Already pure guanidinum chloride (GndCl) solution is remarkable. It contains a significant fraction of guanidinium cations in direct contact, a typically rare feature, which is counterintuitive (on electrostatic grounds) link.
Proteins are unfolded and solutes destabilized in concentrated solutions of GndCl in general. Indeed GndCl is, after urea, the second most common denaturing agent. In the recent article we present different faces of guanidinium action, stabilizing as well as destabilizing which are intimately connected with the anion in action. This work is a joint experimental (spectroscopy & thermodynamics) computational (simulations & theory) study. link