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The effect of electrospray ionization (ESI) conditions on low-energy tandem mass spectra of peptides in the relative molecular mass range 400–1200 was examined. For singly charged peptide ions the source skimmer potential (which determines the degree of acceleration of the ions through the intermediate pressure region in the source) can strongly influence the extent of fragmentation observed in tandem mass spectra, especially at low collision energies. For each peptide there is an optimum skimmer potential which represents a balance between generating ions with sufficient internal energy for subsequent tandem mass spectrometric experiments and inducing the onset of other processes such as source fragmentation. The fragmentation which can be achieved in tandem mass spectra with high skimmer potentials differs from ESI source fragmentation for the same peptides. We have found that fragmentation in ESI mass spectra depends both on skimmer potential and on solvent pH, presumably because the latter determines the proportion of doubly charged species generated from a given peptide. Low-energy tandem mass spectra of peptides following ESI are equally as sensitive to peptide structure and the type of adduct studied (e.g. [M + H]+ vs. [M + NH4]+) as tandem mass spectra obtained following older ionization methods such as fast atom bombardment. 相似文献
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Fish C Green M Jeffery JC Kilby RJ Lynam JM McGrady JE Pantazis DA Russell CA Willans CE 《Chemical communications (Cambridge, England)》2006,(13):1375-1377
The cationic cages nido-[C2Bu(t)2P2E]+ (E = As, Sb), which are isolobal to the cyclopentadienyl cation, adopt square based pyramidal structures with the heavy pnictogen atom at the apex; NMR and computational methods have been used to probe the dynamic behaviour of the complexes. 相似文献
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Butts CP Green M Hooper TN Kilby RJ McGrady JE Pantazis DA Russell CA 《Chemical communications (Cambridge, England)》2008,(7):856-858
The electronic structure of the 1,2,3-triphosphaindenyl ligand suggests that it should exhibit enhanced pi-acceptor properties when compared to the eta(5)-indenyl system; this insight encouraged us to develop a simple synthetic pathway from 1,2-diphosphinobenzene to the 1,2,3-C(6)H(4)P(3) and 2-As-1,3-C(6)H(4)P(2) anions, both of which have been structurally characterised by X-ray crystallography; as a bonus from these studies we also obtained the first structurally characterised organo derivative of the P(8) unit present in Hittorf's phosphorus. 相似文献
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Fish C Green M Kilby RJ McGrady JE Pantazis DA Russell CA 《Dalton transactions (Cambridge, England : 2003)》2008,(28):3753-3758
A high yield of the tetraphosphaladderene, anti-tetraphosphatricyclo[4.2.0.0(2,5)]octa-3,7-diene, is obtained from reaction of the zirconocene 1,3-diphosphabicyclo[1.1.0]butane with Ph(2)SbCl(3) in THF or CH(2)Cl(2). Exploration of the reaction pathway using density functional theory suggests that an envelope-type adduct of Ph(2)SbCl and 1,3-diphosphabicyclo[1.1.0]butane plays a pivotal role in the reaction. The zwitterionic character of this intermediate species allows it to act simultaneously as both an ene and an eneophile, and a symmetry-allowed bimolecular reaction leads to the tetraphosphaladderene species via a spirocyclic intermediate. 相似文献
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Slattery JM Fish C Green M Hooper TN Jeffery JC Kilby RJ Lynam JM McGrady JE Pantazis DA Russell CA Willans CE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(24):6967-6974
Abstraction of a Cl(-) ion from the P-chlorophospholes, R4C4PCl (R=Me, Et), produced the P--P bonded cations [R4C4P--P(Cl)C4R4]+, which reacted with PPh3 to afford X-ray crystallographically characterised phosphine-phosphenium cations [R4C4P(PPh3)]+ (R=Me, Et). Examination of the 31P-{1H} NMR spectrum of a solution (CH2Cl(2)) of [Et4C4P-(PPh3)]+ and PPh3 revealed broadening of the resonances due to both free and coordinated PPh3, and importantly it proved possible to measure the rate of exchange between PPh3 and [Et4C4P-(PPh3)]+ by line shape analysis (gNMR programmes). The results established second-order kinetics with DeltaS( not equal)=(-106.3+/-6.7) J mol(-1) K(-1), DeltaH( not equal)=(14.9+/-1.6) kJ mol(-1) and DeltaG( not equal) (298.15 K)=(46.6+/-2.6) kJ mol(-1), values consistent with a SN2-type pathway for the exchange process. This result contrasts with the dominant dissociative (S(N)1-type) pathway reported for the analogous exchange reactions of the [ArNCH2CH2N(Ar)P(PMe3)]+ ion, and to understand in more detail the factors controlling these two different reaction pathways, we have analysed the potential energy surfaces using density functional theory (DFT). The calculations reveal that, whilst phosphine exchange in [Et4C4P(PPh3)]+ and [ArNCH2CH2N(Ar)P(PMe3)](+) is superficially similar, the two cations differ significantly in both their electronic and steric requirements. The high electrophilicity of the phosphorus center in [Et4C4P]+, combined with strong pi-pi interactions between the ring and the incoming and outgoing phenyl groups of PPh3, favours the SN2-type over the SN1-type pathway in [Et4C4P(PPh3)]+. Effective pi-donation from the amide groups reduces the intrinsic electrophilicity of [ArNCH2CH2N(Ar)P]+, which, when combined with the steric bulk of the aryl groups, shifts the mechanism in favour of a dissociative SN1-type pathway. 相似文献
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Kilby Seth Jin Zhongmin Avachat Ashish Kanies Bryant Woolstenhulme Nicolas Lee Hyoung K. Graham Joseph 《Journal of Radioanalytical and Nuclear Chemistry》2020,324(1):445-446
Journal of Radioanalytical and Nuclear Chemistry - In the original article, Equation 4 was incorrectly published. The correct equation is provided in this correction 相似文献
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A T Ernst M Horn P Kilby M Krishnamoorthy 《The Journal of the Operational Research Society》2010,61(7):1133-1143
The rental fleet scheduling problem (RFSP) arises in vehicle-rental operations that offer a wide variety of vehicle types to customers, and allow a rented vehicle to ‘migrate’ to a setdown depot other than the pickup depot.When there is a shortage of vehicles of a particular type at a depot, vehicles may be relocated to that depot, or vehicles of similar types may be substituted.The RFSP involves assigning vehicles to rentals so as to minimise the costs of these operations, and arises in both static and online contexts. The authors have adapted a well-known assignment algorithm for application in the online context. In addition, a network-flow algorithm with more comprehensive coverage of problem conditions is used to investigate the determination of rental pricing using revenue management principles. The paper concludes with an outline of the algorithms’ use in supporting the operations of a large recreational vehicle rental company. 相似文献
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Stephen M. Mansell Michael Green Richard J. Kilby Martin Murray Christopher A. Russell 《Comptes Rendus Chimie》2010,13(8-9):1073-1081
Me3SiCP may be prepared by dehydrochlorination of Me3SiCH2PCl2 at room temperature in aromatic solvents using DABCO in the presence of AgOTf. Reaction of Me3SiCP with a selection of s-block metals, s-block metal salts and ytterbium effects conversion to a mixture of di- and triphospholide anions. This mixture of anions was subsequently reacted with FeCl2 to yield a mixture of tetra-, penta- and hexaphosphaferrocenes. 相似文献