Acid−Base Controllable Molecular Shuttles

Abstract

Two novel [2]rotaxanes, comprised of a dibenzo[24]crown-8 (DB24C8) macroring bound mechanically to a chemical “dumbbell” possessing two different recognition sitesviz., secondary dialkylammonium (NH2 +) and 4,4‘-bipyridinium (Bpym2+) unitshave been synthesized by using the supramolecular assistance to synthesis provided by, inter alia, hydrogen bonding interactions. One of these rotaxanes bears a fluorescent and redox-active anthracene (Anth) stopper unit. NMR spectroscopy and X-ray crystallography have demonstrated that the DB24C8 macroring exhibits complete selectivity for the NH2 + recognition sites, i.e., that the [2]rotaxanes exist as only one of two possible translational isomers. Deprotonation of the rotaxanes' NH2 + centers effects a quantitative displacement of the DB24C8 macroring to the Bpym2+ recognition site, an outcome that can be reversed by acid treatment. The switching processes have been investigated by 1H NMR spectroscopy and, for the Anth-bearing rotaxane, by electrochemical and photophysical measurements. Furthermore, it is possible to drive the DB24C8 macroring from the dumbbell's Bpym2+ unit, in the deprotonated form of the Anth-bearing rotaxane, by destroying the stabilizing DB24C8−Bpym2+ charge-transfer interactions via electrochemical reduction. The photochemical and photophysical properties of this rotaxane (in both its protonated and deprotonated states) have also been investigated.

Control of Noise in Chemical and Biochemical Information Processing

“…Indeed, chemical processes can be cast [35,36] in the language of computing operations, with signals represented by changes [1][2][3][4][36][37][38][39][40][41][42][43][44][45][46][47][48] in structural, chemical, or physical properties, resulting due to physical, chemical, [77][78][79][80][81][82][83][84] or more than one type [53,[85][86][87] of input. The output signals can be detected spectroscopically [88][89][90][91][92][93] or electrically/electrochemically.…”

Adiabatic operation of a molecular machine

“…This feature facilitates the design of molecular motors (7,8) and rotors (9), devices that can be caused to undergo directional motion by an external source of chemical (10), optical (11), or electrical (12) energy. Control is achieved by incorporating two or more recognition stations (sites where the components of the complex interact strongly) to define several intracomplex binding sites (13,14) and, hence, several configurational states of the molecule. The relative thermodynamic stability of the different sites (and hence states) is controlled by, e.g., protonation/deprotonation, reduction/ oxidation, or absorption of light.…”

Modelization and Simulation of Nano Devices in nano κ Calculus

“…The process can be reversed by addition of acid (e.g., trifluoroacetic acid) and the initial state is restored, passing through the transient state denoted as RbH. Nuclear magnetic resonance, absorption and luminescence spectroscopic experiments, together with electrochemical measurements, indicate [1] that the acid-base controlled switching, which is fully reversible and relatively fast, exhibits a clear-cut on-off behaviour.…”

“…We then apply the nanoκ calculus to describe and analyze the "Rotaxane RaH" [15,1], an instance of rotaxane for which the dynamic behaviour has been experimentally characterized in detail [8]. We have considered two groups of simulations.…”