The S–H⋯N versus O–H⋯N hydrogen bonding in the ammonia complexes with CH3OH and CH3SH

Hydrogen bond interactions between thioethers and amides: A joint rotational spectroscopic and theoretical study of the formamide⋯dimethyl sulfide adduct

The rotational spectrum of the binary adduct of formamide (HCONH₂) with dimethyl sulfide (DMS) has been investigated employing cavity-based Fourier transform microwave spectroscopy combined with theoretical computations. Experimentally, only one isomer of the adduct was unambiguously observed and assigned according to the theoretically predicted spectroscopic parameters, and its rotational spectrum displays the hyperfine splittings associated with the ¹⁴N nuclear quadrupole coupling effect. The observed isomer exhibits C_s symmetry, such that the ∠CSC angle of the DMS subunit is bisected by the ab-plane of the HCONH₂ moiety. The two moieties in the detected isomer are connected via one primary NH···S and two secondary CH···O hydrogen bonds. Quantum theory of atoms in molecules (QTAIM), non-covalent interaction (NCI), natural bond orbital (NBO) and symmetry-adapted perturbation theory (SAPT) approaches were utilized for characterizing the intermolecular interactions occurring in the titled adduct. Additionally, the adduct of HCONH₂ with dimethyl ether (DME) was also theoretically investigated to compare the difference in structure and energy characteristics between the NH···S and NH···O hydrogen bonds.

Impacts of noncovalent interactions involving sulfur atoms on protein stability, structure, folding, and bioactivity

This review discusses the various types of noncovalent interactions in which sulfur atoms participate and their effects on protein stability, structure, folding and bioactivity. Current approaches and recommendations for modelling these noncovalent interactions (in terms of both geometries and interaction energies) are highlighted.

Observation of an Unusually Large IR Red-Shift in an Unconventional S-H···S Hydrogen-Bond

The S-H···S non-covalent interaction is generally known as an extremely unconventional weak hydrogen-bond in the literature. The present gas-phase spectroscopic investigation shows that the S-H···S hydrogen-bond can be as strong as any conventional hydrogen-bond in terms of the IR red-shift in the stretching frequency of the hydrogen-bond donor group. Herein, the strength of the S-H···S hydrogen-bond has been determined by measuring the red-shift (∼150 cm^-1) of the S-H stretching frequency in a model complex of 2-chlorothiophenol and dimethyl sulfide using isolated gas-phase IR spectroscopy coupled with quantum chemistry calculations. The observation of an unusually large IR red-shift in the S-H···S hydrogen-bond is explained in terms of the presence of a significant amount of charge-transfer interactions in addition to the usual electrostatic interactions. The existence of ∼750 S-H···S interactions between the cysteine and methionine residues in 642 protein structures determined from an extensive Protein Data Bank analysis also indicates that this interaction is important for the structures of proteins.

Participation of S and Se in hydrogen and chalcogen bonds

The heavier chalcogen atoms S, Se, and Te can each participate in a range of different noncovalent interactions. They can serve as both proton donor and acceptor in H-bonds. Each atom can also act as electron acceptor in a chalcogen bond.

The infrared study of fluoroform + methyl fluoride mixtures in argon and nitrogen matrices. Evidence of nonlinear blue-shifting complex formation

The FTIR spectra of fluoroform + methyl fluoride mixtures trapped in argon and nitrogen matrices are studied at T~10-30 K. Spectroscopic changes observed in the region of the CH stretching mode of fluoroform are typical for weak blue shifting H - bonds of CH⋯F type. The degeneracy lifting effect found on E - type bands of fluoroform interacted with methyl fluoride suggests the complex formation of a nonlinear form. The experimental results are confirmed by ab initio calculations of fluoroform + methyl fluoride based on the second order Møller-Plesset theory of perturbations utilizing advanced basis set. Nonlinear complexes are stabilized by the basic CH⋯F interaction and additionally by van der Waals-type CD⋯FC contacts between deuterated methyl fluoride and fluoroform.

Thiols as Hydrogen Bond Acceptors and Donors: Spectroscopy of 2-Phenylethanethiol Complexes

Evidence and understanding of sulfur-centered hydrogen bonding, especially where the donor is a thiol, lags far behind that for conventional OH interactions. To help address this deficiency, conformer specific IR spectra of 2-phenylethanethiol (PET) and associated 1:1 solvent complexes have been measured in SH, OH, and CH stretch regions using resonant-two-photon-ionization (R2PI) and IR-UV ion dip spectroscopic techniques. The aromatic and aliphatic CH stretch regions show signature differences between anti and gauche conformers. Supported by ab initio calculations, a PET-water cluster with an OH···S arrangement and a PET-diethyl ether cluster expressing an SH···O interaction were identified. The SH stretch band of the SH···O complex is red-shifted and undergoes significant intensity enhancement compared to the bare molecule, which is characteristic of hydrogen bonding. These findings offer insight into the nature of the thiol functional group as a potential hydrogen bond donor and acceptor.

Formaldoxime hydrogen bonded complexes with ammonia and hydrogen chloride

An infrared spectroscopic and MP2/6-311++G(2d,2p) study of hydrogen bonded complexes of formaldoxime with ammonia and hydrogen chloride trapped in solid argon matrices is reported. Both 1:1 and 1:2 complexes between formaldoxime and ammonia, hydrogen chloride have been identified in the CH2NOH/NH3/Ar, CH2NOH/HCl/Ar matrices, respectively, their structures were determined by comparison of the spectra with the results of calculations. In the 1:1 complexes present in the argon matrices the OH group of formaldoxime acts as a proton donor for ammonia and the nitrogen atom acts as a proton acceptor for hydrogen chloride. In the 1:2 complexes ammonia or hydrogen chloride dimers interact both with the OH group and the nitrogen atom of CH2NOH to form seven membered cyclic structures stabilized by three hydrogen bonds. The theoretical spectra generally agree well with the experimental ones, but they seriously underestimate the shift of the OH stretch for the 1:1 CH2NOH⋯NH3 complex.

Complexes containing CO2and SO2. Mixed dimers, trimers and tetramers

Two stable minima for the 1 : 1 heterodimer of CO₂ : SO₂, both bound by about 2 kcal mol⁻¹. Binding is dominated by charge transfer from O lone pairs of SO₂to CO π* antibonding orbitals.