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801.
Siu CK Ke Y Orlova G Hopkinson AC Michael Siu KW 《Journal of the American Society for Mass Spectrometry》2008,19(12):1799-1807
Dissociations at the N-Cα bond of tryptophan and tyrosine residues are the prevalent pathways in the fragmentations of radical cations of tripeptides
that contain such as residues. This process involves a proton transfer from the β-carbon of the tryptophan or tyrosine residue to the carbonyl oxygen of the amide group, followed by cleavage of the N-Cα bond, generating low-lying proton-bound dimers that dissociate to give each an ionic and a neutral product. Formation of
the [z
n
−H]∢+ or [c
n
+2H]+ ion is a competition between the two incipient fragments for the proton in a dissociating proton-bound dimer. 相似文献
802.
Blagojevic V Bozović A Orlova G Bohme DK 《The journal of physical chemistry. A》2008,112(41):10141-10146
Twenty-five atomic cations, M (+), that lie within the thermodynamic window for O-atom transport catalysis of the oxidation of hydrogen by nitrous oxide, have been checked for catalytic activity at room temperature with kinetic measurements using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. Only 4 of these 25 atomic cations were seen to be catalytic: Fe (+), Os (+), Ir (+), and Pt (+). Two of these, Ir (+) and Pt (+), are efficient catalysts, while Fe (+) and Os (+) are not. Eighteen atomic cations (Cr (+), Mn (+), Co (+), Ni (+), Cu (+), Ge (+), Se (+), Mo (+), Ru (+), Rh (+), Sn (+), Te (+), Re (+), Pb (+), Bi (+), Eu (+), Tm (+), and Yb (+)) react too slowly at room temperature either in their oxidation with N 2O to form MO (+) or in the reduction of MO (+) by H 2. Many of these reactions are known to be spin forbidden and a few actually may lie outside the thermodynamic window. Three alkaline-earth metal monoxide cations, CaO (+), SrO (+), and BaO (+), were observed to favor MOH (+) formation in their reactions with H 2. A potential-energy landscape is computed for the oxidation of H 2 with N 2O catalyzed by Fe (+)( (6)D) that vividly illustrates the operation of an ionic catalyst and qualitatively accounts for the relative inefficiency of this catalyst. 相似文献
803.
Elena S. Bakhvalova Arina O. Pinyukova Alexey V. Mikheev Galina N. Demidenko Mikhail G. Sulman Alexey V. Bykov Linda Z. Nikoshvili Lioubov Kiwi-Minsker 《Molecules (Basel, Switzerland)》2021,26(15)
This work is addressing the arenes’ hydrogenation—the processes of high importance for petrochemical, chemical and pharmaceutical industries. Noble metal (Pd, Pt, Ru) nanoparticles (NPs) stabilized in hyper-cross-linked polystyrene (HPS) were shown to be active and selective catalysts in hydrogenation of a wide range of arenes (monocyclic, condensed, substituted, etc.) in a batch mode. HPS effectively stabilized metal NPs during hydrogenation in different medium (water, organic solvents) and allowed multiple catalyst reuses. 相似文献
804.
2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibers were prepared from two kraft pulps (Norway spruce and mixed eucalyptus) using the TEMPO/NaBr/NaClO system at pH 10 and 22?°C. After reaction and mechanical treatment, the TEMPO-oxidized celluloses were used for preparation of self-standing films and coatings of laminate films on 50-μm-thick polyethylene terephthalate films. Characterization of the films was performed based on water contact angle measurements, laser profilometry, scanning electron microscopy, and field-emission scanning electron microscopy. The purpose of this study is to understand how the measured contact angles are affected by the film’s physical properties (morphology, thickness, density, and roughness). 相似文献
805.
Alexander V. Stepakov Anna G. LarinaVitaly M. Boitsov Alexander P. MolchanovVladislav V. Gurzhiy Galina L. Starova 《Tetrahedron letters》2012,53(27):3411-3415
The reactions of unactivated bis(methylene)cyclopropanes with nitrones and nitrile oxides have been investigated. The 1,1-diaryl-2-isopropylidene-3-methylenecyclopropanes react with the C,N-diarylnitrones to give a mixture of 2,2-dimethyl-1,6-diaryl-3-(diarylmethylene)piperidin-4-ones and 5-methyl-1-aryl-1-(arylamino)-4-(diarylmethylene)hex-5-en-3-ones. 2,3-Dihydro-3-methylenepyridin-4(1H)-ones are obtained by reaction of 1,1-diaryl-2-isopropylidene-3-methylenecyclopropanes with nitrile oxides. 相似文献
806.
Rodriquez CF Orlova G Guo Y Li X Siu CK Hopkinson AC Siu KW 《The journal of physical chemistry. B》2006,110(14):7528-7537
The conformers of gaseous bradykinin, BK, (Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)) and its protonated forms, [BK + H](+), [BK + 2H](2+), and [BK + 3H](3+), were examined theoretically using a combination of the Merck molecular force field, Hartree-Fock, and density functional theory. Neutral BK, [BK + H](+), and [BK + 2H](2+) exist in zwitterionic forms that are stabilized by internal solvation and have compact structures; [BK + 3H](3+) differs by the absence of a salt bridge and adopts an elongated form. The common structural feature in all four BK species is a beta-turn in the Ser(6)-Pro(7)-Phe(8)-Arg(9) sequence. The gas-phase basicity of [BK + H](+) estimated from the calculated protonation energy is in accord with published experimental basicity; population-weighted collision cross-sections of the three ionic forms are in agreement with experimental cross-sections in the literature. 相似文献
807.
Lu YW Keita B Nadjo L Lagarde G Simoni E Zhang G Tsirlina GA 《The journal of physical chemistry. B》2006,110(31):15633-15639
The polyoxometalate (NH(4))(6)H(2)(CeMo(12)O(42)).9H(2)O (abbreviated as Ce(IV)Mo(12)) was synthesized, and its Ce(III) form was obtained by exhaustive electrochemical reduction. Both forms are fairly stable in pH 0.0 media. This stability decreases when the pH increases. The Ce(IV) species, in which the central metal is in the f(0) electronic configuration, is found to fluoresce, a feature that is only straightforwardly explained with the Ce(III) state. As the results of a series of experiments converge to confirm the stability of Ce(IV)Mo(12) in the media studied, a suggested rationale is that the emission originates from a higher-energy ligand-to-metal charge transfer and follows a scheme which is ultimately equivalent to the classical metal-centered fluorescence of Ce(III). Detailed studies of the influences of pH and ionic strength were carried out and suggest that protonated and/or ion-paired assemblies are the fluorescent species. A reproducible increase of the fluorescence intensity of Ce(IV)Mo(12) as a function of time was also observed. 相似文献
808.
Both theoretical and experimental investigations are reported for the gas-phase hydrolysis of the radical cation of ketene, H(2)CCO(*+). Density functional theory (DFT) with the B3LYP/6-311++G(d,p) method indicates that a second water molecule is required as a catalyst for the addition of water across the C=O bond in H(2)CCO(*+) by eliminating the activation barrier for the conversion of [H(2)CCO.H(2)O](*+) to [H(2)CC(OH)(2)](*+). Theory further indicates that [H(2)CC(OH)(2).H(2)O](*+) may recombine with electrons to produce neutral acetic acid. Experimental results of flow-reactor tandem mass spectrometer experiments in which CH(2)CO(*+) ions were produced either directly from ketene by electron transfer or by the chemical reaction of CH(2)(*+) with CO are consistent with formation of an (C(2),H(4),O(2))(*+) ion in a reaction second-order in H(2)O. Furthermore, comparative multi-CID experiments indicate that this ion is likely to be the enolic CH(2)C(OH)(2)(*+) cation. The results suggest a possible mechanism for the formation of acetic acid from ketene and water on icy surfaces in hot cores and interstellar clouds. 相似文献
809.
810.
Vladislav A. Tuskaev Svetlana Ch. Gagieva Dmitry A. Kurmaev Elizaveta K. Melnikova Sergey V. Zubkevich Mikhail I. Buzin Galina G. Nikiforova Viktor G. Vasil'ev Daniele Saracheno Vyacheslav S. Bogdanov Viktor I. Privalov Boris M. Bulychev 《应用有机金属化学》2020,34(11):e5933
Titanium(IV) coordination compounds are effectively used as precatalysts for ethylene polymerization and copolymerization with other olefins. New titanium(IV) complexes 3b – d with ligands containing two diphenylcarbinol fragments linked by the perfluorinated hydrocarbon units –CF2– or –C2F4– were synthesized. The structures of complexes 3b and 3d were determined by X-ray diffraction. Titanium atoms in 3b have a distorted trigonal-bipyramidal coordination environment while spiro-complex 3d is characterized by tetrahedral molecular geometry. The catalytic behavior of complexes activated by mixtures of Bu2Mg and alkylaluminium chlorides from among Me2AlCl, Et2AlCl, EtAlCl2, and Et3Al2Cl3 were studied. The resulting catalytic systems catalyze ethylene polymerization to afford ultra-high molecular weight polyethylene, suitable for modern processing methods, and the solvent-free solid state formation of super high-strength (1.37–2.75 GPa) and high-modulus (up to 138 GPa) oriented film tapes. The same catalytic systems catalyze ethylene copolymerization with 1-hexene to afford high molecular weight semicrystalline elastomeric polymers containing up to 20% of comonomer units. 相似文献