Assessing secondary structure of a dyed wool fibre by means of FTIR and FTR spectroscopies

The paper describes changes in the structure of a wool fibre dyed with model azo dyes. These were direct dyes, non-genotoxic derivatives of carcinogenic benzidine, synthesized specially for the purpose of the experiment. The non-mutagenic benzidine derivatives were: 2,2'-dimethyl-5,5'-dipropoxybenzidine and 5,5'-dipropoxybenzidine. Using FTIR, changes in secondary structure of fibres were assessed in three measuring ranges: 3600-3000, 1700-1400 and 1000-1300 cm(-1). The dyes were found to distinctively affect wave-number shifts of amide A, amide I bands and in the fingerprint area around 1050 cm(-1). It seems that these three areas are related to the sites in which dyes bind with wool fibre keratin. In FTR spectra, the focus was on assessing the changes of peptide bond configuration in the area of amide 1, disulfide area of cystine and the area of the interaction between dyes and wool fibre keratin, i.e. 1250-1600 cm(-1). For analysis, three kinds of materials were selected: (1) raw wool fibres, (2) fibres subjected to deuteration and treated with formic acid, (3) wool fabric. Each of them was dyed with the model azo dyes. The results obtained by both spectroscopies allow for identifying the functional groups responsible for the binding of dyes with keratin fibre. (C) 2003 Elsevier Science B.V. All rights reserved.