Oscar Hinojosa

Photochemical Initiation of Free Radicals in Cotton Cellulose

Cotton cellulose of the Deltapine variety, spun into 7s/3 yarns, was purified hy extraction with hot ethanol. followed 1Iy hoilÍ11,g in dilute sodium hydroxide solution. precautions being takcn to minimi7(’ oxidation hy air. The sodium, hydroxide sulution was remoBed hy washing thycc·llnlc~~e with distilled water; tills was followed 1~)~ souring with dilute acetic acid. neutralizing with dilute ammonium hydroxide, and again washing with di.,tjJ1cd, water ,’1151., ., After conditioning the cellulose ut 21 °C and fji~/ ’ kl 1, the resulting product had a moisture content of’ahout ~r/ and a viscosity-average molecu.lar. weight of about 700.000 ( 12 ~ : ’

Modifications of Cotton Cellulose Surfaces by Use of Radiofrequency Cold Plasmas and Characterization of Surface Changes by ESCA

Radiofrequency (rf) cold plasmas of argon, nitrogen, and air were used to modify cotton fabrics and yarns. Changes in surface characteristics were detected by application of the techniques of electron emission spectroscopy for chemical analyses (ESCA), electron spin resonance, and chemiluminescence. Examples of polymeriza tion of selected monomers and depolymerization of chemically modified cottons within rf plasmas have been used to illustrate potentials of combinations of plasmas and ESCA in cellulose chemistry.

Effect of rf cold plasmas on polysaccharides

Abstract Low temperature-low pressure argon, nitrogen, and air plasmas generated with rf radiation have been used to treat cotton cellulose and other saccharides. The physical and chemical nature of each substrate was altered by the cold plasma. Although no gross topographical changes of the cotton surface were visible even under the electron microscope, plasma-treated cotton wetted more rapidly and more uniformly than its control, and other saccharides were more soluble in water and other chemical reagents (such as ammonium hydroxide) after plasma treatment. Free radicals were created within the cellulose matrix and structures of all other saccharides. ESR signals, which indicate presence of carbon radicals, degenerated asymmetrically, implying that other types of radicals also existed. ESCA spectra of cotton cellulose showed that some carbon atoms had been oxidized and some oxygen atoms reduced during plasma activation. Activated cottons displayed chemiluminescence and had redox powers that varied with their environments. When cotton and organic monomers were simultaneously present in cold plasma, reactive centers initiated polymerization ofthin films upon the cotton surface. Plasmaactivated cottons exhibited the same chemical reactions as a-hydroxyperoxides or their precursors from living organisms.

Applications of AFIS fineness and maturity module and x-ray fluorescence spectroscopy in fiber maturity evaluation

Worldwide round-testing and calibration of the nep-counting and fiber-length mod ules of the Zellweger Uster advanced fiber information system (AFIS) are well advanced. Lack of appropriate quantitative calibration standards for fiber maturity has limited similar development of the prototypic AFIS fineness and maturity (F&M) module. A combination of calcium x-ray fluorescence Spectroscopy (Ca-XRF) and AFIS-F&M map ping of fiber quality from twenty-one days post anthesis (DPA) to boll opening (56 DPA) permits direct comparisons of AFIS-determined fiber physical maturity (as micronAFIS, circularity, and cross-sectional area) with fiber chronological maturity (as DPA) and physiochemical maturity (as Ca-XRF). The AFIS-F&M module is a powerful tool that makes possible quantitative comparisons of fiber maturity across time (during fiber development and in different crop years), across space (different boll and locule positions and different growing areas), within single bolls and locules, and between cotton varieties and species.

Thermal Initiation of Free Radicals in Cotton Cellulose

The mechanism of tlte thermal degradation of cotton cellulose is of fundamental interest in developing nameresistant clothingand otlier textiles. About eighteen degradation products. re~ultingfront the ltyrolyais of cotton cellulose, including gaseous products, organic molecules containing 14) carbon atoms, levogiticos-.tti, and water, been identified. A free radical mechanisrtt ]its been postulated to explain the process of pyrotytic dcg-radation of cotton cellulose and tlte sub-’ sequent rearrangements wlticli yield the products, ~It has also been postulated that a critical step in the formation of levcylucr~sart is the cleavage of the 1,4-gl,~;v;I<tic linkage in the c elitilose’ molecule [7, 1), 10, 11, 131. The apparent energy of activation of the thermal chain cleavage was reported for cotton cellulose as 25.2 kcttl mole r 5 J. This value was based on fluidity iiieistireniriits and was lower than the values of 35 to 40 kcal/ mole for cleavage of the linkage, hased on heterogeneous acid hydrolysis of cotton cellulose 1’121, Experimental data arc presented in this report which indicate that free radicals are. in fact. thermally initiated in cotton cellulose and that the apparent energy of ac~ tivation for free radical formation is higher than that previously reported for thermally initiated chain c1(’aqBg’c but about l’qual to that reporte(1 for chain cletvtge by acid’ hyclrulysis.

Superoxide radicals in intact tissues and in dimethyl sulphoxide-based extracts

Abstract Steady state contents of free radicals were investigated in intact living tissues and in tissue extracts prepared with dimethyl sulphoxide-tetrabutylammonium perchlorate (DMSO-TBAP). DMSO-TBAP was suitable for extraction because free radical artifacts were not generated and hydrous superoxide was both stable and readily spin-trapped for electron paramagnetic resonance (EPR) spectrometry. Intact leaves and roots contained an unresolved radical and paramagnetic manganese. Superoxide was EPR-silent in whole tissues but was spin-trapped in extracts of roots where its steady-state concentration in vivo was approximately 10 −5 M. Ascorbyl radicals were generated upon alkalization of whole tissues and by comminution of tissues in DMSO-TBAP. Aprotic sites for the storage of superoxide in vivo are considered and a role for storage is discussed in regards to cytochemical defence mechanisms of plant protection.

Thermally Initiated Free-Radical Oxidation of Cellulose

Purified cotton cellulose was heated in the resonant cavity of the electron spin resonance spectrometer in static nitrogen, flowing nitrogen, and flowing air and in vacuum. The formation of free radicals in the samples of cotton was monitored at temperatures below 300°C. Cotton was treated with chemical additives and then heated in static nitrogen at atmos pheric pressure. At the same temperature of heating, a much greater concentration of free radicals was formed in purified cotton heated in static nitrogen than in cotton heated in flowing nitrogen or in vacuum. The rate of free-radical forma tion in cotton heated in flowing nitrogen was constant throughout the heating period. Cotton, heated at the same tem peratures and times in flowing air or in static nitrogen, showed a greater concentration of free radicals than cotton heated in flowing nitrogen. The effects of additives or the application of vacuum on the apparent energy of activation for the formation of free radicals in heated cotton were also investigated. The amount of char formed during pyrolysis, as indi cated by the intensity of the free-radical signal, was much greater for samples which contained additives or which were allowed to trap decomposition products than for untreated cotton purged free of volatile decomposition products, as they were formed.

Synthesis of some furoic and thenoic esters of the methyl d-Glucopyranosides, and their stability to high-energy radiation

Abstract The esters obtained by complete esterificatlon of methyl D-glucopyranosides with, respectively, 2-furoyl chloride (β-, 1: α-, 2), 2-furanacryloyl chloride (β-, 3: α-, 4) 5-bromo-2-furoyl chloride (β-, 5: α-, 6) 2-thenoyl chloride (β-, 7: α-, 8) 5-methyl-2-thenoyl chloride (β-, 9: α-, 10) 5-bromothiopheneacryloyl chloride (β-, 11: α-, 12) and 2-thiopheneacryloyl chloride (β-, 13: α-, 14) were subjected to irradiation (2.8 x 1019 eV/gh) in the solid state to a dosage of 7.1 x 1020 eV/g. The e.s.r. spectra of irradiated (irr.) methyl α- and β- d -D-glucopyranoside and irr. esters 1-14 were examined to determine the nature of the radiation damage: those of the unsubstituted d -glucopyranosides contain one very strong doublet and one very strong singlet, indicating that cleavage of the C-I-O bond (doublet) and dehydrogenation of the C-I-H bond (singlet) had occurred. The e.s.r. spectra of irr. furoates 1 and 2 contain strong doublets. but those of 3-6 have none, showing that the glycosidic bonds in the latter are highly stable to radiation damage, but those in 1 and 2 are stable compared to that in methyl α- d -glucopyranoside. The e.s.r. spectra of the irr. thenoic esters indicated that glycosidic bonds to 11 and 12 are highly stable to radiation initiated cleavage (absence of doublets), those in 7-10 are fairly stable (weak doublets), and those in 13 and 14 are more stable (strong doublets) than that in methyl α- d -glucopyranoside (very strong doublet) Radiation-initiated, dehydrogenation reactions were decreased for 7 and 8 (very weak singlets), 9 and 10 (very weak, and weak singlets), and 11 and 12 (strong singlets). compared with those of methyl α- d -glucopyranoside, 13, and 14 (very strong singlets). The radiation stability of these esters may arise from intramolecular transfer of energy to the ester groups, and be followed by dissipation of the energy. The anomeric form of methyl d -glucopyranoside has no influence on the localization of the energy.

Electron-spin resonance study of some irradiated D-glucopyranosides

Abstract The e.s.r. spectra generated in methyl α- D -glucopyranoside (1) and some selected derivatives thereof by high-energy radiation have been examined to determine the nature of the radiation damage. Evaluations of the e.s.r. spectra of irradiated methyl tetra-O-acetyl-α- D -glucopyranoside (2), methyl tetra-O-[(p-ethoxycarbonyl)benzoyl]-α- D -glucopyranoside (3), methyl tetra-O-(p-methoxybenzoyl)-α- D -glucopyranoside (4), methyl tetra-O-(p-nitrobenzoyl)-α- D -glucopyranoside (5), methyl tetra-O-(ochlorobenzoyl)-α- D -glucopyranoside (6), methyl tetra-O-p-tolylsulfonyl-β- D -glucopyranoside (7), methyl tetra-O-nicotinoyl-α- D -glucopyranoside (8), and methyl tetra-O-(phenylcarbamoyl)-α- D -glucopyranoside (9) contained mainly one type of stable free-radical, together with some secondary radical in low concentration. The e.s.r. spectrum of compound 1 consisted of one doublet and one singlet; this observation was explained by assuming that the free electron position is at C-1, so that the cleavage of the C-1O glycosidic bond would give rise to the doublet, and the dehydrogenation of the C-1H bond would give rise to the singlet. For most of the substituted D -glucopyranosides studied, irradiation gave singlet spectra which were explained by assuming the radical site to be C-1 (by the dehydrogenation of the C-1H bond). The aromatic groups present in the substituted D -glucopyranosides were known to protect the glycosides from radiation damage1. In the aromatically substituted D -glucopyranosides, no reducing power was measurable, even when the compounds were irradiated to dosages as high as 5.2 x 1021 eV/g; this was additional evidence that no cleavage of the C-1O glycosidic bond occurs during irradiation of these compounds. The absence of hyperfine splitting of the free electron at C-1 with H-2 was explained by a change in the conformation of the molecule after H-1 had been cleaved. Displacement of the hydrogen atoms would then occur to remove any deformation of the ring caused thereby; this would remove H-2 from the vicinity of the unpaired electron at C-1. No thermally induced free-radicals could be detected in these compounds, unless they were heated to charring.

Electron-spin resonance studies of oxidation photosensitized by ferric chloride, of some alcohols in rigid glasses

Abstract Ferric chloride-photosensitized oxidations of methanol, ethanol, 1-propanol ( 3 ), 2-propanol, 1-butanol ( 5 ), 2-methyl-1-propanol, 2-methyl-2-propanol ( 7 ), 1-pentanol, cyclopentanol, and cyclohexanol were conducted in the cavity of an e sr spectrometer at temperature between −150 and -196°, with high-pressure, mercury lamp as the light source except for rigid glasses of 7 plus ferric chloride, all of the photolyzed alcohols investigated generated e s r-detectable free-radicals. The effects of temperature of the concentrations of the radicals formed in the riged glasses indicated that the production of free radicals derived from alcohols involves an active intermediate trapped in the photolyzed, ferric chloride-alcohol rigid glass. In almost all classes, the intensities of the signals of the e s r-detectable radicals increased after photolysis was discontinued when the temperatures of the photolyzed, rigid galsses were increased, the intensities of the signals generated by the radicals increased initially, until radical recombinations became the predominant raection based on hyperfine splittings of the e s r spectra, a free-radical site could be assigned to the hydroxyl-bearing carbon atom of all of the alcohols investigated, except 3,5 and 7 . As the temperature of the rigid galsses were increased, changes in hyperfine splittings of the e s r spectra of the radicals derived from alcohols were observed, these changes probably reflect increased molecular motion of the photolyzed alcohols.