J.S. Church, A.S. Davie, P.J. Scammells, D.J. Tucker

In Part I of this study we investigated the mechanism of the fixation of Lanasol dyes to the various amino acid side chain sites within wool protein using model compounds in a mixed solvent system. As the dyeing of wool is generally carried out in an aqueous system at the boil it was felt that the model system would be more accurate if the compounds studied were water soluble. This paper reports on the synthesis of the sulfonated version of the model reactive dye compound used in Part I of this study and its subsequent reaction with model wool compounds. In addition, a model compound based on benzene sulfonic acid, and an actual commercial Lanasol dye were also reacted. As in the first part of this study the reaction products were isolated by chromatography and then characterized by proton and carbon-13 NMR, and electrospray mass spectroscopy. In general the results were consistent with those obtained from the study carried out in the acetone/water solvent system. It was confirmed that the dibromo form of the dye reactive group is only converted to the monobromo form in the presence of model wool compounds and that both forms react with model wool compounds to yield the same products. Amines reacted with the model dyes to form a product containing an aziridine ring - no evidence for the proposed reaction of this ring with a second nucleophilic wool site to form a cross-link between two protein chain segments could be detected. In the few cases where an aziridine ring structure was not formed, the products obtained were found to support a Michael addition (1,4-addition) reaction mechanism. Unlike the results found for the mixed solvent system it was found that the wool models for N-terminal groups did not react with the model dye compounds.

J.S. Church, A.S. Davie, P.J. Scammells, D.J. Tucker

The mechanism of fixation of Lanasol dyes, which are distinguished by their a-bromoacrylamido reactive group, to the various amino acid side chain sites within wool protein is quite complex. It has been proposed that the reaction could proceed by either a nucleophilic substitution or Michael addition pathway. We have investigated this mechanism through the reaction between model dye compounds which possess either an α-bromoacrylamido or α,β-dibromopropionamido group and wool mimetics that contain amine, thiol and hydroxyl groups. These latter groups are typical of the reactive sites found in wool proteins. The reactions were carried out in an acetone-water solvent system. The reactions were monitored by HPLC and the products were isolated and then characterised by proton and carbon-13 NMR, and mass spectroscopy. The results of the study confirmed that the dibromo form of the dye reactive group is only converted to the monobromo form in the presence of model wool compounds and that both forms react with these model wool compounds to yield the same products. When the nucleophilic moiety was an amine, the reaction terminated with a product containing an aziridine ring. No evidence for the proposed reaction of this aziridine ring with a second nucleophilic moiety to form a cross-link could be detected. The thiol of cystiene and imidazole of histidine were also found to reaction with the model dyes.

J. S. Church, G. L. Corino, A. L. Woodhead

FT-Raman spectroscopy coupled with amide I band deconvolution was used to monitor the conformational changes of the peptide backbone of sulphite pre-treated wool fibres during stretching. The spectral changes observed are consistent with the transition of α-helical to β-pleated sheet structure. These changes, which are most rapid during the early stages of stretching, can be related to protein secondary structure at both the crystalline and molecular levels. Analysis of the amide III region of the spectra reveals that a very small amount of additional disorder is imparted to the peptide backbone as a result of stretching. The consistency in the widths at half-height of the amide I band components implies that stretching does not significantly change the distribution of peptide chain conformations. From the Raman analysis of cells isolated from the stretched fibres, it is evident that conformational changes occur in both the cuticle and cortex. The most evident change, however, is in the cortical cells.

A. L. Woodhead, F. J. Harrigan, J. S. Church

In this paper we have investigated the use of the chemometrics methods partial least squares (PLS), principal components regression (PCR) and principal component analysis (PCA) to develop both quantitative and qualitative correlations between mid-infrared attenuated total reflectance spectra and variation in chlorination treatments in wool samples. Quantitative correlations were obtained using both PLS and PRC that were significantly improved in terms of both standard errors of prediction and calibration correlation coefficient values over the calibrations obtained by classical least squares regression. These results reflect the variability and complexity of the samples produced by the industrial chlorination process. The chemometric models based on spectral regions that were truncated to include the frequencies where only the primary and intermediate oxidation products are active were found to be significantly better than those based on the full low wavenumber spectral region. PLS calibrations were used successfully to predict chlorination levels of samples obtained from commercial mills. These predictions were found to be in much better agreement with stain test results than those obtained using the least squares approach. The use of PCA to develop qualitative correlations between the chlorinated samples was investigated. It was demonstrated that PCA could be used as a tool to discriminate between samples according to their chemical treatment.

K. R. Millington, J. S. Church

A possible mechanism for the formation of cysteine, cysteic acid and partially oxidized cystine species in keratin following exposure to UVC radiation at 254 nm is proposed. The primary photolysis products are the radical ions RSSR'' and RSSR'-, and it is suggested that partially oxidized cystine species are formed from reactions of the radical cation only. The mechanisms m is supported by Fourier transform IR (FT-IR) and optical reflectance spectroscopy of UVC-treated wool exposed to air, oxygen and nitrogen atmospheres, and by previous electron spin resonance (ESR) studies on disulphides exposed to both UV and ionizing radiation. The mechanism supports the Symons assignment for the sulphur radical “species X” as [RS(SR)SR]', rather than RSS'. Exposure of wool to less energetic UV radiation produces different products via a quenching mechanism involving the formation of the radical anion RSSR'- only, which precludes the formation of oxidized cystine intermediates. The formation of S-sulphonate residues at longer wavelengths suggests that a competing singlet oxygen process may also occur.

J. S. Church, G. Corino, A. L. Woodhead

Wool fibers are comprised of proteins known as α‐keratins and have a complex morphological structure. The major components of this structure, the cuticle and cortical cells, differ in the conformations of their peptide chains as well as their amino acid compositions. High quality Fourier transform Raman spectra of cortical and cuticle cells isolated from fine Merino wool fibers have been obtained. Raman spectroscopy has been shown to be sensitive to the differences in both secondary structure and amino acid composition. The cortical cells were found to be higher in α‐helical content as compared to the cuticle cells, which had an increased disordered content. Specific information, consistent with amino acid analysis results, regarding cystine, tyrosine, tryptophan, and phenylalanine residues, were obtained for both the cortical and cuticle cells. In addition, the Raman spectra provided information about free thiol groups, amino acids residues with amide group side chains, and residues with protonated carboxyl group side chains. Middle ir transmission spectra of these isolated cells were also obtained. In comparison to the Raman data, the middle ir spectra were found to be not as rich in information.

J. S. Church K. R. Millington

The photodegradation of wool keratin is a very complex process that is not well understood. In this work the techniques of Fourier transform Raman and attenuated total reflectance Fourier transform‐infrared spectroscopies have been used to study wool samples irradiated in air using a variety of different sources. The spectra obtained from these samples have been compared with those obtained from wool treated with sodium bisulphite, a reagent well known to produce thiol and S‐sulfonate groups. As an aid for spectral interpretation the Raman and infrared spectra of cystine and those of the sodium and potassium cysteine‐S‐sulfonates have also been obtained. The data suggest that there are two different photolytic reaction pathways involving the cystine residues which are dependent on the wavelength of the applied radiation.

E. A. Carter P. M. Fredericks J. S. Church

Infrared photoacoustic spectroscopy (PAS) is a useful technique for examining sur face-treated wool samples. Sample preparation is simple, and reproducible spectra of adequate signal-to-noise ratio are obtained in a few minutes. The ability of PAS to vary the penetration depth by varying the optical path difference velocity is used to obtain spectra of the near surface region of the samples. These spectra are compared with those taken with a greater penetration depth, which therefore represent more of the bulk wool sample. Samples are chlorinated and chlorinated/neutralized wool from a shrinkproofing process, and wool treated with a proprietary fluoropolymer.