Mechanically interlocked molecular architectures

Summary

In chemistry, mechanically interlocked molecular architectures (MIMAs) are molecules that are connected as a consequence of their topology. This connection of molecules is analogous to keys on a keychain loop. The keys are not directly connected to the keychain loop but they cannot be separated without breaking the loop. On the molecular level, the interlocked molecules cannot be separated without the breaking of the covalent bonds that comprise the conjoined molecules; this is referred to as a mechanical bond. Examples of mechanically interlocked molecular architectures include catenanes, rotaxanes, molecular knots, and molecular Borromean rings. Work in this area was recognized with the 2016 Nobel Prize in Chemistry to Bernard L. Feringa, Jean-Pierre Sauvage, and J. Fraser Stoddart. The synthesis of such entangled architectures has been made efficient by combining supramolecular chemistry with traditional covalent synthesis, however mechanically interlocked molecular architectures

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In macromolecular chemistry, a catenane () is a mechanically interlocked molecular architecture consisting of two or more interlocked macrocycles, i.e. a molecule containing two or more intertwi

Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of th

A rotaxane () is a mechanically interlocked molecular architecture consisting of a dumbbell-shaped molecule which is threaded through a macrocycle (see graphical representation). The two component

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Access to long-chain polyketides by double-elongation reactions

Christopher Flowers

Due to the spongistatins' fascinating and complex molecular architectures, and their important biological activities, these marine macrolides have been the subject of intensive efforts directed towards their total synthesis. As an attractive alternative to isolation from marine microorganisms, which usually provides only minuscule quantities of this family of macrolides, total synthesis aims to deliver sizable amounts of the natural product, along with enabling access to novel structural analogues, for further biological evaluation. These factors, combined with the impressive molecular architectures themselves, present compelling and formidable challenges to contemporary organic synthesis with regard both to strategy and methodology for their total synthesis in the laboratory. To this end, efforts targeting such complex macrolides provide an arena in which the synthetic chemist can develop new and more efficient methodologies and display such advances to the ultimate task of complex target synthesis. Through this process, new levels of stereocontrol and novel strategies to streamline the entire synthetic route help evolve the field as a whole. The synthetic efforts directed at the AB and CD spiroacetals of the northern fragment are herein disclosed. In conjunction with the synthesis of the southern fragment within our group, this renders itself as an original and efficient formal total synthesis of spongistatin 1. The synthesis of these key fragments has been optimized to reduce protections, set up chirality in an efficient and absolute manner and avoid fluctuations in oxidation states. Achievements in these aspects, that are often used to define the art of modern day total synthesis, have resulted in a rapid synthesis of these key fragments. The synthesis of the AB and CD spiroacetals was completed in 7 and 11 steps, respectively, rendering the process competitive with the most rapid previous synthesis to date. The sequences are based around the use of 1,3-bis(trimethylsilyl)-2-methylidenepropane in double elongation Sakurai reactions with both aldehydes and ketones to form advanced functionalized polyketides.

EPFL2010

Influence of molecular architecture on the isothermal time-dependent response of amorphous shape memory polyurethanes

Charly David Azra, Yaobo Ding, Jan-Anders Månson, John Christopher Plummer

The thermomechanical response of a series of thermally activated shape memory polyurethanes (SMPUs), determined by dynamic mechanical analysis (DMA), has been adjusted by systematic modification of the molecular architecture. It is argued that the free recovery behavior of these SMPUs. at temperatures in the vicinity of the calorimetric glass transition temperature is dependent not only on the recovery temperature, but also on the form of the corresponding peak in tan delta in DMA temperature scans at constant frequency. On the basis of simple correlations between recovery rates and the width and shape of the tan delta peak, it is suggested that DMA may provide a relatively simple and rapid means of assessing the potential of the SMPUs with respect both to recovery and shape fixity at a given storage temperature. This in turn allows establishment of a direct link between the shape memory performance and molecular architecture. (C) 2012 Elsevier Ltd. All rights reserved.

Elsevier2013

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Here we present a molecular architecture that can reversibly change the geometric conformation of its π-system backbone via irradiation with two different wavelengths. The proposed ‘molecular actuator’ consists of a photoswitchable azobenzene orthogonally connected to a π-conjugated bithiophene by both direct and aliphatic linker-assisted bonding. Upon exposure to 350 nm light, the trans azobenzene moiety isomerizes to its cis form, causing the bithiophene to assume a semiplanar anti conformation (extended π-conjugation). Exposure to 254 nm light promotes the isomerization of the azobenzene unit back to its initial extended trans conformation, thus forcing the bithiophene fragment to twist out of coplanarity (restricted π-conjugation). The molecular conformation of the bithiophene was characterized using steady-state UV-Vis and nuclear magnetic resonance spectroscopy, as well as ab initio computations. The proposed molecular design could be envisaged as a π-conjugation modulator, which has potential to be incorporated into extended linear π-systems, i.e. via the terminal alfa-thiophene positions, and used to tune their optical and electronic properties.

Royal Soc Chemistry2016

Access to long-chain polyketides by double-elongation reactions

Christopher Flowers

EPFL2010