Laboratory for Biointerfacial Chemistry led by Dr. Halil I. Okur has been adopting innovative multidisciplinary approaches to explore chemical processes occurring at biologically relevant surfaces from lipid membrane assemblies to hydrated proteins. One current research focus is to elucidate ion – macromolecule interactions that occur in an ion-specific fashion. These specific ion effects have direct implications from cell signaling to protein fibril formation. In a recent collaborative study, a molecular level detailed answer has given to the long-lasting scientific question about how cations interact with neutral biomacromolecules.
It has been known for more than 100 years that ion identity and concentration modulate the physical properties of macromolecules. To date, substantial effort has been focused on obtaining a molecular-level understanding of specific effects for anions. By contrast, the role of cations has not been elucidated. Dr. Okur emphasized that in this work, we showed although all cations are on average depleted from the surface of macromolecules, the more strongly hydrated cations, such as calcium and magnesium cations, are able to locally accumulate around the amide oxygen. These cations approach the interface together with the chloride counter-anions as solvent-shared ion pairs. Such an ion-pairing dominated interaction mechanism is rather surprising and serves as the missing important piece of the long-lasting Hofmeister mystery.
More detail about this study can be found in the recent issue of Journal of the American Chemical Society (Molecular Mechanism for the Interactions of Hofmeister Cations with Macromolecules in Aqueous Solution, JACS, 2020, 142, 45, 19094 – 19100. DOI: 10.1021/jacs.0c07214)