Author Archive

Calix[6]arenes as models of enzymes?

When it comes to supramolecular chemistry in water, the best lessons are learnt from nature. Enzymes and antibodies use non-covalent interactions, including hydrogen bonding, coordination to a metal centre and hydrophobic effects, to bind guests extremely strongly. Olivia Reinaud’s group are following suit with their water-soluble funnel calix[6]arene receptor that complexes both Zn2+ cations and primary amines in aqueous solution. 

synergistic interaction of calixarene, heptylamine and Zn(II) for the complex formation

In the presence of both Zn2+ and primary amines, a complex is formed in which the Zn2+ cation is bound by the imidazole groups. The amine is bound to the Zn2+ with favourable hydrophobic interactions between the cavity of the calixarene and the alkyl chain. Interestingly, the calixarene does not complex either of these guests individually, showing that the binding is highly cooperative. This type of complex only forms with primary amines. Considering this selectivity and the type of interactions used, plus the fact that the complex forms in water near pH 7 and a pseudo pKa shift of the bound amine, the authors point out that the complex formation is highly reminiscent of the binding mode of Zn-based enzymes.

This is one of only a few examples of selective encapsulation of primary amines in water, and an inspiring step towards emulating the function of natural metalloenzymes.

Keen to read more? Download Reinaud’s Chemical Science Edge article.

Posted on behalf of Cally Haynes, Chemical Science web writer.

Also of interest:
RSC Macrocyclic and Supramolecular Chemistry Meeting
– 19-20 December 2011
Solvent responsive cage: inducing a pronounced reorganisation of a metallasupramolecular cage complex with a conservative change in solvent polarity

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Blogging about our bloggers

Cally Haynes

I was born in London and studied chemistry at Wadham college, Oxford. I am currently working with Professor Phil Gale at the University of Southampton, after recently completing my PhD in the same group. My research to date has focused on the supramolecular chemistry of anions, and in particular the transmembrane transport of chloride and bicarbonate. I am a member of a highly successful pub quiz team and a keen Arsenal supporter.

Alice Williamson

I was born and raised in Warrington where I completed  A-levels at Priestley College. I then moved a bit further north to spend four great years studying for a Masters in Medicinal Chemistry at the University of Leeds. As part of my degree, I spent a year working in industry at the pharmaceutical company F. Hoffmann La Roche in Basel, Switzerland. I then returned to Leeds to complete my masters research project in the group of Professor Philip Kocienski.In October 2007, I moved to the University of Cambridge to complete a PhD under the supervision of Dr. Matthew J. Gaunt where I have been working on new strategies for catalytic asymmetric arylation. Outside of the lab I enjoy going to gigs, socialising with friends and trying to remember how to play tennis.
 

Sarah Brown

Sarah Brown

Since the completion of my Ph.D. in Professor Duncan Graham’s group (University of Strathclyde) in 2009, I have been working as a post-doctoral researcher in Dr Nial Wheate’s group at the Strathclyde Institute of Pharmacy and Biomedical Sciences. My current research is focused on the development of improved delivery and efficacy of platinum-based anticancer drugs.After a six month career break this year in Zambia, volunteering for a medical NGO, I have been inspired to start my own charity with the help of some friends, which aims to empower teachers in rural schools in Zambia to deliver practical science education that supports the local curriculum using locally available materials.Now back in Glasgow, I am resuming my role as a STEM ambassador as well as rediscovering my penchant for all things (old) lady like; baking, crocheting, sewing and tea.
 

Iain Larmour

Iain Larmour

I was born and bred in Belfast, Northern Ireland, where I studied for a BSc in chemistry at Queen’s University of Belfast, gaining a first class honours before starting a PhD with Dr Steven Bell, where I discovered a passion, along with a small amount of ability, for research.My thesis ended up being focused on superhydrophobic metal coatings, although I spent time on various other interesting spectroscopy and materials based projects along the way. Several papers, a couple of patents and a removed appendix later and I passed my final viva. The Royal Irish Academy awarded my thesis their prize for young chemists for 2008.Deciding that winter nights weren’t quite long enough, I moved north a bit to the University of Strathclyde in Glasgow where I’m undertaking postdoctoral research with Prof. Duncan Graham in the area of single and few molecule detection by surface enhanced Raman spectroscopy. I still carry out unrelated but interesting little side projects when I can and thoroughly enjoy the art of “networking” (socialising with old and new friends). Beyond work, I am a keen photographer with some of my photos recently being exhibited at a local arts festival. I have a long list of places I want to visit to take photographs most of them in hotter climes. Some day I also hope to receive a complimentary RSC mug…one can but dream.
   
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A way of life – chemistry meets biology in Chemical Science

Chemical techniques are critical for studying and manipulating biological systems. Here at Chemical Science, we’ve published a host of great articles at the interface of chemistry and biology. Below is a selection of some of the recent ones. Sign up for our e-alerts and browse our issues to keep up-to-date with the latest exceptional research in this fascinating field.

Ultrafast infrared chemical imaging of live cells
Hemmel Amrania, Andrew P. McCrow, Mary R. Matthews, Sergei G. Kazarian, Marina K. Kuimova and Chris C. Phillips, Chem. Sci., 2011, 2, 107-111

Clickable, photoreactive inhibitors to probe the active site microenvironment of fatty acid amide hydrolase
Susanna M. Saario, Michele K. McKinney, Anna E. Speers, Chu Wang and Benjamin F. Cravatt, Chem. Sci., 2011, DOI: 10.1039/C1SC00336D

Molecular recognition of cytochrome c by designed receptors for generation of in vivo and in vitro functions
Satoshi Shinoda and Hiroshi Tsukube, Chem. Sci., 2011, DOI: 10.1039/C1SC00162K

Diversity in natural product families is governed by more than enzyme promiscuity alone: establishing control of the pacidamycin portfolio
Sabine Grüschow, Emma J. Rackham and Rebecca J. M. Goss, Chem. Sci., 2011, 2, 2182-2186

1H NMR metabolomics combined with gene expression analysis for the determination of major metabolic differences between subtypes of breast cell lines
Miroslava Cuperlovic-Culf, Ian C. Chute, Adrian S. Culf, Mohamed Touaibia, Anirban Ghosh, Steve Griffiths, Dan Tulpan, Serge Léger, Anissa Belkaid, Marc E. Surette and Rodney J. Ouellette, Chem. Sci., 2011, 2, 2263-2270

Rapid fluorescence imaging of miRNAs in human cells using templated Staudinger reaction
Katarzyna Gorska, Ioanna Keklikoglou, Ulrich Tschulena and Nicolas Winssinger, Chem. Sci., 2011, 2, 1969-1975

Methods for converting cysteine to dehydroalanine on peptides and proteins
Justin M. Chalker, Smita B. Gunnoo, Omar Boutureira, Stefanie C. Gerstberger, Marta Fernández-González, Gonçalo J. L. Bernardes, Laura Griffin, Hanna Hailu, Christopher J. Schofield and Benjamin G. Davis, Chem. Sci., 2011, 2, 1666-1676

Engineering DNA aptamers for novel analytical and biomedical applications
Mingxu You, Yan Chen, Lu Peng, Da Han, Bincheng Yin, Bangce Ye and Weihong Tan, Chem. Sci., 2011, 2, 1003-1010

Submit your own hot research to our chemical biology and bioorganic Associate Editors: Benjamin Cravatt and Thomas Carrell.

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Interview with Chemical Science Editor-in-Chief David MacMillan

David MacMillan David MacMillan is the A Barton Hepburn chair, director of the Merck Center for Catalysis and department chair of chemistry at Princeton University, US. His research focuses on organic chemistry and catalysis.

Why did you decide to become a chemist?   

It’s a funny story. I originally went to Glasgow to study physics but the physics lecture theatre was really cold and the chemistry lecture theatre was much warmer so I switched degree. That makes it sound trivial – I obviously liked the subject too. 

What’s going on in your lab at the moment?   

Something I’m really excited about is synergistic catalysis. Instead of using one catalyst to do one reaction (i.e. one activation mode), can you strategically carry out two activation modes in the same reaction such that you find two activating molecules that will react with each other. There are a whole host of different bond connections that can fly out of that – new reactions, new bond formations, high levels of selectivity and enantioselectivity. It is something that nature does but chemists rarely do and so the area is completely wide open.   

Another thing we’re looking at is collective total synthesis: how do you think of ways to strategically build molecules that allow you to build lots of families of natural products as opposed to just one natural product? That would allow you to systematically make things with much higher levels of efficiency. When it comes to using natural products, collective total synthesis makes much more sense, in the same way that a medicinal chemist would much prefer to make a late stage molecule that can be diversified at the end rather than making a different single molecule every single time.   

Aside from your own research, what’s hot in organic chemistry right now?   

The work of Eric Jacobsen is exceptionally interesting – the whole idea of using small numbers of interactions to stabilise transition states, allowing you to go after different ways of activating molecules, for example counter-ion catalysis, which his group does.   

I also find Steve Buchwald’s work amazing because it is chemistry that has a massive impact on a day-to-day basis. To me, that is exceptionally exciting.   

C-H bond activation is one of the great frontiers of the field and there are some really fantastic people doing it – Christina White, Melanie Sanford, Jin-Quan Yu, to name a few. 

You are Editor-in-Chief of Chemical Science. What are the most exciting parts of this role? 

This is unbelievably exciting. People might say ‘does the world need another journal?’ I would argue that the world might not need just another journal but what we do massively need is quality, excellent journals. In my opinion, there are simply not enough of them. A lot of the other journals out there are heterogeneous in quality. With Chemical Science, we’ve found a society publishing group that has really got behind the idea of doing something different and is fully supporting it, both financially and in terms of resources and effort. I was given the chance to put together what I think is the best editorial board in the world. It is an unbelievable group of people – the quality is not surpassed. I believe that if you get great people together with great resources, it thermodynamically has to play out to be this great thing. 

You have received numerous awards throughout your career, including the 2011 ACS award for creative work in synthetic organic chemistry. What do awards mean to you?   

People like me are always cynical about awards and say they don’t mean anything to us until we receive one and then we are exceptionally happy. It makes you feel like you are being recognised by the greater community and that is a superb feeling. You are doing something that you care about and it is nice to know that the community also thinks it is valuable.   

What are the main challenges facing chemists and chemistry?   

There are the big societal challenges that everyone is aware of, such as energy and scarce natural resources. Another challenge is being able to make any molecule we want efficiently and selectively.   

One major thing chemists need to work on is their ability to promote their work to other scientists and the public. This is something we are really not good at in general and if we improved, it would really open doors for us and improve society’s perception of chemistry and its impact.   

You are a consultant for a number of pharmaceutical companies. Can you comment on the current state of the industry and the recent high profile redundancies?   

Pharma is obviously in a state of flux right now.  We are seeing fewer drugs being approved on a yearly basis and there is a constant question as to why. I suspect the real reason is a combination of factors including: (i) the FDA (US Food and Drug Administration) setting unrealistic bars and guidelines for when drug approval is possible, (ii) the push towards company mergers, which leads to fewer approaches towards developing drugs for any given target for society, as well as a net reduction in the number of scientists gainfully employed in the practice of making drugs on a world-wide basis, and (iii) the impact of Wall Street on pharma and the constant push for quarterly short term success at the price of long term success, which is the eight year cycle to produce drugs. The latter has resulted in a lot of lay-offs to save money by cutting R&D. The problem is this is setting the stage for more disappointment in the long term (or killing the goose that lays the golden egg). 

I think there are two bright sides in this gloomy picture. The first is that smart people (and chemists are very smart) will always find a way towards using their talents and to success. This will most likely play out in the form of small companies being built by chemists and biologists who are being pushed out of big pharma. These people will continually push innovation, determination and they will have a buy-in for the companies they form, as opposed to being continually distracted by the fear of losing their job at a larger company. These companies will grow and will provide jobs in the US and Europe for the future. It will take a while, but it will happen. 

The second is that many big pharma companies are in trouble. However, it is my view that the best ones will make it and the not so successful ones will not. The ones that will make it through will prosper and they will see re-growth in the future. As to where these companies will be located, I still see Europe, Japan and the US as the major locales for these companies for many years to come. 

What advice would you give young scientists starting out in their career?   

Follow your dream. Don’t get bogged down by the small, incremental things even if someone tells you you should be doing them. Concentrate on what you really want to achieve. 

What do you do in your spare time?   

I hang out with my family. I have a five year old daughter and an amazing wife. Because of my job, time is limited so I try to spend as much of my free time with them as possible. I am always playing or watching football with my daughter and we go to libraries and go cycling. My favourite thing is quality time with my family. 

What would you be if you weren’t a chemist?   

I’d like to have been a professional football player but I am absolutely terrible at it so there is no way that would ever have happened. Perhaps something in design but it is a really difficult question – chemistry has been my focus for such a long time.

Read some of Professor MacMillan’s latest research in Chemical Science:

The intramolecular asymmetric allylation of aldehydes via organo-SOMO catalysis: A novel approach to ring construction
Phong V. Pham, Kate Ashton and David W. C. MacMillan, Chem. Sci., 2011, 2, 1470

A general approach to the enantioselective -oxidation of aldehydes via synergistic catalysis
Scott P. Simonovich, Jeffrey F. Van Humbeck and David W. C. MacMillan, Chem. Sci., 2011, DOI: 10.1039/c1sc00556a

Also of interest

Diamine ligands in copper-catalyzed reactions
David S. Surry and Stephen L. Buchwald, Chem. Sci., 2010, 1, 13-31

Dialkylbiaryl phosphines in Pd-catalyzed amination: a user’s guide
David S. Surry and Stephen L. Buchwald, Chem. Sci., 2011, 2, 27-50

Hydroxyl-directed C–H carbonylation enabled by mono-N-protected amino acid ligands: An expedient route to 1-isochromanones
Yi Lu, Dasheng Leow, Xisheng Wang, Keary M. Engle and Jin-Quan Yu, Chem. Sci., 2011, 2, 967-971

This interview was also published in Chemistry World.

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Mechanically locked capsule captures oppositely charged guests

By combining hydrogen bonding and mechanical bonding, scientists in Spain have made a mechanically locked capsule that can encapsulate two oppositely charged ions. 

molecular capsule

Pablo Ballester and Marco Chas, at the Institute of Chemical Research of Catalonia, Tarragona, made the capsule’s two hemispheres out of a calix[4]pyrrole and a calix[4]arene. The calix[4]pyrrole uses hydrogen bond interactions to recognise anions or N-oxide  guests while the calix[4]arene provides efficient cation-π and CH-π interactions for co-encapsulated guests. The capsule can fit two neutral or oppositely charged guests and the encapsulation is reversible. 

If this has captured your attention, download Ballester’s Chemical Science Edge article for free and read more.

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Cascades caused by carbenes

Researchers at Monash University in Australia have described the first example of a combined Brønsted/Lewis base cascade catalysis using an N-heterocyclic carbene (NHC) catalyst. David Lupton’s group have reported the synthesis of a variety of different dihydropyranones (2) in a single step from cyclopropyl enol esters (1).

Lisa Candish conducted mechanistic studies, which have enabled the group to suggest a possible catalytic cycle for the transformation. Firstly, catalytic deprotonation of 1a generates the α- or γ-enolate I which undergoes proton transfer to form the cyclopropyl anion II, primed for an electrocyclic ring opening to give allyl anion III. Protonation of III serves to regenerate catalyst 3, enabling its involvement in a second step of the mechanism. Addition of catalyst 3 to ester IV forms hemiacetal V, which undergoes a Claisen rearrangement to generate the final product 2a.

catalytic cycle

Exploitation of this dual Brønsted and Lewis base activation may enable the development of other interesting transformations. Additionally, the use of homochiral NHCs may enable enantioselective transformations in the future.

Lupton’s Chemical Science Edge article is free to download – read it today to find out more.

Researcher’s perspective: 
Determining a possible mechanism for this reaction was extremely challenging and enjoyable. A range of approaches were explored, but most lead to increased ambiguity. It was very satisfying when we came up with a strategy that actually helped clarify the reaction path. As a student this was very rewarding and reminded me of why I initially chose to study organic synthesis. Lisa Candish

Posted on behalf of Alice E. Williamson, Chemical Science web writer.

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Increased silene stability

Patrick Steel’s group at the University of Durham have used computational modelling in combination with experimental studies to generate silene equivalents.

Silenes (2) are compounds containing a silicon–carbon double bond, which are generally so reactive that they are only transient in existence and rapidly rearrange to other products (3). Additionally, methods for the preparation of silenes are often incompatible with a range of functional groups. Photochemical or thermal decomposition of α-silyldiazocarbonyl compounds (1) is an established method for the formation of silenes (2); however, the Wolff rearrangement product (4) is also often formed under these conditions.

The Steel group aimed to generate a silene equivalent via a rhodium-catalysed decomposition of α-silyldiazocarbonyls. Computational studies enabled the group to determine that silene formation was favoured when electron-donating groups were attached to the carbonyl groups. With these results in hand, they synthesised α-hypersilyl diazoesters (5) and found that the resultant silene equivalents (6) were unusually stable and could also undergo reactions with α,β-unsaturated carbonyl compounds (7) to form cyclic silyl enol ethers (8). A subsequent fluoride-mediated fragmentation of the cycloadducts (8) gave 1,5-dicarbonyl products (9 and 10) in good yields.

The group successfully used results from their computational modelling to design more stable and synthetically useful silene equivalents. The mild reaction conditions developed represent an important advance in the use of silene reagents for organic synthesis.

Researcher’s perspective: 
“The general aim of my project was concerned with development of methods for the stereocontrolled functionalisation of alkenes through reaction with readily accessible silenes. I explored the synthetic potential of α-silyldiazocarbonyl compounds as silene precursors.  I carried out the initial computational work at Uppsala University in Sweden under the supervision of Prof. Ottosson. These preliminary investigations identified targets, which I subsequently synthesised at Durham University. Interestingly, I found that α-silyl diazo esters undergo rhodium (II) catalysed decomposition to provide silaoxetene which shows silene-like reactivity. The silaoxetene is formed under very mild conditions, a fact which greatly improves its synthetic potential. I hope this will open the door for the use of silene equivalents in synthetic organic chemistry.” Michal Czyzewski, from the Steel group.

Find out more – download the Edge article for free.

Posted on behalf of Alice E. Williamson, Chemical Science web writer.

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Let’s get physical

Chemical Science has published some exceptional physical chemistry since its launch last year. Below is a selection of recent articles but be sure to browse our issues to keep up-to-date with the latest cutting edge research.

Practical computation of electronic excitation in solution: vertical excitation model
Aleksandr V. Marenich, Christopher J. Cramer, Donald G. Truhlar, Ciro A. Guido, Benedetta Mennucci, Giovanni Scalmani and Michael J. Frisch
Chem. Sci., 2011, DOI: 10.1039/C1SC00313E 

Multi-structural variational transition state theory. Kinetics of the 1,4-hydrogen shift isomerization of the pentyl radical with torsional anharmonicity
Tao Yu, Jingjing Zheng and Donald G. Truhlar
Chem. Sci., 2011, DOI: 10.1039/C1SC00225B

Water-hydroxyl phases on an open metal surface: breaking the ice rules
Matthew Forster, Rasmita Raval, Javier Carrasco, Angelos Michaelides and Andrew Hodgson
Chem. Sci., 2011, DOI: 10.1039/C1SC00355K

Photo-induced charge recombination kinetics in low bandgap PCPDTBT polymer:CdSe quantum dot bulk heterojunction solar cells
Josep Albero, Yunfei Zhou, Michael Eck, Frank Rauscher, Phenwisa Niyamakom, Ines Dumsch, Sybille Allard, Ullrich Scherf, Michael Krüger and Emilio Palomares
Chem. Sci., 2011, DOI: 10.1039/C1SC00514F

Effect of defects on photocatalytic dissociation of methanol on TiO2(110)
Chuanyao Zhou, Zhibo Ma, Zefeng Ren, Xinchun Mao, Dongxu Dai and Xueming Yang
Chem. Sci., 2011, 2, 1980-1983

Energy transfer at metal surfaces: the need to go beyond the electronic friction picture
Christof Bartels, Russell Cooper, Daniel J. Auerbach and Alec M. Wodtke
Chem. Sci., 2011, 2, 1647-1655

Sign up for our e-alerts > 

Submit your own hot research to our physical chemistry associate editors: Kazunari Domen, Haw Yang and Kopin Liu.

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First Accepted Manuscript published

We’ve just published the first article in our new ‘Accepted Manuscript’ service. Atsuhiro Osuka, from Kyoto University, Japan, and colleagues are the first Chemical Science authors to benefit from their research being made available in citeable form even more rapidly. Read their Edge article for free: Phosphorus complexes of a triply-fused [24]pentaphyrin 

All Chemical Science authors are now given the option of publishing their research as an Accepted Manuscript. An Accepted Manuscript is an unedited and unformatted version of an article that is published shortly after acceptance. It is available as a downloadable pdf file. It is then replaced by the fully edited and formatted Advance Article. Find out more >

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Stereoselective cyclisations

Paul Floreancig’s group at the University of Pittsburgh has developed a stereoselective heterocycle synthesis starting from allylic alcohols.

Treatment of allylic alcohol (1) with rhenium heptoxide leads to the formation of a perrhenate ester (2) that undergoes a rearrangement to form a mixture of two ester stereoisomers (3 and 4). Cyclisation occurs through nucleophilic addition to the reactive oxo-carbenium intermediate to form a mixture of kinetic products (5 and 6). Owing to the fact that that ring formation is reversible in some cases, stereoselectivity arises from one product being more thermodynamically favourable; a discovery that the Floreancig group have developed to their advantage.

cyclisation reaction

Stereoselectivity is increased in substrates that are better able to stabilise the oxocarbenium ion of the acyclic intermediate and thermodynamics dictate the stereochemical orientation of the anomeric centre formed.

Youwei Xie, from the Floreancig group, has extended this methodology to enable the construction of bi- and tricyclic structures in good to excellent levels of stereocontrol.

construction of bi- and tricyclic structures  

This methodology enables the synthesis of complex three-dimensional architectures from starting materials containing pre-installed stereocentres. Additionally, a number of biologically active compounds such as didemniserinolipids and pinnatoxins contain bridged bicyclic cores that could be accessed using this chemistry.

Researcher’s perspective:
“It was inspiring to find that allylic alcohol isomerisation could be applied to the construction of so many useful organic substructures. We were very excited to discover that pre-installed stereocentres are capable of controlling new stereocentres through thermodynamically driven equilibration, since this process allows for complex molecule synthesis and minimises the use of chiral reagents.” Youwei Xie

Posted on behalf of Alice E. Williamson, Chemical Science web writer.

Download the group’s Chemical Science Edge article for free.

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