Dinuclear System Research Articles

The Structure of Linkers Affects the DNA Binding Properties of Tethered Dinuclear Ruthenium(II) Metallo-Intercalators.

With the long-term aim of enhancing the binding properties of dinuclear RuII -based DNA light-switch complexes, a series of eight structurally related mono- and dinuclear systems are reported in which the linker of the bridging ligand has been modulated. These tethered systems have been designed to explore issues of steric demand at the binding site and the thermodynamic cost of entropy loss upon binding. Detailed spectroscopic and isothermal titration calorimetry (ITC) studies on the new complexes reveal that one of the linkers produces a dinuclear system that binds to duplex DNA with an affinity (Kb >107 m-1 ) that is higher than its corresponding monometallic complex and is the highest affinity for a non-threading bis-intercalating metal complex. These studies confirm that the tether has a major effect on the binding properties of dinuclear complexes containing intercalating units and establishes key design rules for the construction of dinuclear complexes with enhanced DNA binding characteristics.

Theoretical study on production of heavy neutron-rich isotopes around the N = 126 shell closure in radioactive beam induced transfer reactions

In order to produce more unknown neutron-rich nuclei around N=126, the transfer reactions 136Xe + 198Pt, 136–144Xe + 208Pb, and 132Sn + 208Pb are investigated within the framework of the dinuclear system (DNS) model. The influence of neutron excess of projectile on production cross sections of target-like products is studied through the reactions 136,144Xe + 208Pb. We find that the radioactive projectile 144Xe with much larger neutron excess is favorable to produce neutron-rich nuclei with charge number less than the target rather than produce transtarget nuclei. The incident energy dependence of yield distributions of fragments in the reaction 132Sn + 208Pb are also studied. The production cross sections of neutron-rich nuclei with Z=72–77 are predicted in the reactions 136–144Xe + 208Pb and 132Sn + 208Pb. It is noticed that the production cross sections of unknown neutron-rich nuclei in the reaction 144Xe + 208Pb are at least two orders of magnitude larger than those in the reaction 136Xe + 208Pb. The radioactive beam induced transfer reactions 139,144Xe + 208Pb, considering beam intensities proposed in SPIRAL2 (Production System of Radioactive Ion and Acceleration On-Line) project as well, for production of neutron-rich nuclei around the N=126 shell closure are investigated for the first time. It is found that, in comparison to the stable beam 136Xe, the radioactive beam 144Xe shows great advantages for producing neutron-rich nuclei with N=126 and the advantages get more obvious for producing nuclei with less charge number.

Large-amplitude nuclear motion formulated in terms of dissipation of quantum fluctuations

The potential-barrier penetrability and quasi-stationary thermal-decay rate of a metastable state are formulated in terms of microscopic quantum diffusion. Apart from linear coupling in momentum between the collective and internal subsystems, the formalism embraces the more general case of linear couplings in both the momentum and the coordinates. The developed formalism is then used for describing the process of projectile-nucleus capture by a target nucleus at incident energies near and below the Coulomb barrier. The capture partial probability, which determines the cross section for formation of a dinuclear system, is derived in analytical form. The total and partial capture cross sections, mean and root-mean-square angular momenta of the formed dinuclear system, astrophysical -factors, logarithmic derivatives, and barrier distributions are derived for various reactions. Also investigated are the effects of nuclear static deformation and neutron transfer between the interacting nuclei on the capture cross section and its isotopic dependence, and the entrance-channel effects on the capture process. The results of calculations for reactions involving both spherical and deformed nuclei are in good agreement with available experimental data.

Dinuclear zinc complex catalyzed asymmetric methylation and alkynylation of aromatic aldehydes.

A general AzePhenol dinuclear zinc catalytic system has been successfully developed and introduced into the asymmetric addition of dimethylzinc and alkynylzinc to aromatic aldehydes. In this system, an azetidine derived chiral ligand has proven to be an effective enantioselective promoter. Under the optimal reaction conditions, a series of chiral 1-hydroxyethyl (up to 99% ee) and secondary propargylic alcohols (up to 96% ee) were generated with good yields and enantioselectivities. Additionally, this novel catalytic system showed good functional group compatibility. Remarkably, the substituent's electronic nature alone is not sufficient to allow for exclusive enantioselectivity, an additional substituent's location also had an effect. We proposed that the formation of a stable and structural rigid transition state by the chelation of ortho substituted benzaldehydes to the zinc atom was responsible for the observed higher enantioselectivity. The possible catalytic cycles of both transformations accounting for the stereoselectivity were described accordingly.

A comparative study of magnetization dynamics in dinuclear dysprosium complexes featuring bridging chloride or trifluoromethanesulfonate ligands.

We utilized a rigid ligand platform PyCp22- (PyCp22- = [2,6-(CH2C5H3)2C5H3N]2-) to isolate dinuclear Dy3+ complexes [(PyCp2)Dy-(μ-O2SOCF3)]2 (1) and [(PyCp2)Dy-(μ-Cl)]2 (3) as well as the mononuclear complex (PyCp2)Dy(OSO2CF3)(thf) (2). Compounds 1 and 2 are the first examples of organometallic Dy3+ complexes featuring triflate binding. The isolation of compounds 1 and 3 allows us to comparatively evaluate the effects of the bridging anions on the magnetization dynamics of the dinuclear systems. Our investigations show that although the exchange coupling interactions differ for 1 and 3, the dynamic magnetic properties are dominated by relaxation via the first excited state Kramers doublet of the individual Dy sites. Compounds 1 and 3 exhibit barriers to magnetization reversal (Ueff = 49 cm-1) that can be favorably compared to those of the previously reported examples of [Cp2Dy(μ-Cl)]2 (Ueff = 26 cm-1) and [Cp2Dy(thf)(μ-Cl)]2 (Ueff = 34 cm-1).

Effects of entrance channel on fusion probability in hot fusion reactions**Supported by Natural Science Foundation of Guangdong Province China (2016A030310208). National Natural Science Foundation of China (11605296, 11405278, 11505150, 11635003), Fundamental Research Funds for the Central Universities (15 lgpy 30) and China Postdoctoral Science Foundation (2015M582730)

Within the framework of the dinuclear system (DNS) model, the fusion reactions leading to the compound nuclei 274Hs* and 286Cn* are investigated. The fusion probability as a function of DNS excitation energy is studied. The calculated results are in good agreement with the available experimental data. The obtained results show that the fusion probabilities are obviously enhanced for the reactions located at high place in potential energy surface, although these reactions may have small values of mass asymmetry. It is found that the enhancement is due to the large potential energy of the initial DNS.

Level densities of dinuclear systems

The intrinsic level densities of dinuclear systems formed in heavy-ion reactions are calculated using the single-particle spectra obtained with the modified two-center shell model. The role of the mass asymmetry, deformation parameters, and neck size on the level density as well as their quenching with excitation energy are studied. The extracted level density parameter is compared with that obtained in the sudden approximation. The phenomenological parametrization is suggested to estimate the level density parameters for dinuclear systems and strongly deformed nuclear shapes.

Dinuclear Systems in the Efficient Nickel-Catalyzed Kumada–Tamao–Corriu Cross-Coupling of Aryl Halides

Highly active dinuclear nickel(I) complexes bearing bulky N-heterocyclic carbene ligands have been shown to be involved in the catalytic cycle of the Kumada–Tamao–Corriu cross-coupling reaction of aryl halides. The results of several stoichiometric reactions and kinetics experiments have revealed that monovalent and divalent dinickel species are the active species in the highly efficient, nickel-catalyzed, Kumada coupling reactions of aryl halides.

Influence of hexadecapole deformation on production cross sections of superheavy nuclei

The current heaviest superheavy nuclei (SHN) are experimentally synthesized by using 48Ca to bombard actinide nuclei via fusion reactions. Actinide nuclei often have considerable hexadecapole deformation in addition to quadrupole deformation, which was not considered in previous theoretical studies. With the dinuclear system concept, and by taking the hexadecapole deformation in to consideration in addition to the quadrupole deformation, the hot fusion probability leading to the synthesis of SHN is investigated systematically. Synthesis of superheavy elements 296118 and 295118 by using the 48Ca+251Cf reaction channel is evaluated and discussed, and the maximal evaporation residue cross sections (ERCSs) of the 3n and 4n channels are predicted to be 1.90 and 0.11 pb, respectively. The predicted maximum ERCSs in 3n and 4n evaporation channels of the 249Bk(50Ti,xn) reaction are 0.12 and 0.04 pb, respectively. The most favorable reaction to synthesize the element Z = 120 turns out to be 251Cf(50Ti,xn)120, but the predicted maximum cross section for this reaction is only 67 fb. Therefore, superheavy element 119 may be the most hopeful new element for to be synthesized under some improved experimental conditions in the near future.

Production of neutron-rich transcalifornium nuclei in U238 -induced transfer reactions

In order to produce more unknown neutron-rich transcalifornium nuclei, the collisions of $^{238}\mathrm{U}$ with the targets $^{248}\mathrm{Cm}$, $^{249}\mathrm{Cf}$, and $^{250}\mathrm{Cm}$ are investigated within the framework of the dinuclear system model. The production cross sections of unknown neutron-rich nuclei with $Z=99--104$ in these reactions are predicted. The influences of $N/Z$ ratios and charge numbers of the targets on the production cross sections are studied. It is found that high $N/Z$ ratios of $^{248}\mathrm{Cm}$ and $^{250}\mathrm{Cm}$ targets enhance the production cross sections of neutron-rich transcalifornium nuclei. However, due to high charge number of the target $^{249}\mathrm{Cf}$ the predicted production cross sections of unknown neutron-rich nuclei with $Z=104$ in the reaction $^{238}\mathrm{U}+\phantom{\rule{0.16em}{0ex}}^{249}\mathrm{Cf}$ are higher than those in $^{238}\mathrm{U}+\phantom{\rule{0.16em}{0ex}}^{248}\mathrm{Cm}$. We also have studied the entrance angular momentum effects on production probabilities of transfer products in the reaction $^{238}\mathrm{U}+\phantom{\rule{0.16em}{0ex}}^{248}\mathrm{Cm}$. It is found that the formation probabilities of the final neutron-rich products increase first and then decrease with the increasing $J$.

Interpretation of the mechanism of spontaneous fission of heavy nuclei in the framework of dinuclear system conception

The new approach to the interpretation of the process of spontaneous fission of heavy nuclei is suggested. It is based on nuclear physics data which are obtained in heavy ion collisions. The process of spontaneous fission consists of three sequential stages: clusterization of the valent nucleons of a heavy nucleus into a light nucleus-cluster, which leads to the formation of a dinuclear system; evolution of the dinuclear system which proceeds by nucleon transfer from the heavy to light nucleus and decay of the dinuclear system from the equilibrium configuration into two fragments.

Fusion-fission study at IUAC: Recent results

Several properties observed in heavy ion induced fission led to the conclusion that fission is not always originated from fully equilibrated compound nucleus. Soon after the collision of two nuclei, it forms a di-nuclear system than can fission before a compound nucleus is formed. This process termed quasi-fission is a major hurdle to the formation of heavier elements by fusion. Fission originated before complete equilibration showed anomalously large angular anisotropy and mass distribution wider than what is expected from compound nucleus fission. The standard statistical model fails to predict the outcome of quasi-fission and currently no dynamical model is fully developed to predict all the features of quasi-fission. Though much progress has been made in recent times, a full understanding of the fission dynamics is still missing. Experiments identifying the influence of entrance channel parameters on dynamics of fusion-fission showed contrasting results. At IUAC accelerator facility many experiments have been performed to make a systematic study of fission dynamics using mass distribution, angular distribution and neutron multiplicity measurements in mass region around A ∼ 200. Recent measurement on mass distribution of fission fragment from reaction 19 F +206,208 Pb around fusion barrier energy showed the influence of multi-mode fission in enhancing the mass variance at low excitation energy. In this talk I will present some of these results.

Theoretical study of effects of the entrance channel on the relative yield of complete fusion and quasifission in heavy-ion collisions within a dinuclear system approach

The relative yield of complete fusion and quasifission components for the $^{12}\mathrm{C}+^{204}\mathrm{Pb}, ^{19}\mathrm{F}+^{197}\mathrm{Au}, ^{30}\mathrm{Si}+^{186}\mathrm{W}$, and $^{48}\mathrm{Ca}+^{168}\mathrm{Er}$ reactions which all lead to the compound nucleus $^{216}\mathrm{Ra}$ are analyzed to calculate the entrance channel effects by comparison of capture, complete fusion, and quasifission cross sections, emission barriers (${B}_{\mathrm{fus}}^{*},{B}_{qf}$), as well as complete fusion probability estimated by statistical method within the framework of the dinuclear system model. The difference among complete fusion probabilities calculated by the dinuclear system model for different entrance channels can be explained by the hindrance to complete fusion due to the larger inner fusion barrier ${B}_{\mathrm{fus}}^{*}$ for the transformation of the dinuclear system into a compound nucleus and the increase of the quasifission contribution due to the decreasing of the emission barrier ${B}_{qf}$ of quasifission as a function of the angular momentum. Although these reactions with different entrance channels populate the same compound nucleus $^{216}\mathrm{Ra}$ at similar excitation energies, the model predicts the negligible quasifission probability for reactions having higher entrance channel mass asymmetry and the dominant decay channel is complete fission. For reactions induced by massive projectiles such as $\mathrm{Si}$ and $\mathrm{Ca}$ having lower entrance channel mass asymmetry, the quasifission component is dominant in the evolution of dinuclear system, and the fusion process is extremely hindered.

Evolution of octupole correlations inBa123

High-spin states of Ba123 have been studied via the Cd108(F19,3np)Ba123 fusion-evaporation reaction at a beam energy of 90 MeV. Several E1 transitions linking the positive-parity ν(d5/2+g7/2) band and negative-parity νh11/2 band are observed in Ba123 for the first time. Evidence for the existence of octupole correlations in Ba123 is presented based on the systematic comparisons of the B(E1)/B(E2) branching ratios and the energy displacements in odd-A Ba isotopes. The characteristics of octupole correlation in the odd-ABa123,125 are explained by the state-of-the-art multidimensionally-constrained relativistic mean-field model and cluster model based on the dinuclear system concept.Received 25 April 2016DOI:https://doi.org/10.1103/PhysRevC.94.021301©2016 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCluster modelsCollective levelsLow & intermediate energy heavy-ion reactionsNuclear structure & decaysProperties90 ≤ A ≤ 149Nuclear Physics

Slow Relaxation of Magnetization in an Isostructural Series of Zinc-Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study.

We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %.

New neutron-rich isotope production in 154 Sm+ 160 Gd

Deep inelastic scattering in $^{154}$Sm+$^{160}$Gd at energies above the Bass barrier is for the first time investigated with two different microscopic dynamics approaches: improved quantum molecular dynamics (ImQMD) model and time dependent Hartree-Fock (TDHF) theory. No fusion is observed from both models. The capture pocket disappears for this reaction due to strong Coulomb repulsion and the contact time of the di-nuclear system formed in head-on collisions is about 700 fm/c at an incident energy of 440 MeV. The isotope distribution of fragments in the deep inelastic scattering process is predicted with the simulations of the latest ImQMD-v2.2 model together with a statistical code (GEMINI) for describing the secondary decay of fragments. More than 40 extremely neutron-rich unmeasured nuclei with $58 \le Z\le 76$ are observed and the production cross sections are at the order of ${\rm \mu b}$ to mb. The multi-nucleon transfer reaction of Sm+Gd could be an alternative way to synthesize new neutron-rich lanthanides which are difficult to be produced with traditional fusion reactions or fission of actinides.

Fine-Tuning Ligand to Modulate the Magnetic Anisotropy in a Carboxylate-Bridged Dy2 Single-Molecule Magnet System

A series of dinuclear Dy(III) compounds with the general formula [Dy2(μ2-anthc)4(anthc)2(L)2] (anthc(-) = 9-anthracenecarboxylate, L = 2,2'-bipyridyl (1), 1,10-phenanthroline (2), and 4,7-dimethyl-1,10-phenanthroline (3)) were synthesized and magnetically characterized. These compounds exhibit single-molecule magnet (SMM) behavior in the absence of the direct-current field, which is rarely observed for carboxylate-bridged dinuclear Dy2 system. With the first coordination sphere of Dy(III) centers being fixed, the energy barrier was modulated by sequentially modifying the terminal neutral L ligands in this Dy2 system. Theoretical calculations revealed that the symmetry of the charge distribution surrounding the Dy(III) centers in 1-3 is the decisive factor to determine the relaxation of the SMMs. The combination of the larger charge distribution along the magnetic axis and lower charge distribution in the equatorial plane (hard plane) formed by five coplanar coordination atoms including two N atoms provided by an L ligand led to a strong easy-axis ligand field in these compounds. This work presents a rational method to modulate the dynamic magnetic relaxation of the lanthanide SMMs through fine-tuning electrostatic potential of the atoms on the hard plane.

1,5-Diamido-9,10-anthraquinone, a Centrosymmetric Redox-Active Bridge with Two Coupled β-Ketiminato Chelate Functions: Symmetric and Asymmetric Diruthenium Complexes.

The dinuclear complexes {(μ-H2L)[Ru(bpy)2]2}(ClO4)2 ([3](ClO4)2), {(μ-H2L)[Ru(pap)2]2}(ClO4)2 ([4](ClO4)2), and the asymmetric [(bpy)2Ru(μ-H2L)Ru(pap)2](ClO4)2 ([5](ClO4)2) were synthesized via the mononuclear species [Ru(H3L)(bpy)2]ClO4 ([1]ClO4) and [Ru(H3L)(pap)2]ClO4 ([2]ClO4), where H4L is the centrosymmetric 1,5-diamino-9,10-anthraquinone, bpy is 2,2'-bipyridine, and pap is 2-phenylazopyridine. Electrochemistry of the structurally characterized [1]ClO4, [2]ClO4, [3](ClO4)2, [4](ClO4)2, and [5](ClO4)2 reveals multistep oxidation and reduction processes, which were analyzed by electron paramagnetic resonance (EPR) of paramagnetic intermediates and by UV-vis-NIR spectro-electrochemistry. With support by time-dependent density functional theory (DFT) calculations the redox processes could be assigned. Significant results include the dimetal/bridging ligand mixed spin distribution in 3(3+) versus largely bridge-centered spin in 4(3+)-a result of the presence of Ru(II)-stabilizig pap coligands. In addition to the metal/ligand alternative for electron transfer and spin location, the dinuclear systems allow for the observation of ligand/ligand and metal/metal site differentiation within the multistep redox series. DFT-supported EPR and NIR absorption spectroscopy of the latter case revealed class II mixed-valence behavior of the oxidized asymmetric system 5(3+) with about equal contributions from a radical bridge formulation. In comparison to the analogues with the deprotonated 1,4-diaminoanthraquinone isomer the centrosymmetric H2L(2-) bridge shows anodically shifted redox potentials and weaker electronic coupling between the chelate sites.

Expected production of new exoticαemittersXe108andBa112in complete fusion reactions

The production cross sections of neutron-deficient isotopes $^{108--110}\mathrm{Xe}$ and $^{112--114}\mathrm{Ba}$ in the complete fusion reactions $^{58,56}\mathrm{Ni}+^{54}\mathrm{Fe}$ and $^{58,56}\mathrm{Ni}+^{58}\mathrm{Ni}$ with stable and radioactive beams are studied with the dinuclear system model. The calculated results are compared with the available experimental data. The optimal beam energies and corresponding maximum production cross sections of new isotopes $^{108}\mathrm{Xe}$ and $^{112}\mathrm{Ba}$ are predicted.

ChemInform Abstract: Metal Complexes Based on Native Cyclodextrins: Synthesis and Structural Diversity

AbstractReview: 44 refs.