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Dendritic Architecture (dendritic + architecture)
Selected AbstractsSelf-Association of Bis-Dendritic Organogelators: The Effect of Dendritic Architecture on Multivalent Cooperative InteractionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2010Myungeun Seo Dr. Abstract A series of bis-dendritic gelators consisting of a benzamide dendron and an alkyl dendron were synthesized to investigate the dendritic effect on self-assembly. The gelators with a first-generation benzamide (benzamide- G1) dendron or a first-generation alkyl (alkyl- G1) dendron formed stable gels in most aromatic solvents, and their self-assembled fibrillar networks were imaged by electron microscopy. The unbranched molecule (G0 - G0) or the molecule possessing a second-generation benzamide (benzamide- G2) dendron did not form gels. Differential scanning calorimetry, powder X-ray diffraction, and Fourier transform IR studies revealed that introduction of a dendritic branch strongly affected the molecular packing as well as the strength of intermolecular interactions. Furthermore, concentration-dependent diffusion coefficient measurements and the evaluation of association constants by 1H NMR spectroscopy indicated that bis-dendritic gelators with a benzamide- G1 dendron possessed high association constants and formed large aggregates, whereas molecules with a single benzamide formed dimers in chloroform. The formation of self-assembled fibrillar networks was driven by the multivalent and cooperative hydrogen bonding observed in the benzamide- G1 dendrons. ,,, stacking of aromatic groups and van der Waals interactions between alkyl chains also played roles in the self-assembly process, thus indicating that a spatial balance between two dendrons is important. [source] Elucidation of Architectural Requirements from a Spacer in Supported Proline-Based Catalysts of Enantioselective Aldol ReactionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Kerem Goren Abstract In order to delineate the properties of the spacer architecture responsible for the strong positive dendritic effect exhibited by polymer-supported proline-based catalysts, we prepared two series of polystyrene-bound model catalysts. The first series was based on a linear and partially dendritic spacers (of reduced branching and valency) imitating the length of the second generation spacer, while the second series was based on the first generation dendron spacer with one functional (proline-terminated) and one non-functional arm. Comparative studies of the model and original (fully dendritic) catalysts in the asymmetric aldol reaction of aromatic aldehydes with acetone disclose the features characteristic to the dendritic architecture, such as proximity between the terminal catalytic units and enhanced branching, as crucial for inducing higher yield and enantioselectivity in catalysis. [source] Photophysical and self-assembly behavior of poly(amidoamine) dendrons with chromophore as scaffold: The effect of dendritic architectureJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2008Bing-Bing Wang Abstract Two series of amphiphiles composed of hydrophilic poly(amidoamine) dendrons (from the first to the third generation) as the shell and hydrophobic aromatic chromophores (3,6-di(maleimidyl)-9-phenyl carbazole and 9-(4,-maleimidyl phenyl)-3-maleimidyl carbazole) as the central scaffold were synthesized. The effect of dendritic architecture on the photophysical properties and the self-assembly behavior of these amphiphiles were studied by UV,vis absorption spectroscopy, fluorescence spectroscopy, and transmission electron microscopy (TEM) measurements. Both the generation of dendritic shell and the location of dendrons at the chromophoric scaffold had great effect on the photophysical properties of these amphiphiles. In addition, different spherical aggregates were formed from these amphiphiles in the aqueous solution at different concentrations. Because of the combined effects of steric hindrance and architecture of dendritic shells, the amphiphiles from G2 dendron with central chromophore self-organized into ordered aggregates more readily than that from G1 and G3. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4584,4593, 2008 [source] Effect of dendritic architecture on localized free volume of poly(ether ketone)s as probed by positron annihilation spectroscopyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2004Seung-Yeop Kwak Model poly(ether ketone)s (PEKs) with architectural variations were studied by positron annihilation lifetime spectroscopy (PALS) to estimate the average void sizes on a sub-nanometer scale, in conjunction with the hyperbranched (H-), the linear (L-), and their 50:50 block combination (HLH-) structures. The PALS distribution confirmed the unique molecular architecture of the hyperbranched polymer, consisting of an interior cavity space formed by loosely linked core and chain ends of relatively tighter free volume space. [source] Tiling among stereotyped dendritic branches in an identified Drosophila motoneuron,,THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 12 2010F. Vonhoff Abstract Different types of neurons can be distinguished by the specific targeting locations and branching patterns of their dendrites, which form the blueprint for wiring the brain. Unraveling which specific signals control different aspects of dendritic architecture, such as branching and elongation, pruning and cessation of growth, territory formation, tiling, and self-avoidance requires a quantitative comparison in control and genetically manipulated neurons. The highly conserved shapes of individually identified Drosophila neurons make them well suited for the analysis of dendritic architecture principles. However, to date it remains unclear how tightly dendritic architecture principles of identified central neurons are regulated. This study uses quantitative reconstructions of dendritic architecture of an identified Drosophila flight motoneuron (MN5) with a complex dendritic tree, comprising more than 4,000 dendritic branches and 6 mm total length. MN5 contains a fixed number of 23 dendritic subtrees, which tile into distinct, nonoverlapping volumes of the diffuse motor neuropil. Across-animal comparison and quantitative analysis suggest that tiling of the different dendritic subtrees of the same neuron is caused by competitive and repulsive interactions among subtrees, perhaps allowing different dendritic compartments to be connected to different circuit elements. We also show that dendritic architecture is similar among different wildtype and GAL4 driver fly lines. Metric and topological dendritic architecture features are sufficiently constant to allow for studies of the underlying control mechanisms by genetic manipulations. Dendritic territory and certain topological measures, such as tree compactness, are most constant, suggesting that these reflect the intrinsic molecular identity of the neuron. J. Comp. Neurol. 518:2169,2185, 2010. © 2010 Wiley-Liss, Inc. [source] | ||||||||||