Energetics of the disulfide bridge: An ab initio study

The energetics of the χ χ 3 χ portion of the disulfide bridge have been obtained from an ab initio study of diethyl disulfide. Calculations at the 3‐21G* level were done on relaxed structures at every ∼ 30° in χ and χ , and the additional energies for small Δχ 3 were obtained. Complete E (χ , χ ) and χ (χ , χ ) maps were computed from Fourier series expansions. These results have been used to calculate the energetics of 92 disulfide bridges in known protein structures, and to compare ab initio and molecular mechanics energies for some observed and predicted bridges. The differences found in relative energies and in χ values suggest that present energy functions give a limited description of the structural and energetic properties of the disulfide bridge.