Imidazolium silanethiolates relevant to the active site of cysteine proteases. A cooperative effect in a chain of NH+⋯S− hydrogen bonds

Abstract

Three imidazolium silanethiolates relevant to the active site of cysteine proteases have been synthesized and investigated by X-ray diffraction, IR spectroscopy and computational methods. As indicated by crystallographic and FT-IR data in the solid state, the transfer of proton from thiol to imidazole takes place and a thiolato–imidazolium ion pair is formed. The FT-IR spectra of crystalline imidazolium silanethiolates exhibit intense continua characteristic for systems containing highly polarizable protons. DFT and ab initio HF calculations confirm the transfer of proton and prove the cooperativity of hydrogen bonds in the studied systems.