Natural radioactivity distribution in geological matrices around Kaiga environment

Summary The activity and absorbed dose rate of the naturally occurring radionuclides, viz. ²³⁸U, ²³² Th and ⁴⁰K were determined in soil and rock samples collected around Kaiga site. The mean activity levels (Kaiga soil) of naturally occurring ²³² Th are comparable with that in worldwide soil, while concentrations of ²³⁸U and ⁴⁰K are lower than those in worldwide soil. The absorbed dose rate in outdoor air ranged 20-58 nGy ^. h^-1 with a mean of 33.3 nGy ^. h^-1, which is below the world average of 60 nGy ^. h^-1. The total effective dose rate in outdoor air for soils ranged 25.6-74.4 mSv ^. y^-1 with a mean of 43.0 mSv ^. y^-1. The estimated dose rate at Kaiga is comparable with that estimated at Kakrapar and Rawatbhata and much less than that estimated at coastal sites of India.     

Pulse Radiolysis and Ultra‐High‐Performance Liquid Chromatography/High‐Resolution Mass Spectrometry Studies on the Reactions of the Carbonate Radical with Vitamin B12 Derivatives

The reactions of the carbonate radical anion (CO₃ ^{. ?}) with vitamin B₁₂ derivatives were studied by pulse radiolysis. The carbonate radical anion directly oxidizes the metal center of cob(II)alamin quantitively to give hydroxycobalamin, with a bimolecular rate constant of 2.0×10⁹ M ^?1 s^?1. The reaction of CO₃ ^{. ?} with hydroxycobalamin proceeds in two steps. The second‐order rate constant for the first reaction is 4.3×10⁸ M ^?1 s^?1. The rate of the second reaction is independent of the hydroxycobalamin concentration and is approximately 3.0×10³ s^?1. Evidence for formation of corrinoid complexes differing from cobalamin by the abstraction of two or four hydrogen atoms from the corrin macrocycle and lactone ring formation has been obtained by ultra‐high‐performance liquid chromatography/high‐resolution mass spectrometry (UHPLC/HRMS). A mechanism is proposed in which abstraction of a hydrogen atom by CO₃ ^{. ?} from a carbon atom not involved in the π conjugation system of the corrin occurs in the first step, resulting in formation of a Co^III C‐centered radical that undergoes rapid intramolecular electron transfer to form the corresponding Co^II carbocation complex for about 50 % of these complexes. Subsequent competing pathways lead to formation of corrinoid complexes with two fewer hydrogen atoms and lactone derivatives of B₁₂. Our results demonstrate the potential of UHPLC combined with HRMS in the separation and identification of tetrapyrrole macrocycles with minor modifications from their parent molecule.     

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.     

Density Functional Studies of Coenzyme NADPH and Its Oxidized Form NADP+: Structures,UV–Vis Spectra,and the Oxidation Mechanism of NADPH

Density functional theory has been used to study the biologically important coenzyme NADPH and its oxidized form NADP⁺. It was found that free NADPH prefers a compact structure in gas phase and exists in more extended geometries in aqueous solution. Ultraviolet–visible absorption spectra in aqueous solution were calculated for NADPH with an explicit treatment of 100 surrounding water molecules in combination with the COSMO solvation model for bulk hydration effects. The obtained spectra using the B3LYP hybrid density functional agree quite well with experimental data. The changes of Gibbs free energies ΔG in reactions of NADPH with O₂ observed experimentally in cardiovascular and in chemical systems, that is, NADPH + 2 ³O₂ → NADP⁺ + 2 O₂⁻ + H⁺ and NADPH + ¹O₂ + H⁺ → NADP⁺ + H₂O₂, respectively, were calculated. The NADPH oxidation reaction in the cardiovascular system cannot proceed without activation since the obtained ΔG is positive. The reaction of NADPH in the chemical system with singlet oxygen was found to proceed in two ways, each consisting of two steps, that is, NADPH firstly reacts with ¹O₂ barrierlessly to form NADP⁺ and HO₂⁻, from which H₂O₂ is formed in a spontaneous reaction with H⁺, or ¹O₂ and H⁺ initially form ¹HO₂⁺, which further reacts with NADPH to yield NADP⁺ and H₂O₂. © 2019 The Authors. Journal of Computational Chemistry published by Wiley Periodicals, Inc.     

Theoretical investigations of the low-lying electronic states of the HeC2+ dication

Extended MC SCF computations of the CAS SCF type have been performed on four energetically low-lying electronic states of HeC²⁺ dications. The X ¹Σ⁺ ground state is predicted to be thermodynamically stable by 0.72 eV, while the a ³Π and A ¹Π excited states represent metastable species with barrier heights of 2.19 and 0.20 eV, respectively. The b ³Σ⁺ state exhibits merely a very shallow potential dip with a well depth of only 0.06 eV. The HeC²⁺ dication is therefore predicted to be experimentally observable in the gas phase. Bonding in these unusual dications is discussed and compared to the isoelectronic CH⁺ cation.     

LCGTO MP LSD calculations for the diatomics PdX (X = C,Si, Ge,Sn)

Results are presented of a theoretical study of RhC, PdC, PdSi, PdGe and PdSn metal-alloy diatomics performed with the LCGTO MP LSD method. For the RhC molecule the computed electronic structure and spectroscpic constants are in good agreement with experimental data. The ground state of RhC is found to be ²Σ⁺ withe the lowest-lying excited state, ²II, at 10654 cm⁻¹ above the ground state, in good agreement with experiment and with ab initio CI calculations. For PdC and the other Pd-group IV A dimers the ground state is predicted to be ¹Σ and the two lowest-lying excited state are ³II (at 2718 cm⁻¹ for PdC) and ³gS (at 12164 cm⁻¹ for PdC). Our results are in disagreement with ab initio CI studies for PdC, which found a ³Σ ground state with a ³II lowest-lying excited state, and for PdGe, which found a ³II ground state followed by ³Σ⁻ and ¹Σ⁺.     

Isotope analysis of strontium by multicollector inductively-coupled plasma mass spectrometry: High-precision combined measurement of 88Sr/86Sr and 87Sr/86Sr isotope ratios

The paper describes a new high-precision method for the simultaneous precise determination of ⁸⁸Sr/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr ratios in a single portion of a geological sample by multicollector inductively coupled mass spectrometry (MC-ICP-MS). The isotope analysis is carried out with mass bias effect correction by a combination of internal normalization to the standard Zr-isotope ratio and bracketing standard method (external normalization). Our results for geochemical IAPSO and BCR-1 standard samples are in a good agreement with the published data. The reproducibility of the ⁸⁸Sr/⁸⁶Sr ratio varies from ±0.015 to ±0.05?? (depending on the sample features) and, together with the analysis accuracy, is superior to the previously reported methods of MC-ICP-MS analysis. Still ahead is only double spike thermal ionization mass spectrometry with its ±0.02?? reproducibility. However, the new method allows the simultaneous determination of ⁸⁸Sr/⁸⁶Sr and ⁸⁷Sr/⁸⁶Sr ratios and its productivity is higher by 5 to 6 times. On the other hand, in sample preparation, it is necessary to strive for at least 95% Sr yield from the chromatographic column; otherwise the sorption-desorption process may lead to a 0.6?? ⁸⁸Sr/⁸⁶Sr ratio bias relative to the true value.     

Remarkable Reinforcement of a Supramolecular Gel Constructed by Heteroditopic [18]Crown‐6‐Based Molecular Recognition

The heteroditopic crown ether‐based ligand 1 containing the diazafluorenylimino group as a binding site for the Zn²⁺ and Cs⁺ was synthesized. The ligand 1 can be gelated in DMSO/water with and without Cs⁺ in the presence of the Zn²⁺ ion. Interestingly, the remarkable gelation reinforcement of gel 1 occurred with Cs⁺ in the presence of Zn²⁺, which is due to the formation of a sandwich complex. According to DFT calculations, one Zn²⁺ is bound to two diazafluorenylimino moieties in a tetrahedral structure. In addition, one Cs⁺ ion is bound to two crown‐rings. The Zn²⁺‐diazafluorenylimino ligand gel without Cs⁺ shows a spherical structure with 250–800 nm diameter, whereas the Zn²⁺‐diazafluorenylimino‐based ligand gel with Cs⁺ shows a fiber structure with 60–70 nm diameter and several micrometers of lengths. The rheological properties of the Zn²⁺‐ diazafluorenylimino‐based ligand gel were strongly dependent on the presence of Cs⁺.     

Extraction and DFT study on the complexation of the methylammonium cation with a hexaarylbenzene-based receptor

In methods for quantification of ⁶³Ni, in e.g. reactor coolant water, a chemical separation is required due to ⁶³Ni being a pure beta emitter with limited means of quantification. ⁶⁰Co, a common radionuclide in reactor coolant water, is not completely separated with the commonly used separation procedure, and it is not resolved from ⁶³Ni in the beta spectrum. The separation method discussed in this work consists of TRU resin (Eichrom) and Ni resin (Eichrom). After running the separation procedure, depending on the initial activity of ⁶⁰Co, there may still remain enough ⁶⁰Co to interfere in the measurement of ⁶³Ni. The ⁶⁰Co interference is corrected for via a gamma spectrometric measurement. This correction may, depending on the ⁶³Ni/⁶⁰Co ratio, introduce a large contribution to the measurement uncertainty. The aim of this work was to evaluate the possibility to reduce the measurement uncertainty of ⁶³Ni measurements by adding a second Ni separation to the method. Double Ni separations were performed on reactor coolant water having a ⁶⁰Co activity much higher than the ⁶³Ni activity (⁶³Ni/⁶⁰Co = 0.01), in order to decrease the radioactivity of ⁶⁰Co in the sample. The measurement uncertainty of the ⁶³Ni measurement result was reduced by a factor of about three.     

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   

An Argon–Oxygen Covalent Bond in the ArOH+ Molecular Ion

The OH⁺ cation is a well‐known diatomic for which the triplet (³Σ^?) ground state is 50.5 kcal mol^?1 more stable than its corresponding singlet (¹Δ) excited state. However, the singlet forms a strong donor–acceptor bond to argon with a bond energy of 66.4 kcal mol^?1 at the CCSDT(Q)/CBS level, making the singlet ArOH⁺ cation 3.9 kcal mol^?1 more stable than the lowest energy triplet complex. Both singlet and triplet isomers of this molecular ion were prepared in a cold molecular beam using different ion sources. Infrared photodissociation spectroscopy in combination with messenger atom tagging shows that the two spin isomers exhibit completely different spectral signatures. The ground state of ArOH⁺ is the predicted singlet with a covalent Ar?O bond.     

A pulse radiolysis study of the reactions of the hydrated electron and hydroxyl radical with the oxalate ion in neutral aqueous solution

The rate constants of the reactions of e _aq ^? and the OH^· radical with the oxalate ion in a neutral aqueous solution were measured by means of the pulse radiolysis technique. They were found to be (3.5 ± 0.5) × 10⁷ and (1.5 ± 0.2) × 10⁷ l mol^?1 s^?1, respectively. The radical anion ^?OOC-C^·OO^2? is characterized by an optical absorption band that has a maximum at 270 nm and a molar absorption coefficient of (2400 ± 200) l mol^?1 cm^?1. The radical anion ^·OOC-COO^?, the product of the reaction with the OH^· radical, exhibits absorption that has no maximum and increases in intensity with a decrease in the wavelength extending to the UV region (?₂₂₀ = 1800 l mol^?1 cm^?1). The mechanism of radiation-chemical transformations in aqueous oxalate solutions is discussed.     

SIFDT study of the SO+2/H2 H-atom abstraction reaction

The exothermic H-atom abstraction reaction of SO⁺₂ with H₂ has been studied in a selected ion flow drift tube (SIFDT) over a range of center-of-mass energies from thermal (300 K) to about 0.12 eV. The measured rate coefficient at 300 K is 4.2 × 10⁻¹² cm³ s⁻¹ which is very much less than the Langevin capture rate. The increase in rate coefficient with ion kinetic energy gives a linear Arrhenius-type plot with a slope that indicates a barrier of ∼5 kJ mol⁻¹ exists on the potential surface. The H₂SO⁺₂ potential surface is also explored in an ab initio investigation using the G2 procedure. An (SO⁺₂.H₂)¹ transition state between reactants and products is identified, corresponding to the barrier found from experiments.     

Electronic states and nature of the chemical bond in the molecule CrC by all-electron ab initio calculations

All-electron ab initio Hartree–Fock (HF ), valence configuration interaction (CI ), and multiconfiguration self-consistent-field (CASSCF ) calculations have been applied to investigate the electronic states of the CrC molecule. The molecule is predicted as having four low-lying electronic states, ³∑^?, ⁵∑^?, ⁷∑^?, and ⁹∑^?, separated by an energy gap of 0.55 eV from the next higher-lying state, ¹∑^?, which is followed by the states ⁵Π and ⁷Π. The four lowest-lying electronic states are due to the coupling of the angular momenta of the ⁶S_g Cr⁺ ion with those of the ⁴S_u C^? anion. The chemical bond in the ³∑^? ground state can be viewed as a quadruple bond composed of two σ and two π bonds. One σ bond is due to the formation of a molecular orbital that is doubly occupied. The remaining bonds, i.e., one σ and two π bonds, arise from valence-bond couplings. The π bonds originate from the valence-bond couplings of the electrons in the C 2pπ orbitals with those in the Cr 3dπ orbitals. The σ bond originates from the valence-bond coupling of the C 2pσ electron with an electron in the Cr 4s, 4p hybrid that is polarized away from the C atom.     

An electrochemical study of energy-dependent potassium accumulation in E. coli Part 14. Comparison of K+ uptake characteristics in anaerobically grown cells performing glycolysis or nitrate/nitrite respiration: role of the respiratory chain

The characteristics of H⁺−K⁺ exchange in anaerobically grown wild-type Escherichia coli K12(λ) performing nitrate/nitrite respiration are studied and compared with H⁺−K⁺ exchange in cells performing glycolysis. Unlike glycolysing cells, in which H⁺−K⁺ exchange takes place in two steps with different characteristics and inhibitor effects, H⁺−K⁺ exchange in E. coli K12(λ) with nitrate/nitrite respiration requires only one step. K⁺ uptake with a K_m of 4.5 mM is not sensitive to N,N′-dicyclohexylcarbodimide (DCCD), but is inhibited by arsenate or protonophore. Such a K⁺ uptake is observed in the trkG mutant and is absent in the mutant with the trkA deletion. K⁺ accumulation is greater than 270 mM and the K⁺ gradient between the cytoplasm and the medium is comparable with the measured Δφ. The ratio of H⁺ to K⁺ flux through the membranes in the absence or presence of DCCD varies with the change in K⁺ external activity. A DCCD-sensitive ATPase activity in the isolated membranes of the trkG mutant is not stimulated by K⁺; such activity was lost in the trkG mutant with the deletion of the unc-operon. Moreover, H₂ production by respiring cells is not observed. In addition, K⁺ uptake is osomosensitive and occurs under an upshock (i.e. an increase in the osmolarity of the medium). This osmosensitivity is lost in spheroplasts deprived of periplasmic space. The K⁺-uptaking TrkA system in E. coli worked as an ATP-driven pump by association with F₁F₀ in the united mechanism in glycolysing bacteria, and is assumed to operate as an uniport using ΔμH in cells with nitrate/nitrite respiration. This system has no ATPase activity and cannot carry out intramolecular dithiol-disulfide interconversion leading to H₂ production. The interaction of the TrkA system with the F₁F₀ within the membrane is determined by a respiratory chain. This system is osmosensitive in anaerobically grown cells; osmoregulation can occur in a periplasmic space.     

Infrared Spectrum of the Si3H8+ Cation: Evidence for a Bridged Isomer with an Asymmetric Three‐Center Two‐Electron Si?H?Si Bond

The IR spectrum of Si₃H₈⁺ ions produced in a supersonic plasma molecular beam expansion of SiH₄, He, and Ar is inferred from photodissociation of cold Si₃H₈⁺–Ar complexes. Vibrational analysis of the spectrum is consistent with a Si₃H₈⁺ structure ( 2⁺ ) obtained by a barrierless addition reaction of SiH₄ to the disilene ion (H₂Si?SiH₂⁺) in the silane plasma. In this structure, one of the electronegative H atoms of SiH₄ donates electron density into the partially filled electrophilic π orbital of the disilene cation. The resulting asymmetric Si? H? Si bridge of the 2⁺ isomer with a bond energy of approximately 60 kJ mol^?1 is characteristic for a weak three‐center two‐electron bond, which is identified by its strongly IR active asymmetric Si? H? Si stretching fundamental at about 1765 cm^?1. The observed 2⁺ isomer is calculated to be only a few kJ mol^?1 less stable than the global minimum structure of Si₃H₈⁺ ( 1⁺ ), which is derived from vertical ionization of trisilane. Although more stable, 1⁺ is not detected in the measured IR spectrum of Si₃H₈⁺–Ar, and its lower abundance in the supersonic plasma is rationalized by the production mechanism of Si₃H₈⁺ in the silane plasma, in which a high barrier between 2⁺ and 1⁺ prevents the efficient formation of 1⁺ . The potential energy surface of Si₃H₈⁺ is characterized in some detail by quantum chemical calculations. The structural, vibrational, electronic and energetic properties as well as the chemical bonding mechanism are investigated for a variety of low‐energy Si₃H₈⁺ isomers and their fragments. The weak intermolecular bonds of the Ar ligands in the Si₃H₈⁺–Ar isomers arise from dispersion and induction forces and induce only a minor perturbation of the bare Si₃H₈⁺ ions. Comparison with the potential energy surface of C₃H₈⁺ reveals the differences between the silicon and carbon species.     

PrB7−: A Praseodymium-Doped Boron Cluster with a PrII Center Coordinated by a Doubly Aromatic Planar η7-B73− Ligand

The structure and bonding of a Pr-doped boron cluster (PrB₇⁻) are investigated using photoelectron spectroscopy and quantum chemistry. The adiabatic electron detachment energy of PrB₇⁻ is found to be low [1.47(8) eV]. A large energy gap is observed between the first and second detachment features, indicating a highly stable neutral PrB₇. Global minimum searches and comparison between experiment and theory show that PrB₇⁻ has a half-sandwich structure with C_6v symmetry. Chemical bonding analyses show that PrB₇⁻ can be viewed as a Pr^II[η⁷-B₇³⁻] complex with three unpaired electrons, corresponding to a Pr (4f²6s¹) open-shell configuration. Upon detachment of the 6s electron, the neutral PrB₇ cluster is a highly stable Pr^III[η⁷-B₇³⁻] complex with Pr in its favorite +3 oxidation state. The B₇³⁻ ligand is found to be highly stable and doubly aromatic with six delocalized π and six delocalized σ electrons and should exist for a series of lanthanide M^III[η⁷-B₇³⁻] complexes.     

(Ca,Me)La4Si3O13:Eu3+(Me=Sr,Ba)荧光粉的结构和发光特性

采用高温固相法制备了(Ca,Me)La4Si3O13∶Eu3+(Me=Sr,Ba)系列红色荧光体,考察了Eu3+掺杂浓度和Sr2+,Ba2+置换对荧光体结构和发光特性的影响。Eu3+最佳掺杂浓度为nEu3+∶nLa3+=1∶7,5D0-7F2与5D0-7F1跃迁发射强度比为2.55。Eu3+掺杂使晶胞参数a和c呈线性变小,对c的影响大于a,使a/c比增大。Sr2+和Ba2+分别置换基质中的Ca2+可以形成完全固溶体,晶胞参数随Sr2+或Ba2+的置换量增加呈线性增大,使a/c比减小。各发射峰强度在Sr2+置换量为0.4 mol时出现极大值,但随Ba2+置换量的增加而不断增强,全置换后荧光强度最大。荧光体的色坐标为(0.638 5,0.353 0)。     

Possible overestimation of the external standard quench parameter on Wallac 1220 Quantulus™ with high energetic beta-emitters

The 1220 Quantulus is equipped with an ¹⁵²Eu external source used to determine an external standard quench parameter SQP(E). The relationship between ⁹⁰Sr/⁹⁰Y counting efficiency and SQP(E) was found linear in a defined range of SQP(E) values. This function was fixed after many counting experiences made with ⁹⁰Sr/⁹⁰Y standards. The sasme equation is used for the measurement of ⁹⁰Sr in environmental samples. The first goal of this paper is to objectify an overestimation of the SQP(E) when high energetic beta-emitters like ⁹⁰Y are present (1 to 4% in routine conditions). The second one is to show how this artefact could induce a bias in the calculation of ⁹⁰Sr activity in environmental samples. The median of this overestimation is estimated around 6%. Another approach using ⁸⁵Sr standard is suggested to avoid this overestimation. Provided the chemical composition — and thus the quenching — is similar for the two standards, the counting efficiency measured with the ⁹⁰Sr/⁹⁰Y standard could be related to the SQP(E) value of the ⁸⁵Sr standard. Indeed this one appears to be more robust regarding to the range of activity and to the counting time of the external source.     

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.