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  • Weidner, Steffen (197)
  • Friedrich, Jörg Florian (27)
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Coding and decoding libraries of sequence-defined functional copolymers synthesized via photoligation (2016)
Zydziak, N. ; Konrad, W. ; Feist, F. ; Afonin, S. ; Weidner, Steffen ; Barner-Kowollik, C.
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.
Synthesis of terpene-poly(ethylene oxide)s by t-BuP4-promoted anionic ring-opening polymerization (2012)
Zhao, J. ; Schlaad, H. ; Weidner, Steffen ; Antonietti, M.
Terpene alcohols (menthol, retinol, cholesterol, and betulin) together with the phosphazene base t-BuP4 were used as initiating systems for anionic ring-opening polymerization of ethylene oxide. The polymerizations were conducted in a controlled manner with the initial molar ratio of t-BuP4 to hydroxyl groups of 0.01–0.2, yielding a series of biohybrid polymers comprising terpene entities and poly(ethylene oxide) (PEO) chains with low polydispersities and tunable compositions (57–87 wt% of PEO). Samples were characterized by NMR and UV/visible spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography; thermal properties were studied by differential scanning calorimetry. The concept of this study opens a new toolbox of terpene-based biohybrid polymers with variable properties and functions.
Evidence for laser-induced redox reactions in matrix-assisted laserdesorption/ionization between cationizing agents and target plate material: a study with polystyrene and trifluoroacetate salts (2017)
Zeegers, G. P. ; Steinhoff, R. F. ; Weidner, Steffen ; Zenobi, R.
Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is often applied to assess the dispersity and the end groups of synthetic polymers through the addition of cationizing agents. Here weaddress how these cation adducts are formed using polystyrene (PS) as a model polymer. We analyzed PSby MALDI-MS with a 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylidene]malononitrile (DCTB) as the matrix and a range of trifluoroacetate (TFA) salts as cationizing agents on a range of different targetplate materials (copper, 1.4301 stainless steel, aluminum, Inconel 625, Ti90/Al6/V4 and chromium-, gold-and silver-plated stainless steel). It was found that on a stainless steel substrate the metal cations Al+,Li+, Na+, Cu+and Ag+formed polystyrene adducts, whereas K+, Cs+, Ba2+, Cr3+, Pd2+, In3+, or their lower oxidation states, did not. For the copper and silver substrates, PS and DCTB adduct formation with cations liberated from these target plate materials was observed upon addition of a cationizing agent, which indicates the occurrence of redox reactions between the added TFA salts and the target plate material. Judging from their standard electrode potentials, these redox reactions would not normally occur, i.e.,they require an additional energy input, strongly suggesting that the observed redox reactions are laser-induced. Furthermore, copper granules were found to successfully sequester PS from a tetrahydrofuran(THF) solution, consistent with the view complex formation with the copper target plate can take place prior to the MALDI-MS measurement.
The role of statistics and microenvironment for the photoresponse in multi-switch architectures: The case of photoswitchable oligoazobenzene foldamers (2013)
Yu, Z. ; Weidner, Steffen ; Risse, T. ; Hecht, S.
Systems containing multiple photochromic units possibly display a synergistic interplay of individual switching events and hence potentially give rise to unprecedented photoresponsive behavior. Among such systems photoswitchable foldamers are attractive as the photoisomerization events are coupled to the helix–coil conformational transition. To gain comprehensive insight into the role of the number of switching units (statistics) as well as their specific location and relative orientation in the helix backbone, several series of foldamers have been synthesized and characterized. In these series of foldamers, the local environment of the photoswitchable units was precisely tuned as π,π-stacking interactions were enforced to occur between specific pairs, i.e. azobenzene–azobenzene, azobenzene–tolane, or phenylene–phenylene units. These particular arrangements are reflected not only in the stability of the helical conformation, but also affect the photoresponsive behavior, i.e. the rate of photoisomerization and extent of denaturation. Furthermore, determining the intramolecular spin–spin distance in a series of TEMPO-labeled foldamers with variable chain lengths and different spatial locations of the spin-labels deduced an independent verification of the photoinduced helix–coil transition by ESR spectroscopy. Quantitative analysis of the corresponding ESR spectra shows an excellent correlation of the extent of intramolecular spin–spin coupling and the intensity of the Cotton effect in CD spectroscopy. From all of these results an unusual relationship between the rate of photoisomerization and the extent of photoinduced denaturation could be unraveled, as they are not going hand-in-hand but compete with each other, i.e. the easier the individual switching event is, the harder it becomes to achieve a high degree of unfolding. This insight into the effect of microenvironment on the ease of individual switching events and the role of statistics on the resulting degree of the overall conformational transition is of general interest for the design of multi-switch architectures with improved photoresponse.
Comparison of miniaturized and conventional asymmetrical flow field flow fractionation (AF4) channels for nanoparticle separation (2017)
You, Zengchao ; Meier, Florian ; Weidner, Steffen
The performance of a miniaturized channel for the separation of polymer and metal nanoparticles (NP) using Asymmetrical Flow Field-Flow Fractionation (AF4) was investigated and compared with a conventional AF4 system. To develop standard separation methods, experimental parameters like cross flow, gradient profile and injection time were varied and optimized. Corresponding chromatographic parameters were calculated and compared. Our results indicate that the chromatographic resolution in the miniaturized channel is lower, whereas significantly shorter analyses time and less solvent consumption were obtained. Moreover, the limit of detection (LOD) and limit of quantification (LOQ) obtained from hyphenation with a UV-detector are obviously lower than in a conventional channel, which makes the miniaturized channel interesting for trace analysis.
Separation of polystyrene nanoparticles with different coatings using two-dimensional off-line coupling of asymmetrical flow field flow fractionation and capillary electrophoresis (2019)
You, Zengchao ; Jakubowski, Norbert ; Panne, Ulrich ; Weidner, Steffen
The successful off-line coupling of asymmetrical flow field flow fractionation (AF4) and capillary electrophoresis (CE) for separation of nanoparticles (NPs) with different surface coatings was shown. We could successfully demonstrate that, in a certain NP size range, hyphenation of both techniques significantly improved the separation of differently coated NPs. Three mixtures of polystyrene nanoparticles (PS-NPs) with comparable core sizes but different coatings (no coating/carboxyl-coated) were studied. Separation in either method resulted in non-baseline resolved or non-separated peaks. In contrast, two-dimensional off-line coupling of AF4 and CE resulted in clearly separated regions in their 2 D plots in case of 20 and 50 nm particle mixtures, whereas the 100 nm NP mixture could not be separated at all. Various factors affecting the separation like hydrodynamic diameter or SDS concentration were discussed.
Conducting polymer/SWCNTs modular hybrid materials via Diels-Alder ligation (2013)
Yameen, B. ; Zydziak, N. ; Weidner, Steffen ; Bruns, M. ; Barner-Kowollik, C.
The development of a facile covalent strategy for the fabrication of organic conducting polymers (OCPs)/carbon nanotubes (CNTs) based molecular hybrid materials remains a challenge and is expected to address the detrimental intrinsic bundling issue of CNTs. In view of the pristine CNTs' ability to undergo Diels–Alder reactions with dienes, we report the synthesis of a novel poly(3-hexylthiophene) (P3HT) based organic conducting polymer (OCP) with terminal cyclopentadienyl (Cp) groups. The synthetic strategy employed is based on a combination of in situ end group functionalization via Grignard metathesis (GRIM) polymerization and a subsequent end group switching via reaction with nickelocene. Characterization data from Matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI–TOF MS) fully support the successful synthesis of monofunctional Cp-capped P3HT, which was found to be highly reactive toward dienophile end-capped polystyrene (PS). The Cp-capped P3HT was subsequently ligated to the surface of pristine single walled CNTs (SWCNTs). The resulting P3HT/SWCNTs molecular hybrid material was characterized using thermogravimetric analysis (TGA), elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), and high resolution transmission electron microscopy (HRTEM). The data from TGA, EA, and XPS were used to quantitatively deduce the grafting density. P3HT/SWCNTs prepared with Cp capped P3HT was found to contain 2 times more P3HT than the reference sample, featuring a grafting density of 0.0510 chains·nm–2 and a periodicity of 1 P3HT chain per 748 carbon atoms of the SWCNTs. HRTEM revealed individual SWCNTs wrapped with P3HT whereas in the reference sample P3HT was adsorbed on the bundles of the SWCNTs. The results presented here provide a new avenue for designing novel materials based on CNTs and OCPs.
Coating of carbon fibers with adhesion-promoting thin poly(acrylic acid) and poly(hydroxyethylmethacrylate) layers using electrospray ionization (2015)
Wettmarshausen, Sascha ; Friedrich, Jörg Florian ; Meyer-Plath, Asmus ; Kalinka, Gerhard ; Hidde, Gundula ; Weidner, Steffen
Thin coatings of poly(acrylic acid) (PAA) and poly(hydroxyethylmethacrylate) (PHEMA) were deposited onto carbon fibers by means of the electrospray ionization (ESI) technique in ambient air. These high-molecular weight polymer layers were used as adhesion promoters in carbon fiber–epoxy resin composites. Within the ESI process, the carbon fibers were completely enwrapped with polymer in the upper 10 plies of a carbon fiber roving. As identified with scanning electron microscopy also shadowed fibers in a bundle as well as backsides of fiber rovings were pinhole-free coated with polymers (‘electrophoretic effect'). Under the conditions used, the layers have a granular structure. Residual solvent was absent in the deposit. PAA and PHEMA films did not show any changes in composition and structure in comparison with the original polymers as analyzed by X-ray photo-electron spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Single-fiber pullout tests of coated fibers embedded in epoxy resin showed significantly increased interfacial shear strength. It is assumed that chemical bonds between carbon fiber poly(acrylic acid) and epoxy resin contribute significantly to the improved interactions.
Thiol–ene polymerization of oligospiroketal rods (2017)
Wessig, P. ; Schulze, T. ; Pfennig, A. ; Weidner, Steffen ; Prentzel, S. ; Schlaad, H.
The nucleophilic thiol–ene (thia-Michael) reaction between molecular rods bearing terminal thiols and bis-maleimides was investigated. The molecular rods have oligospiroketal (OSK) and oligospirothioketal (OSTK) backbones. Contrary to the expectations, cyclic oligomers were always obtained instead of linear rigid-rod polymers. Replacing the OS(T)K rods with a flexible chain yielded polymeric products, suggesting that the OS(T)K structure is responsible for the formation of cyclic products. The reason for the preferred formation of cyclic products is due to the presence of folded conformations, which have already been described for articulated rods.
Influence of Chirality on Phase Behaviour of Copolymers Containing Cholesterol as Mesogenic Group (1996)
Weidner, Steffen ; Wolff, D. ; Springer, J.
Phase Behaviour of Copolymers Containing Cholesterol and 4,4' Methoxybiphenyl as Mesogenic Group (1996)
Weidner, Steffen ; Wolff, D. ; Springer, J.
Influence of Spacer Variation on Phase Behaviour of Liquid-Crystalline Copolymethacrylates containing Cholesterol and S-(-)-4,4'-chloropropionyl-oxybiphenyl (1997)
Weidner, Steffen ; Wolff, D. ; Springer, J.
Mass Spectrometry of Synthetic Polymers (2010)
Weidner, Steffen ; Trimpin, s.
Mass Spectrometry of Synthetic Polymers (2008)
Weidner, Steffen ; Trimpin, S.
Matrix-assisted laser desorption/ionization imaging mass spectrometry of pollen grains and their mixtures (2013)
Weidner, Steffen ; Schultze, R.-D. ; Enthaler, B.
RATIONALE The fast and univocal identification of different species in mixtures of pollen grains is still a challenge. Apart from microscopic evaluation and Raman spectroscopy, no other techniques are available. METHODS Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry was applied to the analysis of extracts of single pollen grains and pollen mixtures. Pollen grains were fixed, treated and covered with matrix directly on the MALDI target. RESULTS Clearly resolved MALDI ion intensity images could be obtained enabling the identification of single pollen grains in a mixture. CONCLUSIONS Our results demonstrate the potential and the suitability of MALDI imaging mass spectrometry as an additional method for the identification of pollen mixtures.
Low-temperature polymerization of epsilon-caprolactone catalyzed by cerium triflates (2013)
Weidner, Steffen ; Scheliga, F. ; Kricheldorf, H.R.
Using 22 metal triflates as catalysts, ε-caprolactone is polymerized at 22 °C in bulk. Only five relatively acidic triflates prove active. Three triflates, including the neutral Sm3+, are active using water as initiator. A very low content of cyclics is found in all the experiments. With Ce3+ and Ce4+, polymerizations are performed in CH2Cl2 and in bulk at 2 °C and 22 °C. Low dispersities (down to 1.1) are obtained. At 22 °C, Ce4+ and, even better, Ce3+ also catalyze syntheses of CO2H- and CH2OH-terminated polycaprolactones, whereby higher dispersities and larger fractions of cyclics are obtained. Further polymerizations and polycondensations are catalyzed with protic acids. The results can be explained by a proton-catalyzed activated monomer mechanism.
A new approach of characterizing the hydrolytic degradation of poly(ethylene terephthalate) by MALDI-MS (1997)
Weidner, Steffen ; Kühn, Gerhard ; Werthmann, Barbara ; Schröder, Hartmut ; Just, Ulrich ; Borowski, Renate ; Decker, Renate ; Schwarz, Bärbel ; Schmücking, I. ; Seifert, Ingetraut
The hydrolytic degradation of technical poly(ethylene terephthalate) (PET) was investigated by means of different methods such as size-exclusion chromatography (SEC), viscometry, light-scattering, thin-layer chromatography, end-group titration, and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The long-term degradation was simulated by exposing PET filament yarns to aqueous neutral conditions at 90°C for up to 18 weeks. By means of MALDI-MS and thin-layer chromatography, the formation of different oligomers was obtained during polymer degradation. As expected, an ester scission process was found generating acid terminated oligomers (H-[GT]m-OH) and T-[GT]m-OH and ethylene glycol terminated oligomers (H-[GT]m-G), where G is an ethylene glycol unit and T is a terephthalic acid unit. Additionally, the scission of the ester bonds during the chemical treatment led to a strong decrease in the number of cyclic oligomers ([GT]m). The occurrence of di-acid terminated species demonstrated a high degree of degradation.
Changes in molecular weight distribution of polymers by plasma treatment (1997)
Weidner, Steffen ; Kühn, Gerhard ; Roessner, D. ; Friedrich, Jörg Florian ; Unger, Wolfgang ; Lippitz, Andreas
MALDI/MS - A New Technique in Characterizing Chemical Heterogeneity of Degradation Products of Poly(Ethylene Terephthalate)s (1996)
Weidner, Steffen ; Kühn, Gerhard ; Just, Ulrich ; Werthmann, Barbara ; Decker, Renate ; Schwarz, Bärbel ; Borowski, Renate
Characterization of oligomers in poly(ethylene terephthalate) by matrix-assisted laser desorption/ionization mass spectrometry (1995)
Weidner, Steffen ; Kühn, Gerhard ; Just, Ulrich
Plasmaoxidative Degradation of Polymers Studied by Matrix-assisted Laser Desorption/Ionization Mass Spectrometry (1996)
Weidner, Steffen ; Kühn, Gerhard ; Friedrich, Jörg Florian ; Unger, Wolfgang ; Lippitz, Andreas
Infrared-Matrix-assisted Laser Desorption/Ionization and Infrared-Laser Desorption/Ionization Investigations of Synthetic Polymers (1998)
Weidner, Steffen ; Kühn, Gerhard ; Friedrich, Jörg Florian
Influence of Plasma Treatment on the Molar Mass of Poly(ethylene terephthalate) Investigated by Different Chromatographic and Spectroscopic Methods (1998)
Weidner, Steffen ; Kühn, Gerhard ; Decker, Renate ; Roessner, D. ; Friedrich, Jörg Florian
The influence of different types of low and atmospheric pressure plasma on poly(ethylene terephthalate) (PET) has been studied in terms of changes in molar mass and molar mass distribution. Apart from a variation of plasma gases (oxygen, helium) different types of plasma (microwave, radio frequency, corona discharge) were used for the plasma surface modification. The changes in molar mass and types of functional end groups of lower molar mass products were investigated by means of matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOFMS), whereas the high-molar mass fraction was analyzed by means of size-exclusion chromatography (SEC). The formation of crosslinked products during exposure to a helium plasma, which emits preponderately energy-rich and intense ultraviolet radiation, was proved by means of thermal field-flow fractionation (ThFFF). This method combined with a multiangle laser light scattering (MALLS) detector allows detection of weakly crosslinked polymers and microgels. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1639-1648, 1998
Transesterification in the solid state of cyclic and linear poly(l-lactide)s (2017)
Weidner, Steffen ; Kricheldorf, Hans R.
Poly(l-lactide)s are synthesized and annealed at 120 °C and changes of the molecular weight distribution (MWD) are monitored by matrix-assited laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. For example, benzyl alcohol+SnOct2 causes equilibration of odd- and even-numbered chains and the final goal of the transesterification is the most probable distribution. The underlying intermolecular transesterification is even observed at 100 and 80 °C in the solid state. However, cyclic tin mercaptide catalysts transform the initial most probable distribution into a MWD with maxima, which display a conspicuous fine structure due to a preferential crystallization of certain ring sizes. The optimum ring sizes for the crystallization are provided by ring-ring equilibration. The gradual formation of a special morphology shifts the melting temperature to values up to 187 °C. Annealing of commercial poly(l-lactide) with a cyclic tin catalyst also yields a distribution of mass peaks with a maximum showing the characteristic fine structure.
Cyclization and dispersity of poly(alkylene isophthalate)s (2016)
Weidner, Steffen ; Kricheldorf, H.R. ; Scheliga, F.
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. 0.1–0.7 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.
Spirocyclic bisphenoxides of Ge, Zr, and Sn as catalysts for ring-expansion polymerizations of L- and meso-lactide (2018)
Weidner, Steffen ; Kricheldorf, H. R.
Spirocyclic phenoxides of germanium, zirconium, and tin were prepared from 2,20-dihydroxybiphenyl and 2,20-dihydroxy-1,10-binaphthyl. Ring-expansion polymerizations of L-lactide are mainly studied at 160 or 180 °C. The reactivity of the catalysts increases in the order: Zr < Ge < Sn. Regardless of catalyst, the weight-average molecular weights (Mw) never exceed 50,000 g mol−1. The resulting poly(L-lactide)s are optically pure and have a cyclic architecture. Decreasing temperature and time favor Formation of even-numbered cycles, and at 102 ° cyclics, almost free of odd-numbered rings are obtained. Analogous polymerizations of meso-lactide give similar results >120 °C, but different results at 100 or 80 °C. Surprisingly, bell-shaped narrow molecular weight distributions are obtained <140 °C, resembling the pattern of living polymerizations found for alcohol-initiated polymerizations. An unusual transesterification mechanism yielding narrow distributions of odd-numbered cycles is discovered too.
The Role of Transesterification in SnOct 2 - Catalyzed Polymerizations of Lactides (2017)
Weidner, Steffen ; Kricheldorf, H. R.
l-lactide or meso-lactide are polymerized either at 120 °C where the polymerization process of l-lactide is accompanied by crystallization, or at 180 °C where poly(l-lactide) remains in the molten state. Polymerizations at 120 °C initially yield even-numbered chains (with respect to lactic acid units) having relatively low dispersity, but the fraction of odd-numbered chains increases with time and the entire molecular weight distribution changes. Traces of cyclics are only formed after 7 d. Polymerizations at 180 °C yield equilibrium of even and odd-numbered chains from the beginning, but at low monomer/initiator ratios and short reaction times (<4 h) cyclics are again not formed. They appear at longer reaction times and entail higher dispersities. The results are discussed in terms of five different transesterification mechanisms.
Transesterification in alcohol-initiated ROPs of l- and meso-lactide catalyzed by Sn(II) and Sn(IV) compounds at low temperatures (2018)
Weidner, Steffen ; Kricheldorf, H.
The purpose of this study is to shed more light on the transesterification processes in alcohol-initiated and tin(II) 2-ethylhexanoate (SnOct2)-catalyzed polymerizations of lactides at low or moderate temperatures. Ethanol-initiated polymerizations are conducted in concentrated solutions at 80 °C and a strong dependence of even/odd equilibration on the alcohol/Sn ratio. Around or above 120 °C cyclization of poly(l-lactide) via “backbiting” occurs as a third mechanism. However, poly(m-lactide) shows a higher cyclization tendency and yields cyclics even at 100 °C. Combinations of ethanol and certain cyclic dibutyltin(IV) catalysts also yield cyclic oligomers of l-lactide at 80 °C. Reaction conditions allowing for a total suppression of all transesterification reactions are not found, but even-numbered poly(m-lactide)s with a purity >95% are obtained at 70 or 60 °C.
MALDI-TOF imaging mass spectrometry of artifacts in 'dried droplet' polymer samples (2011)
Weidner, Steffen ; Knappe, Patrick ; Panne, Ulrich
Matrix-assisted laser desorption/ionization-timeof-flight (MALDI-TOF) imaging of polystyrenes with various molecular masses was applied to study spatial molecular mass distribution of polymers in sample spots prepared by the 'dried droplet' method. When different solvents and target surfaces were examined, a segregation of single homologous polymers was observed depending upon the evaporation rate of the solvent. For the observed Patterns left by the evaporating droplet, a hypothesis is offered taking into account different hydrodynamic interactions and diffusion. The results illustrate that spot preparation using the conventionally 'dried droplet' method is prone to artifacts and should be avoided for reliable and reproducible MALDI mass spectrometry experiments with regards to the Determination of molecular masses and mass distributions.
Analysis of modified polyamide 6.6 using coupled liquid chromatography and MALDI-TOF-mass spectrometry (2004)
Weidner, Steffen ; Just, Ulrich ; Wittke, Wolfgang ; Rittig, F. ; Gruber, F. ; Friedrich, Jörg Florian
Matrix-assisted Laser Desorption/Ionization Mass Spectrometry of C36- Alkane degradated by Vacuum Ultraviolet Radiation (1997)
Weidner, Steffen ; Holländer, A. ; Kühn, Gerhard
Determination of chemical and molecular-weight distributions of heterogeneous polymers by means of MALDI-MS coupled with chromatography (2000)
Weidner, Steffen ; Falkenhagen, Jana ; Much, Helmut ; Krüger, Ralph-Peter ; Friedrich, Jörg Florian
A novel software tool for copolymer characterization by coupling of liquid chromatography with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (2007)
Weidner, Steffen ; Falkenhagen, Jana ; Maltsev, Sergey ; Sauerland, V. ; Rinken, M.
The results of copolymer characterization by coupling of chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) techniques and subsequent calculation of copolymer composition using a novel software tool MassChrom2D are presented. For high-resolution mass analysis copolymer samples were fractionated by means of liquid adsorption chromatography (LAC). These fractions were investigated off-line by MALDI-TOF MS. Various mono-n-butyl ethers of polyethylene oxide-polypropylene oxide copolymers (PEO-co-PPO) were investigated. As well as the copolymer composition presented in two-dimensional plots, the applied approach can give additional hints on specific structure-dependent separation conditions in chromatography.
Principle of Two-Dimensional Characterization of Copolymers (2007)
Weidner, Steffen ; Falkenhagen, Jana ; Krüger, Ralph-Peter ; Just, Ulrich
Two-dimensional polymer characterization is used for a simultaneous analysis of molar masses and chemical heterogeneities (e.g., end groups, copolymer composition, etc.). This principle is based on coupling of two different chromatographic modes. Liquid adsorption chromatography at critical conditions (LACCC) is applied for a separation according to the chemical heterogeneity, whereas in the second-dimension fractions are analyzed with regard to their molar mass distribution by means of size exclusion chromatography (SEC). Because appropriate standards for a calibration of the SEC are seldom available, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) was used to substitute the SEC. The LACCC-MALDI MS coupling enables acquiring additional structural information on copolymer composition, which can considerably enhance the performance of this coupled method.
Structure and end-group analysis of complex hexanediol-neopentylglycol-adipic acid copolyesters by matrix-assisted laser desorption/ionization collision-induced dissociation tandem mass spectrometry (2009)
Weidner, Steffen ; Falkenhagen, Jana ; Knop, K. ; Thünemann, Andreas F.
Sequences and end groups of complex copolyesters were determined by fragmentation analysis by means of matrix-assisted laser desorption/ionization collision-induced dissociation tandem mass spectrometry (MALDI CID MS/MS). The complexity of the crude copolyester mixture was reduced by a chromatographic separation followed by a MALDI time-of-flight (TOF) investigation of fractions. Due to overlapping compositional and end-group information a clear assignment of end groups was very difficult. However, the fragmentation of suitable precursor ions resulted in typical fragment ion patterns and, therefore, enabled a fast and unambiguous determination of the end groups and composition of this important class of polymers.
Liquid Adsorption Chromatography near Critical Conditions of Adsorption coupled with Matrix-assisted Laser/Ionization Mass Spectrometry (1999)
Weidner, Steffen ; Falkenhagen, Jana ; Friedrich, Jörg Florian ; Krüger, Ralph-Peter ; Schulz, Günter ; Much, Helmut
Copolymer composition determined by LC-MALDI-TOF MS coupling and 'MassChrom2D' data analysis (2012)
Weidner, Steffen ; Falkenhagen, Jana ; Bressler, I.
The MALDI-TOF MS analysis of copolymers very often results in complex spectra. A chromatographic separation/fractionation prior to the MALDI investigation can be advantageous since the MALDI mass spectra of fractions very often reveal well-resolved peaks of distinguishable copolymer series. For this purpose, different modes of chromatography have been applied. Chromatographic runs were transferred to MALDI targets utilizing a combined air/electrospray deposition device. Using the new MassChrom2D software, fraction-dependent 2D copolymer compositions plots were obtained providing additional information on the chromatographic mode, and enabling fast modification of conditions to increase separation.
LC-MALDI MS for polymer characterization (2010)
Weidner, Steffen ; Falkenhagen, Jana
LC-MALDI-TOF imaging MS: a new approach in combining chromatography and mass spectrometry of copolymers (2011)
Weidner, Steffen ; Falkenhagen, Jana
A new approach that utilizes MALDI-TOF imaging mass spectrometry as a new detector for polymer chromatography is presented. For the first time, the individual retention behavior of single structural units of polyethylene oxide (PEO)/polypropylene oxide (PPO) copolymers and changes of the copolymer composition could be monitored. Composition specific calibration curves could be easily obtained by displaying the copolymer ion intensity data. This approach provides completely new insights in the chromatographic principle of copolymer separation and could be used to easily modify and adapt conditions for separation. In combination with electrospray deposition, homogeneous sample/matrix traces of surprisingly high spatial resolution could be obtained.
Imaging mass spectrometry for examining localization of polymeric composition in matrix-assisted laser desorption/ionization samples (2009)
Weidner, Steffen ; Falkenhagen, Jana
The localization of polymeric composition in samples prepared for matrix-assisted laser desorption/ionization (MALDI) analysis has been investigated by imaging mass spectrometry. Various matrices and solvents were used for sample spot preparation of a polybutyleneglycol (PBG 1000). It was shown that in visibly homogeneous spots, prepared using the dried droplet method, separation between matrix and polymer takes place. Moreover, using -cyano-4-hydroxycinnamic acid (CCA) as matrix and methanol as solvent molecular mass separation of the polymer homologues in the spots was detectable. In contrast to manually spotted samples, dry spray deposition results in homogeneous layers showing no separation effects.
Derivatization of Double Bonds investigated by Matrix-assisted Laser Desorption/Ionization Mass Spectrometry (1997)
Weidner, Steffen ; Decker, R. ; Holländer, A.
Multivariate statistics applied to MALDI-TOF MS data of pollen samples (2016)
Weidner, Steffen
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.
^Mass spectrometry of synthetic polymers applications and limitations of the MALDI-TOF technique (2011)
Weidner, Steffen
MALDI-MS zur Aufklärung des Mechanismus der homogen katalysierten Polymerisation flüssigkristalliner Seitengruppenmethacrylate (1999)
Weidner, Steffen
UV- und IR-MALDI-TOF-MS zur Bestimmung von Molmasse und chemischer Heterogenität von synthetischen Polymeren (1999)
Weidner, Steffen
MALDI-TOF-MS of low-molar mass polyethylene and waxes (2001)
Weidner, Steffen
Erste Untersuchungen zur Infrarot-MALDI-MS von Polymeren (1998)
Weidner, Steffen
MALDI-TOF-MS zur Analytik von synthetischen Polymeren (1999)
Weidner, Steffen
MALDI-MS zur Charakterisierung der Oligomeren nach hydrolytischem und plasmachemischem Abbau von Polymeren (1997)
Weidner, Steffen
MALDI - Untersuchung zur Oberflächenmodifizierung von Polymeren nach Plasmabehandlung (1997)
Weidner, Steffen
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