Determination of 129I/127I ratios in environmental samplesusing neutron activation analysis

Studies on the behavior of ¹²⁹I in the environment are greatly enhanced when the concentration of the radioiodine can be related to stable ¹²⁷I. The background ratios of ¹²⁹I/¹²⁷I of 10^-10 and lower, found in uncontaminated areas, are best measured using accelerator mass spectrometry. However, there are many examples of studies where ratios higher than 10^-8 have been measured, even in places located remotely from nuclear reprocessing activities. In the vicinity of reprocessing plants it is possible to find ratios between 10⁰ and 10^-7, which can be detected easily using neutron activation analysis (NAA). Stable iodine is readily determined at concentrations below 1 mg/kg in environmental materials with instrumental NAA and radiochemical techniques can be used to measure ¹²⁹I to below mBq concentrations. Therefore, where there are elevated concentrations of ¹²⁹I it is possible to use a combination of neutron activation techniques to determine ¹²⁹I/¹²⁷I ratios. This paper describes how NAA is used to measure ¹²⁹I/¹²⁷I ratios in milk, vegetation, and atmospheric samples. Instrumental NAA is used to measure both ¹²⁹I and ¹²⁷I where the ratio is between 10⁰ and 10^-3. A radiochemical procedure is used to measure ¹²⁹I at ratios between 10^-3 and 10^-7, with a thermal neutron flux of 10¹⁶ m^-2·s^-1.     

Production of charge-induced X-rays during PIXE studies using light and heavy ion-beams

A recently discovered phenomenon of excessively high X-ray production is discussed. The high yield is attributed to the build-up of potential on non-conducting targets irradiated with accelerated ion beams, and the subsequent discharge. Ion-beams of¹H⁺,¹H₂ ⁺,²H⁺,²H₂ ⁺,³He⁺,³He²⁺,⁴He⁺,¹⁴N⁺,¹⁴N²⁺,¹⁶O⁺ and²⁰Ne⁺ were used. A new mechanism of X-ray excitation is proposed. The increased X-ray fluxes produced by this process are suitable for analytical applications of high specificity. The mechanism of excitation associated with the process, factors affecting the high X-ray yields, applications and a general overview of the studies undertaken with the various ion beams are given.     

硫族铅化物阳离子低电子态的理论研究

采用我们最近发展的含旋轨耦合的运动方程耦合簇计算电离能(EOMIP-CC)方法,在CCSD级别上计算了硫族铅化物PbS、PbSe、PbTe阳离子低电子态的平衡键长和谐振频率以及绝热和垂直电离能,得到的结果与已有的实验值吻合较好.不考虑旋轨耦合(SOC)的情况下通过与CCSD(T)的计算结果比较,考察了三重激发对计算结果的影响,结果显示考虑三重激发的贡献后得到的键长和频率结果与实验值吻合更好.计算结果表明PbTe+中2Π态的能量分裂明显大于PbS+和PbSe+中2Π态的能量分裂,但是PbTe+中2Π1/2和2Σ1/2态之间的相互耦合则明显弱于PbS+和PbSe+中这两个态之间的耦合.PbTe+中2Π1/2和2Σ1/2态之间耦合很弱,一方面是因为2Σ+态和2Π态的能量差比PbS+和PbSe+中2Σ+态和2Π态的能量差大,另一方面还由于PbTe+中2Π1/2和2Σ1/2态之间的旋轨耦合矩阵元只是PbS+和PbSe+中2Π1/2和2Σ1/2态之间的旋轨耦合矩阵元的一半.这些计算结果为PbS+、PbSe+、PbTe+阳离子的低电子态性质提供了新的理论数据,可以为将来的实验数据提供参考.     

Improved methods of obtaining Nim-trityl-substituted histidine derivatives

Two variants are proposed for the synthesis of N^α-Boc-N^im-tritylhistidiine. The first variant starts from N^α,N^im-di-Boc-histidine, from which the N^im-Boc group is removed with hydrazine hydrate. The N^α-Boc-histidine formed is esterified with chlorotrimethylsilane, tritylated in the imidazole group, and, after the elimination of the trimethylsilyl protection from the carboxyl group, N^α-Boc-N^im-tritylglycine is obtained with a yield of 80%. The second variant starts from N^α,N^im-ditritylhistidine, which, by treatment with hydrochloric acid in acetone and then with dilute ammonia, is converted into N^im-tritylhistidine. From this, by acylation with di-tert-butyl pyrocarbonate, N^α-Boc-N^im-tritylhistidine is obtained with a yield of 91%. The acylation of N^im-tritylhistidine with other alkoxycarbonylating reagents leads to N^α-tert-amyl-, N^α-benzyl-, and N^α-4-methoxybenzyloxycarbonyl derivatives of N^im-tritylhistidine.     

Precise trace rare earth analysis by radiochemical neutron activation

A rare earth group separation scheme followed by normal Ge(Li), low energy photon detector (LEPD), and Ge(Li)−NaI(Tl) coincidence-noncoincidence spectrometry significantly enhances the detection sensitivity of individual rare earth elements (REE) at or below the ppb level. Based on the selected γ-ray energies, normal Ge(Li) counting is favored for¹⁴⁰La,¹⁷⁰Tb and¹⁶⁹Yb; LEPD is favored for low γ-ray energies of¹⁴⁷Nd,¹⁵³Sm,¹⁶⁶Ho and¹⁶⁹Yb; and noncoincidence counting is favored for¹⁴¹Ce,¹⁴³Ce,¹⁴²Pr,¹⁵³Sm,¹⁷¹Er and¹⁷⁵Yb. The detection of radionuclides^152mEu,¹⁵⁹Gd and¹⁷⁷Lu is equally sensitive by normal Ge(Li) and noncoincidence counting;¹⁵²Eu is equally sensitive by LEPD and normal Ge(Li); and¹⁵³Gd and¹⁷⁰Tm is equally favored by all the counting modes. Overall, noncoincidence counting is favored for most of the REE. Precise measurements of the REE were made in geological and biological standards. Prepared for the U.S. Department of Energy under Contract DE-AC06-76RLO 1830.     

CI study of rovibrational dependence of nuclear quadrupole coupling constants of all isotopic variants of OH+ in the X3Σ− state

The ¹⁷O and ²H quadrupole coupling constants of rovibrational levels of ¹⁷O¹H⁺, ¹⁷O²H⁺, and ¹⁶O²H⁺ in their X³Σ⁻ state have been calculated from molecular wave functions that explicitly describe nuclear motion. The ¹⁷O quadrupole coupling is predicted to be strong and its vibrational dependence differs from that known for other nuclei A in the first-row hydrides AH or AH⁺. The deuterium coupling in ¹⁷O²H⁺ and ¹⁶O²H⁺ is found to be weak and its behavior is similar to that of other first-row hydrides. The change with rotational excitation is unimportant. The quadrupole hyperfine patterns of ¹⁷O²H⁺ in its ground state are dominated by the strong oxygen coupling. © 1996 John Wiley & Sons, Inc.     

Structural preferences of cyclopentadienyl and indenyl rings in iridium(I) carbene complexes

Cleavage of the [Ir(η⁴-COD)Cl]₂ dimer in the presence of the corresponding imidazolium salts and the strong base tBuO⁻ leads to the formation of Ir(I) derivatives of N-heterocyclic carbenes. When halide is replaced by NaCp, a mixture of [Ir(η⁴-COD)(NHC^R)(η¹-Cp)] and [Ir(η²-COD)(NHC^R)(η⁵-Cp)] is obtained. The latter is favored for R = Cy, while the former predominates for R = Me. Conversely, [Ir(η⁴-COD)(NHC^R)(η¹-Ind)] is the only product of the reaction with NaInd, despite the R substituent. DFT/B3LYP calculations confirmed that the η¹ coordination mode of the ring gives rise to the most stable structures, namely square planar complexes of 5d⁸ Ir(I). The energy of the 18 electron species containing η²-COD and η⁵-Ind or Cp is higher by 13 and 5 kcal mol⁻¹, respectively. The fluxional behaviour of indenyl, detected by NMR in the solutions of [Ir(η⁴-COD)(NHC^R)(η¹-Ind)], is associated to the low energy of the η³-Ind species required in the conversion process, and is not easily observed in the cyclopentadienyl derivatives, where a similar intermediate is disfavored.     

Stability and Structure of Binary and Ternary Metal Ion Complexes of Orotidinate 5′-Monophosphate (OMP3-) in Aqueous Solution

Abstract

The stability constants of the 1:1 complexes formed between Mg^{2 +}, Ca^{2 +}, Sr^{2 +}, Ba^{2 +}, Mn^{2 +}, Co^{2 +}, Ni^{2 +}, Cu^{2 +}, Zn ²⁺ or Cd ²⁺ and orotidinate 5′-monophosphate (OMP^3-) were determined by potentio-metric pH titrations in aqueous solution (I =0.1 M, NaNO₃; 25°C). In addition to the stability constants of these M(OMP)^? complexes, for several cases also the corresponding acidity constants for the release of the proton from the H(N-3) site were calculated; i.e., the formation of M(OMP-H)^2- complexes was quantified. On the basis of recent measurements for simple phosphate monoesters [R-MP^2-; R is a noncoordinating residue; S.S. Massoud and H. Sigel, Inorg. Chem., 27, 1447-1453 (1988)], evidence is provided that the somewhat increased stability of all the mentioned M(OMP)^? complexes is mainly the result of a charge effect of the carboxylate group (in position 6 of OMP^3-) and not of a direct participation in complex formation; i.e., there are no indications for the formation of significant amounts of macrochelates involving the phosphate and the carboxylate groups. This is different for the M(OMP-H)^2- complexes of Co ²⁺ , Ni²⁺ and Cd²⁺: in these cases significant amounts of macrochelates form; i.e., the metal ion is not only coordinated to the phosphate group but also (in part) to the ionized ^?(N-3) site, which is placed in the neighbourhood of the phosphate residue in the dominating syn conformation of this nucleotide. For the metal ions Mg^{2 +}, Ca²⁺, Sr^{2 +}, Ba²⁺ and Mn^{2 +}, which have in general a rather low affinity for N binding sites, no evidence for the formation of macrochelates is detected. In addition, the stability constants of the ternary Cu(Arm)(OMP)^? complexes, where Arm = 2,2′-bipyridyl or 1,10-phenanthroline, were determined by potentiometric pH titrations. Evaluation of the stability data shows that an equilibrium betweeen an ‘open’ isomer and a Cu(Arm)(OMP)^? species with an intramolecular stack exists; the formation degree of these aromatic ring stacks reaches about 40 percent. Overall it is quite evident that OMP^3- is a versatile ligand with remarkable properties which may be utilized by nature in recognition reactions during the intricate metabolic processes in which this nucleotide is involved.     

RKR potentials and radial wave equation

A RKR-Kaiser potential is obtained for the X¹Σ⁺CO state. This potential is tested through radial wave equation integration. In the application to the A ⁶LiH state there is not self-consistence. To improve it we present a mixed potential that is consistent. This is a Huffaker-RKR-van der Waals potential. This procedure is applicated to X′Σ⁺⁶LiH, A¹Σ⁺⁶LiH and A′Σ⁺⁶LiD states.     

The predissociations of water ions

Experimental relative abundances of D₂O⁺, OD⁺ and D⁺ ions are given as functions of the initial energy of D₂O⁺ ions in the B?²B₂ state. The D⁺ ions are more abundant than expected on the basis of a recent theoretical model. Less kinetic energy is released in D⁺ formation than in OD⁺ formation, for the same excess energy available. It is suggested that OD⁺ formation should be modelled as a statistical reaction, whereas D⁺ formation is more specific. No detailed model can be suggested on present evidence, but it is pointed out that H₂O⁺ (B?²B₂) can be predissociated to OH⁺ by the X? state to H⁺ by the à state, as well as by repulsive states.     

Detection of fallout155Eu and207Bi in a210Pb-dated lake sediment core

Low-energy -ray spectrometry is used to detect fallout¹⁵⁵Eu and²⁰⁷Bi in a²¹⁰Pb-dated sediment core from McKay Lake, Ottawa, Canada. Unlike²⁰⁷Bi which is detected only in two core sections deposited in the mid 1970's,¹⁵⁵Eu is consistently detectable to mid 1960's. A comparison of corresponding¹³⁷Cs and¹⁵⁵Eu inventories in the sediment core indicates that fallout¹⁵⁵Eu derives primarily from the thermal neutron fission of²³⁵U. The derived flux of unsupported²¹⁰Pb at the sediment/water interface is in agreement with previously estimated flux of atmospheric²¹⁰Pb in the Great Lakes region.     

In situ XPS and SIMS analysis of O2+ beam‐induced silicon oxidation

The chemical composition variation of silicon under 4 keV O₂⁺ ion beam bombardment at different incident angles was studied by in situ small‐area XPS. The changes in secondary ion profile (³⁰Si⁺, ⁴⁴SiO⁺, ⁵⁶Si₂⁺, ⁶⁰SiO₂⁺) during oxygen ion beam bombardment also have been monitored. We present a direct correlation of the changes in secondary ion depth profile with surface composition during sputtering. Evolution of the secondary ion profile obtained from SIMS shows similar trends with variation of oxygen concentration in the crater surface measured by XPS. It is shown that when the oxygen ion beam incidence angle is < 40° silicon dioxide is the dominant species on the crater surface and the matrix ion species ratio (MISR) value for ⁴⁴SiO⁺/⁵⁶Si₂⁺ is higher than for ³⁰Si⁺/⁵⁶Si₂⁺. For incidence angles of >40°, the formation of sub‐oxide is favoured and thus the MISR value for ⁴⁴SiO⁺/⁵⁶Si₂⁺ is lower than for ³⁰Si⁺/⁵⁶Si₂. At 40° bombardment there are similar amounts of SiO₂ and sub‐oxides present on the crater surface and the MISR values for ⁴⁴SiO⁺/⁵⁶Si₂⁺ and ³⁰Si⁺/⁵⁶Si₂⁺ are also similar. Copyright © 2004 John Wiley & Sons, Ltd.     

人红细胞摄入Cd2+离子的动力学和机理

不同Cd²⁺离子浓度引起的人红细胞相对溶血率及临界溶血浓度CH⁰已经测定,CH⁰=2.5×10^-4mol·L^-1。Cd²⁺跨膜进入人红细胞遵从一级动力学过程,其一级速率常数为1.2×10^-2h^-1。阴离子通道抑制剂DIDS及K⁺,Na⁺-ATPase抑制剂均可部分抑制人红细胞摄入Cd相似文献   

Limit of the INAA procedure for copper determination based on the64Cu 511 keV line

The²³⁵U/²³⁸U ratio is determined by neutron activation analysis counting the ϕ-rays of short half-lives fission products and²³⁹U. The effect of the neutron spectrum hardening using a⁶LiD converter is also demonstrated. The²³⁵U/²³⁸U ratio is determined using short irradiation, waiting and counting times.     

CHLOROPHYLL PHOTOSENSITIZED VECTORIAL ELECTRON TRANSPORT ACROSS PHOSPHOLIPID VESICLE BILAYERS: KINETICS AND MECHANISM*

Abstract— The characterization and kinetic analysis by laser Rash photolysis of an improved model system for observing chlorophyll a photosensitized electron transfer across a lipid bilayer membrane is described. In this system, the electron acceptor is a water-soluble naphthoquinone, S-(2-methyl-l,4-naphthoquinonyl-3)-glutathione (MGNQ) which is dissolved in the inner aqueous compartments of phospholipid bilayer vesicles, and the electron donor is glutathione (GSH) which is dissolved in the outer aqueous phase. Chlorophyll (Chl) is dissolved in the membrane. Oxidative quenching of the triplet state of Chl by the quinone at the inner surface of the vesicle produces the Chl⁺ and MGNQ^- radicals. Chi⁺ is reduced by GSH at the outer surface of the vesicle (k= 2.6 × 10⁶M^-1 s^-1) in competition with the recombination between Chl⁺. and MGNO^- (k= 2.5 × 10³ S^-1). It is shown that a kinetic mechanism involving competition between recombination, electron transfer across the bilayer, and reduction by donor at the opposite surface can quantitatively account for the decay of Chl⁺. Electron transport across the bilayer is postulated to occur by a two-step mechanism involving electron exchange between Chl and Chl⁺ within the lipid monolayer (k= 3.2 × 10⁶ M^-1 s^-1) and across the bilayer. The rate constant for the latter exchange process approaches 10⁴ s^-1 as the concentration of Chl in the bilayer increases. Under appropriate conditions, approximately 20% of all photons absorbed by the vesicle system result in electron transfer across the mcmbrane from GSH to MGNQ.     

CS+(B2Σ+ → A 2Πi) fluorescence from penning excitation of CS

The energy transfer reation of He(2³S) + CS was studied spectroscopically in a flowing afterglow apparatus. The CS⁺(B²Σ⁺ → A ²Π_i) transition is identified via three members of the Δν = 0 sequence (406–415 nm). The spin-orbit splitting of the (0, 0) band of CS⁺(A ²Π_i) is 301 ± 5 cm^?1. A weak emitting system (280–340 nm) is tentatively identified as CS⁺(B²Σ⁺→ X²Σ⁺).     

ANTENNA EFFECT IN LUMINESCENT LANTHANIDE CRYPTATES: A PHOTOPHYSICAL STUDY

Excited state emission and absorption decay measurements have been made on the cage-type cryptate complexes [M bpy.bpy.bpy]ⁿ⁺, where Mⁿ⁺= Na⁺, La³⁺, Eu³⁺, Gd³⁺ or Tb³⁺ and [bpy.bpy.bpy] is a tris-bipyridine macrobicyclic cryptand. Excitation has been performed in the high intensity ¹π-π* cryptand band with maximum at about 300 nm. Experiments have been carried out in H₂O or D₂O solutions and at 300 and 77 K to evaluate the rate constants of radiative and nonradiative decay processes. For Mⁿ⁺= Na⁺, La³⁺ and Gd³⁺ the lowest excited state of the cryptate is a ³ππ* level of the cryptand which decays in the microsecond time scale at room temperature in H₂O solution and in the second-millisecond time scale at 77 K in MeOH-EtOH. For Mⁿ⁺= Eu³⁺, the lowest excited state is the luminescent ⁵D₀ Eu³⁺ level which in H₂O solution is populated with 10% efficiency and decays to the ground state with rate constants 2.9 × 10³ s^_1 at room temperature and 1.2 × 10³ s^?′ at 77 K. The relatively low efficiency of ⁵D₀ population upon ¹ππ* excitation is attributed to the presence of a ligand-to-metal charge transfer level through which ¹ππ* decays directly to the ground state. For Mⁿ⁺= Tb³⁺ the lowest excited state is the luminescent ⁵D₄ Tb³⁺ level. The process of ⁵D₄ population upon ¹ππ* excitation is ?100% efficient, but at room temperature it is followed by a high-efficiency, activated back energy transfer from the ⁵D₄ Tb³⁺ level to the ³ππ* ligand level because of the relatively small energy gap between the two levels (1200 cm^_1) and the intrinsically long lifetime of ⁵D₄. At 77 K back energy transfer cannot take place and the ⁵D₄ Tb^3* level deactivates to the ground state with rate constant 5.9 × 10² s^-′ (H₂O solution). The relevance of these results toward the optimization of Eu³⁺ and Tb³⁺ cryptates as luminescent probes is discussed.     

Analysis of tryptophan at nmoll(-1) level based on the fluorescence enhancement of terbium-gadolinium-tryptophan-sodium dodecyl benzene sulfonate system

It is found that Tb³⁺ can react with tryptophan (Trp) and sodium dodecyl benzene sulfonate (SDBS), and emits the intrinsic fluoresence of Tb³⁺. The fluorescence intensity can be enhanced by La³⁺, Gd³⁺, Lu³⁺, Sc³⁺ and Y³⁺, among which Gd³⁺ has the greatest enhancement. This is a new co-luminescence system. The studies indicate that in the Tb-Gd-Trp-SDBS system, there is both Tb-Trp-SDBS and Gd-Trp-SDBS complexes, and they aggregate together and form a large congeries. The fluorescence enhancement of the Tb-Gd-Trp-SDBS system is considered to originate from intramolecular and intermolecular energy transfers, and the energy-insulating sheath effect of Gd-Trp-SDBS complex.Under the optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of Trp in the range from 4×10⁻⁸ to 4×10⁻⁵ mol l⁻¹. The detection limit is 10⁻⁹ mol l⁻¹. The proposed method is one of the most sensitive fluoremetries of Trp.     

Influence of Anions on Electrochemical Properties of Polypyrrole-Modified Electrodes

The influence of anions ClO₄ ^–, NO₃ ^–, Cl^–, SO₄ ^2–, and DDS^– (dodecyl sulfate) on the cyclic voltammetric response of polypyrrole-modified electrodes is studied. The change in the film composition is examined by electron probe microanalysis. It is established that essential changes in the shape of voltammograms take place during cycling if the anions are not sufficiently freely mobile in the polymer film and insertion of cations from the solution is necessary to guarantee electroneutrality of the system. Some differences between the mobility of Cl^– ions and ClO₄ ^– or NO₃ ^– ions are in good agreement with the results of semi-empirical quantum chemical calculations showing that the interaction of Cl^– and Br^– ions with pyrrole oligomers is stronger than that of NO₃ ^– or ClO₄ ^– ions. Nevertheless, it is established that the peak current determined from voltammograms increases linearly with the increase of the scan rate with very high correlation coefficient. It means that it is possible to describe the behavior of ClO₄ ^–, NO₃ ^– and Cl^– ions in the framework of the model of free ions. The redox behavior of the PPy films doped with anions of low mobility such as SO₄ ^2– and DDS^– depends essentially on the nature of cations in the test solution. It is found that the mobility of cations increases in the row Li⁺ < Na⁺ < K⁺ < Cs⁺. The mobility of DDS^– ions in the PPy in ethanolic solution is significantly higher and their electrochemical properties are quite similar to PPy|Cl or NO₃ ^– film in aqueous solution.     

Determination of arsenate in natural pH seawater using a manganese-coated gold microwire electrode

Direct electrochemical determination of arsenate (As^V) in neutral pH waters is considered impossible due to electro-inactivity of As^V. As^III on the other hand is readily plated as As⁰ on a gold electrode and quantified by anodic stripping voltammetry (ASV). We found that the reduction of As^V to As^III was mediated by elemental Mn on the electrode surface in a novel redox couple in which 2 electrons are exchanged causing the Mn to be oxidised to Mn^II. Advantage is taken of this redox couple to enable for the first time the electrochemical determination of As^V in natural waters of neutral pH including seawater by ASV using a manganese-coated gold microwire electrode. Thereto Mn is added to excess (∼1 μM Mn) to the water leading to a Mn coating during the deposition of As on the electrode at a deposition potential of −1.3 V. Deposition of As⁰ from dissolved As^V caused elemental Mn to be re-oxidised to Mn^II in a 1:1 molar ratio providing evidence for the reaction mechanism. The deposited As^V is subsequently quantified using an ASV scan. As^III interferes and should be quantified separately at a more positive deposition potential of −0.9 V. Combined inorganic As is quantified after oxidation of As^III to As^V using hypochlorite. The microwire electrode was vibrated during the deposition step to improve the sensitivity. The detection limit was 0.2 nM As^V using a deposition time of 180 s.