Filtern
Erscheinungsjahr
- 2016 (10) (entfernen)
Dokumenttyp
- Zeitschriftenartikel (8)
- Vortrag (2)
Schlagworte
- ICP-MS (2)
- Isotope dilution analysis (2)
- MALDI-TOF MS (2)
- SEC (2)
- Silver nanoparticles (2)
- Abbauverhalten (1)
- Copolyester (1)
- Copolymer sequence (1)
- Cyclics (1)
- Cyclization (1)
- Dispersity (1)
- Field flow fractionation (1)
- HPLC (1)
- High performance liquid chromatography (1)
- Lactide (1)
- MALDI mass spectrometry (1)
- MALDI-TOF MS/MS (1)
- MALDI-TOF Mass Spectrometry (1)
- Multivariate statistics (1)
- Photoligation (1)
- Pollen (1)
- Polycondensation (1)
- Polyesters (1)
- Polysarcosine (1)
- Polyurethane (1)
- Size exclusion chromatography (1)
- Speciation (1)
- Synthesis (1)
- Toxicology (1)
- Universal calibration (1)
- cyclization (1)
- dispersity (1)
- mass spectra (1)
- mass spectrometry (1)
- polycondensation (1)
- polyesters (1)
- polyionic liquids (1)
- reversible addition fragmentation chain transfer (RAFT) polymerization (1)
- surface modification (1)
Eingeladener Vortrag
- nein (2)
Poly(alkylene isophthalate)s were prepared by different methods, either in solution or in bulk. The SEC measurements were evaluated in such a way that all oligomers were included. In solution (monomer conc. 0.10.7 mol/L) large fractions of rings were formed and high dispersities (up to 12) were obtained, which disagree with theoretical predictions. Polycondensations in bulk did neither generate cyclics by 'back-biting' nor by end-to-end cyclization, when the maximum temperature was limited to 210 °C. The dispersities of these perfectly linear polyesters were again higher than the theoretical values. Regardless of the synthetic method monomeric cycles were never observed. Furthermore, SEC measurements performed in tetrahydrofuran and in chloroform and SEC measurements performed in three different institutes were compared. Finally, SEC measurements of five samples were performed with universal calibration and a correction factor of 0.71 ± 0.02 was found for normal calibration with polystyrene.
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.
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.
Designing artificial macromolecules with absolute sequence order represents a considerable challenge. Here we report an advanced light-induced avenue to monodisperse sequencedefined functional linear macromolecules up to decamers via a unique photochemical approach. The versatility of the synthetic strategy—combining sequential and modular concepts—enables the synthesis of perfect macromolecules varying in chemical constitution and topology. Specific functions are placed at arbitrary positions along the chain via the successive addition of monomer units and blocks, leading to a library of functional homopolymers, alternating copolymers and block copolymers. The in-depth characterization of each sequence-defined chain confirms the precision nature of the macromolecules. Decoding of the functional information contained in the molecular structure is achieved via tandem mass spectrometry without recourse to their synthetic history, showing that the sequence information can be read.We submit that the presented photochemical strategy is a viable and advanced concept for coding individual monomer units along a macromolecular chain.
Four classes of unsaturated copolyesters of L-lactide were prepared either from isosorbide or bis(hydroxymethyl)tricyclodecane in combination with fumaric acid or from 1,4-butenediol or 1,4- butynediol with terephthalic acid. All syntheses were performed in such a way that lactide was oligomerized with a diol as the initiator and the resulting oligomers were polycondensed with a dicarboxylic acid dichloride either in a one-pot synthesis or in a two-step procedure. For most copolyesters the SEC measurements gave weight average molecular weights in the range of 30–60 kg mol⁻1 and dispersities in the range of 4.2–6.2. The MALDI-TOF mass spectra displayed a high content of cycles and indicated an irreversible kinetic course of all polycondensations. Glass-transition temperatures (Tg) above 90 °C were only found for two copolyesters of isosorbide. Addition of bromine to copolyesters of 1,4-butenediol yielded flame retarding biodegradable polymers.
Polysarcosine (M-n = 3650-20 000 g mol(-1), D similar to 1.1) was synthesized from the air and moisture stable N-phenoxycarbonyl-N-methylglycine. Polymerization was achieved by in situ transformation of the urethane precursor into the corresponding N-methylglycine-N-carboxyanhydride, when in the presence of a non-nucleophilic tertiary amine base and a primary amine initiator.
Pollen represent one major cause for human allergic diseases. Currently the characterization and identification of pollen is time-consuming since it mainly relies on the microscopic determination of the genus-specific pollen morphology. A variety of new analytical approaches, like Raman - and fluorescence spectroscopy have been proposed in order to develop fast and reliable pollen identification. Recently matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was initially applied for the rapid investigation of such complex biological samples. Taxonomic differences and relations of single pollen grains could be identified.
Both commercially available lyophilized pollen and fresh pollen acquired from biological samples collected in parks and in the Botanical Garden Berlin in the years 2013-2015 were investigated. The samples were prepared by formic acid extraction in the gas phase and spotted with HCCA matrix. A variety of new approaches, like a newly developed MALDI target with micrometer sample spots sizes, were tested for their suitability. The obtained mass spectral data were investigated by principal component analysis (PCA).
The applicability of MALDI-TOF mass spectrometry for the classification of pollen according to their taxonomic relationships was proven. Specifically, chemical differences in the mass spectra at the levels of plant order, genus and in many cases even of species could be identified. Based on these results, further investigations have been undertaken to optimize the sample preparation for the classification of single pollen grains in mixtures of pollens. A novel MALDI-target design was developed to enhance the phenotypic information of pollens in their mass spectra. The combination of mass spectral patterns and multivariate statistics provide a powerful tool for the investigation of structural correlations within mixtures. The results can be used to improve the reconstruction of taxonomic relations of single species in various mixtures and might be useful for the development of a fast routine method to identify pollen based on mass spectrometry.
Polyesters of bisphenol-A, bisphenol-P, catechol, and sebacic acid are prepared and different synthetic methods are compared. The diphenols are condensed with sebacoyl chloride either in dichloromethane/pyridine or in refl uxing chlorobenzene without HCl-acceptor. Further- more, bisphenol-A acetate is polycondensed with sebacic acid in bulk. All experiments are worked up so that fractionation is avoided. The extent of cyclization is estimated by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and the molar mass distribution by size exclusion chromatography (SEC). Polycondensations in solution yield larger fractions of cyclics and higher dispersities (up to 11). Polycondensations in bulk give lower fractions of cycles and dispersities from 4.6 to 6.3 for high molar mass polyesters or 2.8 to 3.5 for low molar mass products. Characteristic curves describing the dependence of the dispersity on the initial monomer concentration are elaborated.
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.