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The classical force field, which is compatible with the Amber force field 99SB, has been obtained for the interaction of Cu(II) with monomer and dimers of amyloid-? peptides using the coordination where Cu(II) is bound to His6, His13 (or His14), and Asp1 with distorted planar geometry. The newly developed force field and molecular dynamics simulation were employed to study the impact of Cu(II) binding on structures and dynamics of A? 42 monomer and dimers. It was shown that in the presence of Cu(II) the ? content of monomer is reduced substantially compared with the wild-type A? 42 suggesting that, in accord with experiments, metal ions facilitate formation of amorphous aggregates rather than amyloid fibrils with cross-? structures. In addition, one possible mechanism for amorphous assembly is that the Asp23-Lys28 salt bridge, which plays a crucial role in ? sheet formation, becomes more flexible upon copper ion binding to the A? N-terminus. The simulation of dimers was conducted with the Cu(II)/A? stoichiometric ratios of 1:1 and 1:2. For the 1:1 ratio Cu(II) delays the A? dimerization process as observed in a number of experiments. The mechanism underlying this phenomenon is associated with slow formation of interchain salt bridges in dimer as well as with decreased hydrophobicity of monomer upon Cu-binding.