排序方式: 共有24条查询结果,搜索用时 15 毫秒
1.
Gamini Gunawardena Derek Pletcher Anjam Razaq 《Journal of Electroanalytical Chemistry》1984,164(2):363-367
Cyclic voltammetry and potential step techniques have been used to study the electrodeposition of indium metal from 1 mol dm?3 potassium chloride, pH 2–4.5, onto a vitreous carbon electrode. It is confirmed that the In/In3+ couple is fast in chloride media and the nucleation and growth of the indium phase is discussed. It is shown that instantaneous nucleation occurs at an overpotential of only a few mV and that the growth of the nuclei is three dimensional. 相似文献
2.
A whole-protein tandem mass spectrometry approach for protein identification based on precursor ion charge state concentration via ion/ion reactions, ion-trap collisional activation, ion/ion proton-transfer reactions involving the product ions, and mass analysis over a narrow m/z range (up to m/z 2000) is described and evaluated. The experiments were carried out with a commercially available electrospray ion-trap instrument that has been modified to allow for ion/ion reactions. Reaction conditions and the approach to searching protein databases were developed with the assumption that the resolving power of the mass analyzer is insufficient to distinguish charge states on the basis of the isotope spacings. Ions derived from several charge states of cytochrome c, myoglobin, ribonuclease A, and ubiquitin were used to evaluate the approach for protein identification and to develop a two-step procedure to database searching to optimize specificity. The approach developed with the model proteins was then applied to whole cell lysate fractions of Saccharomyces cerevisiae. The results are illustrated with examples of assignments made for three a priori unknown proteins, each selected randomly from a lysate fraction. Two of the three proteins were assigned to species present in the database, whereas one did not match well any database entry. The combination of the mass measurement and the product ion masses suggested the possibility for the oxidation of two methionine residues of a protein in the database. The examples show that this limited whole-protein characterization approach can provide insights that might otherwise be lacking with approaches based on complete enzymatic digestion. 相似文献
3.
4.
The synthesis of protein hetero-complex ions via ion-ion reactions in the gas phase is demonstrated in a quadrupole ion trap. Bovine cytochrome c cations and bovine ubiquitin anions are used as reactant species in the stepwise construction of complexes containing as many as six protein sub-units. For any set of reactants, a series of competitive and consecutive reactions is possible. The yield of complex ions for any given sequence of reactions is primarily limited by the presence of competitive reactions. Proton transfer represents the most important competitive reaction that adversely affects protein complex synthesis. In the present data, proton transfer takes place most extensively in the first step of complex synthesis, when single protein sub-units are subjected to reaction with one another. Proton transfer is found to be less extensive when one of the reactants is a protein complex. The generation of hexameric hetero-complexes containing two cytochrome c molecules and four ubiquitin molecules is demonstrated with two different synthesis approaches. The first involved the initial reaction of several charge states of cytochrome c and several charges states of ubiquitin. The sequence of reactions in this example illustrates the array of possible competitive and consecutive reactions associated with even a relatively simple set of multiply charged reactants. The second approach involved the initial reaction of the 9(+) charge state of cytochrome c and the 5(-) charge state of ubiquitin. The latter approach highlights the utility of the multi-stage mass spectrometric (MS(n)) capabilities of the ion trap in defining reactant ion identities (i.e. charge states and polarities) so that synthesis reactions can be directed along a particular set of pathways. 相似文献
5.
6.
7.
S. Lederer H. Winter HP. Winter F. Aumayr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):505-511
The energy loss of hydrogen atoms with energies of 400
eV and 1 keV is studied in coincidence with the number of emitted
electrons during grazing scattering from atomically clean and flat
KI(001) and LiF(001) surfaces. The energy loss spectra for
specific numbers of emitted electrons are analyzed in terms of a
binary interaction model based on the formation of transient
negative ions via local capture of valence band electrons from
anion sites. Based on computer simulations we derive for this
interaction scenario probabilities for the production of surface
excitons, for electron loss to the conduction band of KI, for
emission of electrons, and for formation of negative hydrogen
ions. The pronounced differences of data obtained for the two
surfaces are attributed to the different electronic structures of
KI and LiF. 相似文献
8.
A compact 14.5GHz electron cyclotron resonance (ECR) ion source for the production of slow, multiply charged ions has been constructed,with the plasma-confining magnetic field produced exclusively by permanent magnets.Microwave power of up to 175W in the frequency range from 12.75 to 14.SGHz is transmitted from ground potential via a PTFE window into the water-cooled plasma chamber which can be equipped with an aluminum liner.The waveguide coupling system serves also as biased electrode,and two remotely-controlled gas inlet valves connected via an insulating break permit plasma operation in the gas- mixing mode.A triode extraction system sustains ion acceleration voltages between 1kV and 10kV.The ECR ion source is fully computer-controlled and can be remotely operated from any desired location via Ethernet. 相似文献
9.
Gamini Gunawardena Graham Hills Irene Montenegro Benjamin Scharifker 《Journal of Electroanalytical Chemistry》1982,138(2):255-271
The electrochemical nucleation of mercury on vitreous carbon from solutions of mercurous nitrate in aqueous KNO3 has beenstudied as a function of overpotential and mercurous ion concentration. The nucleation is predominantly progressive and the singlepotential step experiment leads to nuclear number densities and to steady state nucleation rate constants. The double potentialstep experiment is complicated by the progressive nature of the nucleation and largely invalidated by the resultant dispersion ofnuclear sizes. The interpretation of the transients from potentiostatic-galvanostatic and related pulse trains are also complicatedby the similar features and it is suggested that equilibrium steady state and non-steady properties of nucleating systems arebest studied at very small electrodes at which a single nucleus is formed. 相似文献
10.
Sté phane Gaubert Jeremy Gunawardena 《Transactions of the American Mathematical Society》2004,356(12):4931-4950
If is a nonnegative matrix whose associated directed graph is strongly connected, the Perron-Frobenius theorem asserts that has an eigenvector in the positive cone, . We associate a directed graph to any homogeneous, monotone function, , and show that if the graph is strongly connected, then has a (nonlinear) eigenvector in . Several results in the literature emerge as corollaries. Our methods show that the Perron-Frobenius theorem is ``really' about the boundedness of invariant subsets in the Hilbert projective metric. They lead to further existence results and open problems.