is known as a catenane. Imagine a pot of spaghetti cooking and think of the strands tumbling around in the boiling water. Now imagine trying to tie all the ends together at the same time. Most will form individual rings but statistically a small number of those rings will be linked together. Conceptually this sounds easy but the reality is not so straight forward. A secondary problem is that only very small amounts of the linked rings are formed which means most of the starting material is wasted.

As interest in these curious molecules grew their potential application as switches for molecular electronics and sensors became apparent. However, if these applications were ever to be realised the cost of their formation would need to be feasible on a commercial scale. Macrocyclic chemists dream of yields over 50%, yet most chemists would be embarrassed to report a yield like this! However, we must remember that these reactions are inherently unfavourable so to achieve respectable yields we need to ‘stack the deck in our favour’ and try to make the interlocking of the rings more favourable.

Deceptively simple but incredibly effective ways of using what are commonly thought of as weak interactions have been used to hold the two fragments together, making the subsequent formation of the interlocked rings (rather than two separate rings) much more likely.  In a recent report in Chemical Communications, Fraser Stoddart and co-workers at Northwestern University, Texas A&M University and the King Abdullah City for Science and Technology report a significant development in catenane synthesis whereby yields of almost 90% are possible. As almost quantitative conversions are now being reported the commercial application of these molecules, which has for so long been discussed, moves another step closer.

Rapid thermally assisted donor–acceptor catenation
Albert C. Fahrenbach, Karel J. Hartlieb, Chi-Hau Sue, Carson J. Bruns, Gokhan Barin, Subhadeep Basu, Mark A. Olson, Youssry Y. Botros, Abdulaziz Bagabas, Nezar H. Khdary and J. Fraser Stoddart
Chem. Commun., 2012,48, 9141-9143
DOI: 10.1039/C2CC34427K

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