Molecules in 3-D

Holography, which employs laser light to produce accurate three-dimensional images, has long been used by engineers to study stresses in building materials and machine parts. Now one of holography's pioneers is developing a new use for the 30-year-old process. Physicist George Stroke, head of the Electro-Optical Sciences Laboratory of the State University of New York at Stony Brook, has found a way to use holography to see into crystals and view the arrangement of their atoms from inside.

The implications of Stroke's work are important. Scientists must know the three-dimensional structure of biological molecules if they are to understand fully how they are assembled and how they function. A primary means of obtaining this knowledge is X-ray diffraction, a process in which molecules are first crystallized, then examined by X rays. The data collected can be analyzed by computer and then used to draw elaborate "electron density" maps from which complex models can be built.

Stroke's process, developed under a grant from the National Science Foundation, promises to make molecular structures visible. Stroke had been experimenting since 1963 with new ways to utilize holography. But it was not until about a year ago that he and his colleagues--Maurice Halioua, Venugopal Srinivasan and Raghupathy Sarma--hit upon their potentially revolutionary process. Explains Stroke: "We realized that a crystal, in which the atoms are arranged in a repeating array, can be made to produce a sort of hologram, a three-dimensional display of data. What we've figured out is a way of viewing it."

The team first crystallizes the molecule to be studied. The crystal is then examined by standard X-ray diffraction; the X rays that pass through the crystal and bounce off the atoms are used to make a pattern of dots that is recorded by an electronic counter. The diffraction pattern is then processed by computers to determine the relative value of each of its spots. Finally, the spots are printed on a photographic plate, which becomes a hologram of one of the crystal's planes.

Promising Results. To view the hologram is easy. A beam from a helium-neon laser is passed through one lens, which spreads it to cover the entire plate, through the plate itself and then through another lens, which acts as an optical computer and converts the spots into a coherent picture (see diagram). The result is an image showing the arrangement of atoms in one plane of the crystal. This image can be combined with images from other sections to give a three-dimensional view of the crystal's entire atomic structure. Says Stroke: "In the past, all we have been able to produce is a score. Now we can produce real music."

Much work remains to be done before Stroke can write a symphony and show the entire structure of any molecule. But the results thus far are promising. Stroke's pilot study, involving a substance called magnesium bromide tetrahydrofuran, clearly reveals the precise arrangement of the molecule's magnesium, oxygen and carbon atoms in one plane of the crystal. It is more of the molecule than science has yet been able to see.

This file is automatically generated by a robot program, so viewer discretion is required.