Metal Nanoparticles Functionalized with Molecular and Supramolecular Switches

Resorc[4]arene-Modified Gold-Decorated Magnetic Nanoparticles for Immunosensor Development

In recent years, several efforts have been made to develop selective, sensitive, fast response, and miniaturized immunosensors with improved performance for the monitoring and screening of analytes in several matrices, significantly expanding the use of this technology in a broad range of applications. However, one of the main technical challenges in developing immunosensors is overcoming the complexity of binding antibodies (Abs) to the sensor surface. Most immobilizing approaches lead to a random orientation of Abs, resulting in lower binding site density and immunoaffinity. In this context, supramolecular chemistry has emerged as a suitable surface modification tool to achieve the preorganization of artificial receptors and to improve the functional properties of self-assembled monolayers. Herein, a supramolecular chemistry/nanotechnology-based platform was conceived to develop sensitive label-free electrochemical immunosensors, by using a resorcarene macrocycle as an artificial linker for the oriented antibody immobilization. To this aim, a water-soluble bifunctional resorc[4]arene architecture (RW) was rationally designed and synthesized to anchor gold-coated magnetic nanoparticles (Au@MNPs) and to maximize the amount of the active immobilized antibody (Ab) in the proper "end-on" orientation. The resulting supramolecular chemistry-modified nanoparticles, RW@Au@MNPs, were deposited onto graphite screen printed electrodes which were then employed to immobilize three different Abs. Furthermore, an immunosensor for atrazine (ATZ) analysis was realized and characterized by the differential pulse voltammetry technique to demonstrate the validity of the developed biosensing platform as a proof of concept for electrochemical immunosensors. The RW-based immunosensor improved Ab_ATZ loading on Au@MNPs and sensitivity toward ATZ by almost 1.5 times compared to the random platform. Particularly, the electrochemical characterization of the developed immunosensor displays a linearity range toward ATZ within 0.05-1.5 ng/mL, a limit of detection of 0.011 ng/ml, and good reproducibility and stability. The immunosensor was tested by analyzing spiked fortified water samples with a mean recovery ranging from 95.7 to 108.4%. The overall good analytical performances of this immunodevice suggest its application for the screening and monitoring of ATZ in real matrices. Therefore, the results highlighted the successful application of the resorc[4]arene-based sensor design strategy for developing sensitive electrochemical immunosensors with improved analytical performance and simplifying the Ab immobilization procedure.

The Story of the Little Blue Box: A Tribute to Siegfried Hünig

The tetracationic cyclophane, cyclobis(paraquat-p-phenylene), also known as the little blue box, constitutes a modular receptor that has facilitated the discovery of many host-guest complexes and mechanically interlocked molecules during the past 35 years. Its versatility in binding small π-donors in its tetracationic state, as well as forming trisradical tricationic complexes with viologen radical cations in its doubly reduced bisradical dicationic state, renders it valuable for the construction of various stimuli-responsive materials. Since the first reports in 1988, the little blue box has been featured in over 500 publications in the literature. All this research activity would not have been possible without the seminal contributions carried out by Siegfried Hünig, who not only pioneered the syntheses of viologen-containing cyclophanes, but also revealed their rich redox chemistry in addition to their ability to undergo intramolecular π-dimerization. This Review describes how his pioneering research led to the design and synthesis of the little blue box, and how this redox-active host evolved into the key component of molecular shuttles, switches, and machines.

Stimuli-Responsive Adaptive Nanotoxin to Directly Penetrate the Cellular Membrane by Molecular Folding and Unfolding

Biological nanomachines, including proteins and nucleic acids whose function is activated by conformational changes, are involved in every biological process, in which their dynamic and responsive behaviors are controlled by supramolecular recognition. The development of artificial nanomachines that mimic the biological functions for potential application as therapeutics is emerging; however, it is still limited to the lower hierarchical level of the molecular components. In this work, we report a synthetic machinery nanostructure in which actuatable molecular components are integrated into a hierarchical nanomaterial in response to external stimuli to regulate biological functions. Two nanometers core-sized gold nanoparticles are covered with ligand layers as actuatable components, whose folding/unfolding motional response to the cellular environment enables the direct penetration of the nanoparticles across the cellular membrane to disrupt intracellular organelles. Furthermore, the pH-responsive conformational movements of the molecular components can induce the apoptosis of cancer cells. This strategy based on the mechanical motion of molecular components on a hierarchical nanocluster would be useful to design biomimetic nanotoxins.

Multifunctional Switch Based on Spin-Labeled Gold Nanoparticles

The fabrication of multifunctional switches is a fundamental step in the development of nanometer-scale molecular spintronic devices. The anchoring of active organic radicals on gold nanoparticles (AuNPs) surface is little studied and the realization of AuNPs-based switches remains extremely challenging. We report the first demonstration of a surface molecular switch based on AuNPs decorated with persistent perchlorotriphenylmethyl (PTM) radicals. The redox properties of PTM are exploited to fabricate electrochemical switches with optical and magnetic responses, showing high stability and reversibility. Electronic interaction between the radicals and the gold surface is investigated by UV-vis, showing a very broad absorption band in the near-infrared (NIR) region, which becomes more intense when PTMs are reduced to anionic phase. By using multiple experimental techniques, we demonstrate that this interaction is likely favored by the preferentially flat orientation of PTM ligands on the metallic NP surface, as confirmed by first-principles simulations.

Classical and non-classical melatonin receptor agonist-directed micellization of bipyridinium-based supramolecular amphiphiles in water

The addition of molecular recognition units into structures of amphiphiles is a means by which soft matter capable of undergoing template-directed micellization can be obtained. These supramolecular amphiphiles can bind with molecular templates using non-covalent bonding interactions, forming host-guest complexes that hold the amphiphiles together as they undergo micellization. In most cases, such templates are synthesized and designed for a specific molecular recognition motif. It is not clear, however, to what extent these types of amphiphile systems are responsive to members of a biologically derived class of molecular targets, for example, melatonin receptor agonists and their numerous isosteres. Herein, we describe the template-directed micellization and arrangement at the air-water interface of a bipyridinium-based gemini surfactant, driven by the influence of donor-acceptor CT interactions with a series of bioactive classical and non-classical melatonin isosteres. Under the conditions of templation by either 5-methoxytryptophol, N-acetylserotonin, N-acetyltryptamine, or the pharmaceutical agent agomelatine, favorable Gibbs free energies of micellization were observed with decreases in CMC by up to 70%, and concomitant increases of 28% in surface pressure, and decreases of 20% in contact angle versus untemplated solutions. Solid state thermochromic transition temperatures for inkjet-printed patterns of the templated amphiphile solutions were inversely correlated with trends observed for their respective CMCs, and exhibited no correlation to their binding constants. These findings contend for the generalizable use of melatonin receptor agonists as targets and/or templates for chemical systems, which rely on π-stacking donor-acceptor CT interactions in water to facilitate the actions of binding, sequestration, or template-directed self-assembly.

Dynamic covalent synthesis of [2]- and [3]rotaxanes both in solution and on solid supports

Here we demonstrate the application of a dynamic covalent chemistry methodology for the synthesis of [2]- and [3]-rotaxanes not only in solution, but also on solid supports with 65% rotaxane functionalisation of the polymer resins observed.

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Mechanically interlocked materials. Rotaxanes and catenanes beyond the small molecule

An overview of the progress in mechanically interlocked materials is presented. In particular, we focus on polycatenanes, polyrotaxanes, metal–organic rotaxane frameworks (MORFs), and mechanically interlocked derivatives of carbon nanotubes (MINTs).

Stimuli-responsive self-assembly of nanoparticles

Ligand-protected nanoparticles can serve as attractive building blocks for constructing complex chemical systems.

Tuning chain extender structure to prepare high-performance thermoplastic polyurethane elastomers

In this work, a novel strategy is developed to solve the issue of mutually exclusive high mechanical robustness and thermo-stability for thermoplastic polyurethane (PU). A leaf-like and reticulate interfingering superstructure can be seen. The superstructure of polyurethanes can also be tuned by the polarity of chain extender molecular via changing the number for ferrocene redox centres, thus to further enhance the thermal stability and elasticity of PUs. As a result, by incorporating bisferrocene units into the main chain of PU, a high-performance PU elastomer can be synthesized with a highest initial degradation temperature of T_5% of 345 °C, a highest tensile strength of 42.3 MPa with an elongation over 1000%, as well as a toughness of 19.6 GJ m⁻³. These results conclusively suggest that high-performance thermoplastic polyurethane elastomers had great promise for potential application in a wide range of practical fields.

Ester-containing ferrocenyl diols are introduced as chain extenders to tune the polyurethane superstructure to optimize thermo-stability and elasticity simultaneously.

Melatonin-directed micellization: a case for tryptophan metabolites and their classical bioisosteres as templates for the self-assembly of bipyridinium-based supramolecular amphiphiles in water

The bulk solution properties of amphiphilic formulations are derivative of their self-assembly into higher ordered supramolecular assemblies known as micelles and of their ordering at the air-water interface. Exerting control over the surface-active properties of amphiphiles and their propensity to aggregate in pure water is most often fine-tuned by covalent modification of their molecular structure. Nevertheless structural constraints which limit the performance of amphiphiles do emerge when trying to develop more sophisticated systems which undergo for example, shape-defined controlled assembly and/or respond to external stimuli. In this regard, the template-modulated assembly of the so-called "supramolecular amphiphiles" continues to make progress ordering molecules that otherwise have very little to no driving force to aggregate in a prescribed manner in aqueous solutions. Herein we describe the template-modulated micellization and ordering at the air-water interface of bipyridinium-based supramolecular amphiphiles triggered by host-guest interactions with high specificity for the neurotransmitter melatonin over its biosynthetic synthon l-tryptophan and the thermodynamic parameters governing the template-modulated micellization process. When bound to the bipyridinium units of micellized surfactant molecules, melatonin effectively serves as "molecular glue" capable of lowering the CMC by 52% as compared to untemplated solutions. Analysis of this system suggests that a hallmark of donor-acceptor template-modulated micellization in water is a strong positively correlated temperature dependence of the CMC and the absence of a U-shaped CMC-temperature curve. Our findings make a case for the incorporation of l-tryptophan-based metabolites and their classical synthetic pharmaceutical bioisosteres as potential targets/components of donor-acceptor CT-based supramolecular amphiphile systems/materials operating in water.

Molecular control over colloidal assembly

Contemporary chemical and material engineering often takes inspiration from nature, targeting for example strong yet light materials and materials composed of highly ordered domains at multiple different lengthscales for fundamental science and applications in e.g. sensing, catalysis, coating technology, and delivery. The preparation of such hierarchically structured functional materials through guided bottom-up assembly of synthetic building blocks requires a high level of control over their synthesis, interactions and assembly pathways. In this perspective we showcase recent work demonstrating how molecular control can be exploited to direct colloidal assembly into responsive materials with mechanical, optical or electrical properties that can be adjusted post-synthesis with external cues.

Homogeneously Mixed Monolayers: Emergence of Compositionally Conflicted Interfaces

The ability to manipulate interfaces at the nanoscale via a variety of thin-film technologies offers a plethora of avenues for advancing surface applications. These include surfaces with remarkable antibiofouling properties as well as those with tunable physical and electronic properties. Molecular self-assembly is one notably attractive method used to decorate and modify surfaces. Of particular interest to surface scientists has been the thiolate-gold system, which serves as a reliable method for generating model thin-film monolayers that transform the interfacial properties of gold surfaces. Despite widespread interest, efforts to tune the interfacial properties using mixed adsorbate systems have frequently led to phase-separated domains of molecules on the surface with random sizes and shapes depending on the structure and chemical composition of the adsorbates. This feature article highlights newly emerging methods for generating mixed thin-film interfaces, not only to enhance the aforementioned properties of organic thin films, but also to give rise to interfacial compositions never before observed in nature. An example would be the development of monolayers formed from bidentate adsorbates and other unique headgroup architectures that provide the surface bonding stability necessary to allow the assembly of interfaces that expose mixtures of chains that are fundamentally different in character (i.e., either phase-incompatible or structurally dissimilar), producing compositionally "conflicted" interfaces. By also exploring the prior efforts to produce such homogeneously blended interfaces, this feature article seeks to convey the relationships between the methods of film formation and the overall properties of the resulting interfaces.

Fabrication of a mercaptoacetic acid pillar[5]arene assembled nanochannel: a biomimetic gate for mercury poisoning

Mercury ion binding blocks potassium ion channels, which leads to toxicity in vivo. It is challenging to design a simple and efficient artificial system to mimic the sophisticated biological process of mercury poisoning. Herein, based on biomimetic strategies, a tunable mercury(ii) ion-gate modulated by mercaptoacetic acid-pillar[5]arene (MAP5) is reported. By virtue of the unique design of the host-guest competition, potassium ion transport can actualize the reversible switching between "on" and "off" in the absence and presence of mercury ions. Moreover, the MAP5-immobilized nanochannel is highly effective at distinguishing Hg²⁺ from other metal ions and can be used to detect Hg²⁺ and act as an excellent and robust gate valve for developing integrated circuits and nanoelectronic logic devices. This study paves a new way for better understanding the physiological phenomenon of mercury toxicity and shows great promise for biomedical research.

Reversible morphological changes of assembled supramolecular amphiphiles triggered by pH-modulated host–guest interactions

Acid–base modulated host–guest binding at the micellar–water interface triggers reversible oblate ellipsoid-to-lamellar morphological transitions revealing the relationship between and morphology.

Chloride-Anion-Templated Synthesis of a Strapped-Porphyrin-Containing Catenane Host System

The synthesis, structure and anion-recognition properties of a new strapped-porphyrin-containing [2]catenane anion host system are described. The assembly of the catenane is directed by discrete chloride anion templation acting in synergy with secondary aromatic donor-acceptor and coordinative pyridine-zinc interactions. The [2]catenane incorporates a three-dimensional, hydrogen-bond-donating anion-binding pocket; solid-state structural analysis of the catenane⋅chloride complex reveals that the chloride anion is encapsulated within the catenane's interlocked binding cavity through six convergent CH⋅⋅⋅⋅Cl and NH⋅⋅⋅Cl hydrogen-bonding interactions and solution-phase (1) H NMR titration experiments demonstrate that this complementary hydrogen-bonding arrangement facilitates the selective recognition of chloride over larger halide anions in DMSO solution.

Reversible Photoisomerization of Spiropyran on the Surfaces of Au25 Nanoclusters

Au25 nanoclusters functionalized with a spiropyran molecular switch are synthesized via a ligand-exchange reaction at low temperature. The resulting nanoclusters are characterized by optical and NMR spectroscopies as well as by mass spectrometry. Spiropyran bound to nanoclusters isomerizes in a reversible fashion when exposed to UV and visible light, and its properties are similar to those of free spiropyran molecules in solution. The reversible photoisomerization entails the modulation of fluorescence as well as the light-controlled self-assembly of nanoclusters.

Celebrating Soft Matter's 10th Anniversary: Approaches to program the time domain of self-assemblies

Self-regulating reconfigurable soft matter systems are of great interest for creating adaptive and active material properties. Such complex functionalities emerge from non-linear and interactive behavior in space and time as demonstrated by a plethora of dynamic, self-organizing biological structures (e.g., the cytoskeleton). In man-made self-assemblies, patterning of the spatial domain has advanced to creating hierarchical structures via precise molecular programming. However, orchestration of the time domain of self-assemblies is still in its infancy and lacks universal design principles. In this Emerging Area article we outline major strategies for programming the time domain of self-assemblies following the concepts of regulatory reaction networks, energy dissipation and kinetic control. Such concepts operate outside thermodynamic equilibrium and pave the way for temporally patterned, dynamic, and autonomously acting functional materials.

Catenanes: fifty years of molecular links

Half a century after Schill and Lüttringhaus carried out the first directed synthesis of a [2]catenane, a plethora of strategies now exist for the construction of molecular Hopf links (singly interlocked rings), the simplest type of catenane. The precision and effectiveness with which suitable templates and/or noncovalent interactions can arrange building blocks has also enabled the synthesis of intricate and often beautiful higher order interlocked systems, including Solomon links, Borromean rings, and a Star of David catenane. This Review outlines the diverse strategies that exist for synthesizing catenanes in the 21st century and examines their emerging applications and the challenges that still exist for the synthesis of more complex topologies.

Two Stepwise Synthetic Routes toward a Hetero[4]rotaxane

Heterorotaxanes have been emerging as an important class of mechanically interlocked molecules and have attracted much attention in recent years. Driven by the distinguishable host-guest interactions between crown ether macrocycles and ammonium with different sizes, a novel hetero[4]rotaxane was successfully prepared by employing the combination of copper-catalyzed "click" reaction and P(n-Bu)3-catalyzed esterification reaction as stoppering reactions. The hetero[4]rotaxane contains an interlocked species in which a dibenzo[24]crown-8 ring threaded by a dibenzylammonium-containing component with two benzo[21]crown-7 macrocycles at both ends to act as stoppers, and each of the two benzo[21]crown-7 rings is also threaded with a benzylalkylammonium unit to form the second interlocked species. The hetero[4]rotaxane was prepared through two different stepwise synthetic routes, and the complicated chemical structure of the hetero[4]rotaxane was well-characterized by (1)H NMR spectroscopy and high-resolution electrospray ionization (HR-ESI) mass spectrometry. The investigation shows that the construction of complicated topological heterorotaxane can be achieved via distinct approaches with high efficiencies, which may provide a foundation for the construction of more sophisticated heterorotaxane systems or functional supermolecules.

Supramolecular tailoring of protein-nanoparticle interactions using cucurbituril mediators

Supramolecular modification of nanoparticle surfaces through threading of cucurbit[7]uril (CB[7]) onto surface ligands is used to regulate protein-nanoparticle interactions.

Coupled molecular switching processes in ordered mono- and multilayers of stimulus-responsive rotaxanes on gold surfaces

Interfaces provide the structural basis for function as, for example, encountered in nature in the membrane-embedded photosystem or in technology in solar cells. Synthetic functional multilayers of molecules cooperating in a coupled manner can be fabricated on surfaces through layer-by-layer self-assembly. Ordered arrays of stimulus-responsive rotaxanes undergoing well-controlled axle shuttling are excellent candidates for coupled mechanical motion. Such stimulus-responsive surfaces may help integrate synthetic molecular machines in larger systems exhibiting even macroscopic effects or generating mechanical work from chemical energy through cooperative action. The present work demonstrates the successful deposition of ordered mono- and multilayers of chemically switchable rotaxanes on gold surfaces. Rotaxane mono- and multilayers are shown to reversibly switch in a coupled manner between two ordered states as revealed by linear dichroism effects in angle-resolved NEXAFS spectra. Such a concerted switching process is observed only when the surfaces are well packed, while less densely packed surfaces lacking lateral order do not exhibit such effects.

Synthesis of Conducting Polymer-Metal Nanoparticle Hybrids Exploiting RAFT Polymerization

The direct covalent attachment of conducting polymers (CP) to nanoparticles (NP) to form CP-NP nanohybrids is of great interest for optoelectronic device applications. Hybrids formed by covalently anchoring CP to NP, rather than traditional blending or bilayer approaches, is highly desirable. CP-NP nanohybrids have increased interfacial surface area between the two components, facilitating rapid exciton diffusion at the p-n heterojunction. These materials take advantage of the facile solution processability, lightweight characteristics, flexibility, and mechanical strength associated with CPs, and the broad spectral absorption, photostability, and high charge carrier mobility of NPs. We demonstrate the ability to polymerize a hole transporting (HT) polymer utilizing reversible-addition-fragmentation chain transfer (RAFT) polymerization and its subsequent rapid aminolysis to yield a thiol-terminated HT polymer. Subsequent facile attachment to gold (Au) and silver (Ag) NPs and cadmium selenide (CdSe) quantum dots (QDs), to form a number of CP-NP systems is demonstrated and characterized. CP-NP nanohybrids show broad spectral absorptions ranging from UV through visible to the near IR, and their facile synthesis and purification could allow for large scale industrial applications.

Polyrotaxane-mediated self-assembly of gold nanospheres into fully reversible supercrystals

The use of a thiol-functionalized nonionic surfactant to stabilize spherical gold nanoparticles in water induces the spontaneous formation of polyrotaxanes at the nanoparticle surface in the presence of the macrocycle α-cyclodextrin. Whereas using an excess of surfactant an amorphous gold nanocomposite is obtained, under controlled drying conditions the self-assembly between the surface supramolecules provides large and homogenous supercrystals with hexagonal close packing of nanoparticles. Once formed, the self-assembled supercrystals can be fully redispersed in water. The reversibility of the crystallization process may offer an excellent reusable material to prepare gold nanoparticle inks and optical sensors with the potential to be recovered after use.

Rotaxane and catenane host structures for sensing charged guest species

CONSPECTUS: The promise of mechanically interlocked architectures, such as rotaxanes and catenanes, as prototypical molecular switches and shuttles for nanotechnological applications, has stimulated an ever increasing interest in their synthesis and function. The elaborate host cavities of interlocked structures, however, can also offer a novel approach toward molecular recognition: this Account describes the use of rotaxane and catenane host systems for binding charged guest species, and for providing sensing capability through an integrated optical or electrochemical reporter group. Particular attention is drawn to the exploitation of the unusual dynamic properties of interlocked molecules, such as guest-induced shuttling or conformational switching, as a sophisticated means of achieving a selective and functional sensor response. We initially survey interlocked host systems capable of sensing cationic guests, before focusing on our accomplishments in synthesizing rotaxanes and catenanes designed for the more challenging task of selective anion sensing. In our group, we have developed the use of discrete anionic templation to prepare mechanically interlocked structures for anion recognition applications. Removal of the anion template reveals an interlocked host system, possessing a unique three-dimensional geometrically restrained binding cavity formed between the interlocked components, which exhibits impressive selectivity toward complementary anionic guest species. By incorporating reporter groups within such systems, we have developed both electrochemical and optical anion sensors which can achieve highly selective sensing of anionic guests. Transition metals, lanthanides, and organic fluorophores integrated within the mechanically bonded structural framework of the receptor are perturbed by the binding of the guest, with a concomitant change in the emission profile. We have also exploited the unique dynamics of interlocked hosts by demonstrating that an anion-induced conformational change can be used as a means of signal transduction. Electrochemical sensing has been realized by integration of the redox-active ferrocene functionality within a range of rotaxane and catenanes; binding of an anion perturbs the metallocene, leading to a cathodic shift in the ferrocene/ferrocenium redox couple. In order to obtain practical sensors for target charged guest species, confinement of receptors at a surface is necessary in order to develop robust, reuseable devices. Surface confinement also offers advantages over solution based receptors, including amplification of signal, enhanced guest binding thermodynamics and the negation of solubility problems. We have fabricated anion-templated rotaxanes and catenanes on gold electrode surfaces and demonstrated that the resulting mechanically bonded self-assembled monolayers are electrochemically responsive to the binding of anions, a crucial first step toward the advancement of sophisticated, highly selective, anion sensory devices. Rotaxane and catenane host molecules may be engineered to offer a superior level of molecular recognition, and the incorporation of optical or electrochemical reporter groups within these interlocked frameworks can allow for guest sensing. Advances in synthetic templation strategies has facilitated the synthesis of interlocked architectures and widened their interest as prototype molecular machines. However, their unique host-guest properties are only now beginning to be exploited as a sophisticated approach to chemical sensing. The development of functional host-guest sensory systems such as these is of great interest to the interdisciplinary field of supramolecular chemistry.

Progress in the synthesis and exploitation of catenanes since the Millennium

Catenanes - molecules consisting of interlocked macrocyclic rings - have been prepared by templation strategies for some thirty years. The utilization of Cu(I) cation, aromatic donor-acceptor interactions and hydrogen bonding assisted self-assembly strategies has led to the construction of numerous examples of these aesthetically pleasing species. This review seeks to discuss key developments in the synthesis and functional application of catenanes that have occurred since the Millennium. The much expanded range of metal cation templates; the genesis and growth of anion templation, as well as the use of alternative supramolecular interactions (halogen bonding and radical templation) and thermodynamically controlled reactions to synthesize catenanes are detailed. The class of catenanes that may be described as "molecular machines" are then highlighted and to conclude, attempts to fabricate catenanes onto surfaces and into metal organic frameworks (MOFs) are discussed.

Grafting single molecule magnets on gold nanoparticles

The chemical synthesis and characterization of the first hybrid material composed by gold nanoparticles and single molecule magnets (SMMs) are described. Gold nanoparticles are functionalized via ligand exchange using a tetrairon(III) SMM containing two 1,2-dithiolane end groups. The grafting is evidenced by the shift of the plasmon resonance peak recorded with a UV-vis spectrometer, by the suppression of nuclear magnetic resonance signals, by X-ray photoemission spectroscopy peaks, and by transmission electron microscopy images. The latter evidence the formation of aggregates of nanoparticles as a consequence of the cross-linking ability of Fe4 through the two 1,2-dithiolane rings located on opposite sides of the metal core. The presence of intact Fe4 molecules is directly proven by synchrotron-based X-ray absorption spectroscopy and X-ray magnetic circular dichroism spectroscopy, while a detailed magnetic characterization, obtained using electron paramagnetic resonance and alternating-current susceptibility, confirms the persistence of SMM behavior in this new hybrid nanostructure.

Anion sensing by solution- and surface-assembled osmium(II) bipyridyl rotaxanes

We report the preparation of [2]rotaxanes containing an electrochemically and optically active osmium(II) bipyridyl macrocyclic component mechanically bonded with cationic pyridinium axles. Such interlocked host systems are demonstrated to recognise and sense anionic guest species as shown by (1)H NMR, luminescence and electrochemical studies. The rotaxanes can be surface assembled on to gold electrodes through anion templation under click copper(I)-catalysed Huisgen cycloaddition conditions to form rotaxane molecular films, which, after template removal, respond electrochemically and selectively to chloride.

Organic switches for surfaces and devices

The pursuit to achieve miniaturization has tantalized researchers across the fields of chemistry, physics, biology, materials science and engineering for over half a century because of its many alluring potential applications. As alternatives to traditional "top-down" manufacturing, "bottom-up" approaches, originating from the (supra)molecular level, have enabled researchers to develop switches which can be manipulated on surfaces at nanoscale dimensions with deft precision using simple external triggers. Once on surfaces, these organic switches have been shown to modulate both the physical and chemical surface properties. In this Progress Report, we shed light on recent advances made in our laboratories towards integrated systems using all-organic switches on a variety of substrates. Design concepts are revealed, as well as the overall impact of all-organic switches on the properties of their substrates, while emphasizing the considerable promise and formidable challenges these advanced composite materials pose when it comes to conferring function on them.

Preparation of a responsive carbohydrate-coated biointerface based on graphene/azido-terminated tetrathiafulvalene nanohybrid material

A one-step method for the reduction of graphene oxide (GO) to reduced graphene oxide (rGO) is reported taking advantage of the electron-donor properties of an azido-terminated tetrathiafulvalene (TTF-N(3)). The resulting graphene/TTF-N(3) nanohybrid material is characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) spectroscopy, and by electrical and electrochemical means. The accessibility of the azide function to chemoselective modification by any alkyne-terminated partner molecule via Cu(I)-catalyzed "click" chemistry is demonstrated. In a proof of principle and motivated by the importance of glycan-modified materials, many alkynyl-terminated mannose units were grated onto graphene/TTF-N(3). The TTF-mannose units could be released efficiently from the graphene matrix by chemical oxidation of TTF-mannose surface units to TTF(2+)-mannose, using Fe(ClO(4))(3) or the electron-deficient tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT(4+)).