Archive for the ‘Supramolecular’ Category

Capturing C60 in a Crystalline Copolymer Chain

Since its structural realisation in 1985, C60 has garnered much attention in the chemical world for not only its spherical shape, but also its stability, electronic properties and the ability to do chemistry on its surface.

One such avenue that has proven popular in recent times is the incorporation of C60 into one-, two- and three-dimensional arrays, either covalently or non-covalently, in attempts to control the distribution of the molecules in the solid- or solution-phase.  One problem that arises in the synthesis of these extended frameworks, however, is that there often a large amount of disorder and void space in the structure, so it can be difficult to ascertain with much degree of certainty how these C60 molecules are oriented. This uncertainty can consequentially result in the properties and behaviours of the new materials remaining unidentified.

Now, researchers from the University of California, DavisMarilyn Olmstead and Alan Balch – have shown that coordination chemistry can be used to not only generate polymers that covalently link molecules of functionalised C60 in such a manner that can they can be studied crystallographically, but also that these polymers can be used to capture free C60 and C70.

Initially, polymers of C60 were synthesised through the mono-functionalisation of C60 with a piperazyl group, which, on account of its two tertiary amines, can coordinate in a linear fashion with transition metal ions, in this case rhodium(II) acetate. Upon the combination of these two components, a linear one-dimensional polymer was formed, in which it could be seen crystallographically that the C60 moieties were positioned on alternating sides of the polymer chain. These polymer chains were further found to extend into two dimensions through the interdigitation of neighbouring chains in a zipper-like fashion. C60-Rh(II) polymers can capture free C60

Perhaps more interestingly is that when these polymer chains were synthesised in the presence of either C60 or C70, free molecules of C60 or C70 were seen to occupy the void spaces between the C60 molecules of the polymer. Additionally, if a mixture of C60 and C70 was present in the polymer synthesis, it was observed that only C60 was captured by the polymer, most likely as a result of a better geometric match between the polymer and the spherical C60 in preference to the more elongated shape of C70.

This work elegantly demonstrates the generation of not only a self-assembling C60-containing polymer that can be characterised structurally in the solid state, but of one  that can entrap free molecules of C60 selectively over molecules of C70. Based on the properties of free C60 and transition metal complexes, the electronic and chromophoric properties of such a crystalline system could also be expected to offer some noteworthy results.

Read this HOT ChemComm article in full!

Zipping up fullerenes into polymers using rhodium(II) acetate dimer and N(CH2CH2)2NC60 as building blocks
Amineh Aghabali, Marilyn M. Olmstead and Alan L. Balch
Chem. Commun., 2014, Advance Article.
DOI: 10.1039/C4CC06995A

Biography

Anthea Blackburn is a guest web writer for Chemical Communications. Anthea is a graduate student hailing from New Zealand, studying at Northwestern University in the US under the tutelage of Prof. Fraser Stoddart (a Scot), where she is exploiting supramolecular chemistry to develop multidimensional systems and study the emergent properties that arise in these superstructures. When time and money allow, she is ambitiously attempting to visit all 50 US states before graduation.

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Inducing β-Peptide Structures from the Inside Out

The synthesis of tailor-made peptide chains represents a powerful tool for tuning the structure and properties of peptides, allowing for the development of  analogues for medical, technological and synthetic purposes.

For example, the β-peptide is a synthetic peptide, which, in contrast to its naturally-occurring α-peptide analogue, is bonded through the β-carbon rather than the α-carbon. As a result of this seemingly small structural change, alterations in the peptide’s secondary structure and thermodynamic stability are observed.

Adding fluoride groups to peptide chains represents another way to alter and stabilise the folding structure through the presence of stronger hydrogen bonds and the introduction of fluorophilicity. This approach is generally employed for the addition of fluoride groups at ‘remote positions,’ spaced two or more methylene units from the peptide backbone. However, this method has less of an effect on the conformation of the peptide itself, and instead primarily influences the tertiary and quaternary self-aggregation of peptide chains, as a result of the fluorophilic effect of the functionalised peptide chains.

Much less commonly studied is the effect of incorporating fluorine groups in ‘direct proximity’ to the peptide chain, that is, directly attached to the β-carbon, where it is proposed that the intramolecular hydrogen bonding will be directly affected, and consequently, so too will the secondary structure of the peptide chain.

Yasuhiro Ishida and co-workers from the RIKEN Center for Emergent Matter Science have  shown that this ‘direct’ fluorination of β-peptides can, in fact, affect the higher order structures of these peptide chains. Specifically, a hexameric β-peptide was designed, which consisted of cyclohexane-based β-amino acids in the 1-,3-,4- and 6-positions and L-alanine derivatives in the 2- and 5-positions, where the L-alanine methyl groups were either native or perfluorinated.

Irrespective of the degree of perfluorination in the β-peptide, it was found that the chains were arranged in the same left-handed 14-helix structure, with the NH-amide of the second and fifth residues participating in stabilising intramolecular H-bonding interactions. Moreover, it was found that although the presence of fluoride groups did not noticeably alter the overall secondary structure of the β-peptide chains, the stability of these structures was dramatically enhanced, showing the significant effect that fluoride groups can have on the hydrogen-bond donating ability of NH-amides.

This new approach of modifying peptide chains offers an interesting method  for influencing the secondary, and higher order, structures of the compounds, as well as their kinetic and thermodynamic properties. The effect of these structural modifications offers the possibility of tuning the chemical and biological properties of these peptide chains for use in new types of antibiotics and synthetic systems.

Read this HOT ChemComm article in full!

Stabilization of β-peptide helices by direct attachment of trifluoromethyl groups to peptide backbones
Joonil Cho, Kyohei Sawaki, Shinya Hanashima, Yoshiki Yamaguchi, Motoo Shiro, Kazuhiko Saigo and Yasuhiro Ishida
Chem. Commun., 2014, 50, 9855–9858.

About the Writer

Anthea Blackburn is a guest web writer for Chemical Communications. Anthea is a graduate student hailing from New Zealand, studying at Northwestern University in the US under the tutelage of Prof. Fraser Stoddart (a Scot), where she is exploiting supramolecular chemistry to develop multidimensional systems and study the emergent properties that arise in these superstructures. When time and money allow, she is ambitiously attempting to visit all 50 US states before graduation.

 

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2014 Cram Lehn Pedersen Prize in supramolecular chemistry – nominations open

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, recognises significant original and independent work in supramolecular chemistry.

Previous winners include:

photo-ogoshi-300x300.jpgc0sc00329h-p3.gifAmar-Flood.jpg

2013 – Tomoki Ogoshi from Kanazawa University in Japan

2012 – Jonathan Nitschke from the University of Cambridge in the UK

2011 – Amar Flood from Indiana University in the US

Those who are within 10 years of receiving their PhD on 31st December 2013 are eligible for the 2014 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 from your independent work), and if desired, a 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 December 2013.


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The chemists’ enzyme

The title of this post was taken from the website of Barry Trost, one of the world’s leading scientists and author of an astonishing 924 papers. Describing his work, he states:

One major activity in designing new reactions and reagents involves the development of “chemists’ enzymes” – non-peptidic transition metal based catalysts that can perform chemo-, regio-, diastereo-, and especially enantioselective reactions.

Chemists have, for a long time, sought to reproduce the incredible feats of nature. Natural biology has evolved over many years to achieve the efficiency and reactivity that most lab-based chemists could only dream of. Nature achieves this by employing incredibly sophisticated enzymes which are, sadly, almost impossible to replicate by a synthetic chemist due to their complexity. An alternative idea is to use these enzymes as inspiration for new catalysts and try to focus on the general reasons why they work rather than trying to create direct copies.

Supramolecular catalysts for decarboxylative hydroformylation and aldehyde reduction.

Dr Bernhard Breit, Lisa Diab and Urs Gellrich at Albert-Ludwigs-Univertat in Germany have shown in a HOT ChemComm article that a highly selective catalyst can be created when combining a metal catalyst with a directing ligand to control the reaction. In this Communication, they report excellent results using  rhodium, the classic metal of choice for hydroformylation, and a functional group for recognition of the substrate. The net effect of these features combined is that the substrate is held in a specific way at the catalytic site. As a result, the reaction which follows can only occur in a specific way. This is similar to how enzymes control the chirality.

The concept behind this catalyst is one which could be applied to a great number of different reactions – no doubt we can look forward to reading about these in the near future.

Read this HOT ChemComm article today!

Tandem decarboxylative hydroformylation–hydrogenation reaction of α,β-unsaturated carboxylic acids toward aliphatic alcohols under mild conditions employing a supramolecular catalyst system
Lisa Diab, Urs Gellrich and Bernhard Breit
Chem. Commun., 2013, Advance Article
DOI: 10.1039/C3CC45547E, Communication

Ruaraidh McIntosh is a guest web-writer for ChemComm.  His research interests include supramolecular chemistry and catalysis.  When not working as a Research Fellow at Heriot-Watt University, Ruaraidh can usually be found in the kitchen where he has found a secondary application for his redoubtable skills in burning and profanity.

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Azobenzene switching controls movement of oleate assemblies

The study of controlled motion on the molecular scale is leading to the development of materials in which molecular motions can be used to control a macroscopic effect.  In particular, the isomerisation of azobenzene from the stable trans- form to the cis- isomer on irradiation with UV light has been widely used in supramolecular and soft matter chemistry as a simple, controllable molecular switch for this purpose.

In this HOT ChemComm article, scientists from Hokkaido and Kanagawa universities in Japan have investigated the macroscopic motion of some simple oleate assemblies containing azobenzene derivatives.

Simple oleates form a range of supramolecular assemblies under certain pH conditions.  The authors found that mixtures of simple oleates with their new azobenzene containing analogues could also form these assemblies, and investigated the effect of irradiating the structures with UV light.  They found that vesicles containing azobenzene derivatives could be seen to reversibly expand and contract on irradiation.  Additionally, helical multilayer assemblies containing azobenzene derivatives could be forced to reversibly straighten and re-coil using UV light (shown below).

azobenzen oleatesazobenzene helices

This Communication describes an intriguing demonstration that designing controllable, switchable molecular components can create highly organised macroscopic motions, and is a great step towards functional supramolecular machinery.

Read this HOT ChemComm article today:

Macroscopic motion of supramolecular assemblies actuated by photoisomerization of azobenzene derivatives
Yoshiyuki Kageyama,  Naruho Tanigake,  Yuta Kurokome,  Sachiko Iwaki, Sadamu Takeda,  Kentaro Suzukib  and Tadashi Sugawara
Chem. Commun., 2013, Advance Article
DOI: 10.1039/C3CC43488E

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 enjoys travelling and watching football.

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ChemComm-RSC Prizes and Awards Symposium: Supramolecular Chemistry

Last month we were delighted to hold a ChemComm-RSC Prizes and Awards Symposium on supramolecular chemistry at Trinity College Dublin, Ireland. The free one-day event was a great success, with over 160 delegates and a fantastic programme featuring RSC Award winners and leaders in the field.

CC supramolecular symposium

Speakers from the ChemComm-RSC Prizes and Awards Symposium on Supramolecular Chemistry, 24 May 2013, Dublin, Ireland

Speakers included:

  • 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

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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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