Filamentous fungi such as Aspergillus fumigatus are usually harmless. But they can run riot in patients whose immune systems are weakened, perhaps through chemotherapy or because they have AIDS. Current antifungal drugs will not kill a fungus, but only slow its growth. “The scourge of fungal diseases in immunocompromised patients has reached tragic proportions,” says Tony Barrett, a chemist at Imperial College, London. “We need to address this major clinical need now.”

In 1989, scientists at the Japanese pharmaceuticals company Fujisawa found that a soil-dwelling fungus called Streptoverticillium fervens releases a compound that kills other fungi, yet is harmless to mammals. The compound is being called “jawsamycin” because it made up of a chain of carbon triangles called cyclopropyls, which resemble the teeth of a shark.

When Barrett and his Imperial College colleague Krista Kasdorf worked out the full structure of the molecule earlier this year, many chemists despaired of ever manufacturing it. Not only are cyclopropyls intrinsically unstable, but jawsamycin also has 10 chiral centres, or points about which left and right-handed versions of the molecule can form. This gives a total of 1024 possible structures, only one of which corresponds to the compound produced by S. fervens that kills fungi.

But Barrett and Kasdorf have now cracked the puzzle. In a paper to be published in a future issue Chemical Communications, the chemists describe how they synthesised an exact replica of natural jawsamycin using a sequence of just 15 chemical reactions.

They constructed the cyclopropyl triangles by reacting the two carbon atoms of a C=C double bond with a molecule of diiodomedine (CH₂I₂), which provided the third carbon. The reaction was catalysed by a boron compound derived from tartaric acid. This acid can itself exist in two chiral forms, and by choosing the correct one the researchers could produce the proper chiral structure for each cyclopropyl group. “The skill is devising a route that produces an exact copy of the natural molecule, in a pure form, just as Barrett and Kasdorf have done,” says Ken Richardson, an antifungal specialist with Pfizer Central Research in Sandwich, Kent.

Now the molecule has been synthesised, chemists can tinker with the reactions with the aim of making similar compounds that are toxic to a wider range of fungi. (see Diagram)

Facing the Future is the aptly titled book by Michael Allaby which lays into this unholy caravan of antiscience pessimists. In chapter after chapter he confounds their predictions of impending disasters and points out that the future is not likely to be as they envisage, because they have got their facts and theories wrong. He sums it all up in his last chapter: “In uncertain times it is optimism that we need. Unless they are challenged vigorously, the pessimists who rejoice in the predictions of apocalypse may prove themselves right. Their prophecies may prove self-fulfilling because of the despair they have engendered. If the future, as presented to us, is unbelievedly dismal, the only sensible thing to do is ignore it and live for the present …” Which is what many young people are now doing.

Facing the Future is divided into five sections. The first explores the ways in which scientists lost the propaganda war, becoming demonised in popular fiction and films, and criticised as cultural barbarians by the up-market media. The second section explores the flight from rationality. Why has so-called postmodernism taken hold among intellectuals, with its enervating message which says that progress in human affairs is not really possible? There are some postmodernists who dismiss science altogether, seeing it merely as a “construct” of our time, a collection of axioms with no more claim to absolute truth than any other set of axioms that society might care to choose. Forget science – the world is entering the Age of Aquarius, where feelings and empathy will matter more than cold facts and mere logic.

In the third section, Allaby explores some of the myths that sustain the alternative philosophy – such as the idea that we can retreat to a Golden Age, become like the noble savages and live in harmony with our environment, both protecting and being protected by a benign Mother Earth. In this part of the book I became a little worried about Allaby’s own views on population, and he came close to losing my support in his chapter entitled “Food, Famine and the Depletion of Resources”, where he appears to be advocating a laissez-faire approach to the world’s population.

Allaby believes that population will level off at a sustainable number and quotes the Club of Rome, whose forecasts about the future were so influential in the 1960s but were so wrong. The club said that by the 1990s the world would be destabilised by shortages of food, energy and resources, all caused by overpopulation. Thanks to science we have coped with another billion mouths, yet I cannot really believe, as Allaby does, that numbers will eventually stabilise. This assumes that science will remain one step ahead, and be able to meet most of everyone’s needs. With science now in decline, this seems unlikely.

I rejoined Allaby when he returned to his main attack in part four of Facing the Future. This contains the meaty chapters, refuting the philosophy of our opponents, who criticise science because it is reductionist, and by implfication redundant. (Their alternative philosophy is, they claim, holistic and wholesome.) Of course science reduces things to their component parts and analyses their functions; this is why it is so successful. Any other approach for physics, chemistry or molecular biology would be impossible.

Allaby is at his most impressive when he addresses the issues on which the environmentalists have had most success, peddling their exaggerated fears about global warming, nuclear power, food additives, pesticides in farming and environmental pollution – fears based on half-truths and one-eyed observations. Their endlessly repeated assertions are here exposed as non-science and nonsense. Allaby is in danger of being labelled a sceptic by environmentalists. This is their curious term of abuse for scientists who dare to question their statements. Perhaps they don’t realise that to be a scientist you must be a sceptic, or else why bother to investigate anything?

In the final part of Facing the Future, Allaby stands back from this tiny planet and considers our place in the Universe, concluding that we are never likely to make contact with any other life forms, but we should colonise the Solar System where we can. In the end, we humans have just got to make the best of what we have, and science and optimism about the future are the only way forward.

This is a super book. Buy it, cheer yourself up, and revive your faith in science.

CFC manufacture is now almost at an end as a result of the Montreal Protocol of 1987, but large amounts of these chemicals are being collected from old fridges and air-conditioning units and have to be disposed of. Breaking them down into harmless compounds poses problems because CFCs are nonflammable and chemically unreactive – which is why they have been so widely used for 40 years in aerosols, insulation foams and cooling units.

The CFCs can be destroyed by extreme conditions, for instance at very high temperatures and in jets of hot ionised gases, but this is costly (��è����Ƶ, Science, 15 August 1992). Now a group headed by Yoshio Nagata at the Research Institute for Advanced Science and Technology at Osaka University in Japan has found that CFCs in water can be broken down at room temperature with ultrasound – sound waves whose frequency is too high for humans to hear. They report their findings in Chemistry Letters (1995, p 203).

The Japanese chemists studied a dilute solution of the compound called CFC-113, one of the commonest CFCs, which has the chemical formula C₂F₃Cl₃. They discovered that pulses of ultrasound at a frequency of 200 kilohertz caused CFC-113 to react with water and form the gases carbon dioxide and carbon monoxide, as well as hydrochloric acid and hydrofluoric acid, all of which are relatively easily disposed of. With this method, 80 per cent of the dissolved CFC-113 was destroyed within 30 minutes. During this time the temperature of the water rose from 22 °C to only 30 °C.

Chemists believe that ultrasound forms tiny bubbles in the water that instantly collapse, generating very high temperatures and pressures (“Bubbles hotter than the Sun”, ��è����Ƶ, 29 April). Under such conditions water molecules split to form highly reactive hydroxyl (OH) radicals, and these are the agents which attack the CFC molecules.

Nagata and his colleagues proved that CFC-113 was meeting its fate in the bubbles, rather than in the bulk of the liquid, by adding the chemical t-butyl alcohol. This mops up hydroxyl radicals as fast as they form in the water. Because adding the alcohol had little effect on the destruction of the CFC-113, Nagata concludes that the breakdown must be taking place inside the bubbles where the alcohol cannot not reach the radicals.

When the researchers repeated their experiments in an atmosphere of argon instead of air, they found that the rate at which CFC-113 was destroyed trebled. Excluding air is known to amplify the effects of ultrasound in water, although no one yet understands why (see Diagram).

John Slater of Birkbeck College, University of London, is collaborating with the Middlesex Hospital to test the ScanMaster as a noninvasive technique for detecting the presence of H. pylori and diagnosing medical conditions such as kidney problems or diabetes. Because the instrument does not need to be in direct contact with the material it is probing, it should be ideal for analysing a person’s breath to diagnose whether unusual metabolites are present.

“This is not a new idea,” says Neville Freeman, director of Array Tech Chemical Sensors, the company developing the ScanMaster. “Chinese doctors have always smelled a patient’s breath as part of their diagnosis.”

Robert Unwin, a consultant nephrologist at University College Hospital, initially took an interest in the project because of its potential to diagnose kidney problems. But he says that applying the nose to sniff out H. pylori is more promising, since it could cut down on the number of endoscopies, a procedure in which doctors insert a small camera into the patient’s stomach. “It will be very, very useful, at least for screening,” he says.

Array Tech has been given £42 000 by the Department of Trade and Industry to develop the ScanMaster. Freeman says the money will be used to produce a faster version, and ideally one that can recognise any smell in under a second. He also hopes to miniaturise the device.

The electronic nose relies on vibrating quartz crystals, which are coated with a film of absorbent material a micrometre thick. When this layer absorbs volatile compounds, the frequency of the vibrations change, enabling the instrument to detect the presence of materials down to nanogram quantities. A cluster of these quartz crystals, each covered with a different type of absorbent film, forms the heart of the new sensor. Quartz crystals are very stable and resistant to being poisoned or desensitised by the chemical that they are detecting.

The input from each crystal is fed to a computer and combined to create a profile “smell”. This input is compared with a bank of data and a “best fit” profile can be identified within 30 seconds. Other artificial nose projects have relied on a technique, based around conducting polymers (Technology, 7 January).

Likely applications also include quality control in the food and drink industries. Freeman says: “We have also shown that it can identify different oil-based chemicals and could be used as a quick way to check fuel quality.”

This mysterious journey was still being talked about forty years later by no less a scientist than Robert Boyle, of Boyle’s Law fame. He wrote that one of the passengers, then still alive, had said that when the air in the submarine had been consumed, Drebbel was able to refresh it with purer air from a container. Clearly that gas could only have been oxygen. Then again clearly it could not, because oxygen was not to be discovered for another 150 years.

Water Which Does Not Wet Hands begins with the story of the submarine and ends by revealing that oxygen could have been used because Drebbel was conversant with the work of Michael Sendivogius. This Polish alchemist, who lived from 1566 to 1636, knew of oxygen, which he referred to as “the aerial food of life”.

Sendivogius had observed that when potassium nitrate, or nitre as it was then called, was heated gases were evolved. Gentle heating produces oxygen alone, while stronger heating drives off red-brown fumes of nitrogen dioxide and oxygen. In those days nitre was collected from the walls of cesspits and latrines, or from the leachings of manure and soil, and was used to make gunpowder.

This simple salt fascinated Sendivogius. He referred to it as the “central salt” and built his alchemical theories around it. Yet he was determined to remain anonymous. To keep his findings from the eyes of the curious he wrote under various pseudonyms and anagrams, and shrouded his writings in the arcane language of alchemy.

Zbigniew Szydlo, the author of Water Which Does Not Wet Hands, is to be congratulated on a scholarly and meticulously researched account of Sendivogius and his work. (The title comes from one of his allegorical descriptions of nitre.) Szydlo has tracked down all the works of Sendivogius, whose books went through 50 editions in five languages and were in print to the end of the 18th century. He wins the struggle to “make sense of Sendivogius’s writings, separating the few chemical facts from the welter of theory, philosophy and allegory.

The last part of Water that Does Not Wet Hands is taken up with appendixes in which Szydlo translates some of Sendivogius’s writings. If you want to know about the philosopher’s stone, which turns base metal into gold, or the elixir of life, which makes us live for ever, here they are. But be warned: the instructions are difficult to grasp.

For example, in making the philosopher’s stone, we come across the phrase: “the central salt does not accept more water than it needs”, which makes a sort of chemical sense if we are talking about the solubility of potassium nitrate, but this is followed by the instruction: “the fattiness of water, which is not always pure, can be purified by the art”. Work that one out.

Szydlo also tackles two closely related topics in his book: the Rosicrucians, and the work of John Mayow. The Rosicrucians were a secret brotherhood that survived into this century, and the tenets on which it was based, Statutes for a Society of Unknown Philosophers, are translated by Szydlo, who argues convincingly that they are most likely to have been written by Sendivogius.

He also devotes a chapter to John Mayow (1641-79), an Oxford chemist and early fellow of the Royal Society, who wrote about “nitro-aerial particles”, which Szydlo argues are the same as Sendivogius’s “aerial food of life”. Mayow appears to have relied heavily on the Polish alchemist’s works for guidance although he does not acknowledge this.

The real discovery of oxygen came in the 1770s, when both Karl Scheele and Joseph Priestley independently made it, and recognised it as such. Yet the evidence suggests that this gas was known and used 150 years earlier. It may be argued that some alchemists regarded it as the elixir of life – and in a curious way they were right.

Oxalic acid (H₂C₂O₄) is found in large
amounts in rhubarb and cocoa – making up to 0.5 per cent of them – and in
lesser quantities in unripe tomatoes and strawberries. Other foods containing
a lot of oxalic acid are beetroot, currants, gooseberries, oranges, carrots
and cucumbers.

This simple organic acid is regarded as an undesirable component of our
food because it ties up calcium as insoluble calcium oxalate
(CaC₂O₄), which forms stones in the urinary tract.
Gallstones and kidney stones also contain a lot of calcium oxalate.

Sometimes, oxalate can even be fatal. In the First World War, the U-boat
onslaught on British merchant ships caused severe food shortages. A few
housewives, searching for alternative vegetables, served their families boiled
rhubarb leaves. The high levels of oxalic acid in the leaves of this plant led
to some deaths.

Although our bodies naturally contain low levels of oxalate, the chemical
is thought merely to be an end-product of chemical processes, awaiting
excretion because it is of no further use. But this view has been challenged
by Steffen Albrecht, Herbert Brandl and Christoph Scho¨nfels of Dresden
University. They suggest that the levels of oxalate found in the body are too
high for the substance to merely be an end-product of metabolism (Angewandte
Chemie, vol 33, p 1780).

Albrecht and his colleagues have developed a highly sensitive and rapid
method of analysis for oxalate which reveals unexpected variations in the
concentration of the chemical throughout the blood: plasma contains 4.0
micromoles per litre, while serum has 12.3 micromoles per litre. (A micromole
of oxalic acid is 90 micrograms.) The chemists also found that people
undergoing dialysis were releasing higher amounts of oxalate than expected,
and concluded that there is much more intracellular oxalate than
suspected.

Albrecht’s method of analysis is based on the reaction of oxalic acid with
hydrogen peroxide (H₂O₂) and carbodiimide. When this
reaction occurs under strongly acidic conditions, and with a fluorophore
present, light is emitted, and this can be measured. The fluorophore is
excited to a higher energy state and then gives out that energy as a flash
detectable with a sensitive light detector. The method can measure
concentrations of oxalate as low as 0.2 micromoles per litre; other organic
molecules in the system do not interfere, making it an ideal method for
measuring biological samples.

Using this technique, Albrecht and his colleagues measured intracellular
levels of oxalate in human blood cells as high as 2910 micromoles per litre.
This is comparable to concentrations of other substances that are known to be
an essential part of human cells. The Germans therefore wonder whether oxalate
has a part to play, rather than merely being an end-product of metabolism.
They suggest that there could be an oxalate oxidase pathway using oxalic acid
to produce hydrogen peroxide, which can then be used to promote a “burst” of
phagocytes, cells that engulf and break down foreign particles, cell debris
and disease-producing microorganisms.

Physocists may be on the verge of creating ‘superheavy’ elements, surprisingly stable nuclei with atomic numbers greater than 112. Currently, the heaviest known element is meitnerium (Mt), which has an atomic number of 109, but hopes have been raised by a group of Russian and American physicists who have made heavy isotopes of seaborgium (Sg), element 106, and found they live much longer than expected.

Atoms of elements with atomic numbers greater than uranium, element 92, are not found naturally on Earth. This is because their half-lives – the time taken for half the atoms in a sample to decay – are much shorter than the age of the Earth. However, in the past 40 years, heavier elements have been made artificially by bombarding heavy nuclei with smaller ones.

Physicists have found that elements become less and less stable as their atomic number increases. From one element to the next, the half-life of the longest-lived isotope shrinks by about half (see Table).

Elements up to fermium, which has atomic number 100, have half-lives long enough for chemists to carry out experiments and determine their chemical properties. With the post-fermium elements it has proved impossible to make more than a few atoms of each element, and none of the elements has a half-life longer than a few months.

But nuclear physicists have long suspected that an ‘island of stability’ might exist, centred on element 114. Theorists predict that the isotope with 184 neutrons, and hence an atomic mass of 298, should be particularly stable because it has a nucleus with a filled shell of neutrons. The island is thought to extend from element 112 to element 118, and some theorists believe there could be hints of it in even earlier elements.

Now evidence of a fringing reef off the island of stability has been found in the region of element 106. A team of physicists led by Yuri Lazarev of the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, and Ron Lougheed of the Lawrence Livermore National Laboratory in California have made isotopes of seaborgium with atomic masses of 265 and 266.

In a paper in Physical Review Letters (vol 73, p 624), the physicists announce that the half-lives of these isotopes are much longer than anyone expected. Seaborgium-265 decays by emitting an alpha particle with a half-life of between 2 and 10 seconds. Seaborgium-266 has a half-life of between 10 and 30 seconds; it emits an alpha particle of energy 8.63 MeV, then fissions spontaneously. These half-lives are at least ten times greater than have been observed for seaborgium (see Table).

The physicists at Dubna made the isotopes by bombarding nuclei of californium-248, appropriately supplied by Lawrence Livermore, with neon-22 at energies of 116 and 121 MeV. The experiment produced about one atom a day of seaborgium-265 and seaborgium-266. Lazarev and Lougheed focused on seaborgium-266 because it has 160 neutrons, a number expected to make the nucleus stable against spontaneous fission.

‘What is remarkable about this work is how such complex systems, with 160 neutrons and 106 protons, have properties predicted by simple principles,’ says John Hassard of Imperial College, London. ‘We are poised to start making elements which presumably have never before existed in the Universe, and which may have lifetimes long enough to allow for applications.’

The breakthrough has come at the very time Britain has closed down its own facilities for such nuclear research at Harwell, near Oxford.

Fibres several centimetres long have been grown from a salt of an organic
acid. But their molecules are not covalently bonded to each other as they
are in a conventional polymer fibre. Instead, say the American chemists
who made the fibre, they are another example of the growing number of chemicals
known to organise themselves into large structures. Such systems adopt shapes
that appear to be forerunners of biological structures.

To make the fibres, F. M. Menger and S. J. Lee of Emory University in
Atlanta, Georgia, dissolved 5-(hexadecyloxy) isophthalic acid (HIP) in a
hot solution of potassium hydroxide. As the resulting solution cooled, the
chemists observed a tangled mass of fibres forming. HIP consists of a benzene
ring to which are attached two carboxylic acid groups and the 16-carbon
hexadecyl chain. The chemists used enough potassium hydroxide to neutralise
both the acid groups of HIP. However, when they analysed the fibres, they
found that only one of the acid groups had reacted with the alkali. The
fibres were the monopotassium salt of HIP.

Menger and Lee found that their fibres had several unusual features
(Journal of the American Chemical Society, vol 116, p 5987). For instance,
the threads were flexible when wet, but brittle when dry. When they were
wetted again they regained their mechanical strength. Wet fibres were stable
and remained unchanged for more than a year. When sodium, rubidium and caesium
hydroxides were used, similar fibres formed, but fibres did not form with
lithium or ammonium hydroxides. The fibres grew with a range of diameters
and stretching them produced filaments that were several centimetres long.

When Menger and Lee examined the fibres with a scanning electron microscope,
they found that the filaments were not hollow tubules as expected, but were
instead composed of bundles of smaller fibres, the thinnest of which were
about 27 nanometres in diameter. Under the microscope, the chemists also
saw that when the fibre was drawn out, they stretched by becoming thinner
rather than straighter.

Menger and Lee believe that the fibres are made of stacked discs, and
that the edge of each disc consists of a ring of isophthalate groups held
together by strong hydrogen bonds. The formation of these bonds explains
why one acid group resisted neutralisation by the potassium hydroxide. The
acid groups of HIP happen to be in just the right position to maximise the
hydrogen bonding between molecules and also to minimise interference with
the hexadecyl group. If one of the acid groups is placed next to the hexadecyl
group the fibres do not form.

Inside the hydrogen-bonded ring lie the 16-carbon chains, which the
chemists think become entangled with each other. Because the discs are
hydrophobic, they push away water molecules and come together to form a
stack, just as droplets of oil coalesce to form larger globules.

Menger and Lee also propose that the chains from one disc become entangled
with those from neighbouring discs, and that this helps to hold the stack
together. They found that if these chains are shortened from 16 carbons
to 12, then the fibres fail to appear. Attaching two 12-carbon chains to
each molecule also failed to produce fibres. Neither did the fibres form
if the chain was stiffened by the inclusion of a pair of adjacent triple
bonds.

A simple reaction which chemists previously believed impossible has been brought about by a team of chemists in the US. The unprecedented reaction is the transformation of nitrate ions (NO₃)^– into ammonium ions (NH₄)⁺ by simple organic molecules such as methane or ethanol.

The reaction was discovered by Alan Hutson and Ayusman Sen of Pennsylvania State University. They say that if a catalyst could be found to promote it, the discovery could lead one day to a practical way of removing not only nitrogen oxides but also unburnt hydrocarbons from car exhausts (Journal of the American Chemical Society, vol 116, p 4527).

In the reaction, the nitrogen atom gains electrons: in other words, it undergoes reduction. In nature, the reduction of nitrate to nitrite (NO₂)^–, to nitric oxide (NO), and even to nitrogen gas (N₂), happens quite normally. In these conversions, up to four electrons (e^–) are required. However, the direct reduction from NO₃ ^– to NH4+ requires eight electrons:

NO₃ ^– + 10H⁺ + 8e^–/NH₄ ⁺ + 3H₂0

Even metal hydrides, which are extremely electron-rich and are therefore among the strongest reducing agents known, cannot accomplish this transformation in one step. However, Hutson and Sen have brought it about simply by dissolving the nitrate in sulphuric acid, and treating it with simple organic compounds. This is all the more surprising because sulphuric acid is usually thought of as an oxidising agent – a compound which removes electrons, rather than adding them.

The chemists report that a number of commonplace organic chemicals will do the trick. They include hydrocarbon gases such as methane (CH₄) and ethane (C₂H₆), simple alcohols such as ethanol (C₂H₅OH) and propanol (C₃H₇OH), and acetic acid (CH₃CO₂H). None of these chemicals is regarded as a reducing agent, let alone a strong reducing one.

In a typical reaction, Hutson and Sen dissolved sodium nitrate in concentrated sulphuric acid (96 per cent grade), added the organic compound and heated the combination to around 170 degree C. For the gases methane and ethane they used a steel pressure vessel to contain the reactants. They used nuclear magnetic resonance to prove that ammonia had been formed.

In some reactions the chemists found that 100 per cent of the nitrate was converted to ammonia – in the case of ethanol this had happened after only 15 minutes. With methane as the reducing agent, they observed only a trace of ammonia after 20 hours’ heating, but when they added a little mercury(II) sulphate to the solution the yield of ammonia rose to 100 per cent. Hutson and Sen believe that the mercury acts as a catalyst in a reaction that converts methane to methanol, and that it is the methanol that acts as the reducing agent.

Hutson and Sen are now investigating the route by which the reduction occurs. They believe the first step is the conversion of NO₃ ^– to NO₂ ⁺ by the sulphuric acid. What happens next is not clear.

A molecular compass is being used by a group of British chemists could
be used as a sensitive indicator of how groups of atoms behave when attached
to metal catalysts. Knowing how such groups interact with the surface of
metals is the key to designing better catalysts for industry.

Vernon Gibson of the University of Durham has identified two types of
compass: one that points towards the group forming the strongest bond, and
another that points to the weakest bond.

The most useful catalysts for many reactions are members of the group
of elements known as the transition metals. Such metals can have up to 10
valence electrons, and can bond to groups of atoms (which may themselves
be complete molecules) through multiple bonds. Groups that can be bonded
in this way are known as ligands.

The role of a catalyst is often to bring ligands together, to make them
more likely to react. Knowing how strongly the ligands attach to a metal
is the key to understanding how the metal behaves as a catalyst.

Gibson has discovered that when one of the four ligands attached to
a transition metal is a substituted ethylene or acetylene molecule, it behaves
like a compass, and points to the most weakly bonded of the other three
ligands (Angewandte Chemie International, to appear in August).

This happens, in the molybdenum complex Mo(cp)(SC₆F₅)(O)(CF₃CCCF₃),
which contains a cyclopentadienyl (cp) group, a sulphur-containing pentafluorophenylthiolate
(SC₆F₅) group, an oxygen atom (O) and a fluorinated acetylene ligand (F₃CCCCF₃).
The acetylene acts as the compass, fingering the sulphur group as the most
weakly bonded partner. In the corresponding molybdenum complex in which
the oxygen is replaced by a carbon monoxide (CO), the acetylene swings round
to identify the new ligand as the weak point.

On the other hand, the pentylidene ligand, which is doubly bonded to
the metal, points to the molecule which is most strongly bonded. Pentylidene
is the group CHR (where R is the tertiary butyl group C₄H₉).
In the complex Mo(OR)₂(NR)(CHR), which is used in industry as a catalyst
for making polymers by opening rings of carbon atoms and joining them together,
the orientation of the CHR singles out the imide ligand (NR) as the strongest.

Gibson believes that his compass molecules are sensing the so-called
p-bonds between ligands and the metal. These bonds are ancillary to the
normal direct bond and enable extra electron interaction between the two,
which may strengthen the bonding. This interaction may result in a flow
of electron density towards or away from the metal; it is the flow of electrons
towards the metal which is sensed by the compass ligands.

Gibson puts his theory on the line by predicting how compass molecules
will point in complexes which have not yet been made (Journal of the Chemical
Society Dalton Transactions, 1994, p 1607). He and his colleagues are now
trying to design some of them, and determine their structure with the aid
of nuclear magnetic resonance spectroscopy or X-ray analysis.

Choosing a catalyst is still regarded as more of an art than a science.
But if Gibson’s theory is correct, it will allow chemists to probe the mystery
of why some metal compounds make better catalysts than others. Understanding
the bonding is the key to understanding catalytic activity. Gibson is already
designing new catalysts for the manufacture of polyethylene for the chemicals
company BP.