Magnetic fields can modulate the reactivity of singlet oxygen: A new possible magnetoreceptors in living systems

It’s a fact that the reactivity of singlet oxygen is controlled by magnetic fields. This groundbreaking discovery has led researchers to believe that there may be a previously unknown magnetoreceptor in living systems. It is truly remarkable to witness the continuous advancement of scientific knowledge, which starts at the molecular level and broadens our comprehension of the world we inhabit.

Spin is an intrinsic property of the electron. Two electrons can coexist in a single orbital only if they have opposite spins, which is the fundamental basis for chemical bond formation. By manipulating the direction of electron spins, it is possible to control chemical reactions effectively. Since the establishment of spin chemistry and quantum biology in the 1960s, scientists have realized the significant role of spin chemical effects in living systems. However, controlling the relative spin orientation of electrons of reactants has posed a major challenge, particularly in biology. Electrons possess a magnetic moment due to their spin, which enables an external magnetic field to control the direction of their spin. Scientific experiments have unequivocally demonstrated that magnetic fields can significantly influence crucial biological processes such as the migration of birds (known as magnetic compass), circadian rhythm, and neurological activity. The radical pair mechanism (RPM) is an invaluable molecular mechanism for understanding magnetic field effects on chemical kinetics and biological behaviors. However, the RPM’s potential to achieve reliable and reproducible biological functions remains a formidable challenge that requires meticulous and deliberate experimentation.

In a recent study in the National Science Review by Zhang and colleagues, the authors explored how to use magnetic field effects to control cellular events. Interferences from chaos were eliminated by introducing exogenous reactions with radical pair intermediates into biological systems. Singlet oxygen (¹O₂), one of the main types of reactive oxygen species, is the reactant. As an electronically excited form of oxygen, ¹O₂ is highly reactive and plays an essential role in the physiological functions of cells as a regulator for oxidative stress. The reactions of ¹O₂ usually start with electron transfer and the formation of radical pair species, permitting magnetosensitivity of ¹O₂ reactivity due to RPM. The reactions with iodide anion and anthracenes, where intermolecular radical pair [I^•O₂^•−] and intramolecular biradical [^•ROO^•] might act as magnetosensitive species respectively, were examined first. Then, the authors turned to biological molecules and studied the magnetic effect on the oxidation of lipids, which played an important role in redox homeostasis.  A significant “down-up-down” magnetic dependence in the 0–800 mT range was found and can be explained by a combination of low field effect, hyperfine coupling, and Δg mechanisms within the scope of RPM.

So, can the magnetic field regulate reactions in living systems? To answer this, they investigated lipid oxidation in various environments, including organic solution (ethanol), mimics of cell membranes (giant unilamellar vesicles), and living cells. The results showed a consistent trend of magnetic field dependence in all environments, indicating that external magnetic fields can guide harnessing cellular activity by mimicking the reactivity of ¹O₂ in the test tube. The authors also investigated how magnetic fields can regulate ¹O₂-induced cytotoxicity and found that cell viability was indeed magnetically modulated. Furthermore, they performed in vivo anti-tumor photodynamic therapy (PDT) using tumor-bearing mice. The results showed that a 250 mT magnetic field significantly inhibited tumor growth, whereas a low (15 mT) or high (800 mT) field had little effect.

The work presented by Zhang et al. offers a bottom-up approach for incorporating the magnetic field effect (MFE) of chemical reactions into biological systems through the implementation of RPM. The results demonstrate the potential of utilizing MFE to regulate biological processes and aid in the treatment of diseases. This study also provides a definitive answer to the question—whether RPM and spin chemistry are essential components of living systems. In addition, it offers valuable insights into the emerging field of magnetobiology and its potential applications.

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