Structural and Conformational Chemistry from Electrochemical Molecular Machines. Replicating Biological Functions. A Review

Reaction Induced Conformational Change in Polyindole: Polyindole/PVA Film as Biomimetic Sensors of Temperature and Electrical Energetic Conditions

Conducting polymers can mimic the sensing characteristics of biological muscles through utilizing their unique electrochemical reactions. As these reactions occur, alterations in composition prompt changes in biomimetic properties, such as shifts in volume, brought about by the insertion of anions and solvent molecules, resulting in conformational movements. Similar to biological muscles, these electrochemical reaction senses the working variables affecting the reaction rate, through the same two connecting wires. The influence of working temperature and electrical energetic condition on the conformational movements of polyindole manifested as the cooperative actuation of the polymer chain is verified here using a polyindole-coated polyvinyl alcohol (PIN/PVA) film. Cyclic voltammetric (CV) studies revealed that the extent of reaction of polyindole varies linearly with temperature and scan rate. The logarithmic dependence of redox charge obtained from coulovoltammogram with inverse of temperature further proved the temperature sensing characteristics and the influence of temperature on the cooperative actuation of the film. The conformational relaxation increases as the temperature increases through hosting higher number of counter anions with the solvent molecule. The extension of the redox reaction was found to decrease as the scan rate increases. The double logarithmic relation between the consumed redox charge and the scan rate has proved that the electrical energetic condition can influence the conformational movement in a reversible manner. It is also verified from Chronopotentiometric (CP) studies that the consumed electrical energy during the reaction varies linearly with the change in temperature. The results suggest that the PIN/PVA film can act as a biomimetic macro molecular sensor of working temperature and electrical energetic condition as biological muscles do.

Artificial Biomimetic Electrochemical Assemblies

Rapid, selective, and cost-effective detection and determination of clinically relevant biomolecule analytes for a better understanding of biological and physiological functions are becoming increasingly prominent. In this regard, biosensors represent a powerful tool to meet these requirements. Recent decades have seen biosensors gaining popularity due to their ability to design sensor platforms that are selective to determine target analytes. Naturally generated receptor units have a high affinity for their targets, which provides the selectivity of a device. However, such receptors are subject to instability under harsh environmental conditions and have consequently low durability. By applying principles of supramolecular chemistry, molecularly imprinted polymers (MIPs) can successfully replace natural receptors to circumvent these shortcomings. This review summarizes the recent achievements and analytical applications of electrosynthesized MIPs, in particular, for the detection of protein-based biomarkers. The scope of this review also includes the background behind electrochemical readouts and the origin of the gate effect in MIP-based biosensors.

Photo- and Redox-Driven Artificial Molecular Motors

Directed motion at the nanoscale is a central attribute of life, and chemically driven motor proteins are nature's choice to accomplish it. Motivated and inspired by such bionanodevices, in the past few decades chemists have developed artificial prototypes of molecular motors, namely, multicomponent synthetic species that exhibit directionally controlled, stimuli-induced movements of their parts. In this context, photonic and redox stimuli represent highly appealing modes of activation, particularly from a technological viewpoint. Here we describe the evolution of the field of photo- and redox-driven artificial molecular motors, and we provide a comprehensive review of the work published in the past 5 years. After an analysis of the general principles that govern controlled and directed movement at the molecular scale, we describe the fundamental photochemical and redox processes that can enable its realization. The main classes of light- and redox-driven molecular motors are illustrated, with a particular focus on recent designs, and a thorough description of the functions performed by these kinds of devices according to literature reports is presented. Limitations, challenges, and future perspectives of the field are critically discussed.