Concave Molecules Research Articles

Effect of Fusion Manner of Concave Molecules on the Properties of Resulting Nanoboats.

A boat-shaped compound, which can be viewed as the fusion of two concave molecules with crossed quinacridone and indolocarbazole throughout, was synthesized and characterized. The investigation determined that the fusion manner of two concave molecules has little influence on the molecular curvature and aromaticity when compared with its congener containing crossed indolocarbazole throughout. The situation of carbonyl groups is critical in adjusting the electronic structure and physicochemical properties due to the fixed position of nitrogen atoms.

Synthesis of a chiral metallo-capsule composed of concave molecules and chirogenesis upon fullerene binding.

An enantiopure molecular capsule was synthesized quantitatively using complexation of four phosphangulenes as concave molecules with four Zn2+ ions and applied to fullerene binding and chirogenesis. The capsule encapsulated selectively fullerene and its derivatives based on the size of cavity. The fullerene C60 incorporated in the capsule exhibited induced-CD signals at the transitions of C60.

Embedding Heteroatoms and Adjacent Pentagons in Concave Molecules

Bowl-shaped molecules, which can be viewed as fragments of fullerenes, have been extensively studied owing to their interesting fundamental properties derived from their unique geometry, and the possibilities for their further functionalization, with potential applications in the field of materials science. Most of the reported concave compounds are based on corannulene or sumanene, the simplest representative fullerene subunits possessing isolated pentagons. Syntheses of concave molecules bearing adjacent pentagons have rarely been reported. Inspired by the structure of N-heterotriangulene, the construction of bowl-shaped compounds containing two fused pentagons and a central nitrogen atom is discussed. Further surface extension of such concave molecules can result in the formation of boat-shaped compounds containing embedded double isolated nitrogen atoms.

Nitrogen-Centered Concave Molecules with Double Fused Pentagons.

Distinctive concave compounds bearing a nitrogen core and double fused pentagons were synthesized with a palladium-catalyzed intramolecular coupling of 1-chloro-8 H-indolo[3,2,1- de]acridine as the key step. Structural analysis confirmed the formation of bowl-shaped molecules. Experimental characterizations and theoretical calculations reveal the incorporation of nitrogen is crucial to alleviate the pentagon fusing strain, as well as in property regulation.

Synthesis of Monofunctionalized Calix[5]arenes

Seven OH-free and O-permethylated monofunctionalized calix[5]arenes carrying either additional methyl or tert-butyl groups are prepared following fragment condensation protocols. This strategy proves to be superior to previous approaches. Calix[5]arenes with free OH groups all adopt a cone conformation stabilized by a seam of hydrogen bonds at the lower rim. Post-condensation modifications, i.e., methylation of phenolic OH groups or functional group interconversions can also be achieved. Bulky tert-butyl groups are also found to stabilize the cone conformations of O-methylated compounds. These compounds offer versatile functional groups that make these concave molecules interesting building blocks for the synthesis of more sophisticated molecular architectures.

(Invited) Concave Host Molecules Containing Phosphorus Atoms for Fullerenes

The recognition of fullerenes (C60 and its higher analogues) is one of the most intensive research subjects in supramolecular and host-guest chemistry. Bowl-type p-conjugated molecules, for example, corannulene or sumanene, are promising host molecules because their concave surfaces closely resemble fullerene segments and can fit precisely to the convex surface of C60. In particular, these molecules are attractive because of their potential to function as chiral hosts based on “bowl-chirality”. However, racemization easily underwent in many of chiral bowl-type molecules. We envision a strategy for the design of a chiral concave molecule using a phosphorus-doping method, which can play a crucial role in construction of the concave structure. We now report the synthesis of the chiral concave molecule by extension of the p-surface ofphosphorus-containing concave molecule. We synthesized the C 3-symmetric chiral concave mole-cule having a phosphorus atom at the center and resolved the enantiomers. The chiral concave structure was revealed by X-ray analysis. The concave molecule exhibited strong CD signals with a large anisotropy, the detail of which was confirmed by TD DFT calculation. In the co-crystal with C60, four molecules of enantiopure perfectly wrapped the surface of C60. MALDI-TOF mass and NMR spectra also supported the concave-convex interaction between the host molecule and C60. Furthermore, the observa-tion of the ICD signal of the guest fullerene indicates the transfer of the chiroptical properties of the host molecule to the guest. These results suggest that the chiral host is a component of a chiral self-assembled host for C60. The self-assembly of the concave molecules and the properties of the host-guest complex with fullerene will be presented. Figure 1

Synthesis of Phosphorus-Centered and Chalcogen-Bridged Concave Molecules: Modulation of Bowl Geometries and Packing Structures by Changing Bridging Atoms.

A series of phosphorus-centered concave molecules having oxygen and sulfur as bridging atoms, C3v-symmetric P4 and Cs-symmetric P2 and P3, were newly synthesized. The packing diagrams of the concave molecules P1-P4 are dependent on the bridging atoms, columnar structures for P1 and P4, and zigzag structures for P2 and P3. The bowl depth becomes shallower in the order of P1, P2, P3, and P4 as the number of bridging sulfur atoms increases.

Packing concave molecules in crystals and amorphous solids: on the connection between shape and local structure

The structure of the densest crystal packings is determined for a variety of concave shapes in 2D constructed by the overlap of two or three discs. The maximum contact number per particle pair is defined and proposed as a useful means of categorizing particle shape. We demonstrate that the densest packed crystal exhibits a maximum in the number of contacts per particle but does not necessarily include particle pairs with the maximum contact number. In contrast, amorphous structures, generated by energy minimisation of high temperature liquids, typically do include maximum contact pairs. The amorphous structures exhibit a large number of contacts per particle corresponding to over-constrained structures. Possible consequences of this over-constraint are discussed.

Site-selective hexa-hetero-functionalization of α-cyclodextrin an archetypical C₆-symmetric concave cycle.

Access to Cn (n>4) symmetric cyclic concave molecules with a different function on each of their n subunits is an unmet challenge. The reason lies in the lack of a post-functionalization method whose site selectivity is sufficiently understood, predictable and modulable to access most functionalization patterns. Here we disclose a new site-directing rule for a debenzylation reaction on cyclodextrins that solves this problem and allows the unprecedented access to penta- and ultimately hexa-differentiations of such C6 concave cycles. This achievement opens the access to objects with very high-density information.

Phosphorus-containing chiral molecule for fullerene recognition based on concave/convex interaction.

A C3-symmetric chiral concave molecule having a phosphorus atom at the center was synthesized, and its enantiomers were resolved. The chiral concave shape and absolute structure of the concave molecules were revealed by X-ray analysis. The concave molecule exhibited intense chiroptical properties with a large anisotropy, which was derived from molecular orbitals delocalized to the side chains. In the co-crystal with pristine C60, four of the enantiopure concave molecules perfectly wrapped the surface of C60. MALDI-TOF mass, NMR, and circular dichromism spectra also supported the concave/convex interaction between the concave molecule and fullerene. These results suggest that the phosphorus-containing molecule with a concave shape plays an important role as a chiral host molecule for C60.

Comparison of generic force fields for packing of concave molecules

Organic molecules of intrinsic microporosity (OMIMs) are a new class of highly concave molecules, designed to pack inefficiently and create microporous materials. In this work, OMIM-1 was described with full atomistic models using Dreiding, optimised potentials for liquid simulations (OPLS) and Universal force fields to recognise the features enhanced by each force field and assess their ability in representing the structural properties of this new class of materials. In addition, argon adsorption isotherms were modelled to determine the features observed in the isotherm generated by each force field, for future comparison with experimental data.

ChemInform Abstract: Inherently Chiral Concave Molecules — From Synthesis to Applications

AbstractReview: 76 refs.

Can Hetero‐Polysubstituted Cyclodextrins be Considered as Inherently Chiral Concave Molecules?

Can Hetero‐Polysubstituted Cyclodextrins be Considered as Inherently Chiral Concave Molecules?

Can Hetero‐Polysubstituted Cyclodextrins be Considered as Inherently Chiral Concave Molecules?

Can Hetero‐Polysubstituted Cyclodextrins be Considered as Inherently Chiral Concave Molecules?

Inherently chiral concave molecules—from synthesis to applications

This tutorial review covers the recent development in the synthesis and application of molecules and finite assemblies that are chiral owing to their curvature. A modified definition of inherent chirality is provided. Various classes of chiral concave molecules are presented including salphen complexes, cyclic amides, derivatives of sumanene, trioxatricornan or subphthalocyanine, cyclotriveratrylenes, homooxacalix[3]arenes, calixarenes, resorcinarenes, phthalocyanines, corannulenes and cavitands. Some of these bowl shaped compounds exhibit high inversion barriers, comparable with the stability of classical carbon chirality centres, while the others (e.g. hydrogen bonded assemblies) can only be detected by NMR. This review is focused on practical aspects of synthesis, resolution and applications in chiral recognition and asymmetric synthesis.

Synthesis and Recognition Properties of Two Novel Concave Molecules Based on Glycoluril

Two new concave fluorescent molecular clips based on diethoxycarbonyl glycoluril and diphenyl acetylene units have been synthesised by introducing the fluorophores into the receptor. Their recognition properties toward various metal ions were studied by fluorescence spectroscopy. The results demonstrate that they can selectively bind Fe3+ with fluorescence quenching.

Chemical Clockwise Tridifferentiation of α‐ and β‐Cyclodextrins: Bascule‐Bridge or Deoxy‐Sugars Strategies

The selective and efficient functionalisation of large concave molecules is a chemical challenge opening the door to various applications, such as artificial enzymes. We propose here a method, based on deprotection of benzylated cyclodextrins, to selectively access a variety of complex structures with two or three new different functionalities on the primary platform. Our strategy is based on a mechanistic hypothesis involving the approach of an aluminium reagent between the primary oxygen atom and the endocyclic one of the same sugar unit. Due to its cyclic directionality, a change in steric hindrance on a given position of the cyclodextrin has a different effect on the clockwise or the counterclockwise directions. This concept is illustrated and exploited in two complementary ways: deoxygenation of the primary position of two diametrically opposed sugars induces a debenzylation reaction on the neighbouring clockwise sugars of alpha- and beta-cyclodextrins. Reversible capping, or bascule-bridging, of the same pair of sugars has the same effect on the debenzylation of alpha-cyclodextrin, but induces an important change of the geometry of beta-cyclodextrin, hence allowing the selective access to yet another functionalisation pattern. A combined use of deoxygenation and bascule-bridging allows the access to an alpha-cyclodextrin with its three pairs of primary functions differentiated and ready for further modifications. Bascule-bridge or deoxy-sugars are two complementary means to operate steric decompression and induce selective reactions to efficiently access a number of new patterns of functionalities on concave molecules.

Designed self-assembly of a bimolecular calix[4]resorcinarene capsuleheld together by hydrogen bonds

The X-ray crystallographic study of the macrocyclic tetrakis- N[ N−2-hydroxyethyl-piperazino]calix[4]resorcinarene·3CH 3CH 2OH·H 2O ( 3) reveals a self-assembled dimeric capsule-like complex held together by an array of intermolecular hydrogen bonds. Pairs of concave molecules associate directly in bowl-to-bowl fashion and enclose an accessible supramolecular cavity of 190 Å 3 hosting one water and three ethanol molecules. The supramolecular arrangement displays alternating layers of facing bowls and interlocking lower rim aliphatic moieties. The helical conformation of the 2- hydroxyethyl piperazinomethyl moieties displays chirality of a bimolecular capsule frozen in the solid state. 3 crystallises in the triclinic space group P-1 with two symmetry independent molecules in the asymmetric unit. Two enantiomeric capsules form a racemic pair in the unit cell.

Concave carrier molecules: selective transport of copper(II) and lead(II) nitrates through supported liquid membranes

Concave 1,10-phenanthrolines 1 are selective and efficient carrier molecules for membrane transport of copper(II) and lead(II) ions. With competitive membrane transport experiments the selectivity patterns of three concave 1,10-phenanthroline membrane carriers have been determined. Measurements with copper(II) and lead(II) nitrates confirmed the predicted selectivities and revealed high transport rates for 1a and 1b. While 1b shows a high preference for copper(II) nitrate, 1a transports lead and copper nitrates equally well, but with much higher flux. In bulk liquid membranes, the carrier mediated ion flux remained constant over an extended period, whereas it decreased significantly in reused supported liquid membranes, which indicates rapid loss of carrier from the membrane under these conditions.

Self-assembly of carcerand-like dimers of calix[4]resorcinarene facilitated by hydrogen bonded solvent bridges

In the presence of solvent molecules which can act simultaneously as hydrogen bond donors and acceptors, the calix[4] resorcinarene 1 can self-assemble into a dimeric carcerand-like complex utilizing an intricate array of hydrogen bonds with the solvent such that pairs of concave molecules associate indirectly in a rim-to-rim fashion to form a relatively large supramolecular cavity.