Anionic and cationic Hofmeister effects are non-additive for guanidinium salts.

To understand specific ion effects on a molecular level we explore the effect of salts on the rotational mobility of a model amide using dielectric spectroscopy. Based on our previous studies on the effect of strong denaturing anions or cations, here we study the additivity of the anionic and cationic effect. Using salts consisting of denaturing spherical anions and spherical cations we find such salts to affect the amide according to what one expects based on the additive activity of the individual ions. The guanidinium (Gdm+) cation appears to be a notable exception, as our results suggest that GdmI (and accordingly GdmSCN) is less efficient in hindering the rotation of the amide than KI or GdmCl.

Correction: Quantifying transient interactions between amide groups and the guanidinium cation.

Correction for 'Quantifying transient interactions between amide groups and the guanidinium cation' by V. Balos et al., Phys. Chem. Chem. Phys., 2015, 17, 28539-28543.

Quantifying transient interactions between amide groups and the guanidinium cation.

We study the interaction of the guanidinium cation, a widely used protein denaturant, with amide groups, the common structural motif of proteins. Our results provide evidence for direct contact between guanidinium and ∼2 amide groups, but the interaction is transient and weaker than for other cations with high charge-density.