Showing papers by "Serge Pérez published in 2009"

Chapter 5 – Structural Features of Starch Granules I

Abstract: Publisher Summary The amylose and amylopectin molecules, the granule structure, and the natures and amounts of the lipid and protein molecules present in granules vary with the botanical source of the starch. Starch granules are mainly found in seeds, roots, and tubers, but are also found in stems, leaves, fruits, and even pollen. They occur in all shapes and sizes (spheres, ellipsoids, polygons, platelets, irregular tubules) and are long dimensioned. Differences in external granule morphology are generally sufficient to provide unambiguous characterization of the botanical source via optical microscopy. The starch granule is nature's chief way of storing energy over long periods in green plants. The granule is well suited to this role, being insoluble in water and densely packed, but still accessible to the plant's catabolic enzymes. Native starch granules have a crystallinity varying from 15% to 45%, thus, most native starch granules exhibit a Maltese cross when observed under polarized light. Most starch granules are made up of alternating amorphous and crystalline shells, which are between 100 and 400 nm thick. These structures are termed “growth rings.” Birefringence remains unchanged on both polar and equatorial sections of elongated starch granules. Most starch polymers in the granule are in an amorphous state. Most cereal starches give the so called A-type pattern; some tuber starches (e.g. potato) and cereal starches rich in amylose yield the B-type pattern, while legume starches generally give a C-type pattern. The two major macromolecular components of starch are amylose and amylopectin.

Shape: automatic conformation prediction of carbohydrates using a genetic algorithm

Abstract: Background Detailed experimental three dimensional structures of carbohydrates are often difficult to acquire. Molecular modelling and computational conformation prediction are therefore commonly used tools for three dimensional structure studies. Modelling procedures generally require significant training and computing resources, which is often impractical for most experimental chemists and biologists. Shape has been developed to improve the availability of modelling in this field.

Seeing structures and measuring properties with transmission electron microscopy images: A simple combination to study size effects in nanoparticle systems

Abstract: We report on a method to measure the mean inner potential (V0) using transmission electron microscopy. It is based on phase retrieval from a focus series and has allowed to measure V0 as a function of the size for a system of gold nanoparticles. It comes out that V0 increases for particles below 2 nm. The focus series being carried out in conditions close to the high-resolution ones, structural information can be directly obtained. The high-resolution images have revealed that significant structural change occurs below the 2 nm size, which should be related to the V0 increase.