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71.
72.
Lindström F Thurnhofer S Vetter W Gröbner G 《Physical chemistry chemical physics : PCCP》2006,8(41):4792-4797
Here, we exploit the non-invasive techniques of solid-state NMR (nuclear magnetic resonance) and differential scanning calorimetry (DSC) to study the effect of free iso and ante-iso branched chain fatty acids (BCFAs) on the physicochemical properties of lipid membranes. Free fatty acids are present in biological membranes at low abundance, but can influence the cellular function by modulating the membrane organization. Solid state NMR spectra of dimyristoylphosphatidylcholine (DMPC) lipid membranes containing either free 12-methyltetradecanoic acid (a15:0) or free 13-methyltetradecanoic acid (i15:0), show significant differences in their impact on the lipid bilayer. Chain order profiles obtained by deuterium NMR on fully deuterated DMPC-d(67) bilayers revealed an ordering effect induced by both fatty acids on the hydrophobic membrane core. This behavior was also visible in the corresponding DSC thermograms where the main phase transition of DMPC bilayers-indicative of the hydrophobic membrane region-was shifted to higher temperatures, with the iso isomer triggering more pronounced changes as compared to the ante-iso isomer. This is probably due to a higher packing density in the core of the lipid bilayer, which causes reduced diffusion across membranes. By utilizing the naturally occurring spin reporters nitrogen-14 and phosphorus-31 present in the hydrophilic DMPC headgroup region, even fatty acid induced changes at the membrane interface could be detected, an observation reflecting changes in the lipid headgroup dynamics. 相似文献
73.
Stortelder A Hendriks J Buijs JB Bulthuis J Gooijer C van der Vies SM van der Zwan G 《The journal of physical chemistry. B》2006,110(49):25050-25058
The bacteriophage T4 capsid protein gp23 was studied using time-resolved and steady-state fluorescence of the intrinsic protein fluorophore tryptophan. In-vitro gp23 consists mostly of monomers at low temperature but forms hexamers at room temperature. To extend our knowledge of the structure and hexamerization characteristics of gp23, the temperature-dependent fluorescence properties of a tryptophan mutant (W13V) were compared to those of wild-type gp23. The W13V mutation is located in the N-terminal part of the protein, which is cleaved off after prohead formation in the live bacteriophage. Results show that W13 plays a role in the hexamerization process but is not needed to stabilize the hexamer once it is formed. Furthermore, besides the monomer-to-hexamer temperature transition (15-23 degrees C and 12-43 degrees C for wild-type and W13V gp23, respectively), we were able to observe denaturation of the N-terminus in hexameric wild-type gp23 around 40 degrees C. In addition, with the aid of a recently published homology model of gp23, the lifetimes obtained from time-resolved fluorescence measurements could tentatively be assigned to specific tryptophan residues. 相似文献
74.
Josep Marco-Pallarés Ulrike M Kr?mer Saskia Strehl Andrea Schr?der Thomas F Münte 《BMC neuroscience》2010,11(1):1-8
Background
Actions of others may have immediate consequences for oneself. We probed the neural responses associated with the observation of another person's action using event-related potentials in a modified gambling task. In this task a "performer" bet either a higher or lower number and could win or lose this amount. Three different groups of "observers" were also studied. The first (neutral) group simply observed the performer's action, which had no consequences for the observers. In the second (parallel) group, wins/losses of the performer were paralleled by similar wins and losses by the observer. In the third (reverse) group, wins of the performer led to a loss of the observer and vice versa.Results
ERPs of the performers showed a mediofrontal feedback related negativity (FRN) to losses. The neutral and parallel observer groups did similarly show an FRN response to the performer's losses with a topography indistinguishable from that seen in the performers. In the reverse group, however, the FRN occurred for wins of the performer which translated to losses for the observer.Conclusions
Taking into account previous experiments, we suggest that the FRN response in observers is driven by two evaluative processes (a) related to the benefit/loss for oneself and (b) related to the benefit/loss of another person. 相似文献75.
Liang Zheng Ruben T'Kind Saskia Decuypere Simona John von Freyend Graham H. Coombs David G. Watson 《Rapid communications in mass spectrometry : RCM》2010,24(14):2074-2082
There is evidence from our current research on resistance to stibigluconate and from some previous observations that lipid composition may be altered in resistant Leishmania donovani and in order to explore this we required a comprehensive lipidomics method. Phospholipids can be analysed by direct infusion into a mass spectrometer and such methods can work very well. However, chromatographic methods can also be very effective and are extensively used. They potentially avoid ion suppression effects, associate lipid classes with a retention time range and deliver good quantitative accuracy. In the current study three chromatography columns were compared for their ability to separate different classes of lipid. Butylsilane (C‐4), Zic‐HILIC and a silica gel column were compared. The best results were obtained with a silica gel column used in hydrophilic interaction chromatography (HILIC) mode with a mobile phase gradient consisting of (A) 20% isopropyl alcohol (IPA) in acetonitrile (v/v) and (B) 20% IPA in 0.02 M ammonium formate. Using these conditions separate peaks were obtained for triglycerides (TG), phosphoinositols (PI), inositol phosphoceramides (IPC), phosphatidylethanolamines (PE), phosphatidylserines (PS), phosphatidylcholines (PC), sphingosines (SG), lysophosphatidyethanolamines (LPE) and lysophosphatidylcholines (LPC). The methodology was applied to the analysis of lipid extracts from Leishmania donovani and by coupling the chromatography with an LTQ Orbitrap mass spectrometer. It was possible to detect 188 lipid species in the extracts with the following breakdown: PC 59, PE 38, TG 35, PI 20, CPI 13, LPC 11, LPE 2 and SG 10. The fatty acid composition of the more abundant lipids was characterised by MS2 and MS3 experiments carried out by using an LCQ Deca low‐resolution ion trap instrument coupled with the silica gel column. The separation of lipids into well‐defined groups gives extra confidence in their identification and minimises the risk of ion suppression effects. High‐resolution mass spectrometry was necessary in order to be able to differentiate between acyl‐ and acyl‐alkyl‐lipids. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
76.
77.
Annemieke van Dam Janina C. V. Schwarz Judith de Vos Dr. Maria Siebes Dr. Titia Sijen Prof. Ton G. van Leeuwen Prof. Maurice C. G. Aalders Dr. Saskia A. G. Lambrechts 《Angewandte Chemie (International ed. in English)》2014,53(24):6272-6275
No forensic method exists that can reliably estimate the age of fingermarks found at a crime scene. Information on time passed since fingermark deposition is desired as it can be used to distinguish between crime related and unrelated fingermarks and to support or refute statements made by the fingermark donors. We introduce a non‐contact method that can estimate the age of fingermarks. Fingermarks were approached as protein–lipid mixtures and an age‐estimation model was build based on the expected protein and lipid oxidation reactions. Two measures of oxidation are required from the fingermark to estimate its age: 1) the relative amount of fluorescent oxidation products 2) the rate at which these products are formed. Fluorescence spectroscopy was used to obtain these measures. We tested the method on 44 fingermarks and were able to estimate the age of 55 % of the male fingermarks, up to three weeks old with an uncertainty of 1.9 days. 相似文献
78.
Polycondensations of methylmaleic anhydride (citraconic anhydride, CiAh), bromomaleic anhydride (BMaAh), and dichloromaleic anhydride (DCMaAh) with 1,6-hexanediol were conducted in bulk. For polycondensations of CiAh, the triflates of aluminum, bismuth, lanthanum, magnesium, samarium, and scandium were used as catalysts and the best results were obtained with Bismuth triflate. MALDI-TOF mass spectra indicated that the chain growth was limited by cyclization and incomplete conversion, but temperatures above 100°C were not advantageous due to side reactions. Bismuth and samarium triflate catalyzed polycondfensations of BMaAh and DCMaAh were less successful than polycondensations of CiAh. For polycondensations of CiAh, BMaAh, and DCMaAh, only a low extent of isomerization to trans isomers (1–3%) was observed at 100°C, but considerably higher extent at 140°C. 相似文献
79.
Cordula Meyer Saskia Müller Bienvenida Gilbert-Lopez Joachim Franzke 《Analytical and bioanalytical chemistry》2013,405(14):4729-4735
The present study contributes to the evaluation of dielectric barrier discharge-based ambient ionization for mass spectrometric analysis (DBDI-MS) by providing a further step towards an understanding of underlying ionization processes. This examination highlights the effect of physical discharge modes on the ionization efficiency of the DBDI source. A distinction is made between the homogeneous and filamentary discharge mode due to different plasma gases in barrier configurations. Therefore, we first report on discharge modes of DBDI by demonstrating a universally applicable method to classify the predominant modes. Then, the ionization efficiency of these two modes is evaluated by a laser desorption-DBDI-MS with different molecular analytes. Here, the laser desorption is used to deliver neutral analytes which will be ionized by the plasma jet applied as dielectric barrier discharge ionization. With a clear increase of signal intensities in the homogeneous mode in contrast to the filamentary one, the present study indicates a pronounced dependence of the ionization efficiency on the discharge mode allowing further insight into the mechanisms of the ionization process. Figure
He-DBD-jet, propazine mass spectrum, MHCD 相似文献
80.
Dr. Sandra Künzler Saskia Rathjen Katherina Rüger Marie S. Würdemann Marcel Wernke Patrik Tholen Corinna Girschik Dr. Marc Schmidtmann Prof. Dr. Yannick Landais Prof. Dr. Thomas Müller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16441-16449
Cyclic silylated chalconium borates 13 [B(C6F5)4] and 14 [B(C6F5)4] with peri-acenaphthyl and peri-naphthyl skeletons were synthesized from unsymmetrically substituted silanes 3 , 4 , 6 , 7 , 9 and 10 using the standard Corey protocol (Chalcogen Ch=O, S, Se, Te). The configuration at the chalcogen atom is trigonal pyramidal for Ch=S, Se, Te, leading to the formation of cis- and trans-isomers in the case of phenylmethylsilyl cations. With the bulkier tert-butyl group at silicon, the configuration at the chalcogen atoms is predetermined to give almost exclusively the trans-configurated cyclic silylchalconium ions. The barriers for the inversion of the configuration at the sulfur atoms of sulfonium ions 13 c and 14 a are substantial (72–74 kJ mol−1) as shown by variable temperature NMR spectroscopy. The neighboring group effect of the thiophenyl substituent is sufficiently strong to preserve chiral information at the silicon atom at low temperatures. 相似文献