138 research outputs found
Interplay between Structure and Dynamics in Chitosan Films Investigated with Solid-State NMR, Dynamic Mechanical Analysis, and X-ray Diffraction
Modern solid-state NMR techniques, combined with X-ray diffraction, revealed the molecular origin of the difference in mechanical properties of self-associated chitosan films. Films cast from acidic aqueous solutions were compared before and after neutralization, and the role of the counterion (acetate vs Cl⁻) was investigated. There is a competition between local structure and long-range order. Hydrogen bonding gives good mechanical strength to neutralized films, which lack long-range organization. The long-range structure is better defined in films cast from acidic solutions in which strong electrostatic interactions cause rotational distortion around the chitosan chains. Plasticization by acetate counterions enhances long-range molecular organization and film flexibility. In contrast, Cl⁻ counterions act as a defect and impair the long-range organization by immobilizing hydration water. Molecular motion and proton exchange are restricted, resulting in brittle films despite the high moisture content
DNA Fingerprinting of Pearls to Determine Their Origins
We report the first successful extraction of oyster DNA from a pearl and use it to identify the source oyster species for the three major pearl-producing oyster species Pinctada margaritifera, P. maxima and P. radiata. Both mitochondrial and nuclear gene fragments could be PCR-amplified and sequenced. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay in the internal transcribed spacer (ITS) region was developed and used to identify 18 pearls of unknown origin. A micro-drilling technique was developed to obtain small amounts of DNA while maintaining the commercial value of the pearls. This DNA fingerprinting method could be used to document the source of historic pearls and will provide more transparency for traders and consumers within the pearl industry
pH-responsive hydrogel membranes based on modified chitosan: water transport and kinetics of swelling
Determination of N-acetyl content in chitosan samples by CD measurements.
International audienc
pH and CD measurements on fully deacetylated chitosan: application to Cu II - Polymer interactions.
International audienc
Preparation and characterization of N-acetyl glucosamine oligomers by hydrofluoric acid hydrolysis ; conformational studies
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