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  • Weidner, Steffen (73)
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  • Lee, C. (3)
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  • Schwarzinger, C. (3)
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Erscheinungsjahr

  • 2019 (14)
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Referierte Publikation

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Schlagworte

  • MALDI-TOF MS (22)
  • Cyclization (17)
  • MALDI (9)
  • Polylactide (9)
  • Ring-opening polymerization (9)
  • Polycondensation (7)
  • Pollen (6)
  • Catalysts (4)
  • Isosorbide (4)
  • Lactide (4)
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Organisationseinheit der BAM

  • 1.3 Strukturanalytik (73) (entfernen)

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MALDI-TOF MS und MALDI-MSI zur Identifikation und Klassifizierung von Pollen (2019)
Weidner, Steffen
Es werden die letzten Ergebnisse präsentiert, die es ermöglichen, einzelne Pollenkörner unterschiedlicher Arten in Mischungen mittels MALDI-TOF Massenspektrometrie bzw. MALDI-TOF Imaging zu messen und unter Zuhilfenahme multivariater Auswertemethoden zu klassifizieren.
MALDI-TOF-MS for the determination of polymerization mechanisms of biodegradable polymers (2018)
Weidner, Steffen
Eine neue Art einer Ring-Expansion Polymerization (REP) von zyklischen Polylaktiden mittels neuer Katalysatoren wird präsentiert. MALDI-TOF Massenspektrometrie und andere analytische Techniken wurden zur Aufklärung des Mechanismus eingesetzt. Dabei zeigte sich, dass im Gegensatz zu anderen REP, ausschließlich zyklische Polymere gebildet wurden. Diese stellen neue Kandidatenmaterialien für zukünftige neue CRM dar.
Cyclic polylactides via ring-expansion polymerization (2018)
Weidner, Steffen
We will report on a new kind of ring-expansion polymerization (REP) of cyclic esters based of three classes of catalysts. In contrast to REP described previously these new polymerizations are characterized by a self-extrusion of the catalysts resulting in cyclic homopolyesters as the only reaction product. These REP of L-lactide were performed in bulk at temperatures between 100 and 180°C without racemization. A simplified scheme of a REP catalyzed by BuCa or SnBi is presented below. With meso-lactide temperatures down to 60°C were realized. Depending on catalyst, time and temperature with equal quantities of even and odd-numbered cycles a strong predominance of either even or odd-numbered cycles was found.
Hyphenated coupling methods for polymer characterization and identification (2013)
Weidner, Steffen
Einfluss von Feuchte und Nässe auf die Witterungs-induzierte Alterung am Beispiel eines Polyurethans (2017)
Wachtendorf, Volker ; Geburtig, Anja ; Elert, Anna-Maria ; Weidner, Steffen
In diesem Beitrag soll der relative Einfluss des Wassers als Feuchte und Nässe unter den Beanspruchungsfaktoren untersucht werden. Die Unterscheidung von Luftfeuchte und Nässe bezüglich ihrer Wirkung ist dabei notwendig, weil die stehende Nässe zusätzliche Extraktionswirkung besitzt und auch die verfügbare Sauerstoffmenge beeinflusst. Dazu wurde ein Polymer, das im Rahmen des BAM-internen Projektes PolyComp untersucht wird, künstlich bewittert. Hierzu wurde ein Fluoreszenzlampengerät mit UV-A 340 nm Leuchtstoffröhren verwendet, in dessen Probenraum durch zusätzliche Kammern die gleichzeitige Bewitterung unter drei unterschiedlichen Feuchte-Varianten realisiert wurde (bei konstanter Temperatur): • UV und trocken • UV und hohe Luftfeuchte • UV und stehende Nässe Das gleichzeitige Einwirken der einzelnen Einflussfaktoren kann dabei konkurrierende oder aufeinander folgende chemische Reaktionen und physikalische Prozesse und somit ein anderes Ergebnis bewirken, als wenn sie isoliert nacheinander auf eine Probe eingewirkt hätten. Über die erwähnten Varianten hinaus kann auch noch der spezifische Einfluss der UV-Strahlung mit untersucht werden, weil die Proben im Bereich ihrer Befestigung verdeckt sind. Die Methodik und erste Ergebnisse dieser Untersuchung werden präsentiert.
Unprecedented Ionization Processes in Mass SpectrometryProvide Missing Link between ESI and MALDI (2018)
Trimpin, S. ; Lee, C. ; Weidner, Steffen ; El-Baba, T. ; Lutomski, C. ; Inutan, E. ; Foley, C. ; Ni, C.-K. ; McEwen, C.
In the field of mass spectrometry,producing intact, highly-charged protein ions from surfaces is a conundrum with significant potential payoff in application areas ranging from bio-medical to clinical research. Here, we report on the ability to form intact, highly-charged protein ions on high vacuum time-of-flight mass spectrometers in the linear and reflectron modes achievable using experimental conditions that allow effective matrix removal from both the sample surfaces and from the charged clusters formed by the laser Ablation event. The charge states are the highest reported on high vacuum mass spectrometers, yet they remain at only around athird of the highest charge obtained using laser ablation with a suitable matrix at atmospheric pressure. Other than physical instrument modifications, the key to forming abundant and stable highly-charged ions appears to be the volatility of the matrix used. Cumulative results suggest mechanistic links between the ionization process reported here and traditional ionization methods of electrospray ionization and matrix-assisted laser desorp-tion/ionization.
Fundamental studies of new ionization technologies and insights from IMS-MS (2019)
Trimpin, S. ; Inutan, E. ; Karki, S. ; Elia, E. ; Zhang, W. ; Weidner, Steffen ; Marshall, D. ; Hoang, K. ; Lee, C. ; Davis, E. ; Smith, V. ; Meher, A. ; Cornejo, M. ; Auner, G. ; McEwen, C.
Exceptional ion mobility spectrometry mass spectrometry (IMS-MS) developments by von Helden, Jarrold, and Clemmer provided technology that gives a view of chemical/biological compositions previously not achievable. The ionization method of choice used with IMS-MS has been electrospray ionization (ESI). In this Special issue contribution, we focus on fundamentals of heretofore unprecedented means for transferring volatile and nonvolatile compounds into gas-phase ions singly and multiply charged. These newer ionization processes frequently lead to different selectivity relative to ESI and, together with IMS-MS, may provide a more comprehensive view of chemical compositions directly from their original Environment such as surfaces, e.g., tissue. Similarities of results using solvent- and matrix-assisted ionization are highlighted, as are differences between ESI and the inlet ionization methods, especially with mixtures such as bacterial extracts. Selectivity using different matrices is discussed, as are results which add to our fundamental knowledge of inlet ionization as well as pose additional avenues for inquiry. IMS-MS provides an opportunity for comparison studies relative to ESI and will prove valuable using the new ionization technologies for direct analyses. Our hypothesis is that some ESI-IMS-MS applications will be replaced by the new ionization processes and by understanding mechanistic aspects to aid enhanced source and method developments this will be hastened.
Effects of UV radiation on the friction behavior of thermoplastic polyurethanes (2018)
Theiler, Geraldine ; Wachtendorf, Volker ; Elert, Anna Maria ; Weidner, Steffen
The effects of weathering exposure on unfilled and filled thermoplastic polyurethanes (TPU) materials are described as performed under different humidity conditions. For this purpose, a weathering device was used with UV-A 340 nm lamps at a constant temperature of 40 °C. The effects of environmental (UV and humidity condition) degradation on the frictional properties of TPU materials are presented along with surface analyses to characterize the chemistry of the degradative process. Photooxidative degradation of unfilled polymer leads to deterioration of physical and mechanical properties, which affects its tribological behavior significantly. Due to crosslinking, the stiffness of the material increases, reducing drastically the friction coefficient of unfilled TPUs. The frictional behavior of glass fiber reinforced TPU is less affected by radiation.
Separation and quantification of silver nanoparticles and silver ions using reversed phase high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry in combination with isotope dilution analysis (2016)
Sötebier, Carina ; Weidner, Steffen ; Jakubowski, Norbert ; Panne, Ulrich ; Bettmer, J.
A reversed phase high performance liquid chromatography coupled to an inductively coupled plasma mass spectrometer (HPLC-ICP-MS) approach in combination with isotope dilution analysis (IDA) for the separation and parallel quantification of nanostructured and ionic silver (Ag) is presented. The main focus of this work was the determination of the ionic Ag concentration. For a sufficient stabilization of the ions without dissolving the nanoparticles (NPs), the eluent had to be initially optimized. The determined Ag ion concentration was in a good agreement with results obtained using ultrafiltration. Further, the mechanism of the NP separation in the HPLC column was investigated. Typical size exclusion effects were found by comparing results from columns with different pore sizes. Since the recovery rates decreased with increasing Ag NP size and large Ag NPs did not elute from the column, additional interactions of the particles with the stationary phase were assumed. Our results reveal that the presented method is not only applicable to Ag NPs, but also to gold and polystyrene NPs. Finally, IDA-HPLC-ICP-MS experiments in single particle mode were performed to determine the particle cut-off size. The comparison with conventional spICP-MS experiments resulted in a similar diameter and particle size distribution.
Sample loss in asymmetric flow field-flow fractionation coupled to inductively coupled plasma-mass spectrometry of silver nanoparticles (2015)
Sötebier, Carina ; Bierkandt, Frank ; Rades, Steffi ; Jakubowski, Norbert ; Panne, Ulrich ; Weidner, Steffen
In this work, sample losses of silver nanoparticles (Ag NPs) in asymmetrical flow field-flow fractionation (AF4) have been systematically investigated with the main focus on instrumental conditions like focusing and cross-flow parameters as well as sample concentration and buffer composition. Special attention was drawn to the AF4 membrane. For monitoring possible silver depositions on the membrane, imaging laser ablation coupled to inductively coupled plasma mass spectrometry (LA-ICP-MS) was used. Our results show that the sample residue on the membrane was below 0.6% of the total injected amount and therefore could be almost completely avoided at low sample concentrations and optimized conditions. By investigation of the AF4 flows using inductively coupled plasma mass spectrometry (ICP-MS), we found the recovery rate in the detector flow under optimized conditions to be nearly 90%, while the cross-flow, slot-outlet flow and purge flow showed negligible amounts of under 0.5%. The analysis of an aqueous ionic Ag standard solution resulted in recovery rates of over 6% and the ionic Ag content in the sample was found to be nearly 8%. Therefore, we were able to indicate the ionic Ag content as the most important source of sample loss in this study.
Controlled radical polymerization and in-depth mass-spectrometric characterization of poly(ionic liquid)s and their photopatterning on surfaces (2016)
Steinkönig, J. ; Bloesser, F. R. ; Huber, B. ; Welle, A. ; Trouillet, V. ; Weidner, Steffen ; Barner, L. ; Roesky, P. W. ; Yuan, J. ; Goldmann, A. S. ; Barner-Kowollik, C.
The preparation and characterization of poly(ionic liquid)s (PILs) bearing a polystyrene backbone via reversible addition fragmentation chain transfer (RAFT) polymerization and their photolithographic patterning on silicon wafers is reported. The controlled radical polymerization of the styrenic ionic liquid (IL) monomers ([BVBIM]X, X = Cl− or Tf2N−) by RAFT polymerization is investigated in detail. We provide a general synthetic tool to access this class of PILs with controlled molecular weight and relatively narrow molecular weight distribution (2000 g mol−1 ≤ Mn ≤ 10 000 g mol−1 with dispersities between 1.4 and 1.3 for p([BVBIM]Cl); 2100 g mol−1 ≤ MP ≤ 14 000 g mol−1 for p([BVBIM]Tf2N)). More importantly, we provide an in-depth characterization of the PILs and demonstrate a detailed mass spectrometric analysis via matrix-assisted laser desorption ionization (MALDI) as well as – for the first time for PILs – electrospray ionization mass spectrometry (ESI-MS). Importantly, p([BVBIM]Cl) and p([DMVBIM]Tf2N) were photochemically patterned on silicon wafers. Therefore, a RAFT agent carrying a photoactive group based on ortho-quinodimethane chemistry – more precisely photoenol chemistry – was photochemically linked for subsequent controlled radical polymerization of [BVBIM]Cl and [DMVBIM]Tf2N. The successful spatially-resolved photografting is evidenced by surface-sensitive characterization methods such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The presented method allows for the functionalization of diverse surfaces with poly(ionic liquid)s.
Taxonomic relationship of pollen from MALDI TOF MS data using multivariate statistics (2015)
Seifert, Stephan ; Weidner, Steffen ; Panne, Ulrich ; Kneipp, Janina
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has been suggested as a promising tool for the investigation of pollen, but the usefulness of this approach for classification and identification of pollen species has to be proven by an application to samples of varying taxonomic relations.
Degradation of MDI-based polyether and polyester-polyurethanes in various environments - Effects on molecular mass and crosslinking (2019)
Scholz, Philipp ; Wachtendorf, Volker ; Panne, Ulrich ; Weidner, Steffen
Size-exclusion chromatography (SEC) was used to monitor changes of the molecular masses of thermoplastic polyether – and polyester urethane (TPU) exposed to thermal, hydrolytic, and photo-oxidative (UV) Degradation conditions for several days. The thermal treatment was performed at elevated temperatures (100–200 °C) under oxidative (air) as well as non-oxidative (nitrogen) conditions to evaluate the specific influence of oxygen on the degradation. At higher temperatures (≥175 °C) a fast decrease of the molecular masses of both PU accompanied by a high degree of crosslinking was found. At lower temperatures (≤150 °C) the polymers remained widely unaffected by thermal degradation within the investigated degradation interval of up to two weeks. Surprisingly, the influence of oxygen (air) was found to be less distinct. In contrast to that, UV treatment at 25 °C at less than 10% rel. humidity (RH) resulted in a fast crosslinking, whereas the molecular masses of both PU decreased slower than for thermal treatments. The depth of penetration of the UV radiation was estimated using 3D printed PU samples with different thicknesses. Hydrolysis based degradation effects were less significant. Only slight molecular mass changes were detected at temperatures ≤80 °C within a time span of 14 days, while no crosslinking could be measured. Considering the degradation results at the investigated exposure parameters, it could be shown that esterbased PU in general exhibits a significant higher stability compared to ether-based materials.
Analytical toolset to characterize polyurethanes after exposure to artificial weathering under systematically varied moisture conditions (2019)
Scholz, Philipp ; Wachtendorf, Volker ; Elert, Anna Maria ; Falkenhagen, Jana ; Becker, Roland ; Hoffmann, Katrin ; Resch-Genger, Ute ; Tschiche, Harald ; Reinsch, Stefan ; Weidner, Steffen
Polyether and -ester urethanes (PU) were exposed to artificial weathering at 40 °C and artificial UV radiation in a weathering chamber. In 3 parallel exposures, humidity was varied between dry, humid, and wet conditions. Material alteration was investigated by various analytical techniques like size exclusion chromatography (SEC), liquid chromatography-infrared spectroscopy (LC-FTIR), thermal-desorption gas chromatography-mass spectrometry (TD-GC-MS), fluorescence mapping and dynamic mechanical analysis (DMA). Our results show that depending on the weathering conditions, different degradation effects can be observed. By means of SEC an initial strong decrease of the molar masses and a broadening of the mass distributions was found. After a material dependent time span this was followed by a plateau where molar mass changes were less significant. A minor moisture-dependent degradation effect was only found for polyester PU. Fluorescence measurements on two materials revealed an increase in the luminescence intensity upon weathering process reaching a saturation level after about 500 h. The changes in the optical properties observed after different exposure conditions and times were very similar. The TD-GC-MS data showed the fate of the stabilizers and antioxidant in the course of weathering. LC-FTIR measurements revealed a change in peak intensities and the ratio of urethane and carbonyl bands.
Microstructure of polymer-imprinted metal–organic frameworks determined by absorption edge tomography (2019)
Scholz, Philipp ; Ulbricht, Alexander ; Joshi, Y. ; Gollwitzer, Christian ; Weidner, Steffen
Mechanochemically synthesized metal–organic Framework material HKUST-1 in combination with acrylonitrile butadiene styrene polymer was used to form a polymer metal–organic framework composite material by a simple extruder. This composite filament was used for 3D printing. Xray diffraction measurements were used to prove the homogeneous distribution of the metal–organic framework in the polymer on a centimeter scale, whereas X-ray Absorption Edge Tomography using a synchrotron radiation source was able to evaluate the 3D distribution of the metal–organic framework material both in the filament and the resultant printed sample with a resolution of a few lm. Our very first data indicate that, apart from a few clusters having significantly higher Cu concentration, HKUST-1 is distributed homogeneously down to the 100 lm length scale in both polymer bulk materials in the form of clusters with a size of a few lm. Absorption Edge Tomography in combination with data fusion also allows for the calculation of the metal–organic framework amount located on the external polymer surface.
Thermoresponsive poly(N-C3 glycine)s (2013)
Robinson, J.W. ; Secker, C. ; Weidner, Steffen ; Schlaad, H.
Ring-opening polymerization of N-substituted glycine N-carboxyanhydrides (NCAs) was applied to prepare a series of well-defined poly(N-C3 glycine)s (C3 = n-propyl, allyl, propargyl, and isopropyl), polypeptoids, with molecular weights in the range of 1.8–6.6 kg mol–1. Poly(N-isopropyl glycine), a previously unreported polypeptoid, could be obtained by bulk polymerization of the corresponding NCA in the melt. The samples were characterized by spectroscopy (NMR and FT-IR), size exclusion chromatography (SEC), and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI–ToF MS). The polymers could be dispersed in water up to 20–40 g L–1; the poly(N-propargyl glycine) was not soluble in water. Turbidity measurements of the three water-soluble polypeptoids illustrated cloud point temperatures dependent on structural and electronic properties of the side chain. The cloud point temperatures were found to increase in the order C3 = n-propyl (15–25 °C) < allyl (27–54 °C) < isopropyl (47–58 °C). Long-term annealing of the aqueous solution of poly(N-{n-propyl} glycine) and poly(N-allyl glycine) above the cloud point temperature resulted in the formation of crystalline microparticles with melting points of 188–198 and 157–165 °C (differential scanning calorimetry, DSC), respectively, and rose bud type morphology (scanning electron microscopy, SEM).
Stereocomplexation of cyclic polylactides with each other and with linear poly(L-lactide)s (2019)
Meyer, A. ; Weidner, Steffen ; Kricheldorf, H.
Two kinds of cyclic poly(D- and L-lactide)s were synthesized, namely CI labeled samples mainly consisting of even-numbered cycles with low dispersity and CII, CIII or CIV-labeled ones consisting of equal amounts of even and odd-numbered cycles with high dispersity and igher molecular weights (Mw up to 300 000). Furthermore, linear poly L-lactide)s were prepared by initiation with ethanol and in both series the molecular weight was varied. The formation of stereocomplexes from cyclic poly(D-lactide)s and all kinds of poly L-lactide)s was performed in dichloromethane/toluene mixtures. The stereocomplexes crystallized from the reaction mixture were characterized in the virgin state and after annealing at 205 °C. Stereocomplexes free of stereohomopolymers with crystallinities up to 80% were obtained from all experiments in yields ranging from 60 to 80%. Despite the high annealing temperature (maintained for 1 h), little transesterification was observed and the crystallinity slightly increased.
Poly(2‐oxazoline) s Based on Phenolic Acids (2019)
Lüdecke, Nils ; Weidner, Steffen ; Schlaad, Helmut
A series of phenolic-acid-based 2-oxazoline monomers with methoxysubstituted phenyl and cinnamyl side chains is synthesized and polymerized in a microwave reactor at 140 °C using methyl tosylate as the initiator. The obtained poly(2-oxazoline)s are characterized by NMR spectroscopy, MALDITOF mass spectrometry, and size-exclusion chromatography (SEC). Kinetic studies reveal that the microwave-assisted polymerization is fast and completed within less than ≈10 min for low monomer-to-initiator ratios of ≤25. Polymers with number-average molar masses of up to 6500 g mol−1 and low dispersity (1.2–1.3) are produced. The aryl methyl ethers are successfully cleaved with aluminum triiodide/N,N′ diisopropylcarbodiimide to give a poly(2-oxazoline) with pendent catechol groups.
Toward understanding the ionization mechanism of matrix‐assisted ionization using mass spectrometry experiment and theory (2019)
Lee, C. ; Inutan, E. D. ; Chen, J. L. ; Mukeku, M. M. ; Weidner, Steffen ; Trimpin, S. ; Ni, C.-K.
Matrix‐assisted ionization (MAI) mass spectrometry does not require voltages, a laser beam, or added heat to initiate ionization, but it is strongly dependent on the choice of matrix and the vacuum conditions. High charge state distributions of nonvolatile analyte ions produced by MAI suggest that the ionization mechanism may be similar to that of electrospray ionization (ESI), but different from matrix‐assisted laser desorption/ionization (MALDI). While significant information is available for MAI using mass spectrometers operating at atmospheric and intermediate pressure, little is known about the mechanism at high vacuum. Eleven MAI matrices were studied on a high‐vacuum time‐of‐flight (TOF) mass spectrometer using a 266 nm pulsed laser beam under otherwise typical MALDI conditions. Detailed comparisons with the commonly used MALDI matrices and theoretical prediction were made for 3‐nitrobenzonitrile (3‐NBN), which is the only MAI matrix that works well in high vacuum when irradiated with a laser. Screening of MAI matrices with good absorption at 266 nm but with various degrees of volatility and laser energies suggests that volatility and absorption at the laser wavelength may be necessary, but not sufficient, criteria to explain the formation of multiply charged analyte ions. 3‐NBN produces intact, highly charged ions of nonvolatile analytes in high‐vacuum TOF with the use of a laser, demonstrating that ESI‐like ions can be produced in high vacuum. Theoretical calculations and mass spectra suggest that thermally induced proton transfer, which is the major ionization mechanism in MALDI, is not important with the 3‐NBN matrix at 266 nm laser wavelength. 3‐NBN:analyte crystal morphology is, however, important in ion generation in high vacuum. The 3‐NBN MAI matrix produces intact, highly charged ions of nonvolatile compounds in high‐vacuum TOF mass spectrometers with the aid of ablation and/or heating by laser irradiation, and shows a different ionization mechanism from that of typical MALDI matrices.
Simplifying the Preparation of Pollen Grains for MALDI-TOF MS Classification (2017)
Lauer, Franziska ; Seifert, Stephan ; Kneipp, Janina ; Weidner, Steffen
Matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS) is a well-implemented analytical technique for the investigation of complex biological samples. In MS, the sample preparation strategy is decisive for the success of the measurements. Here, sample preparation processes and target materials for the investigation of different pollen grains are compared. A reduced and optimized sample preparation process prior to MALDI-TOF measurement is presented using conductive carbon tape as target. The application of conductive tape yields in enhanced absolute signal intensities and mass spectral pattern information, which leads to a clear separation in subsequent pattern analysis. The results will be used to improve the taxonomic differentiation and identification, and might be useful for the development of a simple routine method to identify pollen based on mass spectrometry.
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