An open quantum system approach to the radical pair mechanism

Isotope effects on radical pair performance in cryptochrome: A new hypothesis for the evolution of animal migration: The quantum biology of migration

Mechanisms occurring at the atomic level are now known to drive processes essential for life, as revealed by quantum effects on biochemical reactions. Some macroscopic characteristics of organisms may thus show an atomic imprint, which may be transferred across organisms and affect their evolution. This possibility is considered here for the first time, with the aim of elucidating the appearance of an animal innovation with an unclear evolutionary origin: migratory behaviour. This trait may be mediated by a radical pair (RP) mechanism in the retinal flavoprotein cryptochrome, providing essential magnetic orientation for migration. Isotopes may affect the performance of quantum processes through their nuclear spin. Here, we consider a simple model and then apply the standard open quantum system approach to the spin dynamics of cryptochrome RP. We changed the spin quantum number (I) and g-factor of hydrogen and nitrogen isotopes to investigate their effect on RP's yield and magnetic sensitivity. Strong differences arose between isotopes with I = 1 and I = 1/2 in their contribution to cryptochrome magnetic sensitivity, particularly regarding Earth's magnetic field strengths (25-65 µT). In most cases, isotopic substitution improved RP's magnetic sensitivity. Migratory behaviour may thus have been favoured in animals with certain isotopic compositions of cryptochrome.

Hypomagnetic Fields and Their Multilevel Effects on Living Organisms

The Earth’s magnetic field is one of the basic abiotic factors in all environments, and organisms had to adapt to it during evolution. On some occasions, organisms can be confronted with a significant reduction in a magnetic field, termed a “hypomagnetic field—HMF”, for example, in buildings with steel reinforcement or during interplanetary flight. However, the effects of HMFs on living organisms are still largely unclear. Experimental studies have mostly focused on the human and rodent models. Due to the small number of publications, the effects of HMFs are mostly random, although we detected some similarities. Likely, HMFs can modify cell signalling by affecting the contents of ions (e.g., calcium) or the ROS level, which participate in cell signal transduction. Additionally, HMFs have different effects on the growth or functions of organ systems in different organisms, but negative effects on embryonal development have been shown. Embryonal development is strictly regulated to avoid developmental abnormalities, which have often been observed when exposed to a HMF. Only a few studies have addressed the effects of HMFs on the survival of microorganisms. Studying the magnetoreception of microorganisms could be useful to understand the physical aspects of the magnetoreception of the HMF.

Magnetic fields and apoptosis: a possible mechanism

The potential therapeutic uses of electromagnetic fields (EMF), part of the nonionizing radiation spectrum, increase with time. Among them, those considering the potential antitumor effects exerted by the Magnetic Fields (MFs), part of the EMF entity, have gained more and more interest. A recent review on this subject reports the MFs' effect on apoptosis of tumor cells as one of the most important breakthroughs. Apoptosis is considered a key mechanism regulating the genetic stability of cells and as such is considered of fundamental importance in cancer initiation and development. According to an atomic/sub-atomic analysis, based on quantum physics, of the complexity of biological life and the role played by oxygen and its radicals in cancer biology, a possible biophysical mechanism is described. The mechanism considers the influence of MFs on apoptosis through an effect on electron spin that is able to increase reactive oxygen species (ROS) concentration. Impacting on the delicate balance between ROS production and ROS elimination in tumor cells is considered a promising cancer therapy, affecting different biological processes, such as apoptosis and metastasis. An analysis in the literature, which allows correlation between MFs exposure characteristics and their influence on apoptosis and ROS concentration, supports the validity of the mechanism.

Magnetic Field Effect on the Oxidation of Unsaturated Compounds by Molecular Oxygen

A quantum-chemical analysis of the effect of a constant magnetic field on radical formation in the processes of chain oxidation of organic compounds by molecular oxygen is presented. The calculation of the total electronic energies and thermodynamic functions of the compounds involved in the reactions was performed by the density functional method with the hybrid exchange-correlation functional of Becke, Lee, Yang and Parr DFT B3LYP/6-311G** using the NWChem software package. The effect of the magnetic field on the individual stages of chain oxidation is associated with the evolution of radical pairs. It is assumed that the dipole–dipole interaction in a radical pair is not averaged by the diffusion of radicals and should be taken into account. To a large extent, the magnetic field effect (MFE) value is influenced by the ratio between the relaxation time of the oscillatory-excited state in the radical pair (tvib) and the relaxation time of the inter-combination transitions (tst). Although the developed technique refers to liquid-phase reactions, it can be used to study the MFE for oxidation of biologically significant compounds in multiphase systems, such as micelles, liposomes and membranes.

Observations about utilitarian coherence in the avian compass

It is hypothesised that the avian compass relies on spin dynamics in a recombining radical pair. Quantum coherence has been suggested as a resource to this process that nature may utilise to achieve increased compass sensitivity. To date, the true functional role of coherence in these natural systems has remained speculative, lacking insights from sufficiently complex models. Here, we investigate realistically large radical pair models with up to 21 nuclear spins, inspired by the putative magnetosensory protein cryptochrome. By varying relative radical orientations, we reveal correlations of several coherence measures with compass fidelity. Whilst electronic coherence is found to be an ineffective predictor of compass sensitivity, a robust correlation of compass sensitivity and a global coherence measure is established. The results demonstrate the importance of realistic models, and appropriate choice of coherence measure, in elucidating the quantum nature of the avian compass.

Anisotropic magnetic field effects in the re-oxidation of cryptochrome in the presence of scavenger radicals

The avian compass and many other of nature's magnetoreceptive traits are widely ascribed to the protein cryptochrome. There, magnetosensitivity is thought to emerge as the spin dynamics of radicals in the applied magnetic field enters in competition with their recombination. The first and dominant model makes use of a radical pair. However, recent studies have suggested that magnetosensitivity could be markedly enhanced for a radical triad, the primary radical pair of which undergoes a spin-selective recombination reaction with a third radical. Here, we test the practicality of this supposition for the reoxidation reaction of the reduced FAD cofactor in cryptochrome, which has been implicated with light-independent magnetoreception but appears irreconcilable with the classical radical pair mechanism (RPM). Based on the available realistic cryptochrome structures, we predict the magnetosensitivity of radical triad systems comprising the flavin semiquinone, the superoxide, and a tyrosine or ascorbyl scavenger radical. We consider many hyperfine-coupled nuclear spins, the relative orientation and placement of the radicals, their coupling by the electron-electron dipolar interaction, and spin relaxation in the superoxide radical in the limit of instantaneous decoherence, which have not been comprehensively considered before. We demonstrate that these systems can provide superior magnetosensitivity under realistic conditions, with implications for dark-state cryptochrome magnetoreception and other biological magneto- and isotope-sensitive radical recombination reactions.

Oxidative Stress and NADPH Oxidase: Connecting Electromagnetic Fields, Cation Channels and Biological Effects

Electromagnetic fields (EMFs) disrupt the electrochemical balance of biological membranes, thereby causing abnormal cation movement and deterioration of the function of membrane voltage-gated ion channels. These can trigger an increase of oxidative stress (OS) and the impairment of all cellular functions, including DNA damage and subsequent carcinogenesis. In this review we focus on the main mechanisms of OS generation by EMF-sensitized NADPH oxidase (NOX), the involved OS biochemistry, and the associated key biological effects.