Silvia Paasch

Application of a chiral metal–organic framework in enantioselective separation

A modular approach for the synthesis of highly ordered porous and chiral auxiliary (Evans auxiliary) decorated metal-organic frameworks is developed. Our synthesis strategy, which uses known porous structures as model materials for incorporation of chirality via linker modification, can provide access to a wide range of porous materials suitable for enantioselective separation and catalysis. Chiral analogues of UMCM-1 have been synthesized and investigated for the enantioseparation of chiral compounds in the liquid phase and first promising results are reported.

Chitin-based scaffolds are an integral part of the skeleton of the marine demosponge Ianthella basta

The skeletons of demosponges, such as Ianthella basta, are known to be a composite material containing organic constituents. Here, we show that a filigree chitin-based scaffold is an integral component of the I. basta skeleton. These chitin-based scaffolds can be isolated from the sponge skeletons using an isolation and purification technique based on treatment with alkaline solutions. Solid-state (13)C NMR, Raman, and FT-IR spectroscopies, as well as chitinase digestion, reveal that the isolated material indeed consists of chitin. The morphology of the scaffolds has been determined by light and electron microscopy. It consists of cross-linked chitin fibers approximately 40-100 nm in diameter forming a micro-structured network. The overall shape of this network closely resembles the shape of the integer sponge skeleton. Solid-state (13)C NMR spectroscopy was used to characterize the sponge skeleton on a molecular level. The (13)C NMR signals of the chitin-based scaffolds are relatively broad, indicating a high amount of disordered chitin, possibly in the form of surface-exposed molecules. X-ray diffraction confirms that the scaffolds isolated from I. basta consist of partially disordered and loosely packed chitin with large surfaces. The spectroscopic signature of these chitin-based scaffolds is closer to that of alpha-chitin than beta-chitin.

Three-dimensional chitin-based scaffolds from Verongida sponges (Demospongiae: Porifera). Part I. Isolation and identification of chitin.

Marine invertebrate organisms including sponges (Porifera) not only provide an abundant source of biologically active secondary metabolites but also inspire investigations to develop biomimetic composites, scaffolds and templates for practical use in materials science, biomedicine and tissue engineering. Here, we presented a detailed study of the structural and physico-chemical properties of three-dimensional skeletal scaffolds of the marine sponges Aiolochroia crassa, Aplysina aerophoba, A. cauliformis, A. cavernicola, and A. fulva (Verongida: Demospongiae). We show that these fibrous scaffolds have a multilayered design and are made of chitin. (13)C solid-state NMR spectroscopy, NEXAFS, and IR spectroscopy as well as chitinase digestion and test were applied in order to unequivocally prove the existence of alpha-chitin in all investigated species.

Three-dimensional chitin-based scaffolds from Verongida sponges (Demospongiae: Porifera). Part II: Biomimetic potential and applications

In order to evaluate the biomedical potential of three-dimensional chitinous scaffolds of poriferan origin, chondrocyte culturing experiments were performed. It was shown for the first time that freshly isolated chondrocytes attached well to the chitin scaffold and synthesized an extracellular matrix similar to that found in other cartilage tissue engineering constructs. Chitin scaffolds also supported deposition of a proteoglycan-rich extracellular matrix of chondrocytes seeded bioconstructs in an in vivo environment. We suggest that chitin sponge scaffolds, apart from the demonstrated biomedical applications, are highly optimized structures for use as filtering systems, templates for biomineralization as well as metallization in order to produce catalysts.

Solid-State NMR Spectroscopy of Metal-Organic Framework Compounds (MOFs)

Nuclear Magnetic Resonance (NMR) spectroscopy is a well-established method for the investigation of various types of porous materials. During the past decade, metal–organic frameworks have attracted increasing research interest. Solid-state NMR spectroscopy has rapidly evolved into an important tool for the study of the structure, dynamics and flexibility of these materials, as well as for the characterization of host–guest interactions with adsorbed species such as xenon, carbon dioxide, water, and many others. The present review introduces and highlights recent developments in this rapidly growing field.

Identification and first insights into the structure and biosynthesis of chitin from the freshwater sponge Spongilla lacustris

This work demonstrates that chitin is an important structural component within the skeletal fibers of the freshwater sponge Spongilla lacustris. Using a variety of analytical techniques ((13)C solid state NMR, FT-IR, Raman, NEXAFS, ESI-MS, Morgan-Elson assay and Calcofluor White Staining); we show that this sponge chitin is much closer to α-chitin, known to be present in other animals, than to β-chitin. Genetic analysis confirmed the presence of chitin synthases, which are described for the first time in a sponge. The presence of chitin in both marine (demosponges and hexactinellids) and freshwater sponges indicates that this important structural biopolymer was already present in their common ancestor.

Chitin-based renewable materials from marine sponges for uranium adsorption

Marine sponges of the order Verongida form three-dimensional networks of fibrous chitin, which can easily be extracted. In the hydrated state, these networks are flexible, mechanically stable and can be cut or pressed into any desired form. Here, we show for the first time that chitin-based networks of sponge origin are useful for effective uranium adsorption. They adsorb uranium from solution with a higher adsorption capacity than many other chitinous sorbents. Up to 288 mg/g could be achieved. Solid-state NMR, infrared, and Raman spectroscopy indicated that the uranyl is bound to the chitin by weak interactions. 90% of the uranyl could be desorbed using diluted hydrochloric acid. Uranium adsorption and desorption did not result in any destruction of the chitin-based material.

Interaction of electrolyte molecules with carbon materials of well-defined porosity: characterization by solid-state NMR spectroscopy

Electrochemical double-layer capacitors (EDLCs or supercapacitors) are of special potential interest with respect to energy storage. Nearly all EDLCs make use of porous carbons as electrode materials. Further tuning of their performance in EDLC applications requires a better understanding of their properties. In particular, the understanding of the interactions between carbon-based materials and electrolyte solutions is of fundamental interest with respect to future applications. Since the capacitance of carbon-based electrode materials is known to depend on the pore size, we have studied different porous carbon materials of well-defined, variable pore size loaded with 1 M TEABF4 in acetonitrile or with pure acetonitrile using solid-state magic angle spinning (MAS) (1)H, (11)B, and (13)C NMR spectroscopy.

Structural flexibility and intrinsic dynamics in the M2(2,6-ndc)2(dabco) (M = Ni, Cu, Co, Zn) metal–organic frameworks

The synthesis and structural flexibility of the metal–organic frameworks M2(2,6-ndc)2(dabco) (DUT-8(M), M = Ni, Co, Cu, Zn; 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane) as well as their characterization by gas adsorption, 129Xe NMR and 13C MAS NMR spectroscopy are described. Depending on the integrated metal atom the compounds show reversible (DUT-8(Ni), DUT-8(Co)), non-reversible (DUT-8(Zn)) or no (DUT-8(Cu)) structural transformation upon solvent removal and/or physisorption of several gases. DUT-8(Co) exhibits a similar structural transformation by solvent removal and adsorption behavior as observed for DUT-8(Ni). DUT-8(Zn) undergoes an irreversible structural change caused by solvent removal. The non-flexible copper containing MOF reveals the best performance concerning porosity and gas storage capacities within the DUT-8 series. Xenon adsorption studies combined with 129Xe NMR spectroscopy are used to study the flexibility of the DUT-8 compounds. 129Xe chemical shift and line width strongly depend on the metal atom. Solid-state 13C NMR spectroscopy has been applied in order to further characterize the organic parts of the DUT-8 frameworks. While DUT-8(Ni) exhibits narrow, well-resolved lines in its “as made” state, the signals of DUT-8(Co) are broadened and shifted over an unusually wide chemical shift range (−72 to 717 ppm). No detectable signals are found in DUT-8(Cu) indicating significantly changed internal dynamics compared to DUT-8(Ni) and DUT-8(Co).

Isolation and identification of chitin in the black coral Parantipathes larix (Anthozoa: Cnidaria)

Until now, there is a lack of knowledge about the presence of chitin in numerous representatives of corals (Cnidaria). However, investigations concerning the chitin-based skeletal organization in different coral taxa are significant from biochemical, structural, developmental, ecological and evolutionary points of view. In this paper, we present a thorough screening for the presence of chitin within the skeletal formations of a poorly investigated Mediterranean black coral, Parantipathes larix (Esper, 1792), as a typical representative of the Schizopathidae family. Using a wide array variety of techniques ((13)C solid state NMR, Fourier transform infrared (FTIR), Raman, NEXAFS, Morgan-Elson assay and Calcofluor White Staining), we unambiguously show for the first time that chitin is an important component within the skeletal stalks as well as pinnules of this coral.