Disulfide-Centered Hydrogen Bonding: Insights from Protein Structure Analysis and IR-UV Double Resonance Spectroscopy

Despite the importance of disulfide bonds in proteins, direct experimental characterization of noncovalent interactions involving their sulfur atoms, particularly sulfur-centered hydrogen bonds (H-bonds), remains underexplored. Here, we present an integrated study combining Protein Data Bank (PDB) analysis, quantum chemical calculations, and gas-phase vibrational spectroscopy. PDB screening revealed disulfide bonds in ∼20% of protein structures, with nearly 20 000 potential O-H···S and N-H···S H-bonds. The O-H···S H-bonds are shorter and more directional than the N-H···S H-bonds, consistent with the topological and energetic analyses of model systems. Mass-selective electronic and IR spectroscopy on the jet-cooled p-cresol-dimethyl disulfide (pCR-DMDS) complex confirmed disulfide-centered H-bonds through red-shifts in S₁ → S₀ electronic transitions and O-H stretching frequencies (Δν_O-H). The experimental Δν_O-H shift and comparative analysis with other H-bond acceptors (H₂S, H₂O, and dimethylsulfide) provide benchmark data on the intrinsic strength of disulfide-centered H-bonds, crucial for refining computational models and enhancing the understanding of their role in protein structure and function.