- Homochiral columns constructed by chiral self-sorting during supramolecular helical organization of hat-shaped molecules
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A library of dendronized cyclotriveratrylene (CTV) crowns substituted with chiral, racemic, or achiral peripheral alkyl chains, including enantiopure R and S branched alkyls, "racemic by mixture", "racemic by synthesis", n-octyl, and n-dodecyl groups was synthesized. In solvophobic solvents and in bulk they self-assemble in helical columns. Their solution and bulk shape-persistent supramolecular structures were determined by a complementary combination of circular dichroism (CD) and UV in solution and thin film, microspot CD in thin film, differential scanning calorimetry combined with fiber X-ray diffraction, computer simulation, and molecular models. In solution, self-assembly via a cooperative mechanism generates single-handed columns from enantiopure CTVs and mixtures of right-and left-handed columns from racemic by mixture, racemic by synthesis, other combinations of R and S, and even from achiral compounds. In bulk state all supramolecular columns form a 3D hexagonal crystalline phase, φhk (P63 symmetry), that can be obtained only from single-handed columns and a columnar hexagonal 2D liquid crystal, φh. The highest order φhk consists of enantiopure single-handed columns that are slightly distorted 12-fold triple helices. The "hat-shaped" dendronized CTV assembles in bent-branch pine-tree columns that allow interdigitation of alkyl groups in adjacent columns regardless of their direction. Enantiomerically rich, racemic, and achiral compositions undergo deracemization in the crystal state by transfer of the transient disc-like conformer of dendronized CTV from column to column during crown inversion. Solid state NMR experiments identified motional processes that allow such transfer. This unprecedented supramolecular chiral self-sorting will impact the creation of functions in complex systems.
- Roche, Cécile,Sun, Hao-Jan,Prendergast, Margaret E.,Leowanawat, Pawaret,Partridge, Benjamin E.,Heiney, Paul A.,Araoka, Fumito,Graf, Robert,Spiess, Hans W.,Zeng, Xianbingon,Ungar, Goran,Percec, Virgil
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supporting information
p. 7169 - 7185
(2014/06/09)
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- Self-assembly of dendritic crowns into chiral supramolecular spheres
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The synthesis and structural and retrostructural analysis of a library of dendronized cyclotriv- eratrylene containing seven nonchiral and sevenchiral self-assembling dendrons is reported. These dendronized cyclotri veratrylenes exhibit a crown conformation that we named dendritic crown.Selected examples of dendritic crowns self-assemble into helical pyrami dal columns that self-organize into columnar crystals or into 2-D columnar hexagonal lattices with intracolumnar order. A second group of dendritic crowns self-assembles into helical pyramidal columns and spherical supramolecular dendrimers that self- organize into cubic and tetragonal lattices. A third group of dendritic crowns self-assembles only in spherical supramolecular dendrimers. The helical pyramidal columns and spherical supramolecular dendrimers assembled from dendronized cyclotriveratrylene containing nonchiral dendrons are chiral but racemic while those generated from chiral dendrons exhibit amplified chirality. Structural analysis by a combination of X-ray diffraction methods and CD experiments demonstrated a new mechanism for the assembly of chiral supramolecular spheres that involves an intramolecular structure containing short fragments of helical pyramidal columns.
- Percec, Virgil,Imam, Mohammad R.,Peterca, Mihai,Wilson, Daniela A.,Heiney, Paul A.
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supporting information; experimental part
p. 1294 - 1304
(2009/06/28)
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- Molecular structure of helical supramolecular dendrimers
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The molecular structure of helical supramolecular dendrimers generated from self-assembling dendrons and dendrimers and from self-organizable dendronized polymers was elucidated for the first time by the simulation of the X-ray diffraction patterns of their oriented fibers. These simulations were based on helical diffraction theory applied to simplified atomic helical models, followed by Cerius2 calculations based on their complete molecular helical structures. Hundreds of samples were screened until a library containing 14 supramolecular dendrimers and dendronized polymers provided a sufficient number of helical features in the X-ray diffraction pattern of their oriented fibers. This combination of techniques provided examples of single-92 and -11 3 helices, triple-61, -81, -91, and -121 helices, and an octa-321 helix that were assembled from crownlike dendrimers, hollow and nonhollow supramolecular crownlike dendrimers, hollow and nonhollow supramolecular disklike dendrimers, and hollow and nonhollow supramolecular and macromolecular helicene-like architectures. The method elaborated here for the determination of the molecular helix structure was transplanted from the field of structural biology and will be applicable to other classes of synthetic helical assemblies. The determination of the molecular structure of helical supramolecular assemblies is expected to provide an additional level of precision in the design of helical functional assemblies resembling those from biological systems.
- Peterca, Mihai,Percec, Virgil,Imam, Mohammad R.,Leowanawat, Pawaret,Morimitsu, Kentaro,Heiney, Paul A.
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supporting information; body text
p. 14840 - 14852
(2009/02/08)
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