³⁴S Isotope Effect on Sulfate Ester Hydrolysis:  Mechanistic Implications

Abstract

In this communication, we report the first determination of 34S kinetic isotope effects (KIEs) for the hydrolysis of sulfate monoesters. The method involves the conversion of the inorganic sulfate, acquired at partial extent of reaction, to SO2, followed by isotope ratio determination by mass spectrometry. The KIEs determined for p-nitrophenyl sulfate and p-acetylphenyl sulfate are 1.0154 (+/-0.0002) and 1.0172 (+/-0.0003), respectively. These results, together with previous peripheral 18O KIE values, are inconsistent with an associative mechanism. The isotope effect method we report should also prove useful for studying the mechanism of other sulfuryl group transfers, including sulfatase and sulfotransferase reactions, as well as sulfate hydrolyses under other conditions.

32S/34S isotope fractionation in plant sulphur metabolism

“…By contrast, sulphate ester hydrolysis fractionates against 34 S. Using phenyl phosphosulphate as a model for PAPS, the limiting step has been shown to be cleavage of the S-O bond, suggesting that the S isotope fractionation during sulphate group cleavage is large (Benkovic & Hevey, 1970). The acid hydrolysis of aryl sulphate monoesters has been shown to fractionate against 34 S by 15-18& (Burlingham et al, 2003). This value is probably at the upper limit of that which would be expected for S-O cleavage, but sulphate hydrolysis in metabolism certainly tends to enrich in 34 S the sulphated compounds left behind.…”

Sulfatases: Structure, Mechanism, Biological Activity, Inhibition, and Synthetic Utility

“…Recently, the uncatalyzed hydrolysis of sulfate esters has also been found to be more dissociative than associative in nature 38. In a dissociative transition state for sulfate ester hydrolysis, the bond forming between the incoming nucleophile and the sulfur atom would be expected to be weak, whereas a more pronounced bond dissociation between the sulfuryl group and the leaving group would result in the accumulation of negative charge on the phenolate oxygen atom.…”

Insights into past ocean proxies from micron-scale mapping of sulfur species in carbonates

“…Information about these individual components is lost during traditional CAS acid extraction. Standard CAS protocols extract the organosulfate component, which undergoes hydrolysis in acidic conditions-a process that can also give rise to a sulfur isotopic fractionation (Burlingham et al, 2003). Thus, complex micron-scale speciation of sulfate within and between individual samples may also contribute to the unexpectedly large scatter usually observed in bulk δ 34 S CAS data (Fike et al, 2015).…”