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As viruses are obligatory intracellular parasites, any step during their life cycle strictly depends on successful interaction with their particular host cells. In particular, their interaction with cellular membranes is of crucial importance for most steps in the viral replication cycle. Such interactions are initiated by uptake of viral particles and subsequent trafficking to intracellular compartments to access their replication compartments which provide a spatially confined environment concentrating viral and cellular components, and subsequently, employ cellular membranes for assembly and exit of viral progeny. The ability of viruses to actively modulate lipid composition such as sphingolipids (SLs) is essential for successful completion of the viral life cycle. In addition to their structural and biophysical properties of cellular membranes, some sphingolipid (SL) species are bioactive and as such, take part in cellular signaling processes involved in regulating viral replication. It is especially due to the progress made in tools to study accumulation and dynamics of SLs, which visualize their compartmentalization and identify interaction partners at a cellular level, as well as the availability of genetic knockout systems, that the role of particular SL species in the viral replication process can be analyzed and, most importantly, be explored as targets for therapeutic intervention.
Synthese einer Bibliothek von Aminosäure-basierten Oligopeptid-Amphiphilen mittels Festphasensynthese, deren kovalente Knüpfung an einen nukleophilen Kern zu C3-symmetrischen Sternmesogenen und die Analyse der Einflüsse der verwendeten Aminosäuren auf die Sekundärstruktur des synthetisierten Moleküls.
Nanodiamond (ND) is a versatile and promising material for bio-applications. Despite many efforts, agglomeration of nanodiamond and the non-specific adsorption of proteins on the ND surface when exposed to bio-fluids remains a major obstacle for biomedical applications. An assortment of branched and linear molecules with superior ability to colloidally stabilize nanoparticles in salt and cell media environment, for up to 30 days, was attached to the ND’s surface.
The building box system with azide as external groups offers a huge variety of binding with many molecules, such as drugs, dyes or targeting molecules, is possible. Clicking, for instance, zwitterions moieties to the chain protects ND surface from protein corona forming when the particles get in contact with biofluids containing proteins.
Thermogravimetric analysis results of the ND surface loading show a significant prevention of up to 98 % of the protein adsorption compared with NDs without zwitterionic headgroups and long colloidal stability when tetraethylene glycol (TEG) are attached to the surface.
The versatility of the modular system to bind not only zwitterionic chains but also clickable functional molecules to fluorescent nanodiamonds (fNDs) demonstrates the potential of the system at the nanodiamond. Using defect structures, such as nitrogen-vacancy (NV) centers, diamond particles, due to their widely non-toxic behavior, can be used as fNDs for photostable labeling, bioimaging and nanoscale sensing in living cells and organisms. To functionalize the fND surface a novel milling technique with diazonium salts was established to perform grafting on poorly reactive HPHT fNDs yielding in high surface loading and high negative zeta potential.
Combining the benefits of TEG and zwitterion containing groups with antibody enabled nucleus targeting ability on fND confirms the enhanced colloidal stability in living cells experiments for the first time. Furthermore, the results indicate an improved corona repulsion compared with fND without zwitterion containing headgroups. As a result, the circulation times were enlarged from 4 (fND without zwitterion chain but with antibody) to 17 (with antibody and zwitterion chains) hours.
In non-biomedical applications, the modular system can be used as a probe for heavy metals by binding it to dyes. Detection of metals in different environments with high selectivity and specificity is one of the prerequisites of the fight against environmental pollution with these elements. Pyrenes are well suited and known for fluorescence sensing in different media.
The applied sensing principle typically relies on the formation of intra- and intermolecular excimers, which is however limiting the sensitivity range due to masking of e.g. quenching effects by the excimer emission. This study shows a highly selective, structurally rigid chemical sensor based on the monomer fluorescence of pyrene moieties bearing triazole groups.
This probe can quantitatively detect Cu2+, Pb2+ and Hg2+ in organic solvents over a broad concentration range, even in the presence of ubiquitous ions such as Na+, K+, Ca2+ and Mg2+. The strongly emissive sensor’s fluorescence with a long lifetime of 165 ns is quenched by a 1:1 complex formation upon addition of metal ions in acetonitrile. Upon addition of a tenfold excess of the metal ion to the sensor, agglomerates with a diameter of about 3 nm are formed. Due to complex interactions in the system, conventional linear correlations are not observed for all concentrations. Therefore, a critical comparison between the conventional Job plot interpretation, the method of Benesi-Hildebrand, and a non-linear fit is presented. The reported system enables the specific and robust sensing of medically and environmentally relevant ions in the health-relevant nM range and could be used e.g. for the monitoring of the respective ions in waste streams.
Nonetheless, often these waste streams end up in sensitive aquacultures, where such sensor technology only works if the probe is water-soluble to monitor the spread and formation of environmental damage from heavy metals. Many chemosensors only work quantitatively in specific solvents and under highly pure conditions. In this thesis a method to stabilize water-insoluble chemosensors on nanodiamonds in saline water while maintaining the sensor efficacy and specificityas as well as colloidal stability is presented. Additionally, the sensor capability is retained in organic solvents. This study provides insight into the absorptivity of pyrene derivatives to the nanodiamond surface and a way to reversibly desorb them.
Moreover, the system proves that in presence of 95 % oxygen atmosphere while the fluoresce measurement the results of the do not vary from the one in argon atmosphere. Furthermore, the presence of common ions in water do not disturb the colloidal stability of the NDs and also no influence the sensor functionality and thus is highly promising candidate for measurement without cumbersome preparation steps.
The future of water-derived hydrogen as the “sustainable energy source” straightaway bets on the success of the sluggish oxygen-generating half-reaction. The endeavor to emulate the natural photosystem II for efficient water oxidation has been extended across the spectrum of organic and inorganic combinations. However, the achievement has so far been restricted to homogeneous catalysts rather than their pristine heterogeneous forms. The poor structural understanding and control over the mechanistic pathway often impede the overall development. Herein, we have synthesized a highly crystalline covalent organic framework (COF) for chemical and photochemical water oxidation. The interpenetrated structure assures the catalyst stability, as the catalyst’s performance remains unaltered after several cycles. This COF exhibits the highest ever accomplished catalytic activity for such an organometallic crystalline solid-state material where the rate of oxygen evolution is as high as ∼26,000 μmol L\(^{–1}\) s\(^{–1}\) (second-order rate constant k ≈ 1650 μmol L s\(^{–1}\) g\(^{–2}\)). The catalyst also proves its exceptional activity (k ≈ 1600 μmol L s\(^{–1}\) g\(^{–2}\)) during light-driven water oxidation under very dilute conditions. The cooperative interaction between metal centers in the crystalline network offers 20–30-fold superior activity during chemical as well as photocatalytic water oxidation as compared to its amorphous polymeric counterpart.
Dye–dye interactions affect the optical and electronic properties in organic semiconductor films of light harvesting and detecting optoelectronic applications. This review elaborates how to tailor these properties of organic semiconductors for organic solar cells (OSCs) and organic photodiodes (OPDs). While these devices rely on similar materials, the demands for their optical properties are rather different, the former requiring a broad absorption spectrum spanning from the UV over visible up to the near‐infrared region and the latter an ultra‐narrow absorption spectrum at a specific, targeted wavelength. In order to design organic semiconductors satisfying these demands, fundamental insights on the relationship of optical properties are provided depending on molecular packing arrangement and the resultant electronic coupling thereof. Based on recent advancements in the theoretical understanding of intermolecular interactions between slip‐stacked dyes, distinguishing classical J‐aggregates with predominant long‐range Coulomb coupling from charge transfer (CT)‐mediated or ‐coupled J‐aggregates, whose red‐shifts are primarily governed by short‐range orbital interactions, is suggested. Within this framework, the relationship between aggregate structure and functional properties of representative classes of dye aggregates is analyzed for the most advanced OSCs and wavelength‐selective OPDs, providing important insights into the rational design of thin‐film optoelectronic materials.
RNA molecules play diverse roles in biological systems. Post-transcriptional RNA modifications and dynamic structures enhance the functional diversity of RNA. A prerequisite for studying their biological significance is the availability of reliable methods for the detection of RNA modifications and structures. Several promising approaches have been developed in the last few decades; however, efficient, and versatile tools are still required to study the dynamic features of RNA. This thesis focuses on the development of nucleic acid catalysts as a tool to address the current needs in studying RNA. The major part of this thesis aimed at the development of deoxyribozymes as a tool for the detection of RNA modifications. Using in vitro selection from a random DNA library, we found deoxyribozymes that are sensitive to N 6 -isopentenyladenosine (i6A), a native tRNA modification and structural analogue of m6A. The in vitro evolution identified three classes of DNA enzymes: AA, AB08, and AC17 DNAzymes that showed distinct response to i6A modification and showed strong discrimination between structural analogues, i.e., m6A and i6A. In the continuation of the project, we attempted to develop RNA-cleaving deoxyribozymes that differentially respond to monomethylated cytidine isomers, 3-methylcytidine (m3C), N4 - methylcytidine (m4C), and 5-methylcytidine (m5C). Several deoxyribozymes were identified from in vitro selection, which are selective for a specific methylated cytidine isomer. The characterization of AL112, AM101, AN05, and AK104 catalysts confirmed the successful evolution of modification-specific and general deoxyribozymes that showed a broad substrate scope. In order to accelerate the DNAzymes discovery, a high throughput sequencing method (DZ-seq) was established that directly quantifies the RNA cleavage activity and cleavage site from deep sequencing data. The libraries contained information about cleavage status, cleavage site and sequence of deoxyribozymes and RNA substrate. The fraction cleaved (FC) data obtained from Dz-seq was validated for a subset of deoxyribozmes using conventional gel based kinetic assay and showed a good linear correlation (R2 = 0.91). Dz-seq possesses a great potential for the discovery of novel deoxyribozymes for the analysis of various RNA modifications in the future. The second objective of the current study was the development of structure-specific RNA labeling ribozymes. Here, we attempted to develop ribozymes that targets RNA of interest by structure-specific interaction rather than base-pairing and focused on a specific RNA G-quadruplex as the target. Two subsequent selection experiments led to the identification of the adenylyltransferase ribozymes AO10.2 and AR9. The partial characterization of these catalysts showed that A010.2 was unable to recognize intact BCL2 structure, but it turned out as the first reported trans-active ribozyme that efficiently labeled uridine in a defined substrate RNA hybridized to the ribozyme. The other ribozyme AR9 was shown to serve as a trans-active, self-labeling ribozyme that catalyzed adenylyl transferase reaction in the presence of the intact BCL2 sequence. Based on these preliminary findings, we envision that AR9 could potentially serve as a reporter RNA by self-labeling in the presence of an RNA G-quadruplex. However, both AO10.2 and AR9 still require more detailed characterization for their potential applications.
Tribenzotriquinacene (TBTQ) is a polycyclic aromatic framework with a particularly rigid, C3v symmetrical, bowl-shaped core bearing three mutually fused indane wings. It has been discussed as a defect center for a nanographene by Kuck and colleagues. Therefore, extended TBTQ structures are promising models for saturated defect structures in graphene and graphene like molecules and could be used to investigate the role of defects for the electronic properties of graphene. With this motivation, three different pi-extended TBTQ derivatives have been synthesized in this work. Several different Scholl reaction conditions were tried to obtain fully annulated product of hexaphenyl substituted TBTQ. The desired benzannulated TBTQ derivative could not be obtained due to unfavourable electron density in the respective positions of the molecule and increased reactivity of the bay position of the precursor. As an another method for benzannulation is the on-surface synthesis of graphene flakes and can be carried out using electron beams e.g. in a tunneling microscope (STM). According to our previous research, the parent system TBTQ and centro-methyl TBTQ on silver and gold surfaces showed that the gas phase deposition of these molecules gives rise to the formation of highly ordered two-dimensional assemblies with unique structural features. This shows the feasibility for the formation of defective graphene networks starting from the parent structures. Therefore, the same deposition technique was used to deposit Me-TBTQ(OAc)3Ph6, and investigate the molecular self-assembly properties directly on the surface of Cu (111). In summary, the substrate temperature dependent self-assembly of Me-TBTQ(OAc)3Ph6 molecules on Cu(111), shows the following evolution of orientations. At room temperature, molecules form dimers, which construct a higher-coverage honeycomb lattice. Furthermore, one of the acetyl group located in the bay positions of the TBTQ core is cleaved and the remaining two induce the metal-molecule interaction. It was presumed that by increasing the temperature to 393 K, the remaining acetyl and methyl groups would beeliminated from the molecular structure.In addition, the smaller TBTQ-Ph6 molecules preferably lie flat on Cu(111) crystal and allowing the molecules to settle into a C3-symmetry and form a dense hexagonal structure.
Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a periphery of linear chains of different lengths, branching in the chain and swallow-tails, are compared. Generally, these disks display broad and stable thermotropic mesophases, with the tangential TTT being superior to the radial isomer. The structure–property relationships of the number of alkyl chains, their position, length and structure were studied.
A series of monomeric chirally substituted indolenine squaraine monomers were successfully synthesized and utilized for the construction of various oligo- and polymers, in order to study their chiroptical properties in terms of exciton chirality. The quaternary carbon atom at the 3-position of the indolenine subunit, as well as the alkyl side chain attached to the indolenine nitrogen were selected as the most suitable site for chiral functionalization.
For the C(3)-chiral derivatives, two synthetic routes depending on the desired substitution at the stereogenic center were established. The chiral side chains were prepared via Evans asymmetric alkylation where the resulting branching point at the 2 position constituted the chiral center. While the chiral substitution only had minor effects on the linear optical properties and geometric structure of the chromophore, all compounds exhibited a distinct and measurable CD signal that correlated with the distance of the chiral center to the central chromophore.
Polymers bearing chiral side chains exhibited a solvent- and temperature-dependent helix-coil equilibrium, which was influenced by the type of side chain used. CD spectroscopy revealed the helical conformation to possess a preferred twist sense, and temperature-dependent measurements showed the degree of homohelicity to be nearly complete in certain cases. Furthermore, a CPL signal was able to be obtained for the helical conformer of one polymer.
Various (co)oligo- and polymers comprising the C(3)-chiral monomers only displayed a solvent-independent J-type absorption behavior and thus did not form helical conformations in solution. CD spectroscopy revealed a solvent-dependent adoption of quasi-enantiomeric conformers, which was elucidated by quantum chemical TDDFT calculations.
Interactions between proteins and carbohydrates with larger biomacromolecules, e.g., lectins, are usually examined using self-assembled monolayers on target gold surfaces as a simplified model measuring setup. However, most of those measuring setups are either limited to a single substrate or do not allow for control over ligand distance and spacing. Here, we develop a synthetic strategy, consisting of a cascade of a thioesterification, native chemical ligation (NCL) and thiol-ene reaction, in order to create three-component polymer conjugates with a defined double bioactivation at the chain end. The target architecture is the vicinal attachment of two biomolecule residues to the α telechelic end point of a polymer and a thioether group at the ω chain end for fixating the conjugate to a gold sensor chip surface. As proof-of-principle studies for affinity measurements, we demonstrate the interaction between covalently bound mannose and ConA in surface acoustic wave (SAW) and surface plasmon resonance (SPR) experiments.