Archive for the ‘Supramolecular’ Category

Supramolecular assembly of polyoxometalate triangles

Polyoxometalates (POMs) are a diverse class of inorganic materials that are of great interest due to their exciting range of redox, conducting, magnetic and catalytic properties. Recent collaborative work from Professor Garry Hanan in Montreal and Professor Bernold Hasenknopf in Paris reports the inclusion of a Lindqvist-type hexavanadate POM as a component of a self-assembling supramolecular framework.

They designed ligand 1 utilising a triol motif to complex the POM in combination with pyridyl groups to serve as binding sites for a transition metal. The reaction of 1 with a suitable decavanadate yielded complex 2, a hexavanadate POM complex that is itself a structurally rigid and spatially well-defined bi-pyridyl ligand. The 60° angle between the coordination vectors of the pyridyl groups led the authors to predict that the coordination of a trans-PdCl2 unit by 2 would result in a supramolecular triangle.

supramolecular assembly of polyoxometalate triangles

Initially the reaction of 2 with [PdCl2(CH3CN)2] in DMAc yielded a complex mixture of products; however, heating to 80 °C for 48 hours led to just a single assembly. This was shown by a number of analytical techniques to be the predicted triangular assembly 3.

This work elegantly uses a classical motif for self-assembly to create a multi-component supramolecular architecture. It is a great step towards the goal of creating functional supramolecular arrays, integrating the desirable properties of POMs into a new framework and bridging the gap between solid state oxides and coordination chemistry.

Researcher’s perspective:
The obtention of discrete coordination-driven POM-based arrays had so far eluded the community, with only a few well characterised coordination polymers. We started this challenging project of a molecular triangle by a simple drawing based on geometrical considerations. A range of conditions were explored, but most lead to complex mixtures except one. This identification of optimal conditions was our first satisfaction. However, we needed solid evidence of the triangular nature of the obtained array to validate our approach as a rational design: a combination of techniques confirmed the successful and selective synthesis of the triangle. As a student, I learnt a lot from the complementary competencies provided by the two groups on a project at the interface of inorganic, organic, supramolecular and coordination chemistry. Dealing with the specific difficulties of each domain has been an exciting challenge that has re-confirmed my choice in academic research. Marie-Pierre Santoni, a student in the research collaboration

To read more about Hanan and Hasenknopf’s work, download their ChemComm article.

Posted on behalf of Cally Haynes, ChemComm web writer.

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81 days until 100 issues…

….and did you know?….

There are 81 articles in ChemComm‘s supramolecular chemistry web themed issue. The issue, guest edited by Philip Gale, Jonathan Sessler and Jonathan Steed, was published to celebrate the International Year of Chemistry 2011.  

Jonathan Sessler and Jonathan Steed are ChemComm Associate Editors, handling supramolecular chemistry communications from North America and the rest of world respectively. Submit your next urgent communication to their editorial offices.

Also of interest
100 days to 100 issues
96 days until 100 issues…
93 days until 100 issues…

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Detecting caffeine

A team of researchers from Switzerland have used a commercially available fluorophore for detecting caffeine in water.

Previous methods for caffeine detection have been based on hydrogen-bonding receptors but these suffer from the need to use organic solvents. Whilst water-based detection has been achieved, the sensitivity and selectivity for caffeine was low.

Inspired by the known affinity of caffeine for polyaromatic compounds, Kay Severin and colleagues discovered that HPTS, a polysulfonated pyrene dye, can be used to selectively probe caffeine in liquid and solid samples. The team used the probe to quantify caffeine levels in soft drinks, coffee and painkillers, proving it can be used as a simpler alternative to HPLC.

Download the ChemComm article to find out more.

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Cram Lehn Pedersen Prize – now open for nominations

 

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Macrocycles for in vivo zinc sensing

Graphical abstract: Modular ‘click’ sensors for zinc and their application in vivoZinc anions are ubiquitously present in the body and involved in many metabolic pathways affecting the proper functioning of the immune system, DNA transcription, reproduction, sexual development, brain function, and more roles are uncovered by studies worldwide.

The presence of abnormally high or low level of zinc in specific organs and areas has been linked to several diseases and conditions, including Alzheimer’s disease, stroke and epilepsy. In the light of these considerations, it is not surprising that many efforts have been devoted to in vivo zinc sensing and quantification.

A significant portion of the research to uncover the correlations between the concentration of metal ions, pathologies and development is performed on animal models such as zebrafish (Danio rerio). Due to their fast development, they can be grown outside the mother’s body, and their embryos are transparent, allowing for a clear observation of their organs without the need for dissection.

Watkinson and Goldup, from Queen Mary University of London, recently focused their effort to the development of a fluorescent sensor for zinc to be used in model studies on zebrafish. The sensor is based on macrocyclic nitrogen-containing rings (cyclen or cyclam) equipped with a fluorescent pendant arm, introduced using a widely known and applied “click” cycloaddition. The sensor’s fluorescence is activated upon coordination of the zinc anion in a scorpionate fashion.

The sensors proved reliable and stable in a wide range of pH, ideal for in vivo use, and a remarkable selectivity for zinc over other possible anions. Competition experiments with twelve different anions showed that only in the presence of Fe3+ and Cu2+ in threefold excess (in relation to zinc) the sensor failed to discriminate between the metals.

To test their performance in biological models, zebrafish eggs were grown in solutions of the sensors and the distribution of fluorescence monitored during their growth, proving not toxic to the subjects. The accumulation of fluorescence concentrated in the eye, the gall bladder and the biliary system, all regions not highlighted by previous sensors, suggesting a different mechanism of absorption for these macrocyclic compounds and different cell permeability.

Although those reported are preliminary results, the characteristics of these sensors may make them a viable candidate for future applications in vivo sensing of zinc pools.

Read the article online or access the ESI (free).

Modular ‘click’ sensors for zinc and their application in vivo
Kajally Jobe, Caroline H. Brennan, Majid Motevalli, Stephen M. Goldup and Michael Watkinson
Chem. Commun., 2011, 47, 6036-6038

Posted on behalf of Dr. Giorgio De Faveri, Web Writer for Catalysis Science & Technology 

This communication is part of the ChemComm Supramolecular Chemistry web themed issue. Check out the web theme page to download other contributions from this exciting issue.

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Supramolecular Chemistry—Introducing the latest web themed issue

Graphical abstract: Supramolecular Chemistry—Introducing the latest web themed issueChemComm issue 21 is now online and includes an Editorial from Philip Gale, Jonathan Sessler and Jonathan Steed, guest editors of the recent Supramolecular Chemistry web themed issue.

Featuring over 60 articles (and growing!), the web theme showcases a collection of cutting edge contributions by international leaders in the field of supramolecular chemistry to mark the International Year of Chemistry 2011.

Browse this exciting web theme today to read the latest urgent communications. You can also catch up on a decade’s worth of progress in supramolecular chemistry by reading the issue’s Highlights in Chemistry.

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New copper complex offers easy access to complex structures

Chemists working at the University of Cambridge in the UK have discovered a new dicopper complex capable of forming diverse supramolecular structures.

The creation of supramolecular structures for a wide variety of uses has been something that chemists have pursued for years and, as such, new methods to access these structures are constantly sought.  Jonathan Nitschke and colleagues are prominent figures in this field and have just reported a new copper complex that self assembles into larger architectures.

The team first assembled the copper complex and then showed they could modified it at two points. This is done either by substitution of solvent molecules with ligands capable of linking multiple complexes or by modifying the imine bonds. Using both these approaches and varying the ligands, it was possible to achieve the templated synthesis of 26- and 52-membered macrocycles. More complex assemblies that utilise this approach are currently being investigated.

Interested in finding out more? Then download Nitschke’s ChemComm article for free today. Also why not check out Dr Nitschke’s mini review and edge article form our sister journal Chemical Science?

Reactivity modulation in container molecules
Boris Breiner, Jack K. Clegg and Jonathan R. Nitschke
Chem. Sci., 2011, 2, 51-56
DOI: 10.1039/C0SC00329H, Minireview

Selective anion binding by a “Chameleon” capsule with a dynamically reconfigurable exterior
Yana R. Hristova, Maarten M. J. Smulders, Jack K. Clegg, Boris Breiner and Jonathan R. Nitschke
Chem. Sci., 2011, 2, 638-641
DOI: 10.1039/C0SC00495B, Edge Article

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ChemComm Emerging Investigator Lectureship – winner announced

On behalf of the ChemComm Editorial Board, I am delighted to announce that Dr Scott Dalgarno (Heriot Watt University, Edinburgh, UK) has won the inaugural ChemComm Emerging Investigator Lectureship.

This annual award recognises an emerging scientist in the early stages of their independent academic career. The Editorial Board commended Dr Dalgarno’s contributions to the field of supramolecular chemistry, in particular the assembly and properties of calixarenes.  

Dr Dalgarno will present his award lecture, entitled ‘Metal-Organic Calixarene Assemblies’, at the following locations:

For more details about these lectures, please contact ChemComm Editor, Robert Eagling.

To find out more about Dr Dalgarno’s research, read these recent ChemComm articles:
Calix[4]arene supported clusters: a dimer of [MnIIIMnII] dimers
Stephanie M. Taylor, Ruaraidh D. McIntosh, Christine M. Beavers, Simon J. Teat, Stergios Piligkos, Scott J. Dalgarno and Euan K. Brechin, Chem. Commun., 2011, 47, 1440-1442

Calixarene supported enneanuclear Cu(II) clusters
Georgios Karotsis, Stuart Kennedy, Scott J. Dalgarno and Euan K. Brechin, Chem. Commun., 2010, 46, 3884-3886

Magnetism in metal–organic capsules
Jerry L. Atwood, Euan K. Brechin, Scott J. Dalgarno, Ross Inglis, Leigh F. Jones, Andrew Mossine, Martin J. Paterson, Nicholas P. Power and Simon J. Teat, Chem. Commun., 2010, 46, 3484-3486

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A rare example of synthon polymorphism

Scientists in India have reported a rare example of synthon polymorphism in co-crystals of 4,4′-bipyridine and 4-hydroxybenzoic acid.

Graphical abstract: Synthon polymorphism and pseudopolymorphism in co-crystals. The 4,4′-bipyridine–4-hydroxybenzoic acid structural landscape

Polymorphism is defined as the ability of a material to exist in more than one form or crystal structure. It has important implications for the properties of such materials; for example in pharmaceuticals, the dissolution rate of a drug can be dependent on the polymorphic form. While this is a common phenomenon in single crystals it is much less common in co-crystals, systems where the structure has at least two distinct components.

Gautam Desiraju from the Indian Institute of Science, found that when 4,4′-bipyridine and 4-hydroxybenzoic acid were dissolved together in a solvent such as methanol they would co-crystallise to form two different polymorphs. They noticed that a third form, a pseudopolymorph, was also present.

If you would like to read more about Desiraju’s discovery then why not download his ChemComm article for free today? This article is also part the ChemComm web themed issue on Supramolecular Chemistry to mark the International Year of Chemistry 2011.

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A supramolecular approach to zwitterionic metal silanides

Zwitterionic metal silanides represent a structurally novel class of tri-coordinated silyl anions in which the cationic metal centre is separated from the silicon anion by internal donor bridges.

Clemens Krempner and co-workers have now reported that key to the synthesis of stable, isolable species is the use of pendant polydonor groups that exclusively bind to the metal cation and serve to prevent self-aggregation. 

Due to the shape of these unusual compounds, the electron pair located at the central silicon anion is available for additional metal binding. This has allowed for the synthesis of hitherto unknown zwitterionic heterobimetallic silanides, by reaction of the zwitterionic metal silanides with boron, aluminium or tungsten-containing species.

To read about these intriguing compounds in more detail, download the ChemComm communication, which is available for free until April 28th.

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