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Segev E Wyttenbach T Bowers MT Gerber RB 《Physical chemistry chemical physics : PCCP》2008,10(21):3077-3082
Evidence from cross section data indicates that ubiquitin +13 ions lose their secondary and tertiary structure in mass spectrometric experiments. These transitions from the folded state into the near linear final structure occur at the experimental temperatures on time scales that are far too long for conventional molecular dynamics simulations. In this study, an approach to mass spectrometric unfolding processes is developed and a detailed application to an ubiquitin +13 ion system is presented. The approach involves a sequence of molecular dynamics simulations at gradually increasing temperatures leading to identification of major intermediate states, and the unfolding pathway. The unfolding rate at any temperature can then be calculated by a Rice-Ramsperger-Kassel (RRK) approach. For ubiquitin +13, three interesting intermediate states were found and the final near linear geometry was computed. The several relevant energy barriers calculated for the process are in the range of 7 to 15 kcal mol(-1). The unfolding time scale at 300 K was computed to be 2 ms. Cross section calculations using a hard sphere scattering model were carried out for the final structure and found to be in good accord with the results of electrospray experiments supporting the theoretical model used. The approach employed here should be applicable to any other solvent-free protein system. 相似文献
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Ramnarayanan R Chan BC Salvitti MA Mallouk TE Falih FM Davis J Galloway DB Bare SR Willis RR 《Journal of combinatorial chemistry》2006,8(2):199-212
The synthesis and analysis of inorganic material combinatorial libraries by a directed-sorting, split-pool bead method was demonstrated. Directed-sorting, split-pool, metal-loaded libraries were synthesized by adsorbing metal salts (H2PtCl6, SnCl2, CuCl2, and NiCl2) and metal standards (Pt, Cu, Ni in HCl) onto 2-mg porous gamma-alumina beads in 96- or 384-well plates. A matrix algorithm for the synthesis of bead libraries treated each bead as a member of a row or column of a given matrix. Computer simulations and manual tracking of the sorting process were used to assess library diversity. The bead compositions were analyzed by energy-dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy, electron probe microanalysis, inductively coupled plasma atomic emission spectroscopy, and inductively coupled plasma mass spectroscopy. The metal-loaded beads were analyzed by laser-activated membrane introduction mass spectroscopy (LAMIMS) for catalytic activity using methylcyclohexane dehydrogenation to toluene as a probe reaction. The catalytic activity of individual beads that showed minimal (approximately 20% of that of Pt on alumina) to high conversion could be determined semiquantitatively by LAMIMS. This method, therefore, provides an alternative to screening using microreactors for reactors that employ catalysts in the form of beads. The directed-sorting method offers the potential for synthesis of focused libraries of inorganic materials through relatively simple benchtop split-pool chemistry. 相似文献
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Low-temperature metallic alloying of copper and silver nanoparticles with gold nanoparticles through digestive ripening 总被引:1,自引:0,他引:1
Smetana AB Klabunde KJ Sorensen CM Ponce AA Mwale B 《The journal of physical chemistry. B》2006,110(5):2155-2158
We describe a remarkable and simple alloying procedure in which noble metal intermetallic nanoparticles are produced in gram quantities via digestive ripening. This process involves mixing of separately prepared colloids of pure Au and pure Ag or Cu particles and then heating in the presence of an alkanethiol under reflux. The result after 1 h is alloy nanoparticles. Particles synthesized according to this procedure were characterized by UV-vis spectroscopy, EDX analysis, and high-resolution electron microscopy, the results of which confirm the formation of alloy particles. The particles of 5.6+/-0.5 nm diameter for Au/Ag and 4.8+/-1.0 nm diameter for Cu/Au undergo facile self-assembly to form 3-D superlattice ordering. It appears that during this digestive ripening process, the organic ligands display an extraordinary chemistry in which atom transfer between atomically pure copper, silver, and gold metal nanoparticles yields monodisperse alloy nanoparticles. 相似文献
297.
A subset U of a group G is called k-universal if U contains a translate of every k-element subset of G. We give several nearly optimal constructions of small k-universal sets, and use them to resolve an old question of Erdős and Newman on bases for sets of integers, and to obtain
several extensions for other groups. 相似文献
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Dr. Laura M. McCaslin Dr. Andreas W. Götz Prof. Mark A. Johnson Prof. R. Benny Gerber 《Chemphyschem》2023,24(5):e202300085
The reaction of N2O5 at atmospheric interfaces has recently received considerable attention due to its importance in atmospheric chemistry. N2O5 reacts preferentially with Cl− to form ClNO2/NO3− (Cl− substitution), but can also react with H2O to form 2HNO3 (hydrolysis). In this paper, we explore these competing reactions in a theoretical study of the clusters N2O5/Cl−/nH2O (n=2–5), resulting in the identification of three reaction motifs. First, we uncovered an SN2-type Cl− substitution reaction of N2O5 that occurs very quickly due to low barriers to reaction. Second, we found a low-lying pathway to hydrolysis via a ClNO2 intermediate (two-step hydrolysis). Finally, we found a direct hydrolysis pathway where H2O attacks N2O5 (one-step hydrolysis). We find that Cl− substitution is the fastest reaction in every cluster. Between one-step and two-step hydrolysis, we find that one-step hydrolysis barriers are lower, making two-step hydrolysis (via ClNO2 intermediate) likely only when concentrations of Cl− are high. 相似文献