A biomolecular magnetic switch by diamagnetic cations

Abstract The magnetism of proteins and their contributions to magnetoreception and other magnetic bio-effects have been debated for decades, mostly focusing on the insufficient iron atoms and lacking physical explanations. Here we show that divalent metal cations alone, including Mg, Ca, and Zn cations, which are not traditional magnetic materials, can abruptly switch aromatic biomolecules from diamagnetic to exceptionally strongly paramagnetic. Remarkably, their paramagnetism is so strong, together with sequence-dependence, enabling the separation of DNA with different sequences under a moderate magnetic field, thus resulting in a DNA magnetophoresis prototype without any magnetic particle addition. Theoretical computations show that water helps stabilize the hydrated MgCl on the single aromatic ring via hydrated cation–π interactions, and the complex of the hydrated MgCl on the single aromatic ring possesses a magnetic moment of 1.0 μ B , which induces the exceptionally strong paramagnetism of the biomolecules with cations. X-ray experiments demonstrate the novel electronic states of the cations adsorbed on aromatic rings, indicating the existence of magnetic moments in the complex. The finding reveals a new origin for the exceptionally strong paramagnetism and biological magnetism, provides new insights into the interactions between biological systems and magnetic fields, and will greatly benefit magnetically controlled applications and beyond.