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

Abstract

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, 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 validate high-level ab initio calculations. The valence shell charge concentration (VSCC) suggests sp3 hybridization of sulfur atoms.