Today, most rockets are fueled by hydrazine, a toxic and hazardous chemical comprised of nitrogen and hydrogen. Those who work with it must be kitted up in protective clothing. Even so, around 12,000t of hydrazine is released into the atmosphere every year by the aerospace industry
Now, researchers are in the process of developing a greener, safer rocket fuel based on metal organic frameworks (MOFs), a porous solid material made up of clusters of metal ions joined by an organic linker molecule. Hundreds of millions of connections join in a modular structure.
Robin Rogers, formerly at McGill University, US, has worked with the US Air Force on hypergolic liquids that will burn when placed in contact with oxidisers, to try get rid of hydrazine. He teamed up with Tomislav Friščić at McGill who has developed ways to react chemicals ‘mechanochemically’ – without the use of toxic solvents.
The pair were interested in a common class of MOFs called zeolitic imidazole frameworks, or ZIFs, which show high thermal stability and are usually not thought of as energetic materials.
They discussed the potential of using ZIFs with the imidazolate linkers containing trigger groups. These trigger groups allowed them to take advantage of the usually not accessible energetic content of these MOFs.
The resulting ZIF is safe and does not explode, and it does not ignite unless placed in contact with certain oxidising materials, such as nitric acid, in this case.
Authorities continue to use hydrazine because it could cost millions of dollars to requalify new rocket fuels, says Rogers. MOF fuel would not work in current rocket engines, so he and Friščić would like to get funding or collaborate with another company to build a small prototype engine that can use it.
Tweaking the chemical structure of the antibiotic vancomycin may offer a new route to tackle the burgeoning problem of antibiotic-resistant bacteria, researchers in Australia have discovered.
Vancomycin has been used since the late 1950s to treat life-threatening infections caused by Gram-positive bacteria, including methicillin-resistant S. aureus (MRSA). The antibiotic works by binding to a precursor of the cell wall component, peptidoglycan, Lipid II, thus inhibiting bacterial growth.
Lipid II is present in both Gram-positive and Gram-negative bacteria. However, in Gram-negative bacteria it is protected by an outer membrane. In Gram-positive bacteria, Lipid II is embedded in the cell membrane but part of the molecule – a pentapeptide component – sticks out, which is what vancomycin binds to.
The researchers at the University of Queensland’s Institute for Molecular Biology (IMB), led by director of superbug solutions Matt Cooper, reasoned that if they could increase the ability of vancomycin to bind to the bacterial membrane, this would make it more difficult for bacteria to develop resistance to it.
‘Our strategy was to add components to vancomycin so that the new derivatives – which we call “vancapticins” – could target more widely the membrane surface,’ explains Mark Blaskovich, senior research chemist at IMB. ‘By providing two binding sites – the membrane surface and the membrane-embedded Lipid II - this allows binding to resistant strains in which the Lipid II has mutated to reduce interactions with vancomycin.’
In addition, the researchers say that the vancapticins have been designed to take advantage of compositional differences between mammalian and bacteria cell membranes – ie bacterial cells have a greater negative charge. The vancapticins have greater selectivity for bacterial cells over mammalian cells, potentially reducing off-target effects and giving a better safety profile. A series of structure–activity studies showed that some of the vancapticins were more than 100 times more active than vancomycin.
Hospital-Associated Methicillin-resistant Staphylococcus aureus (MRSA) Bacteria. Image: NIAID
This membrane-targeting strategy, the researchers say, has the potential to ‘revitalise’ antibiotics that have lost their effectiveness against recalcitrant bacteria as well as enhance the activity of other intravenous-administered drugs that target membrane associated receptors.
John Mann, emeritus professor of chemistry at Queen’s University Belfast, UK, comments: ‘Bacteria have developed numerous strategies to modify the binding, uptake and expulsion of antibiotics, and thus develop resistance. So, it is especially exciting to see the development of these new vancomycin derivatives that enhance the membrane binding properties of the antibiotic, thus enhancing its efficacy and beating the bacteria at their own game.’