This thesis focused on the synthesis and characterization of novel functional materials based on cellulose and graphene derivatives. Cellulose/GO hydrogels were produced as the starting material by dissolving cellulose and dispersing GO in NaOH/urea solution. This method is considered as an efficient, simple, environmentally friendly, and low-cost method. Novel functionalities, such as sensing, catalytic and EMI shielding properties have been “built-in” to cellulose/GO hydrogels. Cellulose/rGO composite films and aerogels were successfully fabricated by dissolving cellulose and dispersing GO in NaOH/urea solution, followed by the chemical reduction with vitamin C as the reducing agent. The cellulose/rGO films and aerogels with various rGO contents were prepared by air-drying and freeze-drying of the prepared cellulose/rGO composite hydrogels. The resultant cellulose/rGO composites prepared by this efficient and simple method show high resistance sensitivity to environmental stimuli like temperature, humidity, liquids, vapours, and strain stress. Thus, the cellulose/rGO films can be applied in detecting human motions and human breath cycles. Liquid temperature, liquid type, and ion concentration also be determined by our cellulose/rGO films. Moreover, the composite aerogels are fast responding and extremely sensitive sensors for vapour detection and testing with good repeatability. It was also revealed that discriminating and quantitative responses can be obtained when analyzing various vapours and different vapour concentrations. For methanol vapour, the aerogel shows linear response to the vapour concentration. Thus cellulose/rGO composite aerogel can be used to quantify methanol vapour concentrations. The efficient, scalable, and environmentally friendly preparation of novel and high-performance of vapour sensing materials with well reproducibility is promising to achieve practical vapour sensing applications. We have successfully presented an effective, facial, simple, and scalable method to form Fe3O4 nanoparticles onto cellulose/GO hydrogels. XRD, FTIR, XPS and TEM indicated that Fe3O4 nanoparticles with good dispersion and uniform size are successfully coated on cellulose matrix and GO sheets. This material was tested as catalyst for the cleaning of dye-contaminated water by oxidation with H2O2.The optimized experiment conditions for AO7 degradation are: [AO7] = 0.1 mM, T = 298 K, [H2O2] = 22 mM, and pH = 3. Under these conditions, the resulting hydrogels display 97 % AO7 removal within 120 min and retained strong degradation performance after twenty consecutive cycles of reuse. Especially, the detailed XPS analysis of cellulose/GO/Fe3O4 and cellulose/Fe3O4 composites indicated that the cellulose/GO/Fe3O4 hydrogel retain its high degradation activity by keeping the ratio of Fe3+/Fe2+ at 2 during the 20 heterogeneous Fenton-like reaction cycles. Therefore, the cellulose/GO/Fe3O4 hydrogel is recommended to test the treatment of other dye-contaminated wastewaters. Cellulose/rGO/Fe3O4 films and aerogels were successfully fabricated by the in-situ grown of Fe3O4 nanoparticles within a cellulose matrix containing rGO sheets. Cellulose/rGO (8 wt.%)/Fe3O4 aerogels with the thickness of 0.5 mm exhibited high EMI shielding performance with the EMI SE value at 32.4-40.1 dB in the 8.2-12.4 GHz frequency range. High loading of rGO and large thickness of the composites are beneficial for the excellent EMI shielding performance of our aerogels. The lightweight aerogel is suitable for the practical application as EMI shielding materials such as spacecraft, aircraft, energy conversion application, and energy storage.

We describe an efficient synthesis of the methylene-bridged biscarbazole alkaloids bismurrayafoline-A, bismurrayafolinol and chrestifoline B–D using an Ullmann-type coupling at the benzylic position.

Advances in flexible and functional metal–organic frameworks (MOFs), also called soft porous crystals, are reviewed by covering the literature of the five years period 2009–2013 with reference to the early pertinent work since the late 1990s. Flexible MOFs combine the crystalline order of the underlying coordination network with cooperative structural transformability. These materials can respond to physical and chemical stimuli of various kinds in a tunable fashion by molecular design, which does not exist for other known solid-state materials. Among the fascinating properties are so-called breathing and swelling phenomena as a function of host–guest interactions. Phase transitions are triggered by guest adsorption/desorption, photochemical, thermal, and mechanical stimuli. Other important flexible properties of MOFs, such as linker rotation and sub-net sliding, which are not necessarily accompanied by crystallographic phase transitions, are briefly mentioned as well. Emphasis is given on reviewing the recent progress in application of in situ characterization techniques and the results of theoretical approaches to characterize and understand the breathing mechanisms and phase transitions. The flexible MOF systems, which are discussed, are categorized by the type of metal-nodes involved and how their coordination chemistry with the linker molecules controls the framework dynamics. Aspects of tailoring the flexible and responsive properties by the mixed component solid-solution concept are included, and as well examples of possible applications of flexible metal–organic frameworks for separation, catalysis, sensing, and biomedicine.

Soft lithographic methods describe a set of printing methods which are widely used for the preparation of structured surfaces. Structured surfaces are essential components in the field of (opto-)electronic devices such as organic light emitting diodes, photovoltaics or organic field effect transistors. In recent years, crucial progress has been achieved in the development of patterned metal coatings for these applications. This review focusses on new strategies for soft lithographical printing of metal structures emphasizing the subtle interplay of printing techniques, metal precursor chemistry, and surface functionalization strategies. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

We report on the surface-catalyzed formal [2+2] and [2+2+2] cycloadditions of ortho-activated tetracene species on a Ag(111) substrate under ultrahigh vacuum conditions. Three different products are obtained: tetracene dimers, trimers, and tetramers. The former results from the formation of a four-membered ring while the other two arise from cyclization into six-membered rings. These on-surface reactions have been monitored by scanning tunneling microscopy and rationalized by density functional theory calculations. Our approach, based on the reaction of ortho-dihalo precursor monomers via formal cycloadditions, establishes an additional method for the highly active field of on-surface synthesis and enables the development of novel 1D and 2D covalent carbon nanostructures.

The electronic and magnetic properties of nanographenes strongly depend on their size, shape and topology. While many nanographenes present a closedshell electronic structure, certain molecular topologies may lead to an open-shell structure. Triangular-shaped nanographenes with zigzag edges, which exist as neutral radicals, are of considerable interest both in fundamental science and for future technologies aimed at harnessing their intrinsic high-spin magnetic ground states for spinbased operations and information storage. Their synthesis, however, is extremely challenging owing to the presence of unpaired electrons, which confers them with enhanced reactivity. We report a combined in-solution and onsurface synthesis of π-extended triangulene, a non-Kekulé nanographene with the structural formula C33H15, consisting of ten benzene rings fused in a triangular fashion. The distinctive topology of the molecule entails the presence of three unpaired electrons that couple to form a spin quartet ground state. The structure of individual molecules adsorbed on an inert gold surface is confirmed through ultrahigh-resolution scanning tunneling microscopy. The electronic properties are studied via scanning tunneling spectroscopy, wherein unambiguous spectroscopic signatures of the spin-split singly occupied molecular orbitals are found. Detailed insight into its properties is obtained through tight-binding, density functional and many-body perturbation theory calculations, with the latter providing evidence that π-extended triangulene retains its open-shell quartet ground state on the surface. Our work provides unprecedented access to open-shell nanographenes with high-spin ground states, potentially useful in carbon-based spintronics.

Nonbenzenoid carbocyclic rings are postulated to serve as important structural elements toward tuning the chemical and electronic properties of extended polycyclic aromatic hydrocarbons (PAHs, or namely nanographenes), necessitating a rational and atomically precise synthetic approach toward their fabrication. Here, using a combined bottom-up in-solution and on-surface synthetic approach, we report the synthesis of nonbenzenoid open-shell nanographenes containing two pairs of embedded pentagonal and heptagonal rings. Extensive characterization of the resultant nanographene in solution shows a low optical gap, and an open-shell singlet ground state with a low singlet–triplet gap. Employing ultra-high-resolution scanning tunneling microscopy and spectroscopy, we conduct atomic-scale structural and electronic studies on a cyclopenta-fused derivative on a Au(111) surface. The resultant five to seven rings embedded nanographene displays an extremely narrow energy gap of 0.27 eV and exhibits a pronounced open-shell biradical character close to 1 (y0 = 0.92). Our experimental results are supported by mean-field and multiconfigurational quantum chemical calculations. Access to large nanographenes with a combination of nonbenzenoid topologies and open-shell character should have wide implications in harnessing new functionalities toward the realization of future organic electronic and spintronic devices.

Signaling molecules are critically important to regulate cellular processes. Therefore, their incorporation into engineered biomaterials is indispensable for the applications in tissue engineering and regenerative medicine. In particular, the functionalization of highly hydrated polymer networks, so-called hydrogels, with the signaling molecules, has been quite beneficial to provide multiple cell-instructive signals. Following this strategy, the incorporation of sulfated glycosaminoglycans (GAGs) into such polymer networks offers unprecedented options to control the administration of signaling molecules via electrostatic interactions. Moreover, mathematical models can be instrumental in designing materials to tune the transport and adjust the local concentration of the signaling molecules to precisely modulate cell fate decisions. Accordingly, this study aims to systematically investigate the impact of different binary poly(ethylene glycol)-glycosaminoglycan hydrogel networks on the transport of signaling molecules by developing and applying mathematical modeling in combination with experimental approaches. The gained knowledge was then applied to modulate the bioactivities of pro-angiogenic growths factor within the binary hydrogel and rationally design a new class of cytocompatible GAG-based materials for the controlled administration of pro-angiogenic growth factors. Firstly, systematic studies on the mobility of signaling molecules within GAG-based polymer networks revealed differential effects of hydrogel network parameters such as mesh size, GAG content, and the sulfation pattern of the GAG building block on the transport of these signaling molecules. Secondly, the effect of the GAG content of the hydrogel and the sulfation pattern of the GAG building block on the bioactivity of hydrogel administrated vascular endothelial growth factor (VEGF) have been analyzed. Since VEGF is a GAG-affine protein that plays a major role in angiogenesis, its ability to promote vascular morphogenesis has been investigated. The simulation and experimental results demonstrated the determining impact of the availability of free (unbound) VEGF as well as the presence of GAGs with a specific sulfation pattern within the polymer network on the formation of the endothelial capillary network within the hydrogel. Finally, a rational design strategy has been applied to extend a GAG-hydrogel platform to allow for a far-reaching control of its cell instructive properties. The resulting materials are independently tunable over a broad range for their mechanical properties and GAG content. The GAG content of the hydrogel matrices, in particular, was shown to modulate the transport of pro-angiogenic growth factors most. Moreover, the hydrogel also supports endothelial vascular morphogenesis. In conclusion, the in here followed approach of combining experimental results and mathematical modeling for predicting the transport of signaling molecules and the rational design concept for customizing GAG-based hydrogel networks provide the fundamentals to precisely modulate cell fate decisions within GAG-based biohybrid polymer networks rationalizing their application for tissue engineering and regenerative medicine

Matrix assisted laser desorption/ionization mass spectrometry (MALDI MS) and the corresponding visualization technique MALDI MS Imaging (MSI) have emerged as important analytical tools in biochemical sciences, e.g., for drug development or to trace the metabolomic changes in cancerous tissues. Initially developed for the detection of high molecular weight compounds (HMWC; M > 1000 Da), in recent years the reliable and reproducible detection of low molecular weight compounds (LMWC; M < 1000 Da) has gained high attention, e.g., in the research fields of metabolomics and lipidomics. By using a protective matrix, the MALDI technique is capable of soft ionization of analytes to prevent their fragmentation or degradation. This matrix is responsible for the spatial separation of the analyte molecules, their protection from the strong laser shots, and their ionization. Commonly used matrices are small organic matrices (SOMs; M < 500 Da), which are utilized in HMWC analytics and recently also in LMWC analytics since they show sufficient absorption of the laser radiation, high crystallinity, and good ionization efficiency. However, their utilization can cause several drawbacks: (i) High background interferences below m/z = 1000 (not MALDI silent), which is disadvantageous specifically for LMWC analytics; (ii) low vacuum stability, which is especially problematic for standard instruments operated under high vacuum (HV); (iii) challenging homogeneous thin-layer coating, potentially causing inconsistent measurement conditions; and (iv) usually no suitability for dual polarity mode experiments, i.e., carrying out positive and negative mode measurements with the same matrix. Polymeric materials are promising candidates for MALDI silent matrices, as the large variety of possible molecular layouts potentially allows to meet all prerequisites of a MALDI matrix: (a) Sufficient ultra-violet (UV) laser radiation absorption, implemented by introducing conjugated π-electron systems in the polymer backbone or side chains; (b) high ionization efficiency, enhanced by adding acidic and/or basic functional groups to the polymer’s molecular structure, potentially also allowing dual polarity mode measurements; (c) MALDI silence, enabled by the high molar mass of the polymer chains; (d) high vacuum stability, also granted by the polymer’s molar mass; and (e) homogeneous thin-films, achieved by multiple available coating methods. Yet, despite their high potential only a handful of polymeric matrices were reported in literature and so far, investigations to develop conscious design strategies are missing. The target of this thesis is to contribute to the field of MALDI silent matrices by developing and investigating different polymers as macromolecular MALDI MS and MSI matrices for LMWC analytics. Therefore, two different strategies were explored: (i) Investigating conjugated polymers, and (ii) polymerizing SOMs. For the first strategy, five conjugated polymers were tested as MALDI matrices for the detection of various LMWCs. Among these, four were found to be excellent matrices, with sufficient ionization efficiencies and rare dual polarity mode suitability and allowed LMWC detection with low background interferences (MALDI silent). A high crystallinity of the matrix (SOM) is reported to be crucial to ensure successful measurements, yet conjugated polymer matrices (CPMs) are semi-crystalline, i.e., they contain crystalline and amorphous domains. Hence, the analytes are expected to be incorporated in the crystalline domains of the CPMs, depending on their degree of crystallization. Therefore, two amorphous CPMs were synthesized and tested, showing similar matrix performances (e.g., ionization efficiencies, dual polarity mode, MALDI silence) as a structurally related semi-crystalline CPM. This indicates that the analytes are incorporated in the amorphous parts of the CPM. The second strategy towards polymeric matrices (PMs) is the polymerization of standard SOMs. As the matrix performance of the corresponding SOMs is known, the performance of the respective polymerized SOMs (P(SOMs)) can be validated against this benchmark. At the same time, polymerization can induce the properties needed to enable efficient LMWC analytics. Therefore, two standard SOMs were modified and polymerized, resulting in P(SOMs), which were vacuum stable and MALDI silent, and showed similar optical properties, analyte scopes and ionization efficiencies in benchmark tests with their respective SOMs. For the fast and facile comparison of the matrix performances of PMs and standard matrices, the graphing software OriginPro was used to visualize, process, and evaluate the acquired mass spectra. To automatize these tasks, a script was programmed using the OriginPro-native programming languages LabTalk and OriginC: X Functions.

Gegenstand der vorliegenden Arbeit war die Synthese von enantiomerenreinen α-substituierten β-Hydroxyestern zu neuartigen 4,5-disubstituieren Oxazolidin-2-onen, die auch als EVANS-Auxilare bekannt sind.