Reactions of dl-homocystine and 3,3′-dithiodipropionic acid with Pd(II) in aqueous hydrochloric solutions. Part II: Kinetics and mechanistic investigations

Palladium(II) Ion Mediated Disulfide/Thiolate Interconversion: Predicting the Disulfide Group State from First Principles

“…We thus believe the expectation of disproportionation to be proportional to the magnitude of Δδ. The largest Δδ is predicted for the dl -homocystine S,S′-binuclear complex making it least stable among other complexes studied what is in accordance with experiment . Therefore, we expect the S,S′-binuclear disulfide complex with the nonheterolysis-like charge redistribution to be nonreactive to solvent, while the reactivity of thiolates with the heterolysis-like bond will depend on whether the bond is open or closed for nucleophilic substitution.…”

“…However, disproportionation of metal complexes of dl -homocystine and 3,3′-dithiodipropionic acid has been observed in experiments. According to EXAFS, the respective disproportionation products are the S-coordinated thiolate and S -sulfinic acid complexes. With experimental and theoretical findings, we conclude the S,S′-coordination to be requisite for disproportionation, and disulfide bond cleavage is associated with irreversible hydrolysis of the complex.…”

“…Spectrophotometric titrations, performed earlier, indicate substantially different interconversion products, given the original structural similarity of all four disulfides. − We believe this effect is specifically due to the presence of Pd 2+ metal ion, which mediates different RSSR/RSH interconversion mechanisms for different disulfides. Indeed, both l -cystine and cystamine form stable S,N′-binuclear and S,S′,N,N′-tetranuclear complexes without cleavage of the disulfide bond. , In opposite, in the interconversion of dl -homocystine and 3,3′-dithiodipropionic acid, which are homologues of l -cystine, the S–S bond undergoes disproportionation under the same conditions.…”

Interaction of Pt(II) and Au(III) with organic disulfides in hydrochloric aqueous solution

“…We have previously reported no disulfide bond cleavage takes place during the stepwise complex formation of L-cystine (H 4 CysS 2+ ) [13,14] and cystamine (H 2 Cyst 2+ ) [15] with Pd(II) in hydrochloric acid solutions. On the other hand, we have reported irreversible disproportionation takes place during the interaction of homocystine (H 4 hCysS 2+ ) and 3,3'-dithiodipropionic acid (H 2 DTDPA) [16] with Pd 2+ yielding sulfinic (RS(O 2 H)M) and thiol (RSM) complexes. This study extends the field of previous studies under similar conditions.…”

Platinum(II)‐mediated disulfide/thiolate interconversion in organic disulfides: Density functional theory thermodynamic study

“…DFT calculations predicted that the formation of S,S 0 -binuclear complexes is a critical intermediate step for determining reaction pathways. The products of these reactions in aqueous solutions are thiolate and sulfinic acid complexes of Pd(II) [17][18][19][20].…”