Katrin Knop

Friedrich-Schiller-University Jena, Jena, Thuringia, Germany

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Publications (16)71.6 Total impact

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    ABSTRACT: The global yield of bananas-one of the most important food crops-is severely hampered by parasites, such as nematodes, which cause yield losses up to 75%. Plant-nematode interactions of two banana cultivars differing in susceptibility to Radopholus similis were investigated by combining the conventional and spatially resolved analytical techniques (1)H NMR spectroscopy, matrix-free UV-laser desorption/ionization mass spectrometric imaging, and Raman microspectroscopy. This innovative combination of analytical techniques was applied to isolate, identify, and locate the banana-specific type of phytoalexins, phenylphenalenones, in the R. similis-caused lesions of the plants. The striking antinematode activity of the phenylphenalenone anigorufone, its ingestion by the nematode, and its subsequent localization in lipid droplets within the nematode is reported. The importance of varying local concentrations of these specialized metabolites in infected plant tissues, their involvement in the plant's defense system, and derived strategies for improving banana resistance are highlighted.
    Proceedings of the National Academy of Sciences 12/2013; · 9.81 Impact Factor
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    ABSTRACT: Star-brush-shaped poly(ε-caprolactone)-block-poly(oligo(ethylene glycol) methacrylate (PCL-b-POEGMA) macromolecules were synthesized and studied by molecular hydrodynamic methods. The values of the intrinsic viscosity, the velocity sedimentation coefficient, the translational diffusion coefficient, and the frictional ratio were obtained in acetone. Molar masses (M) were determined by the Svedberg relation, and the correlations between the hydrodynamic values and the molar mass were obtained in the range of 19 < M × 10–3 g mol–1 < 124. Comparison of the scaling indexes of the intrinsic viscosity and sedimentation velocity coefficient versus molar mass corresponding to the conventional four-arm stars macromolecules with that of the star-brush-shaped copolymer macromolecules shows that the star-brush-shaped PCL-b-POEGMA macromolecules have the more dense organization in space which is connected with their different topology in contrast to the conventional stars macromolecules. The model of the PCL-b-POEGMA macromolecules based on the ensemble of their hydrodynamic characteristics is discussed.
    Macromolecules 10/2013; 46(21):8671–8679. · 5.93 Impact Factor
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    ABSTRACT: The fate of drug delivery systems (DDSs) in vivo is a widely discussed question. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an important tool to localize proteins and small compounds in many different tissues. This basic study was performed as an aid to obtain spatial information on DDSs in the future. LDI and MALDI-TOF MS was used to investigate five drug molecules, i.e. madurahydroxylactone (MHL), tetrakis(4-hydroxyphenyl)porphyrin (THP), chartreusin (Chart), amphotericin B (AmB) and retinoic acid (RA). The drug molecules were analyzed in terms of their efficiency to act as matrix for different homopolymers and the block copolymer poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-b-PCL). The block copolymer was further utilized as a DDS to encapsulate the drug molecules previously investigated as matrices. The obtained DDSs were investigated by MALDI. The spectra obtained with the drugs Chart, MHL, THP and AmB did not reach the quality of the standard matrix RA. Nonetheless, they showed surprisingly good results as matrices for different homopolymers and the block copolymer. However, only the DDSs containing THP as the drug provided spectra where the drug and the block copolymer were detected. These results form the foundation for obtaining mass-related information about the localization of DDSs and drugs in tissues. Copyright © 2013 John Wiley & Sons, Ltd.
    Rapid Communications in Mass Spectrometry 10/2013; 27(19):2201-12. · 2.51 Impact Factor
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    ABSTRACT: The synthesis of amphiphilic star-shaped poly(ε-caprolactone)-block-poly(oligo(ethylene glycol)methacrylate)s ([PCL18-b-POEGMA]4) and poly(ε-caprolactone)-block-poly(oligo(2-ethyl-2-oxazoline)methacrylate)s ([PCL18-b-POEtOxMA]4) is presented. Unimolecular behavior in aqueous systems is observed with the tendency to form supermicelles for both hydrophilic shell types. The comparison of OEGMA and OEtOxMA reveals that rather the molar mass of the macromonomer in the hydrophilic shell than the mere length is the crucial factor to form an efficiently stabilizing hydrophilic shell. A hydrophilic/lipophilic balance of 0.8 is shown to stabilize unimolecular micelles in water. An extensive in vitro biological evaluation shows neither blood- nor cytotoxicity. The applicability of the polymers as drug delivery systems was proven by the encapsulation of the anti-cancer drug doxorubicin, whose cytotoxic effect was retarded in comparison to the free drug.
    Biomacromolecules 06/2013; · 5.37 Impact Factor
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    ABSTRACT: The formation of 4-deoxyaurones, which serve as UV nectar guides in Bidens ferulifolia (Jacq.) DC., was established by combination of UV photography, mass spectrometry, and biochemical assays and the key step in aurone formation was studied. The yellow flowering ornamental plant accumulates deoxy type anthochlor pigments (6'-deoxychalcones and the corresponding 4-deoxyaurones) in the basal part of the flower surface whilst the apex contains only yellow carotenoids. For UV sensitive pollinating insects, this appears as a bicoloured floral pattern which can be visualized in situ by specific ammonia staining of the anthochlor pigments. The petal back side, in contrast, shows a faintly UV absorbing centre and UV absorbing rays along the otherwise UV reflecting petal apex. Matrix-free UV laser desorption/ionisation mass spectrometric imaging (LDI-MSI) indicated the presence of 9 anthochlors in the UV absorbing areas. The prevalent pigments were derivatives of okanin and maritimetin. Enzyme preparations from flowers, leaves, stems and roots of B. ferulifolia and from plants, which do not accumulate aurones e.g. Arabidopsis thaliana, were able to convert chalcones to aurones. Thus, aurone formation could be catalyzed by a widespread enzyme and seems to depend mainly on a specific biochemical background, which favours the formation of aurones at the expense of flavonoids. In contrast to 4-hydroxyaurone formation, hydroxylation and oxidative cyclization to the 4-deoxyaurones does not occur in one single step but is catalyzed by two separate enzymes, chalcone 3-hydroxylase and aurone synthase (catechol oxidase reaction). Aurone formation shows an optimum at pH 7.5 or above, which is another striking contrast to 4-hydroxyaurone formation in Antirrhinum majus L. This is the first example of a plant catechol oxidase type enzyme being involved in the flavonoid pathway and in an anabolic reaction in general.
    PLoS ONE 01/2013; 8(5):e61766. · 3.53 Impact Factor
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    ABSTRACT: Amphiphilic star-shaped poly(ε-caprolactone)-block-poly(oligo(ethylene glycol)methacrylate) [PCLa-b-POEGMAb]4 block copolymers with four arms and varying degrees of polymerization for the core (PCL) and the shell (POEGMA) were used to investigate the solution behavior in dilute aqueous solution using a variety of techniques, including fluorescence and UV/Vis spectroscopy, dynamic light scattering, analytical ultracentrifugation, and isothermal titration calorimetry. Particular emphasis has been applied to prove that the systems form unimolecular micelles for different hydrophilic/lipophilic balances of the employed materials. In vitro cytotoxicity and hemocompatibility have further been investigated to probe the suitability of these structures for in vivo applications. A novel fungicide was included into the hydrophobic core in aqueous media to test their potential as drug delivery systems. After loading, the materials have been shown to release the drug and to provoke therewith an inhibition of the growth of different fungal strains.
    Soft Matter 12/2012; 9(3):715-726. · 4.15 Impact Factor
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    ABSTRACT: In this contribution, linear poly(ethylene imine) (PEI) polymers, which are of importance in gene delivery, are investigated in detail by using electrospray ionization-quadrupole-time of flight (ESI-Q-TOF) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS). The analyzed PEIs with different end groups were synthesized using the polymerization of substituted 2-oxazoline via a living cationic ring-opening polymerization (CROP) and a subsequent hydrolysis under acidic conditions. The main goal of this study was to identify linear PEI polymers in a detailed way to gain information about their fragmentation pathways. For this purpose, a detailed characterization of three different linear PEIs was performed by using ESI-Q-TOF and MALDI-TOF MS in combination with collision-induced dissociation (CID) experiments. In ESI-MS as well as MALDI-MS analysis, the obtained spectra of PEIs resulted in fitting mass distributions for the investigated PEIs. In the tandem MS analysis, a 1,2-hydride shift with a charge-remote rearrangement via a four-membered cyclic transition state, as well as charge-induced fragmentation reactions, was proposed as the main fragmentation mechanisms according to the obtained fragmentation products from the protonated parent peaks. In addition, heterolytic and homolytic cleavages were proposed as alternative fragmentation pathways. Moreover, a 1,4-hydrogen elimination was proposed to explain different fragmentation products obtained from the sodiated parent peaks.
    Biological Mass Spectrometry 01/2012; 47(1):105-14. · 3.41 Impact Factor
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    Macromolecular Chemistry and Physics 06/2011; 212(17):1918 - 1924. · 2.39 Impact Factor
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    ABSTRACT: The molar mass determination of block copolymers, in particular amphiphilic block copolymers, has been challenging with chromatographic techniques. Therefore, methoxy poly(ethylene glycol)-b-poly(styrene) (mPEG-b-PS) was synthesized by atom transfer radical polymerization (ATRP) and characterized in detail not only by conventional chromatographic techniques, such as size exclusion chromatography (SEC), but also by matrix-assisted laser/desorption ionization tandem mass spectrometry (MALDI-TOF MS/MS). As expected, different molar mass values were obtained in the SEC measurements depending on the calibration standards (either PEG or PS). In contrast, MALDI-TOF MS/MS analysis allowed the molar mass determination of each block, by the scission of the weakest point between the PEG and PS block. Thus, fragments of the individual blocks could be obtained. The PEG block showed a depolymerization reaction, while for the PS block fragments were obtained in the monomeric, dimeric, and trimeric regions as a result of multiple chain scissions. The block length of PEG and PS could be calculated from the fragments recorded in the MALDI-TOF MS/MS spectrum. Furthermore, the assignment of the substructures of the individual blocks acquired by MALDI-TOF MS/MS was accomplished with the help of the fragments that were obtained from the corresponding homopolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010
    Journal of Polymer Science Part A Polymer Chemistry 09/2010; 48(20):4375 - 4384. · 3.54 Impact Factor
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    ABSTRACT: Poly(ethylene glycol) (PEG) is the most used polymer and also the gold standard for stealth polymers in the emerging field of polymer-based drug delivery. The properties that account for the overwhelming use of PEG in biomedical applications are outlined in this Review. The first approved PEGylated products have already been on the market for 20 years. A vast amount of clinical experience has since been gained with this polymer--not only benefits, but possible side effects and complications have also been found. The areas that might need consideration and more intensive and careful examination can be divided into the following categories: hypersensitivity, unexpected changes in pharmacokinetic behavior, toxic side products, and an antagonism arising from the easy degradation of the polymer under mechanical stress as a result of its ether structure and its non-biodegradability, as well as the resulting possible accumulation in the body. These possible side effects will be discussed in this Review and alternative polymers will be evaluated.
    Angewandte Chemie International Edition 08/2010; 49(36):6288-308. · 11.34 Impact Factor
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    ABSTRACT: Methoxy poly(ethylene glycol) 2000 (mPEG 2000) samples were substituted via esterification reactions to convert the hydroxyl end group of the mPEG into potential initiators for the cationic ring opening polymerization of 2-oxazolines. These substitution products were investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS); in addition, detailed MALDI-TOF/TOF-collision induced dissociation (CID) MS studies were performed to introduce this method as complementary structural characterization tool allowing the detailed analysis of the prepared macromolecules. The CID of the macroinitiators revealed 1,4-hydrogen and 1,4-ethylene eliminations forming very regular fragmentation patterns which showed, depending on the end groups, different fragmentation series. Furthermore, very pronounced McLafferty + 1 rearrangements (1,5 hydrogen-transfer) of the introduced ester end groups were observed leaving the mPEG molecule as neutral acid. This incisive loss revealed the exact molar mass for each end group and, therefore, represents an important tool for end group determination of functionalized polymers.
    Macromolecular Chemistry and Physics 03/2010; 211(6):677-684. · 2.39 Impact Factor
  • Angewandte Chemie. 01/2010; 122(36):6430-6452.
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    ABSTRACT: The present paper describes matrix-free laser desorption/ionisation mass spectrometric imaging (LDI-MSI) of highly localized UV-absorbing secondary metabolites in plant tissues at single-cell resolution. The scope and limitations of the method are discussed with regard to plants of the genus Hypericum. Naphthodianthrones such as hypericin and pseudohypericin are traceable in dark glands on Hypericum leaves, placenta, stamens and styli; biflavonoids are also traceable in the pollen of this important phytomedical plant. The highest spatial resolution achieved, 10 microm, was much higher than that achieved by commonly used matrix-assisted laser desorption/ionization (MALDI) imaging protocols. The data from imaging experiments were supported by independent LDI-TOF/MS analysis of cryo-sectioned, laser-microdissected and freshly cut plant material. The results confirmed the suitability of combining laser microdissection (LMD) and LDI-TOF/MS or LDI-MSI to analyse localized plant secondary metabolites. Furthermore, Arabidopsis thaliana was analysed to demonstrate the feasibility of LDI-MSI for other commonly occurring compounds such as flavonoids. The organ-specific distribution of kaempferol, quercetin and isorhamnetin, and their glycosides, was imaged at the cellular level.
    The Plant Journal 10/2009; 60(5):907-18. · 6.58 Impact Factor
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    ABSTRACT: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) coupled with CID (collision-induced dissociation) has been used for the detailed characterization of two poly(2-ethyl-2-oxazoline)s as part of a continuing study of synthetic polymers by MALDI-TOF MS/MS. These experiments provided information about the variety of fragmentation pathways for poly(oxazoline)s. It was possible to show that, in addition to the eliminations of small molecules, like ethene and hydrogen, the McLafferty rearrangement is also a possible fragmentation route. A library of fragmentation pathways for synthetic polymers was also constructed and such a library should enable the fast and automated data analysis of polymers in the future.
    Rapid Communications in Mass Spectrometry 03/2009; 23(6):756-62. · 2.51 Impact Factor
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    ABSTRACT: A series of bis-4H-imidazoles 1a-h has been synthesized and characterized. Due to the integration of rigid substructures, the first fluorescent 4H-imidazole 1h which possesses the substructure of pyrrolo-pyrrol was obtained. Upon protonation of bis-4H-imidazoles, a bathochromic shift of 100 to almost 200 nm was observed originating from the transformation of merocyanine chromophores into cyanines. All 4H-imidazoles were reduced chemically yielding bridged 1H-imidazoles which immediately reoxidize when exposed to air. Stable quinomethide-like species 3a,b which represent the SEM form in this four-electron redox system are only observed during the reduction of bis-4H-imidazoles 1a,b. Influenced by larger bridging elements in derivatives 1c–1h, the electronic communication between terminal 4H-imidazoles is impaired. Therefore, detection and isolation of neither quinomethide-like nor biradikaloid SEM forms succeeded. Most likely a very fast electron-transfer-step leads to unsymmetric hybrids, consisting of one 1H- and one 4H-imidazole. The new synthesized derivative 1k is not only such a stable hybrid molecule, but also may be an indication for the existence of non-quinoid SEM-forms.
    Structural Chemistry 06/2008; 19(3):399-405. · 1.77 Impact Factor
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    ABSTRACT: Bora-tetraazapentalenes have been synthesised and characterized; the radical anion shows an unusual thermodynamic stability (semiquinone formation constants K(SEM) of ca. 10(14)).
    Chemical Communications 09/2004; · 6.38 Impact Factor