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101.
Lindsay J. Morrison Jake A. Rosenberg Jonathan P. Singleton Jennifer S. Brodbelt 《Journal of the American Society for Mass Spectrometry》2016,27(9):1443-1453
Dissociation of proteins and peptides by 193 nm ultraviolet photodissociation (UVPD) has gained momentum in proteomic studies because of the diversity of backbone fragments that are produced and subsequent unrivaled sequence coverage obtained by the approach. The pathways that form the basis for the production of particular ion types are not completely understood. In this study, a statistical approach is used to probe hydrogen atom elimination from a + 1 radical ions, and different extents of elimination are found to vary as a function of the identity of the C-terminal residue of the a product ions and the presence or absence of hydrogen bonds to the cleaved residue. 相似文献
102.
Catarina IV Ramos Flávio Figueira Marcelo D Polêto Francisco ML Amado Hugo Verli João PC Tomé M Graça PMS Neves 《Journal of mass spectrometry : JMS》2016,51(5):342-349
Electrospray mass spectrometry/mass spectrometry was used to investigate the gas‐phase properties of protonated expanded porphyrins, in order to correlate those with their structure and conformation. We have selected five expanded meso‐pentafluorophenyl porphyrins, respectively, a pair of oxidized/reduced fused pentaphyrins (22 and 24 π electrons), a pair of oxidized/reduced regular hexaphyrins (26 and 28 π electrons) and a regular doubly N‐fused hexaphyrin (28 π electrons). The gas‐phase behavior of the protonated species of oxidized and reduced expanded porphyrins is different. The oxidized species (aromatic Hückel systems) fragment more extensively, mainly by the loss of two HF molecules. The reduced species (Möbius aromatic or Möbius‐like aromatic systems) fragment less than their oxidized counterparts because of their increased flexibility. The protonated regular doubly fused hexaphyrin (non‐aromatic Hückel system) shows the least fragmentation even at higher collision energies. In general, cyclization through losses of HF molecules decreases from the aromatic Hückel systems to Möbius aromatic or Möbius‐like aromatic systems to non‐aromatic Hückel systems and is related to an increase in conformational distortion. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
103.
Julie A. Spencer Samantha G. Rosenberg Michael Barclay Yung-Chien Wu Lisa McElwee-White D. Howard Fairbrother 《Applied Physics A: Materials Science & Processing》2014,117(4):1631-1644
Standard practice in electron beam-induced deposition (EBID) is to use precursors designed for thermal processes, such as chemical vapor deposition (CVD). However, organometallic precursors that yield pure metal deposits in CVD often create EBID deposits with high levels of organic contamination. This contamination negatively impacts the deposit’s properties (e.g., by increasing resistivity or decreasing catalytic activity) and severely limits the range of potential applications for metal-containing EBID nanostructures. To provide the information needed for the rational design of precursors specifically for EBID, we have employed an ultra-high vacuum (UHV) surface science approach to identify the elementary reactions of organometallic precursors during EBID. These UHV studies have demonstrated that the initial electron-induced deposition of the surface-bound organometallic precursors proceeds through desorption of one or more of the ligands present in the parent compound. In specific cases, this deposition step has been shown to proceed via dissociative electron attachment, involving low-energy secondary electrons generated by the interaction of the primary beam with the substrate. Electron beam processing of the surface-bound species produced in the initial deposition event usually causes decomposition of the residual ligands, creating nonvolatile fragments. This process is believed to be responsible for a significant fraction of the organic contaminants typically observed in EBID nanostructures. A few ligands (e.g., halogens) can, however, desorb during electron beam processing while other ligands (e.g., PF3, CO) can thermally desorb if elevated substrate temperatures are used during deposition. Using these general guidelines for reactivity, we propose some design strategies for EBID precursors. The ultimate goal is to minimize organic contamination and thus overcome the key bottleneck for fabrication of relatively pure EBID nanostructures. 相似文献
104.
This perspective report summarizes recent work on the interactions of the triosmium clusters of general formula Os(3)(CO)(9)(μ(3)-η(2)-L-H)(μ-H) (L = bicyclic benzoheterocycle) with DNA and proteins. The early work focused on how the structure of the benzoheterocycle influenced the binding of the cluster to plasmid DNA, albumin and the inhibition of telomerase. Later, selective binding of the triosmium clusters to guanine was targeted using a range of alkylating functionalities. In connection with these efforts some very recent unpublished work will be presented. Suggestions for future directions in this area and a summary of the problems and difficulties encountered will be discussed. 相似文献
105.
Defects in room-temperature ferromagnetic Cu-doped ZnO films probed by x-ray absorption spectroscopy
We report a comprehensive study of the defects in room-temperature ferromagnetic (RTFM) Cu-doped ZnO thin films using x-ray absorption spectroscopy. The films are doped with 2 at.% Cu, and are prepared by reactive magnetron sputtering (RMS) and pulsed laser deposition (PLD), respectively. The results reveal unambiguously that atomic point defects exist in these RTFM thin films. The valence states of the Cu ions in both films are 2(+). In the film prepared by PLD, the oxygen vacancies (V(O)) form around both Zn ions and Cu ions in the hexagonal wurtzite structure. Upon annealing of the film in O(2), the V(O) population reduces and so does the RTFM. In the film prepared by RMS, the V(O)s around Cu ions are not detected, and the V(O) population around Zn ions is also smaller than in the PLD-prepared film. However, zinc vacancies (V(Zn)) are evidenced. Given the low doping level of spin-carrying Cu ions, these results provide strong support for defect-mediated ferromagnetism in Cu-doped ZnO thin films. 相似文献
106.
Tibor Hianik Martin Fajkus Pavol Tomcik Ivan Rosenberg Pavol Kois Julius Cirak Joseph Wang 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):141-149
Summary. The method of electrostriction was applied to supported bilayer lipid membranes (sBLM) and Langmuir monolayers with the aim to study the peculiarities of the interaction of short oligonucleotides with lipid films and of the
duplex formation between complementary oligonucleotides. The bilayer lipid membranes (sBLM) were formed on an agar support,
whereas Langmuir monolayers were generated on the air-water interface. As an oligonucleotide, the 15-mer 5′-cholesterolphosphoryl-dT15 (CHpdT15) was synthesized. We could show that the interaction of CHpdT15 with sBLM resulted in a considerable increase of the elasticity modulus perpendicular to the membrane plane (E
⊥) and an increase of the surface potential. Interaction of complementary oligodeoxyadenylate (dA15) with sBLM modified by CHpdT15 resulted in a slight increase of the surface potential whereas E
⊥ slightly decreased. CHpdT15 forms monomolecular layers on the air/water interface. Interaction of dA15 with such monolayers resulted in an increase of the surface pressure, probably due to an increase of the surface charge of
the monolayer; similar effects were observed for lipid monolayers modified by CHpdT15. Prospects of using such interactions for detecting DNA hybridization are discussed.
Received June 23, 2000. Accepted (revised) September 19, 2000 相似文献
107.
C. Haberhauer-Troyer M. Crnoja E. Rosenberg M. Grasserbauer 《Analytical and bioanalytical chemistry》2000,366(4):329-331
The surfaces of commercially available polydimethylsiloxane (PDMS) and Carboxen-PDMS fibers for solid-phase microextraction
(SPME) were investigated by optical and electron microscopy. Damage to the coating as well as contamination of new fibers
and a highly variable number of pores in Carboxen-PDMS coatings were observed. Together with the contamination of the fibers
during their use with metallic particles originating from the SPME fiber holder they are possible explanations for the problems
encountered in the analysis of organolead, organotin and organosulfur compounds, such as artifact formation and low repeatability.
Received: 2 August 1999 / Revised: 5 October 1999 / Accepted: 6 October 1999 相似文献
108.
We consider two person zero-sum stochastic games. The recursive formula for the valuesvλ (resp.v
n) of the discounted (resp. finitely repeated) version can be written in terms of a single basic operator Φ(α,f) where α is the weight on the present payoff andf the future payoff. We give sufficient conditions in terms of Φ(α,f) and its derivative at 0 for limv
n and limvλ to exist and to be equal.
We apply these results to obtain such convergence properties for absorbing games with compact action spaces and incomplete
information games. 相似文献
109.
G. A. Zachariadis N. M. Tzollas M. Nikolaou E. Rosenberg 《Biomedical chromatography : BMC》2013,27(3):299-305
A headspace solid‐phase micro‐extraction (HS‐SPME) method was employed in order to study the effect of storage conditions of human urine samples spiked with tributyltin (TBT) using gas chromatography and mass spectrometry. To render the analyte more volatile, the derivatization (ethylation) was made in situ by sodium tetraethylborate (NaBEt4), which was added directly to dilute unpreserved urine samples and in buffers of similar acidity. The stability of TBT in human urine matrix was compared with the stability of TBT in buffer solutions of similar pH value. Critical parameters of storage conditions such as temperature and time, which affect the stability of TBT in this kind of matrix, were examined extensively. The tests showed that the stability of TBT remains practically satisfactory for a maximum of 2 days of storage either at +4 or 20°C. Greater variations were observed in the concentration of TBT in human urine samples at +4°C and lower ones at ?20°C over a month's storage. The freeze–thaw cycles have negative effect on the stability and should be kept to a minimum. The results from spiked urine samples are also discussed in comparison to those acquired from buffer solutions of equal TBT concentration. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
110.