A Macrocycle/Molecular-Clip Complex that Functions as a Quadruply Controllable Molecular Switch

An original self-assembly using a tetrathiafulvalene-based molecular clip for the recognition of fullerene C60

A glycoluril-based molecular clip incorporating tetrathiafulvalene sidewalls self-assembles with fullerene C₆₀ in a 2 : 1 stoichiometry in solution.

Glycoluril-Derived Molecular Clips are Potent and Selective Receptors for Cationic Dyes in Water

Molecular clip 1 remains monomeric in water and engages in host-guest recognition processes with suitable guests. We report the K_a values for 32 1⋅guest complexes measured by ¹ H NMR, UV/Vis, and fluorescence titrations. The cavity of 1 is shaped by aromatic surfaces of negative electrostatic potential and therefore displays high affinity and selectivity for planar and cationic aromatic guests that distinguishes it from CB[n] receptors that prefer aliphatic over aromatic guests. Electrostatic effects play a dominant role in the recognition process whereby ion-dipole interactions may occur between ammonium ions and the C=O groups of 1, between the SO₃^- groups of 1 and pendant cationic groups on the guest, and within the cavity of 1 by cation-π interactions. Host 1 displays a high affinity toward dicationic guests with large planar aromatic surfaces (e.g. naphthalene diimide NDI+ and perylene diimide PDI+) and cationic dyes derived from acridine (e.g. methylene blue and azure A). The critical importance of cation-π interactions was ascertained by a comparison of analogous neutral and cationic guests (e.g. methylene violet vs. methylene blue; quinoline vs. N-methylquinolinium; acridine vs. N-methylacridinium; neutral red vs. neutral red H⁺ ) the affinities of which differ by up to 380-fold. We demonstrate that the high affinity of 1 toward methylene blue (K_a =3.92×10⁷  m^-1 ; K_d =25 nm) allows for the selective sequestration and destaining of U87 cells stained with methylene blue.

Gel properties of T-shaped tetrathiafulvalene–pyridazine conjugates and F4TCNQ-induced morphological transformation

T-shaped organic π-conjugates and their F₄TCNQ charge-transfer (CT) complexes are developed as LMOGs. The morphological changes of the organogels occur obviously due to the CT interaction.

Glycoluril-tetrathiafulvalene molecular clips: on the influence of electronic and spatial properties for binding neutral accepting guests

Glycoluril-based molecular clips incorporating tetrathiafulvalene (TTF) sidewalls have been synthesized through different strategies with the aim of investigating the effect of electrochemical and spatial properties for binding neutral accepting guests. We have in particular focused our study on the spacer extension in order to tune the intramolecular TTF···TTF distance within the clip and, consequently, the redox behavior of the receptor. Carried out at different concentrations in solution, electrochemical and spectroelectrochemical experiments provide evidence of mixed-valence and/or π-dimer intermolecular interactions between TTF units from two closed clips. The stepwise oxidation of each molecular clip involves an electrochemical mechanism with three one-electron processes and two charge-coupled chemical reactions, a scheme which is supported by electrochemical simulations. The fine-tunable π-donating ability of the TTF units and the cavity size allow to control binding interaction towards a strong electron acceptor such as tetrafluorotetracyanoquinodimethane (F4-TCNQ) or a weaker electron acceptor such as 1,3-dinitrobenzene (m-DNB).

Cation-induced pesticide binding and release by a functionalized calix[4]arene molecular host

Ion-controlled switchable progress is very important in many biological behaviors. Here, we reported K(+)-controlled switch, this switch system exhibited excellent carbaryl (G) binding/release by fluorescent (FL), ultraviolet-visible (UV) spectrums and (1)H NMR spectroscopy. More importantly, the K(+)-controlled G binding/release switch based on C4C5 not only in the solution, but also on the surface, promising for the application for the pesticide controlled release.

Enhancement of electron-donating character in alkylated monopyrrolo-tetrathiafulvalene derivatives

Bis-alkyl-substituted monopyrrolo-tetrathiafulvalene (MPTTF) derivatives display stronger affinity to electron-deficient molecular guests in comparison with their non-substituted MPTTF analogues.

Fused glycoluril-tetrathiafulvalene molecular clips as receptors for neutral electron acceptor guests

Glycoluril-based molecular clips incorporating tetrathiafulvalene (TTF) sidewalls have been synthesized, and the efficient binding ability in solution of this host architecture toward m-dinitrobenzene through donor-acceptor interaction has been demonstrated.

Synthesis and single-molecule imaging of highly mobile adamantane-wheeled nanocars

The synthesis and single-molecule imaging of two inherently fluorescent nanocars equipped with adamantane wheels is reported. The nanocars were imaged using 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) as the chromophore, which was rigidly incorporated into the nanocar chassis via Sonogashira cross-coupling chemistry that permitted the synthesis of nanocars having different geometries. In particular, studied here were four- and three-wheeled nanocars with adamantane wheels. It was found that, for the four-wheeled nanocar, the percentage of moving nanocars and the diffusion constant show a significant improvement over p-carborane-wheeled nanocars with the same chassis. The three-wheeled nanocar showed only limited mobility due to its geometry. These results are consistent with a requisite wheel-like rolling motion. We furthermore developed a model that relates the percentage of moving nanocars in single-molecule experiments with the diffusion constant. The excellent agreement between the model and the new results presented here as well as previous single-molecule studies of fluorescent nanocars yields an improved understanding of motion in these molecular machines.

Toward a light-driven motorized nanocar: synthesis and initial imaging of single molecules

A second generation motorized nanocar was designed, synthesized, and imaged. To verify structural integrity, NMR-based COSY, NOESY, DEPT, HSQC, and HMBC experiments were conducted on the intermediate motor. All signals in (1)H NMR were unambiguously assigned, and the results were consistent with the helical structure of the motor. The nanocar was deposited on a Cu(111) surface, and single intact molecules were imaged by scanning tunneling microscopy (STM) at 5.7 K, thereby paving the way for future single-molecule studies of this motorized nanocar atop planar substrates.

Molecular clips and tweezers hosting neutral guests

Intense current interest in supramolecular chemistry is devoted to the construction of molecular assemblies displaying controlled molecular motion associated to recognition. On this ground, molecular clips and tweezers have focused an increasing attention. This tutorial review points out the recent advances in the construction of always more sophisticated molecular clips and tweezers, illustrating their remarkably broad structural variety and focusing on their binding ability towards neutral guests. A particular attention is brought to recent findings in dynamic molecular tweezers whose recognition ability can be regulated by external stimuli. Porphyrin-based systems will not be covered here as this very active field has been recently reviewed.

Switchable V-type [2]pseudorotaxanes

A V-type molecule comprising a 2-[2-[4-(dimethylamino)phenyl]ethenyl]pyridinium cyanine branch and a p-aminophenoxy ethyl side arm was synthesized and can form quite different [2]pseudorotaxanes with cucurbit[7]uril (CB[7]) as a model thread in aqueous solution. The CB[7] ring can be switched reversibly from the cyanine branch to the aminophenoxy ethyl side arm by protonation of the aniline group, and the color of the solution was changed from orange red to yellow.

Molecular transformations of unsaturated thiacrown ethers

Unsaturated thiacrown ethers with 15, 18, and 21 members were oxidized to sulfoxides by the reaction with m-CPBA. The reaction with t-BuOCl at -20 degrees C also afforded sulfoxides, whereas the reaction at room temperature yielded cis-trans isomerized compounds. The cis-trans isomerized compound was also obtained by the photochemical reaction or by the reaction with NCS and NCP. Meanwhile, the reaction with NBS and NBP provided an acetal via 1,2-bridged bromonium intermediate.

Chemical and Constitutional Influences in the Self-Assembly of Functional Supramolecular Hydrogen-Bonded Nanoscopic Fibres

A new series of secondary amides bearing long alkyl chains with pi-electron-donor cores has been synthesized and characterised, and their self-assembly upon casting at surfaces has been studied. The different supramolecular assemblies of the materials have been visualized by using atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is possible to obtain well-defined fibres of these aromatic core molecules as a result of the hydrogen bonds between the amide groups. Indeed, by altering the alkyl-chain lengths, constitutions, concentrations and solvent, it is possible to form different rodlike aggregates on graphite. Aggregate sizes with a lower limit of 6-8 nm width have been reached for different amide derivatives, while others show larger aggregates with rodlike morphologies which are several micrometers in length. For one compound that forms nanofibres, doping was performed by using a chemical oxidant, and the resulting layer on graphite was shown to exhibit metallic-like spectroscopy curves when probed with current-sensing AFM. This technique also revealed current maps of the surface of the molecular material. Fibre formation not only takes place on the graphite surface: nanometre scale rods have been imaged by using TEM on a grid after evaporation of solutions of the compounds in chloroform. Molecular modelling proves the importance of the hydrogen bonds in the generation of the fibres, and indicates that the constitution of the molecules is vital for the formation of the desired columnar stacks, results that are consistent with the images obtained by microscopic techniques. The results show the power of noncovalent bonds in self-assembly processes that can lead to electrically conducting nanoscale supramolecular wires.

An Extremely Stable Host–Guest Complex That Functions as a Fluorescence Probe for Calcium Ions

Herein, we report a crown ether based molecular cage that forms extremely stable supramolecular complexes with dimethyldiazapyrenium (DMDAP) ions in CD(3)CN through the collaboration of multiple weak C-HO hydrogen bonds. The very strong binding affinity in this host-guest system allows the molecular cage to bleach the fluorescence signal of DMDAP substantially in equimolar solutions at concentrations as low as 1 x 10(-5) M. Remarkably, a 1x10(-5) M equimolar solution of the molecular cage and DMDAP is highly selective toward Ca(2+) ions-relative to other biologically important Li(+), Na(+), K(+), and Mg(2+) ions-and causes a substantial increase in the fluorescence intensity of the solution. As a result, this molecular cage/DMDAP complex behaves as a supramolecular fluorescence probe for the detection of Ca(2+) ions in solution.

Reading the operation of an acid/base-controllable molecular switch by naked eye

We report a pH-controllable molecular switch whose switching can be monitored by the naked eye; this system involves the formation of a complex between a [2]rotaxane--featuring dibenzylammonium and 4,4'-bipyridinium stations--and a TTF-side-walled molecular clip.