The Gas Phase Acidities of the Sulfanes H2Sn (n = 1–4)

Inorganic Polysulfides in Solution: Structural Properties and Conformational Isomerism

We present a comprehensive theoretical examination of the structural properties of dianionic polysulfides [Sn]2- (n = 2-6), their conjugated monoacids [HSn]- (n = 2-6), and a selection of 1e--oxidized radical anions [Sn]•- (n = 2-4), in aqueous and dimethyl sulfoxide (DMSO) solutions. We investigated the structures and stabilities of various conformational isomers within these families of compounds by employing Quantum Mechanics-Molecular Mechanics (QM-MM) Molecular Dynamics (MD) simulations. The explicit inclusion of solvent molecules in the calculations revealed stable conformational structures that were previously unreported and might have appreciable concentrations in real systems. The interconversions between the isomeric structures proceed on the order of hundreds of picoseconds and are energetically similar to the isomerization processes in substituted cyclohexanes. We also conducted a detailed analysis of the stability of different isomers of the radical anion [S4]•- in solution. Our findings highlight the significant influence of the solvent on the isomerizations, a result that could be particularly relevant for enhancing the performance of metal-sulfur batteries.

Synthesis, Spectroscopic, and Structural Characterization of Organyl Disulfanides and a Tetrasulfanide

Various room-temperature-stable monoorganylpolysulfanides of the form [X][RS_n] (X = [PPh₄]⁺, [PNP]⁺, [NEt₄]⁺; R = Ph, t-Bu, n ≥ 2) were synthesized in a simple and versatile one-step process starting from sodium thiolates and elemental sulfur. The compounds were characterized by X-ray crystal structure analysis, NMR spectroscopy, microelemental analysis, and electrospray mass ionization spectrometry including collision-induced dissociation experiments. While these salts are well-defined species as crystals, they undergo complex equilibria in solution. In one case, compounds ranging from n = 1-8 have been observed in solution. Structural features, dynamics in solution, as well as thermochromic properties of one of the compounds, [PPh₄][PhS₂], are investigated in detail by temperature- and pressure-dependent X-ray crystal structure analysis. The experimental data are complemented by periodic boundary density functional theory calculations on the crystal structures, as well as energy decomposition analyses.

Power Law Distribution Concerning Absolute Free Energies of Linear Sulfur Chains, Polythiazyls, Polyisoprenes, Linear trans-Polyenes, and Polyynes

After quantum calculations of absolute free energies of polyatomic sulfur derivatives or hydrocarbon oligomer compounds, we have studied the variations of G _n as a function of the number of repeating units n (sulfur atoms or hydrocarbon units, n = 2 to about 60), and observed that these values can be correlated by (a) a nearly perfect linear relationship, G _n = An + B (A and B, constants), with a high accuracy which enables an extrapolation for higher values of n, and (b) a power law:, δ G = G _n/ n - G_{( n-1)} /( n - 1) = C/ n ^d ( C and d, constants). From comparison of variations of the C-C bond lengths, we show that the conjugation of trans-polyenes (up to C₆₀H₆₂) is more important than for polyynes (up to C₆₀H₂).

Chemical Biology of H2S Signaling through Persulfidation

Signaling by H2S is proposed to occur via persulfidation, a posttranslational modification of cysteine residues (RSH) to persulfides (RSSH). Persulfidation provides a framework for understanding the physiological and pharmacological effects of H2S. Due to the inherent instability of persulfides, their chemistry is understudied. In this review, we discuss the biologically relevant chemistry of H2S and the enzymatic routes for its production and oxidation. We cover the chemical biology of persulfides and the chemical probes for detecting them. We conclude by discussing the roles ascribed to protein persulfidation in cell signaling pathways.

Encapsulation and convex-face thiozonolysis of triatomic sulfur (S(3)) with carbon nanotubes

Nanotubes are a class of host cavities increasingly used to encapsulate unstable molecules, yet none have been exploited to host reactive sulfur species, such as thiozone (S(3)). In this paper, density functional theory and (ONIOM) calculations were used to compute single-walled carbon nanotube (SWNT)-thiozone combinations for the inclusion of S(3) into the hollow nanotube space and to rationalize when 1,2,3-thiozonide formation can take place. Nanotube diameter selectivity for the isomerization of the C(2v) form of S(3) to the D(3h) form proved to be elusive. Acyclic C(2v) S(3) was ~6 kcal/mol more stable than cyclic D(3h) S(3) whether it was free or encapsulated within an SWNT. 1,2,3-Thiozonide formation took place on the convex side of nanotubes of low tube radii, such as the armchair (4,4) and (5,5) SWNTs. In terms of the reaction mode of C(2v) S(3), the 1,3-dipolar addition reaction was preferred compared with the [2 + 2] cycloaddition and chelotrope paths.

Entering the leinamycin rearrangement via 2-(trimethylsilyl)ethyl sulfoxides

Attack of cellular thiols on the antitumor natural product leinamycin is believed to generate a sulfenate intermediate that undergoes subsequent rearrangement to a DNA-alkylating episulfonium ion. Here, 2-(trimethylsilyl)ethyl sulfoxides were employed in a fluoride-triggered generation of sulfenate anions related to the putative leinamycin-sulfenate. The resulting sulfenates enter smoothly into a leinamycin-type rearrangement reaction to afford an episulfonium ion alkylating agent. The results provide evidence that the sulfenate ion is, indeed, a competent intermediate in the leinamycin rearrangement. Further, the molecules examined here may provide a foundation for the design of functional leinamycin analogues that bypass the unstable and synthetically challenging 1,2-dithiolan-3-one 1-oxide moiety found in the natural product.

Generation of reactive oxygen species by a persulfide (BnSSH)

Hydropersulfides (RS(x)SH) have been implicated as important intermediates in the cell-killing action of the anticancer natural products leinamycin and varacin. It has been suggested that persulfides can mediate the conversion of molecular oxygen to reactive oxygen species (O2*-, H2O2, and HO*). Here, experiments with synthetic benzyl hydrodisulfide (BnSSH) provide direct evidence that persulfides readily decompose to produce reactive oxygen species under physiologically relevant conditions.

Polysulfide anions II: structure and vibrational spectra of the S4(2-) and S5(2-) anions. Influence of the cations on bond length, valence, and torsion angle

The influence of the cations on bond length, valence, and torsion angle of S4(2-) and S5(2-) anions was examined in a series of solid alkali tetra- and pentasulfides by relating their Raman spectra to their known X-ray structures through a force-field analysis. The IR and Raman spectra of BaS4.H2O and the Raman spectra of (NH4)2S4.nNH3, gamma-Na2S4, and delta-Na2S5 are presented. The similarity of spectra of gamma-Na2S4 with those of BaS4.H2O suggests similar structures of the S4(2-) anions in these two compounds with a torsion angle smaller than 90 degrees. The variations of SS bond length, SSS valence angle, and dihedral angle of Sn2- anions are related to the polarization of the lone pair and electronic charge of the anion by the electric field of the cations. A correlation between the torsion angle and the SSS valence angle is shown as that previously reported between the length of the bond around which the torsion takes place and the dihedral angle value. These geometry changes are explained by the hyperconjugation concept and the electron long-pair repulsion.