Vladimir I. Feldman

Formation and decay of transient xenon dihydride resulting from hydrocarbon radiolysis in a xenon matrix

The formation and decay of transient xenon dihydride upon annealing xenon-hydrocarbon systems irradiated with fast electrons at 15 K was monitored by FTIR spectroscopy. It is concluded that XeH2 is a chemically identical species, which can be generated in different ways. The two bands of these species (positioned at 1181 and 1166 cm−1) show essentially different behaviour with annealing temperature. Evidence for a chemical reaction of xenon dihydride with trans-2-butene occurring in a xenon matrix at 60–70 K was obtained. The addition of electron scavengers results in a dramatic decrease in the XeH2 yield. It is suggested that xenon dihydride results from H atoms rather than from charged precursors.

Isotopic effect on thermal mobility of atomic hydrogen in solid xenon

We have studied thermal mobility of atomic hydrogen in solid Xe using decomposition of water molecules as a source for hydrogen atoms. The formation of various isotopomers of HXeH and HXeOH is monitored at temperatures from 37 to 42 K by using infrared absorption spectroscopy, and the activation energy of this diffusion-controlled process is found to be ∼110 meV. Most importantly, the different mobility for hydrogen isotopes is demonstrated, H being faster than D, and the difference between the corresponding activation energies is estimated to be ∼4 meV. The electron paramagnetic resonance measurements of the thermal decay of H atoms and OH radicals show that the formation of HXeH and HXeOH is controlled by hydrogen mobility. The modeling of thermally activated jumps of hydrogen atoms in a relaxed Xe lattice agrees reasonably with experiment with respect to the isotopic effects but it underestimates the jump rate.

On photochemistry of water in solid Xe: Thermal and light-induced decomposition of HXeOH and HXeH and formation of H2O2

A photochemical study of water (H2 16O, H2 18O, D2 16O, and D2 18O) in solid Xe is described. The water–Xe samples were irradiated at 193 nm and then annealed at 40–50 K, which led to formation of various isotopomers of Xe-containing molecules, HXeOH and HXeH. This diffusion-controlled formation of HXeH and HXeOH consumes the main part of hydrogen atoms generated in the matrix during photolysis. Both photodecomposition profiles and ultraviolet (UV) absorption spectra of HXeOH and HXeH feature a broad absorption band of these species around 240 nm corresponding to the transition to the repulsive excited states. It is also found that HXeOH and HXeH molecules can be thermally destroyed in similar time scales of ∼10 min at about 54 and 66 K, respectively. This clear difference between the decomposition temperatures for HXeOH and HXeH suggests the intrinsic basis of the decomposition process, which possibly occurs over the barriers of the bending coordinates. The absence of strong H–D isotope effect in this th...

Radiation-induced transformations of isolated organic molecules in solid rare gas matrices

The radiation-chemical behaviour of isolated organic molecules in solid rare gas matrices was studied using a combination of ESR and IR spectroscopy. The total radiation-chemical yields of degradation of organic molecules in solid argon and xenon were estimated. The effect of electron scavengers on the radiolysis of organic molecules in solid rare gases reveals that the main primary process is positive hole transfer from matrix to guest molecule. ESR spectra of a number of radical cations (alkanes, ethers, arenes) were characterized in a low-disturbing environment. It was found that the electronic characteristics (IP, polarizability) of the matrix used had crucial effect on trapping and reactions of the isolated radical cations.

Radiation sterilisation of doxorubicin bound to poly(butyl cyanoacrylate) nanoparticles

Doxorubicin-loaded poly(butyl cyanoacrylate) (PBCA) nanoparticles were prepared by anionic polymerisation under non-aseptic conditions. The feasibility of sterilisation of this formulation using either gamma-irradiation or electron beam irradiation was investigated. The irradiation doses ranged from 10 to 35 kGy. Bacillus pumilus was used as the official test microorganism. The bioburden of the untreated formulation was found to be 100 CFU/g. Microbiological monitoring revealed that at this level of the bioburden the irradiation dose of 15 kGy was sufficient for sterilisation of the nanoparticles. The formulation showed excellent stability with both types of irradiation in the investigated dose range. The irradiation did not influence the physicochemical parameters of the drug-loaded and empty nanoparticles, such as the mean particle size, polydispersity, and aggregation stability. The molecular weights of the PBCA polymer as well as the polydispersity indices (M(w)/M(n)) remained nearly unchanged. The drug substance was stable to radiolysis. Additionally, the presence of irradiation-induced radicals was evaluated by ESR spectroscopy after storage of the particles at ambient temperature. The paramagnetic species found in the formulation were mainly produced by irradiation of mannitol and dextran used as excipients.

Infrared absorption and electron paramagnetic resonance studies of vinyl radical in noble-gas matrices

Vinyl radicals produced by annealing-induced reaction of mobilized hydrogen atoms with acetylene molecules in solid noble-gas matrices (Ar, Kr, and Xe) were characterized by Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The hydrogen atoms were generated from acetylene by UV photolysis or fast electron irradiation. Two vibrational modes of the vinyl radical (nu7 and nu5) were assigned in IR absorption studies. The assignment is based on data for various isotopic substitutions (D and 13C) and confirmed by comparison with the EPR measurements and density-functional theory calculations. The data on the nu7 mode is in agreement with previous experimental and theoretical results whereas the nu5 frequency agrees well with the computational data but conflicts with the gas-phase IR emission results.

From triple interpolyelectrolyte-metal complexes to polymer-metal nanocomposites

Nanocomposite polymer materials containing metal or metal oxide particles attract growing interest due to their specific unique combination of physical and electric behavior. Stoichometric triple interpolyelectrolyte-metal complexes (TIMC) are insoluble in water and in aqueous organic media and may include high content of metal ions; concentration of ions is easy to vary in such polymeric systems. Reduction of metal ions is a common method for obtaining nanoparticles. Interpolyelectrolyte complexes reveal high permeability for polar low-molecular substances and salts. Such swelling behavior is important for the reduction of metal ions included in these solids. The properties of triple interpolyelectrolyte-metal complexes and preparation of nanocomposites from these materials using various methods of metal ion reduction are discussed in this work.

Direct visualization of the H-Xe bond in xenon hydrides: xenon isotopic shift in the IR spectra.

IR spectra of xenon hydrides (HXeCCH, HXeCC, and HXeH) obtained from different xenon isotopes ((129)Xe and (136)Xe) exhibit a small but detectable and reproducible isotopic shift in the absorptions assigned to H-Xe stretching (by 0.17-0.38 cm(-1)). To our knowledge, it is the first direct experimental evidence for the H-Xe bond in HXeY type compounds. The shift magnitude is in good agreement with quantum-chemical calculations.

Radiation-induced degradation of alkane molecules in solid rare gas matrices

Abstract The radiation-induced degradation of heptane molecules in solid argon and xenon matrices at 15 K was studied using low-temperature IR spectroscopy. The total radiation-chemical yield of the destruction of heptane molecules in argon (mole ratio 500:1) was estimated to be 1.4 molecule per 100 eV. Methane, vinyl- and trans-vinylene-type olefins, and allyl-type radicals were identified among the main radiolysis products in both matrices. The C-C bond rupture is favoured in argon probably due to formation of excited heptane cations in the hole transfer in this matrix. An indication of the radical cation trapping was obtained in a xenon matrix containing an electron scavenger (Freon-113). The mechanism of the radiation-induced degradation of alkane molecules and the fate of the primary cations in rigid inert media are discussed.

Matrix-Isolation Studies on the Radiation-Induced Chemistry in H2O/CO2 Systems: Reactions of Oxygen Atoms and Formation of HOCO Radical

The radiation-induced transformations occurring upon X-ray irradiation of solid CO2/H2O/Ng systems (Ng = Ar, Kr, Xe) at 8-10 K and subsequent annealing up to 45 K were studied by Fourier transform infrared spectroscopy. The infrared (IR) spectra of deposited matrices revealed the presence of isolated monomers, dimers, and intermolecular H2O···CO2 complexes. Irradiation resulted in effective decomposition of matrix-isolated carbon dioxide and water yielding CO molecules and OH radicals, respectively. Annealing of the irradiated samples led to formation of O3, HO2, and a number of xenon hydrides of HXeY type (in the case of xenon matrices). The formation of these species was used for monitoring of the postirradiation thermally induced chemical reactions involving O and H atoms generated by radiolysis. It was shown that the radiolysis of CO2 in noble-gas matrices produced high yields of stabilized oxygen atoms. In all cases, the temperatures at which O atoms become mobile and react are lower than those of H atoms. Dynamics and reactivity of oxygen atoms was found to be independent of the precursor nature. In addition, the formation of HOCO radicals was observed in all the noble-gas matrices at remarkably low temperatures. The IR spectra of HOCO and DOCO were first characterized in krypton and xenon matrices. It was concluded that the formation of HOCO was mainly due to the radiation-induced evolution of the weakly bound H2O···CO2 complexes. This result indicates the significance of weak intermolecular interactions in the radiation-induced chemical processes in inert low-temperature media.