Archive for January, 2013

Penny Brothers joins ChemComm as Associate Editor

ChemComm warmly welcomes Professor Penny Brothers (University of Auckland, New Zealand) as a new Associate Editor. 

Penny Brothers is now accepting submissions to ChemComm in the areas of porphyrin chemistry, the main group elements and organometallic chemistry.  Her current research interests also include the chemistry of new sustainable materials and inorganic medicinal chemistry. 

Submit your next top-notch, high-impact Communication to Penny Brother’s Editorial Office.

Biography

Penny Brothers was born and grew up in Auckland, New Zealand, and completed her BSc and MSc(Hons) degrees in chemistry at the University of Auckland.  In 1979 she was awarded a Fulbright Fellowship and set off for Stanford University to begin a PhD in chemistry under the supervision of Professor Jim Collman.  Her PhD thesis, and much of her subsequent research work, has centered around the chemistry of porphyrin complexes.Professor Penny Brothers

In 1986 she returned to Auckland and spent two years working as a postdoctoral fellow with Professor Warren Roper in the Department of Chemistry, focussing on organometallic chemistry.  In 1988 she took up her current academic position at the University of Auckland.

She has been a visiting scientist at Los Alamos National Laboratory (2003, 2005, 2006) and a visiting professor at the University of California at Davis (1993), the University of Heidelberg (2003) and the University of Burgundy (2004, 2006).  She has been awarded a Fulbright Senior Scholar Award for 2007.

Her current research brings together her interests in porphyrin chemistry, the main group elements and organometallic chemistry.  She investigates how the porphyrin ligand can be used to modify the chemistry of elements such as boron and bismuth, and as a ligand in complexes containing unusual chemical bonds between transition metal and main group elements.  She has a number of research collaborations in NZ and internationally.

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Novel silicon-mediated transannular cyclopropanation

An intriguing new method of transannular cyclopropanation has been reported by Prof. James Dowden‘s group at the University of Nottingham. This cyclopropanation, mediated by the presence of a trimethylsilyl group, allows the rapid formation of 4-azabicyclo(5.1.0)octenones (3) from simple starting materials. Divinyl beta-lactam (1) was elegantly formed via a Staudinger cycloaddition reaction beginning from 3-trimethylsilylpropenal, 4-methoxyaniline and crotonyl chloride. Next, researchers were able to transform 1 into dihydroazocinone (2) using a thermal Cope rearrangement.

The Dowden group discovered that if 2 was treated with TBAF or aqueous sodium hydroxide, 4-azabicyclo(5.1.0)octenone (3) could be formed. Interestingly, the reaction was dependent on the presence of the silicon group; when the trimethylsilyl group was replaced with an ester, no cyclopropanation occurred. The researchers proposed that the transannular cyclopropanation could be viewed as a Lewis-base–promoted Hosomi–Sakurai reaction proceeding via intramolecular 1,4-conjugate addition. 4-azabicyclo(5.1.0)octenones (3) are an unusual structural motif and it is hoped that this facile method for their construction may facilitate further examination of chemical space interactions.

Read this ‘HOT’ Chem Comm article today:

An unusual silicon mediated transannular cyclopropanation

Bing You,  Kate Hamer,  William Lewis and James Dowden
Chem. Commun., 2013, 49, 795-797
DOI: 10.1039/C2CC37739J
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Liquid crystal relaxation controlled by dopant kinetics

Liquid crystals are an area of intense interest due to their potential use in smart materials such as displays. Cholesteric liquid crystals are of particular interest due to their helical nature and their ability to selectively reflect light over a narrow range of wavelengths. This range can be modified by the inclusion of photo-responsive dopants.  

Dopants include overcrowded alkenes which undergo a stable to unstable (cistrans) transition upon irradiation with UV light. This results in an unwinding and eventual inversion of the cholesteric helix. This is accompanied by a red-shift of the reflection band which then returns close to the original position. However, the handedness of the helix has changed, and therefore the polarization of the light has also changed.  

Helix inversion of a cholesteric liquid crystal.

An important parameter with all liquid crystals is their relaxation step which needs to be suitable for the envisioned application. Nathalie Katsonis and her team have studied cholesteric liquid crystals doped with overcrowded alkenes in an effort to find a general paradigm correlating relaxation kinetics with the rate of helix inversion.  

In their recent Communication, Katsonis’ group shows that the helix relaxation kinetics are fully determined by the kinetics of the light-sensitive dopants. The relaxation of the dopants from unstable to stable is unperturbed by the liquid crystalline environment.  

On the other hand, the presence of the dopants can dramatically accelerate helix inversion. Therefore the inversion can be time-programmed by judicious choice of the dopant. This opens up the great potential of fine tuning cholesteric liquid crystals for smart materials with sophisticated functions.  

For more, read this ‘HOT’ Chem Comm article in full:  

Time-programmed helix inversion in phototunable liquid crystals  

Sarah J. Aßhoff, Supitchaya Iamsaard, Alessandro Bosco, Jeroen J. L. M. Cornelissen, Ben L. Feringa and Nathalie Katsonis
Chem. Commun., 2013, Advance Article
DOI: 10.1039/C2CC37161H
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True racemic crystals: Surprising new insights on preparation and structure

Isopropyl 3,3,3-trifluoro-2-hydroxypropanoate (1) is an important compound for the study of self-disproportionation of enantiomers (SDE), in which an enantiomerically enriched mixture can be separated into enantiopure and racemic portions under achiral conditions. This remarkable separation is made possible by the differences in physicochemical properties of enantiopure and racemic substances. Research led by Professor Vadim A. Soloshonok at the University of the Basque Country has now shed light on the unusual properties of racemic crystals of 1.

True racemic crystals were obtained by sublimation of a mixture of (S)- and (R)- crystal conglomerates at ambient temperature and atmospheric pressure. Surprisingly, when these racemic crystals were analysed, the unit cell was not dimeric in nature as previously thought, but rather contained two distinct (S)- and (R)- enantiomers with no heterochiral H-bonding. The preference of 1 for homochiral intermolecular interactions may explain its extraordinary ability for SDE. Indeed, Soloshonok and co-workers showed that achiral chromatography could be used to obtain enantiopure 1 from an original sample with just 75% ee (see above).

For more, read this ‘HOT’ Chem Comm article today:

Unconventional preparation of racemic crystals of isopropyl 3,3,3-trifluoro-2-hydroxypropanoate and their unusual crystallographic structure: the ultimate preference for homochiral intermolecular interactions

José Luis Aceña, Alexander E. Sorochinsky, Toshimasa Katagiri and Vadim A. Soloshonok
Chem. Commun., 2013, 49, 373–375
DOI: 10.1039/c2cc37491a
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A new way to look at cancer cell detection

A novel cancer cell detection method, based on the interaction between daunomycin (DAN – an anticancer drug used in chemotherapy) and cell membrane components, has been developed by scientists in South Korea.

The method uses the electrochemical and fluorescence behaviour of DAN and uses an aptamer probe immobilised on a conducting polymer-gold nanoparticle composite film.

he aptamer sensor probes using electrochemical impedance spectroscopy and fluorescence microscopy. The method differentiates between cancerous and non-cancerous cells at low concentrations (0.01μM).

Read the ‘HOT’ Communication in full:

Cancer cell detection based on the interaction between an anticancer drug and cell membrane components
Pranjal Chandra , Hui-Bog Noh and Yoon-Bo Shim
Chem. Commun., 2013, DOI: 10.1039/C2CC38235K

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