NMR Spectroscopy Characterization Protocol

The NMR spectra were recorded at a temperature of 25 °C using a Bruker Avance 600 spectrometer (Bruker, Billerica, MA, USA). The nuclear magnetic hydrogen spectrum (¹H-NMR), nuclear magnetic carbon spectrum (¹³C-NMR and DEPT 135°) and two-dimensional nuclear magnetic correlation spectrum (¹³C-¹H HSQC) were measured. The dried samples were dissolved in deuterium oxide and placed in an NMR tube with an inner diameter of 0.5 mm for testing. The test frequency for ¹H-NMR was 600 MHz, and for ¹³C-NMR and DEPT 135° it was 150 MHz [67 (link)]. The number of sample collection points for each type of NMR is 64 K. The number of scans for ¹H-NMR was 128, while the number of scans for other NMRs was 16. The recovery delay was 2 s. The free induction decay (FID) signal measured by the NMR instrument was imported into MestReNova 14.0.1 software (Mestrelab Research, Bajo, Santiago de Compostela, Spain) for Fourier transformation, and the NMR spectra were obtained after phase correction and baseline correction [68 (link)]. The spectra were then saved as ASCII files and imported into SpecAlign 2.4.1 software (University of Oxford, Oxford, England) for peak matching [69 (link)].