Effects of water,methanol, and ethanol on the production of starch-g-polystyrene copolymers by cobalt-60 irradiation

Starch-g-polystyrene copolymers were made by simultaneous ⁶⁰Co irradiation of mixtures of wheat starch and styrene at room temperature. The extent of conversion of monomer to polymer is increased drastically with increasing water content up to a level of about 26 wt % on starch. Methanol had approximately the same effect as water at equivalent concentrations but ethanol was clearly less effective as a promoter of homo- and graft copolymerizations. Drying the starch reduced the conversion to polymer with all promoters but caused the greatest deterioration in the ability of ethanol to promote polymerization. The effects of physically swelling the starch by freeze drying the gelatinized material were also studied, as were preirradiation graft copolymerizations. The effects of promoters on graft polymerization parallel their abilities to scavenge stable radicals in irradiated starch. Water and methanol are better radical scavengers and polymerization promoters because they are better able to disrupt hydrogen bonds and permeate the starch structure. Radiolysis of the promoter is important in the grafting reaction.     

Formation of free radicals in photoirradiated cellulose. V. Effect of temperature

ESR spectra of purified and ferric ion-sensitized celluloses irradiated with ultraviolet light in vacuo at 45, 20, ?80, and ?196°C were recoreded and compared. Generally, several kinds of spectra, viz., singlet, three-line, five-line, and seven-line spectra, were observed. At higher temperatures, only singlet and three-line spectra of stable free-radical species were detected, whereas at lower temperatures such as at ?196°C, two doubled spectra of formyl radicals and hydrogen atoms were also detected in addition to cellulose radicals. It is believed that the intricate spectra observed at low temperatures are superimposed upon spectra generated by free radicals which may or may not be stable at high temperatures. During reirradiation at ?196°C with an alternative light sources, i.e., λ > 2537 Å and λ > 3400 Å, of samples which were irradiated at 20°C or at ?196°C, phenomena indicative of radical transformation and formation of new radicals or of decay of radicals in terms of ultraviolet bleaching were observed on studying the changes of line-shapes and relative signal intensities of the spectra.     

Preparation,morphology, size quantization effect and photocatalytic properties of CdS Q-nanocrystals

Intercommunity of lots of molecules and perturbation of few molecules have been shown in bulk materials because the intermolecular force is very much smaller than that of intramolecules. So, macroscopic solid theories have been applied to investigating their properties. On the other hand, microscopic quantum mechanical theory (or molecular orbital theory) has enabled the study of single molecule. However, it becomes much more complicated to the study on the small-parti- cle species representin…     

Electron spin resonance studies of propagating radicals in polymerization. I. Methacrylate propagating radicals

Ferric chloride-photosensitized free-radical initiation was used to generate propagating radicals in polymerization of methacrylic acid (MAA), allyl methacrylate (AMA), methyl methacrylate (MMA), 1,3-butylene dimethacrylate (1,3-BDMA), hydroxypropyl methacrylate (HPMA), lauryl methacrylate (LMA), hexyl methacrylate (HMA), and methacrylamide (MA) in rigid glasses of methanol or acetone at near liquid nitrogen temperatures. The formation and conformational changes of these propagating radicals at different temperatures were studied by electron spin resonance (ESR) spectroscopy. When methanol was the rigid glass, ·CH₂OH radicals were formed initially and were stable below ?160°C. As the temperature of the rigid glass was increased, the ·CH₂OH radicals reacted with monomer to yield propagating radicals. With the exception of the propagating radical for methacrylamide, the propagating radicals of the methacrylates examined initially generated five-line ESR spectra which gradually changed to nine-line spectra, as temperature of the rigid glass was increased. It was concluded that one type of propagating radical was formed in all cases. However, when the temperature of the rigid glass was increased, the single structural conformation that initially allowed one of the methylene hydrogens and methyl group to interact with the unpaired electron to generate only a five-line spectrum was changed to yield a second conformation that allowed interaction to generate an additional four-line spectrum. Finally, a mixture of the propagating radical for methacrylate monomer in two structural conformations was obtained, and an ESR spectrum consisting of nine lines (5 + 4 lines) was generated. In the case of the propagating radical for methacrylamide this change to yield two structural conformations evidently was hindered, so that only an ESR spectrum consisting of five lines was generated.     

The ESR spectra of p-benzosemiquinone radical anion included in cyclodextrins

The ESR spectra of p-benzosemiquinone radical anion included in cyclodextrins (CyDxs) in aqueous solutions were observed and analyzed. Remarkable differences in the line shape were found between the spectrum in α-CyDx aqueous solution and that in 95% ethanol. They are explained in terms of the suppressed molecular rotation of the radical included in the α-CyDx cavity. The ESR spectra of the radicals included in β- and γ-CyDx in aqueous solutions are identical with that in 95% ethanol, hence in the β- and γ-CyDx cavities the radical rotates as freely as in 95% ethanol.     

Thermal-induced conversion of maleic and fumaric acid anion radicals in poly(methyl methacrylate)

Thermal-induced conversion of maleic and fumaric acid anion radicals produced by γ irradiation at 77 K in poly(methyl methacrylate) (PMMA) was studied by electron spin resonance (ESR) and optical absorption spectroscopic measurements. The ESR spectra of these acid anion radicals change into two-line spectra with a line separation of ca. 10 G by thermal annealing. This spectrum is assigned to a protonated radical of each acid anion radical. Anion radicals of the solutes are relatively stable below the γ transition point of PMMA and the conversion reaction takes place near this point. This means that the molecular motion of matrix molecule affects the radical conversion reaction.     

Electron transfer between two stable radicals

Electron spin resonance (ESR) is a sensitive tool to detect the electron-transfer processes in some specified systems from the change of the ESR signals. In this paper, the interaction between poly(N,N-dimethylaniline) (PDMA) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) was investigated by ESR spectra based on the stability of their radicals in ethanol. It is shown that an electron-transfer process occurs from nitrogen atoms of PDMA molecules to those of DPPH molecules which makes PDMA form more stable radical cations and eliminates the radicals on DPPH.     

氧化锌分散体光反应产生的自由基中间体

溶液中光诱导的电子转移反应已进行了大量的研究。而半导体粉末在水相或非水溶剂中的光化学研究也与自俱增^[1-3]。这种光化学与成像体系、太阳能转换以及光催化或污物的光降解有关。因此,越来越引起人们的重视。     

Photo Switchable Two-step Photochromism in a Series of Ln-Phosphonate(Ln=Dy,Gd, Tb,Y) Dinuclear Complexes

Exploring the discrete complexes with multi-step coloration is still a challenge in the field of electron transfer photochromic materials. Herein, we synthesized a series of dinuclear Ln-diphosphonate compounds[Ln=Dy(1); Gd(2); Tb(3); Y(4)] with a remarkably and reversibly photoactive coloration phenomenon. These compounds showed two-step coloration behavior, which were the first discrete architectures in the reported electron transfer photochromic complexes. This two-step coloration phenomenon was originated from the large distortion of H₃-TPT acceptors, which in turn reduced the π-conjugation of electron acceptors and slowed the decay process of electron transfer. The photogenerated stable doublet radicals originated from electron transfer from diphosphonate donor to polypyridine acceptor in these complexes were detected by UV-Vis and electron spin resonance(ESR) spectra. Furthermore, the photogenerated radicals were estimated by direct current magnetic susceptibilities and variable temperature ESR spectra, suggesting the doublet radicals in the dinuclear structure for all the compounds. This work revealed a series of discrete phosphonate-based systems with a multi-step coloration process, providing a new pathway for designing multicolor photochromic materials with potential photoswitching or other applications.     

Formation of free radicals in photoirradiated cellulose. III. Effect of photosensitizers

The effect of several photosensitizers on the formation of free radicals in cellulose has been investigated. Radicals were generated with ultraviolet light, and examined by means of ESR techniques; irradiations were carried out at 77°K. On irradiation of the sensitized celluloses with light of λ > 3400 Å, samples treated with benzoyl peroxide, hydrogen peroxide, benzophenone, riboflavin, azobisisobutylonitrile, and metallic ions Cr²⁺ and Ni²⁺ exhibited single-line spectra with line widths of 16 to 26 gauss. Samples treated with Pb²⁺ and Fe³⁺ exhibited three-line and five-line spectra, respectively. On irradiation with light of λ > 2537 Å, most of the sensitized samples exhibited five-line spectra with different relative signal intensities. Among these, samples treated with Fe³⁺ manifested the most prominent spectra with the strongest relative signal intensities.     

Formation of free radicals in photoirradiated cellulose. II. Effect of moisture

The effect of moisture content upon free radical formation in celluloses irradiated with ultraviolet light has been studied by means of ESR spectroscopy at 77°K. As studied from the variation of the line-shape and the relative signal intensity of the spectra observed, it is clear that moisture content in the sample greatly influences the formation of free radicals when irradiated with ultraviolet light. The moisture content in the range of 5–7% leads to a significant decrease of radical formation; and alternatively, when moisture content is lower or higher than this range, the formation of free radicals is increased.     

Formation of free radicals in photoirradiated cellulose and related compounds

Free-radical formation in various modifications of celluloses, namely, wood cellulose I, II, III, and IV, rayon cellulose, amorphous cellulose, cotton linters, and absorbent cotton, irradiated with ultraviolet light, has been studied by means of ESR spectroscopy at 77°K. Various types of free radicals were generated from these samples. The line shapes and the signal intensities of the ESR spectra depended greatly upon the degree of crystallinity, the lattice type, and the arrangement of molecules in cellulose. The effect of degree of crystallinity and the amount of sensitizer (Fe³⁺) absorbed revealed that photochemical reactions in cellulose occurred exclusively in the amorphous regions of the polymer. Free radicals formed in these samples behaved distinctively upon a warm-up process. Phenomena of radical migration and formation of new radicals were observed from the sensitized samples of rayon cellulose and amorphous cellulose.     

ESR spectra of photolysis products from inorganic peracids and peroxyhydrates

The O-O bond is broken by low-temperature photolysis in polycrystalline peroxosulfate, peroxophosphate, and electrolytic peroxocarbonate. The radicals are stable at room temperature and their ESR spectra show appreciable hyperfine structure. Solid peroxyhydrates under these conditions give the radicals found in frozen solutions of H₂O₂. The differences in the ESR spectra may serve to distinguish the true peroxides from the peroxyhydrates. Two specimens of peroxocarbonate prepared by chemical methods have been shown in this way to be mixtures of peroxocarbonate with peroxyhydrate.     

L-tryptophan radical cation electron spin resonance studies: connecting solution-derived hyperfine coupling constants with protein spectral interpretations

Fast-flow electron spin resonance (ESR) spectroscopy has been used to detect a free radical formed from the reaction of l-tryptophan with Ce (4+) in an acidic aqueous environment. Computer simulations of the ESR spectra from l-tryptophan and several isotopically modified forms strongly support the conclusion that the l-tryptophan radical cation has been detected by ESR for the first time. The hyperfine coupling constants (HFCs) determined from the well-resolved isotropic ESR spectra support experimental and computational efforts to understand l-tryptophan's role in protein catalysis of oxidation-reduction processes. l-Tryptophan HFCs facilitated the simulation of fast-flow ESR spectra of free radicals from two related compounds, tryptamine and 3-methylindole. Analysis of these three compounds' beta-methylene hydrogen HFC data along with equivalent l-tyrosine data has led to a new computational method that can distinguish between these two amino acid free radicals in proteins without dependence on isotope labeling, electron-nuclear double resonance, or high-field ESR. This approach also produces geometric parameters (dihedral angles for the beta-methylene hydrogens) that should facilitate protein site assignment of observed l-tryptophan radicals as has been done for l-tyrosine radicals.     

Polymerization of Diphenylbutadiyne Derivatives in Solution by Free Radical Initiator

In order to study free radical reactions of aromatic diacetylenes, the reaction of diphenyldiacetylene with di‐t‐butylperoxide was carried out in 1,2‐dichlorobenzene. The presence of t‐butoxy radicals considerably accelerated product formation, and oligomers with number average molecular weights of 700–2000 were obtained. There is no fragment of the t‐butyl group in the oligomers obtained according with the ¹H‐NMR spectrum. Furthermore, it is impossible that the t‐butoxy radicals would have initiated the oligomerization. The intense ESR spectra observed during the reaction at 130°C are due to the diradicals of oligomeric diphenylbutadiyne. It was concluded that the oligomerization proceeds via coupling of diradicals, and not the successive addition of radicals to monomers. The purified product oligomers did not contain carbonyl groups indicating there was no oxidation, and their ESR spectra have revealed that these oligomers contained a substantial amount of living free radicals stable in air at room temperature. The reason why high polymers are not obtained is the steric effect of oligomeric diradicals for coupling, as well as probable cyclization.     

Radical products of γ-radiolysis of 12-crown-4 at 77 K

Paramagnetic products of γ-radiolysis of 12-crown-4 and its solutions in CFCl₃ and CFCl₂CF₂Cl at 77 K were studied by ESR spectroscopy. It was found that the ESR spectra of 12-crown-4 irradiated with γ-rays at 77 K contained superimposing signals of at least two species, the radicals resulting from macrocycle opening -?H-C(H) = O and macrocyclic radicals -O-?H-CH₂-, which are formed with nearly equal yields. It was shown that -O-?H-CH₂-radicals rapidly decayed at temperatures above 140 K. However, the -?H-C(H)=O radicals are stable almost up to the matrix softening temperature. The radical cations of 12-crown-4 are not stabilized in the matrices of Freon 11 and Freon 113, since they undergo transformation to macrocyclic radicals -O-?H-CH₂-via the deprotonation reaction.     

Hydrazyl,Nitronyl-, and imino-nitroxides: Synthesis,properties and reaction with nitric oxide and nitrogen dioxide

Ten novel and stable free radicals of nitronyl-, imino-nitroxide and hydrazyl type compounds were synthesized and their physico-chemical properties investigated. UV-Vis and ESR spectroscopic data, as well as the lipophilicities and specific hydrophobic areas of the compounds are compiled. The reaction of these radical compounds with nitric oxide and nitrogen dioxide was also investigated. The radicals synthesized, show selectivity in their reaction with these nitric oxides, depending on their structure (nitronyl-nitroxide radicals react with NO, while hydrazyl radicals react with NO₂). The processes are easily monitored by UV-Vis or ESR spectroscopy.     

Heterocyclic derivatives of long-chain diacetylenic acids

Acyl derivatives of 2-aminopyridine, 2-aminopyrimidine, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl were obtained from long-chain diacetylenic acyl chlorides and the corresponding heterocyclic compounds. Spreading isotherms of monolayers on a water surface show that lengthening of the hydrocarbon chain and replacement of the pyridyl groups in these compounds by the more hydrophilic pyrimidyl groups render the films more condensed. Long-chain acyl derivatives of nitroxyl radicals form monolayers possesing a low collapse pressure. ESR spectra of Langmuir-Blodgett films of these radicals before and after photopolymerization were recorded.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2009–2012, October, 1995.The authors are grateful to S. A. Dzyuba for his help in recording ESR spectra and for helpful discussion.This work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-04027).     

ESR imaging and FTIR study of thermally treated poly(acrylonitrile-butadiene-styrene) (ABS) containing a hindered amine stabilizer: Effect of polymer morphology, and butadiene and stabilizer content

Electron spin resonance imaging (ESRI) was applied to the study of thermal degradation at 393 K of poly(acrylonitrile-butadiene-styrene) (ABS) prepared by emulsion polymerization and containing 25% wt butadiene (ABS-25B). The polymer was doped with 1 or 2% wt Tinuvin 770 as the hindered amine stabilizer (HAS). The spatial distribution of the HAS-derived nitroxide radicals, obtained by 1D ESRI, was initially homogeneous, but became heterogeneous through sample depth with increasing treatment time, t. The spatial variation of ESR line shaping with sample depth was visualized by 2D spectral-spatial ESRI. ESR spectra along the sample depth, obtained by nondestructive (“virtual”) slicing of the 2D images, were used to deduce the relative intensity of nitroxide radicals present in two dynamically distinct sites; the sites were assigned to butadiene-rich (fast component) and SAN-rich domains (slow component), respectively. 1D and 2D ESRI allowed the determination of the extent of degradation within morphologically-distinct domains as a function of sample depth and treatment time. The results from the ESRI experiments were substantiated by attenuated total reflectance (ATR)-FTIR spectroscopy of the outer layer (500 μm thick) of the polymer. Both techniques indicated faster degradation of polymer samples that contained the higher HAS content, 2% wt. Comparison with the results obtained for a parallel study of ABS prepared by mass polymerization and containing 10% wt butadiene (ABS-10B) indicated clearly that the rate of degradation of the polymer prepared by emulsion polymerization (ABS-25B) is significantly reduced. This result can be explained by the formation of cross-linked “composite” networks during emulsion polymerization, which leads to greater thermal stability.     

Concentration‐Dependent Hydrogen‐Bonding Effects on the Dimethyl Sulfoxide Vibrational Structure in the Presence of Water,Methanol, and Ethanol

The effects of hydrogen bonding between dimethyl sulfoxide (DMSO) and the co‐solvents water, methanol, and ethanol on the symmetric and antisymmetric CSC stretching vibrations of DMSO are investigated by means of Raman spectroscopy. The Raman spectra are recorded as a function of co‐solvent concentration and reflect changes in structure and polarizability as well as hydrogen‐bond donor and acceptor ability. In all cases studied a nonideal mixing behavior is observed. The spectra of the DMSO/water system show blue‐shifted CSC stretching modes. The antisymmetric frequencies are always further blue‐shifted than the symmetric stretching ones. The DMSO/methanol system also features blue‐shifted CSC stretching frequencies but at high mole fractions a pronounced red shifting is observed. In the binary DMSO/ethanol system, the co‐solvent also gives rise to blue shifts of the CSC stretching frequencies but restricted to mole fractions between x=0.38 and 0.45. The different magnitudes and occurrences of both blue‐ and red‐shifted spectral lines are comprehensively and critically discussed with respect to the existing literature concerning wavenumbers and Raman intensities in both absolute and normalized values. In particular, the normalized Raman intensities show a higher sensitivity for the nonideal mixing behavior because they are independent of the mole fraction.