The interaction of 538 MeV 56Fe with 238U

Binary coincident fragments from the ⁵⁶Fe+²³⁸U reaction at 538 MeV have been studied. Fragment energies were measured and fragment masses determined by a kinematic method. Three types of event are defined by suitable adjacent limits in the mass versus energy event space. The angular distributions of cross section, energy and mass have determined for each event region and particular attention paid to that part containing possible fissions following complete fusion. The total reaction cross section consists of about 50 % of binary fragmentation channels. The remaining channels correspond to a ternary process of heavy recoil fission.     

Cp2Fe(PR2)2PdCl2 (R = i-Pr, t-Bu) complexes as air-stable catalysts for challenging Suzuki coupling reactions

[reaction: see text] The use of Cp(2)Fe(PR(2))(2)PdCl(2) (R = i-Pr and t-Bu) in Suzuki coupling reactions were illustrated using a high throughput screening approach. The di-tbpfPdCl(2) catalyst was shown to be the more active catalyst for unactivated and sterically challenging aryl chlorides. Comparison studies using the commercial catalysts dppfPdCl(2), (Ph(3)P)(2)PdCl(2), (Cy(3)P)(2)PdCl(2), DPEPhosPdCl(2), dppbPdCl(2), dppePdCl(2), Pd(t-Bu(3)P)(2), and [Pd(mu-Br)(t-Bu(3)P)](2) were also done for selected cases to demonstrate the superior activities of di-tbpfPdCl(2) and di-isoppfPdCl(2).     

Insulating surface layer on single crystal K $\mathsf{_{3}}\mathsf{C}\mathsf{_{60}}$

Using angle-dependent photoemission spectra of core and valence levels we show that metallic, single crystal K³C₆₀ is terminated by an insulating or weakly-conducting surface layer. We attribute this to the effects of strong intermolecular correlations combined with the average surface charge state. Several controversies on the electronic structure are thereby resolved.Received: 16 July 2004, Published online: 5 November 2004PACS: 71.20.Tx Fullerenes and related materials; intercalation compounds - 73.20.-r Electron states at surfaces and interfaces - 79.60.Bm Clean metal, semiconductor, and insulator surfaces     

Vertically aligned Ni/NiO nanocomposites with abundant oxygen deficient hetero-interfaces for enhanced overall water splitting

Science China Chemistry - The design of heterostructured transition metal-based electrocatalysts with controlled composition and interfaces is key to increasing the efficiency of the water...     

Dynamic stress-concentration factors

The problem of the response of structural discontinuities to short-duration stress pulses is studied experimentally. Employing explosively induced stress pulses in thin plastic plates containing central circular holes, a dynamic stress-concentration factor is determined as a function of pulse frequency. It is concluded, for the loading case, that the dynamic stress concentration is significantly lower than the static value.     

Self-assembly of beta-sheet forming peptides into chiral fibrillar aggregates

The authors introduce a novel mid-resolution off-lattice coarse-grained model to investigate the self-assembly of beta-sheet forming peptides. The model retains most of the peptide backbone degrees of freedom as well as one interaction center describing the side chains. The peptide consists of a core of alternating hydrophobic and hydrophilic residues, capped by two oppositely charged residues. Nonbonded interactions are described by Lennard-Jones and Coulombic terms. The influence of different levels of "hydrophobic" and "steric" forces between the side chains of the peptides on the thermodynamics and kinetics of aggregation was investigated using Langevin dynamics. The model is simple enough to allow the simulation of systems consisting of hundreds of peptides, while remaining realistic enough to successfully lead to the formation of chiral, ordered beta tapes, ribbons, as well as higher order fibrillar aggregates.     

Folding of the 25 residue Abeta(12-36) peptide in TFE/water: temperature-dependent transition from a funneled free-energy landscape to a rugged one

The free-energy landscape of the Alzheimer beta-amyloid peptide Abeta(12-36) in a 40% (v/v) 2,2,2-trifluoroethanol (TFE)/water solution was determined by using multicanonical molecular dynamics simulations. Simulations using this enhanced conformational sampling technique were initiated from a random unfolded polypeptide conformation. Our simulations reliably folded the peptide to the experimental NMR structure, which consists of two linked helices. The shape of the free energy landscape for folding was found to be strongly dependent on temperature: Above 325 K, the overall shape was funnel-like, with the bottom of the funnel coinciding exactly with the NMR structure. Below 325 K, on the other hand, the landscape became increasingly rugged, with the emergence of new conformational clusters connected by low free-energy pathways. Finally, our simulations reveal that water and TFE solvate the polypeptide in different ways: The hydrogen bond formation between TFE and Abeta was enhanced with decreasing temperature, while that between water and Abeta was depressed.     

Strategies for the generation of molecularly imprinted polymeric nitroxide catalysts

[reaction: see text] Two strategies for preparing catalytically active molecularly imprinted nitroxide-containing polymers are outlined. Both strategies rely upon the thermal rearrangement chemistry of tertiary amine N-oxides. To this end, several polymers were prepared and the polymeric nitroxides were revealed by oxidation with m-CPBA. All of the resulting polymeric catalysts proved to be competent mediators of the oxidation of alcohols.