Lattice resolution in natural polymers

Abstract

Recent developments in low-dose electron microscopy have led to reports of crystal lattice fringes in natural polymers extremely sensitive to damage by electron irradiation. In one of these studies, lattice images of (β-chitin from the diatom Thalassiosira-fluviatilis were obtained and subsequent computer processing produced the molecular projection of this biopolymer crystal along its b-axis at 0.35 nm resolution. Similar direct structural studies have not been done yet on the α-chitin which is far the most abundant polymorphic form found in nature. The present work reports the direct imaging of crystallite lattice fringes of α-chitin microfibrils from lobster tendon, with a preliminary analysis of the results in terms of crystallite size and perfection.A typical preparation of α-chitin microfibrils is shown in Figure 1. The image, recorded by diffraction contrast, shows bundles of long microfibrils as well as smaller elements less aggregated and of different length. These smaller elements, composed of shorter crystallites, are the result of the combined action of the acid hydrolysis and of the ultrasound treatment which broke down the originally long microfibrils. When aggregated into larger ribbons, the width of the microfibrils cannot be detrmined due to overlapping, but when viewed individually, the microfibrils exhibit a lateral size of about 10 to 14 nm (see arrows).