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Equipping ZIF particles with a polyelectrolyte membrane provides functional groups at their interface, enabling further conjugations necessary for applications such as targeted drug delivery. Previous approaches to coat ZIF particles with polyelectrolytes led to surface corrosion of the template material. This work overcomes previous limitations by performing a Layer-by-Layer (LbL) polyelectrolyte coating onto ZIF-8 and ZIF-67 particles in nonaqueous environment. Using the 2-methylimidazolium salt of polystyrensulfonic acid instead of the acid itself and polyethyleneimine in methanol led to intact ZIF particles after polyelectrolyte coating. This was verified by electron microscopy. Further, zetapotential and atomic force microscopy measurements confirmed a continuous polyelectrolyte multilayer built up. The here reported adaption to the well-studied (LbL) polyelectrolyte selfassembly process provides a facile method to equip ZIF particles with a nanometer thin polyelectrolyte multilayer membrane.
Zearalenone (ZEN) and its phase II sulfate and glucoside metabolites have been detected in food and feed commodities. After consumption, the conjugates can be hydrolyzed by the human intestinal microbiota leading to liberation of ZEN that implies an underestimation of the true ZEN exposure. To include ZEN conjugates in routine analysis, reliable standards are needed, which are currently not available. Thus, the aim of the present study was to develop a facilitated biosynthesis of ZEN-14-sulfate, ZEN-14-glucoside and ZEN-16-glucoside. A metabolite screening was conducted by adding ZEN to liquid fungi cultures of known ZEN conjugating Aspergillus and Rhizopus strains. Cultivation conditions and ZEN incubation time were varied. All media samples were analyzed for metabolite formation by HPLC-MS/MS. In addition, a consecutive biosynthesis was developed by using Fusarium graminearum for ZEN biosynthesis with subsequent conjugation of the toxin by utilizing Aspergillus and Rhizopus species. ZEN-14-sulfate (yield: 49%) is exclusively formed by Aspergillus oryzae. ZEN-14-glucoside (yield: 67%) and ZEN-16-glucoside (yield: 39%) are formed by Rhizopus oryzae and Rhizopus oligosporus, respectively. Purities of ≥73% ZEN-14-sulfate, ≥82% ZEN-14-glucoside and ≥50% ZEN-16-glucoside were obtained by 1H-NMR. In total, under optimized cultivation conditions, fungi can be easily utilized for a targeted and regioselective synthesis of ZEN conjugates.
Amyloid fibrils are polymers formed by proteins under specific conditions and in many cases they are related to pathogenesis, such as Parkinson’s and Alzheimer’s diseases. Their hallmark is the presence of a β-sheet structure. High resolution structural data on these systems as well as information gathered from multiple complementary analytical techniques is needed, from both a fundamental and a pharmaceutical perspective. Here, a previously reported de novo designed, pH-switchable coiled coil-based peptide that undergoes structural transitions resulting in fibril formation under physiological conditions has been exhaustively characterized by transmission electron microscopy (TEM), cryo-TEM, atomic force microscopy (AFM), wide-angle X-ray scattering (WAXS) and solid-state NMR (ssNMR). Overall, a unique 2-dimensional carpet-like assembly composed of large coexisiting ribbon-like, tubular and funnel-like structures with a clearly resolved protofilament substructure is observed. Whereas electron microscopy and scattering data point somewhat more to a hairpin model of β-fibrils, ssNMR data obtained from samples with selectively labelled peptides are in agreement with both, hairpin structures and linear arrangements.
MALDI time-of-flight mass spectrometry (MALDI-TOF MS) has become a widely used tool for the classification of biological samples. The complex chemical composition of pollen grains leads to highly specific, fingerprint-like mass spectra, with respect to the pollen species. Beyond the species-specific composition, the variances in pollen chemistry can be hierarchically structured, including the level of different populations, of environmental conditions or different genotypes. We demonstrate here the sensitivity of MALDI-TOF MS regarding the adaption of the chemical composition of three Poaceae (grass) pollen for different populations of parent plants by analyzing the mass spectra with partial least squares discriminant analysis (PLS-DA) and principal component analysis (PCA). Thereby, variances in species, population and specific growth conditions of the plants were observed simultaneously. In particular, the chemical pattern revealed by the MALDI spectra enabled discrimination of the different populations of one species. Specifically, the role of environmental changes and their effect on the pollen chemistry of three different grass species is discussed. Analysis of the Group formation within the respective populations showed a varying influence of plant genotype on the classification, depending on the species, and permits conclusions regarding the respective rigidity or plasticity towards environmental changes.
The influence of starting materials and synthesis route on the properties and the structure of cementitious sodium aluminosilicate gels is not fully understood, partly due their amorphous nature and the fact that they often contain residual reactants, which can make the results of single-pulse NMR spectroscopy applied to these materials difficult to interpret or ambiguous. To overcome some of these limitations, 29Si{27Al} TRAPDOR NMR as well as 27Al{29Si} and 27Al{1H} REDOR NMR spectroscopy were applied to materials synthesized by the one-part alkali-activation route from three different amorphous silica starting materials, including rice husk ash. The latter led to formation of a fully amorphous sodium aluminosilicate gel (geopolymer), while the materials produced from the other silicas contained amorphous phase and crystalline zeolites. Application of the double-resonance NMR methods allowed to identify hydrous alumina gel domains in the rice husk ash-based material as well as significantly differing amounts of residual silica in the three cured materials. Four-coordinated Al existed not only in the aluminosilicate gel framework but also in a water-rich chemical environment with only a small amount of Si in proximity, likely in the alumina gel or possibly present as extra-framework Al in the aluminosilicate gel. The results demonstrate how the employment of different silica starting materials determines the phase assemblage of one-part alkali-activated materials, which in turn influences their engineering properties such as the resistance against chemically/biologically aggressive media.
The application of appropriate analytical techniques is essential for nanomaterial (NM) characterization. In this study, we compared different analytical techniques for NM analysis. Regarding possible adverse health effects, ionic and particulate NM effects have to be taken into account. As NMs behave quite differently in physiological media, special attention was paid to techniques which are able to determine the biosolubility and complexation behavior of NMs. Representative NMs of similar size were selected: aluminum (Al0) and aluminum oxide (Al2O3), to compare the behavior of metal and metal oxides. In addition, titanium dioxide (TiO2) was investigated. Characterization techniques such as dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) were evaluated with respect to their suitability for fast characterization of nanoparticle dispersions regarding a particle's hydrodynamic diameter and size distribution. By application of inductively coupled plasma mass spectrometry in the single particle mode (SP-ICP-MS), individual nanoparticles were quantified and characterized regarding their size. SP-ICP-MS measurements were correlated with the information gained using other characterization techniques, i.e. transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The particle surface as an important descriptor of NMs was analyzed by X-ray diffraction (XRD). NM impurities and their co-localization with biomolecules were determined by ion beam microscopy (IBM) and confocal Raman microscopy (CRM). We conclude advantages and disadvantages of the different techniques applied and suggest options for their complementation. Thus, this paper may serve as a practical guide to particle characterization techniques.