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921.
Andreazza HJ Fitzgerald M Bilusich D Hoffmann R Hoffmann P Eichinger PC Bowie JH 《Rapid communications in mass spectrometry : RCM》2008,22(20):3305-3312
Peptides and proteins may contain post-translationally modified phosphorylated amino acid residues, in particular phosphorylated serine (pSer), threonine (pThr) and tyrosine (pTyr). Following earlier work by Lehmann et al., the [M-H]- anions of peptides containing pSer and pThr functionality show loss of the elements of H3PO4. This process, illustrated for Ser (and using a model system), is CH3CONH-C(CH2OPO3H2)CONHCH(3) --> [CH3CONHC(==CH2)CONHCH3 (-OPO3H2)] (a) --> [CH3CONHC(==CH2)CONHCH3-H]- + H3PO4, a process endothermic by 83 kJ mol(-1) at the MP2/6-31++G(d,p)//HF/6-31++G(d,p) level of theory. In addition, intermediate (a) may decompose to yield CH3CONHC(==CH2)CONHCH3 + H2PO4 - in a process exothermic by 3 kJ mol(-1). The barrier to the transition state for these two processes is 49 kJ mol(-1). Characteristic cleavages of pSer and pThr are more energetically favourable than the negative ion backbone cleavages of peptides described previously. In contrast, loss of HPO3 from [M-H]- is characteristic of pTyr. The cleavage [NH2CH(CH2-C6H4-OPO3H-)CO2H] --> [NH2C(CH2-C6H4-O-)CO2H (HPO3)] (b) --> NH2CH(CH2-C6H4-O-)CO2H + HPO3 is endothermic by 318 kJ mol(-1) at the HF/6-31+G(d)//AM1 level of theory. In addition, intermediate (b) also yields NH2CH(CH2-C6H4-OH)CO2H + PO3 - (reaction endothermic by 137 kJ mol(-1)). The two negative ion cleavages of pTyr have a barrier to the transition state of 198 kJ mol(-1) (at the HF/6-31+G(d)//AM1 level of theory) comparable with those already reported for negative ion backbone cleavages. 相似文献
922.
Crossed molecular beams experiments were utilized to explore the chemical reaction dynamics of ground-state cyano radicals, CN(X(2)Sigma(+)), with propylene (CH3CHCH2) together with two d3-isotopologues (CD3CHCH2, CH3CDCD2) as potential pathways to form organic nitriles under single collision conditions in the atmosphere of Saturn's moon Titan and in the interstellar medium. On the basis of the center-of-mass translational and angular distributions, the reaction dynamics were deduced to be indirect and commenced via an addition of the electrophilic cyano radical with its radical center to the alpha-carbon atom of the propylene molecule yielding a doublet radical intermediate: CH3CHCH2CN. Crossed beam experiments with propylene-1,1,2-d3 (CH3CDCD2) and propylene-3,3,3-d3 (CD3CHCH2) indicated that the reaction intermediates CH3CDCD2CN (from propylene-1,1,2-d3) and CD3CHCH2CN (from propylene-3,3,3-d3) eject both atomic hydrogen through tight exit transition states located about 40-50 kJ mol(-1) above the separated products: 3-butenenitrile [H2CCDCD2CN] (25%), and cis/trans-2-butenenitrile [CD3CHCHCN] (75%), respectively, plus atomic hydrogen. Applications of our results to the chemical processing of cold molecular clouds like TMC-1 and OMC-1 are also presented. 相似文献
923.
The reactions between phenyl radicals (C6H5) and propylene (CH3CHCH2) together with its D6- and two D3-isotopologues were studied under single collision conditions using the crossed molecular beams technique. The chemical dynamics inferred from the center-of-mass translational and angular distributions suggests that the reactions are indirect and initiated by an addition of the phenyl radical to the alpha-carbon atom (C1 carbon atom) of the propylene molecule at the =CH2 unit to form a radical intermediate (CH3CHCH2C6H5) on the doublet surface. Investigations with D6-propylene specified that only a deuterium atom was emitted; the phenyl group was found to stay intact. Studies with 1,1,2-D3- and 3,3,3-D3-propylene indicated that the initial collision complexes CH3CDCD2C6H5 (from 1,1,2-D3-propylene) and CD3CHCH2C6H5 (from 3,3,3-D3-propylene) eject both a hydrogen atom via rather loose exit transition states to form the D3-isotopomers of cis/trans-1-phenylpropene (CH3CHCHC6H5) (80-90%) and 3-phenylpropene (H2CCHCH2C6H5) (10-20%), respectively. Implications of these findings for the formation of polycyclic aromatic hydrocarbons (PAHs) and their precursors in combustion flames are discussed. 相似文献
924.
Stable chromium, molybdenum and tungsten nanoparticles are obtained reproducibly by thermal or photolytic decomposition under argon from mononuclear metal carbonyl precursors M(CO)(6) (M=Cr, Mo, W) suspended in the ionic liquids BMim(+)BF(4)(-), BMim(+)OTf(-) and BtMA(+)Tf(2)N(-) (BMim(+)=n-butyl-methyl-imidazolium, BtMA(+)=n-butyl-trimethyl-ammonium, Tf(2)N=N(O(2)SCF(3))(2), OTf=O(3)SCF(3)) with a very small and uniform size of 1 to 1.5 nm in BMim(+)BF(4)(-) which increases with the molecular volume of the ionic liquid anion to approximately 100 nm in BtMA(+)Tf(2)N(-) [characterization by transmission electron microscopy (TEM), dynamic light scattering and transmission electron diffraction (TED) analysis]. 相似文献
925.
Absolute protein quantification has become an important challenge in modern bioanalytical chemistry. Among several approaches
based on mass spectrometric techniques, inductively coupled plasma (ICP) as ionisation source provides element-selective and
sensitive detection of heteroatoms, and thus, a potentially emerging tool in protein analysis. In this work we applied coupling
of capillary liquid chromatography (μLC) and inductively coupled plasma-sector field mass spectrometry (ICP–SFMS) to the separation
and determination of standard proteins. For quantification purposes, post-column isotope dilution of sulfur was applied and
optimised for this type of hyphenated technique. Provided that the protein sequence is known (number of sulfur-containing
amino acids, i.e. cysteines and methionines) the protein amount can then be directly calculated from the determined sulfur
content in a certain protein fraction. In order to prove the reliability of the presented method, two different certified
reference materials were analysed: CRM 393 (human apolipoprotein A-I) and CRM 486 (α-fetoprotein). For CRM 393 excellent agreement
(37.0 ± 1.4 μmol L−1) was obtained with the certificate (37.7 ± 1.8 μmol L−1). However, the recovery rate for α-fetoprotein in CRM 486 was found to be about 60% indicating incomplete elution of the
protein during the chromatographic separation. 相似文献
926.
Lutz Dahlenburg Frank W. Heinemann Dagmar Kramer Ralf Menzel 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(3):m144-m146
In the structure of the title compound, [Ir2Cl3H2(C36H28P2)2]BF4·2CH2Cl2, the bimetallic cation features a confacial bioctahedral structure that is held together by three bridging chloride ions and is very close to C2 symmetric. The hydrides are in a syn orientation (trans to the same halide bridge), and the chelating bis(phosphine) atropisomers display a racemic (R,R)/(S,S) configuration. Because of the high trans‐bond‐weakening influence of the hydride ligands, the Ir—Cl bonds trans to Ir—H [2.5262 (7) and 2.5365 (7) Å] are significantly longer than those opposite the Ir—P linkages [2.4287 (7)–2.4672 (8) Å]. The Ir—P distances vary between 2.2464 (9) and 2.2565 (8) Å. This study illustrates the usefulness of sterically demanding biaryl‐based P2 ligands in the synthesis of halide‐bridged Ir2 complexes, which are valuable precursors of versatile catalysts for homogeneous C=O hydrogenation. 相似文献
927.
928.
Kamil Rahme Julian Oberdisse Dr. Ralf Schweins Dr. Cédric Gaillard Dr. Jean‐Daniel Marty Dr. Christophe Mingotaud Dr. Fabienne Gauffre Dr. 《Chemphyschem》2008,9(15):2230-2236
Hybrid gold–polymer nanoparticles are obtained by self‐assembly of amphiphilic copolymers (Pluronics) in solutions containing preformed gold nanoparticles (diameter ca. 12 nm). Dynamic light scattering, TEM, cryo‐TEM, and small‐angle neutron scattering experiments with contrast variation are used to characterize the structure of the gold–polymer particles. Five Pluronics (F127, F68, F88, F108, P84) with different molecular weights and hydrophilic/hydrophobic balances are investigated. Gold nanoparticles are individually embedded within globules of polymer, even under conditions for which Pluronics micelles do not form in solution. The hybrid particles are several tens of nanometers in size (larger than micelles of the corresponding Pluronics), and the size can be tuned by changing the temperature. 相似文献
929.
Blossey R 《Physical chemistry chemical physics : PCCP》2008,10(34):5177-5183
930.
Luca Münzfeld Milena Dahlen Adrian Hauser Nolwenn Mahieu Senthil Kumar Kuppusamy Jules Moutet Maxime Tricoire Ralf Köppe Léo La Droitte Olivier Cador Boris Le Guennic Grégory Nocton Eufemio Moreno-Pineda Mario Ruben Peter W. Roesky 《Angewandte Chemie (International ed. in English)》2023,62(18):e202218107
Solvation of [(CNT)Ln(η8-COT)] (Ln=La, Ce, Nd, Tb, Er; CNT=cyclononatetraenyl, i.e., C9H9−; COT=cyclooctatetraendiid, i.e., C8H82−) complexes with tetrahydrofuran (THF) gives rise to neutral [(η4-CNT)Ln(thf)2(η8-COT)] (Ln=La, Ce) and ionic [Ln(thf)x(η8-COT)][CNT] (x=4 (Ce, Nd, Tb), 3 (Er)) species in a solid-to-solid transformation. Due to the severe distortion of the ligand sphere upon solvation, these species act as switchable luminophores and single-molecule magnets. The desolvation of the coordinated solvents can be triggered by applying a dynamic vacuum, as well as a temperature gradient stimulus. Raman spectroscopic investigations revealed fast and fully reversible solvation and desolvation processes. Moreover, we also show that a Nd:YAG laser can induce the necessary temperature gradient for a self-sufficient switching process of the Ce(III) analogue in a spatially resolved manner. 相似文献