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Molecular Machines based on Macrocyclic Receptors: Switches and Motors
Published in Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney, Macrocyclic Receptors for Environmental and Biosensing Applications, 2022
Satish Kumar, Priya Ranjan Sahoo, Violet Rajeshwari Macwan, Jaspreet Kaur, Mukesh, Rachana Sahney
A rotaxane is a mechanically interlocked molecular architecture consisting of a ‘dumbbell-shaped molecule’ as a ‘shaft which is threaded through a ‘macrocycle’ (Fig. 9.6). However, if a rotaxane can dissociate into its two components without breaking the covalent bonds since its shaft molecule lacks the bulky groups at the ends which would lock the surrounding cycle on its position is called a pseudorotaxane (Fig. 9.5), however technically pseudorotaxanes are not part of MIMA. In MIMAs, subunits typically interact through non-covalent interactions such as π–π stacking, hydrogen bonding and dispersion interactions (Bazargan and Sohlberg 2018). Depending on how many different components have been combined by non-covalent interactions to assemble the MIM architecture is called [n]rotaxane or [n]pseudorotaxane, where n in the square bracket represents the number of each component.
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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
The first synthesis of a [2]rotaxane was reported by Frisch et al.6 This [2]rotaxane was synthesized in a meager 1 % yield and, until relatively recently, these yields had not been improved upon significantly by chemists. The main reason for the low yields is that the equilibrium depicted in Scheme 1 does not necessarily lie in the favor of the [2]pseudorotaxane. However, with the advent of supramolecular chemistry7 or host-guest chemistry,8 chemists have been able to construct recognition systems where the equilibrium depicted in Scheme I is in favor of the pseudorotaxane. This favoring of pseudorotaxane formation is achieved by choosing molecular components wherein the mutual recognition requirements between the macrocycle and the linear molecule is high, such that they adopt the pseudorotaxane superstructure preferentially. Such a recognition process in which two or more species combine in a particular manner, as prescribed by the noncovalent bonding interactions between them, has been termed selfassembly.9,10
Molecular Devices and Machines
Published in Mihai V. Putz, New Frontiers in Nanochemistry, 2020
Rotaxanes and catenanes are appealing systems for the construction of molecular machines because (i) the mechanical bond allows a large variety of mutual arrangements of the molecular components, while conferring stability to the system; (ii) the interlocked architecture limits the amplitude of the intercomponent motion in the three directions; (iii) the stability of a specific arrangement (co-conformation) is determined by the strength of the intercomponent interactions; and (iv) such interactions can be modulated by external stimulation. The large-amplitude motions that can be achieved with rotaxanes and catenanes are represented schematically in Figure 29.7a–c. Particularly, two interesting molecular motions can be envisaged in rotaxanes, namely (a) translation, i.e., shuttling, of the ring along the axle (Figure 29.7a), and (b) rotation of the ring around the axle (Figure 29.7b). Hence, rotaxanes are good prototypes for the construction of both linear and rotary molecular motors. Systems of type (a), termed molecular shuttles, constitute the most common implementation of the molecular machine concept with rotaxanes (Balzani et al., 2008).
Fault detection and analysis of bistable rotaxane molecular electronic switch - A simulation approach
Published in Journal of Experimental Nanoscience, 2018
Out of the various artificial molecular machines developed rotaxane is well known for its unique shuttling mechanism and its capability to act as a switch. Various external stimuli like redox, light, chemical input etc are used for achieving this shuttling mechanism. Gao et.al describes a shuttling mechanism based on phototrigger mechanism for a rotaxane which consists of identical ring stabilising stations. A photolabile is introduced between the two stations and covalently bonded with the dumbbell thread. Upon irradiation with UV light, the bulk phototrigger is successfully removed which is followed by a fast ring shuttling movement [22]. For the growth of molecular electronics as future technology, a researcher should focus not only on conductance but also on to the structural stability. In this introductory stage of molecular electronics single molecule experiments are more important than multi molecular experiments [5]. In this work, individual rotaxane molecule is analysed for the various CBPQT4+ ring position over the dumbbell and in terms of structural stability, band gap and ionisation energy.