Mary A. Becker

Atomic force microscopy: Bombyx mori silk fibroin molecules and their higher order structure

We performed atomic force microscopy measurements on fibroin molecules from the domestic silkworm, Bombyx mori. At low concentrations, we could observe single protein molecules. The shape of the observed molecules is a rod with long smaller chains extending from the ends. The size of the rod is 60 nm in length and 15 nm in width. At high concentrations, we observed long threadlike aggregates of fibroin molecules, their chains entangled with one another. These results provide insight into the microscopic mechanism of silk-fiber formation.

THE U.S. FIRST LADIES GOWNS: A BIOCHEMICAL STUDY OF SILK PRESERVATION

The degradative changes in silk are investigated with amino acid analysis and solubility under denaturing conditions (7M urea). These biochemical techniques use extremely small samples for quantitative analyses and are capable of detecting chemical alterations at the molecular level. The biochemical results are used to place the fabric samples from a museum collection within the context of artificially aged silks. Analyses of the naturally aged samples reveal two populations: sericin-rich and sericin-depleted. Denaturing solvents such as soap will remove the protective protein coating from sericin-rich fabrics; sericin-depleted fabrics are al- ready a high risk for light-induced damage. The data suggest that silk fabrics manufactured during this cen- tury are likely to have their sericin coatings totally removed and therefore at great risk to light damage.

Thermal properties of seed proteins

Thermal properties of seed proteins, prolamines from rice, wheat and soybean were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), thermal expansion, X-ray diffraction and infrared spectroscopy. Prolamine films cast from aqueous ethanol are amorphous in the random-coil conformation. The glass transition of prolamine is observed at 160, 172 and 150°C for rice, wheat and soybean, respectively. The amorphous prolamine films crystallize at 196, 205 and 199°C for rice, wheat and soybean, respectively. The thermal degradation of prolamine films occurs from 228, 250 and 270°C for rice, wheat and soybean, respectively.

Thermal properties of bombyx mori and several wild silkworm silks Phase transition of liquid silk

The thermal properties of liquid silk from domestic and wild silkworms are investigated. Liquid silks obtained from the silk gland of the domesticated silkworm, Bombyx mori and four wild silkworms, Samia cynthia ricini, Dictyoploca japonica, Antheraea pernyi and Antheraea yamamai were used. The DSC curves for the liquid silk from the domestic silkworm have weak endothermic peaks corresponding to the breaking of hydrogen bonds in the β-form or to the untangling of physical network. The DSC curves for the wild silkworm silks, however, show clear exothermic peaks corresponding to a phase transition from the α-helix conformation to the β-form. Liquid silk from all the different silkworms undergoes a characteristic irreversible phase transition.

Spherulites of Tussah Silk Fibroin. Structure, thermal properties and growth rates

The crystal structure, thermal properties and growth rates of spherulites of the Tussah silk fibroin, produced upon drying of the silk taken directly from the lumen which is essentially a poly(L-alanine)polypeptide, are investigated. Depending on casting conditions, spherulites with either αhelical chain conformation or β parallel sheet structure are produced. The growth rates display a strong positive temperature coefficient, with an apparent transition, which however cannot be related with the formation of two different crystal structures at this stage.

Thermal Properties and Inorganic Composition of silk Fiber

The thermal properties of Bombyx mori silk fibers subjected to heat-treatment were examined by thermogravimetry-differential thermal analysis-Fourier transform infrared absorption spectrometry (TG-DTA-FTIR). Only 1% of the original silk fiber weight remains as cocoon ash after treatment at 550 °C. Inorganic components, such as calcium, potassium, sulfur, magnesium etc., were detected in the cocoon ash by energy dispersion fluorescent X-ray spectrometry. A sharp decrease in weight was observed in the TG data to begin around 280 °C, and an endothermic peak appears at 308 °C as evidenced by DTA curves. The IR bands observed at 2380 cm-1, 1760 cm-1, 1503, 1085 cm-1 and 965 cm-1 become stronger as an exothermic reaction beginning at 280 °C takes place. This is probably due to cleavage of the main chain and the accompanying decomposition of the silk fibers.