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Helical Ribbons (helical + ribbon)
Selected AbstractsSelf-Assembly of Amylin(20,29) Amide-Bond Derivatives into Helical Ribbons and Peptide Nanotubes rather than FibrilsCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2006Ronald C. Elgersma Abstract Uncontrolled aggregation of proteins or polypeptides can be detrimental for normal cellular processes in healthy organisms. Proteins or polypeptides that form these amyloid deposits differ in their primary sequence but share a common structural motif: the (anti)parallel , sheet. A well-accepted approach for interfering with ,-sheet formation is the design of soluble ,-sheet peptides to disrupt the hydrogen-bonding network; this ultimately leads to the disassembly of the aggregates or fibrils. Here, we describe the synthesis, spectroscopic analysis, and aggregation behavior, imaged by electron microscopy, of several backbone-modified amylin(20,29) derivatives. It was found that these amylin derivatives were not able to form fibrils and to some extent were able to inhibit fibril growth of native amylin(20,29). However, two of the amylin peptides were able to form large supramolecular assemblies, like helical ribbons and peptide nanotubes, in which ,-sheet formation was clearly absent. This was quite unexpected since these peptides have been designed as soluble ,-sheet breakers for disrupting the characteristic hydrogen-bonding network of (anti)parallel , sheets. The increased hydrophobicity and the presence of essential amino acid side chains in the newly designed amylin(20,29) derivatives were found to be the driving force for self-assembly into helical ribbons and peptide nanotubes. This example of controlled and desired peptide aggregation may be a strong impetus for research on bionanomaterials in which special shapes and assemblies are the focus of interest. [source] Mesoporous Silicas by Self-Assembly of Lipid Molecules: Ribbon, Hollow Sphere, and Chiral MaterialsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2008Haiying Jin Abstract Using lipids (N -acyl amino acids) and 3-aminopropyltriethoxysilane as structure- and co-structure-directing agents, mesoporous silicas with four different morphologies, that is, helical ribbon (HR), hollow sphere, circular disk, and helical hexagonal rod, were synthesized just by changing the synthesis temperature from 0,°C to 10, 15, or 20,°C. The structures were studied by electron microscopy. It was found that 1),the structures have double-layer disordered mesopores in the HR, radially oriented mesopores in the hollow sphere, and highly ordered straight and chiral 2D-hexagonal mesopores in the disklike structure and helical rod, respectively; 2),these four types of mesoporous silica were transformed from the flat bilayered lipid ribbon with a chain-interdigitated layer phase through a solid,solid transformation for HR formation and a dissolving procedure transformation for the synthesis of the hollow sphere, circular disk, and twisted morphologies; 3),the mesoporous silica helical ribbon was exclusively right-handed and the 2D-hexagonal chiral mesoporous silica was excessively left-handed when the L -form N -acyl amino acid was used as the lipid template; 4),the HR was formed only by the chiral lipid molecules, whereas the 2D-hexagonal chiral mesoporous silicas were formed by chiral, achiral, and racemic lipids. Our findings give important information for the understanding of the formation of chiral materials at the molecular level and will facilitate a more efficient and systematic approach to the generation of rationalized chiral libraries. [source] Formation of Chiral Mesopores in Conducting Polymers by Chiral-Lipid-Ribbon Templating and "Seeding" Route,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2008Chaxing Fan Abstract Conducting polymer nanofibers with controllable chiral mesopores in the size, the shape, and handedness have been synthesized by chiral lipid ribbon templating and "seeding" route. Chiral mesoporous conducting poly(pyrrole) (CMPP) synthesized with very small amount of chiral amphiphilic molecules (usually,<,3%) has helically twisted channels with well-defined controllable pore size of 5,20,nm in central axis of the twisted fibers. The structure and chirality of helical mesopores have been characterized by high-resolution transmission electron microscope (HRTEM), scanning electron microscope (SEM) and electron tomography. The average pore diameters of chiral mesopores were approximately estimated from the N2 adsorption,desorption data and calculated by the conversion calculation from helical ribbons to a rectangular straight tape. The pore size of CMPP has been controlled by choosing different alkyl chain lengths of chiral lipid molecules or precisely adjusting the H2O/EtOH volume ratio. [source] Monodisperse Bile-Salt Nanotubes in Water: Kinetics of Formation,ADVANCED MATERIALS, Issue 6 2005B. Jean Sodium lithocholate forms stabilized cylindrical nanotubes with thin monomolecular walls (see Figure) through fast and complex morphological evolutions. The kinetics of formation can be followed by small-angle X-ray scattering using a brilliant synchrotron source, and are corroborated by cryo-transmission electron microscopy. Coaxial cylinders, helical ribbons, fibrils, and single-walled tubes are found to coexist in the first few minutes of the supramolecular organization process. [source] Backbone-modified amylin derivatives: implications for amyloid inhibitor design and as template for self-assembling bionanomaterials,JOURNAL OF PEPTIDE SCIENCE, Issue 11 2007Ronald C. Elgersma Abstract This report reviews our approach to the design, synthesis and structural/morphological analysis of backbone-modified amylin(20,29) derivatives. Depending on the position in the peptide backbone and the type of amide bond isostere/modification, the amylin(20,29) peptides behave either as inhibitors of amyloid fibril formation, which are able to retard amyloid formation of native amylin(20,29), or as templates for the formation of self-assembled supramolecular structures. Molecular fine-tuning of the hydrogen-bond accepting/donating properties allows the control over the morphology of the supramolecular aggregation motifs such as helical ribbons and tapes, ribbons progressing to closed peptide nanotubes, (twisted) lamellar sheets or amyloid fibrils. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] Self-Assembly of Amylin(20,29) Amide-Bond Derivatives into Helical Ribbons and Peptide Nanotubes rather than FibrilsCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2006Ronald C. Elgersma Abstract Uncontrolled aggregation of proteins or polypeptides can be detrimental for normal cellular processes in healthy organisms. Proteins or polypeptides that form these amyloid deposits differ in their primary sequence but share a common structural motif: the (anti)parallel , sheet. A well-accepted approach for interfering with ,-sheet formation is the design of soluble ,-sheet peptides to disrupt the hydrogen-bonding network; this ultimately leads to the disassembly of the aggregates or fibrils. Here, we describe the synthesis, spectroscopic analysis, and aggregation behavior, imaged by electron microscopy, of several backbone-modified amylin(20,29) derivatives. It was found that these amylin derivatives were not able to form fibrils and to some extent were able to inhibit fibril growth of native amylin(20,29). However, two of the amylin peptides were able to form large supramolecular assemblies, like helical ribbons and peptide nanotubes, in which ,-sheet formation was clearly absent. This was quite unexpected since these peptides have been designed as soluble ,-sheet breakers for disrupting the characteristic hydrogen-bonding network of (anti)parallel , sheets. The increased hydrophobicity and the presence of essential amino acid side chains in the newly designed amylin(20,29) derivatives were found to be the driving force for self-assembly into helical ribbons and peptide nanotubes. This example of controlled and desired peptide aggregation may be a strong impetus for research on bionanomaterials in which special shapes and assemblies are the focus of interest. [source] Synthesis, Structure, Thermal and Magnetic Properties of a New Open-framework Borophosphate: NH4Mn(H2O)2BP2O8·H2O,CHINESE JOURNAL OF CHEMISTRY, Issue 9 2006Heng-Zhen Shi Abstract Using new template agent, a new borophosphate compound, NH4Mn(H2O)2BP2O8·H2O was hydrothermally prepared and structurally characterized. It crystallizes in a hexagonal space group P6122 with lattice parameters a=0.9652(2) nm, c=1.5792(5) nm, V=1.2740(5) nm3 and Z=6. The structure has a three-dimensional open-frame work with borophosphate helical ribbons 1,{[BP2O8]3, and MnO4(H2O)2 octahedra. The water molecules are positioned inside the helical channels. Very interestingly, the ammonium ions are located outside the loop of the free helical ribbons via the strong hydrogen bonds, which is different from the borophosphate analogue reported. The magnetization of the title compound is paramagnetic down to 5 K of the Curie-Weiss type within the measured range of 5,300 K with ,=,7.3 K, indicative of very weak antiferromagnetic interactions. The thermal decomposition of the compound was also described. [source] | |||||||||||||