Tan Kah Kee Science Award in Mathematics & Physicis 2006
Fan Haifu, crystallographer, was born on 15 August 1933 in Guangzhou, Guangdong Province, China. He graduated at the Department of Chemistry, Peking University in 1956 and is now a Professor and senior research scientist in the Institute of Physics, Chinese Academy of Sciences, Beijing, China. He was elected Member of the Chinese Academy of Sciences in 1991 and Fellow of the Third World Academy of Sciences in 2000. A book “Physical and Non-Physical Methods of Solving Crystal Structures?has been written jointly by M. M. Woolfson (Fellow of the British Royal Society) and Fan Haifu, Cambridge University Press，1995.
The Problem of Phase Ambiguity in Single Cystal Structure Analysis
Abstract
Solving crystal structures from their diffraction effects is an inverse problem in physics. The study on the origin, appearance and resolving methods of the phase ambiguity led to the following achievements, which have important applications to both material science and life science.
i)Phase ambiguities are either due to pseudo symmetries in physical space or intrinsic in certain phasing procedures such as single-isomorphous replacement (SIR) and single-wavelength anomalous diffraction (SAD) in protein crystallography.
ii)Phase ambiguities can be divided into two categories, i.e. the translational phase ambiguity and the enantiomorphous phase ambiguity.
iii)A set of modified Sayre equations in n-dimensional space (n≥4) has been set up for breaking the translational phase ambiguity in diffraction analysis of incommensurately modulated structures and composite structures. This led to the establishment of the ab initio determination of incommensurately modulated structures and composite structures without relying on any assumed models. The implementation is carried out by the program DIMS/VEC released in 2000, of which more than 1000 copies have been distributed in 65 countries/areas on the world.
iv)A direct-method probability formula has been derived for breaking the enantiomorphous phase ambiguity intrinsic to protein SAD/SIR data. This led to the direct-method SAD/SIR phasing of proteins, which has been proved more efficient than procedures without using direct methods. The implementation is carried out by the program OASIS, which has been released in 2000 and upgraded with significant modifications in 2005. Since April 2005 more than 300 copies of OASIS have been distributed internationally. Laboratories of protein crystallography in mainland China, France, Japan, Taiwan, UK and USA have reported works on applying OASIS to difficult SAD phasing in solving protein structures.
