New methacryloyldipeptides having the sequences of l-alanyl-glycine ethyl ester (Ala-Gly-OEt), l-valyl-glycine ethyl ester (Val-Gly-OEt), l-leucyl-glycine ethyl ester (Leu-Gly-OEt), and l-isoleucyl-glycine ethyl ester (ILe-Gly-OEt) as side chains were synthesized to evaluate environmental response of its polymer hydrogels, especially solvent and temperature. The swelling values of each hydrogel were reached maximally in a 30/70 vol% water/2-propanol mixture at 10°C, at which the degree of gel swelling v markedly distinct from kind of pendant group, increasing in that order Ile-Gly-OEt>Leu-Gly-OEt>Val-Gly-OEt. The temperature-response was examined for a poly(methacryloyl-ILe-Gly-OEt) hydrogelin the above binary solvent system and it was found that the hydrogel gives a reversible low-temperature-swelling and high-temperature-deswelling.
The primary products of water radiolysis OH., H. and e-aq react with C-phenyl-N-tert-butyl-nitrone(PBN) but not in a simple spin trapping manner. OH. adds mainly to the aromatic ring yielding cyclohexadienyl type radicals, whereas e-aq in pure water forms the PBN anion via the proposed intermediate O.- and alcohol radicals and an imine in the presence of alcohols.
The experimental thermalization lengths, lth, for hot electrons e-hot produced by photoionization of solvated electrons in 3-methylpentane glass are discussed. For electron energies ranging from the initial value E0>1 eV down to 0.1–0.2 eV, the electron e-hot is assumed to loss energy mainly due to excitation of intramolecular vibrations with energy losses σE>kBT. It is concluded that this model is in agreement with experimental data on lth. The spatial distribution of subvibrational electrons is obtained.
Papers mainly published in the last few years on radiation processing of polymeric systems for biomedical applications carried out in different laboratories are reviewed. Radiation-induced polymerization to obtain hydrogels as carriers for immobilization of bioactive agents and for controlled release of drugs is described. Radiation modification of polymers by graft copolymerization and/or crosslinking for the same purposes is also reported. The second part of the paper deals with the work recently carried out in the author's laboratory. Radiation-induced polymerization at low temperatures to obtain matrices susceptible to entrap drugs, including peptides and proteins, is discussed. Radiation grafting of hydrophilic monomers onto relatively new inorganic polymers, i.e. polyphosphazenes, and the properties of such modified polymeric materials, together with their biocompatibility, are summarized.
Our studies indicated that the thickness of the inflammatory layer was the most useful parameter to evaluate tissue response among 13 histological parameters. There was good correlation between the cytotoxicity and the thickness of inflammatory layer. Histological findings showed that the inflammatory layer of radiation vulcanized natural rubber latex (RVNRL) films involved a slightly higher response than the negative implant at the 3rd post operative day although the inflammatory layer showed almost the same degree as the negative controls at the 7th day. The cytotoxic potential of the extracts prepared from RVNRL films was found to be weak by the colony assay. The hemolytic activity was also detected in the extracts of RVNRL films. The lysis of red blood cells and the release of haemoglobin was clearly caused by RVNRL film. Though the cytotoxic and tissue irritative activities of RVNRL are considered much weaker then sulfur-vulcanized latices, it was suggested that RVNRL contains some unknown substances showing weak toxicities including hemolysis.
The absorption band profiles of the solvated electron in aqueous and alcohol glasses at 77, 115 and 300 K were calculated in terms of the theory presented in our previous paper [J. Phys. Chem.95, 6149 (1991)]. We have concentrated our attention on the problem of the IR-absorbing electrons (e-IR) trying to explain their appearance in alcohols, deuterated water and their lack in H2O at low temperatures. The comparison between the experiment and the theoretical model provides new arguments to the discussion on the initial spectra of trapped electrons.
The time-resolved electronic absorption spectra of CN radical, resulting from the laser photolysis of dicyanoacetylene (DCA) at 193 and 248 nm, were analyzed. Detection of the other probable photodissociation product—C3N radical—has not been possible. Photolysis at 193 nm produces CN both in the X2∑+ and in the A2Πi manifolds, the latter—probably populated via a two-photon process—being revealed by a delayed (collision-induced) transfer to the higher vibrational levels of the ground electronic state. Photolysis at 248 nm is an efficient two-photon process. A simplified kinetic model for the decay of CN radical has been proposed and the rate constant for the CN + DCA reaction was derived. Semiempirical INDO/S CI-1 calculations of the DCA valence shell electronic transitions were performed.
The reaction of e-aq with ethylene trihiocarbonate in aqueous medium has been investigated employing pulse radiolysis technique. The bimolecular rate constant for the reaction has been obtained as 3×1010dm3mol−1s−1. A transient absorption spectrum, with λmax at 315 nm, has been observed which is assigned to the neutral radical formed by the protonation of radical anion produced in the reaction of e-aq with ETTC. A similar absorption spectrum was also observed under the condition where the H atom instead of e-aq reacts with ETTC. The transient decayed by second-order kinetics with k2=(9.1±1.0) ×108 dm3 mol−1 s−1. The G(-ETTC) has been determined from 60Co λ-radiolysis as 3.1.
Factors affecting radiation induced defects in lithia aluminosilicate porcelain were investigated. Porcelains with beta-eucryptite (Li2O.Al2O3.2SiO2), its solid solution (SS) (Li2O.Al2O3.3SiO2) and beta-spodumen (Li2O.Al2O3.4SiO2) were prepared and vitrified. Irradiation was performed at room temperature with three fluences from Cf-252. X-ray line profile analysis, thermal expansion and scanning electron microscopy were carried out pre- and post-irradiation.Results showed that when large crystallites were present in strain free body such as beta-spodumen (tetragonal) their sizes were greatly influenced. Both high strain and large crystallite size in hexagonal beta-eucryptite were severely reduced. In the solid solution (SS) beta-eucryptite having minimum crystallite size and strain free level, defects appeared as swelling of the crystallites. Accompanying morphological changes conformed with the above findings. The negativity of thermal expansion increased with low fluences rather than higher ones leading to recovery of induced defects. The optimum neutron fluence, inducing maximum change, proved to be composition dependent. A wave behaviour of the induced change was interpreted in terms of radiation damage followed by saturation and further annihilation.
A combination of various computer simulation techniques is proposed as a tool for the theoretical studies of electron localization in condensed media. The emerging three-stage algorithm with (1) the classical Molecular Dynamics as the initializing part, (2) the Path Integral simulation as the central part and (3) the variational calculations of the absorption spectrum of trapped electron, allows us to calculate the excess electron properties without use of empirical or adjustable parameters. The algorithm was applied to the study of electron localization in mixtures of molten alkali halides. The comparison with the pulse radiolysis experiments is presented for a range of mixture compositions.
The influence of high energies on a gas stream under certain conditions, may produce sulphuric acid. In this case a degree of gas purification of sulphur dioxide of up to 99% is obtained, and energy expenditure is 0.2–1.0 kW per 1 kg of final product. Describing these processes may be recommended as part of their future development and industrial and commercial realization.
Optical absorption spectra of radical anions of poly(1-phenyl-1-propyne)(PPPr) and poly(phenylacetylene)(PPA) were studied in 2-methyltetrahydrofuran (MTHF). The radical anions of the polymers were obtained by γ-radiolysis at 77 K (and 4 K) and pulse radiolysis at ambient temperature and 140 K. There were two different trapping sites for electrons in PPPr dissolved in MTHF. The electron produced by ionizing radiation was initially trapped by a site to form the radical anion which gave rise to an absorption spectrum with λmax at 390 and 560 nm and a shoulder at ca 800 nm. In liquids or warmed matrices, the spectrum relaxed to a new one which was similar to that of the radical anion of trans-β-methylstyrene, a model compound of the polymer. The result suggested that an electron trapped by a shallow site was ultimately localised on a deeper site of the size of a monomer unit. In contrast, the absorption spectrum of PPA- showed a strong IR band which was attributed to a dimer-type radical anion. It was concluded therefore that the excess electron was delocalized over two monomer units in PPA. The difference was interpreted in terms of the twisted main chain structure of PPPr arising from the repulsive interactions between bulky phenyl groups and methyl groups of the polymer.
Electron migration along polymer chain is shown by the pulse radiolysis study of poly(4-vinylbiphenyl-co-1-vinylpyrene) in 2-methyltetrahydrofuran solution. For the copolymer with small vinylpyrene contents (0.34-1.58%), excess electron is initially localized in a biphenylyl side-group to form anion radical, and then transfers to a pyrenyl side-group. The electron transfer is enhanced with the increase in the vinylpyrene content in the copolymer, whereas it is independent of the copolymer concentration in the solution. These results indicate that the electron migrates along the copolymer chain by hopping between neighboring biphenylyl side-groups until it is stably trapped on a pyrenyl side-group. Frequency of the electron hopping is estimated to be 5.2 x 10(9) s-1.Positive charge migration is suggested to occur similarly by the pulse radiolysis of the copolymer in 1,2-dichloroethane solution. It is about one-tenth slower than the electron migration.
Coprecipitated SiO2-Al2O3 (Al2O3 = 33.2 mol %) and Li2O-impregnated SiO2-Al2O3 containing 1, 2.5 and 5 mol % Li2O were prepared. The textural properties were determined by following the adsorption of nitrogen at 77 K. The surface acidities were determined from pyridine adsorption at 423 K. The catalytic conversion of isopropanol on the catalysts prepared was carried out using the pulse microcatalytic technique.The surface area decreased and the pore size increased upon irradiation with gamma-rays (dose greater-than-or-equal-to 30 M rad). The acidity decreased upon impregnation with Li2O and/or irradiation with gamma-rays.
Recent developments in detectors for liquid chromatographic analysis have increased detection sensitivities by several orders of magnitude. Many products in the radiolysis of organic substrates can now be determined at micromolar levels. With this sensitivity it is possible to examine radiolytic systems in detail with doses as low as 100 rads. As a result one can determine initial yields in studies which here-to-fore have not been possible. This presentation describes studies of the oxidation of aromatic systems by HPLC methods involving spectrophotometric detection with diode array detectors. Digital storage of 3-dimensional data makes it possible to display readily the chromatographic data in a variety of formats. As a result one obtains an in depth understanding of the product distribution and considerable insight into the radiation chemical mechanism. These spectroscopic approaches can be supplemented by chromatographic studies employing electrochemical, refractive index, radiochemical and ion detectors which are particularly useful when reference samples of radiolytic products are not available. We illustrate these approaches with results from recent studies of the radiolytic oxidation of substituted naphthalenes and biphenyls where the complex mixtures of isomeric products can be resolved by HPLC methods. These studies provide information on the features which control the position of attack of OH on aromatic systems.
Biologically relevant material is usually associated with considerable amounts of water; e.g. the living cell contains about 70% water. When ionizing radiation interacts with such material one must consider two modes of energy deposition: the direct effect (ionizing radiation is absorbed by the biomolecules) and the indirect effect (ionizing radiation is absorbed by the surrounding water). In the direct effect, radical cations plus electrons, and excited states of the biomolecules are formed. In the indirect effect the water is decomposed resulting in the formation of the water radicals .OH, H. and e(aq)-. These reactive intermediates then interact with the biomolecules. When such systems are irradiated oxygen is often present. As a result of this, the radicals formed in the biomolecules by the various routes are converted into the corresponding peroxyl radicals.In certain cases, e.g. with the nucleobases of DNA, radical cations can be produced in dilute aqueous solutions by radiation-generated SO4.- radicals, and the fate of these nucleobase radical cations studied by pulse radiolysis and product analysis. Attention will be drawn to the fact that frequently some of the reaction products of the radical cations with water are identical to those formed by OH radical attack, but that there are also marked differences.Similarly, protonation of radical anions (formed by the reaction of solvated electrons with the biomolecules) and the reaction of H-atoms with these molecules can lead to radical intermediates with considerably differing characteristics.Our present knowledge of the variety of reactions of the peroxyl radicals occurring in aqueous solutions will be briefly discussed, emphasizing the large variety of HO2./O2.- elimination reactions and pointing to the reversibility of the oxygen addition (RO2. --> R. + O2) in some systems recently studied.
Experimental results on increase of the probability of geminate ion pair separation into free ions caused by photoexcitation of trapped electrons in γ-irradiated 3-methylpentane glasses at 77 K are discussed. The increase is associated with injection of “hot” electrons in the medium. After thermalization the motion of the electrons is suggested to be governed by Smoluchowski's equation until stable trapped electron states occur. The dependence of the mean-square thermalization length on the electron energy in the interval 0.1–1.5 eV and the mean-square length (45 Å) of thermalized precursor of stable trapped electrons are estimated. It is concluded that electron localization precedes to total thermalization and is effective at electron energies <0.1 eV.
Stimule-sensitive hydrogels which respond to changes in various environmental conditions such as temperature, pH, and electric field were synthesized by means of γ-ray polymerization of comonomers. The comonomers consisted of N-isopropylacrylamide, acrylic acid or methacrylic acid and a crosslinker such as diethylene glycol dimethacrylate and polyethylene glycol dimethacrylate. The effects of comonomer composition, alkali treatment of the copolymer and crosslinking on the temperature depending swelling and the shrinkage under electric field were studied comparatively. It was observed that the gels showed a maximum responsiveness at a certain composition of acidic monomer and the alkali treatment enlarged such a maximum composition range. The kind of crosslinkers affected also on the stimule-responsiveness.
Irradiated poly(vinyl chloride) has been characterized by various techniques. The very high doses (up to 20 Mgy) produce dramatic changes in the material. Chemical changes were studied by TGA analysis. Surface morphology and microstructure were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). PVC irradiated at the highest dose, 20 MGy, shows a structure consisting mainly of carbon which, in some cases, is crystalline. This carbon-rich material also shows a particular affinity for the adsorption and desorption (after electron bombardment) of ambient gases, as is clearly shown in electron stimulated desorption (EDS) experiments performed in this study.
An energy spectrum of “subexcitation electrons” produced in liquid water by electrons with initial energies of a few keV is obtained by using a Monte Carlo transport simulation calculation. It is found that the introduction of vibrational-excitation cross sections leads to the appearance of a sharp peak in the probability density function near the electronic-excitation threshold. Electrons contributing to this peak are shown to be more naturally described if a novel energy spectrum, that we propose to name “vibrationally-relaxing electron” spectrum, is introduced. The corresponding distribution function is presented, and an empirical expression of it is given.
