STRUCTURE OF CRYSTAL
STUDY BY X-RAY METHODS »
APPLICATION TO SEVERAL BRANCHES OF SCIENCE
Most solid substances are crystalline to a greater or lesser extent, and for this reason the study of the crystalline state is of great importance to science. The study of crystals by X-ray methods has become known as X-ray crystallography, which has several times “enabled the X-ray crystallographer to forestall the chemist” In this way Dr. B. R. Penfold introduced his topic, “Crystal Gazing with X-Rays,” in his presidential address to the Canterbury University College Scientific Society on Friday evening. Dr. Penfold, who is assistant lecturer in chemistry at the college, spent three years in the Cavendish Laboratory, Cambridge University, in research on X-ray crystallography, under Sir Lawrence Bragg. For this work he was last year awarded a doctorate. “The crystals which are used are very different from those which might constitute the equipment of an efficient gipsy fortune-teller, which would be something like a big glass sphere; the glass of this ‘crystal’ happens to be one of the least crystalline substances,” sail Dr. Penfold. “The crystals which X-rays deal with are so small that if you dropped one on the floor the chances would be very much against your ever finding it.” Dr. Penfold described the technical reasons for using the X-ray method of studying crystals and outlined the stages in a crystal analysis. “The ultimate achievement of an X-ray analysis to fix the position in space of all the atoms making up the substance,” said Dr. Penfold, when referring to some of the applications of X-ray crystallography. “This is a very important piece of knowledge, as it enables many of the chemical and physical properties of the substance to be explained.
Study of Clay Minerals ‘‘Most of the early work in X-ray crystallography was concerned with inorganic compounds. Of the more important achievements, in this field was the structure determination of a number of silicates, leading to the understanding of the make-up of clay minerals, which are of fundamental importance in our soil. Chemical reactions by themselves could have provided no clue to the intricate atomic arrangements involved. “A simpler but hone the less important discovery was the structure of diamond and graphite, which could immediately explain their different properties. ‘‘Now the study of complex organic molecules occupies chief place in this new branch of science. The first great triumph was with penicillin. Here Xray analysis was first to give proof of the molecular configuration. In the past purely chemical methods had generally been sufficient for organic compounds. “Another interesting case where the X-ray crystallographer was able to forestall the chemist was in the structure of the nucleoside indo-adenosine. Indo-adenosine is a derivative of the compound adenosine which is an essential part of the very complex molecules which go to make up living cells. Such components are at present being extensively studied, particularly under Professor A. R. Todd, at Cambridge. “A most significant development, details of which are only just becoming available, concerns the structure determination of the essential component of living cells. It has been described as the ‘biological equivalent of crashing the sound barrier.* “The main component of living cells is nucleic acid. One of these acids is found in all dividing cells, largely if not entirely in the nucleus, where it is an essential constituent of the chromosomes. Chromosomes and Genes
“Many lines of evidence indicate that it is the carrier of a part (if not all) of the genetic specificity of the chromosomes, and thus of the gene itself. Until about two months ago no evidence had been presented to show how it might carry out the essential operation required of genetic material, that of exact self-duplication.” Dr. Penfold said that the latest Xray crystallography in this branch of biology suggested how this self-dupli-cation was. accomplished. Each molecule of the acid consisted of two “chains.” coiled round a common axis and held together by hydrogen bonds. “It is suggested that, before duplication, the weak hydrogen bonds in the structure are broken, and the two chains unwind and separate. Each chain can then combine with a new companion so that there are eventually two pairs instead of one.”
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Bibliographic details
Press, Volume LXXXIX, Issue 27072, 22 June 1953, Page 3
Word Count
696STRUCTURE OF CRYSTAL Press, Volume LXXXIX, Issue 27072, 22 June 1953, Page 3
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