S. Dahaoui et al., CCD charge density study on crystals with large unit cell parameters: The case of hexagonal L-cystine, J PHYS CH A, 103(31), 1999, pp. 6240-6250
The electron density of L-cystine has been analyzed using 110 K single-crys
tal Mo Ka X-ray diffraction data to a resolution of (sin theta/lambda)(max)
= 1.123 Angstrom(-1) with a CCD area detector. Due to the large c-paramete
r (55.9 Angstrom), a discussion is made for choosing the best experimental
data collection strategy and data reduction. A multipolar pseudo-atom densi
ty model was fitted against the 2309 observed data with I > 3 sigma(I), [R(
F) = 0.014, Rw(F) = 0.019, S = 0.73]. The deformation density distribution
and topological analysis of charge density clearly reveals disulfide bridge
characteristic features and sulfur lone pair electron regions which valida
te high-level ab initio calculations. The valence shell charge concentratio
n (VSCC) suggests sp(3) hybridization of sulfur atoms.