The potassium salt of 1 was transmetalated by reaction with (Cp-allyl)ZrCl3(dme), yielding the complex (NC-nacnac)Cp-allylZrCl2 (2). Addition of 1 molar equiv of B(C6F5)3 gave [(C6F5)3B-NC-nacnac]Cp-allylZrCl2 (3), and the subsequent addition of 1 molar equiv of HB(C6F5)2 to 3 gave the hydroborated species [((C6F5)3B-NC-nacnac)Cp-(CH2)3-B(C6F5)2]ZrCl2 (4). The hydroboration of 2 with 1 molar equiv of HB(C6F5)2 gave an insoluble product. This product was fully characterized by 11B and 13C solid-state NMR and IR, which showed that the hydroboration followed by intermolecular adduct formation (R–B(C6F5)2- - -NC- - -R′) occurs, resulting in an organometallic polymer (5). In addition to the CN-free [nacnac]Cp-allylZrCl2 (6), the hydroborated derivative [(nacnac)Cp-(CH2)3-B(C6F5)2] (7) was also prepared. Complexes 2–7 were activated with methylaluminoxane (MAO) and gave active catalysts for ethylene polymerization. The polymers produced were linear and had high molecular weight, with polydispersities (PDI) of less than 2, indicating that the catalysts are single site. The presence of the allyl group on the Cp ring was found to increase the molecular weight of the materials produced. In addition to discrete complexes, an organometallic polymer (5) was formed. This compound is air stable and, while not very soluble, polymerizes ethylene with good activity.
These datasets are part of the Supplementary Information of "Probing a Hydrogen-π Interaction Involving a Trapped Water Molecule in the Solid State". All experimental details are given in the mentioned document.
Abstract DnaB helicases are bacterial, ATP‐driven enzymes that unwind double‐stranded DNA during DNA replication. Herein, we study the sequential binding of the “non‐hydrolysable” ATP analogue AMP‐PNP and of single‐stranded (ss) DNA to the dodecameric DnaB helicase from Helicobacter pylori using solid‐state NMR. Phosphorus cross‐polarization experiments monitor the binding of AMP‐PNP and DNA to the helicase. 13 C chemical‐shift perturbations (CSPs) are used to detect conformational changes in the protein upon binding. The helicase switches upon AMP‐PNP addition into a conformation apt for ssDNA binding, and AMP‐PNP is hydrolyzed and released upon binding of ssDNA. Our study sheds light on the conformational changes which are triggered by the interaction with AMP‐PNP and are needed for ssDNA binding of H. pylori DnaB in vitro. They also demonstrate the level of detail solid‐state NMR can provide for the characterization of protein–DNA interactions and the interplay with ATP or its analogues.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract Understanding the ecological and evolutionary factors that influence species rarity has important theoretical and applied implications, yet the reasons why some species are rare while others are common remain unresolved. As a novel exploration of scientific knowledge, we used network analysis conceptually to visualize the foci of a comprehensive base of >800 studies on plant species rarity within the context of ecology and evolution. In doing so, we highlight existing research strengths that could substantiate novel syntheses and gaps that could inspire new research. Our results reveal strong integrated foci on population dynamics with other ecological concepts. In contrast, despite the potential for ecological and evolutionary processes to interact, few studies explored the interplay of environmental factors and microevolutionary patterns. The cellular and molecular biology, physiology, and plasticity of rare plant species within both ecological and evolutionary contexts similarly provide avenues for impactful future investigations.
Biochemical reactions occurring in highly crowded cellular environments require different means of control to ensure productivity and specificity. Compartmentalization of reagents by liquid-liquid phase separation is one of these means. However, extremely high local protein concentrations of up to 400 mg/ml can result in pathological aggregation into fibrillar amyloid structures, a phenomenon that has been linked to various neurodegenerative diseases. Despite its relevance, the process of liquid-to-solid transition inside condensates is still not well understood at the molecular level. In this work, we use small peptide derivatives that can undergo both liquid-liquid and subsequent liquid-to-solid phase transition as model systems to study both processes at the molecular level. Using solid-state nuclear magnetic resonance (NMR) and transmission electron microscopy, we compare the structure of condensed states of leucine, tryptophan and phenylalanine containing derivatives, distinguishing between liquid-like condensates, amorphous aggregates and fibrils, respectively. A structural model for the fibrils formed by the phenylalanine derivative was obtained by a structure calculation based on NMR distance restraints. Our results show that the fibrils are stabilised by hydrogen bonds and side-chain π-π interactions, which are likely much less pronounced or absent in the liquid and amorphous state. Such noncovalent interactions are equally important for the liquid-to-solid phase transition of proteins, particularly those related to neurodegenerative diseases and our results suggest that aged condensates of these proteins may have partial amyloid-like characteristics.
Abstract Der Nachweis und die Charakterisierung von eingeschlossenen Wassermolekülen in chemischen Gebilden und Biomakromolekülen ist weiterhin eine Herausforderung für feste Materialien. Wir präsentieren hier Protonen‐detektierte Festkörper‐Kernspinresonanzspektroskopie (NMR) Experimente bei Rotationsfrequenzen von 100 kHz um den magischen Winkel und bei hohen statischen Magnetfeldstärken (28.2 T), die den Nachweis eines einzelnen Wassermoleküls ermöglichen, das im Calix[4]aren‐Hohlraum eines Lanthan‐Komplexes durch eine Kombination von drei Arten nicht‐kovalenter Wechselwirkungen fixiert ist. Die Protonenresonanzen des Wassers werden bei einer chemischen Verschiebung nahe Null ppm nachgewiesen, was wir durch quantenchemische Berechnungen bestätigen. Berechnungen mit der Dichtefunktionaltheorie zeigen, wie empfindlich der Wert der chemischen Verschiebung der Protonen auf Wasserstoff‐π‐Wechselwirkungen reagiert. Unsere Studie unterstreicht, wie sich die Protonen‐detektierte Festkörper NMR zur Methode der Wahl für die Untersuchung schwacher nicht‐kovalenter Wechselwirkungen entwickelt, die einen ganzen Zweig molekularer Erkennungsvorgänge in der Chemie und Biologie bestimmen.
