Theoretical and crystallographic data investigations
of noncovalent S***O interactions

Abstract Weak S***O bonding, a specific noncovalent
interaction, plays crucial roles in fields as diverse as
molecular recognition, crystal engineering, and biological
systems. This article presents an ab initio investigation of a
series of dimeric complexes formed between formaldehyde
and several sulfur-containing molecules as electron
accepters. The bond-length change, interaction energy,
topological property of the electron density, and charge
transfer of these S***O bonds have been systematically
investigated. Moreover, a comprehensive search for nonbonded
S***O interactions in proteins was also performed. It
was found that the O atom shows a strong intrinsic tendency
to approach S from the backside of the R–S bond (in
the rs* direction); the S atom tends to approach the O atom
either from the orientation of the lone pair of O (in the no
direction) or from the vertical direction (in the po direction).
Besides, the linearity of this interaction was further
substantiated by the statistical study. As suggested by the
results presented in this study, S***O contacts may control
protein structures to some extent and the unique directional
properties of S***O interactions could be applied in supermolecular
assembly and biological design.