Atomic‐Level Alloying and De‐alloying in Doped Gold Nanoparticles

Atomically precise alloying and de‐alloying processes for the formation of Ag–Au and Cu–Au nanoparticles of 25‐metal‐atom composition (referred to as Ag_xAu_25?x(SR)₁₈ and Cu_xAu_25?x(SR)₁₈, in which R=CH₂CH₂Ph) are reported. The identities of the particles were determined by matrix‐assisted laser desorption ionization mass spectroscopy (MALDI‐MS). Their structures were probed by fragmentation analysis in MALDI‐MS and comparison with the icosahedral structure of the homogold Au₂₅(SR)₁₈ nanoparticles (an icosahedral Au₁₃ core protected by a shell of Au₁₂(SR)₁₈). The Cu and Ag atoms were found to preferentially occupy the 13‐atom icosahedral sites, instead of the exterior shell. The number of Ag atoms in Ag_xAu_25?x(SR)₁₈ (x=0–8) was dependent on the molar ratio of Ag^I/Au^III precursors in the synthesis, whereas the number of Cu atoms in Cu_xAu_25?x(SR)₁₈ (x=0–4) was independent of the molar ratio of Cu^II/Au^III precursors applied. Interestingly, the Cu_xAu_25?x(SR)₁₈ nanoparticles show a spontaneous de‐alloying process over time, and the initially formed Cu_xAu_25?x(SR)₁₈ nanoparticles were converted to pure Au₂₅(SR)₁₈. This de‐alloying process was not observed in the case of alloyed Ag_xAu_25?x(SR)₁₈ nanoparticles. This contrast can be attributed to the stability difference between Cu_xAu_25?x(SR)₁₈ and Ag_xAu_25?x(SR)₁₈ nanoparticles. These alloyed nanoparticles are promising candidates for applications such as catalysis.     

Insights into the N-terminal Cu(II) and Cu(I) binding sites of the human copper transporter CTR1

Abstract

Copper transporter 1 (CTR1) is the main copper transporter in the eukaryotic system. CTR1 has several important roles: It binds Cu(II) ions that are present in the blood; it reduces those Cu(II) ions to Cu(I); and it subsequently transfers Cu(I) to the cytoplasmic domain, where the ion is delivered to various cellular pathways. Here, we seek to identify CTR1 binding sites for Cu(II) and Cu(I) and to shed light on the Cu(II)-to-Cu(I) reduction process. We focus on the first 14 amino acids of CTR1. This N-terminal segment is rich with histidine and methionine residues, which are known to bind Cu(II) and Cu(I), respectively; thus, this region has been suggested to have an important function in recruiting Cu(II) and reducing it to Cu(I). We utilize electron paramagnetic resonance (EPR) spectroscopy together with nuclear magnetic resonance (NMR) and UV-VIS spectroscopy and alanine substitution to reveal Cu(II) and Cu(I) binding sites in the focal 14-amino-acid segment. We show that H5 and H6 directly coordinate to Cu(II), whereas M7, M9, and M12 are involved in Cu(I) binding. This research is another step on the way to a complete understanding of the cellular copper regulation mechanism in humans.     

Nitrogen inversion in cyclic amines and the bicyclic effect

The hitherto unsolved problem of the origin of the unusually high nitrogen inversion-rotation (NIR) barriers in 7-azabicyclo[2.2.1]heptanes (the bicyclic effect) was examined using the natural bond orbital (NBO) approach. Reinvestigating the NIR barrier for tropane by DNMR, we found that NIR barriers increase smoothly on going from nitrogen-bridged bicyclic systems of a larger ring size to the smaller ring homologous systems. The experimental NIR barriers are reproduced with good accuracy using the MP2/6-31G level of theory. The NBO analysis for these and other azabicycles led to the conclusion that the height of these barriers is mostly determined by the energy of the sigma-orbitals of the C(alpha)(-)C(beta) bonds as well as the nitrogen lone pair. Thus, the bicyclic effect is actually an extreme case of a common C(alpha-)N-C(alpha) tripyramid geometry-NIR barrier dependence for N-bridged bicyclic amines. By establishing the rate-determining role of the C(alpha-)N-C(alpha) tripyramid fragment for NIR, we have derived the first sufficiently accurate quantitative correlations amine geometry-NIR barrier for monocyclic as well as bicyclic N-H and N-Me amines (i.e., for an amine set which also includes the bicyclic effect systems).     

Aqueous enantioselective hydrogenation of methyl 2-acetamidoacrylate with Rh-MeDuPHOS occluded in PDMS

A new chiral heterogeneous catalytic system obtained by occlusion of the Rh-MeDuPHOS complex in a polydimethylsiloxane film was tested in the asymmetric hydrogenation of methyl 2-acetamidoacrylate in aqueous medium.     

Tunneling from a 3-dimensional quantum well in an electric field: an analytic solution

We derive the stationary tunneling solution for charged particles moving in a spherical, 3-dimensional zero-range potential plus a constant electric field. From the analytic expression for the wave function we calculate the distribution of the current inside and outside the vacuum barrier. At low field strengths there is a constant spreading of the tunnel current orthogonal to the direction of the applied field. At intermediate field strengths the exact results for the current distribution behave different from the semiclassical predictions.     

Two separable conformers of TATP and analogues exist at room temperature

[reaction: see text] TATP gives rise to two separable conformations because the barrier for interconversion between them is relatively high at room temperature. This kind of behavior is rare in cyclic organic systems and is the result of poor overlap in the "flip-flop" transition state. The crystal structure of the analogous tricyclohexanone triperoxide also indicates the presence of two conformers.     

New measure of electron correlation

We propose to quantify the correlation inherent in a many-electron (or many-fermion) wave function psi by comparing it to the unique uncorrelated state that has the same 1-particle density operator as does /|psi>相似文献