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261.
Williams JP Hilton GR Thalassinos K Jackson AT Scrivens JH 《Rapid communications in mass spectrometry : RCM》2007,21(11):1693-1704
A rapid method for the characterisation of polyglycol esters and ethers is described which uses accurate mass desorption electrospray ionisation (DESI) quadrupole time-of-flight mass spectrometry (Q-ToFMS). The results are combined with newly developed software which aids the interpretation of product ions produced using collision-induced dissociation (CID) of selected precursor ions. The poly(ethylene glycol) (PEG) samples analysed were PEG dibenzoate, PEG monooleate, PEG butyl ether, PEG bis(2-ethyl hexanoate) and PEG diacrylate. Lithium metal was used for cationisation of the PEG oligomers since it yielded the most useful structural information compared with other group I metals. The full scan mass spectra and product ion mass spectra were all obtained in <5 s. Interpretation of the MS/MS product ion spectra, using the product ion interpretation software which incorporates previously developed fragmentation rules, was carried out in <1 s. 相似文献
262.
Michael addition of indole and pyrrole to a variety ofα,β-unsaturated ketones was efficiently promoted by a catalytic amount of GaCl_3 in aqueous media to afford the corresponding products in good to excellent yields. 相似文献
263.
King BT Kroulík J Robertson CR Rempala P Hilton CL Korinek JD Gortari LM 《The Journal of organic chemistry》2007,72(7):2279-2288
Guidelines for the application of the Scholl reaction were developed. Labeling experiments demonstrate that the Scholl reaction fails in small, unsubstituted oligophenylenes (e.g., o-terphenyl) due to oligomerization of the products (e.g., triphenylene). Incorporation of suitably placed blocking groups (e.g., t-butyl) suppresses oligomerization. The well-established directing group effects in electrophilic aromatic substitution predict the outcome of Scholl reactions of substituted substrates. Activating o,p-directing groups (e.g., MeO) direct bond formation o,p, either intramolecularly or intermolecularly. Deactivating o,p-directing groups (e.g., Br) also direct bond formation o,p but yields are lower. Deactivating m-directors (e.g., NO2) suppress reaction. MoCl5 and PhI(OOCCF3)2/BF3.Et2O are general and effective reagents for the Scholl oxidation. Calculations (B3LYP/6-31G(d)) predict the Scholl reaction in alkoxyarenes to proceed via arenium cations, not radical cations. Suzuki-Miyaura couplings were used to generate 12 substituted o-terphenyl derivatives. 相似文献
264.
Martin GE Hilton BD Blinov KA Williams AJ 《Magnetic resonance in chemistry : MRC》2008,46(11):997-1002
Long-range homonuclear coupling pathways can be observed in COSY or GCOSY spectra by the acquisition of spectra with larger numbers of increments of the evolution period, t(1), than would normally be used. Alternatively, covariance processing of COSY-type spectra acquired with modest numbers of t(1) increments, allows the observation of multistage correlations. In this work results obtained from covariance-processed GCOSY spectra are fully analyzed and compared to normally processed COSY and 80 ms TOCSY spectra. Multistage or 'RCOSY-type' correlations are observed when remote protons both exhibit correlations to the same coupling partner e.g. A --> B and B --> C gives rise to an A --> C correlation. In the strict sense, RCOSY-type responses are artifacts albeit providing useful information. Nonbeneficial artifact correlations are observed when protons couple to other protons that overlap or partially overlap. The origin of artifact responses is also analyzed. 相似文献
265.
Matthew J. Pollard Christopher K. Hilton Hongli Li Kimberly Kaplan Richard A. Yost Herbert H. HillJr. 《International Journal for Ion Mobility Spectrometry》2011,14(1):15-22
Since the development of electrospray ionization (ESI) for ion mobility spectrometry mass spectrometry (IMMS), IMMS have been
extensively applied for characterization of gas-phase bio-molecules. Conventional ion mobility spectrometry (IMS), defined
as drift tube IMS (DT-IMS), is typically a stacked ring design that utilizes a low electric field gradient. Field asymmetric
ion mobility spectrometry (FAIMS) is a newer version of IMS, however, the geometry of the system is significantly different
than DT-IMS and data are collected using a much higher electric field. Here we report construction of a novel ambient pressure
dual gate DT-IMS coupled with a FAIMS system and then coupled to a quadrupole ion trap mass spectrometer (QITMS) to form a
hybrid three-dimensional separation instrument, DT-IMS-FAIMS-QITMS. The DT-IMS was operated at ~3 Townsend (electric field/number
density (E/N) or (Td)) and was coupled in series with a FAIMS, operated at ~80 Td. Ions were mobility-selected by the dual
gate DT-IMS into the FAIMS and from the FAIMS the ions were detected by the QITMS for as either MS or MSn. The system was evaluated using cocaine as an analytical standard and tested for the application of separating three isomeric
tri-peptides: tyrosine-glycine-tryptophan (YGW), tryptophan-glycine-tyrosine (WGY) and tyrosine-tryptophan-glycine (YWG).
All three tri-peptides were separated in the DT-IMS dimension and each had one mobility peak. The samples were partially separated
in the FAIMS dimension but two conformation peaks were detected for the YWG sample while YGW and WGY produced only one peak.
Ion validation was achieved for all three samples using QITMS. 相似文献
266.
A. J. W. Hilton 《Combinatorica》1982,2(1):37-51
A variety of results on edge-colourings are proved, the main one being the following: ifG is a graph without loops or multiple edges and with maximum degree Δ=Δ(G), and if ν is a given integer 1≦ν≦Δ(G), thenG can be given a proper edge-colouring with the coloursc
1, ...,c
Δ+1 with the additional property that any edge colouredc
μ with μ≧ν is on a vertex which has on it edges coloured with at least ν − 1 ofc
1, ...,c
v
. 相似文献