Chiral Supramolecules Research Articles

Self-Assembly and Induced Circular Dichroism in Dendritic Supramolecules with Cholesteric Pendant Groups

We report on the solid-state structural features of self-assembled chiral supramolecules based on ionic complexation of chiral cholesteric pendant groups with achiral dendritic macromolecules and show that their optical activity exhibits a systematic change in the ultraviolet/visible light (UV-vis) absorption and enhancement in the circular dichroism (CD) signal, indicating the occurrence of supramolecular chirality, also referred to as induced circular dichroism (ICD). We construct a homologous series of complexes by varying systematically from 1 to 3 the generation of dendritic units contained in dendrons, dendrimers, and dendronized polymers. The structural properties of the complexes are investigated by means of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Depending on the class of dendritic molecule and the generation, lamellar, columnar hexagonal, oblique columnar, and rectangular columnar phases can be found, with a direct correlation among the degrees of freedom of the dendritic macromolecules used and the level of order achieved in the self-assembled solid-state structures. The enhancement of the optical signals of these mesoscopic structures appears to be correlated with their order in the solid state. Complexes with the longest lattice correlation lengths also show the most enhanced CD signals. These results show the unique versatility of dendritic macromolecules as supramolecular templates capable of organizing low molecular weight chiral pendant units into a variety of solid-state structures with amplified optical properties.

Twist Ferrocene Wires from Self-Assembly of Chiral Rod-Coil Organometallics

Inspired by research on organometallics, the incorporation of transition metals into organic derivatives through covalent attachment has become a mature field. Because of improvements in synthesis, the ferrocene-based moiety is now a well-known organometallic moiety. Tunable ferrocene residues provide an attractive method to expand the range of properties. By taking advantage of self-assembly, various self-assembled organometallic morphologies including spheres, cylinders, vesicles, and lamellae with nanoscale iron-rich microdomains can be used in applications such as switches, transistors, and sensors for integration into microelectronic technology. Also, ordered nanostructures transform into semiconducting materials after oxidation and yield iron-rich magnetic ceramics after pyrolysis treatment. Helical morphologies can be obtained from the self-assembly of chiral supramolecules such as chiral liquid crystals, folded oligomers, chiral counterions, chiral dendrimers, dendron rod–coils, chiral homopolymers, chiral block copolymers, and chiral discotic molecules. In our previous studies, the self-assembly of a series of chiral Schiff based rod–coil amphiphiles was systematically examined. The self-assembled helical superstructures could be induced by chiral sugar, and a morphological transformation from helical to platelet-like morphology was driven by simply increasing the hydrophobic chain length at the chain end of the chiral rod–coil amphiphiles. The helical morphology results from the steric-hindrance effect of the chiral sugar packing in the self-assembly. Herein we aim to create iron-rich spiral superstructures by taking advantage of the self-assembly of chiral Schiff based rod–coil molecules that are end-capped with ferrocene (namely, chiral rod–coil organometallics). Figure 1

English

The paper reviews nanoscale science and technology of chiral molecules/macromolecules-under twosubtopics-chiral nanotechnology and nano-chiral technology. Chiral nanotechnology discusses thenanotechnology, where molecular chirality plays a role in the properties of materials, including molecularswitches, molecular motors, and other molecular devices; chiral supramolecules and self-assembled nanotubesand their functions are also highlighted. Nano-chiral technology describes the nanoscale approaches to chiraltechnology such as asymmetric synthesis and catalysis, chiral separation and detection, and enantiomericanalysis. Chiral sensors have also been included. The state-of-the-art chiral research at DMSRDE,Kanpur isalso presented.Defence Science Journal, 2008, 58(5), pp.626-635, DOI:http://dx.doi.org/10.14429/dsj.58.1685

Self-Assembly of Two Chiral Supramolecules with Three-Dimensional Porous Host Frameworks: (Δ){[FeII(phen)3][FeIIINa(C2O4)3]}n and Its Enantiomer

Two chiral supramolecules with enantiomeric three-dimensional porous host frameworks, (Delta){[Fe(II)(phen)(3)][Fe(III)Na(C(2)O(4))(3)]}(n) (1) and (Lambda){[Fe(II)(phen)(3)][Fe(III)Na(C(2)O(4))(3)]}(n) (2) (phen = 1,10-phenanthroline), have been synthesized, and their crystal structures have been determined. The structural analysis shows that compounds 1 and 2 are a pair of enantiomers, both consisting of a three-dimensional porous skeleton formed by (Delta)/(Lambda){[Fe(III)Na(C(2)O(4))(3)](2-)}(n) and guest (Delta)/(Lambda)[Fe(phen)(3)](2+) units. The circular dichroism spectrum measurements confirmed the optical activity and the enantiomeric nature of complexes 1 and 2.

Lanthanitin: A Chiral Nanoball Encapsulating 18 Lanthanum Ions by Ferritin‐Like Assembly

A chiral supramolecule, obtained by self-assembly of 24 chiral ditopic carboxylate ligands, 18 La ions, and two carbonate anions, has been dubbed lanthanitin because of its structural resemblance to ferritin. The picture shows the molecular structure of one enantiomer of lanthanitin. Color code: La blue, carbonate C green, C gray, O red; H omitted.

Chiral Spaces in Supramolecular Assemblies

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Chiral nanotechnology

A review of chiral, nanoscale science and technology is presented, with the subject divided into two topics. The first discusses nanotechnology in the service of asymmetric synthesis, chiral separations, and analysis. The second topic concerns broader research in the nanotechnology realm, where molecular chirality plays a role in the properties of materials, including molecular devices, chiral supramolecules, chiral nanotubes, chiral fullerenes, and DNA nanotechnology.

Facile resolution of racemic terbutaline and a study of molecular recognition through chiral supramolecules based on enantiodifferentiating self-assembly.

An effective resolving agent, (2S, 3S)-di-O-(p-toluoyl) tartaric acid(4), was screened using a 'family' approach to yield direct resolution of (R)-terbutaline (1) with high optical purity and yield. Molecular recognition was studied by X-ray crystallographic analyses of the single crystals of the pair of diastereomeric salts. The more-soluble salt formed a sheet supramolecular structure, and the less-soluble salt formed a columnar supramolecular structure by enantiodifferentiating self-assembly. The water molecule plays an important role during optical resolution, and makes the supramolecular structure of the less-soluble salt more thermodynamically stable than that of the more-soluble salt. Solvent system has little influence on the resolution.

Self-Assembly of Cobaloximes and Rhodoximes with 3-Aminophenylboronic Acid: A Molecular Triangle and a Polymer

The reactions of methylaquacobaloxime and ethylaquacobaloxime with 3-aminophenylboronic acid in water produce supramolecular triangles 3a and 3b respectively, through the reaction of boron with the oxime oxygens of the alkylcobaloxime and the coordination of pyridine to cobalt. The reaction is reversible and strongly pH dependent. The complexes 3a and 3b precipitate immediately from the solution at pH 7, but dissolve quickly at both acidic (below 4) and basic (above 9) pH values. The aggregates are re-formed by readjusting the pH to neutrality and the precipitation-dissolution cycle may be repeated several times without an apparent decrease in yield. The complexes were fully characterised by 1H and 13C NMR spectroscopy. The X-ray structure shows that the neutral chiral supramolecule 3a is a triangle of cobalt atoms with an approximate C3 symmetry. The side of the triangle is about 9.5 A. The ring closure is ensured by the torsion angles around the B−C and C−NH2 bonds, which vary in the range 25−30° and 97−109°, respectively. The reaction of methylaquarhodoxime with 3-aminophenylboronic acid in water at pH 7 results in the displacement of H2O by 3-aminophenylboronic acid only. The polymeric form 4 precipitates from CD3OD in the NMR tube with time. The X-ray structure shows that 4 is a polymeric species with a zig-zag chain arrangement, with Rh···Rh distances of 9.2 A. The chain arrangement is characterized by torsion angles around the B−C and C-NH2 bonds of 61° and 92°, respectively. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Evaluation of Selective Binding Ability in Chiral Supramolecules Using Induced Chirality

Evaluation of Selective Binding Ability in Chiral Supramolecules Using Induced Chirality