Author Archive

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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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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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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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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Probing assembly of supramolecular architectures with non-linear optics

Molecules containing urea and thiourea groups are well known in supramolecular chemistry to self assemble into chains via hydrogen bonding interactions, which can be broken by interaction with ions or polar molecules.


Pritam Mukhopadhyay’s
group in New Delhi have found that, with the right functionalization, this can lead to interesting optical properties in solution.

Molecules such as 1a and 1b were found to have non-linear optical (NLO) behaviour in THF solution. On adding a polar molecule such as methanol, or a strongly coordinating anion such as acetate, the NLO behaviour was reduced. This corresponds to the self-assembled urea chains being disrupted by adding a guest that can compete for hydrogen bonding to the urea NH groups.

With this work, the authors have identified an effective new method to probe the assembly and disassembly of supramolecular architectures.

For more information, you can download the full article (free for a limited time) here.

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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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Macrocycle insulation for molecular wires

Researchers in Texas are using rotaxane formation to sterically protect or “insulate” molecular wires.

Molecular wires, in which an unsaturated linker separates two or more redox active metal sites, are of great research interest. These structures allow phenomena such as electron delocalisation or transport between the two redox sites. John Gladysz’s group at Texas A&M University have an ongoing interest in dimetallic polyynediyl complexes, in which two metal centres are linked by conjugated polyynediyl linkers that they now hope to “insulate” to reduce interactions between wires and the external environment. A previous approach used long alkyl bis-phosphine, which wrapped around the wire in a double helix to complex both metal centres. However, this gave two enantiomers, which interconverted rapidly in solution via uncoiling of the protective ligands.

The Gladysz group are now reporting a straightforward solution to this problem. They found that by synthesising their bis-platinum wire in the presence of a 33-membered macrocycle, they could incorporate the wire as the thread of a rotaxane complex. This provides a more robust protection for the wire which is unaffected by dynamic processes.

This work shows a fantastic application of rotaxane chemistry for protection of a molecular wire. What’s more, the synthesis of this rotaxane is adaptable, and the Gladysz group are working on exciting new and improved systems including longer polyynediyl linkers and redox inactive macrocycles to improve the properties of the insulated wires.

The full communication can be downloaded here.

Cally Haynes

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Chiral self-recognition by simple macrocycles

A recent communication from Isao Azumaya, Aya Tanatani and colleagues describes their work on some macrocycles based on cyclic triamide 1. The bowl-like structure of these macrocycles is reminiscent of well-known supramolecular building blocks such as calixarenes, and the authors hope that they might be similarly applied to constructing supramolecular architectures. These macrocycles have three possible inter-convertible conformations, of which the most stable syn- forms are enantiomeric.

Structure and conformations of cyclic triamide 1 

The group found that a number of triamide-substituted macrocycles such as 2 dimerise into capsule-like structures in the solid state through interactions between the amide groups. Remarkably, 2 formed chiral crystals, as the macrocycles dimerised in the syn-form and only with their own enantiomer. This is the first report of the separation of cyclic triamides without using an additional chiral species, and shows that this particular macrocycle is able to recognise its own enantiomer (in the figure below single enantiomers are shown in the same colour).

cyclic triamide

In solution, a tricarboxylate-substituted macrocycle was shown to interact with a chiral amine guest. This caused induction of chirality in a host in which, in equilibrium in solution, no particular enantiomer is usually favoured.

These simple macrocycles are easy to synthesise and functionalise and have fascinating dynamic behaviour in solution and in the solid state. They are an exciting prospect for application as molecular building blocks with the added potential for host-guest chemistry.

Find out more download the communication for free for limited period.

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