CCD Charge Density Study on Crystals with Large Unit Cell Parameters: The Case of Hexagonal l -Cystine

The electron density of l -cystine has been analyzed using 110 K single-crystal Mo Kα X-ray diffraction data to a resolution of (sin θ/λ) max = 1.123 Å -1 with a CCD area detector. Due to the large c -parameter (55.9 Å), a discussion is made for choosing the best experimental data collection strategy and data reduction. A multipolar pseudo-atom density model was fitted against the 2309 observed data with I > 3σ( I ), [ R ( F ) = 0.014, R W ( 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 validate high-level ab initio calculations. The valence shell charge concentration (VSCC) suggests sp 3 hybridization of sulfur atoms.