LAUSR

Abstract The hydration behaviour of calcium pyrophosphate (CPP) was investigated via Density Functional Quantum mechanical calculations (DFT), carried out on isolated monomeric CPP-water complexes. Formation free energies for the first hydration shell shows that hydrates from the di- to octa-hydrate are formed spontaneously whereas the higher hydrates are unstable when hydration occurs via a concerted mechanism (instantaneous hydration). For this mechanism, the most stable hydrate consist of four water molecules which allows for a balance between repulsive steric crowding interactions in the primary hydration shell and CPP-water attractive interactions in addition to water-water attractive interactions. However, step-wise hydration favours the di- and tetra-hydrates, the former being of greatest stability. The results presented in this novel quantum mechanical study of CPP-hydration, could hold the answer for destabilizing CPP crystals in the joints of rheumatic arthritis patients, thereby facilitating a solution/ treatment for pseudo-gout.