Zur Einwirkung von Ozon auf Wolle und Aminosäuren
Solid histidine shows no reaction during ozonation. In contrast, the ozonation of aqueous solutions of histidine reveals quick and effective oxidation. Ozone consumption during histidine treatment is passing two phases. Depending on the duration of the ozone treatment the consumption rate is decreasing in a ratio of 3.5:1. Histidine ozonation in unbuffered liquors shows a characteristic decline of pH value in three phases. The pH shift towards acidic values points out that the imidazole ring of histidine is preferentially attacked. Depending on the duration of the ozone treatment the formation of about eight decomposition products of different polarity at pH 7.2 are detected by HPLC-analysis. Thin layer chromatography of the ozonation product resulted in the detection of six different products. The composition of the product mixture depends on the pH value of the liquor. Variation of pH within a range of 3 and 11 leads to a higher number of products with increasing pH. At the same time, the amounts of the different products are more equally distributed on increasing pH. At high pH there is no product dominating the mixture whereas at lower pH particular products are preferentially formed. Amino acid analysis of the product mixtures obtained by histidine ozonation without prior hydrolysis showed the formation of aspartic acid (Asp), asparagine (Asn) and serine (Ser). Serine formation is considered to result from secondary decomposition of aspartic acid. As a result of ozonolytic histidine decomposition the formation of acetaldehyde as well as imidazole was found by mass spectroscopic analysis. In addition, a product with high molecular mass (M=305 g/mol) is detected that could not be identified. Ozonation of histidine leads to the formation of different radical species which are detectable by means of electron paramagnetic resonance (EPR) spectroscopy. Formation of these species resp. their stability could be enhanced using spin trapping agents. Impact of ozone on the polyamide fibre Nylon®-6.6 leads to smoothing of the fibre surface in comparison to untreated material. Apparently, ozone is able to remove inhomogeneities from the fibre surface. Using spin trapping agents, formation of radicals in polyamide during ozonation is detected by EPR. Polyglycine shows the same behaviour, while the ozonation of glycine shows no radical formation. These facts point to a direct attack of the peptide bonds during ozonation. Changes in the surface topology of ozone treated wool tops show parallels to chlorine treated wool resulting in shrivelled appearance of the surface. In addition, smoothing effects become apparent due to rounding of the cuticle scales. On parts of the fibre the scales are removed to a very high extent, so the structure can hardly be recognized. In comparison to untreated wool top, a decrease of the felting behaviour is assessed. Ozonation of wool fabrics also leads to a smoothing of the surface. The levelling is due to an extraction of proteinic materials which cover the surface of the single fibres and act as a kind of glue. The fabric obtains a brittle handle. The effectiveness of an ozone treatment of wool with regard to bleaching resp. the extent of weakening the fibre depend on the humidity during the ozone treatment. The fibre is apparently hydrophilized. Chemical composition of wool, i.e. its amino acid composition undergoes significant changing during exposure to ozone. Not only cystine is oxidised to cysteic acid, in accordance with the results of histidine decomposition an increase of the content of the amino acids Asp+Asn and Ser is detected, furthermore, a decrease of the histidine amount in the fibre. Different from polyamide, radical activity is detected in untreated wool top. Nevertheless, radical formation during ozonation of wool is detected. Use of spin trapping agents leads to the detection of additional radical species as well as an increase in intensity of the radical peaks in the EPR spectra.
info:eu-repo/classification/ddc/540, Wolle, Aminosäuren, Ozonisierungsreaktion, Histidin, Nylon, Chemie
Networked Digital Library of Theses and Dissertations
Publikationsserver der RWTH Aachen University