title: Evaluation of Thiol Raman Activities and pKa Values Using Internally Referenced Raman-Based pH Titration.
abstract: Thiols, including organothiol and thiol-containing biomolecules, are among the most important classes of chemicals that are used broadly in organic synthesis, biological chemistry, and nanosciences. Thiol pKa values are key indicators of thiol reactivity and functionality. Reported herein is an internally referenced Raman-based pH titration method that enables reliable quantification of thiol pKa values for both mono- and dithiols in water. The degree of thiol ionization is monitored directly using the peak intensity of the S-H stretching feature in the 2600 cm(-1) region relative to an internal reference peak as a function of the titration solution's pH. The thiol pKa values and Raman activity relative to its internal reference were then determined by curve fitting the experimental data with equations derived on the basis of the Henderson-Hasselbalch equation. Using this Raman titration method, we determined for the first time the first and second thiol pKa values for 1,2-benzenedithiol in water. This Raman-based method is convenient to implement, and its underlying theory is easy to follow. It should therefore have broad application for thiol pKa determinations and verification.
authors.affiliation: Department of Chemistry, Mississippi State University , Starkville, Mississippi 39762, United States.
authors.forename: Nuwanthi
authors.initials: N
authors.lastname: Suwandaratne
authors.affiliation: Department of Mathematical Sciences, DePaul University , Chicago, Illinois 60604, United States.
authors.forename: Juan
authors.initials: J
authors.lastname: Hu
authors.affiliation: Department of Chemistry, Mississippi State University , Starkville, Mississippi 39762, United States.
authors.forename: Kumudu
authors.initials: K
authors.lastname: Siriwardana
authors.affiliation: Department of Chemistry, Mississippi State University , Starkville, Mississippi 39762, United States.
authors.forename: Manuel
authors.initials: M
authors.lastname: Gadogbe
authors.affiliation: Department of Chemistry, Mississippi State University , Starkville, Mississippi 39762, United States.
authors.forename: Dongmao
authors.initials: D
authors.lastname: Zhang
mesh_terms: D008956:Models, Chemical; D012995:Solubility; D013059:Spectrum Analysis, Raman; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D017186:Titrimetry / Q000379:methods
chemical_list: D013438:Sulfhydryl Compounds