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Magnetoreception in Plants
Published in Shoogo Ueno, Tsukasa Shigemitsu, Bioelectromagnetism, 2022
Recent comprehensive calculations for the FAD•−/W•+ RP revealed that the key quantity, the differences in the yield of signaling state at different field directions, might be perplexingly small (Kattnig et al., 2016b). According to Hore et al., the fact that the compass performance in animals surpasses these predictions (e.g., with respect to the acuity of the sensor, its function under very low light intensities, or its sensitivity to weak radio frequency MFs) suggests the presence of a powerful, yet unknown, amplification process and remarkable resilience to decoherence (Hore and Mouritsen, 2016; Kattnig et al., 2016a). The same group recently proposed an extended reaction scheme (Figure 5.4), that is predicted to greatly (by a factor of 10 and more) enhance the compass sensitivity via the so-called “chemical Zeno effect” (Letuta and Berdinskii, 2015), the effect of spin-dependent recombination on the singlet–triplet RP evolution rate and frequency. The chemical Zeno effect changes the S–T recombination rate and, thus, has an effect on the yield of recombination products, quantum beat frequency, chemically induced nuclear polarization, and magnetic isotope effect (Letuta and Berdinskii, 2015). The model of Hore and co-workers relies on a spin-selective reaction of one of the two radicals of the primary pair and a spin-bearing, external scavenger. This scavenger is initially uncorrelated with respect to the RP, a situation that resembles f-pairs, but eventually acquires correlation as a result of its spin selective reactivity, i.e. the chemical Zeno effect. It has been shown that this additional reaction induces singlet−triplet conversion in the original RP and serves as a spin-selective reaction channel. As a consequence, and contrary to previous theories, spin-selective recombination of the primary RP (see Figure 5.3) is no longer essential, and the radicals could thus be farther apart than is necessary for efficient charge recombination. This means that tryptophan tetrads (rather than triads) or systems involving freely diffusing radicals can also give rise to sizable MF effects and that the detrimental effects of inter-radical exchange and dipolar interactions can be minimized. The spin dynamics in these three-radical systems are characterized by doublet-quartet conversions (instead of the conventional singlet−triplet interconversions characteristic of the classical RP mechanism). The doublet state can be formulated as singlet in the A/B- or A/C-manifold in combination with a doublet radical, as shown in Figure 5.4. These singlet substates are, however, not mutually exclusive, i.e., orthogonal.
Understanding foliar accumulation of atmospheric Hg in terrestrial vegetation: Progress and challenges
Published in Critical Reviews in Environmental Science and Technology, 2022
Yanwei Liu, Guangliang Liu, Zhangwei Wang, Yingying Guo, Yongguang Yin, Xiaoshan Zhang, Yong Cai, Guibin Jiang
The atmosphere-foliage Hg flux is a bidirectional process that is highly variable, making foliar Hg(0) emission volumes, and profiles hard to determine (Agnan et al., 2016; Graydon et al., 2006; Sommar et al., 2020). The enriched Hg stable isotope tracer and Hg stable isotopic composition analysis have provided insight into foliar Hg(0) emission (Graydon et al., 2006; Hintelmann et al., 2002; Yuan et al., 2019). As for Hg stable isotopes, mass-dependent fractionation (MDF) occurs during various chemical (e.g., redox and photochemical reactions), biological (e.g., microbial methylation and demethylation) and physical processes (e.g., sorption, diffusion and evaporation), whereas mass-independent fractionation (MIF) of odd-mass Hg isotopes is caused by the nuclear volume effect and the magnetic isotope effect during photochemical processes and equilibrium reactions (Kwon et al., 2020).
New advance in the application of compound-specific isotope analysis (CSIA) in identifying sources, transformation mechanisms and metabolism of brominated organic compounds
Published in Critical Reviews in Environmental Science and Technology, 2022
Jukun Xiong, Guiying Li, Taicheng An
For example, Zakon et al. investigated the carbon and bromine isotope effects of 4-BP, 3-BP, and 2-BP during UV-irradiation in water and ethanol (Zakon et al., 2013). Except for 2-BP in water, inverse high bromine isotope effects (81Br-AKIE < 1) were observed for the other brominated phenols (Table S1). Three brominated phenols in ethanol, and 4-BP in water, became enriched with 13C; however, the carbon isotope composition of 2-BP and 3-BP showed no fractionation in water. Therefore, according to the observed carbon and bromine isotope effect, a superposition of mass-independent magnetic isotope effect (MIE) and mass-dependent kinetic isotope effect (KIE) for phototransformation was proposed to illustrate bromine isotope effects (Eq. 6).
Mercury cycling and isotopic fractionation in global forests
Published in Critical Reviews in Environmental Science and Technology, 2022
Xun Wang, Wei Yuan, Che-Jen Lin, Xinbin Feng
After the litterfall Hg deposition, Hg in soil is subject to microbial reduction during the initial litter decomposition period, as well as weak yet continuous photo-reduction because the canopy shading constrains sunlight reaching into the forest floor (Wang et al., 2016b; Yuan et al., 2020). Since microbial reduction mainly induced the Hg-MDF, the δ202Hg of decomposing litter becomes more positive and the Δ199Hg nearly has a small variation (Lu et al., 2021; Yuan et al., 2020). The dark redox reactions mediated by organic matter and microbial reduction become the predominant processes in a time scale of decades to centuries. These reductions lead to a gradually more positive δ202Hg in organic soil. In addition, the organic matter induced Hg dark redox transformation has a distinct nuclear volume effect (NVE) that leads to a more negative Δ199 Hg, up to −0.1‰ to −0.3‰ shift between the Oa (i.e., well decomposed humus soil) and litters (Guédron et al., 2018; Jiskra et al., 2015; Lu et al., 2021; Yuan et al., 2019a). Photochemical reduction of Hg2+ widely occurs in the environment. Air, foliage and litterfall samples typically exhibit the magnetic isotope effect (MIE) induced a slope of 1 for Δ199Hg versus Δ201Hg (Bergquist & Blum, 2007; Blum et al., 2020; Sonke, 2011). In deep organic soil, the occurrence of organic matter medicated Hg dark redox alter the slope to slightly greater than 1 due to partial NVE yielding of up a slope of ∼1.6 (Guédron et al., 2018; Jiskra et al., 2015; Lu et al., 2021; Yuan et al., 2019a). In mineral and deeper soil, with the mixing of Hg derived from geogenic sources (i.e., rock weathering), the Δ199 Hg gradually become ∼0 because of diminutive Δ199 Hg signatures in rocks (Blum et al., 2014; Guédron et al., 2018; Smith et al., 2008; Sun et al., 2019a).