排序方式: 共有14条查询结果,搜索用时 15 毫秒
1.
2.
Egodapitiya KN Sharma S Hasan A Laforge AC Madison DH Moshammer R Schulz M 《Physical review letters》2011,106(15):153202
We have measured the scattering angle dependence of cross sections for ionization in p+H2 collisions for a fixed projectile energy loss. Depending on the projectile coherence, interference due to indistinguishable diffraction of the projectile from the two atomic centers was either present or absent in the data. This shows that, due to the fundamentals of quantum mechanics, the preparation of the beam must be included in theoretical calculations. The results have far-reaching implications on formal atomic scattering theory because this critical aspect has been overlooked for several decades. 相似文献
3.
4.
The transfers of hydrophilic ions between aqueous and organic phases are ubiquitous in biological and technological systems. These energetically unfavorable processes can be facilitated either by small molecules (ionophores) or by ion-transport proteins. In absence of a facilitating agent, ion-transfer reactions are assumed to be "simple", one-step processes. Our experiments at the nanometer-sized interfaces between water and neat organic solvents showed that the generally accepted one-step mechanism cannot explain important features of transfer processes for a wide class of ions including metal cations, protons, and hydrophilic anions. The proposed new mechanism of ion transfer involves transient interfacial ion paring and shuttling of a hydrophilic ion across the mixed-solvent layer. 相似文献
5.
KA Saeed FO Ayorinde BE Eribo M Gordon L Collier 《Rapid communications in mass spectrometry : RCM》1999,13(19):1951-1957
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used for the characterization of a partially transesterified poly(beta-hydroxyalkanoate), PHA, polymer produced by the bacterial strain Alcaligenes eutrophus using saponified vegetable oils as the sole carbon sources. The transesterification was carried out separately under acidic and basic conditions to obtain PHA oligomers weighing less than 10 kDa. The intact oligomers were detected in their cationized [M + Na](+) and [M + K](+) forms by MALDI-TOFMS. A composition analysis, using the MALDI-TOF spectra, indicate that the oligomers obtained via acid catalysis were terminated with a methyl 3-hydroxybutyrate end group, and those obtained by base catalysis had a methyl crotonate (olefinic) termination. In addition to HB (hydroxy butyrate), the oligomers were found to contain a small percentage of HV (hydroxy valerate). This was independently confirmed using gas chromatography/mass spectrometry (GC/MS). In comparison, the analysis of a commercial PHA polymer, transesterified under identical conditions, only showed the presence of HB, i.e. a pure PHB homopolymer. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
6.
Patrícia Matias José Manuel Lopes Sébastien Laforge Patrick Magnoux Michel Guisnet Fernando Ram?a Ribeiro 《Reaction Kinetics and Catalysis Letters》2008,95(1):193-201
The main features of methylcyclohexane (mch) and n-heptane (n-C7) transformation at 350°C were compared for fresh samples of HMWW, HMFI and HFAU zeolites. With both reactions, the behavior
of HMWW was between those of the medium HMFI and large pore HFAU zeolites. Thus, the values of turnover frequency (TOF) and
of the TOFmch/n-C7 ratio were similar with HMWW and HMFI and much higher with HFAU. In contrast, small differences were found between product
distributions over HMWW and HFAU but large differences between HMWW and HMFI. These observations can be explained by alkane
transformation in the large supercages with 10-MR apertures of HMWW: the narrow apertures limit diffusion of the mch within
the supercages, but not the diffusion of the products which are therefore typical of the transformation within large cages
hence without any steric limitation. 相似文献
7.
8.
Nanopipet voltammetry was used for the first study of ion transfer (IT) reactions between aqueous solutions and neat organic solvents. An extremely wide ( approximately 10 V) polarization window obtained with no electrolyte added to the organic phase allows one to probe charge transfer reactions, which are not normally accessible by electrochemical techniques, for example, the transfer of l-alaninamide cation from water to 1,2-dichloroethane (DCE). While anions (e.g., chloride) and relatively hydrophobic cations (e.g., tetraalkylammonium ions) can be transferred from water to less polar neat solvents such as DCE, the transfers of strongly hydrated metal cations occur only in the presence of organic supporting electrolyte. 相似文献
9.
Laforge FO Kakiuchi T Shigematsu F Mirkin MV 《Langmuir : the ACS journal of surfaces and colloids》2006,22(25):10705-10710
Molecular partitioning and electron-transfer kinetics have been studied at the ionic liquid/water (IL/water) interface by scanning electrochemical microscopy (SECM). The ionic liquid C8mimC1C1N is immiscible with water and forms a nonpolarizable interface when in contact with it. Partitioning of ferrocene (Fc) across the IL/water interface was studied by SECM and found to be kinetically fast with a partition coefficient CIL/CW of 2400:1. The partition coefficient value was measured by SECM under quasi-steady-state conditions without waiting for complete solute equilibration. To investigate the kinetics of the electron transfer (ET) between aqueous ferricyanide and Fc dissolved in IL, a new approach to the analysis of the SECM current-distance curves was developed to separate the contributions of Fc partitioning and the ET reaction to the tip current. Several combinations of different aqueous and nonaqueous redox species were investigated; however, only the Fc/Fe(CN)63- system behaved according to the Butler-Volmer formalism over the entire accessible potential range. 相似文献
10.
The fundamentals of and recent advances in scanning electrochemical microscopy (SECM) are described. The focus is on applications of this method to studies of systems and processes of active current interest ranging from nanoelectrochemistry to electron transfer reactions and electrocatalysis to biological imaging. 相似文献