Highly Emissive Eu(III) Probes for Biological Assays

Luminescent lanthanide complexes are important tools for molecular sensing and cellular staining due to their unique photophysical properties, including their long luminescence lifetimes that permit the use of time-gated measurements. However, a common drawback of such complexes is the non-specific binding associated with their low solubility in biological media. A new class of bright, highly water soluble, and negatively charged sulfonate or carboxylate derivatives of substituted aryl–alkynyl triazacyclononane complexes has been synthesised and their photophysical properties analysed. In addition, new synthetic methodologies have been explored for the introduction of solubilising moieties into the ligand system and for the incorporation of a linkage point for conjugation with biomolecules. Each complex exhibits extremely high quantum yields (up to 38 % in H2O), large extinction coefficients (60,000 M-1 cm-1) and long luminescence lifetimes (1.1 ms). Introduction of the charged solubilising moieties suppresses cellular uptake or adsorption to living cells, making them applicable for labelling and performing assays on membrane receptors. These Eu(III) complexes have been applied to monitor fluorescent ligand binding on cell-surface proteins (G-protein coupled receptors) with time-resolved fluorescence resonance energy transfer (TR-FRET) assays and TR-FRET microscopy. In addition, the introduction of a linkage point for conjugation on the macrocyclic ring provided complete control of the stereochemistry of the final complex. Direct and selective formation of chiral complexes was observed with > 95 % optical purity resulting in an intense circularly polarised luminescence signal

Automated glycan assembly of arabinomannan oligosaccharides from Mycobacterium tuberculosis

Arabinomannan (AM) polysaccharides are clinical biomarkers for Mycobacterium tuberculosis (MTB) infections due to their roles in the interaction with host cells and interference with macrophage activation. Collections of defined AM oligosaccharides can help to improve the understanding of these polysaccharides and the development of novel therapeutical and diagnostic agents. Automated glycan assembly (AGA) was employed to prepare the core structure of AM from MTB, containing α-(1,6)-Man, α-(1,5)-Ara, and α-(1,2)-Man linkages. The introduction of a capping step after each glycosylation and further optimized reaction conditions allowed for the synthesis of a series of oligosaccharides, ranging from hexa- to branched dodecasaccharides

Materials science based on synthetic polysaccharides

Supramolecular architectures, based on synthetic peptides or DNA, are the essence of modernbionanotechnology. Carbohydrates, the most abundant biopolymers in Nature tend to form hierarchicalarchitectures. Limited access to pure and well-defined carbohydrates hampered the molecular levelunderstanding of polysaccharides, preventing the production of tailor-made materials. AutomatedGlycan Assembly produces now well-defined natural and unnatural oligosaccharides for detailedstructural characterization. Defined glycans can assemble into supramolecular materials with differentmorphologies, depending on their chemical structure. Here, we describe how synthetic oligo- andpolysaccharides help to establish structure–property correlations to guide the development of novelpolysaccharide materials

Multivalent glycan arrays

Glycan microarrays have become a powerful technology to study biological processes, such as cell–cell interaction, inflammation, and infections. Yet, several challenges, especially in multivalent display, remain. In this introductory lecture we discuss the state-of-the-art glycan microarray technology, with emphasis on novel approaches to access collections of pure glycans and their immobilization on surfaces. Future directions to mimic the natural glycan presentation on an array format, as well as in situ generation of combinatorial glycan collections, are discussed

The Flexibility of Oligosaccharides Unveiled Through Residual Dipolar Coupling Analysis

The intrinsic flexibility of glycans complicates the study of their structures and dynamics, which are often important for their biological function. NMR has provided insights into the conformational, dynamic and recognition features of glycans, but suffers from severe chemical shift degeneracy. We employed labelled glycans to explore the conformational behaviour of a β(1-6)-Glc hexasaccharide model through residual dipolar couplings (RDCs). RDC delivered information on the relative orientation of specific residues along the glycan chain and provided experimental clues for the existence of certain geometries. The use of two different aligning media demonstrated the adaptability of flexible oligosaccharide structures to different environments

Systematic Hydrogen‐Bond Manipulations To Establish Polysaccharide Structure–Property Correlations

A dense hydrogen‐bond network is responsible for the mechanical and structural properties of polysaccharides. Random derivatization alters the properties of the bulk material by disrupting the hydrogen bonds, but obstructs detailed structure–function correlations. We have prepared well‐defined unnatural oligosaccharides including methylated, deoxygenated, deoxyfluorinated, as well as carboxymethylated cellulose and chitin analogues with full control over the degree and pattern of substitution. Molecular dynamics simulations and crystallographic analysis show how distinct hydrogen‐bond modifications drastically affect the solubility, aggregation behavior, and crystallinity of carbohydrate materials. This systematic approach to establishing detailed structure–property correlations will guide the synthesis of novel, tailor‐made carbohydrate materials

Systematic Hydrogen‐Bond Manipulations To Establish Polysaccharide Structure–Property Correlations

A dense hydrogen‐bond network is responsible for the mechanical and structural properties of polysaccharides. Random derivatization alters the properties of the bulk material by disrupting the hydrogen bonds, but obstructs detailed structure–function correlations. We have prepared well‐defined unnatural oligosaccharides including methylated, deoxygenated, deoxyfluorinated, as well as carboxymethylated cellulose and chitin analogues with full control over the degree and pattern of substitution. Molecular dynamics simulations and crystallographic analysis show how distinct hydrogen‐bond modifications drastically affect the solubility, aggregation behavior, and crystallinity of carbohydrate materials. This systematic approach to establishing detailed structure–property correlations will guide the synthesis of novel, tailor‐made carbohydrate materials

Supramolecular Assembly and Chirality of Synthetic Carbohydrate Materials

Hierarchical carbohydrate architectures serve multiple roles in nature. Hardly any correlations between the carbohydrate chemical structures and the material properties are available due to the lack of standards and suitable analytic techniques. Therefore, designer carbohydrate materials remain highly unexplored, as compared to peptides and nucleic acids. A synthetic D‐glucose disaccharide, DD, was chosen as a model to explore carbohydrate materials. Microcrystal electron diffraction (MicroED), optimized for oligosaccharides, revealed that DD assembled into highly crystalline left‐handed helical fibers. The supramolecular architecture was correlated to the local crystal organization, allowing for the design of the enantiomeric right‐handed fibers, based on the L‐glucose disaccharide, LL, or flat lamellae, based on the racemic mixture. Tunable morphologies and mechanical properties suggest the potential of carbohydrate materials for nanotechnology applications

Exploring the Molecular Conformation Space by Soft Molecule–Surface Collision

Biomolecules function by adopting multiple conformations. Such dynamics are governed by the conformation landscape whose study requires characterization of the ground and excited conformation states. Here, the conformational landscape of a molecule is sampled by exciting an initial gas-phase molecular conformer into diverse conformation states, using soft molecule-surface collision (0.5-5.0 eV). The resulting ground and excited molecular conformations, adsorbed on the surface, are imaged at the single-molecule level. This technique permits the exploration of oligosaccharide conformations, until now, limited by the high flexibility of oligosaccharides and ensemble-averaged analytical methods. As a model for cellulose, cellohexaose chains are observed in two conformational extremes, the typical "extended" chain and the atypical "coiled" chain-the latter identified as the gas-phase conformer preserved on the surface. Observing conformations between these two extremes reveals the physical properties of cellohexaose, behaving as a rigid ribbon that becomes flexible when twisted. The conformation space of any molecule that can be electrosprayed can now be explored