Non-empirical and DFT calculations of <Superscript>19</Superscript>F and <Superscript>13</Superscript>C chemical shifts in the NMR spectra of substituted pentafluorobenzenes

Chemical shifts in ¹⁹F and ¹³C NMR spectra of substituted pentafluorobenzenes are calculated by Hartree-Fock and density functional theory methods. The calculated values are compared with the experimental data known from the literature. It is shown that chemical shifts in non-polar solvents can be predicted sufficiently accurately by the GIAO-DFT(PBE/L22) method. This method is used to predict the ¹⁹F and ¹³C chemical shifts of a heptafluorobenzyl cation in the SbF₅ medium. The best agreement between the calculated and experimental values is achieved when the counterion effect is taken into account.     

Prototropic processes in benzaurins. <Superscript>19</Superscript>F and <Superscript>1</Superscript>H NMR spectra of fluoro- and methylsubstituted 4-hydroxyphenyl-diphenylcarbinols,related fuchsones and benzaurins

Tautomerism of benzaurins and hydration are studied. ¹H and ¹⁹F chemical shifts have been determined for a number of substituted 4-hydroxyphenyl-diphenyl carbinols containing fluorine in a 3-, 3*- or 4*-position, and for similar compounds containing additional methyl groups in a position of 3, 3** or 4**. The same data have been obtained for the fuchsones prepared by dehydration of the above carbinols. On this basis chemical shifts of fluorine in different positions have been evaluated as a monitor of the transformation of 4-hydroxyphenyl group to the semiquinone moiety. The ¹⁹F NMR can be used to monitor the transformation of 4**-fluorobenzaurin and the related 3,3*-disubstituted and 3,3*,5,5*-tetramethylsubstituted compounds to the corresponding carbinols due to the addition of a water molecule and to study the tautomerism of the two latter benzaurins as well as that of 3,3*,4**trifluorobenzaurin. Furthermore, fluorine and methyl group chemical shifts are sensitive to syn-anti-isomerism in substituted fuchsones.     

NMR Spectra of Cyclic Nitrones. 7. The Influence of Substituents and a Hydrogen Bond on <Superscript>14</Superscript>N and <Superscript>17</Superscript>O Chemical Shifts in Derivatives of 3-Imidoazoline 3-Oxide

Derivatives of 3-imidazoline 3-oxide have been studied by ¹⁴N and ¹⁷O NMR methods. Regularities of the influence of substituents and of a hydrogen bond on chemical shifts have been made apparent. The range of changes of the chemical shifts of the nitrogen and oxygen nuclei of the nitrone group has been determined. Both in the ¹⁷O and in the ¹⁴N NMR spectra the signals of the amino derivatives are the highest field signals for the nitrone group, and the lowest field signals are the signals of the cyano derivatives in the series of derivatives investigated. Depending on the substituent (from amino to cyano group) the ¹⁷O chemical shifts varied over a range ∼155 ppm, but the interval of change of the ¹⁴N chemical shifts for the same substituents was ∼110 ppm. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1336–1341. September, 2005.     

Fission studies in the reaction of <Superscript>19</Superscript>F with <Superscript>209</Superscript>Bi at 99.2 MeV

Fission product yield studies in the reaction of 99.2 MeV ¹⁹F with ²⁰⁹Bi have been carried out for the first time using gamma-ray spectrometry. The cross sections for the production of fission products have been determined. The yield distribution of fission products was found to be symmetric and broad with FWHM around 22 mass units and peak near mass 111. The average number of neutrons emitted per fission has been found to be around 6.7. The comparison of the fission products yield distribution of ²⁰⁹Bi using projectiles like ⁴He, ¹²C, ¹⁶O, and ¹⁹F have shown that the mass of symmetric peak increases as the mass of the compound nucleus increases. The high fission yield around mass 112 has been attributed to the presence of deformed neutron shells. The total fission cross section and width of the mass distribution have been found to be low in case of ¹⁶O induced fission as compared to the ⁴He, ¹²C, and ¹⁹F induced fission of ²⁰⁹Bi.     

A <Superscript>1</Superscript>H NMR study of Nile Red solvation

In order to evaluate the capabilities of NMR spectroscopy for investigation of the solvatochromic effect in luminophore solutions, the ¹H NMR chemical shifts of Nile Red in mixtures of solvents with different polarities (benzene, toluene, methanol) has been determined. Their dependence upon the solvent mixture composition has been revealed and binding sites for luminophore and solvent component molecules have been determined. The results of the NMR study are consistent with data on the fluorescence of Nile Red solutions in toluene-ethanol mixtures.     

Determination of <Superscript>241</Superscript>Am/<Superscript>243</Superscript>Am ratios

Determination of ²⁴¹Am/²⁴³Am ratios is required for vanous purposes including assay of Am by isotope dilution techniques. Alpha-spectrometry on electrodeposited sources is a preferred technique for this determination. However, there is an inherent problem of tail contribution which necessitates the use of suitable algorithms to account for the same. Recently, in the frame of a Coordinated Research Program (CRP) of the International Atomic Energy Agency (IAEA), WinALPHA software has been developed which is a combination of an asymmetrical Gaussian for the main part of the peak and a low energy function. Therefore, it was of interest to compare the use of this algorithm with the routinely used method, in our laboratory, based on geometric progression (G. P.) decrease. Since, there are no reference materials available commercially for ²⁴¹Am/²⁴³Am ratios, synthetic mixtures covening a wide range (0.3 to 2.0) of ²⁴¹Am/²⁴³Am α-activity ratios were used and un-ignited electrodeposited sources were prepared for α-spectrometry. The α-spectra obtained using PIPS detector, were evaluated using the two algonthms The ²⁴¹Am/²⁴³Am α-activity ratios obtained were also compared with those determined by thermal ionization mass spectrometry (TIMS). An agreement of about 1% was obtained in the ²⁴¹Am/²⁴³Am ratios determined by the two methods and also by using the two algorithms for α-spectrum evaluation.     

<Superscript>103</Superscript>Rh and <Superscript>17</Superscript>O NMR study of oligomer rhodium(III) sulfates in aqueous solutions

By virtue of ¹⁰³Rh-, ¹⁷O-NMR, electrophoresis in agarose gel, and pH-metry, we report on the formation of rhodium(III) sulfate complexes in aqueous solutions. At higher concentrations of sulfuric acid (above 3 M), more than 90% of metal was found to stay in the state of symmetric polynuclear complexes containing magnetically equivalent rhodium atoms. We also labeled the ¹⁰³Rh-NMR chemical shifts for the complexes with 3, 4 and 6 metal atoms in the spectra.     

Solution <Superscript>1</Superscript>H n.m.r. of paramagnetic Co<Superscript>2+</Superscript>complexes with dioxobis(carboxymethyl)tetraazamacrocycles

Paramagnetic shifts in the ¹H n.m.r. spectra were observed for high-spin Co²⁺ complexes with 12--14-membered tetraazamacrocycles incorporating two amide groups and two pendant carboxymethyl groups. The pseudocontact term due to the dipolar interaction between the metal ion and the resonant protons was calculated on the basis of X-ray structures, and the Fermi contact term due to spin delocalization was determined. The ethylenediamine moiety of the ligand molecule is coordinated in an unsymmetric manner, even in solution, and internal motion (involving conformational change of the macrocyclic frame and exchange of coordinate bonds) is much slower than the n.m.r. observation frequency. In the 12-membered macrocyclic complex Co(L12), three of the eight CH₂ groups fix their orientation in the n.m.r. time scale; in Co(L13) only one CH₂ group fixes its orientation; in Co(L14) all CH₂ groups undergo a rapid reorientation. The facility in internal motion increases with the ring size, and shows a correlation with the chemical stabilities of these Co²⁺ complexes against oxidation; to atmospheric oxygen, Co²⁺(L12) is the most resistant and Co²⁺(L14) is the most susceptible.     

<Superscript>234</Superscript>U/<Superscript>235</Superscript>U activity ratios as a probe for the <Superscript>238</Superscript>U/<Superscript>235</Superscript>U half-life ratio

High-resolution alpha-particle spectrometry was performed on three uranium materials enriched in ²³⁵U. Besides the ²³⁵U peaks, separate peaks belonging to impurity traces of ²³⁴U could be quantified. Relying on the isotopic composition of the uranium, as determined by mass spectrometry, the ratio of the half-lives of ²³⁸U and ²³⁵U was determined via the activity ratio of ²³⁴U and ²³⁵U in the materials. As an intermediate link, the ²³⁴U/²³⁸U half-life ratio was taken from published mass spectrometric analyses of ‘secular equilibrium’ uranium material. The resulting half-life ratio T _1/2(²³⁸U)/T _1/2(²³⁵U) = 6.351±0.031 is in agreement with the commonly adopted half-life values determined by Jaffey et al.     

Determination of <Superscript>151</Superscript>Sm and <Superscript>147</Superscript>Pm using liquid scintillation tracer methods

The long-lived rare earth isotopes ¹⁵¹Sm (90 years, β _max = 76.3 keV) and ¹⁴⁷Pm (2.62 years, β _max = 224.6 keV) are low-yield fission products that generally require lengthy separation procedures to isolate and count by their beta emissions. We will describe novel liquid scintillation counting techniques using radioactive tracers to determine radiochemical yields from an environmental matrix. The recovery of ¹⁵¹Sm is determined from the alpha decay (2.25 MeV) of ¹⁴⁷Sm in the natural Sm carrier and is in excellent agreement with the gravimetric recovery. The ¹⁴⁷Pm recovery is determined by the use of ¹⁴⁵Pm (17.7 years, EC) tracer, custom-produced at LANL using an isotopically enriched target of ¹⁴⁴Sm. We have determined the ¹⁴⁵Pm recovery both from the 37.4 keV k_α1 X-ray, and the electron-capture emissions by LSC. A comparison of these recovery methods is presented.     

Preparation of <Superscript>26</Superscript>Al, <Superscript>59</Superscript>Ni, <Superscript>44</Superscript>Ti, <Superscript>53</Superscript>Mn and <Superscript>60</Superscript>Fe from a proton irradiated copper beam dump

The station for pions cancer therapy was operated at PSI from 1980 to 1992. After a cooling time of 12 years it’s made of copper beam dump was cut and samples were taken for analytical purposes. The sampling collected about 500 g of high active copper chips that can be used for separation of exotic radionuclides. The analyses by gamma spectrometry, LSC and AMS showed main nuclides present to be ⁶⁰Co, ⁵⁴Mn, ²²Na, ⁶⁵Zn, ²⁶Al, ⁵³Mn, ⁵⁹Ni, ⁶³Ni, ⁵⁵Fe and ⁶⁰Fe and ⁴⁴Ti with a daughter nuclide ⁴⁴Sc. In the frame of ERAWAST project a procedure combining selective precipitation and ion exchange for the separation of the rare radionuclides from the copper beam dump was developed. The proposed separation procedure is easy for remote controlled implementation in a hot cell. The ion exchange separation of Ni, Al, Mg, Ti and Fe was complete and high decontamination factors for copper and cobalt were achieved. Based on the developed procedure a remotely controlled system for separation of exotic radionuclides from the copper chips was set up. The full scale system was installed in a hot cell where high activity levels can be handled. In order to evaluate the reliability and functionality of the system extensive tests have been done. During the test period 13.86 g in total of the proton irradiated copper beam dump were processed for separation of ²⁶Al, ⁵⁹Ni, ⁵³Mn, ⁴⁴Ti and ⁶⁰Fe. The results showed that the system was operational and the radionuclide separation was selective with high chemical yield. The procedure manages as well the generated liquid wastes containing high level of ⁶⁰Co activity.     

Adducts of zinc and copper(II) dialkyldithiocarbamate complexes with dialkylamines: Synthesis,EPR, and <Superscript>13</Superscript>C and <Superscript>15</Superscript>N CP/MAS NMR

Crystalline adducts of zinc and copper(II) dithiocarbamate (Dtc) complexes with dialkylamines [M(NHR′₂)(S₂CNR₂)₂] (M = Zn, ⁶³Cu, ⁶⁵Cu; R = CH₃, C₂H₅, or R₂ = (CH₂)₄O; R′ = C₂H₅, C₃H₇) have been preparatively isolated. The structures and spectral properties of the adducts have been studied by EPR and ¹³C and ¹⁵N MAS NMR. Chemisorption of bases on powders of dinuclear dithiocarbamates leads to their dissociation into monomeric adducts. Computer simulation demonstrates that the experimental EPR spectra of isotope-substituted copper(II) adducts have an individual character. The geometry of the copper polyhedra is intermediate between a trigonal bipyramid (TBP) and a tetragonal pyramid (TP). The TBP and TP contributions have been quantified based on EPR data. ¹³C and ¹⁵N MAS NMR data show that the Dtc ligands incorporated into the zinc adduct molecule are structurally nonequivalent. The dependence of the isotropic ¹⁵N chemical shifts of the Dtc groups on the alkyl substituents at the nitrogen atom is interpreted based on the concept of joint manifestation of the (+)inductive effect of the alkyl substituents and the mesomeric effect of the Dtc groups.     

Evaluation of <Superscript>13</Superscript>C NMR spectra of cyclopropenyl and cyclopropyl acetylenes by theoretical calculations

A convenient methodology was developed for a very accurate calculation of ¹³C NMR chemical shifts of the title compounds. GIAO calculations with density functional methods (B3LYP, B3PW91, PBE1PBE) and 6-311+G(2d,p) basis set predict experimental chemical shifts of 3-ethynylcyclopropene (1), 1-ethynylcyclopropane (2) and 1,1-diethynylcyclopropane (3) with high accuracy of 1–2 ppm. The present article describes in detail the effect of geometry choice, density functional method, basis set and effect of solvent on the accuracy of GIAO calculations of ¹³C NMR chemical shifts. In addition, the particular dependencies of ¹³C chemical shifts on the geometry of cyclopropane ring were investigated.     

Improvements on the method for determining of <Superscript>210</Superscript>Pb and <Superscript>210</Superscript>Po in lead

An improved method is proposed to determine the content of ²¹⁰Pb in lead using ²¹⁰Po measured by alpha-ray spectrometry. This improved method, which is based on radiochemical separation by DDTC–toluene extraction, employs EDTA and citrate as masking reagents for the lead ions. To selectively extract polonium from an alkaline solution, the pH dependency was examined using a liquid scintillation counting method. And pH 9 was chosen as an extraction condition. Then ²¹⁰Po was electrodeposited on a stainless steel disk, and the chemical recovery was followed by ²⁰⁹Po tracer. The effectiveness of the new method was validated by the agreement with the analytical results from five samples as determined by gamma-ray spectrometry.     

Measurement of the <Superscript>231</Superscript>Pa/<Superscript>235</Superscript>U ratio for the age determination of uranium materials

The paper describes the age (production date) determination of uranium reference materials using the ²³¹Pa/²³⁵U ratio. Direct addition of ²³⁷Np in secular equilibrium with its ²³³Pa daughter was chosen instead of the regular milking of ²³⁷Np to avoid possible loss of Pa. Sample preparation consists of a fast, one-step procedure. The developed method using ICP-MS for the measurement of ²³¹Pa is more precise than alpha spectrometry and is applicable for freshly produced low-enriched uranium materials. The measured ages are in good agreement with the reported production dates, thus the ²³¹Pa/²³⁵U chronometer can be applied for validation of ²³⁰Th/²³⁴U in nuclear forensics and safeguards.     

Nuclear excitation in <Superscript>176</Superscript>Lu by positron annihilation on K-shell electrons

In the process of nuclear excitation in positron-electron annihilation (NEPEA) experimental results have been found to be larger than theoretical predictions. In our previous works we have analyzed the NEPEA experimental data for 1078 keV in ¹¹⁵In and for 1330 keV in ¹¹¹Cd, respectively, by applying our model of indistinguishable quantum oscillators. In the present work we extend this model to estimate the cross section of nuclear excitation in positron-electron annihilation for ¹⁷⁶Lu from the experimentally measured effective cross section of σ ^eff = (2.6±0.9)·10⁻²⁹ cm². The estimated NEPEA cross section of σ=2.7·10⁻²⁶ cm² is in very good agreement with that of the theoretical prediction σ ^th=2.2·10⁻²⁶ cm².     

Accumulation of <Superscript>137</Superscript>Cs and <Superscript>40</Superscript>K in aboveground organs of tropical woody fruit plants

Distribution of ⁴⁰K and ¹³⁷Cs in tissues of the Citrus aurantifolia was measured by gamma spectrometry. A simple theoretical model is also proposed to describe the temporal evolution of ⁴⁰K activity concentration in such tropical woody fruit species. This model exhibits close agreement with the ⁴⁰K experimental results, in the leaf growing and fruit ripening processes of lemon trees.     

Production of <Superscript>41</Superscript>Ar and <Superscript>79</Superscript>Kr gaseous radiotracers for industrial applications

Radiotracers are extensively used in many industries for trouble shooting and optimization of process parameters leading to considerable savings in time and huge economic benefits. In chemical and petrochemical industries different gases and vapours flowing in the conversion reactors play a major role in the final production. Gaseous radiotracers are ideal to study hydrodynamics of gas phases in process vessels. ⁴¹Ar and ⁷⁹Kr are the preferred gaseous radiotracers for such studies. Owing to the increase in demand from Indian industries for gas phase radiotracers, efforts have been made to produce ⁴¹Ar and ⁷⁹Kr indigenously by irradiation of ⁴⁰Ar and enriched ⁷⁸Kr gaseous targets in research reactors. Prequalification of the containers used, safety aspects concerning accidental rupture and mandatory tests necessary for irradiation of gaseous targets in the reactors have been studied. The paper describes some of the important safety aspects involved and the results of trial irradiations on the production of ⁴¹Ar and ⁷⁹Kr radiotracers. Standardization of suitable assay protocols for their regular production and supply for applications in industries is also described.     

Physicochemical foundations of synthesis of new ferromagnets from chalcopyrites A<Superscript>II</Superscript>B<Superscript>IV</Superscript>C<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>

The results of studying phase equilibria of ternary A^IIB^IVC^V systems have been reported. Physicochemical foundations have been developed for the synthesis of new ferromagnets with Curie temperatures above room temperature structurally compatible with basic semiconducting materials. Methods of synthesis and physicochemical properties of manganese-doped A^IIB^IVC₂^V ferromagnets have been described. The results of theoretical simulation of magnetic properties have been considered and basic approaches to the explanation of the emergence of ferromagnetism in A^IIB^IVC₂^V doped with 3d metals have been surveyed. The most promising ways to produce and study dilute magnetic semiconductors as spintronics materials have been presented.     

Validation of <Superscript>90</Superscript>Sr separation method using molecular recognition product AnaLig<Superscript>®</Superscript> Sr01 gel and extraction chromatography Sr<Superscript>®</Superscript> resin

Two separation techniques for strontium determination using AnaLig^® Sr01 molecular recognition technology and extraction chromatography Sr^®  resin were tested. The methods performance was investigated by analysis of NPL (High Alpha–Beta 2003) intercomparison sample. The results obtained for both procedures were compared in terms of activities and recoveries. Data analysis proved a good agreement with the reference values. The AnaLig^® Sr01 separation method for ⁹⁰Sr determination was successfully validated with the same performance as the Sr^® resin method.