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

Artificial Molecular Machines Powered by Light

The bottom-up construction and operation of mechanical machines of molecular size is a topic of great interest for nanoscience, and a fascinating challenge of nanotechnology. Like their macroscopic counterparts, nanoscale machines need energy to operate. Although most molecular motors of the biological world are fueled by chemical reactions, light is a very good choice to power artificial molecular machines because it can also be used to monitor the state of the machine, and allows systems to be obtained that show autonomous operation and do not generate waste products. By adopting an incrementally staged design strategy, photoinduced processes can be engineered within rotaxane-type structures with the purpose of obtaining light-powered molecular machines. In this short review we will illustrate such an approach by describing some systems investigated in our laboratories

Light-powered autonomous and directional molecular motion of a dissipative self-assembling system

Biomolecular motors convert energy into directed motion and operate away from thermal equilibrium. The development of dynamic chemical systems that exploit dissipative (non-equilibrium) processes is a challenge in supramolecular chemistry and a premise for the realization of artificial nanoscale motors. Here, we report the relative unidirectional transit of a nonsymmetric molecular axle through a macrocycle powered solely by light. The molecular machine rectifies Brownian fluctuations by energy and information ratchet mechanisms and can repeat its working cycle under photostationary conditions. The system epitomizes the conceptual and practical elements forming the basis of autonomous light-powered directed motion with a minimalist molecular design

Trois fenêtres pour un panorama. Contributions des réflexions féministes, genrées et queer produites en Italie dans le cadre des disciplines spatiales à partir des années 1990

L’obiettivo del contributo, scritto in lingua francese, è indagare come gli approccio di genere e queer influenzino la riflessione sulla teoria e le pratiche dello spazio in Italia, mediante l’attività di diverse soggettività. Il background delle autrici proviene da dipartimenti di architettura italiani, dove si sviluppano sia studi urbani che pratiche di progettazione spaziale a diverse scale. Questo contesto è stato contaminato da temi che emergono nella nuvola dei movimenti femministi e transfemministi queer, contaminazioni che rimangono sconosciute e/o non inserite in un quadro di riferimento definito. La mancanza di riconoscimento è - crediamo - almeno in parte legata a una particolarità della sfera italiana: a differenza di altri Paesi, in Italia le istanze dei movimenti non hanno trovato una traduzione istituzionale nella formazione di quadri accademici, come i dipartimenti di genere o di studi queer. Questo discorso ha quindi trovato un posto per la costruzione di sé in contesti diversi e di varia natura, a volte anche in conflitto tra loro. Tale peculiarità, e il carattere trasversale che attribuiamo alla nostra disciplina, ci ha portato a mettere in discussione alcune delle diverse soggettività che giocano un ruolo nella costruzione del dibattito: 1. i gruppi storici del femminismo della differenza, presenza fondamentale caratterizzante del discorso italiano, come confronto persistente con l’ingombrante portata, ricca e costrittiva, del loro patrimonio teorico; 2. i mediatori e le mediatrici che, trasponendo un punto di vista femminista sulla pianificazione, operano in dialogo e negoziazione con le amministrazioni, soprattutto riguardo le questioni aperte dalla natura universalistica e mainstream dell’approccio istituzionale delle politiche urbano di genere; 3. i movimenti transfemministi queer, in opposizione alle soggettività fino ad ora proposte, le cui pratiche spaziali più recenti interessano per la natura sovversiva e creativa della loro radicalità. Il contributo individua il particolare interesse del caso italiano nell’intreccio tra le soggettività e le loro relazioni, che produce un discorso profondo e variegato, trasformando la mancanza di un quadro istituzionale in un fertile scenario produttivo.Cette contribution a pour objectif d’enquêter sur la façon dont une approche genrée et queer influence la réflexion sur la théorie et les pratiques de l’espace en Italie au moyen de l’activité de plusieurs subjectivités

Stereodynamics of E/Z isomerization in rotaxanes through mechanical shuttling and covalent bond rotation

We report on a set of rotaxanes with symmetrical axles equipped with a central amide group that installs E/Z stereoisomerism owing to the ring position along the axle. Isomerization by concomitant rotation about the amide bond and ring shuttling along the axle was thoroughly characterized in different solvents. The results trigger a discussion on core concepts, such as microscopic reversibility and transition state theory, and provide insights for designing molecules capable to transform and transmit motion between subcomponents

Modelizations and Simulations of Nano Devices in nanok calculus

International audienceWe develop a process calculus - the nanok calculus - for modeling, analyzing and predicting the properties of molecular devices. The nanok calculus is equipped with a simple stochastic model, that we use to model and simulate the behavior of a molecular shuttle, a basic nano device currentfly used for building more complex systems

4,4'-Dimethylazobenzene as a chemical actinometer

Chemical actinometers are a useful tool in photochemistry, which allows to measure the photon flux of a light source to carry out quantitative analysis on photoreactions. The most commonly employed actinometers so far show minor drawbacks, such as difficult data treatment, parasite reactions, low stability or impossible reset. We propose herewith the use of 4,4'-dimethylazobenzene as a chemical actinometer. This compound undergoes a clean and efficient E/Z isomerization, approaching total conversion upon irradiation at 365 nm. Thanks to its properties, it can be used to determine the photon flux in the UV-visible region, with simple experimental methods and data treatment, and with the possibility to be reused after photochemical or thermal reset.[GRAPHICS]

Supramolecular assemblies of semiconductor quantum dots and a bis(bipyridinium) derivative : luminescence quenching and aggregation phenomena

We have synthesized CdSe and CdSe–ZnS core–shell luminescent nanocrystal quantum dots and studied their interaction with a ditopic bis(bipyridinium) compound in solution. The latter strongly quenches the luminescence of the quantum dots by a static mechanism, indicating that the nanocrystal and molecular components undergo association in the ground state. Photoexcitation of these inorganic–organic hybrids causes an electron-transfer process from the conduction band of the nanocrystal to the LUMO of the molecule. The ability of the bipyridinium-type species to trigger association of the quantum dots is evidenced by spectrofluorimetric titrations and DLS measurements in solution, and confirmed by TEM experiments on surfaces. The quantum dot–molecule complexes can be disassembled in solution by addition of a calixarene host capable of encapsulating the bipyridinium units of the molecular connector. Our results demonstrate that supramolecular chemistry offers convenient ways to control the aggregation of semiconductor nanocrystals, a crucial task for the generation of nanostructured arrays with well defined properties

Electrochemically Triggered Co-Conformational Switching in a [2]catenane Comprising a Non-Symmetric Calix[6]arene Wheel and a Two-Station Oriented Macrocycle

Catenanes with desymmetrized ring components can undergo co-conformational rearrangements upon external stimulation and can form the basis for the development of molecular rotary motors. We describe the design, synthesis and properties of a [2]catenane consisting of a macrocycle—the ‘track’ ring—endowed with two distinct recognition sites (a bipyridinium and an ammonium) for a calix[6]arene—the ‘shuttle’ ring. By exploiting the ability of the calixarene to thread appropriate non-symmetric axles with directional selectivity, we assembled an oriented pseudorotaxane and converted it into the corresponding oriented catenane by intramolecular ring closing metathesis. Cyclic voltammetric experiments indicate that the calixarene wheel initially surrounds the bipyridinium site, moves away from it when it is reduced, and returns in the original position upon reoxidation. A comparison with appropriate model compounds shows that the presence of the ammonium station is necessary for the calixarene to leave the reduced bipyridinium site

Second-Generation Light-Fueled Supramolecular Pump

open7noFinancial support from the European Research Council (H2020 Advanced Grant 692981 to A.C.)We describe the modular design of a pseudorotaxane-based supramolecular pump and its photochemically driven autonomous nonequilibrium operation in a dissipative regime. These properties derive from careful engineering of the energy maxima and minima along the threading coordinate and their light-triggered modulation. Unlike its precursor, this second-generation system is amenable to functionalization for integration into more complex devices.openCanton, Martina; Groppi, Jessica; Casimiro, Lorenzo; Corra, Stefano; Baroncini, Massimo; Silvi, Serena; Credi, AlbertoCanton, Martina; Groppi, Jessica; Casimiro, Lorenzo; Corra, Stefano; Baroncini, Massimo; Silvi, Serena; Credi, Albert