Reaction Of Bis Research Articles

(Arylimido)niobium(V) Complexes Containing 2-Pyridylmethylanilido Ligand as Catalyst Precursors for Ethylene Dimerization That Proceeds via Cationic Nb(V) Species

(Arylimido)niobium(V) complexes containing 2-pyridylmethylanilido ligand Nb(NAr)X2(L) [L = 2-(2,6-Me2C6H3)NCH2(C5H4N); X = NMe2 (2a,b), OCH(CF3)2 (3a–c), Me (4a–c), CH2SiMe3 (5a); Ar = 2,6-Me2C6H3 (a), 2,6-iPr2C6H3 (b), 2-MeC6H4 (c)] have been prepared, and structures of 3a,b, 4b, and 5a were determined by X-ray crystallography. The dimethyl complexes (4a,b) exhibited catalytic activities for ethylene dimerization in the presence of methylaluminoxane (MAO), whereas the activity by 4c was negligible under the same conditions. Complex 4b showed the highest activity, and the activity at 50 °C was higher than those conducted at 25 and 80 °C. The major product was 1-butene, and 1-hexene was formed by subsequent reaction of ethylene with 1-butene accumulated in the reaction mixture. A first-order relationship between the activity [turnover frequency (TOF)] and ethylene pressure was observed, suggesting that the metal-alkyl species would play a role in this catalysis. The activities further increased remarkably upon addition of [Ph3C][B(C6F5)4] at 50 °C; TOF at the initial stage (5 min) of 2 100 000 h–1 (583 s–1) has been attained. Reactions of the dimethyl complexes (4a,b) with 1.0 equiv of [Ph3C][B(C6F5)4] in Et2O afforded [Nb(NAr)Me(L)]+[B(C6F5)4]−(Et2O)2 (6a,b), and the reaction of 6b with ethylene afforded 1-butene and 1-hexene even in the absence of MAO, clearly suggesting that the cationic species play a role in this catalysis. X-ray absorption near edge structure spectra of the catalyst solutions containing 4b (in toluene at 25 °C) and MAO (10 and 50 equiv) showed no significant differences in the pre-edge peak positions and intensities from that in the dimethyl complex (4b), strongly suggesting that both the oxidation states and the basic structures are maintained upon addition of MAO in these catalyst solutions.

Neutron spectrometry of the 9Be(d (1.45 MeV), n)10B reaction for accelerator-based BNCT

The 9Be(d,n)10B reaction was proposed in the past as a neutron source for Accelerator-Based Boron Neutron Capture Therapy. Based on numerical models and scarce experimental information about the neutron spectra, it was proven that low energy deuterons on a thin target may provide neutron beams of therapeutic quality. In particular, an 8–9 μm target bombarded by 1.45 MeV deuterons presents itself as a convenient option. The aim of this work is to provide experimental validation to these numerical models. For this purpose, neutron spectra at 0°, 35°, 60°, 90° and 123° from a (9 ± 1) μm 9Be target were measured at the CN accelerator of the Laboratori Nazionali di Legnaro. A micro-time projection chamber (μ-TPC) was used as a neutron spectrometer.

Mechanism of the 11B($\alpha$α,t)12C reaction at an energy of 40 MeV, role of exchange processes and collective excitations

The differential cross sections of triton from the 11B($\alpha$,t) reaction with transitions to the ground (0+) and excited states of the 12C nucleus at $ E_{x} = 4.44$ MeV (2+), 7.65 MeV (0+), 9.64 MeV (3-) and 14.08 MeV (4+) have been measured at an $\alpha$-particles energy of 40 MeV. Analysis of the measured angular distributions was carried out in the framework of the coupled reaction channels method considering the contribution of the 8Be cluster exchange mechanism. It is shown that the direct mechanism with proton transfer dominates at an energy of 40 MeV, and the heavy particle transfer is noticeable only at large angles. An exception is the transition to the 14.08 MeV (4+) state, which is possible only by the transfer of the 8Be cluster. It is established that the couplings between the excited states of 12C, arising from the nonsphericity of the nucleus, have little effect on the $ (\alpha, t)$ reaction cross sections in the forward hemisphere, but strongly affect the cross sections at large angles.

Boron delivery for boron neutron capture therapy targeting a cancer-upregulated oligopeptide transporter

Boron neutron capture therapy (BNCT) is a radiotherapy utilizing the neutron capture and nuclear fission reaction of 10B taken up into tumor cells. The most commonly used boron agent in BNCT, p-borono-l-phenylalanine (BPA), is accumulated in tumors by amino acid transporters upregulated in tumor cells. Here, by using dipeptides of BPA and tyrosine (BPA-Tyr and Tyr-BPA), we propose a novel strategy of selective boron delivery into tumor cells via oligopeptide transporter PEPT1 upregulated in various cancers. Kinetic analyses indicated that BPA-Tyr and Tyr-BPA are transported by oligopeptide transporters, PEPT1 and PEPT2. The intrinsic oligopeptide transport activity in tumor cells clearly correlated with PEPT1 protein expression level but not with PEPT2, suggesting that PEPT1 is the predominant oligopeptide transporter at least in tumor cell lines. Furthermore, using BPA-Tyr and Tyr-BPA, boron was successfully delivered into PEPT1-expressing pancreatic cancer AsPC-1 cells via a PEPT1-mediated mechanism. Intravenous administration of BPA-Tyr into the mice bearing AsPC-1 xenograft tumors resulted in significant boron accumulation in the tumors. It is proposed that the oligopeptide transporters, especially PEPT1, are promising candidates for molecular targets of boron delivery in BNCT. The BPA-containing dipeptides would have a potential for the development of novel boron carriers targeting PEPT1.

Synthesis and Structures of Base-Stabilized Cationic Silanethionetungsten Complexes and Reaction with MeOH

The cationic silanethione-coordinated transition-metal complexes [Cp*(OC)3W{S═SiR2(DMAP)}]TFPB (R = Me (6a), Ph (6b), Cp* = η5-C5Me5, DMAP = 4-(dimethylamino)pyridine, TFPB– = B{3,5-(CF3)2C6H3}4–) were isolated by H– abstraction from silylsulfanyl complexes Cp*(OC)3WSSiR2H (5) with Ph3CTFPB, followed by the addition of DMAP. The reaction of 6b with 1 equiv of MeOH afforded methoxysilylsulfanyl complex Cp*(OC)3W(SSiPh2OMe) (7) and [H·DMAP]TFPB (8).

Dependence of neutrons generated by 7Li(p,n) reaction on Li thickness under free-air condition in accelerator-based boron neutron capture therapy system employing solid-state Li target

PurposeAn accelerator-based boron neutron capture therapy (BNCT) system with a solid-state Li target is reported to have degradation of the Li target. The degradation reduces the Li thickness, which may change spectra of the generated neutrons corresponding to the Li thickness. This study aims to examine the relationship between the Li thickness and the generated neutrons and to investigate the effects of the Li thickness on the absorbed dose in BNCT. MethodThe neutron energy spectra were calculated via Monte Carlo simulation for Li thicknesses ranging from 20 to 150 μm. Using the system, the saturated radioactivity of gold induced by reactions between 197Au and the generated neutrons was evaluated with the simulation and the measurement, and those were compared. Additionally, for each Li thickness, the saturated radioactivity was compared with the number of generated neutrons. The absorbed doses delivered by 10B(n,α)7Li, 14N(n,p)14C, 1H(n, g)2H, and (n,n′) reactions in water were also calculated for each Li thickness. ResultsThe measurement and simulation indicated a reduction in the number of neutrons due to the degradation of the Li target. However, the absorbed doses were comparable for each Li thickness when the requisite number of neutrons for BNCT was delivered. Additionally, the saturated radioactivity of 198Au could be a surrogate for the number of neutrons even if the Li thickness was varied. ConclusionsNo notable effect to the absorbed dose was observed when required neutron fluence was delivered in the BNCT even if the degradation of the Li was observed.

Simulation Study on the Feasibility of Current-mode SPECT for B-10 Concentration Estimation in Boron Neutron Capture Therapy

Boron neutron caputure therapy (BNCT) is a promising treatment for invasive tumors. The BNCT utilizes the energy deposition by alpha particle and 7Li created by the neutron capture reaction of 10B. One of the problem of BNCT is the imaging of 10B distribution during the treatment. The gamma rays with the energy of 0.478 MeV emitted by 7Li can be exploited for this purpose. The photon counting of the gamma rays, however, is very difficult due to the high gamma ray background caused by 2.22 MeV gamma rays originated by the neutron reactions with 1H. To overcome this difficulty, the authors propose a method to measure gamma rays as electric current by a “transXend” detector, which had been invented by them for energy-resolved X-ray computed tomography. In this paper, the feasibility study on 10B distribution imaging in a water phantom with a tumor region is shown by simulation studies. For establishing the relationship between electric currents induced in the transXend detector by gamma rays and 10B concentration, the attenuation of gamma rays by the phantom should be taken into account. For this purpose, a neural network was employed. The results showed good agreement with the training data used for the neural network.

From Pincer to Paddlewheel: C-H and C-S Bond Activation at Bis(2-pyridylthio)methane by Palladium(II).

The bis(2-pyridylthio)methanidopalladium(II) pincer complex (1), containing a Pd-C bond, was obtained from the reaction of bis(2-pyridylthio)methane (H2L) with palladium(II) acetate in toluene under reflux. When palladium(II) trifluoroacetate was used, H2L reacted to generate the tetrakis(pyridine-2-thiol)palladium(II) complex (2). Complex 2 was converted to a heterobimetallic palladium(II)-iron(II) paddlewheel complex (3) upon treatment with iron(II) triflate in the presence of a base in acetonitrile at room temperature.

Reactions of a tetrasilabicyclo[1.1.0]but-1(3)-ene with carbon tetrachloride and methanol.

Bicyclo[1.1.0]tetrasila-1(3)-ene 1b was synthesized and isolated as orange crystals. While 1b has a highly distorted Si[double bond, length as m-dash]Si double bond in the bicyclic silicon framework similar to that of the previously reported 1a, 1b has less bulky SiMe3 substituents than SiiPrMe2 substituents that were involved in 1a. Accordingly, the molecular structure and electronic properties of 1b resemble those of 1a, but 1b readily reacts with carbon tetrachloride and methanol. The reaction of 1b with carbon tetrachloride providing a cyclic tetrachlorotetrasilane and an acyclic hexachlorotetrasilane suggests the generation of a 1,3-dichlorobicyclo[1.1.0]tetrasilane and its isomer, a tetrasiladiene, the latter of which was supported by the formation of an acyclic tetrasilane during the reaction of 1b with methanol.

Three new coordination polymers based on bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane: syntheses, structures, multiresponsive luminescent sensitive detection for antibiotics and pesticides, and antitumor activities.

Three novel coordination polymers (CPs), namely, {[Ag2(L)2(Mo4O13)·(CH3CN)]}n (1), {[Zn(L)(1,4-bdc)2·2(1,4-H2bdc)]}n (2), {[Cd(L)(1,4-bdc)0.5]}n (3) have been synthesized under solvothermal conditions by the reaction of bis(4-(4H-1,2,4-triazol-4-yl)phenyl)methane (L) and varied metal salts. Their structures are determined by single X-ray crystal diffraction, and further characterized by elemental analysis, IR, TGA and PXRD. CP 1 with ammonium molybdate as a secondary ligand displays a 2D network with (2,3,3,3,4)-connected net topology and the point symbol of {4·82}6{4·84·10}2{8}, CP 2 and CP 3 with 1,4-H2bdc as a secondary ligand demonstrate 3D structures with different topologies. CP 2 exhibits high sensibility and low detection limit in the recognition of antibiotics (NZF, NFT and FZD) and pesticide (DCN) identification. CP 1 demonstrates good anti-tumor activity toward the tested glioma cells. The possible luminescent sensitivity and anti-tumor mechanisms are also discussed.

Structural and magnetic characterization of Ni(ii), Co(ii), and Fe(ii) binuclear complexes on a bis(pyridyl-triazolyl)alkane basis.

Reactions of bis[5-(2-pyridyl)-1,2,4-triazol-3-yl]alkanes (alkane spacers = -CH2- in L2, -C3H6- in L3, -C4H8- in L4) with M(ii)A2 salts (M = Ni, Co, Fe) resulted in the preparation of five series of mononuclear ([M(L2)(H2O)2]2+, 1a-c) or binuclear ([M2(L3)2(H2O)4]4+, 2a-c; ([M2(L4)2(H2O)4]4+, 3a-c, [M2(L3)2(μ-ox)]2+, 4a-c; [M2(L4)2(μ-ox)]2+, 5a-c) complexes. The crystal structures of ten complexes were determined by single-crystal X-ray crystallography. Magnetic properties of the compounds were characterized by SQUID magnetometry and were analyzed by fitting on a spin Hamiltonian model. It was revealed that Fe(ii) and Co(ii) compounds exhibit non-negligible anisotropy and in the case of 2a-c and 3a-c complexes weak ferromagnetic interactions between the metal centers were observed. In the case of complexes containing an {M2(μ-ox)}2+ core strong antiferromagnetic interactions were observed within the dimer. Remarkably, solid state luminescence of Co(ii) and Fe(ii) complexes (1b, 2b, 3b and 1c, 2c, 3c) was observed.

Определение энергии и флюенсов протонов, коллективно ускоренных в ускорителе с диодом Люса

Plates of boron carbide B4C were used as refractory targets for determination of energy and fluencies of protons collectively accelerated in a Luce diode accelerator by control of 7Be and 13N gamma-radioactivities induced by nuclear reactions 10B(p,α)7Be and 12C(p,γ)13N, respectively. The Luce diode exploited a cylindrical tungsten rod as a cathode and polyethylene washer as an anode, producing pulsed electron beams with durations and currents of up to 100 ns and 30 kA at voltages of 250 kV. The technique allows controlling proton energies within the range of 500-1500 keV and fluencies of up to 5•1013 protons per cm2 per pulse.

Possibility for nuclear physics study based on Pelletron accelerator at Hanoi, Vietnam

In this report, overview of the new installed Pelletron 5SDH-2 accelerator at Hanoi University of Science, Vietnam and possibilities for performing astrophysics-related nuclear reactions based on this accelerator will be described. In addition to that, some preliminary simulation results for designing and optimizing the experimental set-up in studying reactions 10B(α, p)13C with projectile energies in the Gamow-window will be shown.

Conventional and Mechanochemical Syntheses of Copper(I) Iodide Luminescent MOF with Bis(amidoquinoline) and Its Application for the Detection of Amino Acid in Aqueous Solution.

Formation of a copper(I) iodide cluster based luminescent metal-organic frameworks (LMOFs) and its utilization for the detection of cysteine (Cys) in aqueous solution are reported. The reaction of bis(amidoquinoline) ligand (L) with copper(I) iodide afforded an LMOF {[(Cu2I2)L2]·2DMSO} n (1) with a 44-sql topology linked by Cu2I2 clusters as a thermodynamic product. Time- and temperature-dependent PXRD experiments confirmed that the entire formation process for 1 is kinetically and thermodynamically controlled. Interestingly, LMOF 1 was also obtained under the mechanochemical condition. Moreover, LMOF 1 dispersed in water shows a selective quenching for Cys over other amino acids due to the strong affinity of Cys to copper(I) iodide. On the basis of the NMR data of L isolated from the decomposition of 1, the decomposition-displacement mechanism was proposed for the sensing of Cys. This result might be utilized for the practical detection of Cys because the sensing material can be prepared simply, and the sensing process is performed in aqueous media.

Hydroboration of substituted alkynes using a solid polymeric carboxylic acid catalyst

A polymer-supported benzoic acid catalyst for the hydroboration of substituted alkynes with pinacolborane is reported. The robustness of the heterogenous catalyst is demonstrated through catalyst recycle, with comparable reactivity to the homogeneous catalyst. A mechanistic investigation that includes determination of a reaction rate law, 1H and 11B NMR studies, as well elucidation of the H/D kinetic isotope effect is used to identify the pathway through which product formation occurs. The polymer support provided a recoverable handle, with the active sites in close proximity to promote a two-site reaction pathway with the identification of key boryl species through 11B NMR. The activated alkynyl species is converted through a concerted hydroboration mechanism, supported by inverse KIE values, releasing product and regenerating the active site. Kinetic studies, where initial rates are proportional to the concentration of both the pinacolborane and the catalyst, but become inhibited by the alkyne at higher concentrations, suggest that the catalytic cycle can be described by a two-site rate expression with alkyne-derived surface species present during catalysis.

Proposal for determining absolute biological effectiveness of boron neutron capture therapy-the effect of 10B(n,α)7Li dose can be predicted from the nucleocytoplasmic ratio or the cell size.

The relationship between the radiation dose delivered to a tumor and its effect is not completely predictable. Uncertainty in the estimation of the boron concentration in a tumor, variation in the radiation sensitivity of the tumor cells, and the complexity of the interactions between the four types of radiation comprising the boron neutron capture therapy (BNCT) dose contribute to this uncertainty. We reanalyzed the data of our previous papers to investigate the variation in radiosensitivity of tumor cells to the 10B(n,α)7Li dose: the dose generated by the reaction of thermal neutrons and 10B, hereafter the ‘boron-neutron dose’. The radiosensitivities of five tumors (EL4, SAS/neo, SAS/mp53, SCCVII and B16-BL6 melanoma) were examined. For the combination of p-boron-L-phenylalanine (BPA: C9H12BNO4) with neutron irradiation, D0, the cell survival curve for the boron-neutron dose was the smallest for the SAS/neo, followed by the EL4, SAS/mp53, SCCVII and B16-BL6 melanoma, in that order. For the combination of mercaptoundecahydrododecaborate (BSH: Na2B12H11SH) with neutron irradiation, D0 was the smallest for the EL4, followed by the SAS/neo, B16–BL6melanoma, SAS/mp53 and SCCVII, in that order. The relationships between these D0 values and the nucleocytoplasmic ratios (Xncs) or cell size indices (Xcs) obtained by histopathological microslide image were as follows: (D0 = 0.1341Xnc–1.586, R2 = 0.9721) for all tumor types with BPA-BNCT, and D0 = 0.0122Xcs–0.1319 (R2 = 0.9795) for four tumor types (all except the B16-BL6 melanoma) with BSH-BNCT. Based on these results, we proposed a new biologically equivalent effectiveness factor: the absolute biological effectiveness (ABE) factor. The ABE factor is Gy/D0. Thus, the ABE dose is the physical dose multiplied by the ABE factor, and refers to the dose needed to decrease the cell survival rate to e–ABE dose/Gy.

Radiosynthesis of O-(1-[18 F]fluoropropan-2-yl)-O-(4-nitrophenyl)methylphosphonate: A novel PET tracer surrogate of sarin.

O-(1-Fluoropropan-2-yl)-O-(4-nitrophenyl) methylphosphonate is a reactive organophosphate ester (OP) developed as a surrogate of the chemical warfare agent sarin that forms a similar covalent adduct at the active site serine of acetylcholinesterase. The radiolabeled O-(1-[18 F]fluoropropan-2-yl)-O-(4-nitrophenyl) methylphosphonate ([18 F] fluorosarin surrogate) has not been previously prepared. In this paper, we report the first radiosynthesis of this tracer from the reaction of bis-(4-nitrophenyl) methylphosphonate with 1-[18 F]fluoro-2-propanol in the presence of DBU. The 1-[18 F]fluoro-2-propanol was prepared by reaction of propylene sulfite with Kryptofix 2.2.2 and [18 F] fluoride ion. The desired tracer O-(1-[18 F]fluoropropan-2-yl)-O-(4-nitrophenyl) methylphosphonate was obtained in a >98% radiochemical purity with a 2.4%±0.6% yield (n=5, 65minutes from start of synthesis) based on starting [18 F] fluoride ion and a molar activity of 49.9GBq/μmol (1.349±0.329Ci/μmol, n=3). This new facile radiosynthesis routinely affords sufficient quantities of [18 F] fluorosarin surrogate in high radiochemical purity, which will further enable the tracer development as a novel radiolabeled OP acetylcholinesterase inhibitor for assessment of OP modes of action with PET imaging in vivo.

PtII versus PdII-assisted [2 + 3] cycloadditions of nitriles and nitrone. Synthesis of nitrile-derived arylamido platinum(II) and Δ4-1,2,4-oxadiazoline palladium(II) complexes

The reactions of bis(organonitrile) platinum(II) complexes trans-[PtCl2(NCR)2] (R = C6H4(p-HCO), CH2C6H4(p-CH3)) with pyrroline N-oxide −O+NCHCH2CH2CMe2 afford arylamido platinum(II) complexes trans-[PtCl2{(OCR)NCCH2CH2CMe2NH}2] (R = C6H4(p-HCO) (1), CH2C6H4(p-CH3) (2)). The spectral data of 1 and 2 show that the oxadiazoline rings in both cases have opened by a spontaneous NO bond cleavage to form (Z)-p-formyl-N-(5,5-dimethylpyrrolidin-2-ylidene)benzamide or (Z)-N-(5,5-dimethylpyrrolidin-2-ylidene)-2-p-tolylacetamide ligands, respectively, where the N-atoms of the benzamide or acetamide moieties coordinate to platinum(II) metal centre in trans positions. However, the reactions of bis(organonitrile) palladium(II) complexes trans-[PdCl2(NCR)2] with pyrroline N-oxide furnish Δ4-1,2,4-oxadiazoline palladium(II) complexes trans-[PdCl2{NC(R)ONC(H)CH2CH2CMe2}2] (R = C6H4(p-HCO) (3), CH2C6H4(p-CH3) (4)) as the exclusive detected products. Compounds 1–4 have been characterized by IR, 1H, 13C NMR spectroscopy, elemental analyses, ESI+-MS and also, in the case of 1, by single crystal X-ray diffraction analysis.

Phosphorylation of Betti Base with Bis(diethylamino)phosphoryl Chloride

The reaction of bis(diethylamino)phosphoryl chloride with N-Boc-protected 1-(α-aminobenzyl)-2- naphthol (Betti base) proceeded via O-phosphorylation of the phenolic OH group to form the target product as trifluoroacetate salt. The latter reacted with O,O-diethyl thiophosphorylisothiocyanate to give thiourea bearing a chiral Betti base fragment.

Intermolecular hydrogen bonding H···Cl in crystal structure of palladium(II)-bis(diaminocarbene) complex

Abstract The reaction of bis(isocyanide)palladium complex cis-[PdCl2(CNXyl)2] (Xyl=2,6-Me2C6H3) with excess of 4,5-dichlorobenzene-1,2-amine in a C2H4Cl2/MeOH mixture affords monocationic bis(diaminocarbene) complex cis-[PdClC{(NHXyl)=NHC6H2Cl2 NH2}{C(NHXyl)=NHC6H2Cl2NH2}]Cl (3) in moderate yield (42%). Complex 3 exists in the solid phase in the H-bonded dimeric associate of two single charged organometallic cations and two chloride anions according to X-ray diffraction data. The Hirshfeld surface analysis for the X-ray structure of 3 reveals that the crystal packing is determined primarily by intermolecular contacts H–Cl, H–H, and H–C. The intermolecular hydrogen bonds N–H···Cl and C–H···Cl in the H-bonded dimeric associate of 3 were studied by DFT calculations and topological analysis of the electron density distribution within the framework of QTAIM method, and estimated energies of these supramolecular contacts vary from 1.6 to 9.1 kcal/mol. Such non-covalent bonding means that complex 3 is an anionic receptor for the chloride anions.