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1. tRNA Modifications as a Readout of S and Fe-S Metabolism

   Edwards, A.E; Addo, M.A.; Dos Santos, P.C. (July 2021, Methods in molecular biology)

   Dos Santos, P.C. (Ed.)

   Iron-Sulfur (Fe-S) clusters function as core prosthetic groups known to modulate the activity of metalloenzymes, act as trafficking vehicles for biological iron and sulfur, and participate in several intersecting metabolic pathways. The formation of these clusters is initiated by a class of enzymes called cysteine desulfurases, whose primary function is to shuttle sulfur from the amino acid l-cysteine to a variety of sulfur transfer proteins involved in Fe-S cluster synthesis as well as in the synthesis of other thiocofactors. Thus, sulfur and Fe-S cluster metabolism are connected through shared enzyme intermediates, and defects in their associated pathways cause a myriad of pleiotropic phenotypes, which are difficult to dissect. Post-transcriptionally modified transfer RNA (tRNA) represents a large class of analytes whose synthesis often requires the coordinated participation of sulfur transfer and Fe-S enzymes. Therefore, these molecules can be used as biologically relevant readouts for cellular Fe and S status. Methods employing LC-MS technology provide a valuable experimental tool to determine the relative levels of tRNA modification in biological samples and, consequently, to assess genetic, nutritional, and environmental factors modulating reactions dependent on Fe-S clusters. Herein, we describe a robust method for extracting RNA and analytically evaluating the degree of Fe-S-dependent and -independent tRNA modifications via an LC-MS platform. 

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2. Experimental investigation of the effect of nickel on the electrical resistivity of Fe-Ni and Fe-Ni-S alloys under pressure

   https://doi.org/10.2138/am-2020-7301  

   Pommier, Anne (July 2020, American Mineralogist)

   Abstract Electrical resistivity experiments were conducted on three alloys in the iron-rich side of the Fe-Ni(-S) system (Fe-5 wt% Ni, Fe-10 wt% Ni, Fe-10 wt% Ni-5 wt% S) at 4.5 and 8 GPa and up to 1900 K using the multi-anvil apparatus and the 4-electrode technique. For all samples, increasing temperature increases resistivity. At a specified temperature, Fe-Ni(-S) alloys are more resistive than Fe by a factor of about 3. Fe-Ni alloys containing 5 and 10 wt% Ni present comparable electrical resistivity values. The resistivity of Fe-Ni(-S) alloys is comparable to the one of Fe = 5 wt% S at 4.5 GPa and is about three times higher than the resistivity of Fe = 5 wt% S at 8 GPa, due to a different pressure dependence of electrical resistivity between Fe-Ni and Fe-S alloys. Based on these electrical results and experimentally determined thermal conductivity values from the literature, lower and upper bounds of thermal conductivity were calculated. For all Ni-bearing alloys, thermal conductivity estimates range between ~12 and 20 W/(m⋅K) over the considered pressure and temperature ranges. Adiabatic heat fluxes were computed for both Ganymede's core and the Lunar core, and heat flux values suggest a significant dependence to both core composition and the adiabatic temperature. Comparison with previous thermochemical models of the cores of Ganymede and the Moon suggests that some studies may have overestimated the thermal conductivity and hence, the heat flux along the adiabat in these planetary cores. 

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3. High Pressure-behavior of the Fe-S system and composition of the Earth’s inner core

   https://doi.org/10.3367/UFNe.2017.03.038079  

   Bazhanova, Z. G. (February 2017, Physics Uspekhi)

   Using the evolutionary crystal structure predictionalgorithm USPEX, we identify the compositions and crystalstructures of thermodynamically stable compounds in the Fe ±S system at pressures in the range of 100 ± 400 GPa. We findthat at pressures in the Earth's solid inner core (330 ± 364 GPa)two compounds are stable – Fe2S and FeS. In equilibrium withiron, only Fe2S can exist in the inner core. Using the equation ofstate of Fe2S, we find that, in order to reproduce the density ofthe inner core by adding sulfur alone, 10.6 ± 13.7 mol.% (6.4 ±8.4 wt.%) sulfur is needed. An analogous calculation for silicon(where the only stable compound at inner core pressures is FeSi)reproduces the density of the inner core with 9.0 ± 11.8 mol.%(4.8 ± 6.3 wt.%) silicon. In both cases, a virtually identicalmean atomic massMMin the range of 52.6 ± 53.3 results forthe inner core, which is much higher thanMMà49:3 inferred forthe inner core from Birch's law. In the case of oxygen (allowingfor the equilibrium coexistence of suboxide Fe2O with ironunder core conditions), the inner core density can be ex-plained by the oxygen content of 13.2 ± 17.2 mol.% (4.2 ±5.6 wt.%), which corresponds toMMbetween 49.0 and 50.6 

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4. Fe-S clusters masquerading as zinc finger proteins

   https://doi.org/10.1016/j.jinorgbio.2022.111756  

   Pritts, Jordan D.; Michel, Sarah L.J. (May 2022, Journal of Inorganic Biochemistry)
5. Electronic stripe patterns near the fermi level of tetragonal Fe(Se,S)

   https://doi.org/10.1038/s41535-023-00592-5  

   Walker, M.; Scott, K.; Boyle, T. J.; Byland, J. K.; Bötzel, S.; Zhao, Z.; Day, R. P.; Zhdanovich, S.; Gorovikov, S.; Pedersen, T. M.; et al (October 2023, npj Quantum Materials)

   Abstract FeSe_1−xS_xremains one of the most enigmatic systems of Fe-based superconductors. While much is known about the orthorhombic parent compound, FeSe, the tetragonal samples, FeSe_1−xS_xwithx > 0.17, remain relatively unexplored. Here, we provide an in-depth investigation of the electronic states of tetragonal FeSe_0.81S_0.19, using scanning tunneling microscopy and spectroscopy (STM/S) measurements, supported by angle-resolved photoemission spectroscopy (ARPES) and theoretical modeling. We analyze modulations of the local density of states (LDOS) near and away from Fe vacancy defects separately and identify quasiparticle interference (QPI) signals originating from multiple regions of the Brillouin zone, including the bands at the zone corners. We also observe that QPI signals coexist with a much stronger LDOS modulation for states near the Fermi level whose period is independent of energy. Our measurements further reveal that this strong pattern appears in the STS measurements as short range stripe patterns that are locally two-fold symmetric. Since these stripe patterns coexist with four-fold symmetric QPI around Fe-vacancies, the origin of their local two-fold symmetry must be distinct from that of nematic states in orthorhombic samples. We explore several aspects related to the stripes, such as the role of S and Fe-vacancy defects, and whether they can be explained by QPI. We consider the possibility that the observed stripe patterns may represent incipient charge order correlations, similar to those observed in the cuprates. 

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