Analytische Chemie
Filtern
Dokumenttyp
- Zeitschriftenartikel (171)
- Vortrag (98)
- Posterpräsentation (57)
- Forschungsdatensatz (3)
- Dissertation (2)
- Preprint (2)
- Buchkapitel (1)
- Beitrag zu einem Tagungsband (1)
- Tagungsband (Herausgeberschaft für den kompletten Band) (1)
- Sonstiges (1)
Sprache
- Englisch (321)
- Deutsch (15)
- Mehrsprachig (2)
Schlagworte
- Mechanochemistry (69)
- Synchrotron (42)
- BAMline (34)
- In situ (31)
- XANES (22)
- XRD (22)
- MALDI-TOF MS (19)
- XRF (18)
- Nanoparticles (12)
- Polylactide (11)
Organisationseinheit der BAM
- 6.3 Strukturanalytik (338) (entfernen)
Paper des Monats
- ja (2)
We studied the influence of coformers flexibility on the supramolecular assembly of 5-substituted resorcinol. Two cocrystals of orcinol (ORL) with two dipyridine molecules, i.e. 1,2-di(4-pyridyl)ethane (ORLeBPE) and 1,2-di(4-pyridyl)ethylene (ORLeBPY), were prepared by mechanochemical synthesis and slow evaporation of solvent. The new crystalline solids were thoroughly characterized by single crystal Xray diffraction (SCXRD), powder X-ray diffraction analysis (PXRD), Fourier-transform infrared spectroscopy (FT-IR), differential thermal analysis (DTA), and thermogravimetric analysis (TGA). Structural determination reveals that in both cocrystals, the phenolepyridine, i.e. OeH/N(py) heterosynthon takes the main role in the formation of cocrystals. In ORLeBPE, the components form infinite 1D zig-zag chains, which are extended to 2D layer structure by inter-chain CeH/O interactions between BPE hydrogen atoms and hydroxyl oxygen atoms of ORL. In ORLeBPY, the components form a 0D fourcomponent complex. Formation of the discrete assemblies is attributed to the comparative rigid nature of BPY, which restricts the formation of an extended network.
Relaxation phenomena observed in the electrical low-frequency range (approximately 1 mHz-10 kHz) of natural porous media like sandstones is often assumed to be directly related to the dominant (modal) pore throat sizes measured, for instance, with mercury intrusion porosimetry. Attempts to establish a universally valid relationship between pore size and peak Spectral Induced Polarization (SIP) relaxation time have failed, considering sandstones from very different origins and featuring great variations in textural and chemical compositions as well as in geometrical pore space properties. In addition working with characteristic relaxation times determined in Cole-Cole or Debye decomposition fits to build the relationship have not been successful. In particular, samples with narrow pore throats are often characterized by long SIP relaxation times corresponding to long “characteristic length scales” in these media, assuming that the diffusion coefficients along the electrical double layer were constant. Based on these observations, three different types of SIP relaxation can be distinguished. We present a new way of assessing complex pore spaces of very different sandstones in a multi-methodical approach to combine the benefits of mercury intrusion porosimetry, micro-computed tomography, and nuclear magnetic resonance. In this way, we achieve much deeper insight into the pore space due to the different resolutions and sensitivities of the applied methods to both pore constrictions (throats) and wide pores (pore bodies). We experimentally quantify pore aspect ratios and volume distributions within the two pore regions. We clearly observe systematic differences between three SIP relaxation types identified previously and can attribute the SIP peak relaxation times to measured characteristic length scales within our materials. We highlight selected results for a total of nine sandstones. It seems that SIP relaxation behavior depends on the size difference of the narrow pore throats to the wide pore bodies, which increases from SIP Type 1 to Type 3.
In recent years, we have come to appreciate the astounding intricacy of the processes leading to the formation of minerals from ions in aqueous solutions. The original, and rather naive, ‘textbook’ image of these phenomena, stemming from the adaptation of classical nucleation and growth theories, has increased in complexity due to the discovery of a variety of precursor and intermediate species. These include solute clusters (e.g. prenucleation clusters, PNCs), liquid(-like) phases, as well as amorphous and nanocrystalline solids etc.. Does it, however, mean that all the minerals grow through intermediate phases, following a non-classical pathway?
In general, the precursor or intermediate species constitute different, often short-lived, points along the pathway from dissolved ions to the final solids (typically crystals in this context). In this regard synchrotron-based scattering (SAXS/WAXS/total scattering) appears to be the perfect tool to follow in situ and in a time-resolved manner the crystallization pathway because of the temporal and spatial length scales that can be directly accessed with these techniques. In this presentation we show how we used scattering to probe the crystallisation mechanisms of calcium sulfate, This system contains minerals that are widespread in diverse natural environments, but they are also important in various industrial settings. Our data demonstrate that calcium sulfate precipitation involves formation and aggregation of sub-3 nm anisotropic primary species. The actual crystallisation and formation of imperfect single crystals of calcium sulfate phases, takes place from the inside of the in itial aggregates. Hence, calcium sulfate follows a non-classical pathway.
Simultaneous characterization of poly(acrylic acid) andpolysaccharide polymers and copolymers
(2020)
Copolymer products that result from grafting acrylic acid and other hydrophilicmonomers onto polysaccharides have recently gained significant interest in researchand industry. Originating from renewable sources, these biodegradable, low toxicity,and polar copolymer products exhibit potential to replace polymers from fossil sourcesin several applications and industries. The methods usually employed to character-ize these copolymers are, however, quite limited, especially for the measurement ofbulk properties. With more sophisticated applications, for example, in pharmaceu-tics requiring a more detailed analysis of the chemical structure, we describe a newapproach for this kind of complex polymers. Our approach utilizes chromatographyin combination with several detection methods to separate and characterize reactionproducts of the copolymerization of acrylic acid and chemically hydrolyzed starch.These samples consisted of a mixture of homopolymer poly (acrylic acid), homopoly-mer hydrolyzed starch, and – in a lower amount – the formed copolymers. Several chro-matographic methods exist that are capable of characterizing either poly (acrylic acid)or hydrolyzed starch. In contrast, our approach offers simultaneous characterization ofboth polymers. The combination of LC and UV/RI offered insight into the compositionand copolymer content of the samples. Size exclusion chromatography experimentsrevealed the molar mass distribution of homopolymers and copolymers. FTIR inves-tigations confirmed the formation of copolymers while ESI-MS gave more details onthe end groups of hydrolyzed starches and poly (acrylic acids). Evidence of copolymerstructures was obtained through NMR measurements. Finally, two-dimensional chro-matography led to the separation of the copolymers from both homopolymers as wellas the additional separation of sodium clusters. The methods described in this work area powerful toolset to characterize copolymerization products of hydrolyzed starch andpoly(acrylic acid). Together, our approach successfully correlates the physicochemicalproperties of such complex mixtures with their actual composition.
In addition to molar mass distribution (MMD) synthetic polymers often exhibit an additional chemical heterogeneity distribution, expressed by different end groups and other structural variations (e.g. tacticity, copolymer composition etc.). Ionization in MALDI MS is always strongly affected by such chemical properties. For example, the abundance of cyclics in MALDI TOF mass spectra is frequently reported to greatly exceed that of linears. Thus, the MALDI ionization behavior of various neat end-capped linear poly(L-lactide)s and one cyclic poly(L-lactide) was investigated and compared with that of blends of both structures. Moreover, the influence of the cationizing salt was investigated too.
Neat compounds and various blends of cyclic and linear species were prepared and studied using two MALDI TOF mass spectrometers under identical conditions with regard to sample preparation and instrumental conditions, except for the laser power and the salt used for cationization. Polymer samples were additionally characterized by NMR and SEC.
The steady increase of the laser intensity caused an exponential increase of the peak intensities of both linear and cyclic polylactides.The response of linear polylactides (in the investigated molecular mass range), whether as neat polymer or in blends with other linear polylactides was almost similar. This clearly supports our assumption that ionization in MALDI is probably unaffected by the end group structure.The variation of the laser power shows only little effect on the intensity ratio of linear-to linear and cyclic-to-linear polylactides in blends. Whereas neat linear polylactides at all laser intensities have a significantly higher abundance than neat cyclics, in mixtures of both an overestimation of cyclic species in MALDI TOF mass spectra of polylactides was found. However, this is far less distinct than frequently reported for other polymers.Concluding, peak suppression of linear polymers in mixtures of both architectures can be excluded, which also means, that polylactides showing only peaks of cyclic compounds in their MALDI - TOF mass spectra do not contain a significant fraction of linear analogues.
Our study is the first systematic comparison of the MALDI ionization of neat and blended cyclic and linear polylactides.
To better study the impact of nanoparticles on both in vitro and in vivo models, tissue distribution and cellular doses need to be described more closely. Here silver nanoparticles were visualized in alveolar macrophages by means of synchrotron radiation micro X-ray fluorescence spectroscopy (SR-μXRF) with high spatial resolution of 3 × 3 μm2. For the spatial allocation of silver signals to cells and tissue structures, additional elemental labeling was carried out by staining with eosin, which binds to protein and can be detected as bromine signal with SR-μXRF. The method was compatible with immunostaining of macrophage antigens. We found that the silver distribution obtained with SR-μXRF was largely congruent with distribution maps from a subsequent laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of the same tissue sites. The study shows a predominant, though not exclusive uptake of silver into alveolar macrophages in the rat lung, which can be modeled by a similar uptake in cultured alveolar macrophages. Advantages and limitations of the different strategies for measuring nanoparticle uptake at the single cell level are discussed.
A new concept called “Ring-Opening Polymerization (ROP) combined with simultaneous POlyCondensation” (ROPPOC) is presented and discussed. This synthetic strategy is based on the intermediate formation of chains having two end groups that can react with each other. The ROPPOC syntheses are subdivided into three groups according to the nature of the chain ends: two ionic end groups, one ionic and one covalent chain end and a combination of two reactive covalent end groups may be involved, depending on the catalyst. The usefulness for the preparation of cyclic polymers is discussed with a review of numerous previously published examples. These examples concern to following classes of cyclic polymers: polypeptides, polyamides, polyesters, including polycarbonates, and cyclic polysiloxanes. It is demonstrated, that the results of certain ROPPOC syntheses are in contradiction to the Jacobson-Stockmayer theory. Finally, the usefulness of ROPPOCs for the detection of polydisperse catenanes is discussed.
The very strong Lewis acid aluminium chlorofluo-ride (ACF) was loaded with anhydrous HF. The interactionbetween the surface of the catalyst and HF was investigatedusing a variety of characterization methods, which revealed he formation of polyfluorides. Moreover, the reactivity ofthe HF-loaded ACF towards the hydrofluorination of alkyneswas studied.
In the present study, hexamethylene diisocyanate (HMDI) encapsulated poly-thiourea formaldehyde (PTF) (10 wt%) coating was developed in an epoxy-polyamine matrix and their anticorrosion studies on Type SS304 stainless steel substrate have been conducted using electrochemistry techniques. The compact and hydrophobic shell wall of PTF proved to be a potent shell wall material for HMDI encapsulation. The effect of temperature and pH values was found to be decisive factor in the synthesis of microcapsules. The PTF microcapsules were synthesized in acidic condition with a pH value of 3. Over 90% of the core fraction is retained in water after 21 days immersion. However, core content decreased with increasing temperature. The capsules were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Electrochemical Impedance spectroscopy (EIS). Scanning electron microscopic analysis depicts the uniform morphology of coating with a particle size in the range of 1.08 µm–22.06 µm.
The vibrational band at 2271 cm−1 attributed to NCO signal further endorses the successful encapsulation of HMDI into the PTF capsules. Electrochemical testing on steel specifies the appreciable anticorrosion performance of the synthesized poly thiourea formaldehyde (PTF) coating against artificial sea water.
Nickel nanoparticles are an active research area due to their multiple applications as catalysts in different processes. A variety of preparation techniques have been reported for the synthesis of these nanoparticles, including solvothermal, microwave-assisted, and emulsion techniques. The well-studied solvothermal oleylamine synthesis route comes with the drawback of needing standard air-free techniques and often space-consuming glassware. Here, we present a facile and straightforward synthesis method for size-controlled highly monodisperse nickel nanoparticles avoiding the use of, e.g., Schlenk techniques and space-consuming labware. The nanoparticles produced by this novel synthetic route were investigated using small-angle X-ray scattering, transmission electron microscopy, X-ray diffraction, and X-ray spectroscopy. The nanoparticles were in a size range of 4–16 nm, show high sphericity, no oxidation, and no agglomeration after synthesis.
The small-pore framework sodium stannosilicate AV-10, chemical composition Na2SnSi3O9⋅2H2O and known crystallographic structure, was synthesized by hydrothermal crystallization. This stannosilicate is built up of a three-dimensional network of corner-shared SiO4 tetrahedra and SnO6 octahedra. The SnO6 sites are linked to six SiO4 tetrahedra (Sn(6Si)) while each of the two crystallographically different SiO4 units are connected to two SnO6 and SiO4 units (Si(2Si,2Sn)). This material was used as model compound for developing a solid-state MAS NMR strategy aimed on the challenges and possibilities for structural studies, particularly considering the short and medium range order to verify the connectivity of SiO4 and SnO6 of such compounds despite the low natural abundances of 4.68% for 29Si and 8.59% for 119Sn nuclei as a real challenge. 29Si{119Sn} and 119Sn{29Si} REDOR (Rotational-Echo Double-Resonance) NMR measurements after 1H cross-polarization (CP) were carried out. The REDOR curves show a significant change after the “normal” quadratic short time evolution from which both (i) the shortest internuclear 29Si – 119Sn distances (and vice versa) and (ii) the number of corner-sharing SiO4 tetrahedra around the SnO6 octahedra (and vice versa) can be obtained. Based on these data, optimized 29Si {119Sn} and 119Sn{29Si} REPT-HMQC (Recoupled Polarization Transfer-Heteronuclear Multiple-Quantum Correlation, again after 1H CP) experiments were implemented, which directly show those heterogroup connectivity as correlation peaks in a 2D spectrum. This information was also obtained using 2D29Si{119Sn}-J-Coupling NMR experiments. Furthermore, 2D29Si INADEQUATE NMR experiments are also feasible, showing the connectivity of SiO4 tetrahedra. The combination of REDOR, REPT-HMQC, J-Coupling and INADEQUATE experiments yielded a complete analysis of the short and medium range structure of this microporous stannosilicate, in agreement with the previously published structure obtained Ab Initio from powder X-Ray diffraction data (XRD).
The electrocatalytic conversion of water into molecular hydrogen and oxygen under the utilization of excess renewable energies, such as wind power, photovoltaics and hydroelectric power is one possible pathway to establish a sustainable hydrogen economy. The obtained hydrogen is either stored and used in a fuel cell or consumed on-site in industrial applications.
Water electrolysis systems (WES) are based on two half cell reactions, such as oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) which both proceed simultaneously. The OER suffers from slow reaction kinetics and thus limits the overall performance.
The most promising compounds in acidic electrolysis are IrO2 and RuO2. Due to their rare abundance and extremely high price a wide use of acidic WES was prevented. Lowering the catalysts noble metal content by mixing iridium with titanium reduces the production costs.
Thin films are produced by dip coating a solution of metal oxide precursors alongside with a polymer template dissolved in ethanol. The obtained samples are subsequently calcined to the remove the template and adjust crystallinity. Finally, an additional iridium deposition step was performed on the outer surface plane area.
Understanding the influence of structural and morphological aspects on the OER-activity is beneficial to further optimize WES. The current presentation will thus give detailed insights to structural aspects obtained by Raman spectroscopy, small- and wide-angle X-ray scattering which are then combined with electrochemical parameters to deduce structure-activity relationships.
The large-scale mechanochemical reduction of binary sulfides chalcocite (Cu2S) and covellite (CuS) by elemental iron was investigated in this work. The reduction of Cu2S was almost complete after 360 min of milling, whereas in the case of CuS, a significant amount of non-reacted elemental iron could still be identified after 480 min. Upon application of more effective laboratory-scale planetary ball milling, it was possible to reach almost complete reduction of CuS. Longer milling leads to the formation of ternary sulfides and oxidation product, namely cuprospinel CuFe2O4. The rate constant calculated from the magnetometry measurements using a diffusion model for Cu2S and CuS reduction by iron in a large-scale mill is 0.056 min−0.5 and 0.037 min−0.5, respectively, whereas for the CuS reduction in a laboratory-scale mill, it is 0.1477 min−1. The nanocrystalline character of the samples was confirmed by TEM and XRD, as the produced Cu exhibited sizes up to 16 nm in all cases. The process can be easily scaled up and thus copper can be obtained much easier from refractory minerals than in traditional metallurgical approaches.
Ring–Ring Equilibration in Solid, Even-Numbered Cyclic Poly(l-lactide)s and their Stereocomplexes
(2020)
Even-numbered cyclic poly(d-lactide) and poly(l-lactide) are prepared by ringexpansion polymerization. The cyclic pol(l-lactide) is annealed either at 120 or at 160 °C for several days. The progress of transesterification in the solid state is monitored by the formation of odd-numbered cycles via matrix-assisted laser desorption/ionization-time of flight mass spectrometry. The changes of the crystallinity are monitored by differential scanning calorimetry, wideand small-angle x-ray scattering (WAXS and SAXS) measurements. Despite total even-odd equilibration at 160 °C, the crystallinity of poly(l-lactide) is not reduced. Furthermore, the crystallinity of the stereocomplexes of both cyclic polylactides do not decrease or vanish, as expected, when a blocky or random stereosequence is formed by transesterification. This conclusion is confirmed by 13C NMR spectroscopy. These measurements demonstrate that transesterification is a ring–ring equilibration involving the loops on the surfaces of the lamellar crystallites thereby improving crystallinity and 3D packing of crystallites without significant broadening of the molecular weight distribution.
Cyclic poly(L-lactide)s were prepared by ring-opening polymerization combined with simultaneous polycondensation (ROPPOC) in bulk at 160 ° with dibutyltin bis(4-cyanophenoxide) as catalyst. It is demonstrated by MALDI TOF mass spectrometry and 1H NMR end group analyses that cycles are formed by endto-end cyclization in addition to “back-biting” transesterification. Formation of high molar mass cyclic poly L-lactide)s by means of several more reactive ROPPOC catalysts presented previously and in new experiments is discussed. These experimental results, together with theoretical arguments, prove that part of the Jacobson–Stockmayer theory is wrong. The critical monomer concentration, above which end-toend cyclization is seemingly impossible, does not exist and reversible like irreversible polycondensations can theoretically proceed up to 100% conversion, so that finally all reaction products will necessarily adopt a cyclic architecture.
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.
Two mixtures of polystyrene nanoparticles (PS-NPs) with comparable core sizes (20 nm and 50 nm) 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 and can obviouly improve separation resolution.
The analysis of pollen chemical composition is important to many fields, including agriculture, plant physiology, ecology, allergology, and climate studies. Here, the potential of a combination of different spectroscopic and spectrometric methods regarding the characterization of small biochemical differences between pollen samples was evaluated using multivariate statistical approaches. Pollen samples, collected from three populations of the grass Poa alpina, were analyzed using Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, surface enhanced Raman scattering (SERS), and matrix assisted laser desorption/ionization mass spectrometry (MALDI-TOF MS). The variation in the sample set can be described in a hierarchical framework comprising three populations of the same grass species and four different growth conditions of the parent plants for each of the populations. Therefore, the data set can work here as a model system to evaluate the classification and characterization ability of the different spectroscopic and spectrometric methods. ANOVA Simultaneous Component Analysis (ASCA) was applied to achieve a separation of different sources of variance in the complex sample set. Since the chosen methods and sample preparations probe different parts and/or molecular constituents of the pollen grains, complementary information about the chemical composition of the pollen can be obtained. By using consensus principal component analysis (CPCA), data from the different methods are linked together. This enables an investigation of the underlying global information, since complementary chemical data are combined. The molecular information from four spectroscopies was combined with phenotypical information gathered from the parent plants, thereby helping to potentially link pollen chemistry to other biotic and abiotic parameters.
Our aim is to develop a simple and inexpensive method for full field X-ray fluorescence imaging.We combine an energy-dispersive array detector with a coded aperture to obtain high resolution images. To obtain the information from the recorded image a reconstruction step is necessary. The reconstruction methods we have developed, were tested on simulated data and then applied to experimental data. The first tests were carried out at the BAMline @ BESSY II. This method enables the simultaneous detection of multiple elements, which is important e.g. in the field of catalysis.
Imaging with X-rays is a challenging field, due to the optical properties of X-rays. The fabrication of appropriate optics is usually expensive and requires an elaborate manufacturing process. One simpler and less expensive possibility of imaging high energy radiation is coded aperture imaging, a technique well established in astrophysics and also used in nuclear medicine or radiation detection, e.g., for nuclear decommissioning. Our aim is to adapt coded aperture imaging for X-ray fluorescence spectroscopy in the nearfield. In this work we show theoretical considerations and preliminary simulations of Image formation through a coded aperture and three different reconstruction methods to prepare the experiments. We used a new mask based on an inverted modified uniformly redundant array (MURA) that could be used for the construction of a decoding mask for all investigated geometrical arrangements.
The most commonly used reconstruction method, convoluting the detected image with a Decoding mask, does not always deliver satisfactory results. This is more noticeable for small distances between the object, mask and detector. Hence, we developed two new reconstruction methods, one based on iterative algebraic optimization and another one based on a genetic algorithm. Both show good performance even in those cases where the convolution method fails. This provides a basis for further investigations of the ideal parameters for near field coded aperture imaging and refinements of the algorithms. We performed first measurements with a coded aperture at the BAMline at BESSY II and could successfully reconstruct a test object from the obtained recorded images.
Numerous new tin catalysts that enable the synthesis of cyclic polylactides with broad variation in their molecular mass were recently developed. The abundance of cyclics in matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectra is, however, frequently reported to greatly exceed that of linears. Thus, the MALDI ionization behavior of various end-capped linear poly(L-lactide)s and one cyclic poly(L-lactide) was investigated and compared.
Neat compounds and various blends of cyclic and linear species were prepared and studied under identical conditions with regard to sample preparation and instrumental condition, except for the laser power. For this purpose, two different MALDI-TOF mass spectrometers were applied.
Our results reveal that cyclics indeed show a slightly better ionization in MALDI, although their ionization as a neat compound seems to be less effective than that of linear polylactides. The ionization of most linear polylactides investigated does not depend on the end group structure. However, linear polylactides containing 12-bromododecyl end groups reveal an unexpected saturation effect that is not caused by fragmentation of the polymer or the end group, or by electronic saturation of the detector digitizer. Furthermore, polylactides with a 2-bromoethyl end group did not show such a saturation effect.
An overestimation of cyclic species in MALDI-TOF mass spectra of poly(L-lactide)s must be considered, but the commonly assumed peak suppression of linear polymers in mixtures of both structures can be excluded.
CCQM key comparison K-153 Measurement of Specific Adsorption A [mol/kg] of N-2 and Kr on nonporous SiO2 at LN temperature (to enable a traceable determination of the Specific Surface Area (BET) following ISO 9277) has been performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The objective of this key comparison is to compare the equivalency of the National Metrology Institutes (NMIs) and Designated Institutes (DIs) for the measurement of specific adsorption, BET specific surface area) of nonporous substances (sorbents, ceramics, catalytic agents, etc) used in advanced technology.
In this key comparison, a commercial nonporous silicon dioxide was supplied as a sample. Eight NMIs participated in this key comparison, but only five NMI's have reported in time. All participants used a gas adsorption method, here nitrogen and (or) krypton adsorption at 77.3 K, for analysis according to the international standards ISO 15901-2 and 9277.
In this key comparison, the degrees of equivalence uncertainties for specific adsorption nitrogen and krypton, BET specific surface area were established.
Since its introduction mass spectrometric techniques like Matrix-assisted Laser Desorption/ionization (MALDI) and Electrospray Ionization (ESI) have become indispensable for synthetic polymer analyses. Ideally, various polymer properties (monomer structure, masses, mass distribution, end groups) can be determined simultaneously. However, in real life these experiments are always affected by important structural parameters and instrumental limitations.
A short introduction focussing on latest findings with respect to ionisation principles and mechanisms will be given. Recent results from our group will be presented and efforts to avoid common drawbacks of polymer mass spectrometry will be discussed. In this regard, MALDI - Imaging mass spectrometry and the 2D hyphenation of MS with different chromatographic separation techniques were especially useful, since they can provide additional information and reduce the complexity of polymer analyses.
The preparation of new active pharmaceutical ingredient (API) multicomponent Crystal forms, especially co-crystals and salts, is being considered as a reliable strategy to improve API solubility and bioavailability. In this study, three novel imidazole-based salts of the poorly water-soluble salicylic acid (SA) are reported exhibiting a remarkable improvement in solubility and dissolution rate properties. All structures were solved by powder X-ray diffraction. Multiple complementary techniques were used to solve co-crystal/salt ambiguities: density functional Theory calculations, Raman and 1H/13C solid-state NMR spectroscopies. In all molecular salts, the Crystal packing interactions are based on a common charged assisted +N-H SA)...O-(co-former) hydrogen bond interaction. The presence of an extra methyl group in different positions of the co-former, induced different supramolecular arrangements, yielding salts with different physicochemical properties.
All salts present much higher solubility and dissolution rate than pure SA. The most promising results were obtained for the salts with imidazole and 1-methylimidazole co-formers.
Mechanochemistry has become a valuable method for the synthesis of new materials and molecules, with a particular strength for screening and preparing multicomponent crystals. In this work, two novel cocrystals of pyrazinamide (PZA) with pimelic acid (PA) were prepared mechanochemically. Their formation was monitored in real time by in situ synchrotron powder X-ray diffraction. Control over the polymorphic form was obtained through the selective choice of liquid additive via liquid assisted grinding. Slurry experiments and dispersion-corrected density functional theory calculations suggest that Form I is the thermodynamically stable form under ambient conditions. Upon aging, Form II converts to Form I. The stability of Form II upon aging was found to depend strongly on the milling duration, intensity, and material of the milling vessels. Longer or higher energy milling drastically increased the lifetime of the Form II product. For the first time, this work also demonstrates that the choice of milling jar can have a decisive effect on the aging stability of a bulk polymorphic powder. In contrast to material prepared in steel milling vessels, the preparation of Form II in Perspex (PMMA) vessels increased its lifetime 3-fold. These findings offer a new dimension to garnering control over mechanochemical cocrystallization and demonstrate the critical importance of the careful and timely ex situ screening of ball mill grinding reactions. This will be of importance for potential industrial applications of mechanochemical cocrystallization where understanding polymorph longevity is crucial for the development of a robust preparative protocol.
Metal phosphonates are promising materials for applications in fuel cells, due to their high proton conductivity and higher chemical and thermal stability compared to the industry standard (e.g. Nafion®). Additionally, metal phosphonates are precursors to porous carbon materials with evenly distributed centers for ORR catalysis. As a fast and sustainable synthesis, mechanochemistry is the synthesis method of choice. Thorough characterization is carried out by XRD, MAS-NMR, XAS, BET, and DVS.
Nanoparticles (NPs) have become important materials for a variety of chemical technologies. The enhanced surface-area-to-volume ratio of NPs, making them excellent for use as catalyst, in analytical assays, and for antimicrobial applications.
Nickel NPs have exhibited immense potential as important catalyst for the Sabatier reaction, i.e. converting waste to energy via transformation of CO2 into CH4, and could replace the rare earth elements such as Ru, PT, or Rh. In this work we describe the solvothermal synthesis of monometallic and bimetallic nickel nanoparticles.
Monodisperse monometallic Ni NPs were synthesized using Oleylamin as solvent and reducing agent. The nanoparticles were investigated using small angle scattering (SAXS), scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDX), showing that the NPs are stable while the surface is not entirely covered. However, Ni has a high propensity to undergo oxidation, and becoming deactivated by coke formation. Hence, we further explore the preparation of bimetallic NPs, where a second metal is added to stabilize the Ni.
Bimetallic Cu-Ni NPs were synthesized by simultaneous solvothermal reduction. These bimetallic NPs exhibit excellent catalytic properties are promising candidates to be used as catalysts for efficient energy storage.
Perhaps due in no small part to its historical mystique, mechanochemistry has been shrowded in relative obscurity for quite some time. The successes of mechanochemistry in organic synthesis have often been curtailed by a fundamentally limited mechanistic understanding. Lately, however, the community has made great strides towards understanding the fundamentals, as well as large steps forward regarding industrially significant scale-up via twin-screw extrusion. A variety of recent work has traded in some of mechanochemistry’s mystique for simple, straight-forward chemical guidelines.
We present the synthesis of monodisperse monometallic Ni nanoparticles (NPs) and bimetallic NiCu respectively NiCo NPs. The NPs were investigated using SAXS, STEM, EDX, and XANES, showing that the NPs are size tunable and stable while the surface is not entirely covered. Nickel NPs have exhibited immense potential as important catalyst for the Sabatier reaction, i.e. converting waste to energy via transformation of CO2 into CH4.
Nanoparticles (NP) have become important materials for a variety of chemical technologies. The enhanced surface-area-to-volume ratio of NPs, making them excellent for use as catalyst, in analytical assays, and for antimicrobial applications.
Nickel NPs have exhibited immense potential as important catalyst for the Sabatier reaction, i.e. converting waste to energy via transformation of CO2 into CH4, and could replace the rare earth elements such as Ru, PT, or Rh. In this work we describe the solvothermal synthesis of monometallic and bimetallic nickel nanoparticles.
Monodisperse monometallic Ni NPs were synthesized using Oleylamin as solvent and reducing agent. The nanoparticles were investigated using small angle scattering (SAXS), scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDX), showing that the NPs are stable while the surface is not entirely covered. However, Ni has a high propensity to undergo oxidation, and becoming deactivated by coke formation. Hence, we further explore the preparation of bimetallic NPs, where a second metal is added to stabilize the Ni.
Bimetallic Cu-Ni NPs were synthesized by simultaneous solvothermal reduction. These bimetallic NPs exhibit excellent catalytic properties are promising candidates to be used as catalysts for efficient energy storage.
The mechanochemical formation of the ionic cocrystals of glucose (Glc) and sodium salts is presented. Products are formed by co-milling Glc with three sodium salts (NaCl, NaBr, NaI). The reaction pathways of the three ionic cocrystals were investigated using our tandem approach comprising a combination of in situ synchrotron powder X-ray diffraction and Raman spectroscopy.
Nowadays, different nanoparticles have been developed for commercial applications. However, since data on toxicity are barely available, their increasing application in cosmetic products, food and their release in the environment might cause severe problems. Since a range of physical, chemical, and biological characteristics of NPs are closely related to particle size and surface functionalization, precise separation and surface groups quantification is essential to acquire an in-depth understanding of their properties.
In this work, the performance of asymmetrical flow field flow fractionation (AF4) and capillary electrophoresis (CE) for the separation of nanoparticles (NPs) with different sizes, coatings, and coating densities was investigated and optimized.
For the first time, a two-dimensional off-line hyphenation of both techniques (AF4-CE) was developed. The results clearly demonstrated, that AF4-CE hyphenation can significantly improve the separation resolution and reduce the peak broadening in CE. Also, for the first time, CE was employed to determine the coating density of NPs and the results were in good agreement with the values acquired with conductometric titration.
Our aim is to develop a new simple and inexpensive method for full field X-ray fluorescence imaging. We combine an energy-dispersive array detector with a coded aperture. To obtain the information from the recorded image, a reconstruction step is necessary. First tests were carried out at the BAMline at BESSY II. This method enables the simultaneous detection of multiple elements, which is important e.g. in the field of catalysis.
We developed a new method for full field X-ray fluorescence imaging at the BAMline @ BESSY II. We combined an energy dispersive array detector for X-rays with a coded aperture to get high resolution images.
In coded aperture imaging, an object is projected through a mask, producing many overlapping images on the detector. To get the information about the investigated object out of the projected image, a decoding step is necessary.
The first part of our project was to develop the decoding algorithms. We tested the reported reconstruction with an antimask and compared the results with the performance of self-written reconstruction programs based on an iterative and a genetic algorithm. First tests were performed with raytracing simulations.
The next step was the collection of experimental data at the BAMline @ BESSY II (HZB). A test objects could be successfully reconstructed with our newly developed algorithm.
The exploration of metal phosphonates has gained great interest during the last decades, because of their structural diversity. They are promising candidates for a variety of applications ranging from adsorbance to electrocatalysis. The knowledge of the Crystal structure is significant for assigning a coordination polymer for a specific function. We investigated the influence of the fluorination degree of the organic linker on the Crystal packing, the interlayer distance, and the hydrophobicity of the resulting compounds. With fluorinated and nonfluorinated benzylphosphonic acids as starting materials in mechanochemical synthesis, four novel cadmium benzylphosphonates were obtained. Their structures were solved from powder X-ray diffraction.
Cadmium benzylphosphonate Cd(O3PBn)·H2O and its fluorinated derivates Cd(O3PBn-3F)·H2O, Cd(O3PBn-4F)·H2O, and Cd(O3PBn-F5)·H2O were synthesized mechanochemically. The Crystal structures of the compounds were determined based on powder X-ray diffraction (PXRD) data. The influence of the ligand substitution on the crystal structure of the metal phosphonate was determined. The hydrophobicity as a function of degree of fluorination was investigated using dynamic vapor sorption.
Crystalline molecular materials with mechanical flexibility are promising for technological development. This is particularly true for the development of advanced materials with optoelectronic and biomedical applications. While a growing number of mechanically flexible crystalline molecular materials are being reported,1 they remain scarce. At present, most discoveries are serendipitous, as limited design strategies are currently known. Amongst these strategies Desiraju et. al. suggested that elastic materials must contain herringbone structures.2 For plastic crystals, the so-called ‘shape-synthon’ strategy has been developed, in which weak non-covalent interactions are introduced into structures to facilitate mobility of molecules.3 This includes formation of slip planes. Generally, these models have performed very well at predicting and rationalizing the mechanical properties of new materials. Recently, however, a family of one-dimensional covalent networks (coordination polymers; CPs) has been described, which show mechanical elasticity. With drastically different structural chemistry, these systems do not seem to adhere to the currently established rules. Herein, we present the first such system: a plastically bendable crystal of a 1D CP, [Zn(-Cl)2(3,5-Cl2Py)2]n (where 3,5-Cl2Py = 3,5-dichloro pyridine). This CP crystallizes in a tetragonal, and can therefore be bent over two major faces to acute angles without fracturing. We conducted bending and indentation experiments to quantify the mechanical properties of the CP crystal. This was complimented by Vibrational (Raman and Terahertz) spectroscopy and theoretical calculations for deeper understanding of molecular level structural deformation.
Multidrug solids have a potential use to efficiently treat and control a superfluity of medical conditions.
To address the current drawbacks of drug development in R&D, it was targeted to achieve new pharmaceutical solid forms of fenamic acids having improved solubility and thermal stability. Subsequently, five new multicomponent solids consisting of three salt hydrates of trimethoprim (TMP) with mefenamic acid (TMP-MFA-H2O), tolfenamic acid (TMP-TFA-H2O) and flufenamic acid (TMP-FFA-H2O), and two cocrystals of sulfamethazine (SFZ) with flufenamic acid (SFZ-FFA) and niflumic acid (SFZ-NFA) were prepared by liquid assisted grinding. Looking at the structures of active pharmaceutical ingredient (API) molecules, it was quite expected that a wide range of supramolecular synthons would lead to cocrystallization.
New forms were characterized thoroughly by various solid-state techniques, including single crystal X-ray diffraction (SCXRD), which provided details of hydrogen bonding, molecular packing and interactions between drug and coformer. Kinetic solubility at pH 7.4 buffer study has been carried out and a comparison is made with respect to the parent drugs. A significant enhancement of NSAIDs solubility was observed in all salt hydrate systems of TMP. Thus with increasing physicochemical properties such as improved solubility further leads to the enhancement of bioavailability, which has implications to overcoming the formulation related problems of active pharmaceutical ingredients (APIs).
Our aim is to develop a new simple and inexpensive method for full field X-ray fluorescence imaging . We combine an energy dispersive array detector with a coded aperture to obtain high resolution images . To obtain the information from the recorded image a reconstruction step is necessary . The reconstruction methods we have developed , were tested on simulated data and then applied to experimental data . The first tests were carried out at the BAM line @ BESSY II. This method enables the simultaneous detection of multiple elements , which is important e.g. in the field of catalysis.
Mechanochemistry paves the way to simple, fast, and green syntheses. Despite considerable effort, there is a lack in understanding of the underlying mechanisms. In situ investigations help to understand these mechanisms, which occur during a mechanochemical reaction. Here we present a universal strategy for simultaneous real-time in situ analysis, combining X-ray diffraction, Raman spectroscopy, and thermography. The potential of of our approach is shown for diffrent model reactions.
We present the optical sensing of phthalate Esters (PAEs), a group of endocrine-disrupting chemicals. The sensing takes place as changes in the fluorescence emission intensity of aminopyrene covalently bound to the organic ligands of the metal−organic framework compound ZIF-8. In the presence of PAEs, a quenching of the fluorescence emission is observed. We evaluated strategies to engineer colloidal size distribution of the sensing particles to optimize the sensory response to PAEs. A thorough characterization of the modified ZIF-8 nanoparticles included powder X-ray diffractometry, transmission electron microscopy, high-performance liquid chromatography, and photophysical characterization. The presented capability of the fluorophore-functionalized ZIF-8 to sense PAEs complements established methods such as chromatography-based procedures, which cannot be used on-site and paves the way for future developments such as hand-held quick sensing devices.
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.
Our aim is to develop a new method for full field X ray fluorescence imaging at the BAM line @ BESSY II. We will combine an energydispersive array detector for X rays with a coded aperture to get high resolution images . In coded aperture imaging , an object is projected through a mask , producing many overlapping images on the detector . The first part of the project is to perform raytracing simulations to get realistic data and to develop a reconstruction method that allows to get the Information about the investigated object out of the projected image .
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.
Besides conventional scanning X-ray fluorescence imaging at synchrotron sources, full-field X-ray fluorescence (FF-XRF) imaging techniques that do not implicitly require spatial scanning of the sample have become available. FF-XRF has become achievable thanks to the development of a new type of energy dispersive CCD-based 2D detector, also referred to as a 'color X-ray camera (CXC)' or 'SLcam'. We report on different imaging schemes for biological samples using FF-XRF imaging: (a) 2D 'zoom' imaging with pinhole optics using the 'camera obscura' principle; (b) 2D 'fixed magnification' imaging using magnifying polycapillary optics; and (c) 3D-FF-XRF imaging using an X-ray sheet beam or computed tomography (CT). The different FF-XRF imaging modes are illustrated using the crustacean Daphnia magna, a model organism for investigating the effects of metals on organism/ecosystem health, and foraminifera, a class of amoeboid protist. Detailed analytical characterization of the set-up is performed through analyzing various reference materials in order to determine limits of detection (LODs) and sensitivities. Experiments were performed using the BAMline at the BESSY synchrotron (Berlin, Germany) and using the P06 Hard X-ray Microprobe at the PETRAIII synchrotron (Hamburg, Germany).
The elemental analysis of seawater is often critical to the understanding of marine chemistry, marine geochemistry, and the deep-sea ecosystems. Laser-induced breakdown spectroscopy (LIBS) with the advantage of rapid multi-elements detection, has a great potential for in-situ elemental analysis of seawater. In practice, it is crucial to create a compact, low cost and power saving instrument for the long-term deep-sea observation. A recently appeared diode-pumped solid-state (DPSS) laser seems to be a promising candidate as it is both compact and robust. Additionally, its high repetition rate up to hundreds of kHz can provide a considerable throughput for LIBS analysis. However, the DPSS lasers operate at moderate pulse energies, usually less than one mJ, which cannot sustain stable breakdowns in bulk water. To ensure stable laser-induced plasmas underwater with such a μJ-DPSS laser, we introduced an ultrasound source to assist the breakdown process. The phase interface and mass flow generated by the near-field ultrasound can greatly reduce the breakdown threshold and enhance element-specific emissions. Meanwhile, the high repetition-rate pulses can also improve the breakdown probability and generate unique emission lines originated from the water molecule. We further demonstrate that the high repetition-rate DPSS laser combined with the Echelle spectrometer can provide effective quantitative analysis for metal elements in bulk water.