Hot Articles – Page 29 – Chemical Science Blog

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Total synthesis of diazonamide A

11 Jan 2011

US chemists have developed a new highly stereoselective route to a natural product with potent anticancer properties.

David MacMillan and colleagues at Princeton University made the structurally challenging diazonamide A by exploiting three different types of catalysis – Lewis acid, transition metal and organocatalysis – in the key steps.

The principal challenge was stereoselectively installing the C(10) quaternary carbon stereocentre, explains MacMillan, as this aspect of the structure had not been successfully addressed in any of the three completed total syntheses. Using asymmetric iminium catalysis, the team efficiently synthesised the furanindoline core and C(10) centre with high stereoselectivity, which they believe is the most complex and challenging setting in which organocatalysis has been employed to date.

Graphical abstract: Total synthesis of diazonamide A

Find out more by downloading MacMillan’s Chemical Science Edge article.

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Surface enhanced spatially offset Raman spectroscopic imaging – the next dimension

11 Jan 2011

Researchers from the Biophotonics Research Unit of Gloucestershire Hospitals NHS Foundation Trust, in collaboration with scientists from the University of Strathclyde and the Rutherford Appleton Laboratory, have published results of their exploration into surface enhanced spatially offset Raman spectroscopy (SESORS) imaging, a new technique combining surface enhanced Raman scattering (SERS) with spatially offset Raman spectroscopy (SORS).

They achieved, for the first time, imaging of SERS signals recovered from a depth of 20 mm in tissues, opening the way for sampling a number of disease conditions in the same organ at the same time. This could potentially lead to a new methodology for enhanced personalised treatment plans to be developed in realtime.

The Chemical Science Edge article has been highlighted in the following RSC press release:

“UK scientists have explored surface enhanced spatially offset Raman spectroscopy (SESORS) imaging and found that multiplexed surface enhanced Raman scattering (SERS) signals have been recovered non-invasively from a depth of 20 mm in tissues for the first time and reconstructed to produce a false colour image. This approach could be adapted into a clinical setting for disease diagnosis, say the researchers.

The team injected four unique ‘flavours’ of SERS nanoparticles (NPs) into a 20 x 50 x 50 mm porcine tissue block at the corners of a 10 mm square. A transmission Raman data cube was acquired over an 11 x 11 pixel grid made up of 2 mm steps. The signals were reconstructed using the unique peak intensities of each nanoparticle. A false colour image of the relative signal levels was produced, demonstrating the capability of multiplexed imaging of SERS nanoparticles using deep Raman spectroscopy.

A secondary but no less significant achievement was to demonstrate that Raman signals from SERS nanoparticles can be recovered non-invasively from samples 45–50 mm thick. This is a significant step forward in the ability to detect and identify vibrational fingerprints within tissue, say the team.

The prospects for SESORS as a medical tool are significant, say the researchers. There are numerous applications where this approach could have a major impact on rapid specific diagnosis, patient specific treatment selection and treatment monitoring. However, the greatest hurdle will be introducing nanoparticles into the body without fully understanding their excretion mechanism or long term accumulation sites and whether this is likely to have detrimental effects.”

Reference:

N Stone, M Kerssens, G R Lloyd, K Faulds, D Graham and P Matousek, Chem. Sci., 2011, DOI: 10.1039/c0sc00570c

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Hot article roundup – November

14 Dec 2010

Here in the UK we’ve been enduring the coldest start to winter since 1976. Thankfully, we published a great selection of hot Edge articles last month. As per all Chemical Science articles, they are free to access until the end of 2011.

Enjoy!

A ‘hole’ lot of mobility: Chi-Ming Che and colleagues report single crystal organoplatinum complexes with high charge mobility

Fingerprinting red wine: Eric Anslyn and colleagues have developed a sensor that can discriminate between different tannins and fingerprint a wide variety of red wines

Dinitrogen complexation with main group radicals: Spectroscopic evidence for weak but distinct interactions between several main group element radicals and physically dissolved dinitrogen in solution

New class of organic acceptors: A family of push–pull chromophores with a [4]dendralene backbone and a remarkably high propensity for reversible electron uptake

Carbene catalysts for group transfer: Gregory Hillhouse discusses the synthesis and carbene transfer reactivity of dimeric nickel bridging-carbene complexes

Building complex oxides layer-by-layer: Matthew Rosseinsky and colleagues exploit the capabilities of modern thin film deposition to grow an artificial metastable oxide

Carbenoids’ role in silver catalysis: Silver(I)-catalysed reactions of vinyldiazoacetates involve the intermediacy of silver-carbenoid species

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Stereoselective additions with a twist

10 Dec 2010

A helical framework around an electrophilic centre is an effective control element for the stereoselective addition of nucleophiles, according to European scientists.

Stereoselective additions of nucleophiles to trivant carbon atoms are common organic reactions. Chemists often rely on stereogenic elements close to the reactive centres to influence the stereochemical outcome. For example, nucleophiles can preferentially add to one of the two diastereotopic faces of a carbenium ion when there is an α-stereocentre.

Now Jérome Lacour, at the University of Geneva, Switzerland, and colleagues have shown that nucleophiles can also distinguish between the diastereotopic faces of chiral cationic helicenes. Using hydride and organolithium reagents, the group achieved diastereomeric ratios higher than 49:1.

Graphical abstract: Highly selective additions of hydride and organolithium nucleophiles to helical carbenium ions

More information can be found in Professor Lacour’s Edge article.

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Fingerprinting red wine

26 Nov 2010

A sensor that can discriminate between different tannins and be used to fingerprint a wide variety of red wines to confirm their authenticity has been developed by US scientists.

Eric Anslyn and colleagues at the University of Texas at Austin and University of California Davis have developed a sensor made with colour-changing indicators. They used the sensor to test wine samples from different vintners and managed to distinguish between specific flavonoids – chemicals found in fruit and vegetables, tea and red wine – in particular looking at tannins, which are responsible for colour, aging ability and texture.

When wine is added to the sensor, the indicators are displaced, which results in a colour change that can be monitored and recorded. The team found that patterns emerged for different wine varietals. They tested Pinot Noir, Zinfandel, Beaujolais, Cabernet Sauvignon, Shiraz and Merlot and assigned signatures to each wine type. The team could also classify wines from the same varietal. They tested different brands of Shiraz (and Zinfandel in a separate study) and they were able to link the tannins to the genome of the specific grape.

The sensor can assign signatures to different wine types and to wines within types

‘The ability to fingerprint mixtures of metabolic origin, without knowing their exact compositions, has huge potential for applications in medical diagnostics, environmental science and the food industry,’ says Anslyn.

Kim Janda, a detection expert at the Scripps Research Institute in the US, has visions of the sensor being used for ‘biodefense purposes where rapid and accurate identification is at a premium.’ Janda adds: ‘if Anslyn improved the method further he could put sommeliers out of business!’

‘Product authenticity is an important issue with food and beverages, particularly with high value products such as wine,’ says Bob Dambergs, a senior research scientist at the Australian Wine Research Institute, Glen Osmond. ‘Flavonoid compounds define red wines and this study makes clever use of specific interactions of flavonoids with peptides to produce a sensor array with high discriminatory power. Most wine producing countries have strict label-integrity regulations to protect consumers – the availability of rapid analysis methods utilising chemical sensors will facilitate compliance monitoring.’

Fancy reading more? Then why not download and read the Chemical Science Edge Article for yourself, details can be found below:-

Discrimination of flavonoids and red wine varietals by arrays of differential peptidic sensors
Alona P. Umali, Sarah E. LeBoeuf, Robert W. Newberry, Siwon Kim, Lee Tran, Whitney A. Rome, Tian Tian, David Taing, Jane Hong, Melissa Kwan, Hildegarde Heymann and Eric V. Anslyn, Chem. Sci., 2011
DOI: 10.1039/c0sc00487a

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Bismuth medicines: insight into mechanism of action

17 Nov 2010

Scientists have converted a protein from a pathogenic bacterium into a FRET-based fluorescent probe to help find out why bismuth therapeutics can treat gastric illnesses.

Helicobacter pylori is a bacterium that colonises the digestive track and causes chronic gastritis, ulcers and even some gastric cancers. Bismuth-containing medicines are known treatments for H. pylori. It is thought that bismuth ions bind to metal binding sites in H. pylori’s metalloproteins but their exact mechanism of action is unknown.

Chuan He and colleagues at the University of Chicago investigated the metal binding properties of their FRET probe, made from the Hpn protein found in H. pylori, with different biometals in vitro. They showed that the sensor has a high affinity for Ni²⁺ and Zn²⁺ and moderate affinity for Bi³⁺. They then used the sensor in E. coli cells, which act as a model system for H. pylori, to measure uptake of these three ions. To their surprise, E. coli concentrated significant amounts of Bi³⁺, but not Ni²⁺ or Zn²⁺.

Graphical abstract: Metal-binding properties of Hpn from Helicobacter pylori and implications for the therapeutic activity of bismuth

If Bi³⁺ accumulates to similarly high levels in H. pylori, says He, it may target Hpn, eventually killing the bacteria.

Read the Edge article online today and let us know what you think of this work by leaving your comments below.

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Catalytic capsids: the art of confinement

10 Nov 2010

Confining enzymes in a small container increases overall reaction rates but the increase is independent of the number of enzymes encapsulated, claim scientists in the Netherlands.

Jeroen Cornelissen, at the University of Twente, and colleagues used the capsid of the Cowpea Chlorotic Mottle virus to encapsulate enzymes, mimicking the crowded environment enzymes experience in a cell. They found that encapsulated enzymes have a higher activity than free enzymes, which they say is caused by the high confinement molarity of the enzyme and the increased collision rate with its substrate.

: Encapsulation of enzymes in the confined space of a virus capsid influences reaction rates

But increasing the number of enzymes inside the capsid does not increase the reaction rate, says Cornelissen. A capsid rarely contains more than one substrate molecule so one enzyme is sufficient to convert the substrate, he explains.

Want to learn more about the art of confinement? Read the Edge article for free online.

Do you feel confined by the page and colour restrictions placed on you by other journals? Experience the freedom of publishing with Chemical Science by submitting today.

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Building complex oxides layer-by-layer

10 Nov 2010

The Ruddlesden-Popper structure is an archetypal structure in solid state chemistry, consisting of slabs of perovskite units separated by rock salt layers. But conventional high temperature oxide synthesis methods can’t be used to make these structures when the perovskite blocks are greater than three octahedral thick.

Now Matthew Rosseinsky, at the University of Liverpool, UK, and colleagues have exploited the capabilities of modern thin film deposition to grow an artificial metastable oxide where the perovskite block is six octahedral thick and is made of two distinct perovskite units.

Graphical abstract: Cation ordering within the perovskite block of a six-layer Ruddlesden-Popper oxide from layer-by-layer growth – artificial interfaces in complex unit cells

Find out more in their Chemical Science Edge article and let us know your comments on the work below.

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A system that mimics the human nose

05 Nov 2010

Scientists from Switzerland have created a system that mimics the way the human nose recognises scents.

Stefan Matile and colleagues from the University of Geneva made an artificial membrane that can distinguish between a range of odour molecules. Their ‘nose’ uses differential sensing, a form of molecular recognition, to recognise subtle structural differences between the molecules. ‘Our nose works by differential sensing in the membrane and differential sensing has been done almost everywhere except in the membrane,’ says Matile.

The human nose can distinguish over 10,000 different smells using 350 receptors. Smell molecules, known as an odorants, interact with the receptors to create an overall ‘fingerprint’ that is recognised by the brain. Matile’s system works by moving odorants across a lipid bilayer, an artificial cell membrane, using electrostatic interactions. Once across the membrane, this creates a fluorescent response, which is then measured to build up an electronic fingerprint of the smell. The team say they can distinguish a range of commercial perfumes using their nose.

The artificial nose builds up a fingerprint of odour molecules

‘This highlights just how closely related this system is to the human system,’ says Jon Steed, an expert in supramolecular sensing at the University of Durham, Durham, UK, who adds: ‘You can adapt the chemistry to sense whatever you want.’

‘The applications are broad and very promising,’ says Matile. Steed adds that detection of low levels of molecules is important in many areas, for example in the detection of explosives or pollutants. Matile is now studying different forms of membrane transport in the system and how this affects its sensing capability.

Will Dennis

Read the full Edge article for free in Chemical Science.

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Iron complex could prevent cardiovascular disease

02 Nov 2010

Scientists in Israel have shown how an iron-based antioxidant could prevent damage in arteries that leads to cardiovascular disease.

Zeev Gross and team from the Israel Institute of Technology, Haifa, say that iron-corrole complex 1-Fe works by binding to the two types of cholesterol in the body to block the damaging effects of reactive oxygen and nitrogen species.

Reactive oxygen and nitrogen species are naturally present in the body. They modify the structures of cholesterol-delivering, or atherogenic, low-density lipoproteins and cholesterol-removing, or anti-atherogenic, high-density lipoproteins. This modification, known as oxidative stress, makes low-density lipoproteins (LDL, or bad cholesterol) more atherogenic and high-density lipoproteins (HDL, or good cholesterol) less anti-atherogenic.

1-Fe binds tightly to lipoproteins and is carried to the arterial wall

Gross’ team found that 1-Fe decomposes the harmful species in a catalytic fashion and binds tightly to the lipoproteins implying that the antioxidant will be carried all the way to the arterial wall, where the oxidative environment prevails. This is in contrast to current dietary antioxidants that are not as efficient against some reactive species and can damage the lipoproteins and the arterial wall.

The team analysed the 1-Fe/LDL and 1-Fe/HDL complexes in human serum. ‘The bipolarity of the complex is responsible for the high affinity of the corrole to lipoproteins in general,’ says Gross, ‘while coordination of the chelated iron(III) ion in 1-Fe with specific amino acid residues is involved in the selectivity to HDL.’

‘These findings will have a major impact on future antioxidant design,’ says Claus Jacob, an expert on catalytic antioxidants from Saarland University, Germany. ‘It is now possible to attach catalytic antioxidants to the targets of oxidative stress, providing perfect protection against the damage caused by reactive species. This is a promising lead for the development of the next generation of multi-functional, smart antioxidants. Such antioxidants are of particular importance in the field of cardiovascular diseases.’

‘Demonstrating the effects and understanding the variables that determine efficiency of catalytic antioxidants may lead to the design of optimal new drug candidates for treating the most severe diseases affecting human health,’ says Gross. He intends to extend his study to look at macrophages (white blood cells), major contributors to the development of atherosclerotic plaques.

Jennifer Newton

For more details, read Gross’ Chemical Science Edge article.

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