Archive for August, 2014

Improvements to a selective hydrogenation process using ionic liquids

In this ChemComm communication, Peter Claus and co-workers describe an interesting application of room temperature ionic liquids to the selective hydrogenation of 2-hexyne. Unlike many reports in the literature, where an ionic liquid acting as a solvent may enhance a particular reaction, this report outlines a solid supported catalyst system modified with an ionic liquid layer.

Such materials, known as SCILLS, (solid catalyst with an ionic liquid layer) have been investigated in a variety of hydrogenation reactions. In this work the desired reaction is the reduction of 2-hexyne to cis-2-hexene. The catalyst is 1 wt% palladium on silica, modified with various loadings of 3 common ionic liquids: BMIM hexafluorophosphate, BMIM bis(triflouoromethanesulfonyl)imide and N-butyl-N-methylpyrrolidinium dicyanamide ([BMPL][DCA]). The performance of the unmodified catalyst was compared with the yield and selectivity afforded by the SCILL systems. The best results were reported with the dicyanamide ionic liquid SCILL, ([BMPL][DCA]) at 30 wt% ionic liquid loading.

In such a process, there are several reactions that must be suppressed. As the product is an olefin, isomerisation to the trans product must be controlled, as must further hydrogenation to the fully reduced material, hexane. For a number of reasons, based on the nature and amount of chemisorbed hydrogen, and favourable dicyanamide anion interactions with palladium, the dicyanamide SCILL system is particularly effective.

Notably, this system gives improved performance in terms of selectivity and yield over the two best performing commercial catalysts for this task. For example, Lindlar´s catalyst, palladium on calcium carbonate, deactivated with lead, cannot match its performance. In this work, the authors give an example of how ionic liquids can add value to a commercial process, while also offering considerable process improvements, in terms of toxicity and arguably, simplicity. The group’s focus now turns to SCILL activity and stability in a continuous hydrogenation process.

Read this RSC Chemical Communication today!

ionic-liquid layer
Frederick Schwab, Natascha Weidler, Martin Lucas and Peter Claus
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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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Hot ChemComm articles for August

All of the referee-recommended articles below are free to access until 17th September 2014

Nanoscale insight into C–C coupling on cobalt nanoparticles
E. A. Lewis, C. J. Murphy, A. Pronschinske, M. L. Liriano and E. C. H. Sykes  
Chem. Commun., 2014,50, 10035-10037
DOI: 10.1039/C4CC03678F, Communication
From themed collection Scanning Probe Studies of Molecular Systems


A bifunctional curcumin analogue for two-photon imaging and inhibiting crosslinking of amyloid beta in Alzheimer’s disease
Xueli Zhang, Yanli Tian, Peng Yuan, Yuyan Li, Mohammad A. Yaseen, Jaime Grutzendler, Anna Moore and Chongzhao Ran  
Chem. Commun., 2014, Advance Article
DOI: 10.1039/C4CC03731F, Communication


Rapid engineering of versatile molecular logic gates using heterologous genetic transcriptional modules
Baojun Wang and Martin Buck  
Chem. Commun., 2014, Advance Article
DOI: 10.1039/C4CC05264A, Communication


Geometric and redox flexibility of pyridine as a redox-active ligand that can reversibly accept one or two electrons
Richard A. Lewis, K. Cory MacLeod, Brandon Q. Mercado and Patrick L. Holland  
Chem. Commun., 2014, Advance Article
DOI: 10.1039/C4CC05495D, Communication
From themed collection Non-Innocent Ligands


Targeted theranostic prodrugs based on an aggregation-induced emission (AIE) luminogen for real-time dual-drug tracking
Youyong Yuan, Ryan T. K. Kwok, Ruoyu Zhang, Ben Zhong Tang and Bin Liu  
Chem. Commun., 2014, Advance Article
DOI: 10.1039/C4CC05255B, Communication


Anion–π interactions and positive electrostatic potentials of N-heterocycles arise from the positions of the nuclei, not changes in the π-electron distribution
Steven E. Wheeler and Jacob W. G. Bloom  
Chem. Commun., 2014, Advance Article
DOI: 10.1039/C4CC05304D, Communication 

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Radiolabels help evaluate emerging cancer treatment

Researchers in Spain have come up with a way to track the biodistribution of a boron cluster complex used to prepare boron-carrier drugs for a prospective cancer treatment called boron neutron capture therapy (BNCT).

Drugs based on the boron cluster complex COSAN (cobaltabisdicarbollide) exploit the over-expression of membrane receptors in cancer cells to deliver therapeutic levels of 10B across the membrane. Although 10B is a stable isotope, when a beam of low-energy neutrons is applied to the cell, 10B captures a neutron and subsequently decays, releasing a high-energy α-particle and destroying the cell.


Read the full article in Chemistry World»

Read the original journal article in ChemComm – it’s free to access until 26th September:
COSAN as a molecular imaging platform: synthesis and “in vivo” imaging
Kiran B. Gona, Adnana Zaulet, Vanessa Gómez-Vallejo, Francesc Teixidor, Jordi Llop and Clara Viñas  
Chem. Commun., 2014, Advance Article, DOI: 10.1039/C4CC05058D, Communication

 
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