Showing papers by "J. Fraser Stoddart published in 2008"

Enzyme-Responsive Snap-Top Covered Silica Nanocontainers

Abstract: Mesoporous silica nanoparticles, capable of storing a payload of small molecules and releasing it following specific catalytic activation by an esterase, have been designed and fabricated. The storage and release of the payload is controlled by the presence of [2]rotaxanes, which consist of tri(ethylene glycol) chains threaded by α-cyclodextrin tori, located on the surfaces of the nanoparticles and terminated by a large stoppering group. These modified silica nanoparticles are capable of encapsulating guest molecules when the [2]rotaxanes are present. The bulky stoppers, which serve to hold the tori in place, are stable under physiological conditions but are cleaved by the catalytic action of an enzyme, causing dethreading of the tori and release of the guest molecules from the pores of the nanoparticles. These snap-top covered silica nanocontainers (SCSNs) are prepared by a modular synthetic method, in which the stoppering unit, incorporated in the final step of the synthesis, may be changed at will to target the response of the system to any of a number of hydrolytic enzymes. Here, the design, synthesis, and operation of model SCSNs that open in the presence of porcine liver esterase (PLE) are reported. The empty pores of the silica nanoparticles were loaded with luminescent dye molecules (rhodamine B), and stoppering units that incorporate adamantyl ester moieties were then attached in the presence of α-cyclodextrin using the copper-catalyzed azide−alkyne cycloaddition (CuAAC), closing the SCSNs. The release of rhodamine-B from the pores of the SCSN, following PLE-mediated hydrolysis of the stoppers, was monitored using fluorescence spectroscopy.

pH‐Responsive Supramolecular Nanovalves Based on Cucurbit[6]uril Pseudorotaxanes

Abstract: The ability to control the release of molecules from mesoporous silica nanoparticles promises to have far-reaching consequences for drug-delivery applications. Both molecular and supramolecular nanovalves, which regulate the release of guest molecules from nanopores of mesostructured silica nanoparticles, and operate under a range of stimuli including pH, competitive binding, light, and redox control, have been designed and their successful operation demonstrated in organic solvents. These systems are based upon the switching of components that have been tethered to the nanoparticle surfaces, such that access to the entrances of the nanopores can be opened and gated on demand. Since most of the traditional nanovalve designs have been based on [2]pseudorotaxanes and bistable [2]rotaxanes that rely upon donor–acceptor and hydrogen-bonding interactions between the ring and stalk components, they are limited largely to use in organic solvents. However, to realize the potential of nanovalves in therapeutic applications, it is imperative that they not only employ biocompatible components but that they also operate under physiological conditions. For nanovalves to be viable in biological environments, a recognition and binding motif which operates in aqueous media has to be identified, and then tried and tested. Herein, we describe a pH-responsive nanovalve that relies on the ion–dipole interaction between cucurbit[6]uril (CB[6]) and bisammonium stalks, and operates in water. CB[6], a pumpkin-shaped polymacrocycle with D6h symmetry consisting of six glycouril units strapped together by pairs of bridging methylene groups between nitrogen atoms, has received considerable attention because of its highly distinctive range of physical and chemical properties. Of particular interest in the field of supramolecular chemistry is the ability of CB[6] to form inclusion complexes with a variety of polymethylene derivatives, especially diaminoalkanes: the stabilities of these 1:1 complexes are highly pHdependent. The pH-dependent complexation/decomplexation behavior of CB[6] with diaminoalkanes has enabled the preparation of dynamic supramolecular entities which can be controlled by pH. Another important characteristic of CB[6] is its ability to catalyze 1,3-dipolar cycloadditions, such that the reaction between an azide-substituted ammonium ion and an alkyne-containing ammonium ion yields a disubstituted 1,2,3-triazole derivative encircled by a CB[6] ring. In view of these particular properties of CB[6], we set about to employ it as a catalyst for the formation of monolayers of [2]pseudorotaxanes on the surfaces of mesoporous silica nanoparticles so as to generate ultimately pHresponsive, biocompatible nanovalves capable of executing different missions. Mesoporous silica has proven to be an excellent support for the formation of dynamic nanosystems, including nanovalves, because it is chemically stable and optically transparent. In this current study, [2]pseudorotaxanes consisting of bisammonium stalks and CB[6] rings were constructed (Figure 1a,b) on the surface of mesoporous silica nanoparticles, and the pH-dependent binding of CB[6] with the bisammonium stalks is exploited to control the release of guest molecules from the pores of the silica nanoparticles. At neutral and acidic pH values, the CB[6] rings encircle the bisammonium stalks tightly, thereby blocking the nanopores efficiently when employing tethers of suitable lengths. Deprotonation of the stalks upon addition of base results in spontaneous dethreading (Figure 1b,c) of the CB[6] rings and unblocking of the silica nanopores. The silica supports employed were approximately 400nm-diameter spherical particles which contain ordered 2D hexagonal arrays of tubular pores (pore diameters of ca. 2 nm with a lattice spacing of ca. 4 nm) prepared by using a basecatalyzed sol–gel method. The nanopores were templated by cetyltrimethylammonium bromide (CTAB) surfactants, and tetraethylorthosilicate (TEOS) was used as the silica precursor. Empty nanopores were obtained by removal of the templating agents by solvent extraction. The ordered structure and particle morphology were confirmed (Figure 2) by X-ray diffraction (XRD) and scanning electron microscopy. This system was designed (Scheme 1a) such that the nanovalve components could be assembled in a stepwise, divergent manner from the nanoparticle surface outwards. Following solvent extraction, the nanoparticles were heated under reflux in an aminopropyltriethoxysilane (APTES) solution, which afforded the amino-modified nanoparticles 1. These nanoparticles were recovered by vacuum filtration [*] S. Angelos, Dr. Y.-W. Yang, K. Patel, Prof. J. F. Stoddart, Prof. J. I. Zink California NanoSystems Institute and Department of Chemistry and Biochemistry University of California, Los Angeles 405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA) Fax: (+1)310-206-1843 E-mail: stoddart@chem.ucla.edu zink@chem.ucla.edu Homepage: http://stoddart.chem.ucla.edu http://www.chem.ucla.edu/dept/Faculty/jzink/ [] These authors have contributed equally and both should be considered first author.

An acid-base-controllable [c2]daisy chain

Abstract: Artificial molecular-based muscles, which can convert chemical, electrochemical, or photochemical energy into mechanical motion, have attracted attention as a result of their potential for spawning nanoelectromechanical systems (NEMS). Several materials, such as conducting polymers, single-walled carbon nanotubes, and dielectric elastomers, have been developed which exhibit muscle-like behavior at the nanoscale level. However, all these systems rely upon the response of a bulk substance, rather than on the behavior of individual molecules. Recently, artificial muscles have been designed on a molecular scale by taking advantage of conformational changes exerted by electrochemical stimuli. For example, oligothiophene-calix[4]arene copolymers and thiophene-fused annulenes exhibit molecular actuating behavior under redox control while crown-etherannelated oligothiophenes and polyheterocyclic strands have ion-triggered muscle-like properties. Nanoscale molecular motions, based on artificial molecular machines, offer alternative opportunities to design artificial muscle-like materials. Bistable rotaxanes are a promising component for such materials, because relative linear mechanical translocation of the ring and dumbbell components can be achieved upon activation by chemical, electrical, or light irradiation stimuli. Converting such internal molecular motions into practical actuating materials requires relocating these internal motions into components, which, when taken together, exhibit linear expansion and contraction. Sauvage et al. have reported a linear molecular muscle, based on a transition-metal templated, doubly threaded rotaxane, which can undergo the required expansion and contraction motions on the addition or removal of metal ions. On the other hand, we have reported a switchable, palindromically constituted, doubly bistable [3]rotaxane which can be selfassembled onto gold-coated microcantilevers with disulfideterminated tethers emanating from its two rings in such a manner that they can be moved towards and away from each other under redox control. Controllable and reversible deflection of the microcantilevers can be achieved when the integrated system is exposed to the addition of oxidants or reductants (or subjected to oxidizing or reducing electrochemical potentials). Acid–base controllable, bistable, rotaxane-based molecular shuttles have been reported in which a dibenzo[24]crown-8 (DB24C8) ring switches under acid–base control between two different recognition sites on a dumbbell component, where one of the sites is a secondary dialkylammonium (R2NH2 ) center and the other site, an N,N’dialkylated-4,4’-bipyridinium (Bpym) unit. Although this switching has subsequently been employed in the design of more complex machines, such as nanoscale elevators, the mechanical motions are still only relative internal movements, that is to say, there is no contraction/expansion in their overall molecular dimensions. Herein, a bistable molecular architecture incorporating a two-component [c2]daisy chain topology is designed and synthesized (Scheme 1), wherein two mechanically interlocked filaments glide along one another through the terminal crown ether rings and in which the end of each filament is attached to bulky stoppers to prevent

Light‐Induced Charge Transfer in Pyrene/CdSe‐SWNT Hybrids

Abstract: On account of their nano-scale size, large aspect ratio and high conductivity, single-walled carbon nanotubes (SWNTs) have emerged as an attractive choice for conducting composite materials. Composites incorporating SWNTs show percolation dominated conductivity with a much lower volume threshold (volume fraction ≈ 10), compared to those with nanoparticles. Two-thirds of SWNTs are p-type semiconductors with holes as the charge carriers. Using the holeblocking nature of SWNTs, conducting polymers having SWNTs as dopants are effectively used as the hole buffering and electron transport layers in organic light-emitted diodes (OLEDs). For the active layer of OLEDs and organic photovoltaic (OPV) devices, incorporation of SWNTs enhances the charge separation and facilitates charge transport, hence improving the performance, i.e., the short circuit current, the filling factor and power conversion efficiency. However, since SWNTs are a mixture of metallic and semiconducting nanotubes with a small bandgap (≈ 0.6 eV), both electrons and holes in the composite matrix prefer to transfer onto and then be quenched on the SWNTs. Directly incorporating SWNTs into active layers of OLEDs and OPV devices does not facilitate the electron/hole separation, nor does it improve the performances of devices. On the other hand, semiconductor nanoparticles, possessing large and tunable bandgaps (1–2 eV), can be incorporated into conducting polymers to form hybrid solar cells. Holes are transported along the polymer chains and electrons hop along the nanoparticle network. However, nanoparticles with large volume fractions are needed because of their high percolation threshold (>≈30%). By contrast, the volume fraction for the conducting polymer is small, leading to low hole mobility and hence limiting the solar cell efficiency. Semiconductor nanorod-polymer hybrid solar cells benefit from the quasi-one-dimensional (1-D) electron transport along the rods, a mechanism which allows the use of a smaller volume fraction of nanorods and a larger volume fraction of polymer to conduct holes with higher mobilities. Although Alivisatos et al. have demonstrated that longer nanorods lead to higher energy conversion efficiency, nanorods of larger lengths and uniformly distributed diameters are difficult to fabricate. Semiconductor nanoparticle-SWNT hybrids have been the subject of recent interest as a consequence of the development of methods for the chemical modification of SWNTs. Such hybrids are well suited for use in optoelectronic devices, given the tunable bandgap of nanoparticles, quasione-dimensional (1-D) transport of SWNTs, and the ease of chemical fabrication. As part of a drive towards finding applications, an examination of the charge transfer (CT) between the various components of the hybrids is needed. By using such hybrid materials as photo-electrodes, efficient electron transfer from semiconductor nanoparticles, such as CdS, CdSe, and CdTe (donor) to SWNTs (acceptor) has been demonstrated by several groups to lead to increased photon generated current (Fig. 1). The CT also results in photolumiC O M M U N IC A IO N

Template-directed synthesis of donor/acceptor [2]catenanes and [2]rotaxanes

Abstract: The synthesis of mechanically interlocked molecular compounds has advanced by leaps and bounds since the early days of statistical methods and covalent-directing strategies. Template-directed synthesis has emerged as the method of choice for the construction of increasingly complex and functional [2]catenanes and [2]rotaxanes. In particular, mechanically interlocked molecules employing π-donating and π-accepting recognition units have been produced with remarkable efficiencies and show great promise in technologies as diverse as molecular electronics and drug delivery.

Kinetic and Thermodynamic Approaches for the Efficient Formation of Mechanical Bonds

Abstract: Among the growing collection of molecular systems under consideration for nanoscale device applications, mechanically interlocked compounds derived from electrochemically switchable bistable [2]rotaxanes and [2]catenanes show great promise. These systems demonstrate dynamic, relative movements between their components, such as shuttling and circumrotation, enabling them to serve as stimuli-responsive switches operated via reversible, electrochemical oxidation−reduction rather than through the addition of chemical reagents. Investigations into these systems have been intense for a number of years, yet limitations associated with their synthesis have hindered incorporation of their mechanical bonds into more complex architectures and functional materials. We have recently addressed this challenge by developing new template-directed synthetic protocols, operating under both kinetic and thermodynamic control, for the preparation of bistable rotaxanes and catenanes. These methodologies are compatible with the ...

A Redox-Switchable α-Cyclodextrin-Based [2]Rotaxane

Abstract: A bistable [2]rotaxane comprising an α-cyclodextrin (α-CD) ring and a dumbbell component containing a redox-active tetrathiafulvalene (TTF) ring system within its rod section has been synthesized using the Cu(I)-catalyzed azide−alkyne cycloaddition, and the redox-driven movements of the α-CD ring between the TTF and newly formed triazole ring systems have been elucidated. Microcalorimetric titrations on model complexes suggested that the α-CD ring prefers to reside on the TTF rather than on the triazole ring system by at least an order of magnitude. The fact that this situation does pertain in the bistable [2]rotaxane has not only been established quantitatively by electrochemical experiments and backed up by spectroscopic and chiroptical measurements but also been confirmed semiquantitatively by the recording of numerous cyclic voltammograms which point, along with the use of redox-active chemical reagents, to a mechanism of switching that involves the oxidation of the neutral TTF ring system to either its radical cationic (TTF^(•+)) or dicationic (TTF^(2+)) counterparts, whereupon the α-CD ring, moves along the dumbbell to encircle the triazole ring system. Since redox control by both chemical and electrochemical means is reversible, the switching by the bistable [2]rotaxane can be reversed on reduction of the TTF^(•+) or TTF^(2+) back to being a neutral TTF.

Organogel formation by a cholesterol-stoppered bistable [2]rotaxane and its dumbbell precursor

Abstract: The switching properties, gelation behavior, and self-organization of a cholesterol-stoppered bistable [2]rotaxane containing a cyclobis(paraquat-p-phenylene) ring and tetrathiafulvalene/1,5-dioxynaphthalene recognition units situated in the rod portion of the dumbbell component have been investigated by electrochemical, spectroscopic, and microscopic means. The cyclobis(paraquat-p-phenylene) ring in the [2]rotaxane can be switched between the tetrathiafulvalene and 1,5-dioxynaphthalene recognition units by addressing the redox properties of the tetrathiafulvalene unit. The organogels can be prepared by dissolving the [2]rotaxane and its dumbbell precursor in a CH2Cl2/MeOH (3:2) mixed solvent and liquified by adding the oxidant Fe(ClO4)3. Direct evidence for the self-organization was obtained from AFM investigations which have shown that both of the [2]rotaxane and its dumbbell precursor form linear superstructures which we propose are helical in nature.

Folding of a donor–acceptor polyrotaxane by using noncovalent bonding interactions

Abstract: Mechanically interlocked compounds, such as bistable catenanes and bistable rotaxanes, have been used to bring about actuation in nanoelectromechanical systems (NEMS) and molecular electronic devices (MEDs). The elaboration of the structural features of such rotaxanes into macromolecular materials might allow the utilization of molecular motion to impact their bulk properties. We report here the synthesis and characterization of polymers that contain π electron-donating 1,5-dioxynaphthalene (DNP) units encircled by cyclobis(paraquat-p-phenylene) (CBPQT4+), a π electron-accepting tetracationic cyclophane, synthesized by using the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The polyrotaxanes adopt a well defined “folded” secondary structure by virtue of the judicious design of two DNP-containing monomers with different binding affinities for CBPQT4+. This efficient approach to the preparation of polyrotaxanes, taken alongside the initial investigations of their chemical properties, sets the stage for the preparation of a previously undescribed class of macromolecular architectures.

Tetrathiafulvalene Radical Cation Dimerization in a Bistable Tripodal [4]Rotaxane

Abstract: The template-directed synthesis of a bistable tripodal [4]rotaxane, which has cyclobis(paraquat-p-phenylene) (CBPQT4+) as the pi-electron-deficient rings, and tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene units as the pairs of pi-electron-rich recognition sites located on all three legs of the tripodal dumbbell, is described. The chemical and electrochemical oxidation of the [4]rotaxane and its tripodal dumbbell have allowed us to unravel an unprecedented TTF.+ radical cation dimerization. In fact, two types of TTF dimers, namely, the radical cation dimer [TTF.+]2 and the mixed-valence one [(TTF)2].+, have been observed at room temperature for the tripodal dumbbell, whereas, in the case of the [4]rotaxane, only the radical cation dimer [TTF.+]2 is formed. This anomaly can be explained if it is accepted that most of the neutral TTF units in the [4]rotaxane are encircled by CBPQT4+ rings, which renders the formation of the mixed-valence dimer [(TTF)2].+ highly unfavorable.

A tunable photosensor.

Abstract: A pyrene-modified β-cyclodextrin (pyrenecyclodextrin)-decorated single-walled carbon nanotube (SWNT) field-effect transistor (FET) device was fabricated, which can serve as a tunable photosensor to sense a fluorescent adamantyl-modified Ru complex (ADA−Ru). When the light is on (I = 40 W m−2 and λ = 280 nm), the transfer curve of the pyrenecyclodextrin-SWNT/FET device shifts toward a negative gate voltage by about 1.6 V and its sheet resistance increases quickly, indicating a charge-transfer process from the pyrenecyclodextrins to the SWNTs. In contrast, the transfer curve of the pyrenecyclodextrin-SWNT/FET device in the presence of the ADA−Ru complex shifts toward a positive gate voltage by about 1.9 V and its sheet resistance decreases slowly when the light is on (I = 40 W m−2 and λ = 490 nm), showing a charge-transfer process from the pyrenecyclodextrin-SWNT hybrids to the ADA−Ru complex. Because these photoresponse processes are recoverable following the removal of the light, the present photosensor e...

Heterogeneous catalysis through microcontact printing.

Abstract: Minting a Stamp: The preparation of copper metal-coated elastomeric stamps and their use in catalyzing the Cu-catalyzed azide-alkyne cycloaddition reaction heterogeneously through microcontact printing is described. This StampCat process is compared to other conventional surface-functionalization techniques, including traditional microcontact printing and solution-surface-based reactions.

Experimentally-based recommendations of density functionals for predicting properties in mechanically interlocked molecules.

Abstract: Mechanically interlocked molecules (rotaxanes and catenanes) have already revolutionized molecular electronics and have the promise of a similar impact in other areas of nanotechnology, ranging from nanoactuators to in vivo drug nanocarriers. However, it would be most useful to have quantitative criteria for predicting structures, binding, and excitation energies for use in designing molecules with mechanical bonds. We assess here the use of density functional theory (DFT) to a noncovalently bound complex and find that no density functional is fully satisfactory. However, we find that the new M06-suite of density functionals, which include attractive medium-range interactions, leads to dramatic improvements in the structures (error of 0.04 A in the interplanar distances for M06-L compared to 0.42 A for B3LYP) and excitation energies (within 0.08 eV for TD-M06-HF without empirical correction compared to 2.2 eV error for TD-B3LYP). However, M06 predicts the complex to be too strongly bound by 22.6 kcal mol−...

A One‐Pot Synthesis of Constitutionally Unsymmetrical Rotaxanes Using Sequential CuI‐Catalyzed Azide–Alkyne Cycloadditions

Abstract: A one-pot sequential Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) strategy is presented for the synthesis of constitutionally unsymmetrical cyclobis-(paraquat-p-phenylene)-based rotaxanes in good yields from simple starting materials. The methodology consists of performing multiple CuAAC reactions to stopper a pseudo-rotaxane in a stepwise manner, the order of which is controlled through silyl-protection and AgI-catalyzed deprotection of a terminal alkyne. The methodology is highlighted by the synthesis of an amphiphilic branched [4]rotaxane. The methodology increases the ability to access ever more complicated mechanically interlocked compounds to serve in devices as sophisticated and functional molecular machinery.

Polyviologen Dendrimers as Hosts and Charge‐Storing Devices

Abstract: Two dendrimers were designed and synthesized that contain a 1,3,5-trisubstituted benzenoid core and incorporate 9 and 21 viologen (4,4′-bipyridinium) units in their branches in addition to hydrophilic (aryloxy) terminal groups. For comparison purposes, model compounds containing one and two viologen units were also studied. These polycationic dendrimers form strong host–guest complexes with the dianionic form of the red dye eosin in dilute CH2Cl2 solutions. Titration experiments, based on fluorescence measurements, showed that each viologen unit in the dendritic structures becomes associated with an eosin dianion. Electrochemical (in MeCN) and photosensitization (in CH2Cl2) experiments revealed that only a fraction of the viologen units present in the dendritic structures can be reduced. This fraction corresponds to the number of viologen units present in the outer shells of the dendrimers. The reasons for incomplete charge pooling are discussed. Comparison with the behavior of polyviologen dendrimers that are terminated with bulky tetraarylmethane groups and were studied previously enabled the role played by the terminal groups in the redox and hosting properties to be elucidated. Sono stati progettati e sintetizzati due dendrimeri contenenti un'unita benzenica sostituita nelle posizioni 1,3,5 come core, 9 e 21 unita viologeno (4,4′-dipiridinio), rispettivamente, nelle ramificazioni e gruppi idrofilici di tipo arilossi come unita periferiche. In CH2Cl2 questi dendrimeri policationici interagiscono con la forma dianionica dell'eosina dando complessi host–guest in cui, come mostrato chiaramente dalle titolazioni basate su misure di fluorescenza, ogni unita viologeno contenuta nella struttura dendritica si associa con un anione eosina. Esperimenti di riduzione elettrochimica (in MeCN) e fotochimica (in CH2Cl2 e in presenza di un opportuno fotosensibilizzatore) hanno inoltre messo in evidenza che non tutte le unita viologeno contenute nei dendrimeri possono essere ridotte; in particolare, sembra che siano riducibili solo quelle presenti nel guscio dendritico piu esterno. Il confronto con il comportamento di composti modello, contenenti una e due unita viologeno, e di dendrimeri precedentemente investigati, che differiscono da quelli discussi in questo lavoro per la presenza di gruppi terminali piu ingombranti di tipo tetraarilmetano, ha fatto luce sui motivi che inibiscono la riduzione di tutte le unita viologeno contenute nelle strutture dendritiche e ha chiarito se e come la natura dei gruppi terminali influenza le proprieta redox e complessanti di questi dendrimeri.

Template‐Directed Synthesis Employing Reversible Imine Bond Formation

Abstract: The imine bond – formed by the reversible condensation of an amine and an aldehyde – and its applications as a dynamic covalent bond in the template-directed synthesis of molecular compounds, will be the focus of this tutorial review. Template-directed synthesis – or expressed another way, supramolecular assistance to covalent synthesis – relies on the use of reversible noncovalent bonding interactions between molecular building blocks in order to preorganise them into a certain relative geometry as a prelude to covalent bond formation to afford the thermodynamically preferred product. The use of this so-called dynamic covalent chemistry (DCC) in templated reactions allows for an additional amount of reversibility, further eliminating potential kinetic products by allowing the covalent bonds that are formed during the template-directed reaction to be ‘proofread for errors’, thus making it possible for the reaction to search out its thermodynamic minimum. The marriage of template-directed synthesis with DCC has allowed chemists to construct an increasingly complex collection of compounds from relatively simple precursors. This new paradigm in organic synthesis requires that each individual piece in the molecular self-assembly process is preprogrammed so that the multiple recognition events expressed between the pieces are optimised in a highly cooperative manner in the desired product. It offers an extremely simple way of making complex mechanically interlocked compounds – e.g., catenanes, rotaxanes, suitanes, Borromean rings and Solomon knots – from relatively simple precursors.

Template-Directed Synthesis of Donor/Acceptor [2]Catenanes and [2]Rotaxanes

Abstract: The synthesis of mechanically interlocked molecular compounds has advanced by leaps and bounds since the early days of statistical methods and covalent-directing strategies. Template-directed synthesis has emerged as the method of choice for the construction of increasingly complex and functional [2]catenanes and [2]rotaxanes. In particular, mechanically interlocked molecules employing π-donating and π-accepting recognition units have been produced with remarkable efficiencies and show great promise in technologies as diverse as molecular electronics and drug delivery.

Clicked Interlocked Molecules

Abstract: The CuI-catalyzed Huisgen 1,3-dipolar cycloaddition, popularized as “click chemistry,” is one of the latest acquisitions to the synthetic arsenal for the making of mechanically interlocked molecula...

Rotaxanes and Catenanes by Click Chemistry

Abstract: Copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition between terminal alkynes and azides – also known as the copper (Cu)-catalyzed Azide-Alkyne Cycloaddition (CuAAC) – has been used in the syntheses of molecular compounds with diverse structures and functions, owing to its functional group tolerance, facile execution, and mild reaction conditions under which it can be promoted. Recently, rotaxanes of four different structural types, as well as donor/acceptor catenanes, have been prepared using CuAAC, attesting to its tolerance to supramolecular interactions as well. In one instance of a rotaxane synthesis, the catalytic role of copper has been combined successfully with its previously documented ability to preorganize rotaxane precursors, i.e., form pseudorotaxanes. The crystal structure of a donor/acceptor catenane formed using the CuAAC reaction indicates that any secondary [p ··· p] interactions between the 1,2,3-triazole ring and the bipyridinium p-acceptor are certainly not destabilizing. Finally, the preparation of robust rotaxane and catenane molecular monolayers onto metal and semiconductor surfaces is premeditated based upon recent advances in the use of the Huisgen reaction for surface functionalization.

Efficient Routes to Novel Molecular Architectures: Template-Directed Synthesis of Mechanically Interlocked Suitanes

Abstract: The design and synthesis of two recently reported examples of a new class of mechanically interlocked molecules - suitanes - is described. Suitanes consist of a rigid "body" template that is wrapped up in an all-in-one "suit" that fits the body to a T such that the two cannot be separated. These architecturally distinct interlocked molecular compounds are synthesized from a pool of components through a template-directed self-assembly process by taking advantage of dynamic covalent bond formation.