排序方式: 共有53条查询结果,搜索用时 62 毫秒
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LoSecco JM Bionta RM Biewitt G Bratton CB Casper D Chrysicopoulou P Claus R Cortez BG Errede S Foster GW Gajewski W Ganezer KS Goldhaber M Haines TJ Jones TW Kielczewska D Kropp WR Learned JG Lehmann E Park HS Reines F Schultz J Seidel S Shumard E Sinclair D Sobel HW Stone JL Sulak L Svoboda R van der Velde JC Wuest C 《Physical review letters》1985,54(21):2299-2301
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Jurchen JC Cooper RE Williams ER 《Journal of the American Society for Mass Spectrometry》2003,14(12):1477-1487
Gas-phase H/D exchange is widely used for characterizing the structure of ions. However, many structural parameters that affect the rate of H/D exchange are poorly understood, which complicates the interpretation of experimental data. Here, the effects of sodium ion adduction on the rate of H/D exchange with D2O for a series of peptides and peptide dimers with varying numbers of acidic residues are described. The maximum number of sodium ion adducts that can be accommodated by the peptides and peptide dimers in this study is N + 1, where N is the number of free carboxylic acid groups. The formation of methyl-esters at all carboxylic acid groups, or the replacement of all the acidic hydrogens with sodium ions, effectively shuts down H/D exchange with D2O. In contrast, both the rate and the extent of H/D exchange with D2O are increased for most of the peptides and peptide dimers by the adduction of an intermediate number of sodium ions. These results are consistent with the H/D exchange occurring via a salt-bridge mechanism and show that the presence of two carboxylic acid groups is much better than one. The results with peptide dimers also indicate that surface accessibility may not be a dominant factor in the extent of H/D exchange for these ions. 相似文献
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John?F?StinsEmail author G?Caroline?M?van Baal Tinca?JC?Polderman Frank?C?Verhulst Dorret?I?Boomsma 《BMC neuroscience》2004,5(1):49
Background
There is great interest in appropriate phenotypes that serve as indicator of genetically transmitted frontal (dys)function, such as ADHD. Here we investigate the ability to deal with response conflict, and we ask to what extent performance variation on response interference tasks is caused by genetic variation. We tested a large sample of 12-year old monozygotic and dizygotic twins on two well-known and closely related response interference tasks; the color Stroop task and the Eriksen flanker task. Using structural equation modelling we assessed the heritability of several performance indices derived from those tasks. 相似文献7.
Sakari Leino Patrick JC May Paavo Alku Lassi A Liikkanen Hannu Tiitinen 《BMC neuroscience》2007,8(1):78
Background
In the field of auditory neuroscience, much research has focused on the neural processes underlying human sound localization. A recent magnetoencephalography (MEG) study investigated localization-related brain activity by measuring the N1m event-related response originating in the auditory cortex. It was found that the dynamic range of the right-hemispheric N1m response, defined as the mean difference in response magnitude between contralateral and ipsilateral stimulation, reflects cortical activity related to the discrimination of horizontal sound direction. Interestingly, the results also suggested that the presence of realistic spectral information within horizontally located spatial sounds resulted in a larger right-hemispheric N1m dynamic range. Spectral cues being predominant at high frequencies, the present study further investigated the issue by removing frequencies from the spatial stimuli with low-pass filtering. This resulted in a stepwise elimination of direction-specific spectral information. Interaural time and level differences were kept constant. The original, unfiltered stimuli were broadband noise signals presented from five frontal horizontal directions and binaurally recorded for eight human subjects with miniature microphones placed in each subject's ear canals. Stimuli were presented to the subjects during MEG registration and in a behavioral listening experiment. 相似文献8.
DC Muddiman AP Null JC Hannis 《Rapid communications in mass spectrometry : RCM》1999,13(12):1201-1204
Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) has been used to determine the mass of a double-stranded 500 base-pair (bp) polymerase chain reaction (PCR) product with an average theoretical mass of the blunt-ended (i.e. unadenylated) species of 308 859.35 Da. The PCR product was generated from the linearized bacteriophage Lambda genome which is a double-stranded template. Utilization of ethanol precipitation in tandem with a rapid microdialysis step to purify and desalt the PCR product was crucial to obtain a precise mass measurement. The PCR product (0.8 pmol/μL) was electrosprayed from a solution containing 75% acetonitrile, 25 mM piperidine, and 25 mM imidazole and was infused at a rate of 200 nL/min. The average molecular mass and the corresponding precision were determined using the charge-states ranging from 172 to 235 net negative charges. The experimental mass and corresponding precision (reported as the 95% confidence interval of the mean) was 309 406 +/- 27 Da (87 ppm). The mass accuracy was compromised due to the fact that the PCR generates multiple products when using Taq polymerase due to the non-template directed 3'-adenylation. This results in a mixture of three PCR products with nearly identical mass (i.e. blunt-ended, mono-adenylated and di-adenylated) with unknown relative abundances that were not resolved in the spectrum. Thus, the experimental mass will be a weighted average of the three species which, under our experimental conditions, reflects a nearly equal concentration of the mono- and di-adenylated species. This report demonstrates that precise mass measurements of PCR products up to 309 kDa (500 bp) can be routinely obtained by ESI-FTICR requiring low femtomole amounts. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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A new bidentate 2,3-dihydroxyterephthalamide ligand, 2,3-dihydroxy-N,N'-bis(2-methoxyethyl)terephthalamide (TAMmeg), has been prepared. The ligand, its synthetic precursor 2,3-bis(benzyloxy)-N,N'-bis(2-methoxy-ethyl)-terephthalamide (BnTAMmeg), and its iron complex have been structurally characterized by X-ray diffraction. BnTAMmeg crystallizes in the monoclinic space group P2(1)/n with cell parameters a = 14.4976(14) A, b = 11.5569(11) A, c = 16.3905(16) A, beta = 113.621(1) degrees , and Z = 4. TAMmeg crystallizes in the monoclinic space group P2(1)/c with cell parameters a = 13.8060(36) A, b = 8.0049(21) A, c = 19.4346(50) A, beta = 106.855(4) degrees , and Z = 4. Fe[TAMmeg] crystallizes in the triclinic space group P with cell parameters a = 12.9565(14) A, b = 13.4514(14) A, c = 20.2092(21) A, alpha = 102.093(2) degrees , beta = 95.433(2) degrees , gamma = 101.532(2) degrees , and Z = 2. The aqueous protonation and ferric ion coordination chemistry of TAMmeg were examined using potentiometric and spectrophotometric methods. Proton association constants and iron complex formation constants for the ligand are as follows: log beta(011) = 10.32, log beta(012) = 16.49, log beta(110) = 17.9, log beta(120) = 32.1, and log beta(130) = 43.0. The ferric complex of TAMmeg is surprisingly stable for a bidentate terephthalamide iron complex. The only more-stable bidentate terephthalamide iron complex that has been reported contains a ligand with positively charged pendant arms. 相似文献
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