Book Reviews September 1995

Book reviews Sept 1995

There are 2 books reviewed on these pages. Click here for the one on Symmetry by the Hargittais

Methods galore

Physical and Non-Physical methods of Solving Crystal Structures.
By M. M. Woolfson and Fan Hai-Fu. Cambridge University Press: 1995.
Pp 276. ISBN 0 521 41299 4. �45.00, $69.95.
Increasingly, crystal structures are solved by centring a crystal (or a series of crystals) in an x-ray beam and running a series of programs which ultimately list the atomic coordinates and draw appropriate diagrams. The most important skill appears to be the knowledge of which programs to run and how to run them.

This book presents the fundamental ideas which underlie methods of reaching a structural solution, revealing complexities of the basic skeletons which support the smooth, well-rounded, user-friendly automata which serve us : mechanisms which many of us will never look inside. It is suitable for postgraduate students with some grounding in crystallography. It covers methods which have been developed over 50 years, some appropriate for crystals with a dozen atoms in the asymmetric unit, some for electron micrographs of two-dimensionally ordered specimens up to 100� thick. It gives excellent insight into new methods still on the test-bed, and offers tantalising glimpses of better methods just around the corner. It will cause every one of us to question whether the program we just ran was the most appropriate means to solve the structure.

For me, one of the most thrilling chapters was the one entitled Direct Methods, which begins with structure invariants and Harker-Kasper inequalities, and leads right through the tangent formula and higher-order determinants to magic integers and SAYTAN. Here Woolfson is on his home ground, and the presentation is brilliant. The methods for phase extension, for developing solutions to superstructures, for density modification, and the progress of methods for ab initio phasing come over equally well. Perhaps best of all is the final chapter, which presents the use of 3-beam scattering measurements for direct phase observation, in clear and simple terms.

The book is strongly based in "Direct Methods". The protein crystallography sections concentrate on the single isomorphous replacement (SIR) method, and the opportunities to use direct methods to resolve the consequent phase ambiguities (even to the point of describing the Blow & Crick method for phase determination as a treatment of the SIR method). This is justified by the misleading statement that usually one isomorphous derivative can be found with little difficulty, but to find a second may not be straightforward. Anomalous scattering is treated extensively, but the elegant solution created by combining it with SIR (SIRAS) is not brought out. MIRAS is only mentioned in passing (in discussion of the maximum entropy method) and the work by B.W. Matthews and by A.C.T. North on the proper way of combining MIR and AS is not mentioned. Similarly, non-crystallographic symmetry is presented almost entirely from the point of view of small molecule structures, despite its huge importance in the largest structures, especially viruses.

David Blow
August 95


A new Way to See the World


SYMMETRY. A Unifying Concept. by Istv�n and Magdolna Hergittai 1994
222pages 550 photographs, 300 drawings, ISBN 0-936 070-17-X, $18 paperback
Shelter Publications Inc, PO Box 279, Bolinas, California 94924, USA

This addition to the well known books on symmetry by the Hargittais is a picture book of places and objects they have photographed on their travels over 20 years. It attempts to explain the concepts of symmetry in a simple way, using everyday objects. There are 15 sections, including ones on mirror, rotational, translational and spiral symmetries. The diagram on the right is from the section on Band Patterns, (page 135) These are from Hungarian needlework designs. The small triangular motifs beneath each one show the type of repetition.


This is only one of the many useful diagrams with which to explain symmetrical concepts, and perhaps attract more students to crystallography. Other sections cover the symmetries of polyhedra, anti-symmetry, and the last one 'Diamonds and Glass'.


I now realise I should have included balloons in my list of crystallographic toys, (See 'Crystallography News' Dec 93 p 24-26). The Hargittais give a clear explanation of how clusters of balloons can be used to understand how clusters of objects in natural settings form polyhedral shapes. They show how this applies to molecular structures such as sulphur hexafluoride.


The Epilogue ends with a request to the reader, "If you want to contribute to a future book on symmetry write to the authors at: " Istv�n and Magdolna Hargittai, E�tv�s University, H-1431 Budapest, Pf. 117 Hungary


I found this a fascinating book, and am happy to browse through it at any time. The only problem is that booksellers do not think it is about crystallography, so you will not find it by scanning the scientific shelves, it is more likely to be in 'Art and Design'.


Kate Crennell
August 1995

Note added January 1999 This book now available more easily in the UK from Tarquin Publications price �11.99 + postage and packing

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