Producing amyloid cross-β fibrils are one of crucial pathological signs of Alzheimer’s disease (AD) in cerebra. X-ray analysis has shown that copper ion and zinc ion are significantly concentrated in the neurophil of AD patients, which suggests that imbalances of metal ions may be related to the pathogenesis of AD. The Nt-metal ligation occurs in Cu(II)-induced Ab aggregation at mildly acidic pH. At neutral pH, however, copper ion binds to Np, the nitrogen of the histidine imidazole ring, and to deprotonated amide nitrogens or oxygen of the peptide main chain. The chelation of Cu(II) by histidine and main-chain amide groups results in soluble complexes. All geometry optimizations have been carried out by density functional theory (B3LYP) methods to study the soluble coordination complexes which contain copper ion and tetrapeptide (HHQK) of Aβ. Two coordination patterns are provided. One is N(3)O(1) which can form distorted plane square, the other is N(4)O(1) which can form distorted square prick. Six structures have been gained when hydrogen bond in molecule is considered. The populations of the atomic net charges, some frontier molecular orbitals and vibration spectrum of complexes have been investigated for the most stable structure. It is very important that the theory can agree with the experiment very well for vibration spectrum.

Key words: Alzheimer’s disease, Aβ polypeptide, soluble complex, density functional, vibration spectrum