Non-arrhenius behavior of the island density in metal heteroepitaxy: Co on Cu(001)

We present a combined theoretical and experimental study of island nucleation and growth in the deposition of Co on Cu(001)-a prototype for understanding heteroepitaxial growth involving intermixing. Experimentally, ion scattering is employed. Using density-functional theory, we obtain energy barriers for the various elementary processes and incorporate these into a kinetic Monte Carlo program to simulate the heteroepitaxial growth. Both the simulations and the experiments show a unique N-shape dependence of the island density on temperature that stems from the interplay and competition of the different processes involved.     

Multiple time scale simulations of metal crystal growth reveal the importance of multiatom surface processes

A method for extending atomistic computer simulations of solids beyond the nanosecond time scale was used to simulate metal crystal growth on the time scale of laboratory experiments. Transitions involving concerted motion of multiple atoms on the crystal surface are found to lead to remarkably smooth growth of pure Al(100). Cu(100) is found to grow with a rougher surface, consistent with experiments. Not only is the activation energy of the multiatom Al processes surprisingly low, but vibrational entropy also favors processes where many atoms are displaced.     

Electrochemically tuneable hydrogen bonding interactions between a phenyl-urea terminated dendrimer and phenanthrenequinone

Electrochemically tuneable hydrogen bonding interactions are described between a phenyl-urea terminated dendrimer and phenanthrenequinone.     

Model systems for flavoenzyme activity: relationships between cofactor structure, binding and redox properties

A series of flavins were synthesized bearing electron-withdrawing and -donating substituents. The electrochemical properties of these flavins in a nonpolar solvent were determined. The recognition of these flavins by a diamidopyridine (DAP) receptor and the effect this receptor has on flavin redox potential was also quantified. It was found that the DAP-flavin binding affinity and the reduction potentials (E(1/2)) for both the DAP-bound and unbound flavins correlated well with functions derived from linear free energy relationships (LFERs). These results provide insight and predictive capability for the interplay of electronics and redox state-specific interactions for both abiotic and enzymatic systems.     

Eta physics at threshold

The production of - and -mesons in elementary nucleon-nucleon collisions has been investigated at the synchrotrons CELSIUS, COSY and SATURNE. The high-quality proton beam with low emittance and small momentum spread permits to study the creation of these mesons very close to the kinematical threshold, where --due to the rapid growth of the phase space volume-- the total cross-section increases by orders of magnitude over a few MeV range of the excess energy. The magnitude and energy dependence of the total cross-section as well as the occupation distribution of the phase space serve as observables for investigating the mechanisms underlying the production processes and the interaction of mesons with nucleons. The precise data on the and creation via the reactions allowed to settle the general features of the - and -meson production and revealed the sensitivity of the mentioned observables to the nucleon-nucleon-meson final-state interaction. The particular production properties, like for example, the determination of the dominating exchange processes which lead to the excitation of the S ₁₁ nucleon isobar in the case of creation, must be established by confrontation with other observables. The present status of this investigation with an emphasis on the results of the COSY-11 Collaboration is briefly presented. The available data are interpreted in view of the production mechanism and the meson-nucleon interaction.Received: 30 September 2002, Published online: 22 October 2003PACS: 13.60.Le Meson production - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy GeV) - 13.85.Lg Total cross sections - 25.40.-h Nucleon-induced reactions     

Triple-quantum-filtered (23)Na NMR spectroscopy of subcutaneously implanted 9l gliosarcoma in the rat in the presence of TmDOTP(5-1)

The utility of triple-quantum (TQ)-filtered (23)Na NMR spectroscopy for discriminating between intra- and extracellular Na(+)(Na(i)(+) and Na(e)(+), respectively) in a solid tumor in vivo was evaluated using TmDOTP(5-) as a (23)Na shift reagent. Infusion of 80 mM TmDOTP(5-) without added Ca(2+) produced baseline-resolved Na(i)(+) and Na(e)(+) peaks in both single-quantum (SQ) and TQ-filtered (23)Na spectra. The Na(i)(+) signal represented 22+/-4% of the SQ spectrum, but 59+/-10% of the TQ-filtered spectrum. Therefore, the Na(i)(+) contribution in TQ-filtered spectra is much higher than in SQ spectra. Both SQ and TQ-filtered Na(i)(+) signals increased by about 75% 1 h after sacrificing the animal. The TQ-filtered relaxation times did not change during this time, indicating that changes observed in TQ-filtered spectra collected with a preparation time of 3 ms represent changes in the concentration of sodium ions contributing to the TQ-filtered signal. Similar experiments were conducted without TmDOTP(5-) to determine changes in the Na(e)(+) signal in the absence of the shift reagent. The changes in total SQ and TQ-filtered signals 1 h after sacrificing the animal showed that the SQ Na(e)(+) signal decreased by approximately 35%, while the TQ-filtered Na(e)(+) signal did not change significantly. This demonstrates that the TQ-filtered (23)Na signal is relatively insensitive to changes in Na(e)(+) content. To our knowledge, this work represents the first evaluation of multiple-quantum-filtered (23)Na spectroscopy to discriminate between intra- and extracellular Na(+) in a solid tumor in vivo.     

Addition,elimination, exchange,and epimerization in nitro sulfones

Three reactions were studied in the diastereomers of 1‐(benzenesulfonyl)‐2‐nitro‐1‐phenylpropane ( 1A and 1B ) and briefly in related compounds: elimination of the benzenesulfonyl group, epimerization of one diastereomer to the other, and deuterium/hydrogen exchange at the methine group next to nitro in starting material. The two diastereomers showed quite different reactivity. The high melting diasteromer showed rapid elimination and some exchange. The low melting diastereomer (at approximately a half‐life) showed extensive epimerization, and elimination to the alkene, but little exchange. There is little effect of aromatic substituents on reaction course. The situation is complicated by re‐addition of benzenesulfinate to the alkene. The addition reaction was similar to elimination in agreement with the Principle of Microscopic Reversibility expectations. An electron transfer mechanism for addition is calculated to be comparatively favorable. Copyright © 2007 John Wiley & Sons, Ltd.