Patterned Peptide Multilayer Thin Films with Nanoscale Order Through Engineered Liquid Crystallinity

Nanofibrillar Structure and Molecular Mobility in Spider Dragline Silk

“…We also consider the assumption of crystal defects resulting in a breakdown of the l = 2 n extinction as less probable as it has never been observed by SR diffraction experiments on a range of dragline silks. , The presence of the superlattice peak is therefore also difficult to reconcile with a different space group or a superstructure due to a repetitive sequence of other residues, such as serine residues in silk fibroin. ,, This also holds for the assumption of a more or less random distribution of β-sheet nuclei 34 in the amorphous matrix, which is incompatible with the meridional position of the superlattice reflection. We note, however, that the azimuthal width of the superlattice reflection corresponds to the broadening of the oriented equatorial halo due to short-range order as seen by WAXS, which can be separated from the 210 reflection by profile fits. , The azimuthal widths of both WAXS peaks show considerable variability during artificial drawing of dragline silk, which can be related to variations in drawing stress and possibly mechanical action within the spinnerets. , Dragline protein chain-folding models suggest an aggregation of alanine sequences through a backfolding of β-strands via serine−glycine or glycine−asparagine “hairpin loops”. ,,, We tentatively assume that the glycine-rich chains, which do not participate in the formation of a polyalanine block, are constrained into a smectic β-sheet structure, which is laterally disordered due to a mismatch of side groups. A larger orientation distribution of chain axes in the smectic phase would explain the increased azimuthal width of the superlattice reflection as compared to the crystalline domains 002 reflection.…”

“…19,20 Dragline protein chainfolding models suggest an aggregation of alanine sequences through a backfolding of β-strands via serineglycine or glycine-asparagine "hairpin loops". 4,12,34,55 We tentatively assume that the glycine-rich chains, which do not participate in the formation of a polyalanine block, are constrained into a smectic β-sheet structure, which is laterally disordered due to a mismatch of side groups. A larger orientation distribution of chain axes in the smectic phase would explain the increased azimuthal width of the superlattice reflection as compared to the crystalline domains 002 reflection.…”

X-ray Evidence for a “Super”-Secondary Structure in Silk Fibers

“…A true random coil configuration would rule out chiral liquid crystalline behaviors and structures based on rigid asymmetric molecular shapes and packing. Evidence for liquid crystallinity in silk fiber precursor solutions has thus been interpreted largely in terms of the lyotropic (concentration-based) liquid crystallinity of flexible amphiphiles, despite evidence for complex self-assembled chiral structures in the liquid and fiber , that are extremely atypical of lyotropic flexible amphiphiles. Our hydrogels have a swollen lamellar order and appear to lack in-layer order, features typical of flexible lyotropic liquid crystals.…”

“…Due to the complex and multiscale order that characterizes the structures of silks, and those of many other natural fibers and fibrous proteins as well, the various data regarding structure and properties have been integrated into a coherent picture only slowly. A clear validated and integrated description of silk fiber structure and formation is beginning to emerge due to efforts by a number of researchers working on a number of fronts. − …”