排序方式: 共有43条查询结果,搜索用时 15 毫秒
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Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Halling AM Jedicke R Karchin PE Kwan S Leuking LH Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review D: Particles and fields》1994,49(9):R4317-R4320
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Alves GA Amato S Anjos JC Appel JA Astorga J Bracker SB Cremaldi LM Dagenhart WD Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Karchin PE Kennedy C Kwan S Lueking LH de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Passmore D Rafatian A dos Reis AC Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wallace A Wu Z 《Physical review letters》1996,77(12):2388-2391
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Alves GA Amato S Anjos JC Appel JA Bracker SB Cremaldi LM Darling CL Dixon RL Errede D Fenker HC Gay C Green DR Jedicke R Kaplan D Karchin PE Kwan S Leedom I Lueking LH Luste GJ Mantsch PM de Mello Neto JR Metheny J Milburn RH de Miranda JM da Motta Filho H Napier A Rafatian A dos Reis AC Reucroft S Ross WR Santoro AF Sheaff M Souza MH Spalding WJ Stoughton C Streetman ME Summers DJ Takach SF Wu Z 《Physical review letters》1993,70(6):722-725
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Prof. Li Chen Genevieve E. Mullen Myriam Le Roch Cody G. Cassity Prof. Nicolas Gouault Prof. Henry Y. Fadamiro Prof. Robert E. Barletta Prof. Richard A. O'Brien Prof. Richard E. Sykora Prof. Alexandra C. Stenson Prof. Kevin N. West Howard E. Horne Jeffrey M. Hendrich Kang Rui Xiang Prof. James H. Davis Jr. 《Angewandte Chemie (International ed. in English)》2014,53(44):11762-11765
The practical utility of ionic liquids (ILs) makes the absence (heretofore) of reported examples from nature quite puzzling, given the facility with which nature produces many other types of exotic but utilitarian substances. In that vein, we report here the identification and characterization of a naturally occurring protic IL. It can be formed during confrontations between the ants S. invicta and N. fulva. After being sprayed with alkaloid‐based S. invicta venom, N. fulva detoxifies by grooming with its own venom, formic acid. The mixture is a viscous liquid manifestly different from either of the constituents. Further, we find that the change results as a consequence of formic acid protonation of the N centers of the S. invicta venom alkaloids. The resulting mixed‐cation ammonium formate milieu has properties consistent with its classification as a protic IL. 相似文献
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Alexandra C. Stenson 《Rapid communications in mass spectrometry : RCM》2009,23(4):465-476
The interaction between metals and naturally occurring humic substances and the thereby induced issues of bioavailability and hydrogeochemical turnover of metal ions in natural waters have been the subject of intense study for decades. Traditional bulk techniques to investigate metal‐humic binding (e.g. potentiometry and inductively coupled plasma mass spectrometry (ICP‐MS)) can provide quantitative results for the relative abundance and distribution of metal species in humic samples and/or overall binding constants. The shortcoming of these bulk techniques is the absence of structural detail. Ultra‐high‐resolution mass spectrometry, currently the only technique demonstrated to resolve individual humic ions, is not generally employed to provide the missing qualitative information primarily because the identification of metal complexes within the already complex mixtures of humic substances is non‐trivial and time‐consuming to the extent of eliminating any possibility for real‐time manipulation of chelated analytes. Here, it is demonstrated that with tailored selection of the metal ion, it is possible to visually identify large numbers of metal‐humic complexes (~500 for Be2+, ~1100 for Mn2+, and ~1500 for Cr3+) in real‐time as the spectra are being acquired. Metal ions are chosen so that they form primarily even‐m/z complexes with humic ions. These even‐m/z complexes stand out in the spectrum and can readily be characterized based on molecular formulae, which here revealed for example that Suwannee River fulvic acid (SRFA) complexes encompassed primarily highly oxygenated fulvic acids of relatively low double‐bond equivalence. Facile, real‐time identification of even‐m/z metal‐humic complexes additionally allows for the specific selection of metal‐humic complexes for MSn analysis and in‐trap ion‐neutral reactions enabling investigation of metal‐humic complex structure. MS/MS data were collected to demonstrate the potential of the technique as well as highlight some of the remaining challenges. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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A.?I.?DanilovEmail author R.?R.?Nazmutdinov T.?T.?Zinkicheva E.?B.?Molodkina A.?V.?Rudnev Yu.?M.?Polukarov J.?M.?Feliu 《Russian Journal of Electrochemistry》2008,44(6):697-708
Mechanism of copper underpotential deposition at stepped faces of platinum single crystals Pt(hkl) is studied using cyclic voltammetry, scanning probe microscopy, and quantum-chemical modelling. It is shown that the first stage of UPD is one-dimensional decoration of the (100)- or (110)-orientated steps, then copper monolayer forms at (111)-terraces. The final stage is the secondary step decoration. Quantum-chemical modelling, with the using of long-distance potentials of the Cu-Pt and Cu-Cu pair interactions, allows estimating the energy of copper adsorption at different structure elements of the substrate (steps, kinks, terraces) and revealing the succession of the adatom monolayer formation; it also provides additional information for the identifying of the nature of voltametric peaks for different stages of the copper adsorption-desorption. 相似文献
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Kojic acid (5-hydroxy-2-hydroxymethyl-4-pyrone) is known to have a high affinity for transition metals, and it and its derivatized cogeners are used both analytically and clinically. The interactions between kojic acid (KA) and eleven +3 metals (Al(+3), As(+3), Cr(+3), Ga(+3), Fe(+3), In(+3), Yb(+3), Y(+3), Gd(+3), Nd(+3), La(+3)) were examined by electrospray ionization mass spectrometry (ESI-MS) using an ion trap in an aqueous medium. For a subset of five ions, Fourier transform ion cyclotron resonance (FTICR)-MS was conducted to provide accurate mass confirmation of peak assignments for metals having clustering of abundant isotopes. KA readily formed complexes with all the metal ions tested. The most common complexes observed were ML(3)H(+) and M(2)L(5). Different behavior was seen for small and large ionic radius ions, with a relative cut-off between In(+3) ( approximately 80 pm) and Yb(+3) ( approximately 87 pm); a striking trend in % collision energy vs. cluster complexity was revealed. The KA-Cr(+3)complex shows a high affinity for H(2)O molecules in the gas phase, whilst In(+3) shows a preference for dimetal complexes and Y(+3) a deviant behavior when complexed to two neutrals. 相似文献
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Katona BW Rath NP Anant S Stenson WF Covey DF 《The Journal of organic chemistry》2007,72(24):9298-9307
Deoxycholic acid (DCA) is an endogenous secondary bile acid implicated in numerous pathological conditions including colon cancer formation and progression and cholestatic liver disease. DCA involvement in these disease processes results partly from its ability to modulate signaling cascades within the cell, presumably through both direct receptor activation and general detergent mediated membrane changes. To further explore DCA induced changes in cell signaling, we completed a total synthesis of enantiomeric deoxycholic acid (ent-DCA) from achiral 2-methyl-1,3-cyclopentanedione. Using a modified method of the synthesis of ent-testosterone that proceeds through the (R)-(-)-Hajos-Parrish ketone, we have completed the successful synthesis of ent-DCA in 25 steps with a yield of 0.3% with all stereochemical assignments of the product confirmed by X-ray crystallography. Our studies toward this synthesis also uncovered the methodology for the development of a novel A,B-cis steroidal skeleton system containing a C3-C9 single bond as well as conditions to selectively ketalize the typically less reactive 12-carbonyl in poly-keto A,B-cis androgens. The critical micelle concentration (cmc) of ent-DCA, determined by a dye solubilization method, was identical to the cmc of natural DCA. Toxicity studies toward HT-29 and HCT-116 human colon cancer cell lines demonstrated that ent-DCA had similar effects on proliferation, yet showed a markedly decreased ability to induce apoptosis as compared to natural DCA. 相似文献