The 13C solution NMR experiments were performed at 25 ◦C with JEOL -500 NMR spectrometer operating at 125 MHz for 13C nucleus.
The 45◦ pulse with an acquisition time of 1 s and a delay time of 2.5 s was used for the observation.
The spectral width was 34 kHz with data points of 32k. Up to 12k scans were accumulated
13C chemical shifts were calibrated through an internal dioxane peak observed at
66.5 ppm relative to tetramethylsilane at 0.0 ppm.
The sample concentration was 30% (w/v), and a small amount of D2O (5%) was added to the sample solution to obtain a deuterium lock signal.