Degradation of hydroxymaleimide in 2-propanol by irradiation of energetic heavy ions (II)—N2-saturated system

Hydroxymaleimide was irradiated in N₂-saturated 2-propanol solutions by high-energy heavy ions over a wide range of LET values. The differential G-values of the degradation of hydroxymaleimide by irradiation with the heavier ions were lower than those of the lighter ions for the same LET value. An opposite result obtained in the air-saturated system. The degradation efficiency was 1.5 times higher, when the dose rate was 1/10 times lower. When irradiated at an LET value lower than 8 eV/nm, the G-values converged to a value less than that obtained by γ-irradiation.     

Fast-neutron radiolysis of acid water at elevated temperatures

Determination of G-values of water decomposition products in acid formed by irradiation of fast neutrons from a reactor YAYOI at elevated temperatures up to 275°C was carried out with a combination of an aerated and a deaerated Fricke dosimeters and a cerium dosimeter. As a first step, the dosimetry of the radiation field revealed that the average energy of the fast neutrons is 0.8 MeV, and over 90% of the total dose absorbed by the aqueous solutions comes from fast neutrons. At room temperature, G-values evaluated for water decomposition products, G_H + Ge^-_aq = 1.25, G_OH = 0.68, G_H2 = 0.99, G_H2O2 = 1.27 and G_-H2O = 3.21, coincide with those at initial LET of about 4 eV/Å. With increasing temperature, radical products increase and molecular products decrease, and above 150°C, relative G-values of the products seem to be similar to those obtained in γ-radiolysis at room temperature; however, G_-H2O decreases slightly. On the basis of the above results, the temperature effect of water decomposition with fast neutron at elevated temperatures is concluded to be very different from that by γ-rays, where no drastic change in the decomposition pattern with temperature was found.     

Radiation chemistry of tetramethylgermane

A study of the ⁶⁰Co γ-irradiation of tetramethylgermane is reported. The major products are identified and their yields given. Both carbon-hydrogen and carbon-germanium bond scission occur. Hydrogen and methane are the major gaseous products. Ethyltrimethylgermane, hexamethyldigermane, bis(trimethylgermyl) methane and bis(trimethylgermyl)ethane are the major heavier products. The total yield of products indicates that the yield of disappearance of tetramethylgermane, G[—Ge(CH₃)₄], is 10.2 molecules per 100 eV absorbed. An (unidentified) product is formed which captures electrons.     

Isotopic effect in the radiolysis of water. Diffusion-kinetic modelling up to 300°C

Diffusion-kinetic calculations [1-3] have been analysed to determine the isotopic effect in the radiolysis of water with ionising radiation of linear energy transfer characteristics (LET) from 0.2 to 60 eV/nm and at temperatures up to 300°C. This analysis shows that, for low LET radiation, the spur decay of e^- _aq is slower in D₂O and results in a higher yield of e^- _aq, g(e^- _aq), at 10^-7 -10^-6s after the ionisation event. In low LET radiolysis, g(OD) ≈ g(OH) over the whole range of temperature but in high LET radiolysis g(OD) is clearly lower than g(OH). The isotopic effect on the yields of the radical products is enhanced by increasing LET but diminished by increasing temperature. The yields of the molecular products show the opposite isotopic effect to their radical precursors, namely g(D₂) is 10-20% lower than g(H₂) and g(D₂O₂) > g(H₂O₂). A particularly significant difference between g(D₂O₂) and g(H₂O₂) has been found at LET = 20 eV/nm. The isotopic dependence of the g-values estimated for fast neutron radiolysis is also presented.     

Perturbations of molecular extravalence excitations by rare-gas fluids

In this paper we report the results of an experimental study of the vacuum ultraviolet absorption spectra of molecular impurity states of methyl iodide in Ar (density range ? = 0–1.4 g cm^?3) and in Kr (? = 0–2.3 g cm^?3), of carbon disulphide in Ar (? = 0–1.4 g cm^?3) and of formaldehyde in Ar (? = 0–1.25 g cm^?3). The experimental results provide new information regarding medium perturbations of intravalenc transitions, of the lowest extravalence transitions and of transitions to mixed valence—Rydberg configurations, which serve as a diagnostic tool to distinguish between different types of electronic excitations. All the lowest extravalence molecular excitations exhibit appreciable blue spectral shifts at moderate and at high fluid densities, intravalence transitions are practically insensitive to medium effects, while excitations to mixed valence—Rydberg configurations are characterized by a moderate blue spectral shift. New information has been obtained concerning the energetics of molecular ionization processes in a dense fluid. The high n = 2–5 Rydberg states of CH₃l exhibit a large red shift at moderate (? = 0–0.5 cm^?3) Ar densities. The ionization potential E_g and the effective Rydberg constant G for CH₃I in Ar was found to decrease from G = 13.6 eV and E_g = 9.55 eV at ? = 0 and E_g = 9.08 eV and constant G for CH₃l in Ar was found to decrease from G = 13.6 eV and E_g = 9.55eV at ? = 0 and E_g = 9.08 eV and G ≈ 7.15 eV at ? = 0.5 g cm^?3. Experimental evidence was obtained for the identification of n = 2 molecular Wannier impurity states of CH₃I and of CH₂O in liquid Ar. These spectroscopic data result in E_g ≈ 8.6 eV for CH₃I in liquid Ar and E_g ≈ 10.2 eV for CH₂O in liquid Ar.     

Track effects in the radiolysis of aromatic liquids

The chemical effects induced by the track structure of heavy ions have been exploited to show that H₂ production in the radiolysis of simple aromatic liquids (benzene, pyridine, toluene and aniline) is primarily due to second order processes. Similar dependences of H₂ yields on the linear energy transfer, LET, for each of these compounds suggest a common mechanism for H₂ formation. Furthermore, the yields of H₂ are significant at very high LET and they approach that found with aliphatic compounds. Yields of “dimers” (biphenyl, bibenzyl, dipyridyl, and diphenylamine for benzene, toluene, pyridine, and aniline, respectively) have different dependences on LET reflecting the variety of pathways leading to their production. Bibenzyl formation in toluene exhibits a complex dependence on LET suggesting several competing pathways for its production whereas biphenyl formation in benzene is nearly independent of LET suggesting a unimolecular process. Dipyridyl, and diphenylamine yields in pyridine and aniline, respectively, decrease with increasing LET, which indicates that their precursor is being depleted.     

Water radiolysis with heavy ions of energies up to 28 GeV.: 1. Measurements of primary g values as track segment yields

Water radiolysis has been investigated with heavy ions having energies up to 28 GeV provided from the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Sciences (NIRS). Beams of ⁴He²⁺, ¹²C⁶⁺, ²⁰Ne¹⁰⁺, ²⁸Si¹⁴⁺, ⁴⁰Ar¹⁸⁺ and ⁵⁶Fe²⁶⁺ with respective energies of 150, 400, 400, 490, 500 and 500 MeV/u corresponding LET values of 2.2, 13, 30, 54, 92 and 183 eV/nm, respectively, were taken for the irradiation. The LET changes in sample solutions can be neglected due to their high energies for the irradiation of 1-cm cells. Primary g values have been determined for three important products, hydrated electron (e⁻_aq), hydroxyl radical (·OH), and hydrogen peroxide (H₂O₂) as track segment yields (differential yields) under the conditions of neutral pH.With increasing LET, the g values of e⁻_aq and ^·OH decrease from 2.4 and 2.6 in ⁴He²⁺ radiolysis to 0.9 and 1.1 (100 eV)⁻¹ in ⁵⁶Fe²⁶⁺ radiolysis, respectively. It was also found that the primary g value of e⁻_aq is smaller than that of ·OH for any type of ion beam. For the ¹²C⁶⁺ beam, other energies such as 290, 220, 135 MeV/u were taken for the irradiation to investigate the effects of type or atomic number of ions on the measured yields. Furthermore, effects of dissolved oxygen on enhancement of H₂O₂ production have also been investigated with aerated NaNO₃ solutions. The presence of dissolved oxygen caused 15–35% enhancement in H₂O₂ yields for all beams. In addition, the results of the present work were compared with reported track segment yields.     

Quantum chemical DFT calculations of the local structure of the hydrated electron and dielectron

The adiabatic bound state of an excess electron is calculated for a water cluster (H₂O) ₈ ^? in the gas phase using the DFT-B3LYP method with the extended 6-311++G(3df,3pd) basis set. For the liquid phase the calculation is performed in the polarizable continuum model (PCM) with regard to the solvent effect (water, ? = 78.38) in the supermolecule-continuum approximation. The value calculated by DFT-B3LYP for the vertical binding energy (VBE) of an excess electron in the anionic cluster (VBE(H₂O) ₈ ^? = 0.59 eV) agrees well with the experimental value of 0.44 eV obtained from photoelectron spectra in the gas phase. The VBE value of the excess electron calculated by PCM-B3LYP for the (H₂O) ₈ ^? cluster in the liquid phase (VBE = 1.70 eV) corresponds well to the absorption band maximum λ_max = 715 nm (VBE = 1.73 eV) in the optical spectrum of the hydrated electron hydr e _hydr ^? . Estimating the adiabatic binding energy (ABE)e _hydr ^t- in the (H₂O) ₈ ^? cluster (ABE = 1.63 eV), we obtain good agreement with the experimental free energy of electron hydration ΔG ₂₉₈ ⁰ (e _hydr ^? ) = 1.61 eV. The local model (H₂O) ₈ ^2? of the hydrated dielectron is considered in the supermolecule-continuum approximation. It is shown that the hydrated electron and dielectron have the same characteristic local structure: -O-H{↑}H-O- and -O-H{↑↓}H-O-respectively.     

A study of the radiation chemistry of phosphorous compounds

The partial charges of atoms of a number of organophosphorous compounds were calculated by the method of iterative partial equalization of orbital electron negativity (PEOE) presented by Gasteiger and Marsili, and from the calculated partial charges of carbon atoms of the ester alkyl groups in three stereoisomers each for tributylphosphate and dibutylphenylphosphonate, it was found that in all cases the carbon at the α-position to oxygen possesses the largest density of positive charge, such that the C_α—C_β bonds were more readily broken than other C—C bonds. The experimental results supported this conclusion by examining the G-values of gaseous alkane (alkene) radiation products. From the low temperature measured esr spectra of several phosphates and phosphonates γ-irradiated at 77°K and it was seen that these spectra were composed of several radicals formed by different reaction processes. Like TMP, the esr spectrum of dimethyl methylphosphate irradiated in low temperature contained also four kinds of radicals. The net atomic charges as well as the values of mulliken population matrix condensed to atoms were calculated by CNDO/2 MO and by ab initio MO methods for comparison. In all cases the net atomic charges of the carbon in C—P bonds were positive. Since the phosphoryl radical was found in esr spectrum of DMMP, it implied that the C—P bonds were also broken during irradiation. In our work, the products of C—P fission were truly found and their G-values were determined by gas chromatography. For studying of energy transfer, two binary systems (TBP-DPPP and TBP-benzene) were irradiated and the G-values of polymer, di-and monobasic acids were measured and compared. In these systems the intermolecular energy transfer were predominate. DPPP had higher scavenging effect than benzene.     

Antigenes de groupe sanguin : Synthese de glycopeptides Tn representant la partie N-terminale de la glycophorine humaine AN et AMc

This report describes the first synthesis of the triglycosylated pentapeptides H₂N—Leu—Se^*r—Th^*r—Th^*r—Gl^*u—OH et H₂N—Ser—Se^*r—Th^*r—Th^*r—Glu—OH, in which 1 represents the 2-acetamido-2-deoxy α-D-galactopyranosyl residues. These compounds constitute the antigenic aminoterminal portions of respectively human glycophorin A^N and A^Mc. The above compounds were obtained by a stepwise peptide coupling strategy in solution, beginning at the C terminus and proceeding toward the N-terminus, using amino acids or suitably protected and activated O-glycosyl-amino acids. Carbohydrate residues were introduced into the sequence as 2-azido-2-deoxy-α-D-galactopyranosyl-l-serine and l-thréonine derivatives obtained from the reducing sugar and amino acid by the trifluoromethanesulfonic anhydride procedure. Reduction of the azido functions followed by acetylation and catalytic hydrogenolysis afforded the above antigenic T_N glycosylated pentapeptides.     

Radiolysis of tetrachloromethane-water two-phase systems

The radiolysis of two-phase systems CCl₄-water proceeds in kinetical regime up to dose 12 kGy. Groos radiation yields of chloride ions are the same as the radiolysis of saturated solutions in this period. A two-phase rule of additivity is valid and the partial yields for both phases were calculated; G_CCl4(Cl^- = 5.61 ± 0.10 and G_H2O(Cl^-) = 8.29 ± 0.51 molecules/100 eV, respectively.The radiolysis proceeds in diffusional regime at the absorbed dose of more than 50 kGy. The gross radiation yield of chloride ions is determined by hydrolysis of molecular chlorine which is produced with G(Cl₂) = 0.68 ± 0.14 molecules/100 eV. An additional part of chloride ions is produced by radiolysis of substrates which diffuse into both phases with value G_dif(Cl^-) = 2.38 ± 0.31 molecules/eV. This value is approximately three times less than the gross radiation yields in kinetical regime of radiolysis of two-phase systems in saturated solutions of these substrates.     

Kinetics and mechanism of the reactions of C6H12, C5H10 and C6D12 cycloalkanes with peroxynitrous acid in aqueous solution and the gas phase

The c-C₆H₁₂/c-C₆D₁₂ kinetic isotope effect (KIE), the k₆/k₅ rate constant ratio (c-C₆H₁₂/c-C₅H₁₀), and the temperature dependence of these ratios in the gas-phase reactions of cycloalkanes with peroxynitrous acid and OH radicals are identical. The same result was obtained for the reactions in aqueous solution. These data are in accord with the conclusion that OH^· radicals formed in the homolysis of the HO-ONO bond are the active species in the reactions of HOONO with hydrocarbons in aqueous solution and in the gas phase. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 105–110, March–April, 2008.     

60Co-v Radiolysis of a Mixture of Benzene and Cyclohexane in Presence of Diphenyl Mercury

In the radiolysis of cyclohexane in presence of 4×10^?3M diphenylmercury (Hg φ₃) three isomers of hexane, methylcyclopentane (G=0.018), benzene (G=0.42) and cyclohexene (G=0.047) were detected. Addition of benzene in the mixture of cyclohexane and Hg φ₃ formed two isomers of pentane, hexene and one isomer of hexane as additional products, while cyclohexene was eliminated completely. Normally, eight products were detected in presence of 10 to 50% benzene. Total radiolytic yield of products increased in presence of 15 to 25% benzene but in presence of 35 to 50% benzene G values became very low. Considerable amount of hexene is formed in a mixture of benzene and cyclohexane but neither benzene nor cyclohexane in presence of Hg φ₂ formed this compound. In the presence o. benzene and φ₂Hg hexane yield is very much reduced. Protection is observed in presence of 10% as well as 35 to 50% benzene in this system. The plot of benzene concentration in moles/litre versus methylcyclopentane is linear and from the slope of the straight line, the values of rate constants were found to be 2.65×10^?2 litre/mole sec., 5.25×10^?3 litre mole sec., 9×10^?7 litre/mole sec. for methylcyclopentane, cyclohexane and benzene respectively. A plot of G(–c-C₆H₁₂) versus 1/[C₆H₆] also gave a straight line which confirms the sponge type protection in this multicomponent system.     

Application of the “helium excitation standard” procedure to some hydrocarbon Hβ absolute emission cross section measurements

Absolute emission cross sections for H_β radiation are presented. The H_β emission is obtained by dissociative electron excitation of propane, propylene, n-butane and 1-butene under binary collision conditions. Optical excitation functions measured for these transitions are normalized by the “helium excitation standard” procedure, using the 4 ¹S-2 ¹P transition in He as a standard at an electron impact energy of 100 eV. The results obtained are determined with an accuracy of ± 15%. The investigated energy interval is 50–500 eV. The experimental results show that the emission cross sections for H_β radiation are not independent of the number of atoms in the parent molecule.     

过渡金属氢化物和聚集双键化合物反应的研究——Ⅴ.Cp2MH2(M=Zr,Hf)与RNCS(R=n-Bu,c-C6H11,C6H5,2-C10H7)、CS2的反应

本文研究了Cp₂ZrH₂与CS₂、RNCS(R=n-Bu,c-C₆H₁1,C₆H₅,2-C₁₀H₇)和Cp₂HfH₂与c-C₆H₁₁NCS的反应,探讨了在这类新型脱硫反应中锆氢与铪氢配合物化学反应性能上的差异.从以上反应中分     

Thermodynamics of molecular interactions in binary mixtures of non-electrolytes. Molar excess volumes

Molar excess volumes, V^E, for pyridine (A) + α-picoline (B), + β-picoline (B) and + γ-picoline (B) and benzene (A) + toluene (B), + o-xylene (B) and + p-xylene (B) and carbon tetrachloride (A) + n-heptane (B) have been measured dilatometrically as a function of temperature and composition and have been utilized to study B—B and B—B—B interactions in the presence of A via the Mayer—McMillan approach. A model has also been presented to account for these B—B and B—B—B interactions. The V^E data at 308.15 K have also been analysed in terms of the “graph theoretical” approach which describes the V^E data well for all these mixtures at 308.15 K. The “graph theoretical” approach has further been extended to successfully evaluate V^E data for a mixture at any temperature, T₂, when the V^E data at T₁ are known.     

Photoionization of aqueous indole: Conduction band edge and energy gap in liquid water

Previous work on the determination of the photoionization threshold (I_sol) of tryptophan has now been extended to indole as a solute, both in tetramethylsilane (TMSi) and H₂O solvents. In TMSi, electron scavenging by N₂O or photoconductivity measurements lead to the same I_sol value: 4.95 ± 0.1 eV. In water, I_sol is found equal to 4.35 ± 0.1 eV. From these experiments, information on the ionization mechanism, on the oxidized solute and on the solvent can be gained: (i) the scavenger electron affinity does not intervene in the energy balance providing I_sol; (ii) an “effective” ionic radius of indole (1.40 Å) is estimated which suggests that the positive charge remains highly localized on the N-atom of the indole ring; (iii) a value of ?1.2 ± 0.1 eV can be deduced for V_o, the conduction band edge of water; (iiii) from the above findings, the energy gap E_G of pure water, considered as a semi-conductor, would be close to 7 eV. Such a result is discussed in terms of literature data pertaining to electron ejection in pure liquid water and X-ray photoelectron spectroscopy of amorphous ice.     

Steady-state and pulsed studies of the radiation-induced polymerization of methyl methacrylate

In order to quantify our fluorogenic molecular probe studies on the radiation-induced polymerization of methyl methacrylate (MMA), measurements have been made of the monomer conversion, C _M, and polymer molecular weight distribution as a function of dose for bulk MMA polymerized by steady-state (⁶⁰Co γ-rays) and nanosecond-pulsed (3 MeV electrons) radiation. In all cases, C _M was found to increase close to linearly with dose up to ca. 30%. Above this conversion, autoacceleration of polymerization (the gel or Trommsdorff effect) occurs in the γ-irradiated samples. From the low-conversion steady-state data, using dose-rates of 0.21 and 2.7 Gy/s, the parameter 〈k _p〉 ² G(R^.)/2〈k _t〉 = 0.011 and 0.015 lmol^-1 s^-1 (100 eV)^-1 respectively have been determined (with 〈k _p〉 and 〈k _t〉 the average rate coefficients for bimolecular propagation and termination respectively, and G(R^.) the yield of the chain-initiating free radicals per 100 eV (G = 1 (100 eV)^-1 0.1036 μ mol J^-1)). From the 5 Hz repetitive pulse data the value of 〈k _p〉 G(R^.) = 1700 lmol^-1 s^-1 (100 eV)^-1 has been determined. Taking 〈k _p〉 = 342 lmol^-1 s^-1 from the literature results in G(R^.) = 5.0 (100 eV)^-1 and 〈k _t〉 = 2.7 × 10⁷ lmol^-1 s^-1.     

Thermodynamic properties of trilaurylammonium bisulphate in benzene

We have studied the thermodynamic properties of trilaurylammonium bisulphate (TLAH₂SO₄) in benzene at several temperatures by vapour pressure osmometry (VPO). Values of the activity coefficients, γ_i, are given, which allows calculation of the excess thermodynamic functions, G^E, S^E and H^E.