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August 30, 1994, Page 00008 The New York Times Archives

CAPPING a decade of intense research, a team of British chemists has created a molecule consisting of five interlocked rings of atoms, a tiny replica of the symbol of the Olympic games. The molecule is probably useless in itself, but the techniques devised to create it may shed light on the process by which life arose from relatively simple chemicals.

The synthesis of this new molecule, technically called a linear pentacatenane and familiarly named "olympiadane" (pronounced "olympiad-ane) was hailed by chemists as an important step toward understanding how components of a complex molecule can spontaneously join together. An ability to assemble themselves from simple precursors is one of the requisites of prebiotic molecules -- the nonliving building blocks from which the proteins, genetic codes and cellular complexity of living organisms arise.

The achievement was announced recently in the German journal Angewandte Chemie (Experimental Chemistry) by Dr. J. Fraser Stoddart and Dr. David Amabilino and their colleagues at the University of Birmingham in England.

The creation of olympiadane was a tour de force of laboratory technique. Although molecules consisting of rings of carbon and other atoms are common in nature and in the laboratory, the mechanical interlocking of neighboring rings seemed impossible until recently. It can be achieved only by precisely controlling the positions of pieces of the rings before joining them together in a chain. In olympiadane, there are no electronic links between the connected rings; they are held together simply by having been threaded through each other like links in a steel chain.

The procedure for making olympiadane is extremely complicated. There are two main steps in the synthesis, the first of them linking three rings together and the second adding the remaining rings. The process requires eight molecular components. Chemists guide the self-assembly of olympiadane partly by varying the concentrations of the reactants in the solvents in which reactions take place, and by changing temperatures and ultrahigh pressures, Dr. Stoddart said in an interview.

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One of the tools essential to the synthesis is the chemical equivalent of a carpenter's jig, a molecule that can be used to hold raw-material components in their correct relative positions before joining them with permanent electronic bonds. This jig, called a template, attracts molecular fragments floating around in solution to specific regions of the template's structure. The template forms temporary weak bonds with these fragments to hold them in place while they react with each other, and then releases the bonds once the self-assembled product has been created. How Life Began

Moreover, Dr. Stoddart said, the rings in the completed olympiadane molecule can serve as templates for making more molecules, "so we effectively have molecules that are storing information in a very neat way beyond the chemical bond level."

The intricate daisy-chain structure of olympiadane cannot be seen by the naked eye, since the molecule is only four-billionths of a meter long; its structure was confirmed by a technique called nuclear magnetic resonance spectroscopy. But what can be seen, Dr. Stoddart says, is that the substance has "a beautiful purple color."

Since announcing the molecule's existence, his group has created a more complicated branched chain with seven interlocked rings, and is working on another chain with ten rings.

Catenanes -- chain-linked molecules like olympiadane -- are only one of the bizarre new classes of chemicals scientists are creating by processes of self-assembly.

Dr. Julius Rebek Jr. of the Massachusetts Institute of Technology, a leader in this field of chemical synthesis, is one of the scientists particularly interested in mimicking the chemical self-assembly processes that most scientists believe gave rise to life.

One of the latest achievements by Dr. Rebek's research group was the synthesis of a hollow molecule with two complementary halves that fit together like the two halves of a tennis ball. The stitching that holds this tennis ball together is based on hydrogen bonding, a weak chemical union in which a hydrogen atom and an oxygen atom join with each other by sharing a single electron. In the tennis ball the hydrogen atoms along the seam of one half of the molecule bond to oxygen atoms in the other half, and this chemical stitching can be readily opened or closed, as if it were a zipper. Potential Value in Medicine

The hollow tennis ball, which was synthesized by Dr. Rene Wyler, a postdoctoral fellow in Dr. Rebek's group, is large enough that it can entrap smaller molecules like those of the solvent in which the tennis ball is formed. Dr. Rebek says that similar hollow molecules might be used to deliver drugs to specific sites in the body, where the carrier tennis ball molecules would be zipped open to release medicine.

During the last decade many chemists have experimented with another new class of hollow molecules called fullerenes, or "buckyballs," named, because of their geodesic structures, for the late architectural engineer R. Buckminster Fuller. Mr. Fuller exploited geodesic principles in many of his building designs.

Although fullerenes have been synthesized in large sizes, they are assembled from carbon atoms that are interconnected by relatively strong electronic bonds that cannot be readily unzipped. A hollow molecule that can be easily opened and closed might be more useful for delivering pharmaceuticals.

Beyond the use of molecular balls as drug-delivery systems, many scientists see in them one of the features of the prebiotic molecules presumed to have led to life.

The self-assembling tennis ball molecule is too small to contain large molecules, but Dr. Rebek's group is working on a larger version, a chemical "softball." The natural evolution of something like a molecular softball might have been the route along which protein capsules evolved -- the kind of capsules used by viruses to enclose their inner molecules, Dr. Rebek believes.

"We feel, as do other workers," Dr. Rebek wrote in the July issue of Scientific American, "that a key attribute of life is a boundary: a container or cell wall that separates inside from outside and prevents desirable molecules from floating away -- while keeping undesirable ones at bay." Duplicating Attributes of Life

Using hollow softball molecules as containers, Dr. Rebek expects that it will soon be possible to pack them with some of the smaller self-replicating molecules his group has synthesized over the years.

But although such an arrangement of molecules would certainly duplicate some attributes of life, Dr. Rebek foresees large obstacles in deciphering the process by which nature created living cells.

Scientists, he said, will need to discover a mechanism for allowing "our fledgling organism" to harness energy from outside itself, and another mechanism by which this laboratory-made cell can replenish the raw materials it needs to grow and function.

Not all scientists believe that life originated on earth. Some, like Dr. Francis Crick, the co-discoverer of the structure of DNA, believe that primitive forms of life might have landed and taken root on earth after drifting for many eons through space.

But at least since 1953, when Dr. Stanley L. Miller conducted a celebrated experiment in which amino acids, the building blocks of proteins, were created simply by sending miniature lightning bolts through a mixture of methane, ammonia, hydrogen and water, scientists have been searching for the chemical tricks that might have led to life.

In recent years, participants in the quest have included experts in computer programming as well as chemists. Programs have been devised in which simple mathematical entities crawl around computer screens, mimicking some of the behaviors of one-celled organisms. They reproduce, mutate genetically, devour each other, compete, cooperate and behave in complex patterns that evolve spontaneously from simple rules.

"People from various branches of science who are interested in the origins of life gather periodically for meetings," Dr. Rebek said. "The computer people come with their software ideas, and we chemists contribute what we call 'wetware.' It's hard to guess where all this will lead, but it's one of the most interesting questions human beings can ask."

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