We describe the use of quantitative nuclear magnetic resonance spectroscopy (qNMR) to measure rate constants for reactions of thioesters in water. We report rate constants for the acid-catalyzed (ka), base-catalyzed (kb), and pH-independent (kw) hydrolysis] of S-methyl thioacetate, the simplest thioester, accounting rigorously for general-base catalysis and ionic strength. Beyond hydrolysis, we seek to measure rate constants of aminolysis of thioesters in aqueous solution to help access favorable conditions for covalently attaching amines to thioester-functionalized surfaces. All spectra were collected using a 1-D excitation sculpting pulse program for solvent suppression and every quantitative condition was considered before running the NMR experiment.
The thioester functional group is important in bioprocesses such as lipid biosynthesis, protein splicing, ubiquitin-like protein conjugation, and proteolytic degradation by cysteine proteases. Thioester reactions like thiol-thioester exchange have been applied extensively in native chemical ligation as a tool to produce peptide bonds as a bioconjugation technique. Understanding hydrolysis is important in these systems as it disables further reaction of thioesters.
