EPR spectra of γ-irradiated dl-α-alanine supported on molecular sieves

The aim of the work was to collect information concerning boundary effects which are suspected in α-alanine dosimeters consisted of powdered microcrystalline α-alanine and binders. In our experiments the conventional binders were replaced by molecular sieves (MS). MS are inorganic porous materials (host structures) with well organized and uniform intra-crystalline pore systems of nano-scale size. The guest molecules can be either physically adsorbed on very large inner MS surface, or chemically bound to the active sites. They can be also encapsulated inside the intracrystalline cavities. The EPR spectra of gamma irradiated dl-α-alanine supported on NaY, CeY, SOD, mordenite, ZSM-5 and ALPO₄-5 were very similar to that one observed for irradiated microcrystalline dl-α-alanine. In the case of alanine supported on HY an initial EPR spectrum was different and only after some weeks it made resemble to the well known quintet observed in microcrystalline samples. In sodalites synthesized in the presence of dl-α-alanine EPR signal appeared in non-irradiated sample was very low and structureless. The irradiated sample showed a distinct spectrum which was quite different from that one observed for crystalline dl-α-alanine.     

EPR investigations of gamma-irradiated novolacs

EPR investigations of γ-irradiated phenol, p-chlorophenol, o-chlorophenol, 3,5-dichlorophenol and p-cresol novolac are presented. The elimination of a chlorine atom from the phenolic ring must be assumed in the case of chlorinated novolacs. The corresponding aryl radical could only be detected in the case of 3,5-dichlorophenol novolac in a large amount. Furthermore phenoxy and cyclohexadienyl radicals were found in the spectra. The radiation chemical as well as the resist sensitivity are enhanced by chlorination but there is no definite correlation between them.     

EPR investigation of gamma-irradiated anti-emetic drugs

Electron paramagnetic resonance (EPR) spectroscopy was used to investigate the γ-radiation damage in the microcrystalline powder form of two anti-emetic drugs, namely 4-amino-5-chloro-N-[2-(diethylamino)ethyl]-2-methoxy benzamide monohydrochloride monohydrate (metoclopramide) and 9-tetrahydro-9-methyl-3-[(2-methyl-1H-imidazol-1-yl)methyl]-4H-carbazol-4-one monohydrochloride dihydrate (odansetron). EPR measurements proved that both of them contained various stable paramagnetic species after irradiation and relative yielding of free radicals depends on the absorbed dose. The metoclopramide drug exhibited very weak EPR signals before irradiation. Some spectroscopic properties and suggestions concerning possible structure of the radicals are discussed in this paper.     

EPR study on gamma-irradiated fruits dehydrated via osmosis

The shape and time stability of the electron paramagnetic resonance (EPR) spectra of non- and γ-irradiated papaya, melon, cherry and fig samples dehydrated via osmosis are reported. It is shown that non-irradiated samples are generally EPR silent whereas γ-irradiated exhibit “sugar-like” EPR spectra. The recorded EPR spectra are monitored for a period of 7 months after irradiation (stored at low humidity and in the dark). The results suggest longer period of unambiguous identification of the radiation processing of osmose dehydrated fruits. Therefore, the Protocol EN 13708,2001 issued by CEN is fully applicable for the studied fruit samples.     

ESR spectra of gamma-irradiated cellobiose

Conclusions The action of ionizing radiation on cellobiose leads to breakage of the pyranose ring at the C⁵-O bond. A probable mechanism is proposed for the radiation chemical transformations of cellobiose.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2234–2237, October, 1984.     

Metalloporphyrin molecular sieves

Crystal-engineering strategies have been systematically developed for the rational design by self-assembly of diverse metalloporphyrin molecular-sieve materials. Cooperative coordination and hydrogen bonding algorithms of molecular recognition proved particularly useful for this aim. The supramolecular concepts used in the construction of stable nanoporous solids and some unique sieve-type structures obtained thus far are illustrated.     

EPR study of light illumination effects on radicals in gamma-irradiated L-alanine

Exposure of gamma-irradiated L-alanine samples to sunlight and to light from a regular, fluorescent lamp resulted in significant changes in their EPR resonance patterns, both to spectral shapes and intensities. The experimental EPR spectra were numerically decomposed into three components reflecting contributions of three different radicals (R1-R3) generated by ionizing radiation in alanine. The light exposure caused a decay of the measured EPR signal intensity. For similar light intensities and exposure times the decay was much more pronounced in samples illuminated by sunlight than in samples illuminated by the fluorescent lamp. In both cases light-induced decay of R1 radicals was observed. Sunlight illumination resulted in a moderate decay of R2 radicals and in a doubling of the R3 radical population. On the other hand, fluorescent light caused a significant increase of R2 radicals and did not change the amount of R3 radicals. A quantitative analysis of the variations of the three radical contributions to the total EPR spectra upon fluorescent light exposure suggests a net R1-->R2 free radical transformation. These effects of light on the alanine dosimetric signal should be taken into account in dosimetry protocols, assuring protection of alanine dosimeters from extended exposure to light.     

High-frequency EPR spectra of

A detailed multifrequency high-field-high-frequency EPR (95-285 GHz) study has been performed on the single-molecule magnet of formula [Fe8O2(OH)12(tacn)6]Br8 x 9H2O, in which tacn = 1,4,7-triazacyclononane. Polycrystalline powder spectra have allowed the estimation of the zero-field splitting parameters up to fourth order terms. The single-crystal spectra have provided the principal directions of the magnetic anisotropy of the cluster. These results have been compared with an evaluation of the intra-cluster dipolar contribution to the magnetic anisotropy; this suggests that single-ion anisotropy is the main contributor to the magnetic anisotropy. The role of the transverse magnetic anisotropy in determining the height of the barrier for the reversal of the magnetization is also discussed.     

EPR investigation of some desiccated Ascomycota and Basidiomycota gamma-irradiated mushrooms

The suitability of the EPR spectroscopy for detection of γ-irradiation in five species of dried mushroom, currently used in gastronomy: yellow morel—Morchella esculenta, (L.) Pers. (Phylum Ascomycota), button mushroom—Agaricus bisporus (J.E.Lange), Agaricus haemorrhoidarius Fr., golden chantarelle—Cantharellus cibarius Fr., as well as oyster mushroom—Pleurotus ostreatus (Jacq. ex Fr.) (Phylum Basidiomycota) is presented and discussed. Although after irradiation at doses up to 11 kGy, all specimens presented well defined EPR spectra, only A. bisporus EPR signal was enough stable to make detection possible after 18 months.     

Titanium-containing silica mesoporous molecular sieves

An analysis was made of the conditions for the synthesis of titanium-containing mesoporous silica molecular sieves and their effect on the stereochemical structure, the coordination of the titanium, and the catalytic characteristics. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 03039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 3, pp. 135–158, May–June, 2000.     

Equilibrium modeling of xylene adsorption on molecular sieves

The separation of xylene isomers is an important application in separation processes that is based on their adsorption properties on different adsorbents. In this work, the Price and Danner method was employed with a neural network to investigate the adsorption behavior of binary systems of p-xylene/m-xylene, p-diethyl benzene/m-xylene, and p-diethyl benzene/p-xylene and the ternary system of p-diethyl benzene/m-xylene/p-xylene at 130 and 175 °C. The Redlich–Kister, Wilson, and NRTL models were used to determine the activity coefficients in the adsorbed phase. Comparison with experimental data from the literature indicated that the proposed thermodynamic model would best determine surface excess when it is used along with the Redlich–Kister activity coefficient model.     

介孔分子筛研究新进展

介孔分子筛材料作为催化剂或催化剂载体为有机大分子参与反应提供了有利的空间构型和择形活性中心,在石油加工工业中具有潜在的应用优势。但由于介孔分子筛材料的水热稳定性比较低,且酸性较弱,极大地影响了其在催化领域中的广泛应用。本文综述了近年硅基介孔分子筛的改性研究进展,重点讨论了在提高介孔分子筛酸性和水热稳定性方面的研究工作。     

分子筛对葡萄糖淀粉酶的吸附性能研究

测定了黑曲霉葡萄糖淀粉酶(E.C.3.2.1.3)在三种改性的、具有中孔和大孔的分子筛上的吸附等温线并将吸附量和吸附等温线的形状与分子筛的等电点、孔容、孔径及酸性相关联。讨论了孔结构和不同酶吸附量对分子筛固定化葡萄糖淀粉酶活力的影响。发现葡萄糖淀粉酶在再造孔分子筛上的单层饱和吸附量与再造孔的方法密切有关,三种不同再造孔方法制得的分子筛具有不同的骨架Si/Al比、不同的孔分布和比表面积。不同的Si/Al比导致不同的酸性质和等电点。酶吸附量与载体的表面酸性、等电点以及吸附时溶液的pH有关。分子筛对酶的吸附以静电作用为主。其次,当中孔孔径和孔容越大时,单层饱和吸附量亦越大。随着分子筛对葡萄糖淀粉酶的吸附量增加,固定化酶的活力增大,但固定化酶的比活力随吸附量的增加、中孔孔容和孔径的减小而下降。     

Thermogravimetry of molecular sieves note 1

Water-saturated molecular sieves were studied with a derivatograph. Apparent activation energies and orders of reaction were calculated and interpreted on the basis of the structures of the samples.     

Three-dimensional DNA crystals as molecular sieves

DNA has proved to be a successful nanoscale building block because of its inherent programmability and its predictable structural features. One long-standing goal of DNA nanotechnology has been the rational design and assembly of three-dimensional (3D) DNA crystals for use as molecular scaffolds, in molecular electronics assembly, and as molecular sieves. Here we demonstrate that rationally designed 3D DNA crystals with mesoporous features can function as molecular sieves by selectively adsorbing proteins based on size.     

Mesoporous molecular sieves and nanoperiodic materials

A review is given of literature data and some results of the authors on different approaches to the synthesis and the physicochemical properties of mesoporous molecular sieves and nanoperiodic structures made from inorganic oxides, phosphates, heteropolyacids, and surfactants. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prospekt Nauki, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 33, No. 5, pp. 322–337, September–October, 1997.