DESIGNER science is coming of age. Scientists are combining the growing understanding of processes and structures at the molecular, atomic and subatomic levels with computer modelling techniques to synthesise new products. And, they are now discovering that their theoretical simulations are borne out by reality.

Scientists hitherto used trial-and-error methods to obtain a new material or compound that could actually knock out a pernicious pathogen. But now, in two areas of science -- new materials and new drug development -- they are turning to computer-aided design to build substances whose properties they can predict.

Using this method, scientists at Harvard University in the US have developed a material, which they claim could be harder than even diamond, while a group of researchers from Australia and the United Kingdom say they have developed an effective drug against the influenza virus.

Harder than diamond

WHICH is the hardest substance? Three Harvard University researchers say they have fabricated a material whose pure version could be harder than diamond (Science, Vol 261, No 5119). The wonder substance is a solid composed of carbon and nitrogen atoms.

The scientists -- Charles Lieber, Yuan Z Lu and Chunming Niu -- were inspired by a theory put forward by Marvin L Cohen, a physicist at University of California at Berkeley, who used a computer to simulate new atomic structures and predict their properties.
Shorter bonds Cohen postulated that the closer the atoms in the simulated structures, the harder the resulting material.

In 1989, Cohen theorised that to be harder than diamond, which is a form of carbon, a material should consist of three atoms of carbon attached to four atoms of nitrogen as the bond between carbon and nitrogen atoms would be shorter than the bond between any two carbon atoms in diamond. Since then, a number of groups have tried to synthesise the material, but Lieber's group was the first to be successful.

They produced this material in a vacuum chamber containing a piece of graphite. A laser beam striking the graphite released carbon atoms, while nitrogen and helium were fed into the chamber through a nozzle where the nitrogen molecules were split into atoms just before they entered the chamber. The vacuum prevented the nitrogen atoms from recombining to form molecules before they reacted with the carbon. The inert helium also helped keep the nitrogen atoms separate giving the carbon and nitrogen atoms enough time to link up with each other.

The new material has immense commercial potential as a substitute for artificial diamond, which is used in abrasion resistant coatings and to dissipate heat in ever smaller microelectronic devices. However, it is too early to tell how the carbon nitride material would compare in cost with synthetic diamond.

...smarter than influenza

USING computers, researchers have developed a drug that promises to become the world's first effective bulwark against all strains of the influenza virus, one of the biggest killers of this century.

The development of an anti-influenza virus agent has met with little success, as the virus has the ability to modify its surface antigens leaving the immune system unable to cope with essentially new antigens. The virus strains can exchange genetic material and have thus been able to overcome resistance offered by the host even after vaccination (Nature, Vol 363, No 6428).

However, a drug designed by an international team of researchers led by Mark von Itzstein of Monash University in Australia, combats the virus by targeting sialidase -- an enzyme critical to the virus and present in all its strains. Scientists attempted to develop synthetic substances that would compete with the substance on which the enzyme was to act, making it difficult for the enzyme to catalyse the essential reactions that could lead to spread of disease in a human body.
Synthetic derivative In 1969, a synthetic derivative of sialic acid, called DANA, was found to inhibit sialidase in the test-tube. But it failed to perform as well in a living organism. It was later discovered that though DANA clung to the enzyme, it left a pocket uncovered, allowing the enzyme to continue its activity.

Following the unravelling of the crystalline structure of sialidase in 1982, the researchers began their quest for drugs that could inhibit this enzyme. They made a version of sialic acid that matched the active site of sialidase. As a result, "the virus is trapped on the surface of an infected cell and cannot spread", explains Itzstein. Moreover, the drug is specific to influenza virus sialidases, with little or no effect on those found elsewhere, such as in sheep liver.

But the drug's efficacy in human beings is yet to be proved. Besides, the virus may alter itself into a strain impervious to the drug. Nevertheless, the specificity of the new anti-influenza compound for one type of sialidase brings hope that disease-specific inhibitors of this enzyme may be developed. Biochemist Gary Taylor of the University of Bath in the UK, however, cautions that as very little is known about mammalian sialidases, drug designers would have to avoid compromising the inhouse activities of these enzymes.