  Gravitational settling of 22Ne in cooling white dwarfs can affect the outcome
of thermonuclear supernovae. We investigate how the supernova energetics and
nucleosynthesis are in turn influenced by this process. We use realistic
chemical profiles derived from state-of-the-art white dwarf cooling sequences.
The cooling sequences provide a link between the white dwarf chemical structure
and the age of the supernova progenitor system. The cooling sequence of a 1
M_sun white dwarf was computed until freezing using an up-to-date stellar
evolutionary code. We computed explosions of both Chandrasekhar mass and
sub-Chandrasekhar mass white dwarfs, assuming spherical symmetry and neglecting
convective mixing during the pre-supernova carbon simmering phase to maximize
the effects of chemical separation. Neither gravitational settling of 22Ne nor
chemical differentiation of 12C and 16O have an appreciable impact on the
properties of Type Ia supernovae, unless there is a direct dependence of the
flame properties (density of transition from deflagration to detonation) on the
chemical composition. At a fixed transition density, the maximum variation in
the supernova magnitude obtained from progenitors of different ages is ~0.06
magnitudes, and even assuming an unrealistically large diffusion coefficient of
22Ne it would be less than ~0.09 mag. However, if the transition density
depends on the chemical composition (all other things being equal) the oldest
SNIa can be as much as 0.4 magnitudes brighter than the youngest ones (in our
models the age difference is 7.4 Gyr). In addition, our results show that 22Ne
sedimentation cannot be invoked to account for the formation of a central core
of stable neutron-rich Fe-group nuclei in the ejecta of sub-Chandrasekhar
models, as required by observations of Type Ia supernovae.
