Diastereoselective proton transfer: a route to enantiomerically pure half-sandwich rhenium complexes

The diastereomeric methyl rhenium complex [CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}(CH3)] was prepared in two steps from chiral racemic [CpRe(NO)(CO)(NCMe)]BF4 and the chiral racemic phosphine P(Me)(Ph)(2-C6H4NMe2). The unlike diastereomer reacts preferentially with MeSO3H to give the ring-closed ionic complex unlike-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 along with unreacted like-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}(CH3)], which is easily separated and converted to like-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3. Starting from (R)-P(Me)(Ph)(2-C6H4NMe2), the diastereomerically and enantiomerically pure complexes (RRe,SP)-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 and (SRe,SP)-[CpRe(NO){P(Me)(Ph)(2-C6H4NMe2)}]MeSO3 were obtained. Thus, this reaction sequence demonstrates a highly diastereoselective proton transfer from a functionalized chiral phosphine to a transition metal. Furthermore, it provides efficient access to enantiomerically pure half-sandwich rhenium complexes.     

Measurement of activation cross sections of the proton induced nuclear reactions on palladium

Excitation functions of proton induced reactions on Pd are important for medical radioisotope production, for activation analysis, for development of low activation materials and other purposes. No experimental data exist in the literature for low and medium energy range protons. A detailed study of the excitation functions was performed up to 80 MeV proton energy by using the stacked foil irradiation technique and gamma-ray spectrometry. The irradiations were carried out at the external beam lines of the AVF cyclotron at the Tohoku University. Japan (80 and 70 MeV) and the CGR 560 cyclotron at the Vrije Universiteit Brussels (38, 29 and 17 MeV). The beam intensity, the incident energy and the energy degradation were controlled by a method based on flux constancy via normalization to the parallel measured excitation functions of ^natAl(p,x)^22,24Na and ^natCu(p,x)^56,58Co, ^62,65Zn monitor reactions. Excitation functions for direct and cumulative cross sections have been measured for the production of ^{105mg,106m,110m}Ag, ¹⁰¹Pd, ^101mRh and ⁹⁷Ru radionuclei. Calculations for the excitation functions using the Alice-IPPE code were performed with a view to estimate the weight of the different contributing reactions and to check the trend and the magnitude of the obtained experimental data.     

Laboratory standard for radionuclides in nuclear waste

A laboratory standard for the determination of long-lived radionuclides in nuclear waste has been prepared using concrete as matrix. It will be used to check sample preparation procedures, chemical separations and methods for the determination of nuclides, e.g., nuclear counting techniques or mass spectrometry. The material chosen was a fine-grained ready-to-use cement mixture, to which the following radionuclides were added:⁶⁰Co and¹³⁷Cs as -ray-emitting nuclides,⁹⁹Tc,⁹⁰Sr and⁵⁵Fe as radionuclides emitting pure -radiation or low-energy electrons, and²³³U,²³⁷Np,²³⁸Pu and²⁴¹Am as -emitters. Care was taken to attain a homogeneous distribution of the nuclides in the standard material. Pieces of about 1 g were formed as suitable and representative samples. Repeated analyses were carried out with the standard to check its homogeneity. The analytical procedures are described in brief. The pieces of the standard material have the same content of nuclides within ±5% at a 95% level of confidence.     

Determination of relative and absolute abundance of stable nitrogen isotopes by proton induced nuclear reactions

Thick-target yield of γ-rays emitted in the reactions¹⁴N(p,p′γ₁)¹⁴N and¹⁵N(p,αγ₁)¹²C were measured as a function of bombarding energy in order to select the conditions favoring the employment of these reactions in nitrogen isotopic analysis. The applicability of these reactions in the determination of relative as well as absolute nitrogen isotopic abundances was demonstrated at 4.3 MeV bombarding energy. Supported in part by the International Atomic Energy Agency, Vienna, Austria.     

Excitation functions of proton induced nuclear reactions on natural tellurium up to 18 MeV for validation of isotopic cross sections

Summary Excitation functions of proton induced nuclear reactions on natural Te were investigated up to 18 MeV. Cross sections for production of ^{121,123,124,126,128,130g}I and ^121gTe were measured. The new experimental data were compared with the results of ALICE-IPPE model calculations and with data found in the literature and measured on natural or enriched Te targets. The new data can be effectively used for validation of recommended cross sections of medically relevant ¹²³I and ¹²⁴I.     

Synthesis and reactions of isocyanate and carbamoyl complexes of rhenium

Re(CO)₂(NO)(PPh₃)₂ reacts with aroyl azides RCON₃ (R = C₆H₅, p-CH₃C₆H₄) in benzene to form isocyanate complexes of formula Re(CO)(NO)-(PPh₃)₂(RCONCO) (I). When the reaction is carried out in protic solvents such as ethanol, carbamoyl derivatives of formula Re(NCO)(NO)(PPh₃)₂-(CONHCOR) (II) are obtained, which give Re(NCO)(NO)(PPh₃)₂(CO)(NHCOR) when dissolved in chloroform, a terminal carbonyl ligand being formed from the carbamoyl group.I can be transformed into II by reaction with gaseous HCl, via [Re(CO)-(NO)(PPh₃)₂ {C(OH)=NCOR}]⁺Cl^- followed by anion exchange with NaN₃. II reacts with mineral acids HX (X = Cl, BF₄) to give amide derivatives of formula [Re(NCO)(NO)(PPh₃)₂(CO)(NH₂COR)]⁺ X^- which when X = Cl can be easily transformed into Re(NCO)(NO)(PPh₃)₂(CO)Cl, the amide ligand being removed. Both the protonation reactions of I and II are reversible. IR and ¹H NMR data of the new compounds and the mechanisms of formation of I and II are reported and discussed.     

Production of radionuclides for nuclear therapy and environmental studies

This work is devoted to the production of the radionuclides used in nuclear medicine and as radiotracers for environmental research. Production methods for high LET radionuclides (⁶⁷Ga, ⁷⁷Br, ¹¹¹In, ²¹¹At) that are promising for radioimmunotherapy are proposed. Production techniques for short-lived analogues of highly radiotoxic long-lived fission products (Tc, Se, Sr) are developed. The techniques are based on extraction and chromatographic separation from a cyclotron target irradiated by α-particles and deuteron beams.     

Phosphinic complexes of rhenium and tungsten in reactions with stereoindicators

Stereoindicators (cis-4,4′-dimethoxystilbene (DMS) or cis-α,β-dinitrostilbene (DNS)) were used to investigate the donor/acceptor properties of the complexes trans-[ReCl(N₂)(dppe)₂] or trans-[W(CO)₄(dppe)]. The former induced cis/trans conversion of DMS, and the latter cis/trans conversion of DNS, both resulting from charge transfer (in the first case from DMS to the rhenium complex and, in the second case, from the tungsten cofnplex to DNS). The rhenium complex acts as an acceptor, and the tungsten complex as a donor in the framework of the stereoindicator approach.     

The measurement of neutron-induced radionuclides from Chinese nuclear weapons tests

The concentrations of neutron-induced radionuclides have been measured in ground level air during the period between 1976 and 1981 at Nagoya (35° N, 137° E), Japan. Six Chinese atmospheric nuclear weapons tests were conducted by the government of China at Lop Nor (40° N, 90° E) during the period 1976–1981. The Chinese nuclear tests of November 17, 1976 (the 21st test) and October 16, 1980 (the 26th test), high-yield devices, produced⁵⁴Mn,⁵⁵Fe and⁸⁸Y whose production reactions are⁵⁴Fe(n, p),⁵⁶Fe(n, 2n) and⁸⁹Y(n, 2n), respectively. The tests of September 26, 1976 (the 19th test), September 17, 1977 (the 22nd test) and March 15, 1978 (the 23rd test), low-yield devices, produced⁵⁴Mn,⁵⁷Co and⁵⁸Co whose production reactions are⁵⁴Fe(n, p),⁵⁸Ni(n, pn) and⁵⁸Ni(n, p) respectively. No neutron activation product from the 24th test (December 14, 1978) was observed.     

Preparation and protonation reactions of aryl complexes of manganese and rhenium

Aryl M(κ¹-Ar)(CO)_nP_5−n [M = Mn, Re; Ar = C₆H₅, 4-CH₃C₆H₄; n = 2, 3; P = P(OEt)₃, PPh(OEt)₂, PPh₂OEt] and Re(κ¹-C₆H₅)(CO)₃[Ph₂PO(CH₂)₃OPPh₂] complexes were prepared by allowing hydrides MH(CO)_nP_5−n to react first with triflic acid and then with the appropriate aryl lithium (LiAr) compounds. The complexes were characterized spectroscopically (IR and ¹H, ³¹P, ¹³C NMR) and by the X-ray crystal structure determination of Re(κ¹-C₆H₅)(CO)₃[Ph₂PO(CH₂)₃OPPh₂] derivative. Protonation reaction of the aryl complexes with HBF₄ · Et₂O lead to free hydrocarbons Ar-H and the unsaturated [M(CO)_nP_5−n]⁺ cations, separated as solids in the case of [Re(CO)₃P₂]BF₄ derivatives.     

A time-dependent emission of some radionuclides from overheated nuclear fuel

The physico-chemical characteristics of partieles emitted by an overheated nuclear fuel may be significantly modified when they are put in contact with an oxidizing atmosphere at temperatures of the order of 700–900°C. This so-called “maturation” stage induces reactions between radioelements and the UO_x matrix of the acrosol particles. These reactions, in turn, deeply influence the solubility of radioelements in the environment. This paper presents experiments aimed at describing the behavior of characteristic radioactive elements present in nuclear fuel (Cs, Sr, Tb), which are emitted as a consequence of an accidental thermal excursion. As the sequence of radionuclide emission from the nuclear fuel depends on the volatility of their chemical forms, it has to be expected that the maturation stage itself is a time-dependent process in the sequence of emission events.     

Monitoring of environmental radiation and radionuclides around nuclear fuel cycle facilities from 1989 to 1995

Aomori Prefectural Govemment and Japan Nuclear Fuel Limited started environmental radiation monitoring around Nuclear Fuel Cycle Facilities in April 1989. External radiation is measured by NaI(TI) scintillator and Themoluminescence dosimeter. The level of external radiation is relatively low in the winter due to snow. We have collected terrestrial samples of drinking water, soil, agricultural products and marine samples of seawater, sea sediment, seafood, etc. periodically. We have measured many radionuclides and fluoride in these samples. In soil sample,^239+240Pu ratio to¹³⁷Cs was almost constant at all sampling points. A correlation was observed between salinity and concentration of tritium, uranium and fluoride in lake water of Lake Obuchinuma. The correlation between¹³⁷Cs and^239+240Pu in lake sediment was observed in each lake.     

Radiochemical analysis of radionuclides difficult to measure for waste characterization in decommissioning of nuclear facilities

Some radiochemical analytical methods for the determination of important beta-radionuclides for decommissioning are presented. An analytical method is briefly described, which is used for the determination of ³H and ¹⁴C in steel and aluminum by combustion using commercial oxidizer. A leaching method was developed for the determination of ³H in the contaminated silica gel. A simple distillation method is presented for the determination of ¹⁴C in heavy water and wastewater sample. A method developed for the simultaneous determination of ³H, ¹⁴C, ³⁶Cl, ⁵⁵Fe, ⁶³Ni, ⁴¹Ca and ¹²⁹I in concrete, graphite, aluminium, lead, and steel is presented. The developed methods have been successfully used to analyse various materials for characterization of the waste during the decommissioning of Danish nuclear reactors.     

Long-range proton transfer in aqueous Acid-base reactions

We study the mechanism of proton transfer (PT) in the aqueous acid-base reaction between the photoacid 8-hydroxy-1,3,6-pyrenetrisulfonic acid (HPTS) and acetate by probing the vibrational resonances of HPTS, acetate, and the hydrated proton with femtosecond mid-infrared laser pulses. We find that PT takes place in a distribution of hydrogen-bound reaction complexes that differ in the number of water molecules separating the acid and the base. The number of intervening water molecules ranges from 0 to 5, which, together with a strongly distance-dependent PT rate, explains the observed highly nonexponential reaction kinetics. The kinetic isotope effect for the reaction is determined to be 1.5, indicating that tunneling does not play a significant role in the transfer of the proton. Rather, the transfer mechanism is best described in terms of the adiabatic PT picture as it has been formulated by Hynes and co-workers [Staib, A.; Borgis, D.; Hynes, J. T. J. Chem. Phys. 1995, 102, 2487. Ando, K.; Hynes, J. T. J. Phys. Chem. B 1997, 101, 10464.], where solvent fluctuations play an essential role in forming the correct hydrogen-bond configuration and solvent polarization to facilitate PT.     

Excited-state proton transfer reactions of 10-hydroxycamptothecin

Time-resolved and steady-state emission characterization of 10-hydroxycamptothecin reveals a rich but less complex proton-transfer behavior than its parent hydroxyquinoline. The electronic effect of the additional electron-withdrawing ring makes the excited-state both less basic and more acidic than the parent and adds to the class of high-acidity excited-state proton donors in photochemistry and photobiology.     

Bifunctional rhenium complexes for the catalytic transfer-hydrogenation reactions of ketones and imines

The silyloxycyclopentadienyl hydride complexes [Re(H)(NO)(PR(3))(C(5)H(4)OSiMe(2)tBu)] (R=iPr (3 a), Cy (3 b)) were obtained by the reaction of [Re(H)(Br)(NO)(PR(3))(2)] (R=iPr, Cy) with Li[C(5)H(4)OSiMe(2)tBu]. The ligand-metal bifunctional rhenium catalysts [Re(H)(NO)(PR(3))(C(5)H(4)OH)] (R=iPr (5 a), Cy (5 b)) were prepared from compounds 3 a and 3 b by silyl deprotection with TBAF and subsequent acidification of the intermediate salts [Re(H)(NO)(PR(3))(C(5)H(4)O)][NBu(4)] (R=iPr (4 a), Cy (4 b)) with NH(4)Br. In nonpolar solvents, compounds 5 a and 5 b formed an equilibrium with the isomerized trans-dihydride cyclopentadienone species [Re(H)(2)(NO)(PR(3))(C(5)H(4)O)] (6 a,b). Deuterium-labeling studies of compounds 5 a and 5 b with D(2) and D(2)O showed H/D exchange at the H(Re) and H(O) positions. Compounds 5 a and 5 b were active catalysts in the transfer hydrogenation reactions of ketones and imines with 2-propanol as both the solvent and H(2) source. The mechanism of the transfer hydrogenation and isomerization reactions was supported by DFT calculations, which suggested a secondary-coordination-sphere mechanism for the transfer hydrogenation of ketones.     

Tables of gamma rays emitted by radionuclides produced through photonuclear reactions

The tables have been prepared as an auxiliary for the interpretation of results in photoactivation analysis. They include data concerning the disintegration of radionuclides produced by (γ, n) reactions on all stable isotopes with a relative abundance greater than 1% and by (γ, p) reactions on elements withZ≤39. The γ-rays are listed in ascending order of the energies; half-lives, intensities and other useful informations are also included.     

Experimental determination of k 0 nuclear data for the cesium radionuclides

The current (official) k ₀ nuclear data for the cesium radionuclides was determined circa 1987 and was partially adopted from older literature. In this work we aimed at the redetermination of experimental k ₀, Q ₀ and $\bar{E}$ _r factors with metrological care. The results are in good agreement with more recent results from other authors. Our Q ₀ and $\bar{E}$ _r values were 2–15 and 25 % different, respectively. The k ₀ factors were determined according to the cadmium subtraction technique, resulting in values 3–7 % different than the official ones. Our precision and accuracy is discussed.     

Bimodal proton transfer in acid-base reactions in water

We investigate one of the fundamental reactions in solutions, the neutralization of an acid by a base. We use a photoacid, 8-hydroxy-1,3,6-trisulfonate-pyrene (HPTS; pyranine), which upon photoexcitation reacts with acetate under transfer of a deuteron (solvent: deuterated water). We analyze in detail the resulting bimodal reaction dynamics between the photoacid and the base, the first report on which was recently published. We have ascribed the bimodal proton-transfer dynamics to contributions from preformed hydrogen bonding complexes and from initially uncomplexed acid and base. We report on the observation of an additional (6 ps)(-1) contribution to the reaction rate constant. As before, we analyze the slower part of the reaction within the framework of the diffusion model and the fastest part by a static, sub-150 fs reaction rate. Adding the second static term considerably improves the overall modeling of the experimental results. It also allows to connect experimentally the diffusion controlled bimolecular reaction models as defined by Eigen-Weller and by Collins-Kimball. Our findings are in agreement with a three-stage mechanism for liquid phase intermolecular proton transfer: mutual diffusion of acid and base to form a "loose" encounter complex, followed by reorganization of the solvent shells and by "tightening" of the acid-base encounter complex. These rearrangements last a few picoseconds and enable a prompt proton transfer along the reaction coordinate, which occurs faster than our time resolution of 150 fs. Alternative models for the explanation of the slower "on-contact" reaction time of the loose encounter complex in terms of proton transmission through a von Grotthuss mechanism are also discussed.