Chain-Folded Lamellar Stacking Structure of the Crystalline Fraction of Silk Fibroin with Silk II Form Studied by 2D C-C Homonuclear Correlation NMR Spectroscopy.

The structure of silk fibroin (SF) is a subject of significant interest due to its remarkable physical properties; however, its atomic-level structure is still not conclusive. We previously proposed a lamellar stacking structure for the crystalline fraction (Cp) with β-turns occurring every eighth amino acid. In this study, we took the following steps: At first, a model of the chain-folded lamellar stacking structure in antipolar and antiparallel β-sheet layers was constructed.

Quantitative Analysis of Solid-State Homonuclear Correlation Spectra of Antiparallel β-Sheet Alanine Tetramers.

Poly-l-alanine (PLA) sequences are a key element in the structure of the crystalline domains of spider dragline silks, wild silkworm silks, antifreeze proteins, and amyloids. To date, no atomic-level structures of antiparallel (AP)-PLA longer than Ala have been reported using the single-crystal X-ray diffraction analysis. In this work, dipolar-assisted rotational resonance solid-state NMR spectra were observed to determine the effective internuclear distances of C uniformly labeled alanine tetramer with antiparallel (AP) β-sheet structure whose atomic coordinates are determined from the X-ray crystallographic analysis.

Multiple-component covalent organic frameworks.

Covalent organic frameworks are a class of crystalline porous polymers that integrate molecular building blocks into periodic structures and are usually synthesized using two-component [1+1] condensation systems comprised of one knot and one linker. Here we report a general strategy based on multiple-component [1+2] and [1+3] condensation systems that enable the use of one knot and two or three linker units for the synthesis of hexagonal and tetragonal multiple-component covalent organic frameworks. Unlike two-component systems, multiple-component covalent organic frameworks feature asymmetric tiling of organic units into anisotropic skeletons and unusually shaped pores.

Solubilization mechanism and characterization of the structural change of bacterial cellulose in regenerated states through ionic liquid treatment.

A statistical approach was used to characterize the heterogeneous structures of bacterial cellulose samples pretreated with four kinds of ionic liquids (ILs). The structural heterogeneity of these samples was measured by Fourier transform infrared spectroscopy as well as solid-state NMR methods such as cross-polarization magic-angle spinning and dipolar-assisted rotational resonance. The obtained data matrices were then evaluated by principal components analysis.