Signaling Recognition Events with Fluorescent Sensors and Switches.

Self-Assembly of Discrete Cyclic Nanostructures Mediated by Transition Metals

The development in the field of coordination polymers or metal-organic coordination networks, MOCNs (metal-organic frameworks, MOFs) is assessed in terms of property investigations in the areas of catalysis, chirality, conductivity, luminescence, magnetism, spin-transition (spin-crossover), non-linear optics (NLO) and porosity or zeolitic behavior upon which potential applications could be based.

/pdf/engineering-coordination-polymers-towards-applications-3joywh2v74.pdf

Engineering coordination polymers towards applications

Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

Fascination with supramolecular chemistry over the last few decades has led to the synthesis of an ever-increasing number of elegant and intricate functional structures with sizes that approach nanoscopic dimensions Today, it has grown into a mature field of modern science whose interfaces with many disciplines have provided invaluable opportunities for crossing boundaries both inside and between the fields of chemistry, physics, and biology This chemistry is of continuing interest for synthetic chemists; partly because of the fascinating physical and chemical properties and the complex and varied aesthetically pleasing structures that supramolecules possess For scientists seeking to design novel molecular materials exhibiting unusual sensing, magnetic, optical, and catalytic properties, and for researchers investigating the structure and function of biomolecules, supramolecular chemistry provides limitless possibilities Thus, it transcends the traditional divisional boundaries of science and represents a highly interdisciplinary field

In the early 1960s, the discovery of ‘crown ethers’, ‘cryptands’ and ‘spherands’ by Pedersen,1 Lehn,2 and Cram3 respectively, led to the realization that small, complementary molecules can be made to recognize each other through non-covalent interactions such as hydrogen-bonding, charge-charge, donor-acceptor, π-π, van der Waals, etc Such ‘programmed’ molecules can thus be self-assembled by utilizing these interactions in a definite algorithm to form large supramolecules that have different physicochemical properties than those of the precursor building blocks Typical systems are designed such that the self-assembly process is kinetically reversible; the individual building blocks gradually funnel towards an ensemble that represents the thermodynamic minimum of the system via numerous association and dissociation steps By tuning various reaction parameters, the reaction equilibrium can be shifted towards the desired product As such, self-assembly has a distinct advantage over traditional, stepwise synthetic approaches when accessing large molecules

It is well known that nature has the ability to assemble relatively simple molecular precursors into extremely complex biomolecules, which are vital for life processes Nature’s building blocks possess specific functionalities in configurations that allow them to interact with one another in a deliberate manner Protein folding, nucleic acid assembly and tertiary structure, phospholipid membranes, ribosomes, microtubules, etc are but a selective, representative example of self-assembly in nature that is of critical importance for living organisms Nature makes use of a variety of weak, non-covalent interactions such as hydrogen–bonding, charge–charge, donor–acceptor, π-π, van der Waals, hydrophilic and hydrophobic, etc interactions to achieve these highly complex and often symmetrical architectures In fact, the existence of life is heavily dependent on these phenomena The aforementioned structures provide inspiration for chemists seeking to exploit the ‘weak interactions’ described above to make scaffolds rivaling the complexity of natural systems

The breadth of supramolecular chemistry has progressively increased with the synthesis of numerous unique supramolecules each year Based on the interactions used in the assembly process, supramolecular chemistry can be broadly classified in to three main branches: i) those that utilize H-bonding motifs in the supramolecular architectures, ii) processes that primarily use other non-covalent interactions such as ion-ion, ion-dipole, π–π stacking, cation-π, van der Waals and hydrophobic interactions, and iii) those that employ strong and directional metal-ligand bonds for the assembly process However, as the scale and degree of complexity of desired molecules increases, the assembly of small molecular units into large, discrete supramolecules becomes an increasingly daunting task This has been due in large part to the inability to completely control the directionality of the weak forces employed in the first two classifications above Coordination-driven self-assembly, which defines the third approach, affords a greater control over the rational design of 2D and 3D architectures by capitalizing on the predictable nature of the metal-ligand coordination sphere and ligand lability to encode directionality Thus, this third strategy represents an alternative route to better execute the “bottom-up” synthetic strategy for designing molecules of desired dimensions, ranging from a few cubic angstroms to over a cubic nanometer For instance, a wide array of 2D systems: rhomboids, squares, rectangles, triangles, etc, and 3D systems: trigonal pyramids, trigonal prisms, cubes, cuboctahedra, double squares, adamantanoids, dodecahedra and a variety of other cages have been reported As in nature, inherent preferences for particular geometries and binding motifs are ‘encoded’ in certain molecules depending on the metals and functional groups present; these moieties help to control the way in which the building blocks assemble into well-defined, discrete supramolecules4

Since the early pioneering work by Lehn5 and Sauvage6 on the feasibility and usefulness of coordination-driven self-assembly in the formation of infinite helicates, grids, ladders, racks, knots, rings, catenanes, rotaxanes and related species,7 several groups - Stang,8 Raymond,9 Fujita,10 Mirkin,11 Cotton12 and others13,14 have independently developed and exploited novel coordination-based paradigms for the self-assembly of discrete metallacycles and metallacages with well-defined shapes and sizes In the last decade, the concepts and perspectives of coordination-driven self-assembly have been delineated and summarized in several insightful reviews covering various aspects of coordinationdriven self-assembly15 In the last decade, the use of this synthetic strategy has led to metallacages dubbed as “molecular flasks” by Fujita,16 and Raymond and Bergman,17 which due to their ability to encapsulate guest molecules, allowed for the observation of unique chemical phenomena and unusual reactions which cannot be achieved in the conventional gas, liquid or solid phases Furthermore, these assemblies found applications in supramolecular catalysis18,19 and as nanomaterials as developed by Hupp20 and others21,22

This review focuses on the journey of early coordination-driven self-assembly paradigms to more complex and discrete 2D and 3D supramolecular ensembles over the last decade We begin with a discussion of various approaches that have been developed by different groups to assemble finite supramolecular architectures The subsequent sections contain detailed discussions on the synthesis of discrete 2D and 3D systems, their functionalizations and applications

Supramolecular coordination: self-assembly of finite two- and three-dimensional ensembles.

The parts of a molecule are connected by chemical bonds such as the covalent bond, the ionic bond, the hydrogen bond, etc. However, as described in many examples in this book, the parts of a molecule cannot split if the rings are interlocked. These parts might be otherwise themselves individual molecules. Many fascinating experimentally observed structures are given in this book. A good pictorial representation of catenanes, rotaxanes and knots is shown on page 246. In 1997 Summer when I was attending an IUPAC Congress where Stoddart gave a lecture, I considered having "Molecule of the Year" reported in our journal Molecules every year, and a molecule in my mind was olympiadane (page 254 of this book). Twelve chapters appear in this book prepared by twelve international leading experts and their collaborators and associates. Every chapter of this multi-author book is written by one or more authors on different but related subjects. The mathematical characterization of these molecular structures and the prediction of their existence are presented. The other authors mainly describe the design and preparation of these compounds. The twelve chapters listed are the following: 1 Chemical Topology-Statistical Musings 2 A Knot-Theoretical Approach to Molecular Chirality

Molecular Catenanes, Rotaxanes and Knots

Transition-metal-containing rotaxanes can behave as linear motors at the molecular level. The molecules are set into motion either by an electrochemical reaction or using a chemical signal. In a first example, a simple rotaxane is described that consists of a ring threaded by a two-coordination-site axle. The ring contains a bidentate ligand, coordinated to a copper center. The axle incorporates both a bidentate and a terdentate ligand. By oxidizing or reducing the copper center to Cu(II) or Cu(I) respectively, the ring glides from a given position on the axle to another position and vice versa. By generalizing the concept to a rotaxane dimer, whose synthesis involves a quantitative double-threading reaction triggered by copper(I) complexation, a molecular assembly reminiscent of a muscle is constructed. By exchanging the two metal centers of the complex (copper(I)/zinc(II)), a large-amplitude movement is generated, which corresponds to a contraction/stretching process. The copper(I)-containing rotaxane d...

Shuttles and muscles: linear molecular machines based on transition metals.

The search for aesthetically attractive molecules has been a concern going back to the origin of chemistry. The criteria for beauty have obviously changed with time, being connected to analytical and synthetic tools. The ability of synthetic chemists to build more and more complicated structures has been developing spectacularly; recently highly sophisticated molecular architectures have been achieved. Transition metals can form molecular clusters whose arrangements are remarkably beautiful. In particular, platinum carbonyl clusters lead to geometrical figures whose regularity and harmony were completely unexpected not so long ago.' Dodecahedrane2 is another example whose importance stems both from the amount of work involved and from the cultural significance of the geometrical shape reached. This smart molecule represents the achievement of considerable efforts, and it remains today one of the mast difficult patterns to be synthesized. Clearly, the imagination of the chemist is dependent on the power of the synthetic tool. As the latter becomes more and more powerful, the synthetic chemist will be able to conceive and then to construct molecules that were not envisaged previously. Concurrently, the analytical chemist becomes able to recognize molecular structures mi(cycbpropanes. cyclopropenes; syime~ts and r e a m ) and total synthesii of chlysanhmic acids. h. Dmmchauchecker has been a member of the Centre Natlonal de la Recherche Scientitique since 1970. and she did postdoctwal work with Prof. K. 6. Sharpless (MIT. CambrkJge. MA, 1973-1974) on the study of new organoselenium compounds. She joined Prof. J. P. Sauvage's group in 1981. and her present research field is the synthesis of topologically novel molecules. 121and [3]-catenanes.

Interlocking of molecular threads: from the statistical approach to the templated synthesis of catenands

Une nouvelle famille de molecules : les metallo-catenanes

Towards Synthetic Molecular Muscles: Contraction and Stretching of a Linear Rotaxane Dimer We are grateful to M. Jean-Daniel Sauer and Dr. Roland Graff for high-field NMR experiments, Hélène Nierengarten and Raymond Hubert for mass determinations. M.C.J. thanks the European Commission for a Grant (TMR Contract No. ERBFMBICT972547). We also thank the CNRS for financial support (Programme Physique et Chimie du Vivant).

Christiane Dietrich-Buchecker

Papers

Molecular Catenanes, Rotaxanes and Knots

Shuttles and muscles: linear molecular machines based on transition metals.

Interlocking of molecular threads: from the statistical approach to the templated synthesis of catenands

Une nouvelle famille de molecules : les metallo-catenanes