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121.
Matthew Brantley Behrooz Zekavat Brett Harper Rachel Mason Touradj Solouki 《Journal of the American Society for Mass Spectrometry》2014,25(10):1810-1819
Presence of unresolved ion mobility (IM) profiles limits the efficient utilization of IM mass spectrometry (IM-MS) systems for isomer differentiation. Here, we introduce an automated ion mobility deconvolution (AIMD) computer software for streamlined deconvolution of overlapped IM-MS profiles. AIMD is based on a previously reported post-IM/collision-induced dissociation (CID) deconvolution approach [J. Am. Soc. Mass Spectrom. 23, 1873 (2012)] and, unlike the previously reported manual approach, it does not require resampling of post-IM/CID data. A novel data preprocessing approach is utilized to improve the accuracy and efficiency of the deconvolution process. Results from AIMD analysis of overlapped IM profiles of data from (1) Waters Synapt G1 for a binary mixture of isomeric peptides (amino acid sequences: GRGDS and SDGRG) and (2) Waters Synapt G2-S for a binary mixture of isomeric trisaccharides (raffinose and isomaltotriose) are presented. Graphical Abstract
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122.
A. Yu. Plotski A. A. Sysoliatin A. I. Latkin V. F. Khopin P. Harper J. Harrison S. K. Turitsyn 《JETP Letters》2007,85(7):319-322
The experimental results for the propagation of high-power pulses in fibers with length-varying chromatic dispersion are presented. 相似文献
123.
Zen Harper 《Integral Equations and Operator Theory》2006,54(1):69-88
In this paper, we study a discrete version of the Weiss Conjecture. In Section 1 we discuss the Reproducing Kernel Thesis
and in Section 2 we introduce the operators which concern us. Section 3 shows how to relate these operators to Carleson embeddings
and weighted composition operators, so that we can apply the Carleson measure theorem to obtain conditions for boundedness
and compactness of many weighted composition operators. Section 4 contains Theorem 4.4 which is a discrete version of the
Weiss Conjecture for contraction semigroups, and finally Section 5 shows how the usual (continuous time) Weiss Conjecture
is related to the discrete version studied here; in fact they are equivalent (for scalar valued observation operators). The
main advantage of the discrete version is that it is technically simpler – the observation operators are automatically bounded
and the functional calculus can be achieved using power series. 相似文献
124.
125.
This paper shows that a voltammetric artefact is observed when quaternary ammonium electrolytes are used for voltammetric analysis in non-polar media. This artefact arises due to the slow desorption of quaternary ammonium ions from the electrode surface and hence the potential at the outer Helmholtz plane (oHp) becomes sweep rate dependent. It was found that the slower the ion desorption the greater the distortion in the voltammogram. Both anion and cations were found to have an effect on the reversibility of processes both positive and negative of the potential of zero charge (pzc). It is suggested that this artefact can also explain deviations in measured rate constants obtained by different techniques in more polar solvents. 相似文献
126.
127.
J.M.E. Harper 《Physics letters. A》1974,47(1):69-70
A method of preparing superconducting palladium hybride by electrolysis is described. The relationship of the superconducting transition temperature to hydrogen concentration and the behavior of the hydrogen clustering temperature at high concentrations are reported. 相似文献
128.
Boyd DR Sharma ND Harrison JS Malone JF McRoberts WC Hamilton JT Harper DB 《Organic & biomolecular chemistry》2008,6(7):1251-1259
A series of twelve benzoate esters was metabolised, by species of the Phellinus genus of wood-rotting fungi, to yield the corresponding benzyl alcohol derivatives and eight salicylates. The isolation of a stable oxepine metabolite, from methyl benzoate, allied to evidence of the migration and retention of a carbomethoxy group (the NIH Shift), during enzyme-catalysed ortho-hydroxylation of alkyl benzoates to form salicylates, is consistent with a mechanism involving an initial arene epoxidation step. This mechanism was confirmed by the isolation of a remarkably stable, optically active, substituted benzene oxide metabolite of methyl 2-(trifluoromethyl)benzoate, which slowly converted into the racemic form. The arene oxide was found to undergo a cycloaddition reaction with 4-phenyl-1,2,4-triazoline-3,5-dione to yield a crystalline cycloadduct whose structure and racemic nature was established by X-ray crystallography. The metabolite was also found to undergo some novel benzene oxide reactions, including epoxidation to give an anti-diepoxide, base-catalysed hydrolysis to form a trans-dihydrodiol and acid-catalysed aromatisation to yield a salicylate derivative via the NIH Shift of a carbomethoxy group. 相似文献
129.
Birchall K Gillet VJ Harper G Pickett SD 《Journal of chemical information and modeling》2008,48(8):1543-1557
A new machine learning method is presented for extracting interpretable structure-activity relationships from screening data. The method is based on an evolutionary algorithm and reduced graphs and aims to evolve a reduced graph query (subgraph) that is present within the active compounds and absent from the inactives. The reduced graph representation enables heterogeneous compounds, such as those found in high-throughput screening data, to be captured in a single representation with the resulting query encoding structure-activity information in a form that is readily interpretable by a chemist. The application of the method is illustrated using data sets extracted from the well-known MDDR data set and GSK in-house screening data. Queries are evolved that are consistent with the known SARs, and they are also shown to be robust when applied to independent sets that were not used in training. 相似文献
130.
Brett Harper Elizabeth K. Neumann Sarah M. Stow Jody C. May John A. McLean Touradj Solouki 《Analytica chimica acta》2016
Ion mobility (IM) is an important analytical technique for determining ion collision cross section (CCS) values in the gas-phase and gaining insight into molecular structures and conformations. However, limited instrument resolving powers for IM may restrict adequate characterization of conformationally similar ions, such as structural isomers, and reduce the accuracy of IM-based CCS calculations. Recently, we introduced an automated technique for extracting “pure” IM and collision-induced dissociation (CID) mass spectra of IM overlapping species using chemometric deconvolution of post-IM/CID mass spectrometry (MS) data [J. Am. Soc. Mass Spectrom., 2014, 25, 1810–1819]. Here we extend those capabilities to demonstrate how extracted IM profiles can be used to calculate accurate CCS values of peptide isomer ions which are not fully resolved by IM. We show that CCS values obtained from deconvoluted IM spectra match with CCS values measured from the individually analyzed corresponding peptides on uniform field IM instrumentation. We introduce an approach that utilizes experimentally determined IM arrival time (AT) “shift factors” to compensate for ion acceleration variations during post-IM/CID and significantly improve the accuracy of the calculated CCS values. Also, we discuss details of this IM deconvolution approach and compare empirical CCS values from traveling wave (TW)IM-MS and drift tube (DT)IM-MS with theoretically calculated CCS values using the projected superposition approximation (PSA). For example, experimentally measured deconvoluted TWIM-MS mean CCS values for doubly-protonated RYGGFM, RMFGYG, MFRYGG, and FRMYGG peptide isomers were 288.8 Å2, 295.1 Å2, 296.8 Å2, and 300.1 Å2; all four of these CCS values were within 1.5% of independently measured DTIM-MS values. 相似文献