Stabilization of H and D atoms in Aggregates of Kr Nanoclusters Immersed in Superfluid Helium

Impurity–helium condensates containing krypton atoms and also atoms and molecules of hydrogen isotopes have been studied via an electron spin resonance (ESR) technique. Analysis of the ESR spectra shows that most of the H and D atoms reside in molecular layers (H₂ or D₂) formed on the surfaces of Kr nanoclusters. The thickness of the molecular films was found to determine the rates of recombination of the atoms into molecules, with atoms in the thinner films recombining much more slowly. Very large average concentrations were obtained for H atoms (10¹⁹ cm^?3) and D atoms (3?10¹⁹ cm^?3) in these experiments.     

Specific features of deuterium and tritium labeling of SB258585

Samples of SB258 585 labeled with hydrogen isotopes were synthesized. [²H]SB258 585 containing one ²H atom per molecule and [³H]SB258585 with the molar radioactivity of 15 Ci mmol^?1 were obtained in preparative amounts. From 0.18 to 1.5 ²H atoms were incorporated, on the average, into an SB 258 585 molecule depending on the reaction conditions. The isotope exchange efficiency strongly depends not only on the catalyst-substrate ratio and on the reaction temperature, but also on processes occurring on the support surface. The isotope effects strongly influence the degree of deuterium or tritium incorporation into the samples in cases when the organic compound largely decomposes in the course of the reaction.     

Selective Tritium Labeling by a Solid-Phase Procedure

Ways were considered how substrates that contain such reactive centers as halogen atoms and double bonds can be labeled with tritium by solid-phase isotope exchange. The feasibility was demonstrated for tritium labeling by selective solid-phase dehalogenation, hydrogenation, and isotope exchange. Highly labeled vitamin K₁, dihydrofusicoccin, and thyroxine and its derivatives were prepared.     

Nonequilibrium processes in reactions of hot tritium atoms with cooled solid targets. Influence of the atomizer temperature on formation of labeled substances

A system consisting of a cold target and “hot” atoms generated by dissociation of tritium on a tungsten wire was studied with the aim to determine conditions for preparing tritium-labeled organic compounds with the maximal radiochemical yield. The influence of the atomizer temperature on the result of the reaction of tritium atoms with amino acids and tetraalkylammonium bromides was studied; homological series of the substrates were examined with the aim to evaluate the contributions of functional groups and hydrocarbon tail to the processes occurring in the target. The dependence of the yield of the labeled parent compound on the atomizer temperature varied in the range 1600–2000 K was determined. The rates of decarboxylation and deamination sharply grew with increasing temperature of the tungsten wire. The highest yield of labeled amino acids was attained at an atomizer temperature of 1800–1900 K, and at higher temperature their yield decreased. The difference between the activation energies of the elimination of the carboxy and amino groups and of the isotope exchange of hydrogen for tritium in the C-H bond appeared to be 93 and 59 kJ mol^?1, respectively. For alkyltrimethylammonium bromides with the alkyl radicals C₁₂H₂₅, C₁₄H₂₉, and C₁₆H₃₃, the yield of the labeled parent compound reached 80–90% and was virtually independent of the atomizer temperature. The capability of tritium atoms to penetrate into the targets was evaluated. For the exponential model of the attenuation of the flow of tritium atoms inside the target, the attenuation factor for freeze-dried amino acids and alkyltrimethylammonium bromides as targets was 1.8 nm^?1.     

A Comparative Study of the Reactions of Thermally Activated Tritium with Sugars and Diazines and of Solid-Phase Catalytic Hydrogenation of These Compounds with Tritium

The feasibility of the labeling procedure involving thermal activation (TA) of tritium was examined with the substrates that are commonly labeled by solid-phase catalytic hydrogenation (SCH) with tritium. Comparative characteristics of SCH and TA as procedures for tritium labeling of sugars and diazines were obtained. These two methods ensure comparable rates of tritium incorporation into purine and pyrimidine bases. The SCH allows preparation of tritium-labeled compounds with the maximum possible molar radioactivity. The molar radioactivity of the same compounds labeled using TA did not exceed 37 TBq mol⁻¹, because only a small fraction of the substrate could react with atomic tritium. Longer reaction times and increased amounts of tritium taken into the reaction resulted in stronger degradation of the substrates. On the assumption that the reactive tritium atoms penetrate into the target to a depth of 0.5 nm, the actual specific radioactivity of the labeled compound in the zone accessible for atomic tritium reaches 0.2–2 PBq mol⁻¹. Ways are suggested to increase the molar radioactivity of compounds labeled using thermal activation of tritium.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 284–288.Original Russian Text Copyright © 2005 by Sidorov, Badun, Baitova, Baitov, Platoshina, Myasoedov, Fedoseev.     

Use of methyl <Emphasis Type="Italic">p</Emphasis>-toluenesulfonate labeled with hydrogen isotopes as a donor of methyl group

Methyl p-toluenesulfonates TosOCH₂ ³H and TosOCH₂ ²H containing, on the average, 0.5 atom of hydrogen isotope per molecule were prepared by catalytic dehalogenation of bromomethyl p-toluenesulfonate TosOCH₂Br with tritium and deuterium. Mass-spectrometric analysis showed that the label is fully localized in the methoxy group. The use of this reagent allowed preparation of isotopically labeled biologically active compounds containing the fragments -OCH₃, -COOCH₃, -SCH₃, etc.     

Comparative Study of Reaction of Atomic Tritium with Glucosamine and Amino Acids

Reaction of amino acids (glycine and serine) and amino sugar (glucosamine) with atomic tritium generated by thermal dissociation of molecular tritium on a tungsten filament was studied. A frozen aqueous solutions and a freeze-dried mixture of these compounds was bombarded with tritium atoms is a special vacuum unit. The relative yield of the labeled compounds was determined as influenced by the reaction conditions (residual pressure in the system and bombardment time) and target type (frozen solution and freeze-dried mixture). Formation of labeled products is almost independent of the tritium pressure. The ratio of the formation rates of labeled serine and glycine in the frozen solution and freeze-dried mixture bombarded with atomic tritium for 45–270 s was 1.66±0.15 and 1.44±0.13, respectively. At shorter reaction time (15 s), the ratio increases to 3.5±0.2 and 2.0±0.4, respectively. The formation rate of [³H]glucosamine in the mixture is higher at a shorter bombardment time. The radioactivity ratio of labeled glucosamine and glycine formed in frozen solutions and freeze-dried mixture in 15 s was 26.0±2.3 and 6.8±0.6, respectively. At longer reaction time, the relative yield of [³H]glucosamine sharply decreases owing to stronger radiolysis of labeled glucosamine on exposure to tritium beam.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 281–283.Original Russian Text Copyright © 2005 by Badun, Ksenofontov, Lukashina, Pozdnyakova, Fedoseev.     

Radiochemical diagnostics of thermal hydrolysis of aluminum trichloride

Thermal hydrolysis of aluminum chloride was studied using ³⁶Cl and ³H tracers in combination with energy-dispersive and morphological (scanning electron microscopy) analyses. Pure partially hydrated AlCl₃ or mixtures of AlCl₃ and AlCl₃ 6H₂O were used as initial materials. It was found that Al₇O₁₀Cl 2H₂O microtubes along with isometric microparticles are formed in the course of thermal hydrolysis due to evaporation and partial hydrolysis of the initial AlCl₃. In this case, AlCl₃ 6H₂O acts as a source of water vapor, whereas chlorine atoms contained in this compound do not pass into the microtube material. The tests with water labeled with tritium also showed no incorporation of tritium in microtubes. Thus, thermal hydrolysis of AlCl₃ proceeds predominantly by the recrystallization mechanism.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 454–457.Original Russian Text Copyright © 2004 by Baronov, Berdonosov, Baronova, Melikhov.     

Deuterium trapping measurements in aluminum and plasma-sprayed aluminum coatings

Bulk and plasma-sprayed aluminum samples were bombarded with 10 keV D₃⁺ to a standard fluence of 10¹⁸ atoms cm^-2 at implant temperatures of 100–400 °C. Gas re-emission, thermal desorption and D(³He,α)H measurements were conducted. The results indicate that the saturation deuterium trapping level was about 10¹⁶-10¹⁷ atoms cm^-2 and was primarily confined to about the first 0.2 μm depth. Trapping of about 10¹⁶ atoms cm^-2 was still observed after anneals to 530 °C.     

Long term stability of H atoms in HD-D2-He solids

No Heading We employed en electron spin resonance (ESR) technique for investigating the long term behavior of hydrogen and deuterium atoms in the HD-D₂ impurity helium solids that were created by sending a gas mixture [H₂]:[D₂]:[He]= 1:4:100 through a radio-frequency electrical discharge into a volume of superfluid ⁴He at T = 1.5 K. H and D atoms were stabilized inside nanoclusters of impurity molecules. The exchange tunneling reactions D + H₂ HD + H and D + HDD₂ + H proceeded to eliminate D atoms and increase the concentration of H atoms in the HD-D₂ impurity-helium solids. Local concentrations of H atoms inside the molecular nanoclusters of order 10²⁰ cm^–3 were achieved. The high concentration of H atoms was stable during 40 hours storage of the sample at T = 1.35 K. These solids are possible candidates for collective quantum phenomena of atomic hydrogen if the Bose-Einstein degeneracy regime can be attained.PACS numbers: 61.46. +w, 67.40.Yv, 76.30.–v.     

Crystal structure of double acetates SrAnO<Subscript>2</Subscript>(OOCCH<Subscript>3</Subscript>)<Subscript>3</Subscript>·3H<Subscript>2</Subscript>O [An = Np(V), Pu(V)]

The crystal structure of isostructural Pu(V) and Np(V) acetates of the general composition SrAnO₂Ac₃ · 3H₂O (Ac = CH₃COO^?) was determined. The structures are based on complex anions [AnO₂Ac₃]^2? and Sr²⁺ cations combined into a three-dimensional framework with water molecules located in framework cavities. The An(V) atoms are characterized by the hexagonal-bipyramidal oxygen surrounding; the equatorial plane is formed by the O atoms of three acetate groups. The coordination surrounding of the Sr atom is a tetragonal antiprism formed by the O atoms of acetate ions and water molecules. The bond lengths within the coordination sphere decrease in passing from Np(V) to Pu(V): the average An=O and An-O bond lengths are 1.828(5) and 2.549(6) Å for Np and 1.811(4) and 2.530(4) Å for Pu, respectively.     

ESR and X-ray Investigations of Deuterium Atoms and Molecules in Impurity-Helium Solids

Impurity-helium solids created by injecting deuterium atoms and molecules into superfluid ⁴He have been studied via electron spin resonance (ESR) and x-ray diffraction methods. We measured the g-factor, the hyperfine constant and the spin-lattice relaxation time of D atoms in D-D₂-He solids. These measurements show that D atoms are mainly stabilized in D₂ clusters. Using an x-ray method we found the size of D₂ clusters to be ～90Å in diameter and the densities of D₂ molecules in the samples to be of order 2.5?10²¹ cm^?3 . The highest average concentration of D atoms achieved in D-D₂-He solids was ～1.5?10¹⁸ cm^?3 . The local concentrations of D atoms within D₂ clusters is found to be large (～2?10¹⁹ cm^?3).     

Tritium Labeling of Androst-4-ene-3,17-dione by Liquid-Phase Selective Hydrogenation and Factors Affecting the Process

Androstenedione labeled with tritium at positions 1 and 2 was prepared. The molar radioactivity of the sample prepared using homogeneous catalysts was as high as 1.4-1.5 PBq mol^{- 1}. [1,2-³H]Androst-4-ene-3,17-dione can be converted into the [1-³H]steroid with the molar radioactivity of 0.9 PBq mol^{- 1}.     

Stabilization of High Concentrations of Nitrogen Atoms in Impurity-Helium Solids

Impurity-helium (Im-He) solids created by injecting gaseous helium with an admixture of nitrogen atoms and molecules into superfluid ⁴He have been studied via electron spin resonance (ESR). We have studied the efficiency of stabilization of N atoms in Im-He samples prepared from nitrogen-helium gas mixtures with different fractions of nitrogen varying from 0.25% to 4%. Some of the observed ESR spectra of N atoms in the Im-He samples are very broad. The highest local concentration of N atoms determined from dipole-dipole broadening of the ESR line is ～8×10²⁰ cm^?3. The highest average concentrations of N atoms in N-N2-He solids were much lower (of order 10¹⁹ cm^?3). The samples with high concentrations of N atoms were stable in liquid helium, and remained stable even after draining liquid helium from the sample at T≤3.5 K.     

Matrix Isolation of H Atoms at Low Temperatures

The recent history of the matrix isolation of atomic free radicals at low temperatures started with a research program at the US National Bureau of Standards and continued with the important breakthrough at Chernogolovka in Russia where a jet containing atomic free radicals was directed onto the surface of superfluid ⁴He. The samples collected consisted of gel-like substances made up of molecular nanoclusters, allowing the atomic free radicals to be isolated from one another and studied at 1.3 K. More recently, techniques were developed at Turku University which have been made the region T<1 K accessible for studies of H atoms entrapped in H₂ films. Very high concentrations of H atomic free radicals (??10¹⁸?C10¹⁹ cm^?3) have been attained using both the Turku and Chernogolovka methods. A discussion of the most recent experiments at Cornell and Turku will be given. Microwave and mm wave electron paramagnetic resonance techniques have been employed in these experiments. These techniques permitted studies of the exchange tunneling chemical reaction D+HD??H+D₂. Diffusion of H atoms through solid H₂ proceeds via the reaction H+H₂??H₂+H, leading to recombination (H+H??H₂). Quantum overlap of H atoms is thought to be responsible for exotic behavior of H atoms in solid H₂ films below 1 K, including a significant departure from the Boltzmann distribution of the relative populations of the two lowest hyperfine levels of atomic H.     

X-ray diffraction study of calcium nitrate tetrahydrate melt at 328 K

The hydration structure of calcium nitrate tetrahydrate, Ca(NO₃)₂ · 4.1 H₂O, melt at 328 K has been investigated by X-ray scattering and correlation method. Analysis of the radial distribution function and model fitting revealed that in the hydrate melt, a Ca²⁺ ion is surrounded by about six oxygen atoms, 4.1 of which come from water molecules at the average distance of 0.241 nm, 2.0 coming from the nitrate ions at the average distance of 0.254 nm. In the first coordination shell of the melt, the formation of a direct Ca²⁺-NO ₃ ^– correlation, such as contact ion pairs, was suggested. The hydration structure of the melt analysed was compared with that of Ca(NO₃)₂ · 3.5H₂O melt previously reported, and the decrease from nine of the reported melt to six in this melt was observed in the number of the nearest neighbour oxygen atoms around a Ca²⁺ ion. This implies that in the highly concentrated aqueous solution, the structure of the first coordination shell around the cation changes markedly with a small difference in the water molecule content.     

Synthesis and Preliminary Biological Evaluation of 99mTc Tricarbonyl Ropinirole as a Potential Brain Imaging Agent

Ropinirole, a non-ergoline dopamine agonist, was labeled with ^99mTc tricarbonyl {[^99mTc(CO)₃·(H₂O)₃]⁺} with the aim of obtaining a new brain imaging agent. For in vivo use, the radiosynthesis of ^99mTc tricarbonyl ropinirole was performed by heating a solution containing ropinirole and the precursor, ^99mTc tricarbonyl, on a boiling water bath for 30 min. The influence of the substrate amount and pH on the reaction was studied to optimize the synthesis. The biodistribution and scintigraphic studies demonstrate the suitability of ^99mTc tricarbonyl ropinirole as a novel tracer for brain tumor imaging.

     

Synthesis and study of compounds of the general formula MITh2(VO4)3 (MI = Li, Na, Ag, K, Rb, Cs, Tl)

Double vanadates of thorium and univalent metals with r(M^I) < 1.6 Å were prepared by high-temperature solid-phase reactions. Representatives of this series with larger M^I atoms were prepared by the solgel method. The compounds crystallize in three structural types: zircon for Li and Na derivatives, scheelite for AgTh₂(VO₄)₃, and potassium thorium vanadate for the compounds containing K, Rb, Cs, and Tl. Thus, two morphotropic transitions are observed in the series of the compounds studied. The bands in the IR spectra were assigned, and the effect of the site symmetry of the VO₄ tetrahedra on the number of absorption bands was revealed. The incongruent melting points of the compounds were determined by differential scanning calorimetry.     

Atomic Hydrogen in Thick H2 Films at Temperatures 0.05�C2?K

We describe experiments on hydrogen atoms stabilized in a 100 ??m thick H₂ film at temperatures between 0.05 and 2 K. The molecular hydrogen matrix was condensed directly from natural hydrogen gas. The H atoms are produced with a plasma discharge at temperatures below 1 K and studied with electron spin resonance. H densities of 2×10¹⁹ cm^?3 in solid H₂ were reached. As observed earlier in thin H₂ films, we found a high stability of atomic populations and strong deviation from Boltzmann statistics of lowest two hyperfine states at the lowest temperatures. In thick films we found that the ESR resonance lines consisted of two closely spaced components with different widths indicating separate regions of high and low concentrations of H atoms in the H₂ matrix. Upon warming, the two components show very different rates of recombination with the higher density component having a faster recombination rate at T>1 K. We discuss the atomic interactions and mobility, and also the structure of the samples of H atoms in the H₂ matrix.     

Thermogravimetry of α,ω-diaminoalkanes used in synthesizing ZSM-5

Thermogravimetry was determined on a series of α,ω-diaminoalkanes, in which the alkane chain contained from three to eight carbon atoms, that were located in zeolite ZSM-5 during synthesis. Of the series, 1,6-diaminohexane functions best as a template, and this was attributed to its having a size that most neatly fits into the zeolite structure; the other molecules were either too small or too large. It was found that the channels were not completely filled and, on average, there were 5.3 diaminoalkane molecules per unit cell of the zeolite. Further, the organic compound within the zeolite had undergone partial deamination during synthesis.