Ian H. Leaver

Trapping of radical intermediates in the photoreduction of benzophenone

Abstract Radical intermediates formed during the photoreduction of benzophenone by alcohols, amines, phenols, sulphides, thiols, ethers, hydrocarbons and amides have been trapped by t-nitrosobutane and the resulting nitroxide radicals characterized in situ by ESR. In the case of 2,6-di-t-butylphenols and aliphatic sulphides evidence was obtained for radicals other than those expected.

Fluorescent whitening agents—a survey (1974-82)

Abstract This survey presents a comprehensive coverage of the literature on fluorescent whitening agents for the period 1974 to mid-1982. It is intended to serve researchers in the field by providing an up-to-date summary of the published literature on the synthesis, textile applications and analysis of fluorescent whitening agents. The survey does not cover the use of fluorescent whitening agents as additives for soaps and detergents. The latter part of the survey describes the light fading reactions of five technologically important classes of fluorescent whitening agent. Recent progress in understanding the photochemical processes that are responsible for fading, and the factors that influence the light stability of fluorescent whitening agents in a polymeric environment, are summarized.

X-Ray Photoelectron Spectroscopic Study of the Wool Fiber Surface:

The surface analysis technique of x-ray photoelectron spectroscopy (XPS) has been used to investigate the chemical composition and reactivity of the wool epicuticle. Approximate relative proportions of protein and lipid material in the epicuticle have been deduced from the surface elemental ratios; the sulfur content of the proteins in the epicuticle was estimated to be about 9% by weight. Treating wool with potassium t-butoxide in anhydrous t-butanol, a reagent that is reported to cause specific epicuticle modification, caused only minor changes in the elemental composition of the fiber surface. There were marked changes, however, in the sulfur (2p) photoelectron spec trum. Approximately one third of the cystine residues in the epicuticle were converted to cysteic acid residues. Evidence was also obtained for the partial conversion of cystine residues into lanthionine residues.

SENSITIZED PHOTO‐OXIDATION OF WOOL AND SILK BY A TRIAZINYLSTILBENE

Abstract— The photo‐oxidation of wool and silk treated with a fluorescent brightening agent (a triazinylstilbene) has been studied. Complete amino acid analyses of the irradiated keratins showed that in the presence of this sensitizer, only tryptophyl and histidyl residues were susceptible to photodecomposition; the former were oxidized at a faster rate than the latter. Sixty per cent of the tryptophyl residues in silk were photo‐oxidized during a 4 hr exposure to an artificial light source designed to simulate summer sunlight conditions. The rate of discoloration of the irradiated silk fabric, measured spectrophotometrically, was found to parallel closely the rate of photo‐oxidation of the tryptophyl residues in the fabric.

PHOTOREDUCTION OF CRYSTAL VIOLET IN SOLUTION AND IN POLY(VINYL ALCOHOL) FILMS

Abstract— The photolysis of crystal violet oxalate has been studied in aqueous and non‐aqueous solutions and in films of poly(viny1 alcohol) at room temperature. Evidence has been obtained from electron‐spin‐resonance, absorption and fluorescence spectroscopy for the formation of the semireduced dye radical, tri‐(p‐dimethylaminophenyl)methyl, both in solution and in the solid state. Electron spin resonance and luminescence spectra of the radical produced by electrolytic reduction of the dye are also reported.

SENSITIZED PHOTOOXIDATION OF WOOL BY FLUORESCENT WHITENING AGENTS. A DIRECT SPECTRAL STUDY

Abstract—A fluorescence spectral study has been made of the photochemical behaviour of two types of fluorescent whitening agents, a naphthotriazolylstilbene and a bistriazinylaminostilbene, in single fibres of wool. The photodecomposition of each molecule of the naphthotriazolylstilbene is accompanied initially by the photooxidation of up to 7 residues of trp in the fibre. Amino acid analyses show that his and met residues are also photooxidized. Inhibition of the photooxidation of these amino acids by sodium azide suggests that singlet oxygen is involved in the reaction.

Confocal Laser Raman Microprobe Studies of Keratin Fibers

A laser-based Raman microprobe/confocal microscope has been used to provide structural information on the constituent proteins in several keratins including wool, human hair, and feathers. Depth-profiling studies have revealed differences between the outer (cuticle) and inner ( cortex ) regions of human hair fibers with respect to the molecular orientation and chemical composition of the constituent proteins. Raman microprobe measurements are applied to the identification and distribution analysis of textile auxiliaries on wool fibers. The advantages and utility of the Raman micro probe technique for investigating single textile fibers are also discussed.

Depth Profile Analysis of Keratin Fibers by FT-IR Photoacoustic Spectroscopy

The depth profiling capability of Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) has been used to distinguish spectroscopically between the surface layer (cuticle) and the interior (cortex) of intact keratin fibers. The thermal diffusion lengths of wool and hair fibers, calculated as a function of the wavenumber and optical scanning velocity of the interferometer, indicate a depth resolution of the order of a micrometer. Shifts in the amide I and II bands to lower wavenumbers were observed with increasing velocity of the interferometer, consistent with differences in protein structure between the bulk and surface regions of the fiber. On the basis of these spectral changes, the location of the cuticle/cortex interface below the fiber surface can be determined.

ON THE ROOM TEMPERATURE PHOSPHORESCENCE OF WOOL KERATIN

Abstract—A study has been made of the room‐temperature phosphorescence behaviour of wool keratin and its major constituent proteins. The 290 nm induced phosphorescence of wool, previously thought to decay by second‐order kinetics, is shown to consist of two separate components which decay exponentially with lifetimes of 0.18 × 0.03 and 1.45 × 0.25 s. Selective oxidation of the tryptophyl residues eliminates the long‐lived phosphorescence, but has no effect on the short‐lived component. The latter is variable in its intensity, and depends upon the history of the fibre. The origins of the different emissions are discussed, and the possible involvement of the phosphorescent species in the photochemical reactions leading to discoloration of the fibre are considered.

Studies in Wool Yellowing Part XXII: ESR Investigations of the Action of UV Radiation

A study has been made of the photo-induced free radicals in thiourea/formaldehyde- treated wool and fluorescent-brightened wool after exposure to near uv radiation in the wavelength region 2900-4000 A, and the results are compared with the observed changes in the electronic absorption spectra. Thiourea/formaldehyde treatment of wool significantly protects cystyl residues from disulfide bond rupture which otherwise occurs on irradiation with uv light of wavelength 2900-3200 A, and there are characteristic changes in the reflectance spectra of treated wools, associated with the reduced concentration of R.CH2S. radicals. Fluorescent-brightened wool exhibits an almost identical electron spin resonance (ESR) spectrum to that of untreated wool, when irradiated in the region 2900-3200 A, but, when exposed to 3650 A radiation, a greatly increased yield of free radicals is ob served in the brightened wool. Photosensitization of the protein by the fluorescent brightener is suggested as the most likely mechanism.