Sulfur, Not Too Far Behind O, N, and C: SH···π Hydrogen Bond

Abstract

We report hydrogen-bonded complexes of H(2)S with indole and 3-methyl indole stabilized by the S-H...pi interaction. It is interesting to discover that although sulfur and its hydrides are known as poor hydrogen-bond donor/acceptors, sulfur is not too far behind oxygen, nitrogen, and carbon in regard to forming the pi-type hydrogen bonds. This report also extends the scope of our earlier studies from sigma-type hydrogen-bonded complexes of sulfur (O-H...S and N-H...S sigma-type hydrogen-bonded complexes) to pi-type hydrogen-bonded complexes of sulfur (S-H...pi pi-type hydrogen-bonded complexes). The experiments were carried out using the supersonic jet expansion technique, and the complexes were probed using laser-induced spectroscopy such as laser-induced fluorescence (LIF), resonant two-photon inonization (R2PI), and fluorescence dip infrared spectroscopy (FDIRS). The FDIR spectroscopy revealed that while there was no shift in the N-H stretch, the S-H stretch was red shifted by about 21 cm(-1). For the H(2)O complexes of indole and 3-methylindole, however, there was a significant red shift in the N-H stretch. These observations suggest that H(2)O forms a NH...O type complex, whereas H(2)S prefers to form a SH...pi type complex. The experimental results were complemented by ab initio calculations and energy decomposition analysis. The binding energies for both the sigma-type and pi-type hydrogen-bonded M.L complexes (M = indole and 3-methylindole; L = H(2)O and H(2)S) were calculated by extrapolating MP2 interaction energies to the complete basis set limit. The calculated M.H(2)S (sigma-type) interaction energy (2.74 kcal/mol) was considerably smaller than that of the M.H(2)S pi-type hydrogen-bonded complex (4.89 kcal/mol), which is exactly opposite of the trend found for the M.H(2)O complexes. This is consistent with the experimental observations. Comparison of the S-H...pi interaction with the other type of X-H...pi (X = C, N, and O) shows that the S-H...pi interaction is the strongest among them. In all of the pi-type HB complexes, the dispersion energy component has significant contribution to the total binding energy.

Functionally Important Aromatic–Aromatic and Sulfur−π Interactions in the D2 Dopamine Receptor

“…In addition to a lack of hydrogen atom resolution in the crystal structure, computational studies disagree whether the face of aromatic side chains preferentially interact with the lone pairs of the sulfur atom or through an SH-π interaction 47,49,50 . Our fluorination experiments are unable to distinguish between the two scenarios because both occur through an electrostatic interaction with the face of W6.48.…”

Comparison of CH···O, SH···O, Chalcogen, and Tetrel Bonds Formed by Neutral and Cationic Sulfur-Containing Compounds

“…Although its earliest conception considered only highly electronegative atoms like O, F, and N as donor and acceptors [1][2][3] , this picture has broadened considerably over recent years [4][5][6][7][8][9][10][11][12][13][14][15][16][17] . For example, despite some early resistance to the idea, the S atom is now recognized as a legitimate proton donor atom [18][19][20][21][22][23] . Also among those atoms which are now known to serve as proton donor is C, despite its nominally low electronegativity [24][25][26][27][28][29][30][31][32][33][34] .…”

Experimental Quantification of Electrostatics in X–H···π Hydrogen Bonds

“…2,7,8 Statistical analysis of the protein databank has shown that O-H···π, N-H···π, C-H···π and S-H···π interactions all occur frequently in proteins. 6,8,9 From theoretical studies it has been proposed that the electrostatic contribution to π-hydrogen bonding for different hydrogen bond donors decreases in the order of O-H ≈ S-H > N-H > C-H due to the differences in partial charges, 10,11 while the dispersion contribution decreases in the order of S-H > C-H > N-H > O-H due to trends in atomic polarizabilites (sulfur has a three times larger polarizability than oxygen and nitrogen). 10–14 …”