A theoretical assessment of the primary hydration shell formation for calcium pyrophosphate

Abstract

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.