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1950S: Radiocarbon Dating Discoveries of the last six decades 60 years of innovation To celebrate the international year of chemistry, James Mitchell Crow looks back at some of the discoveries and developments made by chemists over the past six decades that have made the biggest difference to our lives, and to understanding the world around us 1950s: radiocarbon dating Where do we come from? What that the first historical date of any was life like for our ancestors? real certainty has been established.’ Such questions have long played The laborious early techniques on the mind of humans, and thanks for measuring the amount of to chemistry – and the action of radiocarbon in a sample required cosmic rays – we now have a good literally counting the slow decay part of the answer. of radiocarbon atoms in a sample Shortly before the second world using a gieger counter. ‘Today, using TIME @ LIFE PICTURES / GETTY IMAGES GETTY / PICTURES LIFE @ TIME war, researchers studying Earth’s accelerator mass spectrometry upper atmosphere made a discovery [AMS] we actually measure the that would revolutionise our ability to carbon-14 atoms individually, peer into the past, allowing us to date and not the decay that comes off ancient sites and artefacts produced of them, so we can now measure by people as much as 50 000 years much older samples in a much ago. Cosmic rays colliding with the shorter amount of time – instead top of the atmosphere were found of months, something in the order to be generating neutrons, which of tens of minutes,’ says Stewart react with nitrogen-14 to form Fallon, head of the radiocarbon carbon-14, ejecting a proton in the dating laboratory at the Australian process. This produces a steady National University in Canberra. input of radioactive carbon into the AMS needs so little material biosphere, which decays with a half- that specific compounds can be life of about 5600 years. chromatographically extracted from It was Willard Libby and his a sample for dating individually. colleagues at the University of Thanks to Libby’s work, history Chicago, US, that turned this now extends far further back observation into a tool to accurately Willard Libby received During his work to establish in time. The technique has also date objects from our distant past – a the 1960 Nobel prize the technique’s reliability, Libby proved to be useful in fields outside discovery that won Libby the 1960 in chemistry for his discovered how challenging archaeology. Fallon uses it to study Nobel prize in chemistry. pioneering work on archaeology had been up to that the uptake of radiocarbon by giant All organisms absorb carbon-14 carbon-14 dating point. ‘The first shock we had was corals in the sea since the burst during their lives, through when our advisors informed us of carbon-14 released into our photosynthesis or by consuming that history extended back only atmosphere during the era of nuclear food, but stop absorbing any more 5000 years,’ Libby recalled during weapons testing. This data gives an at the point of death. From that his Nobel acceptance speech. ‘We accurate picture of ocean circulation point onwards, their radiocarbon had thought initially that we would over the past 50 years, information component slowly falls as it decays be able to get samples all along the that can be used to test ocean current back to nitrogen-14. Libby showed curve back to 30 000 years. In fact, models, which are being developed that this steady decline in carbon-14 it is at about the time of the First in part to help predict the impact of reveals any organic object’s age. Dynasty in Egypt (around BC3100) climate change. 38 | Chemistry World | March 2011 www.chemistryworld.org 1960s: silicon chips It is hard to imagine life without computers to be fitted inside missiles, the now-ubiquitous silicon chip. and for the Apollo moon missions. Chemists might not be the first band In the intervening years, silicon of researchers to get the credit for became the domain of engineers TEXAS INSTRUMENTS TEXAS its development, but in fact many rather than scientists. But today the chemical breakthroughs were needed input of chemists is becoming crucial before the electrical engineers could again, says Javey. ‘All of a sudden, the take over to produce silicon-based dimensions of silicon chips have come integrated circuits. down to a size that chemists have been ‘Many of the initial developments working at for decades – at the level in the field were made by chemists of macromolecules. So chemists have learning about silicon and its become involved again, developing material properties,’ says Ali Javey, new nanoscale materials, fabrication who researches nanomaterials for techniques, and doping with control technological applications at the down to a few atomic layers.’ University of California, Berkeley, This is one of the areas where Javey US. From finding ways to make ultra- Texas Instruments’ chips. In 1961, US company Texas himself works. ‘We need to be able pure semiconductor-grade silicon, ‘Molecular Electronic Instruments, one of the pioneers of to place dopants within 1–2nm thick to doping the material by infusing in Computer’ of 1961 on integrated circuit silicon technology, layers. Conventional techniques are atoms of other elements to tune its the left, dwarfed by a demonstrated their ‘Molecular no good for that.’ semiconducting properties, chemists conventional computer Electronic Computer’ to the US However, it could be in fundamental initially played a leading role. with the same Air Force, which was ‘150 times materials chemistry that the next ‘Developing reactions to chemically electronic function smaller and 48 times lighter’ than a big chip technology breakthrough etch the silicon and ways to pattern conventional computer of the time comes. ‘The coming direction – the integrated circuit – that’s all with the same processing power. The where chemists are playing a major chemistry,’ Javey adds. technology really took off thanks to role – is in developing new types It was in the 1960s that all these interest from the US military and of architecture based on flexible developments finally came together the space race. Some of the earliest substrates rather than on rigid silicon to produce the first practical silicon chips were used in the first guidance wafers,’ says Javey 1970s: the statins In 1971, Japanese pharmaceutical biosynthesis, and the link between also working in the area. In 1987, chemist Akira Endo set himself an high cholesterol levels and coronary lovastatin, developed by scientists at ambitious challenge: to identify heart disease. Today, cardiovascular Merck and Co, became the first statin compounds that could lower disease is the leading cause of death to receive regulatory approval by the cholesterol levels in the blood, worldwide, in countries rich US Food and Drug Administration a then-recently discovered risk and poor, but at the time it (FDA). Pfizer’s Lipitor (atorvastatin) factor linked to coronary heart was primarily a disease of the has become the biggest selling disease. Forty years later, tens of western world. pharmaceutical of all time. millions of people have benefited Cholesterol is taken up from ‘The challenge now is moving from the family of drugs that Endo the diet, but can also be produced statins from treatment to prevention,’ discovered, known as the statins. in the liver if dietary sources are says Wald, who in 2000 along with In the future, many millions lacking. Endo hypothesised that, colleague Malcolm Law first proposed more could be taking these rather than blocking cholesterol the idea of a cardiovascular ‘polypill’, medicines, as their use uptake from food, the best way a combination of cheap, safe and increasingly shifts from to reduce cholesterol levels in the effective drugs proven to lower treatment to prevention. Mevastatin – isolated blood would be to inhibit the body’s cholesterol and blood pressure. ‘I think the discovery of the statins in the 1970s – is cholesterol-producing pathway. Currently, statins are prescribed is comparable in importance to the considered the first Endo started by looking in based on various risk factors. But Wald discovery of antibiotics,’ says Nicholas statin microbes, reasoning that they might argues that reaching the age of 55 is Wald, director of the Wolfson Institute have evolved metabolites to block sufficient risk alone, and is about to of Preventive Medicine at Queen Mary steroid biosynthesis for self-defence. start a polypill trial to test the theory. University of London, UK. ‘The story Two years and 6000 microbes later, ‘The problem is that beyond middle of penicillin is well known – everyone Endo had a hit – the fungus Penicillium age, everyone’s blood pressure and has heard of Alexander Fleming. But citrinum was producing a compound, cholesterol are high – certainly higher not of Akira Endo – he’s an unsung dubbed ML-236B, which blocked than when that person was 20. That hero of pharmaceutical chemistry.’ lipid synthesis. That compound is now increase is the driver behind the high In 1968, Endo returned to Japan to known as mevastatin. rates of stroke and heart disease.’ work for the Sankyo pharmaceutical By the end of the decade, the Whatever the next step in the company, after a two year postdoctoral first clinical trials of the drug were statin story, it is clear that Akira Endo stint in the US. While abroad he underway – by which time other deserves greater recognition for his had learned about cholesterol medicinal chemistry groups were leading role in its development. www.chemistryworld.org Chemistry World | March 2011 | 39 Discoveries of the last six decades 1980s:the polymerase chain reaction (PCR) As with many of the great scientific The oligonucleotides added to the discoveries, there’s a story behind mixture act as primers for each new the discovery of the polymerase strand, which are extended into chain reaction (PCR).
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