The biological effects of weak magnetic fields have long been a subject of scientific inquiry, with increasing evidence supporting their influence on biochemical, physiological, and behavioural processes. This review describes three primary mechanisms of magnetoreception that have been identified in migrating animals: use of magnetite in sensitive cells, sensitive electroreceptors, and spin dynamics in cryptochrome radical pairs. It also critically examines the potential of the radical-pair mechanism to serve as a universal explanation for the diverse non-sensory biological effects of weak magnetic fields, including extremely low-frequency magnetic fields, static magnetic fields, and hypomagnetic conditions. Understanding how weak magnetic fields influence radical-pair processes could revolutionize our approach to bioelectromagnetic interactions and provide new avenues for development of medical and technological applications. Future research should focus on direct real-time monitoring of radical-pair-mediated biochemical reactions, evaluating the interplay between magnetic fields, light exposure, and temperature, and refining theoretical models to bridge the gap between quantum-scale interactions and macroscopic biological effects. Addressing these questions will be essential in determining whether the radical-pair mechanism can serve as a unifying principle in magnetobiology.

Photoinduced oxidation of anserine and carnosine by triplet 3,3',4,4'-tetracarboxy benzophenone (TCBP) has been investigated in aqueous solution using time-resolved laser flash photolysis and chemically induced dynamic nuclear polarization (CIDNP). Rate constants of oxidation via triplet quenching were obtained over a wide pH range. The formation of radical pairs as a result of quenching was proven by the observation of CIDNP effects. For comparison with anserine, pH dependences of the quenching rate constant and CIDNP were obtained for the photoreaction of TCBP with 1- and 3-methyl histidine, while the results for carnosine were compared with those previously obtained for histidine. The obtained pH dependences were described in terms of quenching rate constants and relative CIDNP enhancement factors for five reactant pairs corresponding to their exact protonation states. In the case of carnosine and histidine, maxima of the observed quenching rate constant and CIDNP amplitude coincide, while in the case of methylated compounds, these maxima diverge. In the case of anserine, under biologically relevant conditions at pH ∼ 6 ÷ 7, an additional pair of reactants was discovered that provides an anomalously high CIDNP enhancement factor, exceeding that of other radical pairs by at least 2 orders of magnitude. This pair consists of the anserine cation radical with protonated amino group and the TCBP anion radical with two deprotonated carboxyl groupsa chemical structure that potentially facilitates the formation of a pair of transient radicals with an extended lifetime, resulting in a significant increase in CIDNP.

Light-responsive molecules that can release drugs upon light absorption have attracted significant interest in chemistry and biology. BODIPY-based photoremovable protecting groups, or photocages, have recently emerged as especially promising tools in this respect. However, the exact photorelease mechanism is still not fully understood. We study the photochemical decomposition of meso-Methyl-BODIPY-conjugated epinephrine using 1H nuclear magnetic resonance and chemically induced dynamic nuclear polarization (CIDNP) techniques. After irradiation, epinephrine was detected only in trace amounts, whereas its oxidation product, adrenochrome, was the predominant product. Surprisingly, the CIDNP study has shown that the electron transfer (ET) in this reaction does not proceed from epinephrine to the BODIPY moiety, but rather occurs between two BODIPY cores. To validate this hypothesis, we applied the CIDNP method to detect photoinduced ET between two model BODIPY molecules in solution. In addition, the radical cation of BODIPY has been detected for the first time by CIDNP under photolysis in the presence of the electron acceptor-chloranil. The hyperfine interaction (HFI) constants of the BODIPY radical cation were estimated from the CIDNP spectrum, and they are in agreement with the HFI constant predicted by density functional theory calculations. Due to high enhancement coefficients, the CIDNP technique allows for to detection of polarized BODIPY products at very low concentrations.

Photoinduced reactions between photosensitizers and nucleic acids represent a fundamental mechanism in photodynamic therapy (PDT), primarily involving light-mediated oxidative damage to DNA. This study elucidates the interaction of a novel anthraquinone derivative, 2-phenyl-4-(butylamino)naphtho[2,3-h]quinoline-7,12-dione (Q1), with nucleotides using a combination of NMR spectroscopy, chemically induced dynamic nuclear polarization (CIDNP), and molecular dynamics simulations. We demonstrate that Q1 forms complexes with guanosine (GMP), adenosine (AMP), and cytidine (CMP) monophosphates in the dark, with the highest stability constant observed for the Q1/GMP complex. Upon photoexcitation, electron transfer occurs exclusively from GMP to Q1, generating a semiquinone radical anion and a neutral guanyl radical. The CIDNP data allowed for an estimation of the triplet state energy of Q1, ET(Q1) = 2.1 ± 0.1eV. Also, irradiation at 520nm enhances the cytotoxicity of Q1 against MDA-MB-231 (human breast adenocarcinoma) and A549 (lung carcinoma) cell lines. We conclude that the specific photoinduced radical reaction between Q1 and guanine bases is a component of its cytotoxic mechanism, establishing Q1 as a promising candidate for further development in PDT applications.

The Earth’s geomagnetic field (GMF) is a fundamental environmental signal for plants, with its perception rooted in quantum biology. Specifically, the radical pair mechanism (RPM) explains how this weak force influences electron spin states in metabolic pathways, providing a framework for its profound biological impact. Research shows that a hypomagnetic field (hMF) directly reduces the production of reactive oxygen species (ROS), creating a quantum signature in plants. This is a counterintuitive finding, as it suggests the plant perceives less oxidative stress and, in response, downregulates its antioxidant defenses. This multi-level effect, from a quantum trigger to molecular and metabolic changes, ultimately affects the plant’s growth and phenotype. This review suggests a possible link between the GMF and plant health, identifying the GMF as a potential physiological modulator. Manipulating the magnetic field could therefore be a novel strategy for improving crop resilience and growth. However, the fact that some effects cannot be fully explained by the RPM suggests other quantum mechanisms are involved, paving the way for future research into these undiscovered processes and their potential inheritance across generations.

Low Magnetic Fields Stimulate Cardiac Mitochondrial Bioenergetics with a Bell-Shaped Response: Possibly Via a Radical Pair Mechanism

Hetero-nuclear multiple quantum coherences build a basis of multi-dimensional nuclear magnetic resonance (NMR) and are typically established through scalar coupling-based polarisation transfers in liquids, starting from 1H due to the low population of the other spin nuclei. Here, the presence of heteronuclear double and triple quantum spin orders resulting from in-situ photochemically induced dynamic nuclear polarisation (photo-CIDNP) was explored with 13C,15N-labelled tyrosine and Atto Thio 12 acting as photosensitizer. From the longitudinal spin orders, double and triple quantum coherences are obtained by a single pulse. Hence, the 1H,13C double coherence is detected in a [1H, 13C]-heteronuclear single quantum coherence experiment and alike without the initial insensitive nuclei enhanced by polarisation transfer (INEPT) pulse train. The photo-CIDNP signal intensities of double and triple quantum spin orders/coherences were evaluated to be only about one order of magnitude less than for single quantum. This suggests that the photo-CIDNP polarisation enhancements of the double and triple quantum coherences/spin orders are in the order of a factor of 105 for the double and 109 for the triple coherence. These extensive enhancements are attributed to the concerted spin sorting of the nuclei within a single molecule, which originates from the radical pair mechanism of photo-CIDNP hyperpolarisation.

Cryptochrome flavoproteins are prime candidates for mediating magnetic sensing in migratory animals via the radical pair mechanism (RPM), a spin-dependent process initiated by photoinduced electron transfer. The canonical FAD – tryptophan radical pair exhibits pronounced anisotropic hyperfine couplings, enabling sensitivity to geomagnetic fields. However, maintaining spin coherence under physiological conditions and explaining responses to weak radiofrequency fields remain unresolved challenges. Alternative radicals, such as superoxide $({\rm O}_2^{•−})$ and ascorbate $({\rm Asc}^{•−}),$ have been proposed to enhance anisotropy or suppress decoherence. This reviewsummarizes the quantum basis of magnetoreception, evaluates both canonical and alternative radical pair models, and discusses amplification strategies including triads, spin scavenging, and bystander radicals. Emphasis is placed on how molecular geometry, exchange and dipolar interactions, and hyperfine topology modulate magnetic sensitivity. Key open questions and future directions are outlined, highlighting the need for structural and dynamical data under physiological conditions.

Hyperpolarization techniques such as dynamic nuclear polarization (DNP), chemically-induced dynamic nuclear polarization (CIDNP), and parahydrogen-induced polarization (PHIP) enhance the sensitivity of NMR spectroscopy and MRI, but the associated antiphase magnetization patterns often relax faster than those of conventional in-phase signals. This study analyzes the spin-lattice relaxation matrix for single-quantum transitions in an isolated, weakly coupled two-spin AX system to identify eigenvectors and eigenvalues that govern the time evolution of in-phase and antiphase longitudinal magnetization. The analysis predicts that AX antiphase magnetization, such as that generated by PHIP hydrogenations in high magnetic field, can relax up to twice as fast as the in-phase magnetization of traditional inversion-recovery or saturation-recovery experiments. To validate these predictions, a dedicated NMR pulse sequence was used to selectively generate and monitor antiphase magnetization. trans-Cinnamic acid in deuterated DMSO served as a model compound, with the hydrogen atoms on its central conjugated double bond forming a weakly coupled AX spin system with a large scalar coupling (>16 Hz). The large scalar coupling allowed for the separate integration of the two lines in each doublet. Experimental results confirm an accelerated relaxation of antiphase magnetization but also reveal that in-phase relaxation is influenced by double-quantum transitions, which do not contribute to the relaxation of antiphase magnetization. The findings of this study highlight the importance of distinguishing in-phase from antiphase relaxation, providing a basis for optimizing hyperpolarization experiments with explicit consideration of antiphase signal dynamics.

Biomolecules that constitute life on Earth are chiral, but the precise mechanism by which homochirality emerged remains a mystery. In this work, it is demonstrated that reactions of radical pairs, where one of the radical electron spins is polarized, can be enantioselective. This phenomenon arises from transient coherent quantum dynamics of the radical pair electron spins, which is known to occur even in warm and noisy condensed phase environments, where energetic perturbations much smaller than thermal energy can have strong effects on reactivity. A quantitative theory is presented based on the molecular theory of chirality-induced spin selectivity (CISS), where electron exchange interactions and chirality-dependent spin-orbit coupling effects control enantioselectivity. This theory provides useful bounds on the maximum enantiomeric excess for these reactions, which are found to be consistent with previous experiments. The enantioseletive radical pair mechanism presented here provides an alternative mechanistic basis to a recent proposal that spin-polarized photoelectrons from magnetite provided the initial chiral symmetry breaking necessary for the inception of homochirality in Nature and suggests a new strategy for asymmetric synthesis using spin-polarized electrons.

The spin-chemical radical pair mechanism (RPM) has emerged as a leading theory for explaining the biological effects of low-intensity magnetic fields. These intriguing effects occur when the quantum system of radicals is well isolated from the disturbing influence of the environment. In other words, these effects are closely related to the spin coherence relaxation time τ, but an explicit relationship has not yet been established. In our study, we found an analytical solution to the Liouville-Neumann equationfor an open system made up of two electrons and one nucleus, considering minimal interactions while concentrating on spin relaxation and chemical kinetics. This solution, supported by numerical integration, highlights the crucial role of quantum coherence. A straightforward expression is proposed that describes the RPM effect as a function of τ, within the ranges of magnetic field strength H and rate κ of chemical kinetics relevant to magnetobiology. Our findings reveal that RPM effects become significant only when fundamental relation γHτ>1+κτ holds: it controls the magnitude of the effects, and it is consistent with the principles of spin chemistry. Additionally, by comparing our results with existing experimental data, we estimate that the plausible spin decoherence times in magnetosensitive radical pairs within cryptochromelike proteins range from units to tens of nanoseconds. The effects of radio-frequency magnetic fields at the nT level were also examined, taking into account decoherence. These effects turned out to be negligible and incapable of disrupting the RPM patterns. The role of the quantum Zeno effect in magnetobiology is inspected from the perspective of the τ dependence of the RPM effect.

Photoinduced intramolecular electron transfer (ET) is essential for understanding charge transport in biological and synthetic systems. This study examines ET in peptide His-Glu-Tyr-Gly (1) and the conjugate His-Gln(BP)-Tyr-Gly (2) with benzophenone (BP) as a photoactive electron acceptor and His or Tyr as donors. Time-resolved and field-dependent chemically induced dynamic nuclear polarization (CIDNP) techniques were employed to investigate ET mechanisms and kinetics. Peptide 1 with 3,3’,4,4’-tetracarboxy benzophenone as a photosensitizer initially forms two types of radical with radical center at either His or Tyr residue, the consequent intra- and intermolecular ET electron transfer from Tyr residue to the His radical takes place with rate constants ke(intra)=(1.5±0.5)×105 s− 1 and ke(inter)=(1.3±0.4)×107 M− 1s− 1 at pH 8.8. Conjugate 2 forms two types of biradicals under irradiation: with radical centers at Tyr and BP across the entire pH range, and with radical centers at His and BP at slightly basic pH. Field-dependent CIDNP revealed nonzero electronic exchange interaction (2Jex = − 8.78 mT) at acidic pH, indicating proximity between BP and Tyr radicals. Low-field CIDNP spectra showed strong emissive polarization patterns, with pH-dependent exchange interaction and biradical geometry. Notably, no electron transfer from tyrosine to histidine radicals was observed in the conjugate 2, distinguishing its behavior from peptide 1.

This study advances the theoretical foundation of photo-chemically induced dynamic nuclear polarization (photo-CIDNP)-a powerful mechanism for enhancing nuclear spin sensitivity without microwave irradiation. Using an operator-based effective Hamiltonian approach, we derive precise resonance matching conditions and identify key dipolar scaling factors governing the photo-CIDNP Hamiltonian under both static and magic-angle spinning conditions. Our analytical formulation of coherent evolution of photoexcited singlet state exhibits strong agreement with numerical simulations, reinforcing the validity of our theoretical framework. By unraveling the intricate interplay of spin parameters in the radical-pair mechanism, our findings provide critical insights into optimizing photo-CIDNP efficiency and guiding the rational design of tailored molecular systems. The ability to develop highly efficient photo-CIDNP sensitizers marks a crucial step toward harnessing hyperpolarized nuclear magnetic resonance and magnetic resonance imaging, paving the way for next-generation advancements in biomedical imaging and materials science.

Improving the photosensitization efficiency represents a critical challenge in photodynamic therapy (PDT) research. While cyanines exhibit potential as photosensitizers (PSs) due to their large extinction coefficients and excellent biocompatibility, the inherent limitations in intersystem crossing severely affect therapeutic efficacy. Herein, we proposed a bottom-up magnetically enhanced photodynamic therapy (magneto-PDT) paradigm employing fluorobenzene-substituted pentamethine cyanine as type-I reactive oxygen species generators. Based on the radical pair mechanism and magnetic field effect, the notable difference in g-factors (Δg) between PSs and oxyradicals enabled magnetically responsive amplification of Cy5-3,4,5-3F-mediated hydroxyl radical (•OH) and superoxide anion radical (O2•-) production, achieving maximum yield enhancements of 66.9 and 28.0% respectively at 500 mT. This magnetically augmented oxyradicals generation exhibited universal cytotoxicity superiority over conventional PDT protocols in various cancer cell models. Notably, the semi-inhibitory concentration (IC50) of murine mammary carcinoma 4T1 cells demonstrated a remarkable reduction under both normoxic and hypoxic conditions, with the most pronounced decrease observed in normoxia from 0.91 μM (PDT alone) to 0.38 μM (magneto-PDT). The significantly magneto-enhanced therapeutic performance effectively inhibited orthotopic tumor growth. This magneto-PDT paradigm established a novel strategy for manipulating spin-dependent photosensitization processes in biological applications.

Electromagnetic radiation at telecommunication frequencies has been reported to have biological effects, particularly affecting the production of reactive oxygen species, raising the question of potential mechanisms. In this study, we explored whether the radical pair mechanism (RPM) could account for these effects. Given that telecommunication frequencies are much higher than those associated with typical hyperfine interactions in biological systems, any effects would necessarily be non-resonant. Our computational simulations confirm that the RPM cannot explain these effects under experimental conditions due to the negligible influence of low-amplitude oscillating fields. We find that observable effects on radical pairs at telecommunication frequencies would require hyperfine coupling constants that are precisely fine-tuned to values far exceeding those naturally occurring in biological systems. We conclude that another mechanism must be responsible for the effects of telecommunication frequency fields in biological systems.

There are few well-established biophysical mechanisms by which external magnetic fields can influence the biochemistry of molecules in living systems. The radical pair mechanism is arguably the most promising. In this mini-review I summarize the characteristics of radical pairs in a way that may be useful to those engaged in the field of magneto-oncology. The intention is to help researchers decide whether an observed biomedical magnetic field effect could have its origin in radical pair biochemistry. Armed with a physically plausible interaction mechanism, it may be possible to devise and refine a theoretical model and thereby iteratively optimise therapeutic protocols. Such an approach may also help identify experimental artefacts.

Sincethe middle of the 20th century, long-distance avianmigrationhas been known to rely partly on geomagnetic field. However, the underlyingsensory mechanism is still not fully understood. Cryptochrome-4a (ErCry4a),found in European robin (Erithacus rubecula), a night-migratory songbird, has been suggested to be a magneticsensory molecule. It is sensitive to external magnetic fields viathe so-called radical-pair mechanism. ErCry4a is primarily locatedin the outer segments of the double-cone photoreceptor cells in theeye, which contain stacked and highly ordered membranes that couldfacilitate the anisotropic attachment of ErCry4a needed for magneticcompass sensing. Here, we investigate possible interactions of ErCry4awith a model membrane that mimics the lipid composition of outer segmentsof vertebrate photoreceptor cells using experimental and computationalapproaches. Experimental results show that the attachment of ErCry4ato the membrane could be controlled by the physical state of lipidmolecules (average area per lipid) in the outer leaflet of the lipidbilayer. Furthermore, polarization modulation infrared reflectionabsorption spectroscopy allowed us to determine the conformation,motional freedom, and average orientation of the α-helices inErCry4a in a membrane-associated state. Atomistic molecular dynamicsstudies supported the experimental results. A ∼1000 kcal mol–1 decrease in the interaction energyas a result of ErCry4a membrane binding was determined compared tocases where no protein binding to the membrane occurred. At the molecularlevel, the binding seems to involve negatively charged carboxylategroups of the phosphoserine lipids and the C-terminal residues ofErCry4a. Our study reveals a potential direct interaction of ErCry4awith the lipid membrane and discusses how this binding could be anessential step for ErCry4a to propagate a magnetic signal furtherand thus fulfill a role as a magnetoreceptor.

This study presents a numerical simulation approach to investigate singlet-triplet interconversion effects in organic materials with rigid molecular structures that facilitate the photogeneration of charge-separated (CS) states, such as zwitterions resulting from intramolecular electron transfer. Our approach enables the detailed modeling of electron and nuclear spin-dependent observables, including magnetic field-affected reaction yields (MARY) and chemically induced dynamic nuclear polarization (CIDNP). The equilibrium solution of the stochastic Liouville equation can be obtained with simple algebraic manipulation by noting the relationship between the Laplace transform of the density operator and the time-domain representation of the same operator. Experimental MARY and CIDNP data are modeled as functions of key external and internal system parameters, such as magnetic field strength, hyperfine interactions, and exchange couplings. This allows for exploring processes that are otherwise experimentally inaccessible, providing deeper insights into the spin dynamics of the photoinduced CS state. Understanding these interconversion processes is not only essential for the fundamental photochemistry studies but also for the rational design and development of novel organic materials for photovoltaics and photocatalysis. Our results demonstrate the significant impact of singlet-triplet interconversion on the overall efficiency of charge separation and recombination processes, highlighting the importance of spin dynamics in the design of next-generation organic photovoltaic materials.

Little strokes fell big oaks: The use of weak magnetic fields and reactive oxygen species to fight cancer.

<sec>Near-zero-field nuclear magnetic resonance (NMR) has become a rapidly developing spectroscopic and imaging method, providing promising opportunities for portable diagnostics and fast chemical analysis. A key technology is the atomic magnetometer, and its ongoing improvements have sparked growing interest in potential clinical applications.</sec><sec>The near-zero-field NMR has long been limited by weak signal strength, but recent developments in the hyperpolarization method have provided an effective solution to this problem. Dissolution dynamic nuclear polarization (dDNP), parahydrogen-based polarization schemes (PHIP/SABRE), chemically induced dynamic nuclear polarization (CIDNP), and spin-exchange optical pumping (SEOP) have all demonstrated preliminary feasibility in this context.</sec><sec>By combining such hyperpolarization strategies with near-zero-field detection, strong signals can be obtained without the need of traditional high-field magnets. This capability opens new pathways for applying near-zero-field NMR to both chemical sensing and biomedical imaging, enabling compact tools for rapid analysis and diagnostic applications. Here, we review the recent progress of the intersection of near-zero-field NMR and hyperpolarization techniques.</sec>