| Autor: |
Vazquez de Vasquez MG; Department of Chemistry & Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States., Wellen Rudd BA; Department of Chemistry, Ohio Wesleyan University, Delaware, Ohio 43015, United States., Baer MD; Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Beasley EE; Department of Chemistry & Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States., Allen HC; Department of Chemistry & Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States. |
| Abstrakt: |
The binding of group II metal cations such as Ca 2+ and Mg 2+ has been largely categorized as electrostatic or ionic using carboxylate symmetric and asymmetric stretching frequency assignments that have been historically used with little regard for the solvation environment of aqueous solutions. However, given the importance of these cations and their binding mechanisms related to biological function and in revealing surface enrichment factors for ocean to marine aerosol transfer, it is imperative that a deeper understanding be sought to include hydration effects. Here, infrared reflection-absorption and Raman spectra for surface and solution phase carboxylate binding information, respectively, are compared against bare (unbound) carboxylate and bidentate Zn 2+ :carboxylate spectral signatures. Spectral non-coincidence effect analysis, temperature studies, and spectral and potential of mean force calculations result in a concise interpretation of binding motifs that include the role of mediating water molecules, that is, contact and solvent-shared ion pairs. Calcium directly binds to the carboxylate group in contact ion pairs where magnesium rarely does. Moreover, we reveal the dominance of the solvent-shared ion pair of magnesium with carboxylate at the air-water interface and in solution. |
