New Insight into an Old Puzzle – The Hofmeister Universality Investigated by Atomic Force Microscopy

TYPECondensed Matter Seminar
Speaker:Prof. Uri Sivan
Affiliation:Physics, Technion
Location:Lidow Nathan Rosen (300)
Abstract:Hofmeister and his PhD student, Lewith, discovered 125 years ago that different

ions promote protein precipitation to a markedly different extent. They ranked ions

according to their precipitation power in a series known today as the Hofmeister

series. Since then, scientists discovered dozens of other ion-specific phenomena

including surface tension, ion transport through biological and inanimate membranes,

ion specific channels, colloidal stability, enzyme activity, bacterial growth, and more.

Remarkably, with only few exceptions, the same Hofmeister order of ions or its

reverse were discovered to characterize the effect of ions on this myriad of ostensibly

different phenomena, strongly suggesting the existence of an underlying common

microscopic mechanism. The universality reflected in the Hofmeister series has

turned this problem into one of the fundamental puzzles in biophysics and the physics

of soft matter. It motivated extensive research and fundamental discoveries in topics

such as water and ion rearrangement next to surfaces. At the same time, cracking the

Hofmeister universality proved more challenging than naively anticipated.

In the past few years, our lab has been employing Atomic Force Spectroscopy to

measure the effect of different ions on the force acting between two surfaces in

solution. The full force vs. distance curves obtained this way provided significant new

insight into the Hofmeister puzzle and suggested, in combination with recent optical

measurements, a tentative picture of the underlying physics to be presented in the talk.