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Macrocyclic Receptors Synthesis, History, Binding Mechanism: An Update on Current Status
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
Rotaxanes and catenanes are mechanically interlocked macrocyclic receptors. Such supramolecular architectures attracted considerable attention owing to their potential application in emerging areas such as switches and molecular machines owing to the free movement of interlocked components. Several triggers like metal ion, hydrogen bonding and π–π stacking are continuously being utilized for the development of rotaxanes and catenanes (Evans 2019).
Interlocked Systems in Catalysis and Switching
Published in Jubaraj Bikash Baruah, Principles and Advances in Supramolecular Catalysis, 2019
The catalysis based on dynamic systems stems from three fundamental aspects.1–2 These aspects are: (a) to utilise conformational flexible or fluxional systems for catalysis, (b) to take advantage of building an interlocked system by controlled reactivity and (c) to limit or enhance reactivity of a particular site by organizing the interlocked system differently. In the general practice of catalysis, there is a preference for a particular conformation to enhance activity; hence, the first aspect is routine. This aspect is evident in functional features of transient species imparting selectivity in catalytic reactions. The second and third aspects are on the utilization of interlocked systems. In supramolecular chemistry, interlocked systems are formed between covalently linked multicomponent systems. They may arise from the insertion of a dumbbell-shaped axle or an axlelike structure accommodating one or more molecules with ringlike structures. These types of interlocked systems are known as rotaxanes. A rotaxanelike structure may be created from a single-component system where a long chain is attached to a ring and the chain adopts adequate geometry to insert the free end into the ring. The interlocked structures formed between two or more rings or closed structures interlocked to each other are known as catenanes. One or more components of interlocked molecules have a definite trajectory and path for movement within the interlocked system. In the case of rotaxanes, the paths of movement of the ring/s over the different identified positions with functional groups located on the axle are of major concern in catalysis. Similarly, for a catenane catalyst, the circular path traced by a component is a point of focus. A halt of a ring over a catalyst would conceal a catalytic site, whereas moving the ring away would expose the catalytic site. The situation may be described by the schematic diagrams shown in Figure 4.1. These motions are characteristic of interlocked systems and are guided by stimuli, the solvent, the reactant, light, heat, pressure, temperature and so on. As the positions of the rings are easily changed, such changes affect and control the reactivity of catalytic sites by providing suitable space and orientation to the catalytic site to react or not with a substrate. The circular and translational motion of the ring component is represented in drawing marked as 4.1a. In the case of the rotation of two interlocked systems, it may be unidirectional or in the opposite directions. These motions are modulated by the hierarchy of binding units located at different points on the rings or axle.
Polyoxometalate-based catenane as sensing material for electrochemical detection of dopamine
Published in Journal of Coordination Chemistry, 2021
Hong Han, Jingquan Sha, Chang Liu, Yu Wang, Chunyao Dong, Mingjun Li, Tiying Jiao
Amperometric detection method is a sensitive electrochemical quantitative technique with rapid response capability and can provide an evaluation of the main characteristics of sensors, such as sensitivity, selectivity, and the detection limit, so the amperometric i-t responses of PMo12[6]catenane- and PMo12[6]catenane/rGO-GCE were conducted by successive addition of several concentrations of DA to a stirring 0.1 M PBS (pH = 2.0) for 1600s at 50 s interval. As shown in Figure 7, there is a well-defined and stable amperometric response, and the electrode responds quickly to added DA in response time less than 2 s in PMo12[6]catenane- or PMo12[6]catenane/rGO-GCE electrodes. In the calibration curve, the good linear correlation from 1 to 90 μM (R2 = 0.9923) for PMo12[6]catenane-GCE and 1–44 μM (R2 = 0.9967) for PMo12[6]catenane/rGO-GCE were observed, and the corresponding linear regression equations are expressed as I = 0.09678 + 0.01816 ×CDA and I = 0.202 + 0.02456 × CDA, respectively. As a result, the limit of detection (LOD) was calculated as 0.890 μM and 0.065 μM (S/N = 3), respectively, which is lower than reported modified electrodes (Table 1), implying that PMo12[6]catenane- and PMo12[6]catenane/rGO-GCE are superior for electrochemical sensing of DA. This may be explained as follows: First, the unique catenane structure provides excellent stability and an electron transmission pathway. Second, PMo12[6]catenane has relatively good electrochemical reversibility, fast electron transfer ability and stable redox forms. Third, when rGO was introduced, PMo12[6]catenane/rGO possesses the large surface area, abundant active sites, and good conductivity, which are essential for improving the electrochemical activity. As a consequence, the best amplifying effect for DA detection is obtained due to cooperation of the components in the PMo12[6]catenane/rGO-GCE.