A Dualistic Arrangement of a Chiral [1]Rotaxane Based on the Assembly of Two Rings and Two Rods

We demonstrate the synthesis and chiroptical proper -ties of doubled molecules of a chiral [1]rotaxane, based on the assembly of an achiral ring of a phenylacetylene macrocycle (6PAM) and a p-phenylene ethynylene rod. Two molecules of [1]rotaxane constituted the doubled molecule through the ring fusion of 6PAMs to a 10PAM, which assured stationary occupation relative to each optically active unit. The absorption properties of the 10PAM-based doubled molecule and 6PAM-based original unit were consistently characterized by the independent existence of m-phenylene ethynylene ring(s) and p-phenylene ethynylene rod(s). Thus, molar circular dichroism (CD) was directly compared between the doubled molecule (n = 2) and the original unit (n = 1) to show that molar CD was increased more than expected by an increase in the number of units, or by an increase in absorbance. Due to the invariance of the configuration and the relative occupation of two units arranged adjacent to each other in 10PAM, one more comparison was available with an isomeric molecule of two rings and two rods in a threaded-and-unthreaded form. The additional arrangement of an optically inactive unit in an unthreaded form also led to an increase in molar CD, compared to that of the original chiral unit in a threaded form

N,N,N′,N′-Tetra­kis(2-hydroxy­ethyl)terephthalamide

The mol­ecule of the title compound, C16H24N2O6, which lies on a crystallographic inversion centre in the centre of the benzene ring, adopts an anti conformation in terms of the relative orientation of two amide carbonyl groups. One pair of the 2-hydroxy­ethyl groups is partially disordered with site occupancy factors of 0.811 (2) and 0.189 (2). The dihedral angle between the amide group and central benzene ring is 67.0 (2)°. Two O—H⋯O and one bifurcated O—H⋯(O,O) hydrogen bonds are present, resulting in a three-dimensional network

Stereospecific winding of polycyclic aromatic hydrocarbons into Trinacria propellers

The stereospecific trimerization of enantiomerically-pure binaphthols with hexakis(bromomethyl)benzene gives access in one step to enantiomerically-pure molecular propellers, in which three binaphthyl rings are held together through dioxecine rings. X-Ray diffraction analysis revealed that three out the six naphthyl moieties are folded in a (EF)3-type arrangement held by three intramolecular C-H…π interactions. This slips outward the three remaining naphthyl rings in a blade-like fashion, just like in three-folded propeller components. This peculiar conformation shows striking similarity to the mythological Sicilian symbol of Trinacria, from which the name "trinacria propeller" derives. The propeller conformation is also preserved in chlorinated solutions, as displayed by the presence of a peak at 4.7 ppm typical of an aromatic proton resonance engaged in a C-H…π interaction. The denaturation of the propeller-like conformation is obtained at high temperature, corresponding to activation energy for the ring inversion of ca. 18.2 kcal mol-1. Notably, halide-functionalized molecular propellers exposing I-atoms at the leading and trailing edges could be prepared stereo- and regiospecifically by choosing the relevant iodo-bearing BINOL derivative

Intelligent Chiral Sensing Based on Supramolecular and Interfacial Concepts

Of the known intelligently-operating systems, the majority can undoubtedly be classed as being of biological origin. One of the notable differences between biological and artificial systems is the important fact that biological materials consist mostly of chiral molecules. While most biochemical processes routinely discriminate chiral molecules, differentiation between chiral molecules in artificial systems is currently one of the challenging subjects in the field of molecular recognition. Therefore, one of the important challenges for intelligent man-made sensors is to prepare a sensing system that can discriminate chiral molecules. Because intermolecular interactions and detection at surfaces are respectively parts of supramolecular chemistry and interfacial science, chiral sensing based on supramolecular and interfacial concepts is a significant topic. In this review, we briefly summarize recent advances in these fields, including supramolecular hosts for color detection on chiral sensing, indicator-displacement assays, kinetic resolution in supramolecular reactions with analyses by mass spectrometry, use of chiral shape-defined polymers, such as dynamic helical polymers, molecular imprinting, thin films on surfaces of devices such as QCM, functional electrodes, FET, and SPR, the combined technique of magnetic resonance imaging and immunoassay, and chiral detection using scanning tunneling microscopy and cantilever technology. In addition, we will discuss novel concepts in recent research including the use of achiral reagents for chiral sensing with NMR, and mechanical control of chiral sensing. The importance of integration of chiral sensing systems with rapidly developing nanotechnology and nanomaterials is also emphasized

Controlled helical senses of twisting in two-, three- and four-layer cyclophanes with planar chirality

We synthesized planar chiral cyclophanes with multiple pairs of helical conformations that were generated by twisting at the interlayer. Three- and four-layer cyclophanes preferred a homochiral form with a single sense of twisting through intramolecular transmission of planar chirality. Alternatively, a heterochiral form was dominant in a two-layer cyclophane consisting of two achiral planes that were stacked orthogonally

Planar chiral desymmetrization of a two-layered cyclophane and control of dynamic helicity through the arrangement of two nonstereogenic centers

We designed a planar chiral two-layered cyclophane, which is inherently achiral but desymmetrized by the arrangement of two nonstereogenic centers. We demonstrate the control of dynamic helicity that is generated by the helical twisting of two-layered planes in the cyclophane, where methyl and cyclohexylmethyl groups act as directing groups

Dynamic helical cyclophanes with two quadruply-bridged planes arranged in an "obverse and/or reverse" relation

We describe the design of two types of cyclophanes that generate dynamic helicity through the twisting of two planes in a clockwise or counterclockwise direction to give (M)- or (P)-helicity. We used a rectangular and anisotropic plane of 1,2,4,5-tetrakis(phenylethynyl) benzene (TPEB), since it can be stacked in pairs in two ways, in parallel or orthogonally, to be identified as distinct cyclophane molecules. We adopted a synthetic strategy for obtaining these two cyclophanes as a mixture using a macrocyclic intermediate that possessed two rotatable phenyl rings. We introduced necessary parts into the rotators to give a mixture of rotational isomers leading to a parallel or orthogonal arrangement of TPEBs, and then doubly bridged two planes of TPEB to form quadruply-bridged cyclophanes. We consider that such two planes in each cyclophane are in an "obverse and/or reverse" relation. In each cyclophane, we found unique dynamic helical forms with (M)- or (P)-helicity as well as an inherently non-chiral form. Normally, the screw-sense preference of dynamic helicity would be controlled through the intramolecular or supramolecular transmission of central chirality, when a chiral auxiliary is attached to the cyclophanes or a chiral guest is allowed to form a complex with the cyclophanes. In a case where two different substitution groups were used on bridging units to generate planar chirality in each cyclophane, the screw-sense preference was controlled through the arrangement of these substitution groups, and did not depend on the transmission of central chirality. Two different substitution groups desymmetrize the enantiomeric forms with (M)- or (P)-helicity generated in each dynamic helical cyclophane so that two dynamic helical forms with (M)- or (P)-helicity can be in a diastereomeric relation. Thus, a particular screw sense of dynamic helicity can be preferred, regardless of whether or not the two substitution groups possess some chiral element

Complexation-induced inversion of helicity by an organic guest in a dynamic molecular propeller based on a tristerephthalamide host with a two-layer structure

A tristerephthalamide host exhibited two helical geometries with (M)- and (P)- helicity, respectively, in terms of the twisting direction of a two-layer structure, and the helical preference switched upon complexation with a ditopic guest. In both uncomplexed and complexed states, the intramolecular transmission of chirality was responsible for the control of helicity

Dynamic or undynamic chirality generated by helical arrangement of a shape-persistent ring and rod doubly bridged in a molecule

We synthesized molecular assemblies of a ring and rod that were covalently bound in a molecule. The bridged components were helically arranged in a threaded or unthreaded form to show unique chiroptical properties based on shape-persistent m-phenylacetylene rings with six, five and four units and phenylene-ethynylene rods