Since we don’t have seminar, you get a paper review
I had this masterful plan to write about today’s seminar from Dr. Tobias (UC Irvine), including a review of the professor’s work, direct quotes from lunch with him, and notes from his talk at the end of the day.
Unfortunately weather has kept the speaker away, so instead I think I’ll just review a recent paper!
Fortunately for us, Dr. Tobias was a co-author on a recent paper in Science discussing specific ion effects in solution. The paper is a minireview of recent literature that goes against the conventional wisdom of what salts are doing in solution. The seminal work on salt’s action in a solution was done in the late 1800’s by Franz Hofmeister. The common thought is that adding salts to a solution causes widespread changes in the structure of water (water’s rapidly shifting morass of hydrogen bonds is what keeps it liquid rather than gas at room temperature - adding salt is thought to influence this network on a large scale).
Computational chemistry experiments, however, have indicated that salt effects are more local, and only influence water molecules nearby the ions of the salt. Other biophysical measurements also seem to call the long-range bulk model of salt effects into question. Experiments also indicate that certain ions may concentrate at the interface between two solvents (or at the air/solvent interface), while others stay away from the interface.
This work is interesting, both from purely theoretical as well as practical standpoints. Theoretically, it demonstrates that the simplistic view of salts based on the Hofmeister series smooths over some details which may be minor but significant. This has practical applications in the field of crystallography, where scientists often use solvents with varying salts and salt concentrations to carefully induce their proteins to crystallize. This crystallization process is poorly understood, and it’s almost certain that these sorts of specific ion effects are at least partially involved.
Tobias, D.J., Hemminger, J.C. (2008). CHEMISTRY: Getting Specific About Specific Ion Effects. Science, 319(5867), 1197-1198. DOI: 10.1126/science.1152799
