Archive for November, 2011

New gels for tissue engineering

New guanosine-based gels for use as tissue engineering scaffolds have been made by scientists in the US. The gels can gel aqueous solutions and cell media at physiological salt concentrations. They are also injectable and non-toxic to cells.

Previous gels have had limited use because of poor lifetime stability and the need for specific salt concentrations or pH values that are not physiological. These new gels form helical assemblies rather than the quartet assemblies that are normally found in guanosine gelators. This allows them to form hydrogels at physiological salt concentrations – as low as 0.5wt% in 100mM NaCl.

The researchers acknowledge that there are issues to be addressed, such as the development of gel systems that allow cell adhesion without added gelatine, and studies into the lifetime of the gels in cell media.


Reference:
Toward Potential Supramolecular Tissue Engineering Scaffolds Based on Guanosine Derivatives

L E Buerkle, H A von Recum and S J Rowan, Chem. Sci., 2011
DOI:
10.1039/c1sc00729g

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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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Solvent responsive cage

It is possible to induce a pronounced structural reorganisation of a metallasupramolecular cage complex with a very conservative change in solvent polarity, say researchers from Switzerland and Turkey.

Solvent-switchable nanostructures reported so far operate via solvent-induced reduction or stabilisation of non-covalent interactions. This cage switches from octanuclear prismatic in chloroform to tetranuclear in dichloromethane. The key to success here is the incorporation of metallacrown recognition units into flexible nanostructures, which allowed generation of solvent specific bonding pockets.

 

Reference:
A solvent-responsive coordination cage

B Kilbas, S Mirtschin, R Scopelliti and K Severin, Chem. Sci., 2011
DOI:
10.1039/c1sc00779c

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Cross-shaped compound can tell the difference

A molecule that can distinguish between structurally similar carboxylic acids and organoboronic acids – a significant analytical challenge – has been made by US researchers. The molecule is a cruciform (cross-shaped).

Identifying compounds with closely related structures like this is important to identify counterfeited, decomposed or compromised pharmaceuticals, food additives and alcoholic beverages. The compound can distinguish between 12 carboxylic acids and nine organoboronic acids. It works by binding to the compounds and giving a different fluorescent signal for each one.

Reference:
Identification of Carboxylic and Organoboronic Acids and Phenols with a Single Benzobisoxazole Fluorophore
J Lim, D Nam and O S Miljanic, Chem. Sci., 2011
DOI: 10.1039/c1sc00610j

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RSC Macrocyclic and Supramolecular Chemistry Meeting

The RSC Macrocylic and Supramolecular Chemistry meeting (MASC-11) is taking place on the 19th and 20th December 2011 at the University of Bath, UK.

A number of high profile authors will be speaking at the meeting including Chem Soc Rev Associate Editor, Professor Phil Gale, and Professor Kay Severin who is giving the Chemical Science sponsored lecture. To find out more about Professor Severin’s research, download his latest Chemical Science articles:

Dr Jonathan Nitschke will be delivering the Dalton Transactions lecture as a result of being awarded the 2011 Dalton Transactions European/African Lectureship earlier on this year. Jonathan has also recently been awarded the ChemComm 2012 Cram Lehn Pedersen award.

Read more about Jonathan’s research by downloading his Chemical Science articles: 

ChemComm, Chemical Science and Chem Soc Rev Deputy Editor, Joanne Thomson, will be attending the event. If you would like to arrange a meeting with Joanne, please email her at the Editorial Office.

To attend MASC-11, register before the 12th December 2011. The deadline for poster abstract submissions is 1st December.

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Cascading construction of contiguous chiral centres

Researchers from the University of Reading have designed an organocatalysed cascade reaction for the construction of nitrocyclohexanes 4.

This elegant domino reaction enables the union of two achiral reagents to generate products containing up to five contiguous stereocentres in excellent levels of enantio- and diastereoselectivity.

thiourea catalysed construction of nitrocyclohexanes

André Cobb’s group employed a thiourea catalyst 3 to initiate a Michael-Michael cascade reaction between nitro-esters 1 and nitro-styrenes 2. The catalyst is thought to first coordinate to the nitro-ester prior to intramolecular deprotonation at the α-position to generate a nitronate. Synchronous coordination with nitrostyrene enables the first stereoselective Michael addition to generate a second nitronate primed for cyclisation onto the conjugated ester.

This cascade process demonstrates the power of organocatalysis for the asymmetric assembly of complex molecular architecture from simple starting materials.

Read more – download Cobb’s Edge article.

Researcher’s perspective:
The asymmetric synthesis of densely functionalised molecules with up to five contiguous stereocentres in one pot has been a difficult task until now. Our simple new cascade reaction has achieved just this with the synthesis of complex nitrocyclohexanes in excellent stereocontrol. This methodology has then been successfully employed in the synthesis of an alpha-lycorane derivative which is of potential medicinal interest.   
Sundaram Rajkumar, from the Cobb group
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DNA does maths

A DNA-based computational device with variable input has been developed by scientists led by Nadrian Seeman in the US. Previous examples of DNA-based computers have used fixed systems, but here they used the same system with different settings. This means that the system could be reusable, unlike other systems that perform one computation and then can’t be used again.

prototiles for performing the computation
prototiles for performing the computation

The readout of the system is obtained by algorithmically assembling gold nanoparticles. Although arranging gold nanoparticles by DNA self-assembly has been reported, this is the first time such an arrangement of nanoparticles has been obtained as the result of a computation.  The system may be considered as a first step in an assembly of a programmed array incorporating nanomechanical devices or other varieties of biochemical, chemical or materials systems that can be organised as the result of a simple computation.

Reference:
A Programmable Transducer Self-Assembled from DNA
B Chakraborty, N Jonoska and N C Seeman, Chem. Sci., 2011
DOI: 10.1039/c1sc00523e

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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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