Core Rearrangement Research Articles

What a Difference an Electron Makes: Structural Response of Saddle‐Shaped Tetraphenylene to One and Two Electron Uptake

AbstractCyclooctatetraene (COT) and COT2− dianion are well‐known as archetypical non‐aromatic and aromatic systems, respectively. However, despite a wealth of studies the effect of one electron addition to the eight‐membered ring remains equivocal. Herein, we report the first stepwise electron addition to tetrabenzo[a,c,e,g]cyclooctatetraene (TBCOT or tetraphenylene), accompanied by isolation and structural characterization of the mono‐ and doubly‐reduced anions. The X‐ray crystallographic study reveals only a small asymmetric distortion of the saddle‐shaped core upon one electron uptake. In contrast, the doubly‐reduced product exhibits a severely twisted conformation, with a new C−C bond separating the COT ring into two fused 5‐membered rings. The reversibility of the two‐fold reduction and bond rearrangement is demonstrated by NMR spectroscopy. In agreement with experimental results, computational analysis confirms that the reduction‐induced core rearrangement requires the addition of the second electron.

Divergent Age-Dependent Conformational Rearrangement within Aβ Amyloid Deposits in APP23, APPPS1, and AppNL-F Mice.

Amyloid plaques composed of fibrils of misfolded Aβ peptides are pathological hallmarks of Alzheimer's disease (AD). Aβ fibrils are polymorphic in their tertiary and quaternary molecular structures. This structural polymorphism may carry different pathologic potencies and can putatively contribute to clinical phenotypes of AD. Therefore, mapping of structural polymorphism of Aβ fibrils and structural evolution over time is valuable to understanding disease mechanisms. Here, we investigated how Aβ fibril structures in situ differ in Aβ plaque of different mouse models expressing familial mutations in the AβPP gene. We imaged frozen brains with a combination of conformation-sensitive luminescent conjugated oligothiophene (LCO) ligands and Aβ-specific antibodies. LCO fluorescence mapping revealed that mouse models APP23, APPPS1, and AppNL-F have different fibril structures within Aβ-amyloid plaques depending on the AβPP-processing genotype. Co-staining with Aβ-specific antibodies showed that individual plaques from APP23 mice expressing AβPP Swedish mutation have two distinct fibril polymorph regions of core and corona. The plaque core is predominantly composed of compact Aβ40 fibrils, and the corona region is dominated by diffusely packed Aβ40 fibrils. Conversely, the AβPP knock-in mouse AppNL-F, expressing the AβPP Iberian mutation along with Swedish mutation has tiny, cored plaques consisting mainly of compact Aβ42 fibrils, vastly different from APP23 even at elevated age up to 21 months. Age-dependent polymorph rearrangement of plaque cores observed for APP23 and APPPS1 mice >12 months, appears strongly promoted by Aβ40 and was hence minuscule in AppNL-F. These structural studies of amyloid plaques in situ can map disease-relevant fibril polymorph distributions to guide the design of diagnostic and therapeutic molecules.

Total Synthesis and Anti-Inflammatory Evaluation of Osajin, Scandenone and Analogues.

In this study, the total synthesis of osajin, scandenone and their analogues have been accomplished. The key synthetic steps include aldol/intramolecular iodoetherification/elimination sequence reactions and a Suzuki coupling reaction to assemble the tricyclic core, chemoselective propargylation and Claisen rearrangement reactions to obtain natural compounds. In addition, we also designed and synthesized twenty-five natural product analogues. All synthetic compounds were screened for anti-inflammatory activity against tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Collectively, Compound 39e and 39d were considered as promising lead compounds for further development.

Diachronic evolvement from tetra-icosahedral to quasi-hexagonal close-packed bimetal clusters

Here we report a diachronic evolvement from tetra-icosahedral Au30Ag12(CCR)24 to quasi-hcp (hexagonal close-packed) Au47Ag19(CCR)32 which might be proceeded by the interface shrinking followed by the core rearrangement and surface polymerization.

Interlayer Sliding Phonon Drives Phase Transition in the Ph-BTBT-10 Organic Semiconductor.

In the field of organic electronics, the semiconductor 7-decyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) has become a benchmark due to its high charge mobility and chemical stability in thin film devices. Its phase diagram is characterized by a crystal phase with a bilayer structure that at high temperature transforms into a Smectic E liquid crystal with monolayer structure. As the charge transport properties appear to depend on the phase present in the thin film, the transition has been the subject of structural and computational studies. Here such a process has been investigated by polarized low frequency Raman spectroscopy, selectively probing the intermolecular dynamics of the two phases. The spectroscopic observations demonstrate the key role played by a displacive component of the transition, with the interpenetration of the crystal bilayers driven by lattice phonon mode softening followed by the intralayer rearrangement of the molecule rigid cores into the herringbone motif of the liquid crystal. The mechanism can be related to the effectiveness of thermal annealing to restore the crystal phase in films.

Electrically driven free shear flows in a duct under a transverse uniform magnetic field

A mathematical model of two-dimensional electrically driven laminar plane free shear flows in a straight duct under the action of an applied spanwise uniform magnetic field is considered. The mathematical approach is like that used in the research of Hunt and Williams (J. Fluid. Mech., 31, 705, 1968) and Kolesnikov and Kalis (Magnetohydrodynamics, vol. 57, 2021, no. 2). A system of stationary partial differential equations with two unknown functions of velocity and induced magnetic field is solved. The electric current is injected into the liquid by means of two couples of linear electrodes located vis-à-vis on opposite duct walls, perpendicular to the magnetic field. Three cases are considered. One pair of electrodes is current supplied and, depending on the direction of electric current injection on the electrode pair, two coinciding or two counter flows are also driven. At Hartmann numbers Ha >> 1, quasi-potential cores are formed in these flows, bounded by lateral Shercliff free boundary layers parallel to the field and two Hartmann layers on the walls perpendicular to the field. As a result, almost all of the injected current passes through these layers. An increase of the magnetic field leads only to an internal rearrangement of the potential cores of the flows. The Hartmann number varies in the range from 1 to 100. Figs 15, Refs 11.

Reversible structural rearrangement of π-expanded cyclooctatetraene upon two-fold reduction with alkali metals.

The chemical reduction of a π-expanded COT derivative, octaphenyltetrabenzocyclooctatetraene (1), with lithium or sodium metals in the presence of secondary ligands affords a new doubly-reduced product (1TR2-). The X-ray diffraction study revealed a reductive core rearrangement accompanied by the formation of a single C-C bond and severe twist of the central tetraphenylene core. The reversibility of two-electron reduction and core transformation is further confirmed by NMR spectroscopy and DFT calculations.

Synthetic Studies toward the Berkeleyacetal Core Architecture.

Berkeleyacetals are structurally complex natural products that have shown potent anti-inflammatory activity. The presence of a highly dense oxygen functionality and a polycyclic ring system presents significant synthetic challenges. Herein, we report an efficient strategy for the construction of the tetracyclic core system of berkeleyacetal. Our synthetic strategy features two cycloadditions ([4+2] and [5+2]) to forge the tetracyclic core and Achmatowicz rearrangement for the preparation of the cyclization substrates containing B and E rings.

On the ligand role in determining the compact or extended metallic core architecture in gold superatoms. Evaluation of electronic and optical properties from relativistic DFT for [Au11(dppp)5]3+ and [Au11(dppe)6]3+ clusters

The rational synthesis of well-defined clusters requires further understanding of the fundamental aspects related to the stabilization of preferred isomers over other possible species. Atomically-precise gold superatoms offer useful templates to evaluate the role of the characteristics of the ligand shell in the resulting structure. Herein, we explore the the role of different diphenyl ligands in the determining a compact Au11 core, or extended Au9 + 2Au core, provided experimentally by [Au11(dppp)5]3+ and [Au11(dppe)6]3+ clusters, with variable bridging chain length. Our findings highlight the contribution from ligand-ligand and core-ligand interactions, and the core rearrangement, which favors the experimentally characterized compact [Au11(dppp)5]3+ cluster, by 34.4 kcal·mol−1 in comparison to the hypothetical [Au11(dppe)5]3+ owing to the decrease in the bridge from -(CH2)3- to -(CH2)2-, increasing the steric crowding within the cluster. For the extended Au9 + 2Au core, the contrary case is found, where the experimentally characterized [Au11(dppe)6]3+ cluster is favored by 49.2 kcal·mol−1 in comparison to the hypothetical [Au11(dppp)6]3+ species. The obtained optical characteristics, denotes a similar visible absorption profile for the compact core species, which contrast to the extended Au9 + 2Au core, which is more sensible to the ligand, as accounted by the calculated optical profile.Thus, the overall structure is determined mainly by the contribution from the ligand shell characteristics and the resulting core-ligand, underlying designing aspects towards tunable clusters for building blocks of nanostructured materials.

Nuclear matter density distributions of the neutron-rich He6,8 isotopes from a sum-of-Gaussian analysis of elastic proton scattering data at intermediate energies

Differential cross sections for elastic $p\text{\ensuremath{-}}^{6}\mathrm{He}$ and $p\text{\ensuremath{-}}^{8}\mathrm{He}$ scattering, measured in inverse kinematics at high momentum transfer up to the first diffraction minimum and at projectile energies around 700 MeV/u at GSI Darmstadt, are analyzed applying the sum-of-Gaussians (SOG) method based on the Glauber multiple-scattering theory. The rms point matter radii of $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ are deduced to be 2.29(6) fm and 2.53(7) fm, respectively, in close agreement with those from former analyses using phenomenological parametrizations for describing the matter distributions. With the aid of the measurement at high momentum transfer, the overall radial density distributions of $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ are precisely deduced using the SOG method, in particular at small radii. A pronounced core rearrangement by adding the valence neutrons to an $\ensuremath{\alpha}$-like core to form $^{6}\mathrm{He}$ and $^{8}\mathrm{He}$ is elucidated, and briefly discussed.

Solvent-driven reversible transformation between electrically neutral thiolate protected Ag25 and Ag26 clusters

Two atom-precise silver nanoclusters [Ag25Cl2(Tab)14(PhCOO)11(DMF)4](PF6)12 (Ag25, DMF=N,N-dimethylformamide) and [Ag26Cl2(Tab)14(PhCOO)13(DMAc)4](PF6)11(Ag26, DMAc=N,N-dimethylacetamide) were synthesized based on the electrically neutral thiolate protective ligand, 4-(trimethylammonio)benzenethiolate (Tab). The weak Ag-S interaction in Tab-protected silver nanoclusters allows to insert or leave a single silver atom in the Ag-S skeleton through solvent-trigger core fragmentation and re-arrangement, thereby realizing the reversible conversion of Ag25 and Ag26 for the first time.

Stable meso-Aryl β-Alkyl Hybrid Sapphyrin with a Warped π-Conjugation Circuit and Neo-Confused Sapphyrin-Silver(I) Complex.

A meso-aryl and β-alkyl substituted sapphyrin and its rhodium(I) and silver complexes were synthesized. This sapphyrin was so stable that the non-inverted and warped structure could be analyzed by X-ray crystallography even in its neutral state. Its bis-rhodium(I) complex has a more planar structure than the sapphyrin with enhanced aromaticity over the conjugation circuit. On the other hand, silver metalation of the sapphyrin caused a marked core rearrangement into a neo-confused sapphyrin derivative with a C(α)-N bond and a twisted macrocycle.

Role of polarization interaction in photoionization of negative ions of alkali metals

Photoionization processes of negative ions of sodium, potassium, and rubidium were investigated. Calculations of the dependence of the photoionization cross section on the photon energy were performed within the Random Phase Approximation with Exchange for outer subshells (RPAE) and within the Generalized Random Phase Approximation with Exchange (GRPAE) for inner subshells. The latter theoretical approach includes both many-electron correlations and core rearrangement due to escape of one of the electrons from the system. The results of calculations for the negative sodium ion were found to be in good agreement with experimental data. Better agreement was achieved by allowing dynamical polarization of the electron core. It manifests itself as a many-electron response to variation of the external electromagnetic field, which results from the excitation of the many-electron system. Detailed study of the main mechanisms determining the cross section dependence profile was carried out. These mechanisms are the inter- and intrachannel correlations acting as a many-electron response to the external field, the electron core rearrangement, and the dynamic polarization. Besides sodium and potassium ions, photoionization of rubidium ion was investigated. A new method accounting for polarization corrections to optical transition amplitudes based on combination of the Dyson equation and RPAE is proposed.

Oxygen Reduction Reaction Activity and Durability for Model Pt Shell Layers on Ir(111) Prepared by Molecular Beam Epitaxy

Introduction The core-shell type nanostructure, that is composed of ultra-thin Pt coating on other transition metal nanoparticles have attracted much attention from the viewpoints of cathode electrode catalysts in polymer electrolyte fuel cell (PEFC). Compressive strain of the Pt-shells induced by lattice mismatch and direct electronic interaction between the Pt shell and core elements influences electronic properties of the Pt shell layers and, thereby, contributing to enhanced oxygen reduction reaction (ORR) activity [1]. However, because of operating conditions of PEFC, i.e., low pH, high positive potentials, ORR activity of the core-shell catalysts decline through dissolution of core elements and rearrangements of surface Pt atoms. Considering standard electrode potentials, iridium is stable among the transition metals and Pt-shell/Ir-core nanoparticles might be stable under the PEFC operating conditions. However, at present, relationship between Pt-Ir bimetallic surface structures and ORR properties has been less reported [2]. In this study, we prepared well-defined Pt/Ir(111) bimetallic surfaces by molecular beam epitaxy (MBE) in ultra-high vacuum (UHV) and studied the ORR activity and durability. Experimental Ir(111) single crystal substrate was cleaned by Ar+ sputtering and annealing at 1273 K in UHV. Various-monolayers(ML)-thick Pt was deposited onto the clean Ir(111) substrate by an electron beam evaporation method at the substrate temperature of 673K. The resulting surface structures were verified by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM) in UHV. The UHV-fabricated samples were transferred to electrochemical evaluation systems set in a N2-purged glove box without air exposure. CV and LSV measurements were conducted in N2-purged and O2-saturated 0.1 M HClO4, respectively. The ORR activity was evaluated from j k values at 0.9 V vs. RHE by using the Koutecky-Levich equation. EC degradation of the Pt/Ir(111) surface was evaluated by applying potential cycles between 0.6 V (3s) and 1.0 V (3s) vs. RHE in the O2-saturated solution at room temperature. Results and Discussion Fig. 1 (a) summarizes CV curves of the MBE-prepared nML-thick Pt/Ir(111) (n=1-4: Pt n ML/Ir(111)) and clean Pt(111). All CV curves of the Pt nML/Ir(111) show symmetrical peaks similar to the clean Pt(111) (so-called butterfly peak) in the region of OH adsorption and desorption (0.6-1.0 V), accompanied with remarkable decrease in hydrogen adsorption and desorption charges (0.05-0.35 V). The CV features are typical for highly-ORR-active Pt-based bimetallic surfaces reported to date, suggesting that the topmost surfaces comprise pure Pt(111) lattice. Fig. 1 (b) presents changes in j k during potential cycles loading between 0.6 and 1.0 V. Initial ORR activity enhancement factors for the 2ML, 3ML and 4ML-thick Pt shell layers can be estimated to be ×24, ×12 and ×8, respectively compared with the clean Pt(111). Because Ir lattice constant is smaller than Pt, the Ir(111) substrate should induce compressive surface strain on the Pt-shell. As a result, the ORR activity is enhanced. Furthermore, because compressive strain of the Pt shell layers should be relaxed with increasing the Pt shell layer thickness, the initial activity enhancement factors decreased with increasing the thickness. After the 5000 potential cycles loading, the enhancement factors for the Pt2ML/Ir(111) decreased to ×2 vs. clean Pt(111) indicating that compressive surface strain is easily released by the potential cycle loading. In contrast, particularly, the initial activity of the 4ML-Pt-shell remains nearly unchanged even after the 5000 cycles loading: the activity is the highest among the other well-defined Pt-M(111) bimetallic systems, e.g., Pt/Pd(111) [3], Pt-skin surfaces of Pt-Ni(111) [4] and Pt-Co(111) [5], reported in our laboratory. The results can be explained by 3D migration of the surface Pt atoms during the potential cycle loading and by release in compressive strain in Pt shell. Therefore, the results suggest that Pt-Ir bimetallic system can be expected to be applied to ORR catalysts for practical use. Acknowledgement This study was supported by new energy and industrial technology development organization (NEDO) of Japan and Grant- in Aid for young scientists (B) from the Japan society for the promotion of science (N. T.).

Divergent Syntheses of Carbazole Alkaloids Clausenapin, Indizoline, Claulansine M, and Clausenaline D.

We described the first total syntheses of clausenapin, indizoline, claulansine M, and a novel synthetic route to clausenaline D via divergent method. Key steps involved TFAA-mediated intramolecular acylation to construct the carbazole core and subsequent Claisen rearrangement to generate key intermediates for further elaboration to target molecules.

The Tangled Nature Model for organizational ecology

The Tangled Nature Model--a biologically inspired model of evolutionary ecology--is described, simulated, and analyzed to show its applicability in organization science and organizational ecology. It serves as a conceptual framework for understanding the dynamics in populations of organizations. A salient dynamical feature of this model is the spontaneous generation of a symbiotic group of core organizations. This core, consisting of several dominating species, introduces a mesoscopic level between that of the individual and the whole system. Despite prolonged periods of stability, this core is disrupted at random by parasitic interactions causing sudden core rearrangements. The size distribution of the core organizations is log-normal as predicted by theory and supported by empirical findings. As a simple application of the model, we study the adaptation of organizations to changes in resource availability in terms of population size, population diversity, and ecological efficiency. We find evidence that a temporary reduction in resources forces a consolidation resulting in a sustained increase in overall efficiency, suggesting that such reductions can be applied strategically to drive incremental improvements.

Multidimensional high harmonic spectroscopy of polyatomic molecules: detecting sub-cycle laser-driven hole dynamics upon ionization in strong mid-IR laser fields.

High harmonic generation (HHG) spectroscopy has opened up a new frontier in ultrafast science, where electronic dynamics can be measured on an attosecond time scale. The strong laser field that triggers the high harmonic response also opens multiple quantum pathways for multielectron dynamics in molecules, resulting in a complex process of multielectron rearrangement during ionization. Using combined experimental and theoretical approaches, we show how multi-dimensional HHG spectroscopy can be used to detect and follow electronic dynamics of core rearrangement on sub-laser cycle time scales. We detect the signatures of laser-driven hole dynamics upon ionization and reconstruct the relative phases and amplitudes for relevant ionization channels in a CO2 molecule on a sub-cycle time scale. Reconstruction of channel-resolved complex ionization amplitudes on attosecond time scales has been a long-standing goal of high harmonic spectroscopy. Our study brings us one step closer to fulfilling this initial promise and developing robust schemes for sub-femtosecond imaging of multielectron rearrangement in complex molecular systems.

Pathway toward large two-dimensional hexagonally patterned colloidal nanosheets in solution.

We report the solution self-assembly of an ABC block terpolymer consisting of a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer tail tethered to a fluorinated polyhedral oligomeric silsesquioxane (FPOSS) cage in 1,4-dioxane/water. With increasing water content, abundant unconventional morphologies, including circular cylinders, two-dimensional hexagonally patterned colloidal nanosheets, and laterally patterned vesicles, are sequentially observed. The formation of toroids is dominated by two competing free energies: the end-cap energy of cylinders and the bending energy to form the circular structures. Incorporating the superhydrophobic FPOSS cages enhances the end-cap energy and promotes toroid formation. Lateral aggregation and fusion of the cylinders results in primitive nanosheets that are stabilized by the thicker rims to partially release the rim-cap energy. Rearrangement of the parallel-aligned FPOSS cylindrical cores generates hexagonally patterned nanosheets. Further increasing the water content induces the formation of vesicles with nanopatterned walls.

The Tangled Nature Model for Organizational Ecology

The Tangled Nature Model, a biologically inspired model of evolutionary ecology, is described, simulated and analyzed to show its applicability in organization science and organizational ecology, both as a conceptual framework and as a tool for qualitative prediction about real organizations. We find that a symbiotic group of core organizations is generated, with the core disrupted at random by parasitic interactions causing sudden core rearrangements. This core is a spontaneously generated mesoscopic level of structure between the individual and whole system level. As a simple application of the model, we study the adaptation of organizations to changes in resource availability in terms of population size, population diversity, and ecological efficiency. We find evidence that a temporary reduction in resources forces a consolidation resulting in a sustained increase in overall efficiency, suggesting that such reductions can be applied strategically to drive incremental improvements.

Fragmentation of uracil after electron capture by doubly charged ions

Single electron capture from molecular uracil (C4H4N2O2) by doubly-charged He2+, C2+, and O2+ atomic ions followed by the fragmentation of uracil ions has been studied using time-of-flight mass-spectrometry at the collision velocity range 0.13–0.65 a.u. The uracil ion fragmentation mechanism has been clarified by the arrival time correlation analysis for all ion-fragments produced in a single collision. Electron capture with ionization cross section has been determined from experiment. As shown, single electron capture in reaction of uracil with C2+ leads to high fragmentation probability of the resulting uracil ion. The role of electron core rearrangement in the C2+ and O2+ atomic ions is discussed.