Orientation of silk III at the air-water interface

A threefold helical crystal structure of Bombyx mori silk fibroin has been observed in films prepared from aqueous silk fibroin solutions using the La ngmuir-Blodgett (LB) technique. The films were studied using a combination of transmission electron microscopy and electron diffraction techniques. Fi lms prepared at a surface pressure of 16.7 mN/m have a uniaxially oriented crystalline texture, with the helical axis oriented perpendicular to the pl ane of the LB him. Films obtained from the air-water interface without comp ression have a different orientation, with the helical axes lying roughly i n the plane of the film. In both cases the d-spacings observed in electron diffraction are the same and match a threefold helical model crystal struct ure, silk III, described in previous publications. Differences in the relat ive intensities of the observed reflections in both types of oriented sampl es, as compared to unoriented samples, allows estimations of orientation di stributions and the calculations of orientation parameters. The orientation of the fibroin chain axis in the plane of the interfacial film for uncompr essed samples is consistent with the amphiphilic behavior previously postul ated to drive the formation of the threefold helical silk III conformation. (C) 1999 Elsevier Science B.V. All rights reserved.