Dissolution mechanism of Bombyx mori silk fibroin in a CaCl2 aqueous solution studied with 13C, 1H and 43Ca NMR spectroscopies.

13C NMR spectra of Bombyx mori silk fibroin in a CaCl2 aqueous solution observed as a function of CaCl2concentration. This spectra changed markedly at more than 3.5 M CaCl2 concentration. The decrease in the high resolution NMR-detectable peaks and broadening of the detected peaks were observed. This phenomenon can be regarded as the so-called polymer effect of the silk fibroin and reflects the change in the hydrated state around the Ca2+ and Cl- ions. The latter conclusion was based on the 1H and 43Ca NMR spin-lattice relaxation times of the CaCl2 aqueous solution. The dissolution process of the silk fibroin power in the conc. CaCl2 aqueous solution was monitored by the observation of the high resolution 13C NMR peaks.