ABSTRACT
(Per)thionitrite (SNO- /SSNO- ) intermediates play vital roles in modulating nitric oxide (NO) and hydrogen sulfide (H2 S) dependent bio-signalling processes. Whilst the previous preparations of such intermediates involved reactive H2 S/HS- or sulfane sulfur (S0 ) species, the present report reveals that relatively stable thiocarbonyl compounds (such as carbon disulfide (CS2 ), thiocarbamate, thioacetic acid, and thioacetate) react with nitrite anion to yield SNO- /SSNO- . For instance, the reaction of CS2 and nitrite anion (NO2 - ) under ambient condition affords CO2 and SNO- /SSNO- . A detailed investigation involving UV/Vis, FTIR, HRMS, and multinuclear NMR studies confirm the formation of SNO- /SSNO- , which are proposed to form through an initial nucleophilic attack by nitrite anion followed by a transnitrosation step. Notably, reactions of CS2 and nitrite in the presence of thiol RSH show the formation of organic polysulfides R-Sn -R, thereby illustrating that the thiocarbonyls are capable of influencing the pool of bioavailable sulfane sulfurs. Furthermore, the availability of both NO2 - and thiocarbonyl motifs in the biological context hints at their synergistic metal-free activations leading to the generation of NO gas and various reactive sulfur species via SNO- /SSNO- .
ABSTRACT
Although nitrite-to-NO transformation at various transition metals including Fe and Cu are relatively well explored, examples of such a reaction at the redox-inactive zinc(II) site are limited. The present report aims to gain insights into the reactivity of nitrite anions, nitrous acid (HONO), and organonitrite (RONO) at a dizinc(II) site. A phenolate-bridged dizinc(II)-aqua complex [LH ZnII (OH2 )]2 (ClO4 )2 (1H -Aq, where LH =tridentate N,N,O-donor monoanionic ligand) is illustrated to react with t BuONO to provide a metastable arene-nitrosonium charge-transfer complex 2H . UV-vis, FTIR, multinuclear NMR, and elemental analyses suggests the presence of a 2 : 1 arene-nitrosonium moiety. Furthermore, the reactivity of a structurally characterized zinc(II)-nitrite complex [LH ZnII (ONO)]2 (1H -ONO) with a proton-source demonstrates HONO reactivity at the dizinc(II) site. Reactivity of both RONO (R=alkyl/H) at the phenolate-bridged dizinc(II) site provides NO+ charge-transfer complex 2H . Subsequently, the reactions of 2H with exogenous reductants (such as ferrocene, thiol, phenol, and catechol) have been illustrated to generate NO. In addition, NO yielding reactivity of [LH ZnII (ONO)]2 (1H -ONO) in the presence of the above-mentioned reductants have been compared with the reactions of complex 2H . Thus, this report sheds light on the transformations of NO2 - /RONO (R=alkyl/H) to NO/NO+ at the redox-inactive zinc(II) coordination motif.
ABSTRACT
The controlled generation of hydrogen sulfide (H2S) under biologically relevant conditions is of paramount importance due to therapeutic interests. Via exploring the reactivity of a structurally characterized phenolate-bridged dinuclear zinc(II)-aqua complex {LZnII(OH2)}2(ClO4)2 (1a) as a hydrolase model, we illustrate in this report that complex 1a readily hydrolyses CS2 in the presence of Et3N to afford H2S. In contrast, penta-coordinated [ZnII] sites in dinuclear {(LZnII)2(µ-X)}(ClO4) complexes (7, X = OAc; 8, X = dimethylpyrazolyl) do not mediate CS2 hydrolysis in the presence of externally added water and Et3N presumably due to the unavailability of a coordination site for water at the [ZnII] centers. Moreover, [ZnII]-OH sites present in the isolated tetranuclear zinc(II) complex {(LZnII)2(µ-OH)}2(ClO4)2 (4) react with CS2, thereby suggesting that the [ZnII]-OH site serves as the active nucleophile. Furthermore, mass spectrometric analyses on the reaction mixture consisting of 1a/Et3N and CS2 suggest the involvement of zinc(II)-thiocarbonate (3a) and COS species, thereby providing mechanistic insights into CS2 hydrolysis mediated by the dinuclear [ZnII] hydrolase model complex 1a.
