Broadband Cavity-Enhanced Detection of Magnetic Field Effects in Chemical Models of a Cryptochrome Magnetoreceptor

Abstract

Broadband cavity-enhanced absorption spectroscopy (BBCEAS) is shown to be a sensitive method for the detection of magnetic field effects (MFEs) in two flavin-based chemical reactions which are simple models for cryptochrome magnetoreceptors. The advantages of optical cavity-based detection and (pseudo-white-light) supercontinuum radiation have been combined to provide full spectral coverage across the whole of the visible spectrum (425 < λ < 700 nm). This region covers the absorbance spectra of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) as well as their photogenerated radicals. To illustrate the power of this technique, BBCEAS has been used to record the spectral dependence of MFEs for photoinduced radical pairs formed in the intermolecular reaction of FMN with lysozyme and the intramolecular photochemistry of FAD. These reactions have been chosen for their photochemical similarities to cryptochrome proteins which have been proposed as key to the magnetic compass sense of many animals including birds. In experiments performed using low protein concentrations (10 μM) and 1 mm optical path-lengths, absorbance changes as small as 1 × 10(-7) (representing <0.1% MFEs) have been detected with good signal-to-noise offering the prospect of sensitive MFE detection in cryptochrome.

Optical Absorption and Magnetic Field Effect Based Imaging of Transient Radicals

“…Although this reaction has been carefully studied by conventional [10,11] and high-sensitivity cavity enhanced techniques, [12] this LFE has not previously been resolved. This reveals the high sensitivity of this approach, which detected the feature using as ample volume of only 5 mLa nd as econd lock-in time constant of only 300 ms.I ff lavin-based RPs are responsible for biological magnetoreception, then the LFE represents the most likely mechanism by which fields as small as the geomagnetic field (30-50 mT) might deliver ac hemical response.…”

Inhomogeneous ensembles of radical pairs in chemical compasses

“…One is based on mechanical forces on magnetite particles34, the other, explored further here, posits a quantum coherent process involving photoinduced radical pair reactions within photoreceptor proteins with cryptochromes as candidate photo-magnetoreceptors567. Although the sensory mechanism is still unclear8910, a number of recent studies lend support to the radical pair mechanism1112, its physiological basis131415 and the suggested cryptochrome proteins as photo-magnetoreceptors161718192021, thereby raising the possibility that a chemical sensor could operate in biological systems. Figure 1 illustrates key elements of a radical-pair-based magnetic compass system within a bird.…”

Optical Absorption and Magnetic Field Effect Based Imaging of Transient Radicals

“…By acquiring single (Figure 3, main) and double (Figure 3, inset) modulation MARYc urves at ag reater magnetic field resolution (and as uitably small MF modulation depth of 0.35 mT peak-to-peak in the double modulation case) it was possible to successfully resolve and confirm aLFE. Although this reaction has been carefully studied by conventional [10,11] and high-sensitivity cavity enhanced techniques, [12] this LFE has not previously been resolved. This reveals the high sensitivity of this approach, which detected the feature using as ample volume of only 5 mLa nd as econd lock-in time constant of only 300 ms.I ff lavin-based RPs are responsible for biological magnetoreception, then the LFE represents the most likely mechanism by which fields as small as the geomagnetic field (30-50 mT) might deliver ac hemical response.…”