Characterization of Microbial Poly(ε-L-lysine) and Its Derivatives by Solid-State NMR

摘要

The molecular structure and conformation of microbial poly(ε-L-lysine) (ε-PL) and its derivatives in aqueous solution and in the solid-state have been studied with liquid-state ~1H and ~(13)C NMR, and solid-state ~(13)C and ~(15)N NMR, together with FT-IR, FT-Raman, and circular dichroism (CD) techniques. CD and vibrational spectroscopic results indicate that ε-PL assumes a p-sheet conformation in aqueous solution and in the solid state. Solid-state ~(13)C NMR spectra of the crystalline and the amorphous components were obtained separately by utilizing difference in ~(13)C spin-lattice relaxation times between the two components. The degree of crystallinity was estimated to be 63%. Conformation models of the crystalline component were also discussed. Chemically modified derivatives of ε-PL, ε-PL/MO and ε-PL/DC were prepared through reactions with methyl orange (MO) and dabsyl chloride (DC), respectively. Characterization of these derivatives was carried out by solid-state ~(13)C and ~(15)N NMR. In ε-PL/MO side chain a-amino groups of ε-PL are involved in ionic bonds with methyl orange (MO) to form poly-ionic complexes, (ε-PL)-NH_3~+ SO_3 -(MO). In contrast, the a-amino groups react with DC in c-PL/DC to form covalent sulfonamide bonds, (ε-PL)-NH-SO_2-(DC). The ~(15)N NMR data are consistent with these structures.