Na2b4o7

ZnFe₂O₄ spinel single crystals were synthesized using the high-temperature solution growth method. Powders of reagents ZnO (Sigma Aldrich; 99.99%) and Fe₂O₃ (Sigma Aldrich; 99.995%) and solvent anhydrous Na₂B₄O₇ (Sigma Aldrich; >99%) were ground together. The initial powder mixture was loaded in a 20-mL platinum crucible, tightly covered by a platinum lid, heated to T_g at a rate of 50 °C/h, and held at T_g for 12 h. The ratios of solvent to solute, defined as s = (mol Na₂B₄O₇)/(mol 3d cations Zn and Fe), were maximized from solubility studies to achieve solute saturation at each T_g; s =0.94 for T_g = 1,000 °C, and s =1.4 for T_g = 850 °C. The crucibles were rotated inside the box furnaces throughout the synthesis process, with a rate of 96 rpm for T_g = 850 °C and 48 rpm for T_g = 1,000 °C. For T_g = 1,250 °C, either no rotation or a rotation rate of 24 rpm was used. ZnFe₂O₄ single crystals grow during the slow-cooling process, with a rate of −2 °C/h in the temperature range of 1,250 to 950 °C for T_g = 1,250 °C, −1.2 °C/h in the range of 1,000 to 800 °C for T_g = 1,000 °C, and −0.26 °C/h in the range of 850 to 750 °C for T_g = 850 °C, respectively. Afterward, the furnace was cooled down to room temperature naturally. Octahedron-shaped crystals (SI Appendix, Fig. S1) were extracted by etching in 7% HCl solution at 150 °C.

For conditioning the fungus for metabolomics experiments, a 6 mm diameter mycelia-covered agar plug of the actively growing colony margin was transferred to the center of a fresh petri dish (94 mm × 16 mm, Greiner Bio-One GmbH, Kremsmünster, Austria) containing minimal medium (0.52 g L⁻¹ KCl (Roth); 0.52 g L⁻¹ MgSO4 × 7(H₂O) (Roth); 1.52 g L⁻¹ KH₂PO₄ (Fluka) 0.0004 g L⁻¹ Na₂B₄O₇ × 10(H₂O) (Roth); 0.004 g L⁻¹ CuSO₄ × 5(H₂O) (Sigma-Aldrich, Burlington, MA, USA); 0.008 g L⁻¹ FeSO₄ × 7(H₂O) (Roth); 0.008 g L⁻¹ MnSO₄ × 4(H₂O) (Sigma-Aldrich, Burlington, MA, USA); 0.005 g L⁻¹ Na₂MoO₄ × 7(H₂O) Sigma-Aldrich, Burlington, MA, USA); 0.08 g L⁻¹ ZnSO₄ × 7(H₂O) (Roth); 2.64 g L⁻¹ (NH₄)₂SO₄ (Roth); 1.6% Agarose (NEEO ultra-quality; Roth, Karlsruhe, Germany) pH 5.5). Moreover, 10 g L⁻¹ native or labeled glucose was used as a sole carbon source. For cultivation on native (¹²C) glucose, D (+)-glucose (≥99.5% purity; Sigma-Aldrich, Burlington, MA, USA) was used. For the global labeling of the metabolome, the fungus was cultivated on ¹³C₆ glucose (U-¹³C₆ D (+)-glucose; 99.9%; Cambridge Isotope Laboratories, Inc., Woburn, MA, USA). Cultures were incubated for 3 days at 25 °C.