De novo design of ligands for metal separation. Annual progress report, September 15, 1996--September 14, 1997

'The specific aim of this report is to parameterize force field to reproduce geometries and relative energetics of metal-ligand complexes for cesium, strontium, plutonium, uranium, americium and other relevent alkali, transition, lanthanide and actinide metals. As an initial attempt to examine parametrization, Dr. Yasuo Takeuchi has examined parameters for iron in combination with the molecular mechanics force field. The authors realize that most of the current ad hoc methodogies used to model metal interactions in the past do not have a firm theoretical foundation for modeling the d and f orbitals. They have, therefore, started a collaboration with Prof. Anders Carlsson of the Department of Physics to provide a theoretically correct functional form for the metal force field. Prof. Carlsson has an extensive track record in the derivation of the form of angular force fields from analysis of the quantum-mechanical electronic structure. His most important related works have treated the angular forces around transition-metal (TM) atoms in an aluminum host, the angular forces in elemental bcc transition metals, and the origins of angular and torsional forces in well-bonded s-p systems. They propose to apply the basic ideas of these calculations to developing force laws for transition metal ions in biomolecules. Of particular relevance to the proposed work is his study analyzing angular forces around transition metal (TM) atoms embedded in an aluminum host. Such TM atoms have a profound effect on the host structure, often entirely reassembling the host structure in order to satisfy the angular bonding constraints around the TM atoms. For example, at a concentration of only 1 {approximately} TM to 12 {approximately} Al, the transition metals Mn, Mo, Tc, W, and Re form the Al{sup 12}W structure, in which the underlying fcc aluminum lattice is disassembled and reassembled into icosahedra which surround the transition-metal atoms. The Al{sup 12}W structure is a body-centered cubic arrangement of such icosahedra. This behavior is analogous to that of several transition metals in proteins and other potential hosts, for example the formation of square-planar or Jahn-teller distorted octahedral structure by Cu{sup 2+} ions in many proteins. In both cases, the transition metal atom or ion has strong preferences regarding its angular environment. Of course, other effects, such as steric constraints on the ligands, are also important and dominate in some cases.