by David Bradley
Reactions that take place in cosmic dust could help explain why there is so much water in deep space according to chemist David E Williams of University College London.
Williams and his colleagues have designed an experiment that can look at the energy of reactions where hydrogen and other atoms join together to form simple, small molecules such as H2, H2O and CO.
Astronomers David A Williams and Jonathan Rawlings also at UCL have postulated that hydrogen molecules split apart by ultra-violet starlight must recombine on the surface of cosmic dust in a highly efficient catalytic reaction to account for the amounts of water and hydrogen measured in space. They need solid data to prove their theory.
Richard Jackman in the Electrical Engineering Department has made a diamond-like carbon that behaves like cosmic dust. Chemist Williams says that he and his colleagues will be able to carry out some fundamental experiments using very cold hydrogen atoms to try and mimic cosmic reactions in the laboratory.
The researchers cool a beam of hydrogen atoms using liquid helium to 10 K close to the temperature of deep space. They can then direct this beam at their slightly warmer 'cosmic dust' (up to 100 K) on to which other hydrogen atoms have been bonded. Williams anticipates that the only product of this reaction will be dihydrogen formed in a recombination reaction. The team uses highly sensitive time-gated time-of-flight mass spectrometry coupled with resonant-enhanced multiphoton ionization to detect any molecules formed.
UCL colleagues David Clary, Andrew Fisher and Adam Fairbrother, are applying a new theory of quantum scattering to calculate the reaction course. 'The calculations will give predictions of the reaction efficiency and vibrational energy distribution of the product,' explains Williams, 'we will compare the results to the experiment and assess which of the two possible mechanisms is best.' The team can then work out which occurs in outer space.
According to Williams, there also appears to be a lot of water 'up there' and lots of other compounds too. Studying the reaction sequences 'down here' will help them understand why.
Bug vaccineScientists in the USA have developed an experimental vaccine against the bacterium Escherichia coli O157.
E coli O157 has caused several major outbreaks of food poisoning around the world, which have led to a number of fatalities. It usually affects the young and elderly the worst but antibiotics are almost always ineffective - a vaccine for those at risk would be much more use.
Shousun Szu and colleagues at the National Institute of Child Health and Human Development in Bethesda, Maryland have linked a sugar-like molecule from the E coli O157 cell surface - a polysaccharide antigen - to an inactivated toxin from another bacterium, Pseudomonas aeruginosa. The sugar-like molecule has no effect on its own, but when it is linked to the toxin protein it forms an antigen that can stimulate the immune system into action, much as a real sugar-protein conjugate from an invading pathogen.
The team then vaccinated volunteers and found that they produced antibodies to the sugar-like molecule. When they tested these antibodies in the test-tube against E coli O157 they found that each volunteer could produce enough to kill the microbe. The levels of antibodies remained stable for at least six months, according to Szu.
Szu says the team will soon be move on to phase 2 in children - one of the main risk groups.
Building up steroidsA new way to build steroid molecules in a single reaction has been devised by British chemists. The new method could cut down considerably on waste in making these important drug precursors.
Steroids are usually made up of four fused carbon rings with different chemical groups - such as hydroxys (OH) and methyls - attached to different points on the system giving each steroid its particular chemical and biological properties. Nature produces steroids relatively easily using enzymes but for the chemist, side-reactions are nearly always a major problem involving extra steps in the process with associated waste and solvents.
Gerald Pattenden and his colleagues at the University of Nottingham decided that enough was enough and set about finding a way to fuse the rings together to form the steroid skeleton with far less fuss and waste.
Most chemical syntheses begin with a starting material convert it into an intermediate, isolate this from residual starting material and side products, then convert the intermediate into the next intermediate and so on until the product is formed. Pattenden's team realised that a straight chain trienone molecule with an carbonyl oxygen at one end and three reactive carbon-carbon double bonds and a cyclopropane ring of three carbon atoms at the other would have the right geometry to form four rings in a cascade. They anticipated they could effectively bypass all the tedious intermediate steps and go straight from starting material to product.
To initiate their reaction, the researchers used a radical - an uncharged molecule with a 'spare' electron. The initiator sends a single electron from the carbonyl oxygen to the cyclopropane group by way of the double bonds. In this first step, two rings are formed at the oxygen end. This leaves the spare electron sitting on the bond next to the cyclopropane ring. The electron then hops on to the other dangling end of the molecule producing a third large ring. In the final cascade step, a bridge forms across the ring making the four steroids rings.
Pattenden says that his team has not stopped at four rings. There are several larger steroid systems found in nature, in tree gums and resins, for instance, some with five, six and more rings. The team has already made up to eight-ring steroids and is working on an eleven-ring system. He adds that these molecules will have utility in creating more complex molecular architectures where sheets of steroid ring systems might be formed by cascading the radical back and forth across the outer edge, making a kind of functionalised graphite sheet. Applications outside medicinal chemistry in fullerene and supramolecular chemistry might then be possible.