Near‐infrared, infrared and Raman spectra of native starch and cationic quaternary ammonium starches prepared by different reaction methods were recorded. An interpretation of the spectra is given that takes the structural changes of the starch molecules and the degree of substitution (DS) into consideration. The near‐infrared spectra of the cationic starches showed additional bands compared to native starch at about 6010 cm−1 and 4438 cm−1, which are assigned to the first overtone of the stretching vibration and to a combination band of the CH3 groups in the trimethyl ammonium substituent. No significant changes in the infrared spectra of the cationic starches could be observed due to strong absorption bands of OH and H2O. By contrast, the Raman spectra of the cationic starches showed characteristic bands of the trimethyl ammonium substituent at about 3030, 970 and 761 cm−1. Plots of the ratios of intensity of the 761 cm−1 band to an unchanged starch band at 938 cm−1 versus DS gave linear curves which could be used for DS determination. Furthermore, the use of a NIR calibration model for DS determination with a standard error of calibration (SECV) of 0.003 is reported.
Thin films of hydroxyl (POH) and carboxyl (PCOOH) terminated aromatic hyperbranched polyesters (HBPs) were prepared by spin coating on silicon wafers and subsequently annealed above their glass transition temperature (Tg). The surface properties and the swelling behaviour of these films in aqueous buffer solutions were studied as a function of annealing time using contact angle measurements and ellipsometry. Non‐annealed films were hydrophilic with surface free energies of 51 mJ/m2 for POH and 49 mJ/m2 for PCOOH, respectively. The swelling behaviour of the polymer films in buffer solution with pH 7.4 was described in terms of changes of the thickness and effective refractive index of the swollen layer. Under identical conditions a lower water uptake was found for hydroxyl terminated HBPs (POH) which were annealed more then 2 h. The lower water uptake correlates with the surface properties of the films. The annealed films were less hydrophilic. Their surface free energy was 38 mJ/m2 independent of the annealing. Films of carboxyl terminated HBPs (PCOOH) showed similar surface properties after annealing. However, these films were unstable under the same conditions in aqueous solutions. Stable PCOOH films were obtained by additional covalent binding to the substrate using an epoxy silane as a coupling agent.
Raman microscopic measurements were used to analyse the detailed chemical composition and structure of three old papers dating from the 15th and 19th centuries. Raman mapping measurements were performed on the surface and along the cross‐section of the papers with a lateral resolution of 1 μm. The resulting Raman images visualise the detailed chemical structure of the papers including all components such as the different types of cellulose fibre, filler pigments, sizing agents, colour pigments and also inadvertently added trace particles, such as minerals or products of biological activity. The results of the paper analysis are discussed in connection with their use for the detailed characterisation and dating of paper.This study demonstrates the great potential and the possibilities offered by Raman microscopy or Raman imaging for chemical paper analysis. Raman microscopy allows new insights into the chemical composition and structure of old papers and could considerably enhance the understanding of former papermaking practices and also combat forgery and the fraud of documents and artworks on paper.
SYNOPSISThough the strong affinity of Congo red and thioflavin S for amyloid deposits has been known for a long time, the binding mechanism of these biological dyes to amyloid sites is still not understood. In the present work, the competition of these two dyes for binding in Alzheimer amyloid is investigated. Analyses by optical microscopy and microspectrofluorimetry were performed on several series of stained diseased brain sections. Microspectrofluorimetric analyses showed that bound Congo red and bound thioflavin S have characteristic spectra in which the fluorescence maxima are distinct of those for the free dyes. Both, optical microscopic analyses and fluorescence measurements of stained brain sections indicated that Congo red and thioflavin S compete with each other at the same interacting site on diseased cerebral tissue. The staining efficiency of the replacing dye seems to be a maximum for a concentration of about 1%.
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