Dpx 400 nmr spectrometer

A sample of ecumicin (1) was prepared by weighing 4.00 mg (±0.01 mg) into a microcentrifuge tube using a Mettler Toledo XS105 Dual Range analytical balance, followed by addition of 600 µL of methanol-d₄ (99.8%). The solution was transferred to a 5 mm NMR tube using a Pressure-Lok gas syringe (VICI Precision Sampling Inc., Baton Rouge, LA, USA). The final concentration of the ecumicin sample was 6.67 mg/ml. After acquiring a ¹H NMR spectrum at 400.13 MHz on a Bruker DPX-400 NMR spectrometer equipped with a 5-mm QNP (4-nucleus) probe, the solution was transferred back to a microcentrifuge tube and 200 µL of it was later transferred to a 3 mm NMR tube. A ¹H NMR spectrum was also measured at 899.94 MHz with a Bruker AVANCE-II-900 NMR spectrometer, equipped with 5-mm TCI triple resonance inverse detection cryoprobe and z-axis pulse field gradient. All ¹H NMR experiments were acquired at 298 K (25 °C) using the standard Bruker pulse sequence (“zg”), with qHNMR parameter optimization. The probes were frequency tuned and impedance matched prior to data collection. Chemical shifts (δ_H) are expressed in ppm relative to the residual protonated solvent signal (¹H 3.310 ppm), and coupling constants (ⁿJ_H,H) are given in Hertz (Hz).