1. Chemical,
Biological and Radiological Sciences, Defence Science and Technology Laboratory, Porton Down, Salisbury, Wiltshire SP4 0JQ, U.K.
2. Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, U.K.
3. Centre
for Theoretical Chemistry and Physics, Institute of Natural and Mathematical
Sciences, Massey University, Auckland 0632, New Zealand
4. School
of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, U.K.