The reaction thermodynamics of hydrogen sulfide decomposition into hydrogen and diatomic sulfur

Synthesis and antiproliferative properties of a new ceramide analog of varacin

“…For ceramide 1 , we suggest that S 3 is the reactive intermediate underlying bioactivity. Reactive sulfur species (Sato et al, 1987; Lee et al, 2002; Münchberg et al, 2007; Anwar, 2008; Nielsen et al, 2011; Czepukojc et al, 2013a; Czepukojc et al, 2013b) such as diatomic sulfur, S 2 , can arise in other polysulfanes (Abu-Yousef and Harpp, 1998; Abu-Yousef, 2006; Zysman-Colman and Harpp, 2007; Rys et al, 2008; Startsev et al, 2015). Relatedly, the antiproliferative activity of Bittman’s ceramide-disulfane conjugate, N -(4′,5′-dithiaheptanoyl)- D -erythro-ceramide, was correlated to a reduction in cellular glutathione (GSH) levels in cancer cells (Bittman et al, 2007).…”

The Reaction Mechanisms of H2S Decomposition into Hydrogen and Sulfur: Application of Classical and Biological Thermodynamics

“…Of the special interest is the diatomic sulfur in the ground triplet state X 3 Σ -g , which can be obtained in the gas phase only (?) on the surface of metal catalysts via H 2 S decomposition [7][8][9]20]. The standard thermodynamical reference data [18] are concerned with the metastable single state a 1 ∆ g of this molecule (Table 1).…”

“…Reversibility of the reaction (1) means that process runs equally well forwards and backwards and is always in a near equilibrium state. In accordance with the rule of spin conservation, diatomic sulfur formed in the reaction (1) is in the metastable singlet state which does not convert into the ground triplet state even at high temperature and in the presence of metal catalysts [7][8][9]: 1 S 2 (gas) ≠ 3 S 2 (gas) (2) As is well known, diatomic sulfur is isoelectronic to oxygen [10,11], therefore the S 2 ground state is a triplet X 3 Σ -g and the first exited state is a singlet a 1 ∆ g which is above the ground state by ∼4400 cm -1 (Table 1). However, unlike to singlet oxygen which is spontaneously converted into the ground triplet state [12], the diatomic singlet sulfur prefers to aggregate from the gas phase into the solid S 8 structure.…”

“…Actually, H 2 S is a stable molecule at ambient conditions and exists for a long period of time in the absence of action of external forces. However, on passing H 2 S over metal catalysts at room temperature, two reaction products are observed which are hydrogen and gaseous sulfur [7][8][9]. Hence, the reaction is likely to occur at the …”

“…An unexpected, unpredictable phenomenon was observed when hydrogen sulfide was passed through metal catalysts at room temperature: along with hydrogen, diatomic gaseous sulfur was discovered as a reaction product [7][8][9]20]. Pt (111) is ∼45 kcal/mol [22], while molecular hydrogen desorbs from the surface even at 230 K [23].…”