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排序方式: 共有129条查询结果,搜索用时 31 毫秒
61.
Thomas P. Forbes R. Brent Dixon David C. Muddiman F. Levent Degertekin Andrei G. Fedorov 《Journal of the American Society for Mass Spectrometry》2009,20(9):1684-1687
An initial investigation into the effects of charge separation in the Array of Micromachined UltraSonic Electrospray (AMUSE)
ion source is reported to gain understanding of ionization mechanisms and to improve analyte ionization efficiency and operation
stability. In RF-only mode, AMUSE ejects, on average, an equal number of slightly positive and slightly negative charged droplets
due to random charge fluctuations, providing inefficient analyte ionization. Charge separation at the nozzle orifice is achieved
by the application of an external electric field. By bringing the counter electrode close to the nozzle array, strong electric
fields can be applied at relatively low DC potentials. It has been demonstrated, through a number of electrode/electrical
potential configurations, that increasing charge separation leads to improvement in signal abundance, signal-to-noise ratio,
and signal stability. 相似文献
62.
D. Keith Williams Alexander L. Kovach David C. Muddiman Kenneth W. Hanck 《Journal of the American Society for Mass Spectrometry》2009,20(7):1303-1310
Fourier transform ion cyclotron resonance mass spectrometry has the ability to realize exceptional mass measurement accuracy
(MMA); MMA is one of the most significant attributes of mass spectrometric measurements as it affords extraordinary molecular
specificity. However, due to space-charge effects, the achievable MMA significantly depends on the total number of ions trapped
in the ICR cell for a particular measurement, as well as relative ion abundance of a given species. Artificial neural network
calibration in conjunction with automatic gain control (AGC) is utilized in these experiments to formally account for the
differences in total ion population in the ICR cell between the external calibration spectra and experimental spectra. In
addition, artificial neural network calibration is used to account for both differences in total ion population in the ICR
cell as well as relative ion abundance of a given species, which also affords mean MMA values at the parts-per-billion level. 相似文献
63.
We report the results of abundant plasma protein depletion on the analysis of underivatized N-linked glycans derived from plasma proteins by nanoLC Fourier-transform ion cyclotron resonance mass spectrometry. N-linked glycan profiles were compared between plasma samples where the six most abundant plasma proteins were depleted (n = 3) through a solid-phase immunoaffinity column and undepleted plasma samples (n = 3). Three exogenous glycan standards were spiked into all samples which allowed for normalization of the N-glycan abundances.
The abundances of 20 glycans varying in type, structure, composition, and molecular weight (1,200–3,700 Da) were compared
between the two sets of samples. Small fucosylated non-sialylated complex glycans were found to decrease in abundance in the
depleted samples (greater than or equal to tenfold) relative to the undepleted samples. Protein depletion was found to marginally
effect (less than threefold) the abundance of high mannose, hybrid, and large highly sialylated complex species. The significance
of these findings in terms of future biomarker discovery experiments via global glycan profiling is discussed. 相似文献
64.
Yang HB Das N Huang F Hawkridge AM Muddiman DC Stang PJ 《Journal of the American Chemical Society》2006,128(31):10014-10015
The first self-assembly of nanoscale metallodendrimers that have a hexagonal cavity as a core via the directional-bonding approach is reported. All metallodendrimers were characterized by multinuclear NMR (1H and 31P), mass spectrometry (ESI-MS and ESI-FT-ICR), and elemental analysis. 相似文献
65.
Yang HB Das N Huang F Hawkridge AM Díaz DD Arif AM Finn MG Muddiman DC Stang PJ 《The Journal of organic chemistry》2006,71(17):6644-6647
The synthesis and characterization of three new supramolecular complexes 6-8 (a rhomboid and two hexagons) via coordination-driven self-assembly are reported in excellent yields (>90%). These assemblies have 2,6-di(4,4'-dipyridyl)-9-thiabicyclo[3.3.1]nonane 2 as the bridging tecton. All assemblies were characterized by multinuclear NMR (1H and 31P), mass spectrometry (ESI-MS and ESI-FT-ICR), and elemental analysis. The X-ray structure of the 120 degrees tecton 2 is also discussed. 相似文献
66.
Hierarchical Self‐Assembly of Supramolecular Hydrophobic Metallacycles into Ordered Nanostructures 下载免费PDF全文
Jing Zhang Dr. Riccardo Marega Li‐Jun Chen Nai‐Wei Wu Xing‐Dong Xu Prof. Dr. David C. Muddiman Prof. Dr. Davide Bonifazi Prof. Dr. Hai‐Bo Yang 《化学:亚洲杂志》2014,9(10):2928-2936
We describe herein the hierarchical self‐assembly of discrete supramolecular metallacycles into ordered fibers or spherical particles through multiple noncovalent interactions. A new series of well‐defined metallacycles decorated with long alkyl chains were obtained through metal–ligand interactions, which were capable of aggregating into ordered fibroid or spherical nanostructures on the surface, mostly driven by hydrophobic interactions. In‐depth studies indicated that the morphology diversity was originated from the structural information encoded in the metallacycles, including the number of alkyl chains and their spatial orientation. Interestingly, the morphology of the metallacycle aggregates could be tuned by changing the solvent polarity. These findings are of special significance since they provide a simple yet highly controllable approach to prepare ordered and tunable nanostructures from small building blocks by means of hierarchical self‐assembly. 相似文献
67.
Guillaume Robichaud Jeremy A. Barry Kenneth P. Garrard David C. Muddiman 《Journal of the American Society for Mass Spectrometry》2013,24(1):92-100
Mass spectrometry imaging (MSI) allows for the direct monitoring of the abundance and spatial distribution of chemical compounds over the surface of a tissue sample. This technology has opened the field of mass spectrometry to numerous innovative applications over the past 15 years. First used with SIMS and MALDI MS that operate under vacuum, interest has grown for mass spectrometry ionization sources that allow for effective imaging but where the analysis can be performed at ambient pressure with minimal or no sample preparation. We introduce here a versatile source for MALDESI imaging analysis coupled to a hybrid LTQ-FT-ICR mass spectrometer. The imaging source offers single shot or multi-shot capability per pixel with full control over the laser repetition rate and mass spectrometer scanning cycle. Scanning rates can be as fast as 1 pixel/second and a spatial resolution of 45 μm was achieved with oversampling.
Design and integration of a versatile IR-MALDESI imaging source offering multi-shot capability with a commercial FT-ICR mass spectrometer 相似文献
68.
Gokce E Shuford CM Franck WL Dean RA Muddiman DC 《Journal of the American Society for Mass Spectrometry》2011,22(12):2199-2208
Normalization of spectral counts (SpCs) in label-free shotgun proteomic approaches is important to achieve reliable relative
quantification. Three different SpC normalization methods, total spectral count (TSpC) normalization, normalized spectral
abundance factor (NSAF) normalization, and normalization to selected proteins (NSP) were evaluated based on their ability
to correct for day-to-day variation between gel-based sample preparation and chromatographic performance. Three spectral counting
data sets obtained from the same biological conidia sample of the rice blast fungus Magnaporthe oryzae were analyzed by 1D gel and liquid chromatography-tandem mass spectrometry (GeLC-MS/MS). Equine myoglobin and chicken ovalbumin
were spiked into the protein extracts prior to 1D-SDS- PAGE as internal protein standards for NSP. The correlation between
SpCs of the same proteins across the different data sets was investigated. We report that TSpC normalization and NSAF normalization
yielded almost ideal slopes of unity for normalized SpC versus average normalized SpC plots, while NSP did not afford effective
corrections of the unnormalized data. Furthermore, when utilizing TSpC normalization prior to relative protein quantification,
t-testing and fold-change revealed the cutoff limits for determining real biological change to be a function of the absolute
number of SpCs. For instance, we observed the variance decreased as the number of SpCs increased, which resulted in a higher
propensity for detecting statistically significant, yet artificial, change for highly abundant proteins. Thus, we suggest
applying higher confidence level and lower fold-change cutoffs for proteins with higher SpCs, rather than using a single criterion
for the entire data set. By choosing appropriate cutoff values to maintain a constant false positive rate across different
protein levels (i.e., SpC levels), it is expected this will reduce the overall false negative rate, particularly for proteins
with higher SpCs. 相似文献
69.
Walker SH Lilley LM Enamorado MF Comins DL Muddiman DC 《Journal of the American Society for Mass Spectrometry》2011,22(8):1309-1317
A library of neutral, hydrophobic reagents was synthesized for use as derivatizing agents in order to increase the ion abundance
of N-linked glycans in electrospray ionization mass spectrometry (ESI MS). The glycans are derivatized via hydrazone formation
and are shown to increase the ion abundance of a glycan standard more than 4-fold. Additionally, the data show that the systematic
addition of hydrophobic surface area to the reagent increases the glycan ion abundance, a property that can be further exploited
in the analysis of glycans. The results of this study will direct the future synthesis of hydrophobic reagents for glycan
analysis using the correlation between hydrophobicity and theoretical non-polar surface area calculation to facilitate the
development of an optimum tag for glycan derivatization. The compatibility and advantages of this method are demonstrated
by cleaving and derivatizing N-linked glycans from human plasma proteins. The ESI-MS signal for the tagged glycans are shown to be significantly more abundant,
and the detection of negatively charged sialylated glycans is enhanced. 相似文献
70.
Blake SL Walker SH Muddiman DC Hinks D Beck KR 《Journal of the American Society for Mass Spectrometry》2011,22(12):2269-2275
Color Index Disperse Yellow 42 (DY42), a high-volume disperse dye for polyester, was used to compare the capabilities of the
LTQ-Orbitrap XL and the LTQ-FT-ICR with respect to mass measurement accuracy (MMA), spectral accuracy, and sulfur counting.
The results of this research will be used in the construction of a dye database for forensic purposes; the additional spectral
information will increase the confidence in the identification of unknown dyes found in fibers at crime scenes. Initial LTQ-Orbitrap
XL data showed MMAs greater than 3 ppm and poor spectral accuracy. Modification of several Orbitrap installation parameters
(e.g., deflector voltage) resulted in a significant improvement of the data. The LTQ-FT-ICR and LTQ-Orbitrap XL (after installation
parameters were modified) exhibited MMA ≤ 3 ppm, good spectral accuracy (χ2 values for the isotopic distribution ≤ 2), and were correctly able to ascertain the number of sulfur atoms in the compound
at all resolving powers investigated for AGC targets of 5.00 × 105 and 1.00 × 106. 相似文献