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Organic: Self-sorting compound mixtures

05 Jun 2012

A judicious choice of precipitation conditions can lead to self-sorting of equilibrating mixtures of aromatic aldehydes and substituted anilines into a handful of imine products, say researchers from the US.

You might expect to get quite a few different products but because the least soluble imine precipitates, the mixture re-equilibrates to generate more of that compound. Eventually, all precursors to the least soluble imine are exhausted and the mixture is reduced in complexity. Only the most and the least soluble imines are produced without any of the “in between” species.

A mixture of as many as nine imines could be self-sorted into just three compounds, they say.

Precipitation-driven self-sorting of imines
Rio Carlo Lirag , Karolina Osowska and Ognjen Š. Miljanić
DOI: 10.1039/C2OB25736J

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Chemical biology and medicine: New anti-cancer mechanism for drug compounds

01 Jun 2012

Serbian chemists have synthesised a similar compound to the anti-cancer drug paclitaxel, but while this new compound is also bad news for cancer cells, the mechanism it uses is quite different – autophagy instead of apoptosis. Paclitaxel causes cancer cells to self destruct, but cancer can become wise to this and become resistant. The new analogue uses autophagy to kill the cancer – a method of attack that’s getting increasing attention for anti-cancer drugs.

A novel C,D-spirolactone analogue of paclitaxel: autophagy instead of apoptosis as a previously unknown mechanism of cytotoxic action for taxoids
Milena Trmcic, Radomir Matovic, Gordana Tovilovic, Biljana Ristic, Vladimir Trajkovic, Zorana Ferjancic and Radomir Nikola Saicic
DOI: 10.1039/C2OB25514F

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Nanoscale engineering of wound beds

13 Apr 2012

A collagen-binding peptide with applications in wound healing has been developed by scientists in the US. The peptide is able to invade the strands of collagen, forming a strong and stable non-covalent bond at room temperature. Pendant drug molecules could be attached to the peptide and anchored at the wound site to aid wound healing…

Read the full article at Chemistry World, or read the OBC paper:

Peptides that anneal to natural collagen in vitro and ex vivo
Sayani Chattopadhyay, Christopher J. Murphy, Jonathan F. McAnulty and Ronald T Raines
DOI: 10.1039/C2OB25190F

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Picking out cysteine for health study

23 Mar 2012

A highly selective indicator for the amino acid cysteine has been designed by scientists from the US and China to monitor levels in human plasma. Elevated cysteine levels have been linked with motor neurone disease, Parkinson’s disease and Alzheimer’s disease.

Cysteine is an essential amino acid and plays an important role in cell functions. Its structure contains both a sulfhydryl (-SH) and an amino group (-NH₂), both of which are reactive. Previous detectors have focused on reactions with the sulfhydryl group, but it has been tricky to detect cysteine over other SH-containing biomolecules in the blood, such as glutathione and the closely related homocysteine.

Row of sample vials with a blank control (clear and colourless), cysteine (pink), homocysteine (clear and colourless) and glutathione (clear and colourless)

The indicator molecule reacts with the sulfhydryl and amino parts of the cysteine molecule to form a pink compound that's fluorescent under UV light. No such reaction is seen with other biothiols

Robert Strongin from Portland State University, Portland, and co-workers, have found a way to overcome this problem, by designing a fluorescent sensor called a chemodosimeter (so called because the visible change is due to an irreversible reaction). They used an indicator molecule that reacts with both the sulfhydryl and amino parts of the cysteine molecule.

‘We can detect cysteine selectively due to its unique chemistry, which we have complemented with our indicator design,’ explains Strongin. ‘There is a very selective reaction that turns the indicator on.’ The cysteine’s sulfhydryl group reacts with the indicator molecule to form a colourless compound. The amino part attacks an ester group on the indicator molecule to form a pink compound that is fluorescent under UV light. When tested with other amino acids or SH-containing molecules, no colour change or fluorescence could be seen.

‘Compared to designing probes for the detection of metal ions or inorganic anions, analytes such as cysteine tend to be far more problematic. The work provides convincing evidence that a clever design can overcome such obstacles,’ says Michael Heagy, an expert in fluorescent chemosensors for biological molecules at the New Mexico Institute of Mining and Technology, US.

In the future, Strongin plans to develop the approach to make other specialised indicators for non-polar metabolites, such as amino acids, sugars and phospholipids.

A seminaphthofluorescein-based fluorescent chemodosimeter for the highly selective detection of cysteine
Xiaofeng Yang , Yixing Guo and Robert M. Strongin
DOI: 10.1039/C2OB25178G

Read the original article at Chemistry World

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Computers look at life-giving reactions in space

24 Feb 2012

Theoretical chemistry could answer some questions about how life on earth originated, say Australian researchers.

Although we know amino acids were vital in the genesis of life, how they first appeared on earth is still under much debate. One theory is that they were introduced from space, having been synthesised in molecular clouds from simpler radicals. However, at almost absolute zero temperatures, it would be very difficult for any molecular collision to overcome the activation energy barrier. Unfortunately, owing to these extreme conditions, it is impossible to conduct laboratory experiments to investigate this.

Noticing that a number of possible interstellar reactions involve hydrogen transfer, John Bowie and Tianfang Wang at the University of Adelaide considered the possibility that they may be assisted by hydrogen tunnelling effects. Hydrogen tunnelling occurs when hydrogen atoms or nuclei take part in a reaction without having to overcome an energy barrier; instead they ‘tunnel’ through it. The team used high level computational methods to study how tunnelling affects isomerisation reactions that may either help or hinder the synthesis of biologically important molecules.

Molecules of life are thought to have been introduced to earth by collisions from comets or meteorites

‘Let us propose, for example, that ?CH₂NH₂and ?CN react to form the glycine precursor NH₂CH₂CN,’ explains Bowie, ‘if [?CH₂NH₂] isomerises rapidly to CH₃NH?, then the proposed synthesis is not practical.’

They found that although these reactions show significant tunnelling effects, the rate constants for most of them would still be too slow for reaction to occur.

Holger Somnitz, a theoretical chemistry expert at the University of Duisburg-Essen, Germany, appreciates the information obtained. ‘The [researchers] have quantified the effect of tunnelling. and provided valuable information on the potential energy along the minimum energy path,’ he says. However, he points out that the true impact of the work will only be revealed after experimental confirmation of the interstellar existence of the studied radicals.

Recognising the usefulness of the information obtained from their calculations, the researchers are now turning their attention to tunnelling effects in other fields of interest, such as in proteomics.

Hydrogen tunnelling influences the isomerisation of some small radicals of interstellar importance. A theoretical investigation.
Tianfang Wang and John H. Bowie
DOI: 10.1039/C2OB07102A

Read the original article at Chemistry World

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Organic & Biomolecular Chemistry Blog

Author Archive

Organic: Self-sorting compound mixtures

Chemical biology and medicine: New anti-cancer mechanism for drug compounds

Nanoscale engineering of wound beds

Picking out cysteine for health study

Computers look at life-giving reactions in space

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