Chemical Science Blog

Carbon nanotube (CNT) fragments are exciting materials for the fields of supramolecular chemistry and nanotechnology. This is due to their tunable optical and physical properties, as well as their potential for host-guest chemical interactions. The authors from Boston and Drexel Universities and co-workers, report here for the first time, the synthesis of the radical cation of [8]-cycloparaphenylene, prepared by reaction of [8]-cycloparaphenylene with the oxidant triethyloxonium hexachloroantimonate (Et3O+SbCl6-
). A vivid colour change, from yellow to orange to deep purple, accompanied the oxidation. The product remained stable when dry for several days, and was readily reduced back to [8]-cycloparaphenylene on reaction with zinc dust.

Surprisingly, electron paramagnetic resonance (EPR) experiments on solutions of the radical cation, did not give detailed information, other than a characteristic signal for one unpaired electron.  The material also proved difficult to crystallise in a pure form. Therefore, the focus shifted to photophysical, electrochemical and theoretical properties. As seen in the figure above, on the right, the radical cation of [8]-cycloparaphenylene has two major absorptions at at 535 and 1115nm, which follow closely the values determined by density functional calculations (DFT), and are characteristically different to the parent neutral material.

Theoretical calculations also suggest a change to a highly delocalised structure in the radical cation and its dimer with the neutral compound, compared to benzene like character in [8]-cycloparaphenylene. This should prove useful for potential applications in electronic and photovoltaic devices. Detailed results from computational studies on the electronic structures of the radical cation of [8]-cycloparaphenylene ([8]-CPP) and its resonance dimer, as well as the 6, 10 and 12 ring-containing ‘hoops’ are given. This article sheds valuable new light on the properties of  intra- and inter-molecularly delocalised systems based on cycloparaphenylenes.

Read this HOT Chemical Science Edge Article today!

Photophysical and theoretical investigations of the [8]cycloparaphenylene radical cation and its charge-resonance dimer
Matthew R. Golder, Bryan M. Wong and Ramesh Jasti
Chem. Sci., 2013, Advance Article
DOI: 10.1039/C3SC51861B

Kevin Murnaghan is a guest web-writer for Chemical Science. He is currently a Research Chemist in the Adhesive Technologies Business Sector of Henkel AG & Co. KGaA, based in Düsseldorf, Germany. His research interests focus primarily on enabling chemistries and technologies for next generation adhesives and surface treatments. Any views expressed here are his personal ones and not those of Henkel AG & Co. KGaA.

In the presence of half mustard, the dithiol does not react with the squaraine dye so the dye’s blue colour is visible

Scientists in the US are trying to develop a new detection system for the chemical warfare agent mustard gas. 

There is no antidote to mustard gas, which burns the skin, eyes and respiratory system. Victims not killed by an attack are left severely incapacitated. It is an environmentally persistent chemical and its cruel effects can take around 12 hours to take hold. A cheap and simple sensor to alert civilians and emergency responders to its presence is obviously desirable. 

Eric Anslyn and Vinod Kumar at the University of Texas at Austin are getting closer to such a system. With the knowledge that chlorine atoms in mustard gas will readily react with good nucleophiles like thiols, they have designed a dithiol and squaraine dye system to give a clear colour change in the presence of the mustard gas simulant 2-chloroethyl ethyl sulfide, also known as half mustard. 

Researchers from South Korea have reported the chemical modification of graphene nanoplatelets using a solid-state technique, which has led to a dramatic improvement in their solubility in a wide variety of solvents.

(a) Mechanochemically driven solid-state Diels–Alder reaction between active carbon species by ball-milling in the presence of maleic anhydride (MA) or maleimide (MI). SEM images: (b) pristine graphite, (c) MA-GnPs, (d) MI-GnPs.

Graphene, a single-layer two-dimensional sheet of aromatic carbon atoms, has attracted a lot of interest since the realization of its unique electric, optical, mechanical and thermal properties. These properties can be further exploited and improved upon the functionalization, either covalently or non-covalently, of the graphene surface. The catch-22 is that unfunctionalized graphene is inherently insoluble, making it difficult to modify chemically, but its properties can typically be improved solely through chemical modification. As a result, much work has been carried out to develop methods of facilitating the covalent modification of graphene – in higher yields and more easily than currently possible.

Jong-Beom Baek and his team at the Ulsan National Institute of Science and Technology (UNIST) have achieved such a feat by increasing the solubility of graphene nanoparticles using, for the first time, a dry ball-milling reaction. Using Diels-Alder [4+2] cycloaddition reactions between graphene nanoplatelets (derived from the ball-milling of graphite) and either maleic anhydride or maleimide, O and N atoms were selectively introduced to the edges of graphene nanoplatelets in reasonable yields. As a result, the nanoplatelets showed good dispersability in both protic and polar aprotic solvents, including in neutral water. This is a significant achievement, as the Diels-Alder reaction allows for a large range of functional groups to be attached to the graphene edges and offers a general method for the chemical modification of graphene.

– by Anthea Blackburn

Read this HOT ChemComm article in full!

Mechanochemically driven solid-state Diels–Alder reaction of graphite into graphene nanoplatelets
Jeong-Min Seo, In-Yup Jeon and Jong-Beom Baek
Chem. Sci., 2013, Advance Article
DOI: 10.1039/C3SC51546J, Edge Article

Anthea Blackburn is a guest web writer for Chemical Science.  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 working on the incorporation of porphyrins into topologically interesting and mechanically interlocked molecules. When time and money allow, she is ambitiously attempting to visit all 50 US states before graduation.

Metallohelices with activity against cisplatin-resistant cancer cells; does the mechanism involve DNA binding?
Viktor Brabec, Suzanne E. Howson, Rebecca A. Kaner, Rianne M. Lord, Jaroslav Malina, Roger M. Phillips, Qasem M. A. Abdallah, Patrick C. McGowan, Alison Rodger and Peter Scott
Chem. Sci., 2013, Advance Article
DOI: 10.1039/C3SC51731D, Edge Article

Free to access until 13th October 2013

Topological isomerism in a chiral handcuff catenane
Karel J. Hartlieb, Anthea K. Blackburn, Severin T. Schneebeli, Ross S. Forgan, Amy A. Sarjeant, Charlotte L. Stern, Dennis Cao and J. Fraser Stoddart
Chem. Sci., 2013, Advance Article
DOI: 10.1039/C3SC52106K, Edge Article

Free to access until 13th October 2013

Development of cell-impermeable coelenterazine derivatives
Eric Lindberg, Shin Mizukami, Keiji Ibata, Takashi Fukano, Atsushi Miyawaki and Kazuya Kikuchi
Chem. Sci., 2013, Advance Article
DOI: 10.1039/C3SC51985F, Edge Article

Free to access until 13th October 2013

Monolayers of trimesic and isophthalic acid on Cu and Ag: the influence of coordination strength on adsorption geometry
Izabela Cebula, Hao Lu, Michael Zharnikov and Manfred Buck
Chem. Sci., 2013, Accepted Manuscript
DOI: 10.1039/C3SC52137K, Edge Article

Free to access until 13th October 2013

Scientists in the US have successfully used a template directed protocol to synthesise two topological isomers of a handcuff catenane. Handcuff catenanes are mechanically interlocked molecules where two covalently bound rings, called the ditopic host, are interlocked by a third ring threaded through both rings of the ditopic host. Only three other mechanically interlocked molecules with the handcuff topology have been reported before – they are very difficult to synthesise.

Previous handcuff catenanes have all been achiral and have only demonstrated one way to thread the third ring through the diptopic host. The handcuff catenane made by Fraser Stoddart and colleagues at Northwestern University has two distinctive topologies – it is impossible for one to be converted into the other, unless covalent bonds are broken and then re-made. The stereochemistry demonstrated by Stoddart’s handcuff catenanes is interesting because as well as being topologically chiral they also display Euclidian chirality.

The different isomers of the handcuff catenane and their relationship to one another

The different isomers of the handcuff catenane and their relationship to one another
A template directed synthesis between the π-electron-rich bis-1,5-dioxynaphtho[50]crown-14 and the precursors of two fused π-electron-deficient cyclobis(paraquat-p-phenylene) cyclophanes was used to make the topologically complex molecules. The handcuff catenanes could have future applications in molecular switches.

This article appeared in Chemistry World on 9^th September 2013.

You can also read the original journal article in Chemical Science:
Topological isomerism in a chiral handcuff catenane
Karel J. Hartlieb, Anthea K Blackburn, Severin Thomas Schneebeli, Ross S Forgan, Amy Sarjeant, Charlotte L Stern, Dennis Cao and J. Fraser Stoddart
Chem. Sci., 2013, Accepted Manuscript, DOI: 10.1039/C3SC52106K