Size switches

Synthetic Molecular Machines and Polymer/ Monomer Size Switches that Operate Through Dynamic and Non-Dynamic Covalent Changes... 

Abstract The present chapter is focused on how synthetic molecular machines (e.g. shuttles, switches and molecular motors) and size switches (conversions between polymers and their units, i.e., conversions between relatively large and small molecules) can function through covalent changes. Amongst the interesting examples of devices herein presented are molecular motors and size switches based on dynamic covalent chemistry which is an area of constitutional dynamic chemistry. 

Keywords Constitutional changes Covalent changes Dynamic covalent chemistry Molecular machines Molecular motors Molecular switches Polymer/monomer switches Reversible polymers Size switches... 

Polymer/Monomer Size Switches Switching Between Small and Large Molecular Sizes... 

In the second part of this chapter are presented systems involving reversible and controlled conversions - through covalent changes - between relatively large (polymers) and small (monomers) molecules, which can be considered as size switches. 

Synthetic Molecular Machines and Polymer/Monomer Size Switches... 

Fig. 13 The reversible conversion (here, mediated by metal ions M) of a copolymer (A-B) into a much smaller molecule (here, a macrocycle ABM) can be seen as a size-switch which consists of a dramatic change of molecular size (molecular diameter) modulated through external stimuli, and operates through dynamic covalent chemistry. See also Fig. 15...

A system where the conversion between a macrocycle and a polymer is modulated by chemical effectors/stimuli was described by Ulrich and Lehn [58,59]. They set up a reversible effector-controlled constitutional switch between a polymer and a macrocycle (Fig. 15) in a dynamic covalent system. This is a sequential one-pot size-switch or polymerization-degree-switch and it involves covalent changes in the constitution through breaking and formation of covalent bonds of the imine type. 

A polymer/monomer (polymer/repeat-unit or polymer/macrocycle) switch may become of practical importance where a polymer decorated with certain groups has specific size-dependent properties that the monomeric units do not have. The modulation of the conversion between polymeric and monomeric (or macrocyclic) states would also result in the modulation of these properties. Moreover, such size switches, represented by polymerization/depolymerization processes that operate under the control of external events, are examples of environmentally-friendly recyclable polymers (reduction of waste treatment). As well, if the polymer has low solubility and the polymer/monomer switch can work in spite of this, then it becomes possible to reversibly generate a precipitating (solid) polymeric material from a liquid solution of monomer. 

The default numerical integration algorithm uses a variable step size. Switching to a fixed step size eliminated the oscillation problem. To achieve this, go to Run on the upper toolbar in Aspen Dynamics, select Solver Options and click the Integrator page tab. The window shown in Figure 8.43a opens on which the step size can be changed to Fixed. 

Figure 5.1 Three compounds that were synthesized for studies in computing using electrostatic potentials. 1 is a molecular three-terminal junction that could be used as a molecular interconnect. 2 is a molecular-sized switch for which there is a corresponding equivalent of a source, drain and gate terminals of a bulk solid state FET. 3 is a can be an active OR or a passive NOR gate if positive logic is used or an AND or NAND gate if negative logic is used. ...

In conjunction with a calibration on any specific chromatography, the linear range of the components of interest shall be determined. The linearity is established for any new chromatograph and reestablished whenever the instrument has undergone a major change (that is, replaced detectors, increased sample size, switched column size, or dramatically modified run parameters). 

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