The plaque reads: ‘In this laboratory on 20 July 1982, Allen Hill, Tony Cass and Graham Davis made the crucial discovery which led to the development of a unique electronic blood glucose sensor now used by millions of diabetics worldwide.‘ It was originally developed in the early 1980s in the Inorganic Chemistry Laboratory at the University of Oxford, and in 2012 a Chemical Landmark Plaque for the Glucose Sensor was unveiled on the location. Today a range of different redox pairs, not only the ferrocene–ferrocenium couple, can be used in these devices but the ferrocene procedure was an important breakthrough. The device measures this current, and converts it to micromoles of glucose per litre on the display. So for every glucose molecule in the blood sample, to re-oxidise the enzyme, two ferrocenium cations are turned into ferrocene.To regenerate the original ferrocenium cation, the device passes an electric current between two electrodes, electrolyzing the ferrocene. The device does this with two ferrocenium cations, which is a ferrocene molecule stripped of one electron and now containing Fe 3+ instead of Fe 2+. When one glucose molecule has been oxidised, the enzyme has taken up two electrons from the glucose and it needs to get rid of them before it can take on anther glucose molecule. These devices use exactly the same enzyme that oxidises glucose in the body, glucose oxidase, but immobilised in a solution. It is not a replacement for the small protein insulin, but instead a vital part of the small electronic devices that measure blood sugar levels. Less obvious is that sufferers from diabetes often use this molecule several times a day. Of which, among other things, you can make good quality tubes that are vital parts in keeping a large city safe from the infectious diseases that plagued Victorian times. Perhaps not so surprisingly metallocene compounds can make good catalysts, for example to help making things like polyethylene and polypropylene. And the answer is yes both the particular ferrocene molecule and the whole class of sandwich compounds have practical applications. The similarity to benzene made chemists adopt the name ferrocene.Īpart form the intrinsic beauty of an object we cannot see, is it good for anything you may ask. This is exactly the same situation as in the benzene molecule, the hexagonal C 6H 6, and the same explanation for its stability holds, partly due to the symmetric beauty I mentioned before. This means that apart from the ten electrons holding the ring together in five single carbon–carbon bonds, it has six extra electrons whooshing around above and below the pentagon. These are not triangular, but shaped like regular pentagons, making a molecule of unusual symmetric beauty.įerrocene owes its unusual stability to the fact that when one proton is removed from the cyclopentadiene molecule, C 5H 6, it becomes the flat and aromatic cyclopentadienyl ion, C 5H 5 –. The two flat objects are cyclopentadienyl ions, each with a single negative charge. They share not the triangular shape of the classic English sandwich, but the characteristic of squeezing something between two flat objects, namely a metal ion, in the case of ferrocene the iron 2+ ion. Nobody had ever seen a molecule like this before.įerrocene was the first example of the now very large class of compounds unceremoniously known as sandwich compounds, and more formally as metallocenes. When, a few months later, it became clear what this unusual compound looked like, it must have been like meeting a giraffe for the first time when you’re used only to sheep, cows and horses. It also survived meeting such notorious killers of organometallic molecules as water, acids or bases. It caused quite a stir, since no stable molecule composed of only a hydrocarbon and a transition metal were known before, and this compound could be kept in air at room temperature without spontaneously igniting. Its first report in the literature, however, was by two different groups in December 1951 and February 1952. It is unclear when ferrocene was first made, but it seems to have been recorded as a ‘yellow sludge’ in the late 1940s by process technicians inspecting pipes at a Union Carbide cracker, which was used in the manufacturing of the small hydrocarbon cyclopentadiene from dicyclopentadiene.
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