Chemistry World Blog

Swifts make a round-trip of 22 000 kilometres each year from west Africa to northern Europe, one of the longest migratory journeys of any bird. But how do they not get lost on their way? Put me in a car in Senegal and tell me to drive to London without a map or signposts and I would almost certainly end up hopelessly circulating the Ulan Bator ring road.

The trick to a bird’s sense of direction may be the ability to ‘see’ the Earth’s magnetic field lines and fly accordingly either with or against them. This idea was put forward as early as the 1970s, but understanding the chemical intricacies that gives birds this sixth sense are only now coming to light.

Scientists at Oxford University had previously managed to make synthetic molecules that were highly sensitive to small changes in magnetic field and relied on light activated radical formation. The research suggested that a similar biological process in birds could be responsible for their navigational skills, but experimentally this had never been shown.

Published in PNAS this week and in collaboration with the Universities of Freiburg, Berlin and Munich, the Oxford researchers isolated and analysed photolyase proteins – close relatives of the cryptochrome proteins found in the eyes of birds – in E. coli bacteria. Both families of proteins were known to create radicals upon activation with light.

The researchers found that small but significant differences in the number of radicals produced were observed when light was shone on the bacteria either in the presence or the absence of a strong magnetic field – 200 times bigger than Earth’s magnetic field. It is the first time that this biological mechanism has been shown to be affected by magnetic fields and further supports the hypothesis that cryptochrome proteins are responsible for a bird’s in-built sat-nav.  

Of course, the strength of the magnetic field bears little resemblance to that of the Earth’s. But the researchers emphasise that with careful optimisation of experimental conditions they hope to see differences in photoinduced radical generation using much weaker magnetic inputs, on a par with that of Earth’s own magnetic field.

One thought: when the Large Hadron Collider is switched on tomorrow, will the huge magnets mean that all migratory birds will now do 27 kilometre circuits of the French and Swiss countryside instead of reaching their desired destination?

Apparently the MRSA superbug can’t stand cannabis. But students everywhere will be disappointed to know that free NHS supplies are not on the agenda.

Published in the Journal of Natural Products, UK and Italian researchers have looked at the antibiotic potential of cannabinoids, the active ingredients in cannabis. These compounds are known to be potent antibacterial agents in plants but their potential to act as an antibiotic has never been assessed.

The group isolated five major cannabinoids, including the pshycotropic agent tetrahydrocannibinol (THC). Each compound was chemically varied at one or two positions but the central cannabinoid core was maintained throughout. They tested all the compounds against six strains of MRSA bacteria, and in all cases, found that the compounds were not only potent (1-2μg/mL) but were equally effective against every strain.

Compare this to other antibiotics used in the fight against MRSA such as erythromycin and tetracycline and what becomes clear is that it is not the potency of cannabinoids that is so valuable but rather their unselective mode of action.

This finding led the researchers to believe that cannabinoids operated through a completely different antibacterial mechanism to traditional antibitoics.

Their hypothesis they say is backed up by the fact that cross-resistance between microbial and plant antibacterial agents is extremely rare. In fact, they add, it is perfectly possible that these compounds may simply escape the bacterial resistance mechanism completely.

We will have to wait and see if they can figure out the exact mechanism to either prove or disprove this hypothesis.

Cannabinoids, more specifically the non-psychoactive varieties, could well be added to the arsenal of drugs aimed at tackling multi-drug resistant bacteria, although it is reasonable to believe that as with most drugs bacteria will quickly build up a resistance to them.

The finding does however illustrate the potential potency of known plant antibacterial agents and offers scientists a library of compounds to test that could be as, if not more, effective against MRSA bacteria.

Check out the coverage at chemblog (Marijuana vs. MRSA) as well.

Ref: G Appendino et al. J. Nat. Prod. 2008 DOI:10.1021/np8002673

Whether molecular devices represent the future of data processing, transfer and storage is a discussion for another time. For now, I will keep my opinion to myself, but I have to confess that when I see a report of a new molecular device, whether it is a switch, a shuttle, a valve or a motor (to name just a few), my eyes light up and I have to read on.

The concept of a molecular device is simple, probably why I like them so much. All that’s required of a compound is that it can exist in at least two stable and different conformations that are interchangeable, typically through the careful control of an external stimulus (pH, temperature, light etc.). Providing that each gives a different response that can be detected then it’s done, and you’re on/off system is complete. Simple, I hear you say, but putting it into practice is another story.  

Reported in the Journal of the American Chemical Society this week, is a new switch that provides a platform to perform both read-write and read-only processes.

Using a UV active compound with a large aromatic ring system, Scottish researchers were able to switch between two conformational states by changing the pH of the reaction mixture. This represents a read-write scenario. Taking this one step further, they then managed to irreversibly ‘lock’ each of the conformations in position, now a read-only system, which depending on the chosen conformation, relied on either an oxidation or reduction reaction.

Each of the four conformation states gave a unique UV response and the complete conversion to the desired product was observed in every case, a must for any viable molecular device. To illustrate the robustness of the system, the pH dependent switching was cycled three times prior to any ‘locking’ step.

The researchers are quick to acknowledge that until they successfully immobilise their system onto a surface, it cannot be considered a true molecular device. In the meantime, the debate as to the future of molecular devices continues.

On a recent trip to the US, I realised that I gradually began to feel more and more unwell whilst watching TV. I quickly gave up on trying to pinpoint the cause of my hypercondriatic state (as it turns out even a snivel materialised), but a report in the British Medical Journal this week sparked me into a rethink.

Anyone watching US TV, even for just a few minutes, will quickly realise that you are being bombarded with aggressive pharmaceutical advertising. With unrelenting claims of better creams, faster acting pills and multi-purpose lotions, it is unsurprising that the symptoms of the classic ‘man cold’ quickly materialised in me.

As it turns out, however, pharmaceuticals may be wasting their time and money ($5 billion annually) with direct-to-consumer advertising, according to recent claims by Harvard researchers.

The research looked at consumer trends in Canada relating to three prescription-only drugs; Enbrel (rheumatoid arthritis), Nasonex (nasal allergies) and Zelnorm (irritable bowel sydrome), following the launches of advertising campaigns of each in the US. The group targeted Canadian citizens for two reasons. Firstly, direct-to-consumer advertising is banned in Canada. Secondly, the country has a significant population of French speaking residents.

Getting straight to the point, with much of the US media and advertising leaking across the border, these two factors meant a direct comparison of consumer trends between English speakers and French speakers could be made. The researchers are however quick to acknowledge however that the French speaking control group is not absolutely perfect.

The research found that direct-to-consumer advertising had no effect on the sales of Enbrel and Nasonex, with prescription patterns remaining identical in both English and French speaking groups. They did observe a noticeable spike in sales of Zelnorm, but this was relatively short-lived and after a few years, prescriptions between the two groups resumed identical patterns. The FDA has since pulled Zelnorm from the market with concerns that increases the risk of heart attacks and strokes.

The researchers conclude by saying that money spent by the pharmaceuticals would be far better placed marketing the drugs directly to doctors.

No-one is going to fall off the back of their chair when I say that lighting a match in an atmosphere with no oxygen is impossible. However, knowing the exact levels of oxygen required to sustain fire is, it appears until now, something that has not been thoroughly scrutinised.

It may seem of little consequence on face value, but in Science this week, Irish researchers claim that the oxygen lower limit for combustion should be redefined from the existing level of 12% to 15% (the present day atmospheric oxygen level standing at 20.9%). If correct, the current hypotheses for two of the ‘big five’ mass extinction events in primordial Earth may have to be rewritten.

The experimental set-up was relatively self-explanatory – an 8m³ room equipped with hot plate, thermal imaging system and full atmospheric, humidity and temperature control. Experimental burns of pine wood, moss, matches, paper and a candle conducted at 20^oC revealed that none could maintain a flame in an atmosphere with less than 15% oxygen content.

With this result in hand and prior knowledge of the prevalence of wildfires throughout the Mesozoic period – 250 to 65 million years ago – the researchers were able to conclude that atmospheric oxygen levels throughout this period must have been 15% or greater. This contradicts previous reports that attribute two mass extinction events in this period to short-term deficiencies in atmospheric oxygen levels.

The researchers don’t hazard a guess at an alternative hypothesis for the mass extinction events, but if anyone has any good suggestions (that lack any alien involvement) let us know.

A humble spice could make mouldy toast a thing of the past. Spanish researchers have reported that the incorporation of cinnamon essential oil into wax paraffin packaging can prolong the freshness of bread by up to 10 days.

Clearly fed up with stale bread for breakfast, the researchers had previously looked at the antimicrobial activity of three essential oils: oregano, thyme and cinnamon, against food-borne microorganisms. All three were shown to be effective against various strains of bacteria, but cinnamon came out on top when it came to mould.

It is the first time that active packaging has been proposed for this kind of food. Looking specifically at the growth of Rhizopusstolonifer stolonifer mould in white bread, the researchers found that only 6% (w/w) of the essential cinnamon oil was required to completely inhibit the growth of the mould.

The mould inhibition was found to be directly related to the amount of cinnamaldehyde, responsible for the distinctive smell of cinnamon. Infused into the bread over three days, the inference is that the bread takes on the taste of cinnamon.  

For those of you who don’t a fancy cinnamon infused BLT for lunch, it looks like you will have to put up with stale, old, mouldy bread for the time being.

A spat has broken out over the validity of research published in Science last year by palaeontologists at North Carolina State University, lead by Mary Schweitzer.

The research closely matched protein sequences from a 68-million-year-old Tyrannosaurus rex bone to those found in modern day chickens, and appeared to better define the evolutionary link between reptiles and birds. Mass spectrometry data of seven linked proteins were highlighted however supplementary information of any further data collected has never been released. The researchers claim that this is for reasons of data protection.

In a damning comment published this week in Science, Pavel Pevzner, a computer scientist at the University of California, begins by saying, ‘Imagine a monkey typing random keys on a typewriter and let us assume that the monkey is given 100,000 attempts to generate six-letter words … Nobody would be surprised if some of the 100,000 words turned out to be correctly spelled words.’

Pevzner goes on to say that the without being able to analyse the complete (and extremely large) data set, it is impossible to verify the results, ‘as false protein identifications are unavoidable in the field of proteomics.’

In the same issue of Science, a rebuttal by John Asara, part of the Scweitzer team responsible for the mass spectrometry data, defends the research, claiming that both rigorous computational methods as well as additional analytical and biochemical techniques were used to validate the data.

He concludes, ‘Overall, the comment by Pevzner et al. does not change any of our original conclusions that collagen fragments from a T. rex fossil bone were extracted and sequenced and that they match better as a group to chicken collagen than to any other protein from any other organism.’

We will wait and see if dinosaurs really were chickens after all.

I think it’s fair to say that religion and science haven’t always existed in perfect harmony. It is perhaps ironic then that to clear the air, a church may be exactly the place to go.

Researchers at the Queensland University of Technology in Australia have discovered that gold painted, stained glass windows play a key role in purifying the air.

Nanoparticles of gold in the paint, when activated by sunlight, are able to destroy volatile organic compounds (VOC) in the air, says principal investigator Zhu Huai Yong. For centuries people have admired the windows as colourful works of art, however in modern times, they can be considered to be gold nanostructures capable of purifying the air photocatalytically.

The by-product of the catalytic reaction is carbon dioxide, comparatively safe in the small quantities produced.

The research opens the door to the possibility that gold nanoparticles could be used to drive chemical reactions. ‘This technology is solar-powered and very energy efficient because only the particles of gold heat up.’ says Yong. ‘In conventional chemical reactions, you heat up everything which is a waste of energy.’

Perhaps medieval glaziers, the nanotechnologists of their time, knew more about chemical science than we previously thought!

Over-the-counter skin creams could increase the likelihood of skin cancer. A study has found that commonly used moisturising creams significantly increase the development rate of non-melanoma skin cancer in UVB pre-treated mice – but not humans, yet! 

Whilst investigating the potential of caffeine as an agent for the inhibition of skin cancer, US researchers innocently selected four commercially available skin creams to act as potential caffeine vehicles: Dermabase, Dermovan, Eucerin and Vanicream.

As a precaution, they chose to first assess the possible carcinogenic properties of one of the creams, Dermabase. To their suprise, the analysis revealed significant increases in both number and volume of tumours in mice. 

The research took a consequent U-turn with individual tests then carried out on each of the four creams. All showed significant tumourigenic effects after a 17 week trial period. The worst offender, Dermovan, demonstrated a 95% increase in the number of developed tumours compared with the control mice.

Human relevance

It is fair to say that the onset of skin cancer in mice follows a recognisable course to that of human skin cancers.  However, reaching conclusions as to whether these findings can be applied to humans must be done with extreme caution. 

‘Mice models have been used for years and have translated well to humans’ says principal investigator Allan Conney. ‘Epidemiology work is now needed to determine whether our findings also apply to the human population.’

Interestingly, a Custom Blend cream lacking both sodium lauryl sulphate and mineral oil, a known stimulator of UVB tumourigenesis, was also used in the study. The cream demonstrated no significant increases in either number or volume of tumours per mouse.

Industry Interest

A patent application has been filed for the Custom Blend cream on behalf of the university and Johnson and Johnson.  Although the researchers were keen to point out that they recieved no funding from Johnson and Johnson, the patent application would suggest a real interest and concern from the  leading manufacturers. 

The researchers were unable to comment further on either the chemical components responsible or the cellular mechanism involved. Nor were they explicit in saying where, if anywhere, the future directions lay.

DOI: 10.1038/jid.2008.241 (to go live on release of paper later today)

The idea of the ‘invisible’ cloak/man/car has been around for years. It describes the prospect of a three-dimensional (meta)material having a negative refractive index or an ability to reverse the natural direction of light.

Successful 2D and 3D materials have been constructed that can render an object invisible to longer microwave radiation (and indeed near visible light for 2D sheets). The holy grail however still remains to create a 3D bulk metamaterial that can effectively ‘bend’ visible light backwards.

To be published in Nature later this week, researchers at the University of California, Berkeley, have taken a step closer to this goal.  They have reported the first metamaterial to show effects of negative refraction on wavelengths as short as 1.5µm (near-IR range) within a 3D bulk material.

The material is made up of alternately stacked layers of conductive silver and non-conductive magnesium fluoride. It is then cut into a nanoscale-sized ‘fish-net’ pattern using focussed ion-beam milling. This allows the passing light to expend less energy travelling through the metal layers. 

The result is a series of circuits that respond together and in opposition to the magnetic field of incoming light, a property described as optical magnetism. In this scenario, both electrical and magnetic fields in a light wave move backward through the material. In other words, a negative refractive index has been achieved. 

To be published in Science later this week and from the same research group, a second metamaterial has been developed. In this case, the bending backwards of red visible light, with wavelengths down to 660nm, has been achieved. Interestingly, however, in this case this has been achieved without technically achieving a negative refractive index. In a similar vein to the result published in Nature, the metamaterial relies on the interspersal of conductive nanowires within porous aluminium oxide.

Both papers highlight the progress made by metmaterialists in the quest for the ‘invisible’ cloak. The prospect of being able to blend into the environment (quite literally) may still be a distant pipe dream, however powerful applications, particularly in the field of optics, could be seen sooner than we think.