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991.
J Jornet-Somoza B Lasorne MA Robb HD Meyer D Lauvergnat F Gatti 《The Journal of chemical physics》2012,137(8):084304
In a previous work [B. Lasorne, M. A. Robb, H.-D. Meyer, and F. Gatti, "The electronic excited states of ethylene with large-amplitude deformations: A dynamical symmetry group investigation," Chem. Phys. 377, 30-45 (2010); and ibid. 382, 132 (2011) (Erratum)], we investigated the electronic structure of ethylene (ethene, C(2)H(4)) in terms of 17 dominant configurations selected at the multiconfiguration self-consistent field level of theory. These were shown to be sufficient to recover most of the static electron correlation among the first valence and Rydberg states at all geometries. We also devised a strategy to build a 17-quasidiabatic-state matrix representation of the electronic Hamiltonian for curvilinear coordinates using dynamical symmetry. Here, we present fitted surfaces in the form of a generalised vibronic-coupling Hamiltonian model for two nuclear coordinates, CC bond stretching and torsion. Dynamic electron correlation is included into the electronic structure to improve the energetics of the Rydberg states at the multireference configuration interaction level of theory. The chemical interpretation of the adiabatic states of interest does not change qualitatively, which validates our choice of underlying quasidiabatic states in the model. The absorption spectrum is calculated with quantum dynamics and partially assigned. This first two-dimensional model shows a surprisingly good agreement with the experimental spectrum. 相似文献
992.
C Lescot B Darses F Collet P Retailleau P Dauban 《The Journal of organic chemistry》2012,77(17):7232-7240
Transition-metal-catalyzed C-H amination via nitrene insertion allows the direct transformation of a C-H into a C-N bond. Given the ubiquity of C-H bonds in organic compounds, such a process raises the problem of regio- and chemoselectivity, a challenging goal even more difficult to tackle as the complexity of the substrate increases. Whereas excellent regiocontrol can be achieved by the use of an appropriate tether securing intramolecular addition of the nitrene, the intermolecular C-H amination remains much less predictable. This study aims at addressing this issue by capitalizing on an efficient stereoselective nitrene transfer involving the combination of a chiral aminating agent 1 with a chiral rhodium catalyst 2. Allylic C-H amination of terpenes and enol ethers occurs with excellent yields as well as with high regio-, chemo-, and diastereoselectivity as a result of the combination of steric and electronic factors. Conjugation of allylic C-H bonds with the π-bond would explain the chemoselectivity observed for cyclic substrates. Alkanes used in stoichiometric amounts are also efficiently functionalized with a net preference for tertiary equatorial C-H bonds. The selectivity, in this case, can be rationalized by steric and hyperconjugative effects. This study, therefore, provides useful information to better predict the site of C-H amination of complex molecules. 相似文献
993.
Three-component reactions of oxetan-3-ones with isocyanides and carboxylic acids produce 3,3-disubstituted oxetanes in good yields. Good levels of diastereocontrol (dr = 4:1) can be achieved in these Passerini reactions when the oxetane nucleus possesses a bulky cyclohexyl substituent at C–2. The (2S1,3R1)-stereochemistry of the major diastereomer was confirmed by X-ray crystallography after ester hydrolysis, and a possible mechanism to account for the diastereofacial selectivity is presented. 相似文献
994.
The comparison of proteins separated on 2DE is difficult due to gel-to-gel variability. Here, a method named comparative fluorescence gel electrophoresis (CoFGE) is presented, which allows the generation of an artificial protein grid in parallel to the separation of an analytical sample on the same gel. Different fluorescent stains are used to distinguish sample and marker on the gel. The technology combines elements of 1DE and 2DE. Special gel combs with V-shaped wells are placed in a stacking gel above the pI strip. Proteins separated on the pI strip are electrophoresed at the same time as marker proteins (commercially available purified protein of different molecular weight) placed in V-wells. In that way, grids providing approximately 100 nodes as landmarks for the determination of protein spot coordinates are generated. Data analysis is possible with commercial 2DE software capable of warping. The method improves comparability of 2DE protein gels, because they are generated in combination with regular in-gel anchor points formed by protein standards. This was shown here for two comparative experiments with three gels each using Escherichia coli lysate. For a set of 47 well-defined samples spots, the deviation of the coordinates was improved from 7% to less than 1% applying warping using the marker grid. Conclusively, as long as the same protein markers, the same size of pI-strips and the same technology are used, gel matching is reproducibly possible. This is an important advancement for projects involving comparison of 2DE-gels produced over several years and in different laboratories. 相似文献
995.
Benjamin Heuwers Dominik Quitmann Frank Katzenberg Joerg C. Tiller 《Macromolecular rapid communications》2012,33(18):1517-1522
Lightly cross‐linked natural rubber (NR, cis‐1,4‐polyisoprene) was found to be an exceptional cold programmable shape memory polymer (SMP) with strain storage of up to 1000%. These networks are stabilized by strain‐induced crystals. Here, we explore the influence of mechanical stress applied perpendicular to the elongation direction of the network on the stability of these crystals. We found that the material recovers its original shape at a critical transverse stress. It could be shown that this is due to a disruption of the strain‐stabilizing crystals, which represents a completely new trigger for SMPs. The variation of transverse stress allows tuning of the trigger temperature Ttrig(σ) in a range of 45 to 0 °C, which is the first example of manipulating the transition of a crystal‐stabilized SMP after programming. 相似文献
996.
Bythell BJ Hendrickson CL Marshall AG 《Journal of the American Society for Mass Spectrometry》2012,23(4):644-654
We report the use of unimolecular dissociation by infrared radiation for gaseous multiphoton energy transfer to determine
relative activation energy (Ea,laser) for dissociation of peptide sequence ions. The sequence ions of interest are mass-isolated; the entire ion cloud is then
irradiated with a continuous wave CO2 laser, and the first order rate constant, kd, is determined for each of a series of laser powers. Provided these conditions are met, a plot of the natural logarithm of
kd versus the natural logarithm of laser power yields a straight line, whose slope provides a measure of Ea,laser. This method reproduces the Ea values from blackbody radiative dissociation (BIRD) for the comparatively large, singly and doubly protonated bradykinin
ions (nominally y
9
and y
9
2+
). The comparatively small sequence ion systems produce Ea,laser values that are systematic underestimates of theoretical barriers calculated with density functional theory (DFT). However,
the relative Ea,laser values are in qualitative agreement with the mobile proton model and available theory. Additionally, novel protonated cyclic-dipeptide
(diketopiperazine) fragmentation reactions are analyzed with DFT. FT-ICR MS provides access to sequence ions generated by
electron capture dissociation, infrared multiphoton dissociation, and collisional activation methods (i.e., b
n
, y
m
, c
n
, z
m
•
ions). 相似文献
997.
Pittman JJ Manard BT Kowalski PJ Marcus RK 《Journal of the American Society for Mass Spectrometry》2012,23(1):102-107
Polypropylene (PP) capillary-channeled polymer (C-CP) films have parallel, μm-sized channels that induce solution wicking
via capillary action. Efficient mass transport from the solution phase to the channel surface leads to adsorption of hydrophobic
protein solutes. The basic premise by which C-CP films can be used as media to manipulate analyte solutions (e.g., proteins
in buffer), for the purpose of desalting or chromatographic separation prior to MALDI-MS analysis is presented here. Cytochrome
c and myoglobin prepared in a Tris-HCl buffer, and ribonuclease A, lysozyme, and transferrin prepared in phosphate buffered
saline (PBS), are used as the test solutions to demonstrate the desalting concept. Protein analysis is performed after deposition
on a C-CP film with and without a water washing step, followed by spray deposition of a typical sinapinic acid matrix. Extracted
MALDI mass spectra exhibit much improved signal-to-noise characteristics after water washing. A mixture of cytochrome c and myoglobin (2 μL of 2.5 μM each in Tris-HCl buffer) was applied, washed with water and spatially separated via simple
capillary action (wicking) using a reversed-phase solvent composition of 0.1% trifluoroacetic acid (TFA) in 50:50 acetonitrile
(ACN):H2O. Subsequent application of sinapinic acid followed by imaging of the film using MALDI-MS reveals that as the protein solution
is wicked down the film, separation occurs. 相似文献
998.
In headspace (HS) analysis, a fumigant is released from a commodity into a gas-tight container by grinding, heating, or microwaves. A new technique uses HS-solid-phase microextraction (SPME) for additional preconcentration of fumigant. HS-SPME was tested for detection of phosphine (PH3), chosen for examination because of its wide use on stored commodities. PH3 was applied to 50 g wheat in separate 250 mL sealed flasks, which were equipped either with a septum for conventional HS analysis or with one of four HS-SPME fibers [100 microm polydimethylsiloxane (PDMS), 85 microm carboxen (CAR)/PDMS, 75 microm CAR/PDMS, and 65 pm PDMS/divinylbenzene (DVB)]. The wheat was heated at 45 degrees C for 20 min. In conventional HS analysis, a gaseous aliquot (80 pL) was taken from the HS and injected into the GC instrument. In the HS-SPME procedure, the fiber was removed from the HS and exposed in the heated injection port of the GC instrument. In all cases, PH3 was determined under the same chromatographic conditions with a GC pulsed flame photometric detector. In a comparison of the efficacy of the fibers, the bipolar fibers (CAR/PDMS and PDMS/DVB) contained more PH3 than the aliquot in the conventional HS analysis; larger size bipolar fibers extracted PH3 more efficiently than smaller fibers (e.g., 85 > 75 > 65 microm). The nonpolar fiber (PDMS) contained no PH3. Four fortification levels of PH3 on wheat were tested: 0.01, 0.05, 0.1, and 0.3 microg/g. The response of each bipolar fiber increased with the fortification levels, but the conventional HS analysis detected no fumigant at the lowest fortification level of 0.01 mg/g. Under the conditions of the validation study, the LOD was in the range of 0.005-0.01 ng PH3/g wheat. 相似文献
999.
Creating first-in-class medications to treat human disease is an extremely challenging endeavor. While genome sequencing and genetics are making direct connections between mutations and human disorders at an unprecedented rate, matching molecular targets with a suitable therapeutic indication must ultimately be achieved by pharmacology. Here, we discuss how the integration of chemical proteomic platforms (such as activity-based protein profiling) into the earliest stages of the drug discovery process has the potential to greatly expand the scope of proteins that can be pharmacologically evaluated in living systems, and, through doing so, promote the identification and prioritization of new therapeutic targets. 相似文献
1000.
Rosario-Amorin D Duesler EN Paine RT Hay BP Delmau LH Reilly SD Gaunt AJ Scott BL 《Inorganic chemistry》2012,51(12):6667-6681
A four-step synthesis for 4,6-bis(diphenylphosphinoylmethyl)dibenzofuran (4) from dibenzofuran and a two-step synthesis for 4,6-bis(diphenylphosphinoyl)dibenzofuran (5) are reported along with coordination chemistry of 4 with In(III), La(III), Pr(III), Nd(III), Er(III), and Pu(IV) and of 5 with Er(III). Crystal structure determinations for the ligands, 4·CH(3)OH and 5, the 1:1 complexes [In(4)(NO(3))(3)], [Pr(4)(NO(3))(3)(CH(3)CN)]·0.5CH(3)CN, [Er(4)(NO(3))(3)(CH(3)CN)]·CH(3)CN, [Pu(4)Cl(4)]·THF and the 2:1 complex [Nd(4)(2)(NO(3))(2)](2)(NO(3))(2)·(H(2)O)·4(CH(3)OH) are described. In these complexes, ligand 4 coordinates in a bidentate POP'O' mode via the two phosphine oxide O-atoms. The dibenzofuran ring O-atom points toward the central metal cations, but in every case it is more than 4 ? from the metal. A similar bidentate POP'O' chelate structure is formed between 5 and Er(III) in the complex, {[Er(5)(2)(NO(3))(2)](NO(3))·4(CH(3)OH)}(0.5), although the nonbonded Er···O(furan) distance is reduced to ~3.6 ?. The observed bidentate chelation modes for 4 and 5 are consistent with results from molecular mechanics computations. The solvent extraction performance of 4 and 5 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions is described and compared against the extraction behavior of n-octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (OΦDiBCMPO) measured under identical conditions. 相似文献