A quantum mechanical analysis of an experimental ensemble comprising 128 conformers of the protein ubiquitin has been carried out with the aid of LMO-SCF-COSMO calculations. The permanent dipole moment of the protein fluctuates in the range from 131 to 283 D while the energy-weighted average dipole has a magnitude of 197 D. The HOMO-LUMO energy gap of the conformational ensemble ranges from 7.389 to 8.397 eV and appears to being affected mainly by fluctuations in the HOMO energy. An inspection of the frontier orbitals of the IN conformers indicates that their localization is not affected by the protein dynamics. (c) 2005 Elsevier B.V. All rights reserved.